| Nickel is an important metal material and its alloys are widely used.Nickel-based alloys have excellent properties,good high-temperature strength,corrosion resistance,anti-friction wear and fatigue resistance.It is applied as powder on the base material to form a protective coating,which effectively protects the base material and gives full play to the excellent performance of the nickel-base alloy,and it is economical and environmentally friendly,so that the nickel base alloy is widely used.As the working conditions become more and more demanding,when the coating process is optimized to a certain extent,the performance of the traditional nickel-base alloy coating can no longer meet some of the more demanding operating conditions.Therefore,in order to better play and improve the performance of the coating,cryogenic treatment of the nickel-base alloy coating was used in this study to further inprove the performance of the coating to meet the increasing demand for use.The Ni 25,Ni 35,Ni 45,Ni 60 self-fluxing Ni-based alloy powder was selected as the coating material.The flame cladding technology was used to clad it on the surface of the 45#steel substrate to prepare the sample,and then the sample was placed in liquid nitrogen at-196 ?.The cryogenic treatment of different processes was carried out in liquid nitrogen at 2h,8 h,24 h and 48 h.The performance of the samples after cryogenic treatment was tested,Rockwell hardness tester and friction and wear tester were used for hardness testing and friction and wear performance tests,respectively,to analyze the cryogenic treatment of Ni 25,Ni 35,Ni 45,Ni 60 self-fluxing nickel-base alloy coatings.The influence of mechanical properties was investigated.Microscopic observation,energy spectrum analysis and phase analysis of the coatings were performed by optical microscopy,scanning electron microscopy and X-ray diffractometry to investigate the mechanism of the effect of cryogenic treatment on the coating properties.Different cryogenic treatment of Ni 25 self-fluxing Ni-based alloy coating with flame cladding showed that the coating was well bonded to the substrate and no cracking occurred.When the cryogenic treatment time is 2 h,the hardness of the coating is the highest,reaching 40.44 HRD.The friction and wear properties of the coating are the best,and the wear amount is reduced to 0.0367 g.Therefore,cryogenic treatment can improve the mechanical properties of Ni 25 self-fluxing nickel-base alloy coating.The cryogenic treatment for 2 hours is the best,the hardness is increased by 5.5%,and the wear loss is reduced by 67.28%.The microstructure,element content and phase analysis of the coating have revealed that the refinement and homogenization of the network structure and the precipitation of Cr23C6 are the main reasons for the improvement of the mechanical properties of the coating.The cryogenic treatment of flame-clad Ni 35 self-fluxing nickel-base alloy coatings by different processes revealed that the coating was well bonded to the substrate and no cracking occurred.When the cryogenic treatment time is 2 h,the hardness of the coating is the highest,which is 59.44 HRD.When the cryogenic treatment time is 8h,the friction and wear properties of the coating are the best,and the wear amount is reduced to 0.01735 g.Therefore,cryogenic treatment can improve the mechanical properties of flame-clad Ni 35 self-fluxing Ni-based alloy coatings,and the best cryogenic treatment is 8 h.The coating hardness is 59.25 HRD,hardness is increased by 3.51%,and wear volume is reduced by 54.22%.The microstructure,element content and phase analysis of the coating have revealed that the refinement and homogenization of the network structure and the precipitation of secondary carbides of Cr7C3 are the main reasons for the improvement of the mechanical properties of the coating.The cryogenic treatment of Ni 45 self-fluxing nickel-base alloy coating with flame cladding showed that the coating was well bonded to the substrate and no cracking occurred.After cryogenic treatment,the hardness of the coating is increased but not obvious.When the cryogenic treatment time was 8 hours,the hardness of the coating reached 59.4 HRD and the hardness increased by 1.71%.When the cryogenic treatment time is 2 h,the friction and wear properties of the coating are the best,the wear amount is reduced to 0.00295 g,and the wear amount is reduced by 80%.Therefore,cryogenic treatment can improve the mechanical properties of Ni 45 self-fluxing nickel-base alloy coating.The microstructure,element content and phase analysis of the cryogenic treatment coating show that after the cryogenic treatment of the coating,the network structure of the coating is destroyed,and an uneven block structure that is unfavorable to friction and wear properties is formed.The change of the structure is the main reason that affects friction and wear performance.Different cryogenic treatment of Ni 60 self-fluxing Ni-base alloy coating on flame cladding shows that the coating is well bonded to the substrate and no cracking occurred.After cryogenic treatment,the hardness of the coating is increased but not obvious.When the cryogenic treatment time is 8 h,the hardness of the coating reaches a maximum of 72.14HRD,an increase of 1.98%.When the cryogenic treatment time is 24 h,the friction and wear properties of the coating are the best,the wear amount is reduced to 0.0023 g,and the wear amount is reduced by 80.17%.Therefore,cryogenic treatment can improve the mechanical properties of flame-clad Ni60 self-fluxing nickel-base alloy coatings.The microstructure,element content and phase analysis of the cryogenic treatment coating show that,after cryogenic treatment,the grid structure is refined,the grid is expanded and uniform,and the optimization of the coating structure is the main reason for the improvement of the mechanical properties of the coating.The experimental results show that the effective deep cryogenic treatment time for Ni 25,Ni 35,Ni 45,Ni 60 self-fluxing nickel-base alloy coatings is 2-8 h,and when the cryogenic treatment time is 2-8 h,the hardness of the coating reaches the highest,and then for a long time of cryogenic treatment,the hardness of the coating does not increase but decreases.Moreover,the effect of cryogenic treatment on the hardness of Ni 25 and Ni 35 coatings is higher than that of Ni 45 and Ni 60 coatings.It is considered that due to the low carbon content of Ni 25 and Ni 35,the particles in the original micro structure of the coating are less,the hardness is low,and the carbonization after cryogenic treatment is precipitated.The coating hardness of the coating is obviously improved.Ni 45 and Ni 60 coatings have high carbon content,and the original coating has more particulates and high hardness.Therefore,the coating hardness after cryogenic treatment is not significantly improved.The friction and wear properties of the coating are similar to those of the coating hardness.When the cryogenic treatment time is between 2 and 8 hours,the friction and wear properties of the coating are the best.The analysis shows that the micro structure of the coating also affects the friction and wear properties.The uniform network structure is advantageous for the tribological properties of the alloy coating. |
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