Carbides Evolution and Mechanical Behavior of Co-Cr-Nb-W Alloy
Carbides transformation during heat-treatment process has a significant effect on the mechanical properties of superalloys.The distribution and evolution mechanism of carbides and their effects on high-temperature tensile properties of Co-Cr-Nb-W wear-resistant alloy during heat treatment process were investigated by XRD,SEM,EPMA,and TEM.There are two carbides transformation processes in the Co-Cr-Nb-W alloy during brazing simulation and aging:MC+matrix=M6C and M23C6+matrix=M6C.The fracture mechanism of the Co-Cr-Nb-W alloy under high temperature tensile stress is a hybrid mechanism of ductile fracture and brittle fracture,and the interface between the bulk primary carbide and the matrix is easy to become the source of crack source.The heat treatment process eliminates the lamellar M23C6,which is easy to cause grain boundary migration,induces the precipitation of fine M6C particles around the skeleton MC,improves the interdendritic element segregation,promotes the formation of high-density overlapping stacking fault bands in the matrix,and increases the tensile strength of the alloy at 1000 ℃ by about 20 MPa.
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