The Design and Preparation of New Fe_(21-x)CoNiCuAlTi_x High-Entropy-Alloy Wear- and Corrosion-Resistant Coatings and an Investigation of Their Performance

Abstract

The purpose of this study is to prepare new Fe_(21-x)CoNiCuAlTi_x alloy coatings and to investigate the phase composition, microstructure, wear resistance, and corrosion resistance of these high-entropy-alloy coatings with varying Ti content. High-entropy Fe_(21-x)CoNiCuAlTi_x (x = 0; 2; 4; 6; 8) alloy coatings were prepared on 65Mn steel substrates via laser cladding. The results showed that the addition of Ti promoted the formation of the BCC phase, which increased the hardness of the coatings and improved their wear resistance due to the hardening of the solid solution and grain refinement. The microhardness of the coating was 689.08HV_0.2 at x = 8, 2.056 times that of the base metal, and the wear resistance was 2.565 × 10⁻⁷ g/(N·m). The corrosion potential and corrosion current density were −0.199 V and 3.513 × 10⁻⁷ A/cm², respectively, indicating excellent corrosion resistance. The addition of titanium significantly enhanced the formation of the BCC phase, improved the microstructure through solid-solution hardening and grain refinement, and caused lattice distortion. These effects, as well as the formation of solid bonds, significantly improved the wear and corrosion resistance of the coatings.

1. Introduction

Laser cladding is a state-of-the-art surface modification and repair technology that uses a high-energy laser beam as a heat source to fuse the coating material to the substrate [1,2,3]. This process creates a metallurgical bond that forms a reinforcing layer on the substrate surface, which, after rapid curing, improves properties such as wear and corrosion resistance [4,5]. Laser cladding offers many advantages over other surface modification processes, including high deposition rates, minimal substrate thinning, strong metallurgical bonding between the coating and substrate, a high degree of automation, environmental friendliness, and the ability to accommodate workpieces with different geometries [6,7,8].

Currently, it is not uncommon to see research on the preparation of high-performance coatings using laser cladding technology. Wang et al. [9] prepared iron-based amorphous coatings on the surface of AISI 1020 steel tubes using high-speed laser cladding technology. Their results showed that the coatings obtained at a scanning speed of 50 mm/s exhibited a clear three-layer hardness distribution, with the second layer being the hardest. This phenomenon was mainly attributed to amorphous strengthening, fine-grain strengthening, and martensitic strengthening. The bottom region of the coating contained budding crystals with prominent iron aggregation. The amorphous content of the coatings showed an increasing and then decreasing trend with increasing scanning speed. In particular, the amorphous phase content of the 130 mm/s coating was as high as 95%. Differential scanning calorimetry (DSC) confirmed the presence of amorphous phases in the bottom and middle regions of the 50 mm/s coating. Electrochemical experiments demonstrated the excellent corrosion resistance of the 130 mm/s coating, as evidenced by the maximum corrosion potential (−0.471 V), the minimum corrosion current density (2.7 × 10⁻⁶ A/cm²), and the maximum polarization resistance (22,149 Ω·cm²). This excellent performance was attributed to the presence of an amorphous phase and the formation of a chromium oxide layer on the surface, which provided strong protection to the substrate. In a study by YUAN et al. [10], Ni45 alloy powders were deposited on a steel substrate using conventional low-speed laser cladding and high-speed laser cladding processes. The cladding efficiency, surface morphology, cross-sectional microstructure, microhardness, wear resistance, and corrosion resistance of the Ni45 alloy coatings prepared by both conventional and high-speed laser cladding were comparatively analyzed. The results indicated that the thickness of the high-speed laser cladding coating was significantly lower than that of the conventional laser cladding coating. Compared to conventional laser cladding, high-speed laser cladding achieved a cladding speed of 76.86 m/min and a cladding efficiency of 156.79 cm²/min. The microstructures of both coatings exhibited the same growth pattern, but the high-speed laser cladding coating displayed a finer and denser microstructure with narrower columnar crystal spacing, approximately 6 µm. It was found that the cooling rate of the conventional laser cladding coating was lower than that of the high-speed laser cladding coating, and as the cladding speed increased, the cooling rate progressively increased. The cross-sectional microhardness of the conventional laser cladding coating was relatively uniform at 337 HV0.2, while the surface microhardness of the high-speed laser cladding coating increased to approximately 543 HV0.2. Additionally, the wear resistance and corrosion resistance of the high-speed laser cladding coatings were superior to those of the conventional laser cladding coatings, and these properties further improved with increasing cladding speed.

