Co-Cr-Nb-W合金碳化物组织转变及力学性能研究

Carbides Evolution and Mechanical Behavior of Co-Cr-Nb-W Wear-resistance Alloy

摘要:

热处理过程中的碳化物转变对高温合金的力学性能影响显著。本实验采用XRD、SEM、EPMA、TEM等技术研究了Co-Cr-Nb-W耐磨合金热处理过程中碳化物的析出类型、分布特征、演变机理及其对高温拉伸性能的影响。Co-Cr-Nb-W耐磨合金主要在钎焊和时效热处理后使用,该过程中主要发生如下两个碳化物转变过程：MC + matrix = M₆C和M₂₃C₆+ matrix = M₆C。合金在高温拉伸应力下的断裂机制为韧脆混合机制,块状初生碳化物与基体之间的界面容易成为裂纹萌生源。热处理过程消除了容易引起晶界迁移的片层状共晶M₂₃C₆,在骨架状MC周围析出了细小的M₆C,同时改善了枝晶间元素偏析,促进基体中形成高密度的交叠层错带,使得合金在1000℃下的抗拉强度提高了约20MPa。

Abstract:

Carbides transformation during heat-treatment process has a significant effect on the mechanical properties of superalloys. XRD, SEM, EPMA, and TEM were used to investigate 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. 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 (SF) bands in the matrix, and increases the tensile strength of the alloy at 1000℃ by about 20 MPa.