Research Advances in Additively Manufactured High-Entropy Alloys: Microstructure, Mechanical Properties, and Corrosion Resistance

Abstract

High-entropy alloys have garnered significant attention due to their unique composition and exceptional properties. Additive manufacturing technology, with its distinctive processing methods, offers new options for the fabrication of high-entropy alloys. However, due to the diversity of high-entropy alloys and additive manufacturing technologies, it is imperative to provide a comprehensive overview of the high-entropy alloys produced using various additive manufacturing methods. This paper presents a summary of the microstructure, mechanical properties, and corrosion resistance of high-entropy alloys fabricated using different additive manufacturing techniques. This paper initially reviews the impact of various additive manufacturing process parameters and the influence of different elements on the microstructure of additively manufactured high-entropy alloys. Subsequently, it discusses the effects of different additive manufacturing techniques on mechanical properties and summarizes four strengthening mechanisms in additively manufactured high-entropy alloys. Additionally, the corrosion resistance of various additively manufactured high-entropy alloys is summarized. Finally, based on the review of additively manufactured high entropy alloys presented in this paper, the current challenges and future research directions are proposed.

1. Introduction

High-entropy alloys (HEAs) are a novel class of alloys composed of five or more principal elements, with each element constituting an atomic fraction ranging from 5% to 35% [1,2]. Since HEAs were first proposed in 2004, the attention to HEAs has increased rapidly [3]. HEAs exhibit superior properties, including exceptional strength and ductility, superior physical and chemical properties, as well as outstanding wear resistance and corrosion resistance, which provide benefits to their unique core effects, including a high-entropy effect, lattice distortion, slower diffusion, and cocktail effect. Engineering materials have strict requirements for mechanical properties. HEAs show possible application potential in the fields of aerospace, automotive, chemical, and energy. Currently, the mechanical properties of HEAs mainly are regulated by two patterns, including adjusting the chemical composition of HEAs and controlling the manufacturing method. HEAs contain multiple major elements, offering a broad space for regulation. Adjusting the chemical compositions of HEAs affects the phase composition and microstructure, resulting in improvement in the mechanical property. Additionally, the different fabricated methods provide heterogeneous solidification strategies, also affecting the microstructure of HEAs. Vacuum arc melting and casting techniques are currently primary methods for the fabrication of HEAs. However, traditional casting methods are limited in their ability to produce large-sized and complex-structured HEA components. Additive manufacturing techniques create new options to produce HEAs. Additive manufacturing technology directly fabricates parts from digital models using a layer-by-layer material deposition process [4,5,6]. This method has great advantages over the traditional method, especially in the production of complex parts and enabling rapid prototyping. This makes additive manufacturing technology have potential applications in various fields.

This paper aims to provide a comprehensive analysis on additively manufactured HEAs, including production methods, microstructures, mechanical properties, and corrosion resistance. On this basis, we provide a perspective on the future development and direction of additively manufactured HEAs based on the existing research foundation.

2. Additive Manufacturing Methods for HEAs

Figure 1 shows the additive manufacturing methods and their history of development. The main additive manufacturing technologies for HEAs are laser powder bed fusion (PBF), laser-directed energy deposition (DED), and binder jet printing (BJP) [3]. Laser powder bed fusion (PBF) can be divided into laser powder bed fusion (LPBF) and electron beam powder bed fusion (EPBF). Laser-directed energy deposition (DED) is divided into directed energy deposition laser beam (DED-LB), directed energy deposition electron beam (DED-EB). and directed energy deposition arc melting (DED-Arc).

PBF technology fabricates HEAs by melting its feedstock [7]. This technology is capable of processing parts with complex shapes and forming the final part directly from the 3D model without subsequent machining. The grain size of the HEA parts prepared with LPBF is finer than those with EPBF due to its higher solidification rate [8]. DED technology produces HEAs by depositing layer upon layer of directly melted powders or wires. This method can be utilized for surface strengthening of components and tools, modification and repair of damaged parts and tools, as well as the processing and manufacturing of multi-material composite workpieces [9,10,11]. HEAs manufactured using DED technology have high forming accuracy and good surface quality. Unfortunately, the forming efficiency is low, and the forming size is limited. Owing to the appropriate binder properties and good processability of AlCoCrFeNi and CoCrFeMnNi high-entropy alloys (HEAs), binder jet printing (BJP) technology is currently mainly used for the fabrication of these two materials [3,12,13]. Despite its advantages of high production efficiency and simple process, the selection of binders remains challenging. Moreover, the shrinkage rate of the materials during the manufacturing process is also difficult to control and predict.

3. Microstructure of Additively Manufactured HEAs

3.1. Effect of Additive Manufacturing Methods on Microstructure

The microstructure of HEAs has an important effect on strength, hardness, and corrosion resistance. The microstructure of additively manufactured HEAs is often determined by a combination of factors, such as additive manufacturing methods, processing parameters, and heat treatment parameters. Therefore, it is necessary to study the microstructure of additively manufactured HEAs. The LPBF and DED-LB techniques are capable of preparing HEAs with single-phase and multiphase structures. Lin et al. [14] found that FeCoCrNiMo_0.5 HEA prepared using the LPBF technique had a smaller grain size than that prepared using the DED-LB technique. Additionally, grain sizes of HEAs can be controlled through the manipulation of scanning strategies [15]. Using the methods of DED and EPBF, it is hard to accurately control the grain morphology of HEAs [3]. The grain sizes of HEAs constructed using the EPBF method have been reported to be in between those of parts prepared with casting and using the LPBF method [16]. For BJP technology, the HEAs produced by BJP technology generally exhibit porous structures, which can adversely affect the application of the material performance [12,13]. In addition to this, the classic CrMnFeCoNi HEA has been demonstrated to achieve well-formed grain sizes using a variety of additively manufactured technologies.

Table 1. Microstructure of HEA fabricated using different additive manufacturing methods.

