Influence of cold-work and aging heat treatment on strength and ductility of MP35N

MP35N (35% Co, 35% Ni, 20% Cr, and 10% Mo) is a superalloy that exhibits a remarkable combination of high strength and high fracture toughness. This alloy derives its strength mainly from two processes — cold work and a subsequent aging heat treatment. This study examines the influence of the amount of cold-work, imposed in the drawing and the rolling processes, and the subsequent aging heat treatment on the strength and ductility (which is also an indicator of toughness) of this alloy. It was found that high levels of cold-work followed by the aging heat treatments resulted in a drastic drop in the ductility of the alloy. This drastic loss of ductility was correlated with appearance of macro-scale shear bands in the samples. The physical origin of these localized shear bands is investigated in this paper. Furthermore, this study established a processing window for MP35N (in cold-drawing and cold-rolling processes) where the aging heat treatment provides the desired increase in the strength without adversely influencing the ductility of the alloy.