Influence of aging heat treatment on microstructure and mechanical properties of a novel polycrystalline Ni3Al-based intermetallic alloy

Abstract

A novel polycrystalline Ni₃Al-based intermetallic alloy was prepared using the vacuum induction melting process. Subsequently, the alloy was subjected to the solution-treatment underwent two different aging processes: 870 °C for 24 h in air cooling, referred to as AT 1, and 1060 °C for 4 h in air cooling followed by 870 °C for 24 h in air cooling, referred to as AT 2. The effects of different aging processes on the microstructure and mechanical properties of the polycrystalline Ni₃Al-based intermetallic alloys were analyzed. Results indicated the cubicity of the primary γ′ phase within the dendritic γ+γ′ structure of the AT 2 sample was significantly enhanced, yielding the best overall mechanical properties for the alloy. The percentage elongation increased from less than 3 % for the AT 1 sample to about 4.5 %, highlighting a notable enhancement in room temperature tensile plasticity. The creep rupture time at 1100 °C/30 MPa reached 113 h. The α-Cr particles in the As-cast and solid solution alloy gradually transformed into Cr₂₃C₆ during the aging process, exhibiting the orientation relationships of (020)_Cr23C6||(010)_γ' and [103]_Cr23C6||[103]_γ'. High-temperature aging treatments resulted in Cr₂₃C₆ particles that provided enhanced precipitation strengthening effects, thereby improving the creep rupture performance of the Ni₃Al-based intermetallic alloys. Following high-temperature aging, a four-layer interface structure formed around the blocky γ′ matrix phase, which altered the alloy's fracture mechanism from a brittle intergranular fracture to a ductile transgranular fracture.