Investigation of Homogenization and its Influence on the Repair Welding of Cast Allvac 718Plus

Paper in proceeding, 2010

Heat treatment experiments have been carried out to bring understanding to the efficacy of different temperatures and dwell times on the degree of homogenization of the cast Allvac 718Plus alloy which is prone to segregation mainly due to its high content of niobium. The effect of homogenization on weld repair was also examined. The homogenization heat treatment temperatures ranged from 1050°C to 1200°C with 1hr, 5 hrs and 10 hrs dwell times. The degree of homogenization was measured as the reduction of the amount of Laves phase by manual point counting in an optical microscope at high magnification. Longer range, interdendritic, patterns were established through line scan EDS analysis in SEM. It was found that short time (1hr) does not significantly reduce the amount of Laves phase whereas 5 hrs and 10hrs are much more efficient. Interdendritic homogenization does not occur to any measurable extent even at the highest temperature and longest dwell time (1200°C-10hrs) which was also reflected in bulk macro Vickers hardness tests. In the weld repair tests, one of the most homogenized material conditions (1125°C-5hrs +1200°C-10hrs) turned out to be the most prone to cracking while the number of weld cracks after a moderate homogenization heat treatment (1125°C-5hrs) was much smaller .