Search Results (42)

This work studies the fabrication of CoCrFeNiMo high-entropy alloy (HEA) coatings via coaxial powder-fed laser cladding, addressing porosity and impurity issues in conventional methods. The HEA coatings exhibited eutectic/hypereutectic microstructures under all laser power conditions. A systematic investigation of laser power effects (1750–2500 W) reveals that 2250 W optimizes microstructure and performance, yielding a dual-phase structure with FCC matrix and dispersed σ phases (Fe-Cr/Mo-rich). The coating achieves exceptional hardness (738.3 HV_0.2, 3.8× substrate), ultralow wear rate (4.55 × 10⁻⁵ mm³/N·m), and minimized corrosion current (2.31 × 10⁻⁴ A/cm²) in 3.5 wt.% NaCl. The friction mechanism of the CoCrFeNiMo HEA coating is that in high-speed friction and wear, the oxide film is formed on the surface of the coating, and then the rupture of the oxide film leads to adhesive wear and abrasive wear. The corrosion mechanism is the galvanic corrosion caused by the potential difference between the FCC phase and the σ phase. Full article

In this study, FeCoNiCrAl high-entropy alloy (HEA) coatings were fabricated on Q235 steel surfaces using laser cladding (LC) to enhance corrosion resistance in harsh environments. The laser processing parameters (laser power, defocus distance, and scanning speed) were optimized using response surface methodology (RSM), establishing a mathematical model to guide the process. The optimized coatings demonstrated strong metallurgical bonding to the substrate, with a microstructure comprising Al-Ni-rich B2 phases and Cr-Fe-rich BCC phases. Elemental segregation was effectively mitigated as energy density decreased, leading to significant improvements in corrosion resistance. Electrochemical tests in 3.5 wt.% NaCl and 0.5 mol/L H₂SO₄ solutions showed that the optimized coating (laser power: 800 W, scanning speed: 450 mm/min, defocus: −15 mm) exhibited exceptionally low corrosion current densities of 1.78 × 10⁻⁷ A/cm² and 1.07 × 10⁻⁵ A/cm², respectively. The passive film on the optimized coating surface consisted of stable oxides, with low oxygen vacancy densities of 1.937 × 10²³ cm⁻³ in NaCl and 4.967 × 10²¹ cm⁻³ in H₂SO₄, significantly enhancing its resistance to localized and uniform corrosion. These results demonstrate the effectiveness of RSM-based optimization in producing HEA coatings with superior corrosion resistance suitable for applications in highly corrosive environments. Full article

To investigate the effect of recovery treatment on the microstructure and tribological properties of ultrasonic impact-treated Al₂FeCoNiCrW_0.5 high-entropy alloy coatings, laser cladding technology was used to fabricate coatings on a G10450 steel substrate, followed by ultrasonic impact treatment (UIT) and recovery treatment (HR, 300 °C). The results showed that the Al₂FeCoNiCrW_0.5 high-entropy alloy coating consisted of BCC and FCC phases. Ultrasonic impact treatment slightly broadened the XRD diffraction peaks, while the recovery treatment had minimal effect on them. Ultrasonic impact also refined the coating grains. Ultrasonic impact treatment increased the coating hardness from 738 HV_0.5 to 856 HV_0.5. Although the subsequent post-annealing slightly reduced the hardness to 806 HV_0.5, it significantly improved wear resistance, with wear loss decreasing from 3.273 mm³ to 2.881 mm³, representing a 15% reduction in wear rate. The improvement in wear resistance was attributed to a change in the wear mechanism of the high-entropy alloy coating. Before and after post-annealing, the mechanism transitioned from abrasive wear, adhesive wear, and oxidative wear to primarily abrasive wear and oxidative wear. Additionally, the recovery treatment transformed the surface from hard and brittle to ductile and resilient. Full article