High-entropy alloys (HEAs) differ from the concept of conventional alloys with a single basic element in that they contain multiple basic elements. High-entropy alloys typically consist of at least five elements, and their atomic content ranges from 5% to 35% [11,12,13]. Their innovative composition gives HEAs unique high-entropy effects, slow diffusion effects, strong lattice distortion effects, and cocktail effects, resulting in high mechanical properties and corrosion resistance [14,15,16,17,18].

Because of its composition design flexibility and excellent performance, and since the high-entropy alloy design concept put forward for the research and application of laser cladding technology provides a new idea, at present, the high-entropy alloy composition design is more common in research. WANG et al. [19] used laser cladding technology to prepare high-entropy alloy coatings on the surface of Q345 welded structures. Their experiments specifically analyzed the effect of chromium and aluminum content on corrosion resistance and its intrinsic mechanism. Their results showed that FeCoCr1.5NiAl coatings exhibited good metallurgical bonding and promoted the formation of hard and brittle BCC phases, thus improving wear resistance. The FeCoCrNiAl(_y) notation refers to a high-entropy-alloy system, where _y represents the variable aluminum (Al) content, which was adjusted to study its influence on the alloy’s microstructure and mechanical properties. In the FeCoCrNiAl(_y) high-entropy alloy, the metallurgical bonding remained stable. As the aluminum content increased, cracks appeared in the coating, which further promoted the formation of the BCC phase and thus improved the hardness and wear resistance. However, the corrosion resistance decreased with increasing aluminum content. Due to the presence of chromium, aluminum, and other elements known for their corrosion resistance, high-entropy alloy coatings are able to form a dense oxide film in saline and neutral salt spray environments. This oxide film effectively prevented the development of corrosion, providing 99.1% protection efficiency for the weld, 98.4% for the heat-affected zone, and 96.6% for the base metal. These findings indicate that the coatings provided excellent protection against corrosion in all zones. Although the FeCoCrNiAl(_y) high-entropy-alloy coatings exhibited excellent wear resistance due to the formation of the BCC phase, their corrosion resistance was highly dependent on the chromium and aluminum content. The optimum balance between hardness, wear resistance and corrosion resistance was achieved at a specific composition, especially when y = 1.5, which made the coatings very effective in protecting welded joints in corrosive environments. Xu et al. [20] prepared AlxCoCrFeNiTi1-x/SiC (x = 0.5, 0.8 molar ratio) high-entropy-alloy coatings by introducing SiC ceramic particles to AISI1045 steel through laser cladding. The microstructures, phase compositions, mechanical properties, and corrosion resistance of the prepared coatings with and without SiC particles were thoroughly investigated and compared. They found that the added SiC particles decomposed into Si and C during laser cladding processing, which was proven to have an important influence on the formation of the microstructure of the alloy coatings. In the Al0.5 alloy coating, the cubic L21 precipitation in the disordered BCC matrix transformed into a coarse lath-like microstructure consisting of an L21 and an FCC matrix in Al0.5/SiC. At the same time, a finer woven network structure appeared in the Al0.8/SiC alloy coating, which corresponded to the increase in the volume fraction of the B2 phase. The microhardness of the Al0.8/SiC alloy coatings increased from 637 HV0.2 to 718 HV0.2 for Al0.8 with the addition of SiC, and the friction coefficient decreased from 0.40 to 0.31. On the contrary, the SiC particles negatively affected the microhardness of the Al0.5/SiC alloy coatings, which decreased from 743 to 679 HV0.2, due to the coarsening of the microstructure and the decrease in flexible FCC solids. This was due to the coarsening of the microstructure and the increase in the proportion of flexible FCC solid solution. In the Al0.5 alloy coatings, the coefficient of friction reached a minimum value of 0.29, and there was a mixed wear mechanism of abrasion and delamination wear. In addition, the pitting potentials of both Al0.5/SiC and Al0.8/SiC were lower than those of the SiC-free alloy coatings. The dissolution of SiC particles contributed to the breakdown of cusp crystals and the expansion of interphase lattice dislocations, which reduced the pitting resistance of the coatings.