Alloys	Process	Microstructure	Ref
FeCoCrNiMo0.5	LDED	Columnar crystals	[14]
FeCoCrNiMo0.5	LPBF	Columnar crystals	[14]
CrMnFeCoNi	LPBF	Layered dendrites	[17]
AlCoCrFeNi	EPBF	Equiaxed crystals	[18]
TiNp+ CrMnFeCoNi	LPBF	Columnar crystals	[19]
CrMnFeCoNi	DED-LB	Dendritic grains	[20]
TiZrNbMoV	PBF	Dendritic grains	[21]
FeMnCoCrSi	PBF	Columnar dendrites	[22]
AlCrFeNiV	PBF	Columnar crystals	[23]
AlCoCrFeNi	EPBF	Equiaxed crystals	[18]
AlCrFeNiV	LPBF	Columnar grains, Subgrains	[23]
NiAlCoCrCuFe	LPBF	Dendritic grains	[24]
AlCoCrFeNiMn	LPBF	Equiaxed grains	[25]
AlCrMnFeCoNi	DED-LB	Columnar grains	[26]
Al0.5FeCoCrNi	LPBF	Columnar grains, Equiaxed grains	[27]
Al0.3CoCrFeNi	LPBF	Columnar grains	[28]
Al0.5CoCrFeNi	LPBF	Dendritic grains	[29]
Al0.2Co1.5CrFeNi1.5Ti0.3	LPBF	Equiaxed grains	[30]
CxAl0.26CoFeMnNi	LPBF	Dendritic grains	[31]
AlCoFeNiSmTiVZr	LPBF	Equiaxed grains, Cauliflower-like grains	[32]
AlCrFeNiCuNbx	DED-LB	Dendritic grains	[33]
CoCrFeMnNi	LPBF	Columnar grains, Equiaxed grains	[34]
CrMnFeCoNi	LPBF	Nanograins	[35]
CoCrFeNiMn	LAAM	Columnar grains, Equiaxed grains	[36]
CoCrFeNiMn	LPBF	Columnar grains, Equiaxed grains	[16]
CoCrFeNiMnTix	PBF	Columnar grains	[37]
CoCrFeNiMn	PBF	Columnar grains, Equiaxed grains	[38]
TiNbTaZrMo	LPBF	Columnar grains, Equiaxed grains	[39]
NbMoTaW	LPBF	Lamellar martensite grains	[40]
NiCrWFeTi	LPBF	Columnar grains	[41]

summarizes the microstructure of HEAs fabricated using different additive manufacturing methods.

3.2. Effect of Composition of HEAs on Microstructure

CrFeCoNi HEAs have become the basis for fabricating different HEAs. Various microstructures of HEAs are achieved by adding other elements into CrFeCoNi. Numerous researchers have incorporated Al into CrFeCoNi HEAs and investigated the formation process of the BCC phase [28,42,43]. Columnar, honeycomb-like mixtures were observed in this HEA system with different Al contents fabricated using both PBF and DED methods [3,44,45]. The addition of Al elements in the HEA system can reduce the generation of intermetallic compounds and refine the grains [46]. In addition, Al elements can promote the formation of the BCC phase. As a result, AlxCrFeCoNi HEAs have become the most studied single-phase or multiphase HEAs. As shown in Figure 2a,b, AlxCrFeCoNi HEAs were prepared using laser additive manufacturing. They found that AlxCrFeCoNi HEAs exhibited FCC single-phase, FCC + BCC, and completely BCC single-phase structures with varying Al content [46,47,48,49]. Due to the differences in solidification rates and thermal gradients between the melting preparation and additively manufactured preparation, dual-phase FCC + BCC structures of HEAs were generated. Wei et al. [50] prepared AlxCrFeCoNi (x = 0.07 − 0.88) HEA using the LPBF method and found that grain morphology and phase composition are closely related to the x value. As shown in Figure 2c, when x is in the range from 0.07 to 0.5, a single-phase FCC structure is observed. When x is between 0.67 and 0.78, the microstructure is in the BCC stage; when x is 0.88, the BCC stage transitions to the B2 stage. This change is attributed to Al-induced lattice distortion and valence electron concentration. Interestingly, AlxCrFeCoNi HEAs prepared using the DED-LB technique (Figure 2d) were also found to give different phase structures for different x [51]. When x is 0.3, the single-phase FCC phase was observed (Figure 2e,f). As shown in Figure 2g,h, when x is 0.7, the HEAs exhibits a two-phase structure. The reason why the element Al can introduce the formation of the BCC structure is that the electronic configuration of Al allows it to exhibit both metallic and non-metallic characteristics [52]. This phase change can be interpreted as an increase in the lattice constant of the alloy due to an increase in the Al element, thus destroying the original FCC structure. Therefore, in HEA systems fabricated using PBF and DED, Al content affects grain morphology and phase composition. Al reduces intermetallic compound generation, refines grains, suppresses the FCC phase, and promotes the formation of the BCC phase. Different preparation methods lead to differences in the structure of the FCC + BCC duplex phase, and the phase transition caused by the change in Al content is attributed to the increase in the lattice constant due to the addition of Al, which destroys the FCC structure and introduces the BCC phase.

Numerous reports have indicated that Mn elements can influence the microstructure of HEAs. Zhang et al. [52] found that the microstructure of AlCoCrFeNiMnx (x = 0, 0.25, 0.5, 0.75, 1) transitions from coarse dendritic structures to finer dendritic structures and subsequently to columnar dendritic structures (Figure 3a–c) with changing Mn contents. Relatively similar elemental segregation exists between the dendritic (DR) and inter-dendritic (ID) regions of the alloy. Tong et al. [53] prepared CrMnFeCoNi HEAs using LPBF, and it can be seen in Figure 3d that columnar dendrites and equiaxed grains are the main microstructures of CrMnFeCoNi HEAs. Wang et al. [35] prepared CrMnFeCoNi HEAs using LPBF, and the results revealed the microstructure exhibits a layered structure including nanograin formation, elemental segregation and precipitation, a cellular dislocation structure, deformation twinning, and deformation-induced phase transitions. The additively manufactured CrMnFeCoNi HEA possesses a single-phase FCC structure, and its microstructure predominantly consists of columnar dendrites and equiaxed grains. The CrMnFeCoNi HEA fabricated using DED-LB exhibits a dendritic structure. Moreover, Mn tends to segregate at the grain boundaries due to the lower scanning speed [54,55]. However, employing appropriate process parameters can reduce or even eliminate the segregation of Mn elements [56].

