| H13 steel as a hot work die steel is widely used at home and abroad,and possesses high hardenability,wear resistance,toughness and good cold and hot fatigue.However,under the severe conditions of friction and extrusion of high-temperature metals,thermal wear as one of the main failure modes of H13 steel often leads to early failure of H13 steel.Surface treatment with laser cladding can effectively improve the high temperature wear resistance of H13 steel.The reasearch used laser cladding to prepare wear-resistant coatings on the surface of H13 steel,and micro-analysis of coatings was performed by SEM,XRD,XPS,etc.High-temperature wear tests were performed at 400,500 and 600?for coatings and H13 steel.The high-temperature wear behavior and wear resistance of the coatings were studied in comparison with H13 steel.The morphology,phase,and composition of the worn surface and cross-section of the coatings were studied by SEM,XRD,Raman,etc.The analysis was carried out,and the high-temperature wear mechanism and anti-wear mechanism of the coatings were discussed.Multi-pass and multilayer laser cladding method was successfully used to prepare iron-based alloy coatings with different Ni content on the surface of H13 steel.The research showed that the coatings were free of defects such as holes and cracks,and showed good metallurgical bonding with the substrate.Each coating exhibited similar solidification structure.The structure of the first layer was cellular crystals,columnar crystals,and equiaxed crystals in order from bottom to top,and the second layer was mainly equiaxed crystals or equiaxed dendrites.As the Ni content increased,the matrix phase of the coating changed from?-Fe to?-?Fe,Ni?.XRD and XPS test results showed that Al3Ni,AlNi and Fe3Al precipitated in the coatings.The hardness of the coating decreased with the increase of Ni content,and the thermal stability of each coating was significantly better than that of H13 steel,and thermal stability of coating 4 was the most excellent.The results of high temperature friction and wear test showed that the wear rate of each coating increased with the increase of temperature and load,and the wear rate of coatings 1 to 4 gradually decreased with the increase of Ni content,and then coating 5 and6 increased slightly.In particular,the wear rates of the coating 4 at 400,500,and 600?were almost below 5×10-6mm3/mm.In contrast,except for 500?,the wear rate of H13steel was almost higher than 5×10-6mm3/mm at 400 and 600?,and the wear rate reached33×10-6mm3/mm at 600?and 150N.Therefore,compared with H13 steel,the coating had excellent high temperature wear resistance.It could be found that these laser cladding coatings could effectively improve the high temperature wear performance.Based on the analysis of the wear behavior and characteristic of each coating and H13steel,it could be found that the wear mechanism of each coating at 400-600?was oxidation mild wear and mild-severe transition of oxidation wear.The wear mechanism of coating 4 was oxidation mild wear.The wear of H13 steel at 400-600?was mainly in the mild-severe transition of oxidation wear,and even plastic extrusion wear occurred at 600?and 150N.The high-temperature wear resistance of the coating was mainly related to the tribo-oxides and the thermal stability of the coating.Under high temperature wear,the subsurface of the coating maintained high hardness?basically above 450 HV?,and the tribo-oxide layer was sufficiently supported to fully protect it,and fell in oxidation mild wear.When the subsurface was softened and the hardness decreased to 300-400HV,the tribo-oxide layer did not get sufficient support and only played a part of the protection role,entering the mild-severe wear transition zone of oxidation wear;when the subsurface hardness drops to 250HV,the subsurface had undergone plastic deformation and flow,and could not support the tribo-oxide layer.Therefore,the tribo-layer was severely cracked and peeled off,which lost its protective effect and entered plastic extrusion wear. |
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