The formation mechanisms and growth kinetics of Al3 Ni and Al3Ni2 in Ni-Al diffusion couple prepared by electrodeposition of Ni on Al substrate were investigated. The nickel coating with 20 μm thickness was applied o...The formation mechanisms and growth kinetics of Al3 Ni and Al3Ni2 in Ni-Al diffusion couple prepared by electrodeposition of Ni on Al substrate were investigated. The nickel coating with 20 μm thickness was applied on 6061 aluminum alloy by direct current electroplating. The samples were then heat-treated for different durations at 450, 500 and 550 °C under argon atmosphere. The intermetallic phases were identified by means of scanning electron microscopy（SEM）, energy dispersive spectrometry（EDS） and X-ray diffraction（XRD）. The results showed that the formation of intermetallic phases consisted of two important steps. The first step was the lateral growth of intermetallic phase from separate sites, resulting in the formation of a continuous layer. The second step was the growth of the continuous intermetallic layer in the direction perpendicular to the interface. However, excessive increase in thickness of intermetallic phases led to the detachment of reaction products, i.e., Al3 Ni and Al3Ni2, from the substrate. It was also observed that aluminum was the dominant diffusing element during Al3 Ni growth, while nickel diffusion was dominant during Al3Ni2 growth. The growth kinetics of both Al3 Ni and Al3Ni2 phases obeyed a parabolic law.展开更多
Ni-P-SiC_(P) coatings were deposited on 42CrMo steel by electroless plating.The surface morphologies and phase structures of the Ni-P-SiC_(P) coatings processed under different SiC_(P) concentrations at different heat...Ni-P-SiC_(P) coatings were deposited on 42CrMo steel by electroless plating.The surface morphologies and phase structures of the Ni-P-SiC_(P) coatings processed under different SiC_(P) concentrations at different heat treatment temperatures were analyzed.The microhardness,corrosion resistance,and wear resistance of the Ni-P-SiC_(P) coatings were studied.Results show that Ni-P-SiC_(P) coatings exhibit cauliflower-like morphology.Increasing the SiC_(P) concentration can reduce the size of cellular structure.The microhardness and corrosion resistance are initially increased and then decreased with the increase in SiC_(P) concentration.The maximum microhardness and corrosion potential are 7379 MPa and−0.363 V,respectively,when the SiC_(P) concentration is 5 g/L.The Ni-P-SiC_(P) coatings exhibit an amorphous structure,and the width of the diffuse diffraction peak becomes narrower with the increase in SiC_(P) concentration.It is suggested that SiC_(P) inhibits the deposition of P and promotes the microcrystalline transformation.After heat treatment at 350℃,the Ni-P-SiC_(P) coatings are crystallized,resulting in the precipitation of Ni3P phase.Heat treatment at 400℃ for 1 h maximizes the structure.The synergistic effect of the Ni3P precipitate phase and SiC_(P) dispersion phase promotes the densification of the cellular structure,leading to the optimal microhardness(13828 MPa),optimal corrosion resistance(−0.277 V),and excellent wear resistance.The wear mechanism is dominated by micro-cutting abrasive wear with slight adhesive and oxidative wear.展开更多
文摘The formation mechanisms and growth kinetics of Al3 Ni and Al3Ni2 in Ni-Al diffusion couple prepared by electrodeposition of Ni on Al substrate were investigated. The nickel coating with 20 μm thickness was applied on 6061 aluminum alloy by direct current electroplating. The samples were then heat-treated for different durations at 450, 500 and 550 °C under argon atmosphere. The intermetallic phases were identified by means of scanning electron microscopy（SEM）, energy dispersive spectrometry（EDS） and X-ray diffraction（XRD）. The results showed that the formation of intermetallic phases consisted of two important steps. The first step was the lateral growth of intermetallic phase from separate sites, resulting in the formation of a continuous layer. The second step was the growth of the continuous intermetallic layer in the direction perpendicular to the interface. However, excessive increase in thickness of intermetallic phases led to the detachment of reaction products, i.e., Al3 Ni and Al3Ni2, from the substrate. It was also observed that aluminum was the dominant diffusing element during Al3 Ni growth, while nickel diffusion was dominant during Al3Ni2 growth. The growth kinetics of both Al3 Ni and Al3Ni2 phases obeyed a parabolic law.
基金Science Research Project of Handan Bureau of Science and Technology(21422075242)。
文摘Ni-P-SiC_(P) coatings were deposited on 42CrMo steel by electroless plating.The surface morphologies and phase structures of the Ni-P-SiC_(P) coatings processed under different SiC_(P) concentrations at different heat treatment temperatures were analyzed.The microhardness,corrosion resistance,and wear resistance of the Ni-P-SiC_(P) coatings were studied.Results show that Ni-P-SiC_(P) coatings exhibit cauliflower-like morphology.Increasing the SiC_(P) concentration can reduce the size of cellular structure.The microhardness and corrosion resistance are initially increased and then decreased with the increase in SiC_(P) concentration.The maximum microhardness and corrosion potential are 7379 MPa and−0.363 V,respectively,when the SiC_(P) concentration is 5 g/L.The Ni-P-SiC_(P) coatings exhibit an amorphous structure,and the width of the diffuse diffraction peak becomes narrower with the increase in SiC_(P) concentration.It is suggested that SiC_(P) inhibits the deposition of P and promotes the microcrystalline transformation.After heat treatment at 350℃,the Ni-P-SiC_(P) coatings are crystallized,resulting in the precipitation of Ni3P phase.Heat treatment at 400℃ for 1 h maximizes the structure.The synergistic effect of the Ni3P precipitate phase and SiC_(P) dispersion phase promotes the densification of the cellular structure,leading to the optimal microhardness(13828 MPa),optimal corrosion resistance(−0.277 V),and excellent wear resistance.The wear mechanism is dominated by micro-cutting abrasive wear with slight adhesive and oxidative wear.