The effects of other elements and HEA systems on microstructure have also been widely studied. Gwalani et al. [57] utilized the DED method to fabricate AlCrFeMoVx HEA systems. The results demonstrated that V has a good solubility in AlCrFeMo HEAs. An increase in V content leads to an increase in grain size. Wu et al. [58] added the element V to CrFeCoNiNb hydroxides and showed that the microstructure of the V-free alloys consisted mainly of columnar dendritic crystals and fine C14 Laves phases. When V atoms replace some Nb atoms, the volume fraction of the C14 Laves phase decreases from 12.32% to 6.62%, which leads to a decrease in the size and amount of the C14 Laves phase, but the size of the dendrites becomes slightly coarser. Similar to elemental Al, elemental Zr is also capable of promoting the formation of the BCC phase. Sarswat et al. reported that the addition of Zr to AlCoFeNiSmTiVZr HEA promoted the formation of the BCC phase in the FCC matrix [32]. Dobbelstein et al. [59] used the DED-LB technique to prepare NbTaTiZr HEAs to investigate the effect of the ratio of Zr to Nb on the microstructure; the experimental setup is shown in Figure 4a. The results indicate that a high concentration of Zr is conducive to the formation of a dual BCC phase. In the Zr-enriched BCC regions, Ta elements segregate at the grain boundaries, forming a Ta-enriched secondary BCC phase. Furthermore, increasing the ratio of Zr to Nb yields a finer microstructure (Figure 4b). In brief, the impact of Zr elements on the microstructure is primarily manifested in its ability to form intermetallic compounds [59]. Similar to Zr and Al, the addition of Mo and Ta elements also favors the formation and stabilization of the BCC phase in the alloy [60].

With the increasing demand for material performance, the doping of particulate compounds such as WC, TiN, and NbC in additively manufactured HEAs has been studied. Li et al. [61] prepared CrMnFeCoNi-WC composites using the DED method. With the addition of WC particles, the grain size became smaller and smaller (Figure 5a–c). Moreover, Cr23C6 precipitation-reinforced phases were formed. Zhang et al. [62] prepared CrMnFeCoNi + WCx (x = 0 − 8 wt %) using LPBF. As can be seen in Figure 5d–g, the grain refinement is obvious with the increase in WC addition, especially for the HEAs with the addition of 8 wt % WC. It has been demonstrated that a high concentration of WC particles inhibits grain growth at the grain boundaries during the LPBF process. In addition to doping WC particles to alter grain size, researchers have also introduced NbC particles into the HEA system. Li et al. [63] investigated the effect of doping NbC on the microstructure of AlCoCrFeNi HEAs. They found that AlCoCrFeNi HEA exhibits a mixture of BCC and FCC phases. Moreover, the microstructure has many elongated massive grains and a few equiaxed grains. The addition of NbC particles leads to a reduction in the FCC phase distributed at the grain boundaries. The grain growth of HEAs is inhibited due to the strong pinning effect of NbC particles. Furthermore, the addition of TiN particles to HEAs has been studied [20,64,65]. The results indicate that the microstructure is isotropic, and the grain size is very fine. The incorporation of these compound particles can effectively reduce grain size. Doping compounds such as WC, TiN, and NbC into additively manufactured HEAs can make the materials exhibit isotropic microstructures and fine grain sizes. The addition of these compounds can effectively reduce the grain size and improve the material properties.

3.3. Effect of Additively Manufactured Process on Microstructure

The preparation process parameters of additively manufactured HEAs play an important role in microstructure [34,66,67,68].

Table 2. Summary of fabrication process and microstructural characteristics.

Materials	Methods	Scanning Speed (mm/s)	Power (W)	Microstructural Characteristics	Ref
(CoCrFeMnNi) 100 −x /TiCx	PFB	/	100 400 700	Dendritic structure composed of FCC and TiC phases	[73]
CrFeCoNi	PBF	800	400	Honeycomb and columnar subgrain structures	[44]
CrFeCoNi	PBF	800–2000	200–400	Single-phase FCC structure	[71]
CrMnFeCoNi	DED-LB	8.3	1000	Refined equiaxed grains	[61]
CrMnFeCoNi	PBF	200–1200	200	Refined equiaxed grains	[20]
CrMnFeCoNi	PBF	200, 600	90	Fine grains	[70]
AlCoCrFeNiCu	PBF	90	140	Dendrites, FCC phase	[24]
FeCoCrAlCu	DED	40–20	100–2500	Ultrafine nanograins	[75]
FeCoCrAlCu	DED	1–15	1000–3000	Fibrous fine microstructure	[76]
CrMnFeCoNi	PBF	800	370	Fine dendritic grains	[17]

shows the effect of process parameters on the microstructure of HEAs. Currently, a variety of additively manufactured processes are being explored. Parameters for preparing HEAs by DED technology have covered the laser power range of 300–3700 W and scanning speeds of 100–6000 mm/min. The process parameters for the preparation of HEA using the DED-Arc methods correspond to the wire feed rates in the range of 5–10 m/min, arc voltages in the range of 22–25 V, and scanning speeds in the range of 8–100 mm/min [3]. Among these parameters, the laser power determines the energy radiated by the laser per unit area, while the scanning speed determines the time that the laser stays on the sample [69]. Park et al. [70] investigated the effect of laser scanning speed on the microstructure of CrMnFeCoNi HEAs. The results indicated that higher scanning speeds led to finer grain sizes (Figure 6a,b), suggesting that energy input is dependent on the scanning speed. Zhou et al. [71] fabricated FeCoCrNiC_0.05 HEAs using laser powers ranging from 200 to 400 W and scanning speeds between 800 and 2000 mm/s. The results revealed that the grain size decreased with higher laser power or lower scanning speeds. As shown in Figure 6c–e, the grains in the three distinct regions exhibit random orientations. Equiaxed grains are observed in the middle and lower sections, while columnar grains are present in the upper section. This is attributed to differences in the temperature gradient and cooling rate. Zhu et al. [72] utilized the PBF technique to prepare Fe_49.5Mn₃₀Co₁₀Cr₁₀C_0.5 HEAs with process parameters of P = 180 W and v = 1000 mm/s. Fe_49.5Mn₃₀Co₁₀Cr₁₀C_0.5 HEAs exhibits a hierarchical microstructure consisting of equiaxed grains and columnar structures (Figure 7). Akinwande et al. [73] fabricated CrMnFeCoNi HEA by varying laser power. They found that the microstructure of HEAs depends on the solidification velocity (V) and the temperature gradient (G). A high G/V ratio promotes the formation of columnar grains, while a low G/V ratio favors the formation of equiaxed grains [69]. For example, Guan et al. [74] observed that a decrease in the G/V ratio makes the grain structure transition from columnar to equiaxed grains (Figure 6f).

