排气阀Pyromet31V合金混晶组织研究

Study on Mixed Grains in Pyromet31V Superalloys for Exhaust Valve

Pyromet31V合金具有优异的蠕变断裂强度、抗热腐蚀和抗热疲劳等性能,是制备汽车发动机排气阀的关键材料。采用OM和SEM研究排气阀不同区域内的晶粒组织、晶内γ’相和晶界碳化物形貌及合金混晶组织的演化行为。结果表明:排气阀头部中心区域为细晶区,而外部为粗晶区,中间部位为混晶区,各区域内晶粒尺寸呈双峰分布;混晶组织区域内γ’析出相及M_(23)C_(6)碳化物分布与细晶区和粗晶区的相当,没有出现明显的成分偏析。进一步观察对比变形前后的晶粒组织发现,排气阀头部混晶组织形貌与原始棒料中晶粒组织密切相关,表明变形工艺对其晶体组织结构影响较小。

Pyromet31V alloy has been used in the valves of engine for its excellent creep fracture strength,hot corrosion resistance and thermal fatigue resistance. In this work,the grain structure,the morphologies of intragranular γ’ phase and grain boundary of carbide in the different areas of exhaust valve,as well as the evolution behavior of alloy mixed crystal were studied by OM and SEM. The results showed that the fine grains located in the central region of exhaust valve head,the coarse grains distributed in the boundary,and mischcrystal structure dispersed between the two regions. A bimodal distribution of grain size was also found in each area. Moreover,the distribution of γ’ precipitates and M_(23)C_(6) carbides in the mixed grain region was similar to that in the fine and coarse grain region,and Composition segregation was not observed. In addition,mischcrystal morphology of the exhaust valve head was closely related to the grain morphology of the original bar, indicating that the hot deformation process had little effect on the mixed grains microstructures.