Previous studies have focused on the laser cladding of high-entropy alloys (HEAs) on untreated H13 steel, yielding promising results. However, there is limited research on laser cladding HEAs on heat-treated H13 steel, which is more common in the automotive mold industry. In this study, CoCrFeNiAl/WC high-entropy alloy composite coatings were fabricated on heat-treated H13 steel using laser cladding, addressing the gap in applying HEAs on heat-treated tool steels. The influence of the WC content on the phase composition, microstructure, and mechanical properties of the composite coating was investigated. The coating exhibits a dual-layer microstructure consisting of a working layer and a transition layer with different compositions. The results indicate that the CoCrFeNiAl/WC working layer primarily consists of FCC phases. As the WC content increases, metallurgical reactions occur in the working layer, forming (Fe,Co)₃W₃C, Co₄W₂C, and Cr₇C₃ carbide precipitates. This significantly enhances the hardness and wear resistance of the coating, with the final hardness being 1.23 times that of the substrate, the wear weight loss being only 0.21 times that of the substrate, and the average friction coefficient being only 0.82 times that of the substrate. Full article

The Ti-6Al-4V alloy is widely utilized in the aerospace industry for applications such as turbine blades, where it is valued for its mechanical strength at high temperatures, low specific gravity, and resistance to corrosion and oxidation. This alloy provides crucial protection against oxidation and thermal damage. A thermal barrier coating (TBC) typically consists of a metallic substrate, a bond coating (BC), a thermally grown oxide (TGO), and a topcoat ceramic (TC). This study aimed to investigate laser parameters for forming a TBC with a NiCrAlY bond coating and a zirconia ceramic topcoat, which contains 16.0% equimolar yttria and niobia. The coatings were initially deposited in powder form and then irradiated using a CO₂ laser. The parameters of laser power and beam scanning speed were evaluated using scanning electron microscopy and X-ray diffraction. The results indicated that the optimal laser scanning speed and power for achieving the best metallurgical bonding between the substrate/BC and the BC-TGO/TC layers were 70 mm/s at 100 W and 550 mm/s at 70 W, respectively. Laser-based layer formation has proven to be a promising technique for the application of TBC. Full article

CoCrFeNiTiAl high-entropy alloy coatings have been prepared by laser cladding technology based on response surface methodology (RSM). The results show that the effects of laser power, cladding speed, and pulse width on the dilution rate and microhardness of the high-entropy alloy coatings are investigated. Among the single-factor results, the laser power has the most significant effect on the properties of high-entropy alloy coatings, followed by the cladding speed, while the pulse width has no significant effect. In the interaction term analysis, the interaction term of laser power and pulse width has a remarkable effect on both output responses, whereas the interaction term of pulse width and cladding speed only has a considerable effect on microhardness, while the interaction term of laser power and cladding speed has an insignificant effect on both output responses. The optimum parameters for the preparation of high-performance high-entropy alloy coatings are found at laser power P = 676.73 W, cladding speed V = 5 mm/s, and pulse width P₀ = 9 ms. The microstructures of the high-entropy alloy coating prepared with optimal process parameters have been characterized, which show that the metallurgical bonding between the cladding layer and the substrate is strong and without obvious defects such as porosity and cracks. Full article

In this paper, the texture evolution of the Ni-5%W alloy baseband with different strain variables (ε_vM = 3.9, 4.9, and 5.1) during rolling and annealing was studied using the electron back scattering diffraction (EBSD) technique. The results indicate that after high-temperature annealing at 1150 °C, all three strain levels of the alloy substrates can achieve a strong cubic texture, with a content exceeding 99% (<10°). However, the texture evolution trajectory is significantly influenced by the strain level. When the content of cubic texture in the alloy substrates under strain levels of 3.9 and 5.1 is the same, significant temperature differences exist. Additionally, the different strain levels result in varying nucleation rates and growth rates of cubic texture in the Ni-5%W alloy substrates. The study reveals that in the alloy substrates under strain levels of 3.9 and 4.9, recrystallized cubic grain nuclei grow within a layered structure, resulting in larger grain sizes and lower nucleation rates. In contrast, in the alloy substrates under a strain level of 5.1, recrystallized cubic grain nuclei form from small equiaxed grains, leading to higher nucleation rates but smaller grain sizes, competing with random orientations. In the later stages of nucleation, recrystallized grains in the alloy substrates under a strain level of 5.1 exhibit a significant size advantage, rapidly growing by engulfing randomly oriented grains. Compared to the alloy substrates with lower strain levels, the recrystallized cubic grains in the alloy substrates under a strain level of 5.1 have higher nucleation rates and faster growth rates. Full article

