Influence of γ′ and grain boundary carbide on tensile fracture behaviors of Nimonic 263

Tensile fracture behaviors of Nimonic 263 after three different heat treatments have been investigated. Standard heat treatment produces 10% γ′ coupled with precipitate free zones (PFZs), and M₂₃C₆ carbide densely distributed at grain boundaries (GBs). Alternative heat treatment causes dense distribution of GB carbides and precipitation of 1–3% γ′ with the absence of PFZs. Solution-treated sample has neither γ′ nor M₂₃C₆ carbide. Room temperature tensile tests indicate both standard and alternative heat-treated samples show intergranular fracture, but the elongation of the latter is two times larger than that of the former. The combined effect of GB carbides and intensive slip bands accounts for the intergranular fracture. The γ′ volume fraction affects elongation. Solution-treated sample displays transgranular fracture mode. Lack of restriction to dislocation mobility in grains interior and the weak interaction between GBs and dislocations are responsible for the transgranular fracture. The effect of PFZs on fracture mode may be negligible.