Few studies have been reported on the compositional design of high-entropy alloys with more than five elements. Therefore, in this study, we designed new Fe_(21-x)CoNiCuAlTi_x high-entropy-alloy wear- and corrosion-resistant coatings, and prepared composite coatings on the surface of a 65Mn substrate by changing the content of Ti elements, and studied the microstructure and performance of coatings with different Ti contents.

2. Materials and Methods

2.1. Experimental Materials

The test substrate was a Φ60 mm × 15 mm 65Mn plate. Oxide film and oil on the surface of the substrate were removed with sandpaper and cleaned with anhydrous ethanol. High-entropy FeCoNiCuAl alloy powder (45–105 μm) and pure Ti spherical powder (53–105 μm) were selected as test powders, and different weight proportions of the powders were weighed and mixed using an electronic scale according to the experimental program. The composition of the test powders is shown in

Table 1. Chemical composition of FeCoNiCuAl high-entropy alloys with different Ti contents/wt%.

	Ti	Fe	Cu	Ni	Al	Co
0	0	21	24.12	22.47	10.49	Bal.
Ti2	2	19	24.12	22.47	10.49	Bal.
Ti4	4	17	24.12	22.47	10.49	Bal.
Ti6	6	15	24.12	22.47	10.49	Bal.
Ti8	8	13	24.12	22.47	10.49	Bal.

, and the powders in different proportions were fed into a ball mill with a rotational speed of 200 rpm and a mixing time of 120 min. Figure 1 shows a schematic diagram of the laser cladding principle.

The testing equipment utilized an IPG-3000W laser(Oxford, MA, USA) to deposit five different powders on the surface of 65 Mn substrates, creating a powder bed. Through process parameter mapping, the optimal parameters were selected as follows: a laser power of 1600 W, a scanning speed of 10 mm/s, a spot diameter of 3 mm, an overlap of 1.5 mm, a focal length of 40 mm, and an argon gas flow rate of 10 L/min for protection.

2.2. Test Methods and Characterization

The coating was cut into specimens of the required size to be tested using an EDM wire cutter. The hardness specimens were treated with 600-mesh abrasive paper, and the microhardness of the coatings on the substrates was measured using an HV1000Z Vickers hardness tester with the following equipment parameters: an applied load of 200 g, time preservation of 10 s, and a pitch of 0.15 mm. The metallographic specimens were polished with 240-mesh, 600-mesh, 1000-mesh, and 2000-mesh sandpaper as well as alumina solution, and the microstructure of the coatings after etching in aqua regia for 20 s was observed using a 4XC metallographic microscope. The XRD specimens were treated with 600-mesh sandpaper and then analyzed by an XD-3 X-ray diffractometer with the following parameters: an operating voltage of 36 kV, an operating current of 24 mA, an X-ray tube with a copper target, a step width of 0.02 degrees, a scanning speed of 4°/min, and a range of 10–90°. Jade 6 software was used for coating phase analysis after scanning. After the friction specimens were ground with 600-mesh sandpaper to ensure a uniform surface finish, they were subjected to a ball-on-disk tribological test using a CHMT23 tribometer. The test parameters were set as follows: a wear track radius of 6 mm, a rotational speed of 500 rpm, and a test duration of 30 min. The mass loss of the specimens before and after the wear test was measured using a high-precision electronic balance, and the corresponding wear rate was calculated based on the mass difference. The wear morphology and surface characteristics of the specimens were subsequently analyzed using a Zeiss EVO-18 scanning electron microscope (SEM) to evaluate the wear mechanisms and microstructural changes. After the electrochemical specimens were treated with 600-mesh and 1000-mesh sandpaper, the polarization curves and impedance spectra of the coatings were obtained by using a three-electrode test to analyze the corrosion behavior after immersing the specimens in NS4 solution for 6 h using a CHI660E electrochemical workstation.