Nowadays, there are many surface treatment methods for aluminium alloys; the most commonly used of these is the chemical dip galvanizing process, which is complicated due to its use of large quantities of corrosive drugs. In order to simplify the process, this paper proposes a new electromagnetic induction heating activation method instead of the zinc dipping process. The method works as follows: The substrate is first degreased and then activated. The activation process starts by soaking the degreased substrate in an activation solution, taking it out after ten minutes, and placing it into an induction heating unit. The activation solution is sprayed onto the surface of the substrate while heating, using the energy generated by high temperatures to complete the activation reaction. The surface of the activated substrate forms a nanoscale film of nickel, which is finally utilised as a catalytic centre for ENP (an advanced surface treatment process that deposits a very uniform layer). The optimisation of important parameters of the non-destructive activation process was determined using the L9 Taguchi method. The main parameters ranged from 0.15 L/min to 0.25 L/min for spray rate, 200 °C to 400 °C for heat treatment temperature, and 1:4, 1:5, and 1:6 for Ni²⁺ and H₂PO₄⁻ ion concentration ratios. The above data were derived from a single variable and were analysed using Minitab 20 software. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy spectrometry (EDS), and ultrasonic experiments were used to characterize and analyse the surface morphology, composition, and bond strength of the coatings. The results show that the nanoscale nickel particles can completely cover the surface of the substrate, forming a layer of nano-film. After activation and ultrasonic cleaning for 30 s at an ultrasonic frequency of 40 KHz and a power of 80 W, the surface nano-film was not destroyed, which proves that it had a high bonding strength. After the application of the plating, the plated surface had a compact microstructure, and the continuity was good. Therefore, compared with the currently commonly used zinc dipping process, this process has the advantages of being a low-cost, simple operation, and non-destructive and environmentally friendly activation process for the substrate. Full article

This study examines the effects of different addition levels of tungsten (W) content on the microstructure, corrosion resistance, wear resistance, microhardness, and phase composition of coatings made from FeCoCrNiAl high-entropy alloy (HEA) using the laser cladding technique. Using a preset powder method, FeCoCrNiAlW_x (where x represents the molar fraction of W, x = 0.0, 0.2, 0.4, 0.6, 0.8) HEA coatings were cladded onto the surface of 45 steel. The different cladding materials were tested for dry friction by using a reciprocating friction and wear testing machine. Subsequently, the detailed analysis of the microstructure, phase composition, corrosion resistance, wear traces, and hardness characteristics were carried out using a scanning electron microscope (SEM), X-ray diffractometer (XRD), electrochemical workstation, and microhardness tester. The results reveal that as the W content increases, the macro-morphology of the FeCoCrNiAlW_x HEA cladding coating deteriorates; the microstructure of the FeCoCrNiAlW_x HEA cladding coating, composed of μ phase and face-centered cubic solid solution, undergoes an evolution process from dendritic crystals to cellular crystals. Notably, with the increase in W content, the average microhardness of the cladding coating shows a significant upward trend, with FeCoCrNiAlW_0.8 reaching an average hardness of 756.83 HV_0.2, which is 2.97 times higher than the 45 steel substrate. At the same time, the friction coefficient of the cladding coating gradually decreases, indicating enhanced wear resistance. Specifically, the friction coefficients of FeCoCrNiAlW_0.6 and FeCoCrNiAlW_0.8 are similar, approximately 0.527. The friction and wear mechanisms are mainly adhesive and abrasive wear. In a 3.5 wt.% NaCl solution, the increase in W content results in a positive shift in the corrosion potential of the cladding coating. The FeCoCrNiAlW_0.8 exhibits a corrosion potential approximately 403 mV higher than that of FeCoCrNiAl. The corrosion current density significantly decreases from 5.43 × 10⁻⁶ A/cm² to 5.26 × 10⁻⁹ A/cm², which suggests a significant enhancement in the corrosion resistance of the cladding coating. Full article

