Investigation on hot sizing process based on creep mechanism for laser cladded thinwalled titanium alloy components

摘要

Laser cladding is proved to be an effective technique to repair damaged components. However, the generation of thermal stresses due to the heat input and temperature gradient during the laser cladding process is a common issue that leads to a serious distortion in the thin-walled components. It is frustrated to correct distorted titanium alloy components on account of its physical and mechanical properties. In this study, the hot sizing method based on the mechanism of creep aging forming is applied to straighten a laser cladding Ti-6Al-4V thin-walled part. Initially, a local surface damaged part was repaired by laser cladding; accordingly, a bending distortion was induced. Afterward, the hot sizing process (HSP) was used to correct the laser cladding component by first heating the part to 730 degrees C and then maintaining it for 300 min. With the aid of a three-coordinate measuring instrument, a x-ray stress analyzer, a microhardness tester, and a scanning electron microscope, the parameters such as part distortion, residual stress, microhardness, and microstructure before and after HSP were measured accordingly. It shows that a severe distortion with a maximum deflection of 2.939 mm was observed for the titanium component after the laser cladding process. The distortion is significantly decreased to a value of 0.454 mm after HSP. Microhardness of the cladding layer increased from 503.4HV(0.2) to 627.3HV(0.2) by 24.6%. The stress generation and evolution mechanism during laser cladding and hot sizing processes were also analyzed. It was found that the HSP influenced the residual stress in the substrate and the laser cladding layer in different ways. Residual stresses in the substrates were decreased to zero, whereas that of the cladding layer keep a large value even if they decreased greatly. By comparing the microstructure of the laser cladding layer before and after HSP, it is found that the creep movement causes the grain refinement. The effectiveness of the hot sizing method in eliminating the distortion of laser repaired thin-walled parts was validated.