In addition to scanning speed and power, factors such as volumetric energy density (VED), cooling rate, and scanning strategy also significantly influence the microstructure. For the PBF technique, the microstructure (grain morphology) of alloys can be modified by adjusting the VED [3]. Niu et al. [77] observed that the relative density of AlCoCrFeNi-based HEAs increased with increasing VED. As shown in Figure 8, the growth direction, size, and grain boundary characteristics of the HEAs vary with changes in VED. It has been reported that an increase in cooling rate transforms dendritic microstructures into equiaxed and columnar structures [78]. The microstructure of the HEAs fabricated using DED-LB at a higher cooling rate exhibits a layered dendritic structure, while the HEAs produced using PBF exhibits columnar grains with a specific growth direction. The laser scanning strategy is an important parameter used to control and mitigate microstructural defects. An appropriate scanning scheme is crucial for HEAs, as it not only enables the sample to achieve a uniform and ultra-fine microstructure but also improves its mechanical properties [69]. Guo et al. [68] revealed the effect of scanning strategy on the microstructure of CoCrFeMnNi- (N, Si) HEAs constructed using LPBF. It was shown that the HEAs exhibited different microstructural features using 45° and 67° scanning rotations. Xiang et al. [79] employed unidirectional and bidirectional scanning schemes and observed a transition from columnar grains to equiaxed grains in the subsequent layers. Jin et al. [80] utilized three different scanning strategies to fabricate CrMnFeCoNi HEAs, and the results indicated that the scanning strategy influences the grain structure.

4. Mechanical Property

4.1. Hardness

The microhardness of materials is an important parameter for evaluating the mechanical properties of additively manufactured HEAs.

Table 3. Hardness of additively manufactured HEAs.

HEAs	Method	Hardness(HV)	Ref
CrFeCoNi	PBF	205–238	[83]
CrFeCoNi	PBF	251–267	[84]
CrFeCoNi	PBF	187–196	[85]
AlCoCrFeNi	PBF	270	[86]
AlCoCrFeNi	PBF	632.8	[87]
AlCoCrFeNi	PBF	389–495	[18]
CrFeCoNiC0.05	PBF	340	[88]
CrMnFeCoNi	PBF	254–268	[89]
CrMnFeCoNi	PBF	200–300	[90]
CrMnFeCoNi	PBF	212	[91]
CrMnFeCoNiTix	PBF	460–900	[37]
AlCoCuFeNi	PBF	541	[42]
WMoTaNb	PBF	826	[40]
WMoTaNbV	PBF	664	[92]
NbMoTaTi	PBF	422	[93]
CrMnFeCoNi	PBF	152.6–161.6	[16]
CrMnFeCoNi+WC	PBF	310.6	[62]
NbTaTiMo	PBF	452	[94]
FeCoCrNiMo0.5	PBF	840.89	[14]
FeCoCrNiMo0.5	DED	784.9	[14]
CrMnFeCoNi	DED	195	[17]
CrMnFeCoNiTix	DED	182–973	[95]
AlCoCrFeNi	DED	543	[96]
AlCoCrFeNi	DED	520–628	[97]
AlCoCrFeNi	DED	538	[98]
Al0.3CoCrFeNi	DED	205.3–212.3	[99]
AlCrFeMoVx	DED	485–581	[57]
Ni2.1CoCrFe0.5Nb0.2	DED	260	[100]
AlMoNbTa	DED	646	[101]
TiZrNbHfTa	DED	509	[9]
AlCoCrFeNi	BJP	530	[12]

lists the hardness of various HEAs fabricated using different additively manufactured techniques. It can be concluded that the hardness of HEAs varies significantly depending on the additively manufactured method. Due to the slower cooling rate of PBF, the hardness of the AlCoCrFeNi HEAs produced using PBF is relatively lower compared to that produced using DED. This higher hardness is attributed to the finer microstructure generated by the latter. Additionally, the hardness of HEAs with a BCC phase structure is higher than that of HEAs with an FCC phase structure [49]. For AlxCrCuFeNi HEAs obtained using DED, the hardness increases with the increase in Al elements [1]. The hardness of AlCoCrFeNi HEAs gradually decreases from the top of sample to the bottom due to an increasing FCC phase [18]. This agrees with the results of Gwalani et al. [51]. Dobbelstein et al. [59] fabricated TiZrNbTa HEAs using DED technology and found that the hardness increased from approximately 220 HV to around 400 HV, with increasing Zr content. Gwalani et al. [57] fabricated compositionally graded AlCrFeMoVx HEAs. As the V content increased, the hardness of the alloy rose from 485 HV to 581 HV. This strengthening effect is attributed to solid solution strengthening. Li et al. [81] found that the hardness of the WNbMoTa HEAs increases from 459.2 ± 9.7 HV to 497.6 ± 5.6 HV with increasing W content. This increase in hardness is attributed to the refinement of the grain size. Li et al. [75] used DED-LB to fabricate a finer microstructure of FeCoCrAlCu HEAs without microcracks, resulting in a significant increase in hardness, which is attributed to the addition of yttria partially stabilized ZrO₂. Additionally, the incorporation of NbC and TiN particles into HEAs would also enhance the hardness [62,82]. In summary, the enhancement of material hardness can be achieved by accelerating the cooling rate of the additive manufacturing process. In addition, the introduction of Al or V elements to the original material can also be considered to improve the hardness of the material.

4.2. Mechanical Properties

Different additively manufactured methods, process parameters, and elements have varying effects on the tensile strength of HEA materials.

Table 4. Tensile properties of HEAs obtained using different preparation processes.