3. Results and Discussion

3.1. Morphology of Laser-Clad HEA Specimens

Figure 2 shows the surface morphology of the Fe_(21-x)CoNiCuAlTi_x coating, indicating that the addition of Ti improves the surface quality of the coating, enhancing its flatness and homogeneity [21]. Figure 2e shows that too much Ti concentrates stresses and causes defects such as holes and cracks in the coating.

3.2. Physical Phase Analysis of Coatings

Figure 3 shows the XRD spectrum of the Fe_(21-x)CoNiCuAlTi_x composite coating. The results show that the high-entropy Fe_(21-x)CoNiCuAlTi_x coating exhibits a single FCC phase corresponding to the solid solution of Fe and Ni at x = 0; as the Ti content increases to x = 2, a BCC phase begins to develop in the coating. At this stage, the phase structure consists of the FCC and BCC phases associated with the Ti solid solution. With the addition of titanium, the intensity of the BCC diffraction peak gradually increases and reaches a maximum at x = 8. This observation indicates that the addition of titanium alters the crystal structure and phase composition of the alloy. The leftward shift in the BCC diffraction peak with increasing titanium content indicates that larger titanium atoms are added to the BCC phase in solid solution, resulting in lattice distortion [22]. The BCC structure has a lower slip coefficient and higher dislocation resistance than the FCC structure, so the formation of the BCC phase is advantageous [23].

3.3. Microstructural Analysis of Coating

Figure 4 shows the microstructures of the Fe_(21-x)CoNiCuAlTi_x coatings. a₁, b₁, c₁, d₁, and e₁ correspond to the middle of the different coatings, and a₂, b₂, c₂, d₂, and e₂ correspond to the bottom of the coatings at the junction with the substrate. It can be seen that the coating with x = 0 is mainly composed of equiaxed crystals with a uniform grain distribution, a compact arrangement, and obvious grain boundaries. With the addition of the Ti element with x = 2, the coating grain is obviously refined, and point-like short rod-like precipitates appear on the grain boundaries. At x = 4, it can be seen that some small particles are precipitated inside the grains, which are uniformly dispersed, and the coating is mainly composed of columnar dendritic crystals when the content of the Ti element is increased to x = 8. Due to the high melting point of Ti, the extremely high temperature during the cladding process causes the precipitation of Ti elements, resulting in an increase in solid solution, while the Ti elements in the solidification process will form fine TiC, TiB2, and other compounds; these compounds play the role of heterogeneous nucleation, thus improving the coating microstructure of the grain, in order to enhance the performance of the coating [24]. The addition of the Ti element forms compounds with high hardness such as TiC, and the diffuse distribution of such compounds can significantly enhance the microhardness of the coating.

