The effect of annealing twin-generated special grain boundaries on HAZ liquation cracking of nickel-base superalloys

The susceptibility to weld heat-affected-zone (HAZ) liquation cracking of wrought Waspaloy and Alloy 718 was quantified by using hot ductility testing. The intergranular (IG) cracking behavior of these alloys was influenced by long term isothermal heat treatments. Such long holds at the solution temperature resulted in continuous grain growth in Waspaloy. However, the IG liquation cracking was not solely controlled by grain size. Annealing twin-generated special grain boundaries increased in volume fraction as grain size increased and reduced the tendency for IG cracking. Intense delta phase precipitation occurred in Alloy 718 following the long isothermal holds. delta phase pinning of grain boundaries restricted grain growth and hence the fractional increase of special grain boundaries. However, special grain boundaries did provide resistance to IG liquation cracking once the delta-phase was dissolved using a rejuvenation heat treatment. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.