Methods	HEAs	Power (W)	Speed (mm/s)	YS (MPa)	UTS (MPa)	EI%	Ref
PBF	FeCoCrNi + C	250 300 350 400 400 400	800 800 800 800 1000 1200	630 635 630 638 643 656	776 788 786 797 789 783	9.6 11.3 11.9 13.5 11.5 7.7	[71]
PBF	FeCoCrNi + C	400	800	638	795	13.5	[44]
PBF	FeCoCrNi	200	300	600	745	32	[83]
PBF	FeCoCrNi	150	270	572	691	17.9	[15]
PBF	CoCrFeMnNi	90	600	774.9	923.3	30.8	[106]
PBF	CoCrFeMnNi	280	800	620	730	12	[107]
PBF	CoCrFeMnNi	400	800–4000	519	601	34	[34]
PBF	CoCrFeMnNi	160–290	1500–2500	510	609	34	[45]
PBF	CoCrFeMnNi	1000–1400	8.3	290	535	55	[102]
PBF	CoCrFeMnNi	600–1000	13.3	346	566	27	[54]
PBF	CoCrFeMnNi + TiNp	250	450	/	1100	8	[64]
PBF	CoCrFeMnNi + TiC	200	200–1200	/	1036	12	[20]
PBF	CoCrFeMnNi + TiC	375	1600	/	1059 1100	15.3 18	[65]
PBF	AlCoCuFeNi	205	1000	1342	1471	0.9	[42]
PBF	Al0.5CoCrFeNi	320	800	609	878	/	[29]
PBF	Al0.2Co1.5CrFeNi1.5Ti0.3	/	/	1235 1042	1550 1343	10.7	[30]
PBF	CoCrFeNiTi	160	650	777.2	1178	26.4	[108]
PBF	FeCoCrNiSi0.05	/	/	715	932	31	[109]
PBF	Ni6Cr4WFe9Ti	300	2500	742	972	12.2	[110]
DED	CoCrFeNiMn	880	10	714	852	41.2	[36]
DED	CoCrFeNiMn	300	600	448	620	57	[111]
DED	CoCrFeNiMn	200	/	530	780	27	[80]
DED	CoCrFeNiMn	400	5	517	650	26	[55]
DED	CoCrFeNiMn	1400	500	290	535	55	[102]
DED	CoCrFeNiMn	/	/	232	647	58	[112]
DED	Al0.3CoCrFeNi	1000	1000	483.3	504.7	0.67	[99]
DED	AlCoCrFeNi2.1	800	10	768	1238	23	[113]
DED	CoCrFeNiMn + WC	1000	500	675	845	9	[61]

summarizes the mechanical properties of HEAs obtained using different fabrication methods. Among them, YS refers to the yield strength, UST indicates the ultimate tensile strength, and EI signifies the elongation. Previous studies have shown that the CrMnFeCoNi HEAs produced by additively manufacturing exhibits superior yield strength compared to its cast counterpart, due to its finer microstructure [3]. Furthermore, the HEAs fabricated using DED technology experience rapid solidification, which introduces more dislocations, resulting in a higher yield strength compared to the HEAs produced using PBF-LB technology. In addition, HEAs fabricated using PBF-EB technology exhibit higher ductility. Shuo et al. [102] adjusted the ratio of columnar to equiaxed grains by varying the laser power, ultimately achieving improved mechanical properties. The importance of scanning speed and laser power process parameters in fabricating materials with better mechanical properties has been demonstrated [71]. In addition, some researchers have attempted to add other elements to HEAs to enhance their mechanical performance. Wang et al. [103] employed nitrogen doping in CoCrFeNi HEAs, and the results showed that the addition of nitrogen led to the formation of twinning and dislocations, as well as intersecting slip bands, as shown in Figure 9a, thereby improving the mechanical properties. Zhou et al. [71] added carbon to the FeCoCrNi HEAs, which increased the tensile strength to 797 MPa. This improvement is attributed to grain refinement and solid solution strengthening induced by the addition of carbon. Subsequently, the effect of Si addition on the mechanical properties was investigated. Hou et al. [104] found that the strength of the HEAs increased with the addition of Si. The Si element stabilized the FCC phase and promoted phase transformation-induced plasticity by adjusting twinning strain during deformation. This allowed total elongation to exceed 30%. The combined effects of multiple strengthening mechanisms, including dislocations, deformation twinning, and phase transformation, significantly enhanced the strength of the HEAs (Figure 9b). Additionally, WC was added to the DED-fabricated CrMnFeCoNi HEAs, resulting in a high tensile strength of 800 MPa and an elongation of 37%. The improvement in mechanical properties is likely attributed to the formation of Cr₂₃C₆ strengthening phases [61]. Amar et al. [105] added TiC to CrMnFeCoNi HEAs, and the CrMnFeCoNi HEAs with 5 wt% TiC exhibited a tensile strength of 723 MPa and a tensile strain of 32% (Figure 9c). The improvement in mechanical properties is attributed to the introduction of micro-sized TiC reinforcing phases. Therefore, different additive manufacturing methods, process parameters, and elemental additions have significant effects on the tensile properties of HEAs. Additive manufacturing technology significantly enhanced the yield strength of HEAs compared to conventional casting due to finer grain size microstructure. Among them, DED technology has higher yield strength than the PBF-LB technology due to the introduction of more dislocations by rapid solidification, while the PBF-EB technology exhibits higher ductility. By adjusting process parameters such as laser power and scanning speed, the grain morphology can be optimized to further enhance the material properties. In addition, elemental doping such as N, Si, and WC is also an important means to enhance the performance of HEAs. These studies show that a combination of strengthening mechanisms can significantly enhance the strength and ductility of HEAs.

5. Strengthening Mechanism

The strengthening mechanisms of additively manufactured HEAs primarily include refined crystalline strengthening [61,114,115,116], dislocation strengthening [15,16,28,45,72,116], solid solution strengthening [71,116,117], and precipitation strengthening [30,32,61,111,118].

Zhou et al. [88] found that Cr23C6 mainly accumulates at the grain boundaries (Figure 10a,b). These carbides restrict grain growth, resulting in fine grains. As a result, the mechanical properties of the HEAs are enhanced. Li et al. [34] fabricated CoCrFeMnNi HEAs using PBF technology, and the results showed that the mechanical properties of HEAs are enhanced due to grain refinement (Figure 10c). In addition, Yang et al. [110] developed novel Ni₆Cr₄WFe₉Ti HEAs with a fine-grained structure. The high grain boundary density (Figure 10d–i) enables the HEAs to exhibit a fracture strength exceeding 970 MPa and a tensile elongation of up to ~12.2% at room temperature. Subsequently, Gao et al. [111] found fine BCC phases at the grain boundaries of the FCC matrix, and the printed HEAs demonstrated an excellent combination of high strength and outstanding ductility. This was attributed to the synergistic effect of high cooling rates and the precipitation strengthening of BCC phases at the grain boundaries.

