Effect of casting defects on high cycle fatigue life of fully lamellar TiAl alloy

Abstract

The casting defects existed in a directional fully lamellar TiAl alloy Ti-47.5Al-2.5V-1.0Cr-0.2Zr (at.%). The proper hot isostatic pressing (HIP) was used to decrease the size or change the shape of the casting defects under the condition to remain the structure of the alloy unchanged. The effect of the remained defects on the high cycle fatigue properties of the alloy was studied in the present investigation. The result showed that two kind defects of the bulk micro-porosity and the bridged porosity interface existed in the alloy after the HIP. It has been found that the bulk micro-porosity defects affect the high cycle fatigue life at 750°C more significantly compared with the bridged porosity interface defects. And the effect of the defects on the fatigue life was related to the defect size, shape and location. The fatigue life decreased with the increasing defect area/size and the decreasing curvature radius of the defect because of the stress concentration at the defect tip. The fatigue life of the specimens with the defects at the subsurface was significantly longer than that of the surface.

Keywords:

• TiAl
• High cycle fatigue
• HIP
• Casting defects