退火处理对新型Ni-Co-Cr基粉末高温合金微观组织与性能的影响

基于Thermo-Calc热力学计算软件及相应的Ni基合金数据库,模拟计算一种新型Ni-Co-Cr基粉末高温合金可能的平衡析出相及其与温度的关系;采用金相显微镜、扫描电子显微镜(SEM)并结合定量分析软件,对合金在不同退火制度下的晶粒与γ′相的演化行为进行分析;同时,利用纳米压痕仪研究退火制度对合金力学性能的影响。结果表明:合金中γ′相的溶解温度约为1154℃。当退火温度低于1000℃时,γ′相均以近球形为主,其尺寸及含量随退火温度的升高和保温时间的延长变化不大;γ′相对晶粒生长起到了有效的钉扎作用,合金的晶粒尺寸无明显增长。当退火温度高于1000℃时,γ′相的形貌逐渐向方形或花瓣状转变,且随着保温时间的延长有分裂的趋势;退火温度的升高使γ′相的尺寸及含量均有较大幅度的降低,合金的晶粒尺寸也有较明显的增加。随着退火温度的升高和保温时间的延长,合金的硬度逐渐降低,但弹性模量无明显变化。综合考虑退火后挤压态合金的微观组织和硬度,优化的退火制度在1000℃、1~2 h条件下进行。

Effect of annealing treatment on microstructure and properties of a new Ni-Co-Cr based powder superalloy

Based on the Thermo-Calc thermodynamic calculation software and the corresponding database of Ni-Co-Cr based alloy,the possible equilibrium phases in a new nickel-based powder superalloy and its relationship with temperature were simulated.The evolutions ofγgrain and γ′phase under various annealing conditions were analyzed by optical microscopy and scanning electron microscopy(SEM)combining with the quantitative analysis software.At the same time,the influence of annealing condition on the mechanical properties of the alloy was studied by nanoindentation.The results show that the dissolution temperature of γ′phase for the alloy is about 1154℃.When the annealing temperature is lower than 1000℃,the γ'phase mainly exhibits spherical morphology.Increasing the annealing temperature and the holding time lead to limited variation in the size and volume fraction of γ'phase.The grains slowly grow due to the effective pinning of the undissolved γ′phase.When the annealing temperature is higher than 1000℃,the morphology of γ′phase gradually changes from spherical to cubical or petaloid shape.In the case of longer holding time,γ′phase exhibits a tendency of splitting from a large precipitates to several small ones.The increase of annealing temperature results in significant decreasing in the size and volume fraction of γ′phase so that the grain size of the alloy also increases rapidly.The nanoindentation test reveals that,as annealing temperature and holding time increase,the hardness of the alloy gradually decreases,while the elastic modulus does not change apparently.Comprehensively considering the microstructure and hardness of the as-annealed alloys,the annealing treatment of the as-extruded alloy is suggested to be at the temperature of 1000℃ and the holding time between 1 and 2 h.