Additively manufactured HEAs have a high dislocation density, and this dislocation network can impede the movement of internal dislocations during deformation, thereby enhancing the mechanical properties of material. As shown in Figure 11a,b, CrMnFeCoNi HEAs fabricated using laser additively manufacturing generates a high density of dislocations, which enhances the mechanical properties [55]. In Ma et al.’s study [119], dislocation strengthening was primarily attributed to the addition of Fe-based amorphous alloys (Figure 11c–h). As shown in Figure 11i–m, the HEAs exhibit a large number of low-angle grain boundaries. The dislocation strengthening mechanism is related to the subgrain. These subgrains and dislocation networks form during the non-equilibrium solidification process and have a significant impact on the strength and plasticity of the material [23].

Solid solution strengthening occurs due to lattice distortions. These distortions increase the resistance to dislocation movement, making slip more difficult, thereby increasing the strength and hardness. For laser additively manufacturing methods, the incorporation of interstitial atoms such as C, N, and O into HEAs leads to lattice distortions. HEAs containing small amounts of interstitial atoms will exhibit interstitial solid solution strengthening [69]. The addition of carbon to HEAs can achieve solid solution strengthening and dislocation strengthening, leading to improved mechanical properties. Wu et al. [44] used carbon as a solute and CoCrFeNi as a solvent, causing solid solution strengthening in the HEAs. Zhu et al. [72] introduced carbon to achieve solid solution strengthening, which enabled the alloy to activate both twinning-induced plasticity and phase transformation-induced plasticity mechanisms, resulting in a better strength and plasticity combination. The effect of various V elements on solid solution strengthening was subsequently studied [57], and the results showed that the addition of V Influenced the lattice parameters, thereby increasing solid solution strengthening. Solid solution strengthening was achieved with increasing V concentration (Figure 12a), and the hardness of the alloy increased from 0.3 Hv to 18.5 Hv. Yang et al. [120] found that the addition of Si significantly improved the hardness of HEAs. In AlCrCuFeCoNi HEAs, the hardness increased from 200.5 HV to 751.8 HV with the addition of Si, due to the solid solution strengthening effect (Figure 12b). Additionally, the addition of TiC and TiN has also been used to improve mechanical performance. Amar et al. [105] indicated that the effect of TiC mainly improved the mechanical properties of CrMnFeCoNi-based HEAs, especially the yield strength and tensile strength, but sacrificed some ductility. This strengthening effect was primarily due to the introduction of micro-sized TiC phases, which hindered the propagation of slip bands and thus enhanced the strength of material. Furthermore, the addition of TiN also improved mechanical performance [20]. Subsequently, Pegues et al. [121] added refractory metals Ta and Nb to CrMnFeCoNi HEAs, which have very different melting points from the HEAs matrix. This caused partial melting and differences in powder flowability, which in turn affected the microstructure and mechanical properties of alloy. As shown in Figure 12c, as the Ta content increased, the hardness also gradually increased, especially near the equiatomic composition, where the hardness significantly increased, indicating the enhanced solid solution strengthening effect. Lin et al. also observed the presence of solid solution strengthening mechanisms in the additively manufactured FeCoSiCrNi [109].

The precipitates formed by additively manufactured HEAs can enhance hardness and plasticity. Nano-sized precipitates in additively manufactured HEA materials mainly include carbide phases, γ′ phase, B2 phases, and D022 phases [γ′′ phase] [69]. He et al. [122] observed that in CoCrNiFeNb_0.25 HEA, the unstable γ′′ phase eventually transformed into the stable ε phase. These precipitates can enhance the mechanical properties of the material. Yuan et al. [123] found that L12 precipitates were dispersed in the matrix and enriched at subgrain boundaries. After annealing, the microhardness and yield strength of the HEA billet were significantly improved. Zhang et al. [124] studied the effect of Al content on the mechanical properties of CoCrFeNi3 HEAs prepared using DED. As the Al content increased, the structure transformed from an FCC phase and L12 precipitates to a dual-phase FCC coexisting with a BCC phase (Figure 13). The increase in hardness was attributed to solid solution strengthening and precipitation strengthening. Additionally, after adding Nb and Ti/Al elements to HEAs, γ′′ [125] and γ′ [126], nano-precipitates were formed, and the presence of these precipitates enhanced the mechanical properties. Furthermore, Joseph et al. also found that adding different amounts of Al to CoCrFeNi HEAs resulted in the formation of B2 precipitates, which reinforced the material [47,48]. Therefore, the introduction of appropriate precipitates to form precipitate strengthening phases is an effective strategy to improve the mechanical properties of materials.

Figure 14 illustrates the strengthening mechanisms of additively manufactured HEAs and their relationship. HEAs with fine grains are formed by increasing the solidification rate, resulting in the enhancement of mechanical properties. Furthermore, the high-temperature gradient in additively manufactured methods offers a high density of initial dislocations, which also plays a positive role in enhancing the mechanical performance of material. Another factor that enhances dislocation density is the precipitate phase. The precipitates are formed by adding other elements that suppress grain growth and form fine grains. Then the dislocation movement is hindered, positively affecting the dislocation strengthening mechanism. The improvement in the mechanical properties of HEAs are the result of the synergistic effects of grain boundary strengthening, solid solution strengthening, dislocation strengthening, and precipitation strengthening.

Appropriate additive manufacturing methods and process parameters can achieve superior mechanical properties compared to conventional casting. Liu et al. [127] conducted a comparative study on the microstructure and mechanical properties of CrMnFeCoNi HEAs fabricated using DED and conventional casting. The results indicated that the DED-fabricated samples exhibited higher hardness and yield strength due to their higher dislocation density and more pronounced grain boundary strengthening effects compared to the cast materials. Qiu et al. [128] found that CrMnFeCoNi HEAs manufactured using LPBF demonstrated exceptional mechanical properties. Compared to the cast materials, the dislocation density of LPBF-fabricated HEAs increased by over 100%, resulting in superior mechanical properties. Additively manufactured CrMnFeCoNi HEAs, characterized by a higher density of grain boundaries and enhanced resistance to dislocation cation movement, exhibited better tensile properties and yield strength than cast HEAs [3]. Joseph et al. [47] fabricated AlxCoCrFeNi HEAs using both DED and casting methods. The results showed that the DED-fabricated AlxCoCrFeNi HEAs had higher hardness, primarily attributed to their finer grain size. Dobbelstein et al. [59] manufactured TiZrNbHfTa HEAs using DLD. Compared to cast alloys, the DLD-fabricated alloys exhibited higher strength and better microstructural homogeneity.