3.4. Microhardness of Coatings

Figure 5 shows the microhardness of the Fe_(21-x)CoNiCuAlTi_x coating. The average hardness of the coating tends to increase with the addition of Ti elements, showing a positive correlation with Ti content. At x = 0, the average hardness of the coating is 518.63HV_0.2; at x = 2, the average hardness of the coating is 551.44HV_0.2; at x = 4, the average hardness increases significantly to 626.25HV_0.2; for x = 6, the average microhardness of the coating is 674.04HV_0.2; and for x = 8, the average microhardness of the coating is 674.04HV_0.2. The maximum microhardness of the coating for x = 8 is 689.09HV_0.2. The maximum microhardness of the x = 8 coating is 689.08HV_0.2, which is 32.86% higher than the coating without titanium and 105.14% higher than the average hardness of the base metal, 335.14HV_0.2.

This is mainly because the addition of Ti elements strengthened the solid solution of the coating and promoted grain refinement: the radius of Ti atoms is larger than that of other elements in the melt, and the high-temperature solid-solution state dissolves into other phases, resulting in a strongly distorted solid-solution lattice [25]. Combined with the microstructure and X-ray diffraction analysis, the addition of the Ti element effectively promotes the formation of a BCC phase in the composite coatings, and at the same time, it obviously has a refining effect on the grain structure and enhances the mobility of the dislocations between the grains [26], which therefore results in the enhancement of the microhardness of the composite coatings.

3.5. Frictional Wear Behavior of Coatings

3.5.1. Average Coefficient of Friction and Wear Rate

Figure 6a shows the average friction coefficient of the Fe_(21-x)CoNiCuAlTi_x coating. In the first wear phase, the sliding friction between the coating material and the friction partner is unstable, so the friction coefficient increases significantly in this phase, indicating that the coating has entered the stable wear phase, since the friction coefficient tends to stabilize. The combination of Figure 6a and

Table 2. Friction coefficient of Fe_(21-x)CoNiCuAlTi_x high-entropy-alloy composite coating.

Coatings	Coefficient of Friction	Average Coefficient of Friction	Dispersion Errors (Standard Deviation)
HEA	0.391	0.49	0.07
	0.517
	0.550
Ti2	0.415	0.44	0.04
	0.501
	0.413
Ti4	0.386	0.43	0.05
	0.497
	0.416
Ti6	0.491	0.42	0.06
	0.354
	0.403
Ti8	0.216	0.26	0.03
	0.285
	0.291

,

Table 3. Wear amount of Fe_(21-x)CoNiCuAlTi_x high-entropy-alloy composite coating.

Coatings	Amount of Wear/g	Average/g	Dispersion Errors (Standard Deviation)
HEA	0.0218	0.022	0.003
	0.0194
	0.0260
Ti2	0.0138	0.015	0.004
	0.0112
	0.0212
Ti4	0.0097	0.010	0.0006
	0.0101
	0.0111
Ti6	0.0048	0.007	0.0013
	0.0077
	0.0073
Ti8	0.0039	0.006	0.002
	0.0049
	0.0086

and

Table 4. Wear rate of Fe_(21-x)CoNiCuAlTi_x high-entropy-alloy composite coating.

Coatings	Wear Rate g/(N·m)	Average g/(N·m)	Dispersion Errors (Standard Deviation)
HEA	9.64 × 10−7	9.9 × 10−7	1.2 × 10−7
	8.58 × 10−7
	11.50 × 10−7
Ti2	6.10 × 10−7	6.9 × 10−7	1.9 × 10−7
	4.95 × 10−7
	9.38 × 10−7
Ti4	4.29 × 10−7	4.6 × 10−7	2.6 × 10−8
	4.47 × 10−7
	4.91 × 10−7
Ti6	2.12 × 10−7	2.9 × 10−7	5.7 × 10−8
	3.41 × 10−7
	3.23 × 10−7
Ti8	1.72 × 10−7	2.6 × 10−7	8.9 × 10−8
	2.17 × 10−7
	3.80 × 10−7

shows that the average friction coefficient of the coating at x = 0 is 0.486, and the corresponding wear mass and wear rate are also the highest at 0.0224 g and 9.907 × 10⁻⁷ g/(N·m), respectively. The coefficient of coated friction is inversely proportional to the increase in Ti element content, and the average coefficient of coated friction decreases with increasing Ti element content, with the average coefficient of coated friction decreasing significantly at x = 8. The average coated friction coefficient decreases significantly to 0.264 and shows a stable wear rate; the significant decrease to 0.264 is accompanied by the lowest values of wear mass and wear rate, 0.0058 g and 2.565 × 10⁻⁷ g/(N·m), respectively.

