Effect of preweld microstructure on HAZ liquation cracking of Rene 80 superalloy

The objective of this work was to study the microstructure of as cast, solution treated and overaged Rene 80 superalloy before and after welding treatment. Studies focused on identifying heat affected zone ( HAZ) liquation cracking mechanism and the effect of preweld microstructure on it. The formation of HAZ liquation cracking or microfissuring is found to be strongly dependent on constitutional liquation of grain boundary precipitates. These liquated precipitates in the as cast state contain MC carbides and particularly gamma/gamma' eutectic islands. While in the overaged condition they consist of the MC carbides and borides. Also HAZ grain boundary liquation and subsequent resolidification occur in overaged Rene 80 during welding. MC carbide liquation can be observed at the weldment of solution treated Rene 80 but the intensity of this liquation is not enough for liquid film formation and then cracking. X-ray mapping of MC carbide forming elements, give further evidence on the liquid film formation at hot cracking regions. It shows the enrichment from tungsten and lower amounts of molybdenum and titanium.