To improve the wear resistance of TC4 titanium alloy, two types of wear-resistant coatings were applied to the surface using laser melting: Ni60 + 50% WC and d22 powder priming. The phase composition and microstructure of the coatings were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and energy spectroscopy (EDS). The mechanical properties of the coating were tested using an HV-1000 micro-Vickers hardness tester, an HRS-2M high-speed reciprocating friction and wear tester, and a WDW-100D electronic universal testing machine. The results show that Ni60 + 50% WC composite coating and d22 priming + (Ni60 + 50% WC) composite coating mainly consist of W₂C, TiC, Ni₁₇W₃, Ni₃Ti, and Ti_xW_1−x phases. Compared to the TC4 substrate, the microhardness of both coatings is significantly higher, approximately 2.8 times the microhardness of the substrate. In frictional wear experiments, the average friction factors of the two coatings and the TC4 substrate are 0.476, 0.55, and 0.865, respectively, and the wear of the two coatings is only 0.0559–0.0769 that of the TC4 substrate, with a significant increase in wear resistance, nearly 17 times higher than that of the substrate. The coating shows flaking, shallow abrasion marks, and granular debris, dominated by adhesive wear and fatigue wear, while the TC4 substrate shows more furrows on the surface, dominated by abrasive wear. The shear bond strengths of the Ni60 + 50% WC composite coating and the d22 powder primed + (Ni60 + 50% WC) composite coating were 188.19 MPa and 49.11 MPa, respectively. Conclusion: both coatings significantly improve the hardness and wear resistance of the TC4 titanium alloy substrate surface, with the Ni60 + 50% WC composite coating performing better in hardness, wear resistance, and bond strength. Full article

This study investigated how process parameters of laser cladding affect the microstructure and mechanical properties of WC-12Co composite coating for use as a protective layer of continuous caster rolls. WC-Co powders, WC-Ni powders, and Ni-Cr alloy powder with various wear resistance characteristics were evaluated in order to determine their applicability for use as cladding materials for continuous caster roll coating. The cladding process was conducted with various parameters, including laser powers, cladding speeds, and powder feeding rates, then the phases, microstructure, and micro-hardness of the cladding layer were analyzed in each specimen. Results indicate that, to increase the hardness of the cladding layer in WC-Co composite coating, the dilution of the cladding layer by dissolution of Fe from the substrate should be minimized, and the formation of the Fe-Co alloy phase should be prevented. The mechanical properties and wear resistance of each powder with the same process parameters were compared and analyzed. The microstructure and mechanical properties of the laser cladding layer depend not only on the process parameters, but also on the powder characteristics, such as WC particle size and the type of binder material. Additionally, depending on the degree of thermal decomposition of WC particles and evolution of W distribution within the cladding layer, the hardness of each powder can differ significantly, and the wear mechanism can change. Full article

In order to enhance the quality of diamond composite materials, this work employs a Cu-Co-Fe and Ni-Cr-Cu pre-alloyed powder mixture as a transition layer, and utilizes laser-welding technology for saw blade fabrication. By adjusting the laser-welding process parameters, including welding speed and welding power, well-formed welded joints were achieved, and the microstructure and mechanical properties of the welded joints were investigated. The results demonstrate that the best welding performance was achieved at a laser power of 1600 W and a welding speed of 1400 mm/min, with a remarkable tooth engagement strength of up to 819 MPa. The fusion zone can be divided into rich Cu phase and rich Fe phase regions, characterized by coarse grains without apparent preferred orientation. The microstructure of the heat-affected zone primarily consists of high-hardness brittle quenched needle-like martensite, exhibiting a sharp increase in microhardness up to 550 HV. Fracture occurred at the boundary between the fusion zone and the heat-affected zone of the base material, where stress concentration was observed. By adjusting the welding parameters and transition layer materials, the mechanical properties of the joints were improved, thereby achieving a reliable connection between diamond composite materials and the metal substrate. Full article