According to the comprehensive analysis of the film phases, lattice structure analysis, and micro-scratch analysis, the formation of the BCC phase is due to the presence of Ti. The slip coefficient of the BCC phase is lower than that of the FCC phase, the slip hardness is higher, the strength of the BCC structure is higher, the surface stacking density is lower, and the strength of the BCC phase is higher. In addition, dislocation motion at an atomic scale leads to high interlattice friction [27], and the presence of Ti leads to the formation of TiC and other compounds of high hardness at the same time, which significantly improves the wear resistance of the coating. The solid-solution strengthening and micrograin hardening due to the addition of Ti elements, combined with the large distortion of the lattice due to the large difference in atomic radii, leads to an increase in the microhardness of the coating. In general, there is a positive correlation between the microhardness of the coating and wear resistance. Thus, the wear resistance of the coating increases with increasing Ti content.

3.5.2. Coating Surface Wear Morphology and Wear Mechanism

Figure 7 shows the wear scar morphology of the Fe_(21-x)CoNiCuAlTi_x coating. The wear scar morphology of the coating at x = 0 has many deep grooves and furrows in the friction direction due to the presence of fine coarse particles between the coating surface and the lower friction surface and plastic deformation near the grooves, indicating abrasive wear, which is the corresponding wear mechanism. Discontinuous grooves, gaps, holes, and raised layers are observed on the coating surface after wear at x = 2 and x = 4, indicating that the interaction of the particles formed between the friction substrate and the coating during the wear process has created grooves on the coating surface. When adhesive and abrasive wear occur simultaneously, the abrasive residue on the surface continues to interact with the coating surface after polishing by adhesive wear, resulting in the formation of grooves. When the Ti element content increases, there is visible lightening of the grooves on the surface of the coating, and when x = 8, there are almost invisible furrows; at this time, the abrasive wear is dominated by the existence of slight adhesive wear, thus proving that the incorporation of Ti elements can significantly enhance the wear resistance of the coating.

3.6. Corrosion Behavior of Coatings

Figure 8a shows a kinetic potential polarization curve of the Fe_(21-x)CoNiCuAlTi_x coating in NS4 solution, and Figure 8b illustrates the impedance spectra of the coating in corrosive solution. According to the Tafel extrapolation method [28], we analyzed the electrochemical corrosion parameters of the coating, as shown in Table 3. The electrochemical corrosion theory points out that the corrosion potential indicates the tendency of a material to corrode. A more positive value indicates that its tendency to corrode in corrosive environments is lower, and these are inversely proportional to each other. The self-corrosion current density indicates that the material corrosion phenomenon occurs at the rate of the rate criterion, the greater the value, the faster the corresponding corrosion rate is faster, and these are proportional to each other. The relationship with corrosion current density can be a visual response to the material’s corrosion resistance performance [29].

According to the electrochemical parameters shown in

Table 5. Electrochemical corrosion parameters of Fe_(21-x)CoNiCuAlTi_x high-entropy-alloy composite coating in NS4 solution.

