After welding with TIG, PWHT cracks are observed in the HAZ regions in nickel base superalloy XH67MB. So what could be done to avoid / overcome this problem.
Please read this web-page http://www.phase-trans.msm.cam.ac.uk/2003/nickel.html
It was written quite clear that main problem is y/y' phase ratio. While cracking accurs in HAZ, but not in welds, the only way to improve situation is changing algorithms of heat input during welding and/or heat treatment. Phase diagram is presented in the article mentioned above, I think it should be used in your research