Fabrication of W- and Co-free wear-resistant cermets is a vital task in modern machinery due to the toxicity of Co-based products and poor availability of Co and W containing raw materials. In this paper, a TiC-NiMo coating produced by laser-directed energy deposition (L-DED) on a Ti-6Al-4V substrate was demonstrated. Mechanical alloying of TiC, Ni and Mo powders followed by spray-drying was proposed to fabricate a feedstock spherical composite powder suitable for an L-DED machine. It was shown that this method is more applicable in the case of a TiC-containing composition than gas atomization and plasma spheroidization methods. The size of the resulting particles was in the range of 10–100 μm while the size of the 70 vol.% was in the range of 45–75 μm. L-DED provided a good adhesion of the coating, though the presence of pores and transverse cracks was also observed. The coating’s hardness was up to 1500 HV, which is not inferior to the hardness of known TiC-based cermets and is promising for obtaining a good wear resistance of the coating. It was shown that it depended on the thickness due to the mixing zone influence. The coating structure contained TiC- and Mo-based precipitates and a Ni-based binder. The weight loss of the coating samples after an abrasive wear test with 4000 revolutions of a testing wheel was 0.0464 g and that can be considered insignificant. The wear did not lead to the appearance of new defects and cleavage of the coating. Further optimization of the component ratio and L-DED parameters could help to improve the performance of the coating and make this technology rather promising to improve the wear resistance of machinery parts working in high-wear environments. Full article

The growing interest in intermetallic and metal–intermetallic materials and coatings is based on the number of favorable properties they possess, primarily mechanical. However, the lack of data on their corrosion resistance has largely limited their scope of application. In this study, the corrosion destruction mechanisms of coatings formed on substrates made of AISI 321 steel and Aluchrom W (fechralloy) were investigated. The coatings were created by alloying in an aluminum melt followed by diffusion annealing to form the ultimate intermetallic structure. Corrosion resistance was studied under cyclic exposure to a humid marine atmosphere simulator and potentiostatic tests in an aqueous NaCl solution. Corrosion destruction parameters were determined, and mechanisms for each type of coating were revealed. The conducted studies allowed us to determine the electrochemical parameters of the corrosion destruction process and its mechanisms. It was shown that the corrosion rates during potentiostating for coatings on substrates Cr15Al5 and 12Cr18Ni10Ti differed by almost twofold. Two different mechanisms of corrosion are proposed. The first is associated with the formation of Al₂O₃ and MgO oxide films, which at the initial stage protect only local areas of the coating surface on Cr15Al5. The second is determined by the diffusion of titanium atoms during annealing to the coating surface on a 12Cr18Ni10Ti steel substrate with the formation of TiC carbide at the grain boundaries. Full article

Laser cladding is a new technology for fabricating coatings with good properties, such as wear resistance, lubrication, and corrosion resistance. Usually, parts of 45 steel are used as a shaft under conditions of high-speed rotation or friction and wear, and they have a short service life and sometimes cause accidents. In order to avoid serious accidents, a cladding coating made from a Ni-based alloy with ceramic particles was fabricated via laser technology on a substrate of 45 steel in this research. The microstructure and properties were investigated via SEM, EDS, XRD, and a wear and friction tester. The results show that there was an obvious boundary between the cladding coating and the substrate. The main phases were γ(Fe, Ni), WC, TiC, Cr₂Ti, and Cr₂₃C₆. In the middle of cladding coating, the microstructure was composed of dendrite and cellular crystals, while the microstructure was composed of equiaxial crystals in the bonding region. Inside the cellular crystal, the main phase was γ~(Fe, Ni), which occasionally also showed the appearance of some white particles inside the cellular crystal. Compared with the cellular crystal, the boundary had less of the Fe and Ni elements and more of the Cr and W elements. The amount of C element around the dendrite crystal was more than that around the boundary of cellular crystal due to the long formation time of dendrite. The white particles around the boundary were carbides, such as WC and Cr₂₃C₆ phases. Meanwhile, the segregation of the Si element also appeared around the boundaries of the crystal. The maximum microhardness was 772.4 HV_0.5, which was about 3.9 times as much as the substrate’s microhardness. The friction coefficients of the 45 steel substrate and Ni-based alloy coating were usually around 0.3 and 0.1, respectively. The Ni-based coating had a smaller coefficient and more stable fluctuations. The wear volume of the cladding coating (0.16 mm³) was less than that of the substrate (1.1 mm³), which was about 14.5% of the wear volume of 45 steel substrate. The main reason was the existence of reinforced phases, such as γ~(Fe, Ni), Cr₂₃C₆, and Cr₂Ti. The added small WC and TiC particles also enhanced the wear resistance further. The main wear mechanism of the cladding coating was changed to be adhesive wear due to the ceramic particles, which was helpful in improving the service life of 45 steel. Full article