6. Corrosion Resistance

The characteristics related to the microstructure of HEAs are summarized above. The microstructure of HEAs affects not only the mechanical properties, but also the corrosion resistance. HEAs with a high content of corrosion-resistant elements are expected to be a promising material for corrosion protection. The additively manufactured methods, heat treatment parameters, addition of different elements, and process parameters all influence corrosion resistance.

Table 5. Summary of corrosion current density for various additively manufactured methods and different materials.

Materials	Methods	Solution	Corrosion Current Density (A/cm2)	Corrosion Potential (V)	Ref
FeCoNiCrMn	PBF	3.5 wt% NaCl	9.333 × 10−2	−1.186	[119]
FeCrCoNiMoB1.1Si1.2	DED (1800 W) DED (2200 W) DED (2600 W) DED (3000 W)	3.5 wt% NaCl	7.24 × 10−6 3.39 × 10−6 2.40 × 10−6 4.16 × 10−6	−0.4231 −0.3177 −0.2760 −0.3437	[129]
AlCoCrFeNi	PBF PBF (500 °C) PBF (800 °C) PBF (1000 °C)	0.5 mol/LH2SO4	4.9924 × 10−8 3.9822 × 10−8 4.22382 × 10−8 4.2092 × 10−8	−0.1812 −0.1899 −0.2382 −0.2060	[130]
CoCrFeNiMo0.2	DED	3.5 wt% NaCl	1.84 × 10−9	−0.192	[131]
CoCrFeNi	DED	3.5 wt% NaCl	3.17 × 10−7	−0.265	[131]
CoCrFeNiMo0.2	DED	1 mol/L H2SO4	2.28 × 10−8	−0.406	[131]
CoCrFeNi	DED	1 mol/L H2SO4	4.87 × 10−5	−0.724	[131]
FeAlNiCoTiZrV FeAlNiCoV0.9Sm0.1 FeAlNiCoTiZrV0.95Sm0.5 FeAlNiCoTiV0.9Sm0.1	PBF	3.5 wt% NaCl	−4.44 −5.08 −4.96 −5.171	−0.755 −0.655 −0.666 −0.628	[32]
FeCrCuTiV	PBF	3.5 wt% NaCl	0.114	−0.084	[132]
Hf0.5Nb0.5Ta0.5Ti1.5Zr	As-cast	3.5 wt% NaCl	0.34	−0.73	[133]
AlCoCrFeNi	DED (800 °C) DED (1000 °C) DED (1200 °C)	0.6 M NaCl	0.117 0.129 0.089	−0.2641 −0.2596 −0.2409	[134]
NbMoTaW	PBF	3.5 wt% NaCl	8.716 × 10−11	−0.09157	[40]
CoCrFeMnNi	PBF	3.5 wt% NaCl	4.737 × 10−7	−0.265	[135]

summarizes the corrosion current densities of various additively manufactured HEAs.

6.1. Comparison of Corrosion Resistance of Cast and Additively Manufactured HEAs

The main additively manufactured technologies used for the fabrication of HEAs are LPBF and EPBF technologies. Fujieda et al. [108] studied the CoCrFeNiTi HEAs produced using LPBF and EPBF technologies and found that the CoCrFeNiTi HEAs produced using LPBF exhibited better corrosion resistance compared to that produced using EPBF. This improvement was attributed to the more uniform microstructure, more homogeneous chemical composition, and the finer grain size. Xia et al. [132] compared the corrosion resistance of FeCrCuTiV HEAs produced using DED-LB and cast HEAs. The results showed that the HEAs produced using DED-LB had a higher corrosion potential (Ecorr) and lower corrosion current (Icorr), indicating better corrosion resistance for the HEAs prepared using DED technology. This was attributed to the lower volume fraction (31.5%) of Cu-enriched phases in the DED-produced HEAs compared to the cast sample (44.7%). Additionally, the more uniform structure and finer grain size of the DED-produced HEAs (Figure 15a,b) contributed to its enhanced corrosion resistance. Xu et al. [135] studied the corrosion resistance of CoCrFeMnNi HEAs produced using PBF technology compared to cast CoCrFeMnNi HEAs in NaCl solution. The results showed that the PBF-produced HEAs exhibited more uniform composition and finer grain size, while the cast HEAs primarily consisted of coarse dendritic crystals with an average grain size greater than 34 μm. The Icorr of the PBF-produced HEAs was 58% lower than that of the cast HEAs, indicating superior corrosion resistance. This improvement was mainly attributed to the rapid solidification and complex thermal cycles during PBF, which resulted in fine grains and multi-scale microstructures in the PBF-HEAs, as well as a high Cr content in the passive film that enhanced the stability of the passive film. However, Thapliyal et al. [136] investigated the corrosion resistance of the LPBF-produced Fe38.5Mn20Co20Cr15Si5Cu1.5 HEA system. They found that the corrosion resistance of Fe38.5Mn20Co20Cr15Si5Cu1.5 HEA produced using LPBF is worse than the cast HEAs studied by Nene et al. [137]. The LPBF-produced Cu-HEAs were prone to microcracks and voids (Figure 15c). Furthermore, the accumulation of Cu near corrosion pits led to the formation of localized pitting corrosion (Figure 15d–f). The corrosion resistance of Cu-HEAs could be improved by adjusting the LPBF process parameters, including grain size, phase distribution, and porosity. Due to the numerous advantages of HEAs and the clear disadvantages of conventional cast stainless steels, the corrosion resistance of traditional cast stainless steels and additively manufactured HEAs has been studied. Zhang et al. [40] investigated the corrosion resistance of NbMoTaW HEAs produced by PBF and 316 L stainless steel. The results showed that the NbMoTaW HEAs had a lower Icorr. This better corrosion performance was primarily attributed to the contribution of easily passivating elements such as Nb, Mo, and Ta in the alloy. In conclusion, due to the advantages of additively manufactured technology, HEAs produced using appropriate process parameters can achieve better corrosion resistance than traditional cast HEAs.