Coatings	Ecorr/V	Icorr/A/cm2
HEA	−0.349	1.714 × 10−6
Ti2	−0.309	1.094 × 10−6
Ti4	−0.307	5.966 × 10−7
Ti6	−0.289	4.761 × 10−7
Ti8	−0.199	3.513 × 10−7

, when x = 0, the corrosion potential of the coating has a minimum value of −0.349 V and the corresponding corrosion current density has a maximum value of 1.714 × 10⁻⁶ A/cm². With a constant increase in titanium content, the corrosion potential of the coating gradually approaches a positive value and the corrosion current density decreases. At a corrosion potential of −0.199 V (x = 8), the wear resistance of the coating containing the Ti element is 42.98% higher than that of the coating without the Ti element. The corrosion current density is 3.513 × 10⁻⁷ A/cm², an increase of 387.8%. This is because the Al element in the high-entropy Fe_(21-x)CoNiCuAlTi_x alloy forms an Al₂O₃ oxide layer and the Ti element forms a dense and stable TiO₂ oxide layer [30]. The addition of Ti significantly improves the microstructure of the coating and reduces the corrosion rate by reducing the grain size. Ti and other elements can form stable intermetallic compounds and reduce corrosion rates at grain boundaries [31,32]. Intergranular compounds can reduce intergranular corrosion caused by potential drift and improve the corrosion resistance of the coating.

4. Conclusions

In this study, Fe_(21-x)CoNiCuAlTi_x high-entropy-alloy coatings were designed and applied to 65 Mn substrates using laser melting technology. The coatings’ physical phase composition, microstructure, tribological behavior, and corrosion resistance were analyzed by varying the Ti content. The key findings are as follows:

• The Fe_(21-x)CoNiCuAlTi_x coating initially exhibits a single FCC phase at x = 0, where the FCC phase corresponds to Fe and Ni solid solutions. Upon the introduction of Ti, a BCC phase begins to emerge, attributed to the Ti solid solution. As the Ti content increases, the BCC diffraction peaks intensify, reaching their maximum at x = 8. This indicates that the addition of Ti alters the alloy’s crystal structure, promoting the formation of the BCC phase. Furthermore, the corresponding FCC diffraction peaks shift to the left with increasing Ti content, suggesting that the incorporation of Ti induces lattice distortion.
• For the coating with the addition of Ti elements, the microstructure of the grain is significantly refined due to the high melting point of Ti and the high temperature of the laser cladding process precipitation, resulting in an increase in the solid solution, while Ti elements in the solidification process form stable TiC, TiB2, and other compounds; these compounds play a role in heterogeneous nucleation, which promotes the refinement of the coating grains. The distribution of Ti elements forms TiC and other high-hardness compounds, which can significantly improve the microhardness of the coating.
• The comprehensive coating physical phase analysis, tissue structure analysis, and microhardness analysis show that due to the addition of Ti elements to promote the formation of a BCC phase, compared to an FCC phase, the coating’s slip coefficient is smaller, it cannot slip as easily, and it has higher strength, and the presence of Ti will generate TiC and other high-hardness compounds at the same time, which greatly improves the abrasion resistance of the coatings; the addition of Ti elements to the coatings enhances both solid-solution strengthening and fine-grain strengthening. The significant lattice distortion caused by the atomic radius difference in the Ti atoms contributes to this effect. This distortion leads to an increase in the microhardness of the coatings, resulting in improved wear resistance as the Ti content is increased.
• As the Ti content increases, the corrosion potential of the Fe_(21-x)CoNiCuAlTi_x coating gradually shifts to a more positive value, and the corrosion current density decreases. At x = 8, the corrosion potential reaches −0.199 V, representing a 42.98% increase compared to the coating without Ti addition. The corrosion current density at this composition is 3.513 × 10⁻⁷ A/cm², an improvement of 387.8%. This enhancement is attributed to the formation of Al₂O₃ and TiO₂ oxide films by the Al and Ti elements, respectively. The introduction of Ti significantly refines the microstructure, reducing the corrosion rate through grain size refinement. Additionally, Ti and other elements stabilize intermetallic compounds, further reducing the corrosion rate at grain boundaries and enhancing the overall corrosion resistance of the coating.