Ductility and Fracture Behavior of Polycrystalline Ni3Al Alloys

Abstract

AbstractThis paper provides a comprehensive review of the recent work on tensile ductility and fracture behavior of Ni3AI alloys tested at ambient and elevated temperatures. Polycrystalline Ni3Al is intrinsically brittle along grain boundaries, and the brittleness has been attributed to the large difference in valency, electronegativity, and atom size between nickel and aluminum atoms. Alloying with B, Mn, Fe, and Be significantly increases the ductility and reduces the propensity for intergranular fracture in Ni3 Al alloys. Boron is found to be most effective in improving room-temperature ductility of Ni3Al with <24.5 at. % Al.The tensile ductility of Ni3Al alloys depends strongly on test environments at elevated temperatures, with much lower ductilities observed in air than in vacuum. The loss in ductility is accompanied by a change in fracture mode from transgranular to intergranular. This embrittlement is due to a dynamic effect involving simultaneously high localized stress, elevated temperature, and gaseous oxygen. The embrittlement can be alleviated by control of grain shape or alloying with chromium additions. All the results are discussed in terms of localized stress concentration and grain-boundary cohesive strength.