钛合金熔模精密铸件表面微裂纹形成过程研究

Formation of Micro Cracks in Investment Castings of Titanium Alloy

目的 表征钛合金熔模精密铸件表面组织的特性,研究其如何形成表面微裂纹的过程。方法 通过对钛合金精铸件表面微裂纹形貌进行观察,对表面α层的化学成分、显微硬度进行表征,并通过三点弯曲实验模拟α层在拉应力状态下开裂倾向。结果 微裂纹为冷裂,深度在α层范围内。α层的片层组织较铸件内部组织粗大,O含量和硬度高于铸件内部,在拉应力状态下较铸件内部容易导致裂纹萌生和扩展。结论 钛合金精铸件在凝固过程形成α层,在后续的冷却过程中形成的拉应力或翘曲变形导致相对脆弱的α层形成了表面微裂纹。

The paper aims to study features of surface microstructure of titanium alloy investment castings and the for-mation of micro cracks. Morphology on surface micro cracks of titanium alloy investment castings was observed to characterize chemical elements and micro-hardness of α-case. Three-points-bending test was carried out to simulate the cracking tendencies of α-case under pulling. The results show that micro cracks in α-case came into being during cooling of castings. Its depth was within the range of α-case. Lamella organization of α-case was high than that in the inner. The O content and harness were also higher than them in the casting. Cracks were likely to emerge in casting under pressing. The titanium alloy investment casting generates α-case in solidification. Pulling stress and warping in subsequent cooling lead to occurrence of surface micro cracks on α-case which is vulnerable.