Effect of heat treatment and hot working on microstructure and mechanical properties of a novel nickel base superalloy

The microstructure and mechanical properties of a novel nickel base superalloy intended for manufacturing of die tools and parts for gas turbine engine have been investigated. The superalloy designated as SLZhS-1R had the following composition: Ni-47(Al, Cr, Co, Ta, W, Hf)-0.2(C, B) (wt. %). The as-cast superalloy was subjected to homogenization and heterogenization heat treatment, which is typically performed before hot working. However, the heat treatment led to appearance of platelike precipitates, which are not favorable for the hot workability. Therefore, the superalloy was subjected to hot working taking the as-cast condition as the initial one. To do it, unidirectional hot forging at a temperature slightly below the.' solvus temperature with a strain rate of epsilon' similar to 10(-2) s(-1) was carried out. The as-cast superalloy showed reasonable workability that allowed producing sound forgings. The forging procedure provided formation of mixed microstructure consisted of coarse non-recrystallized and fine recrystallized. grains. EBSD analysis of the forged workpiece showed that the fraction of highangle grain boundaries was insignificant. The hot forging resulted in dynamic recovery, whereas recrystallization processes occurred only locally near the. grain boundaries. Tensile tests were carried out for the heat treated and hot forged conditions as well as for the as-cast condition. The heat treated and especially the forged and heat treated condition showed appreciably higher strength and ductility as compared to those of the