Ni-25Cr-20Co合金时效组织结构及性能研究

在Thermo-Calc热力学软件模拟计算基础上,采用光学显微镜、扫描电子显微镜、能谱检测和透射电子显微镜研究了Ni-25Cr-20Co合金在长期时效过程中析出相的变化情况及对性能的影响,理论分析了γ′相颗粒粗化对合金拉伸变形过程中第二相与位错交互作用机制的影响。结果表明:经750℃时效后合金中析出MC、M_(23)C_6和γ′相,γ′相的体积分数约为16%。长期时效后,γ′相颗粒的平均尺寸与时间t符合LSW理论,受溶质原子扩散及γ/γ′界面能的影响。时效后合金的拉伸强度明显增加,随时效时间的延长,拉伸强度逐渐降低。随γ′相的粗化,拉伸变形过程中第二相与位错交互作用的机制由位错热攀移机制→位错切割机制→Orowan绕越机制转变为位错热攀移机制→Orowan绕越机制→位错切割机制。

Microstructure and Properties of Ni-25Cr-20Co Alloy After Long-term Aging

Based on Thermo-Calc software,the microstructure and mechanical properties of Ni-25Cr-20Co alloy after long-term aging at 750 ℃ was investigated using OM,SEM,TEM and tensile testing.The relationship between dislocation resistance mechanism and γ′ phase size was calculated.The results show that MC,M23C6 and γ′ phase are the main precipitates,the volume fraction of γ′ phase is 16％.The growth kinetic of γ′ phase follows LSW theory,affecting by the diffusion of solute atoms and interface energy of γ/γ′.The tensile strength increases obviously after aging treatment.The tensile strength decreases with the extending aging time.Deformation mechanism in stretching process is changed with the growth of γ′ phase.When γ′ phase is small,deformation mechanism is climb mechanism→cut mechanism→Orowan mechanism.Deformation mechanism switch to climb mechanism→Orowan mechanism→cut mechanism when γ′ phase exceed critical value.