6.2. Effect of Heat Treatment on Corrosion Performance

Heat treatment is an effective method for improving the corrosion resistance of additively manufactured HEAs. Fujieda et al. [108] found that heat treatment significantly affects the corrosion resistance of CoCrFeNiTi HEAs. Heat treatment alters the microstructure of CoCrFeNiTi HEAs, particularly the size and distribution of ordered particles, which in turn influences the corrosion resistance of material. In another study [138], the authors used a combination of EPBF and solution treatment to fabricate Co1.5CrFeNi1.5Ti0.5Mo0.1 HEAs. The results showed that solution treatment enhanced the pitting potential by promoting the homogenization of finely ordered phase particles. Pang et al. [130] studied the effect of different heat treatment temperatures on the corrosion resistance of AlCoCrFeNi HEAs produced using DED technology. The results indicated that the best corrosion resistance was achieved at a heat treatment temperature of 500 °C, which was attributed to the increased segregation of Cr, Al, Fe, and Ni elements in the alloy and the formation of a single BCC phase structure. This may contribute to the development of a more uniform passive film. Wang et al. [134] found that AlCoCrFeNi HEAs treated at 1200 °C exhibited better corrosion resistance than those treated at 800 °C and 1000 °C. This was due to the precipitation of FCC phases in the B2 matrix during heat treatment. Melia et al. [112] found that heat treatment promotes the homogenization of the microstructure in CoCrFeMnNi HEAs produced using DED at high temperatures, reducing chemical segregation and consequently minimizing the formation of micro-electrochemical couples.

6.3. Effect of Elements and Preparation Process Parameters on Corrosion Performance

The effect of adding different elements and using various process parameters during additively manufacturing on the corrosion resistance of HEAs has also been studied. For example, Sarswat et al. [32] used DED technology to fabricate AlCoFeNiTiV_0.9Smx HEAs with varying amounts of Sm. The study showed that the HEAs doped with Sm exhibited good corrosion resistance. After high-temperature corrosion tests, the material showed a single-phase FCC structure without significant surface cracking. The addition of Sm may help form a more compact and uniform microstructure, thereby enhancing the corrosion resistance of the system. In another study [139], researchers found that the addition of Ti to AlCoFeNiV_0.9Sm_0.1 HEAs increased the corrosion potential. Unfortunately, the addition of Ti led to the formation of Laves phases, which are more susceptible to localized corrosion. Ma et al. [119] added Fe-based amorphous alloy to FeCoNiCrMn HEAs, and the results showed an 18.9% reduction in corrosion current density. This can be attributed to the addition of Cr from the Fe-based amorphous alloy, improving the stability of the passive film. The influence of additively manufactured process parameters on corrosion performance was also studied. Xie et al. [129] investigated the effect of different laser powers on the corrosion performance of FeCrCoNiMoB_1.1Si_1.2 HEAs. The results showed that the corrosion resistance first increased and then decreased with increasing laser power, with the best corrosion resistance observed at 2600 W. This could be due to the enrichment of Mo at dendrite and cell boundaries, which may help form a more effective passive film. Wang et al. [131] prepared CoCrFeNiMo_0.2 HEAs with varying laser powers and compared the resulting corrosion resistance. The results indicated that the grain size of HEA increased with increasing laser power. Larger grains might lead to fewer grain boundaries, potentially reducing the path for corrosion media to penetrate, thus improving corrosion resistance.

7. Summary and Outlook

In this paper, a systematic review of the current research status of additively manufactured HEAs is carried out, focusing on summarizing the effects of elemental composition and process parameters on the microstructure. On this basis, the mechanical properties and corrosion properties of additively fabricated HEAs are discussed. It is shown that the material properties can be improved by selecting appropriate process parameters, doping elements, and post-treatment methods. A useful reference for researchers working with HEAs is provided to help one rationalize the selection of additively manufactured technologies and to facilitate the development of novel HEA compositions. However, the complexity of the additively manufactured HEA process poses new challenges to material properties. The microstructure, uniformity of chemical composition, cracks, porosity, and other defects of additively manufactured HEAs are difficult to precisely control. This review provides a good reference for the usefulness of additively manufactured HEAs. From this review, the future recommendations and challenges for additively manufactured HEAs are as follows:

(1)

Selection of elements

The additively manufactured HEAs primarily utilized CrFeCoNi and CrMnFeCoNi systems. For the exploration of novel HEAs, new alloying elements can be introduced to develop new HEAs systems. For instance, the addition of non-metal elements such as C or Si can enhance the mechanical properties of HEAs. The design of new HEAs systems may consider incorporating rare earth elements, as well as low-density metals such as Si, Li, Mg, and transition metals. These materials are considered to be challenging for additive manufacturing.

(2)

Other additively manufactured processes

Currently, the binder jetting additively manufacturing methods are mainly applied to the AlCoCrFeNi and CoCrFeMnNi HEA systems. HEAs fabricated using DED and PBF technologies experience thermal stresses, making it essential to develop new binders and employ binder jetting techniques to address this issue. Although HEAs produced using additive manufacturing methods were reported in 2015, the development has been slow. Therefore, it is crucial to explore other additively manufactured technologies for the fabrication of HEAs.

(3)

Optimization of process parameters

HEAs prepared using DED and PBF generally have defects such as porosity and cracks. The impact of these defects on material properties is enormous. Therefore, it is essential to eliminate these defects to ensure the excellent mechanical properties of HEA-based laser-printed components. During the DED and PBF additively manufacturing processes of HEAs, increasing the energy input or adding other alloying elements can help prevent the formation of excessive defects. In addition, based on the summary in this paper, it can be seen that the subsequent use of different scanning strategies can also help to improve the microstructure of additively manufactured HEAs.

(4)

For other performance studies

For additively manufactured HEAs, most studies have focused on the mechanical properties. However, research on characteristics such as fatigue life, fractured toughness, and corrosion resistance remain limited, and these functional properties are yet to be fully explored. Regarding corrosion, some researchers have primarily compared the corrosion resistance of HEAs produced using traditional casting methods with those produced using additive manufacturing. However, there is limited research on the effects of different elements, manufacturing parameters, and additively manufactured techniques on corrosion resistance and fatigue life. Additively manufactured HEAs, designed with a functional focus, offer new possibilities for the use and design of HEAs. Therefore, it is crucial to explore other performance aspects of additively manufactured HEAs.

(5)

Computer predictive modelling

The current development of additively manufactured HEAs is dominated by iterative experiments to obtain optimal solutions. Such an approach is both time-consuming and labor-intensive. Deep learning can be utilized to develop new additively manufactured HEAs [140], accelerating the development of novel HEAs. Machine learning can be applied to predict various properties of additively manufactured HEAs, such as surface roughness, density, fatigue performance, and tensile strength. This approach allows for the extraction of hidden relationships between process parameters and alloy properties from large experimental datasets, effectively shortening the development cycle for specific alloy process parameters and reducing research and development costs.