Fabrication and mechanical properties of the NiAl sheet with a 3-dimensional network structure prepared by Ni nets and Al foils

Abstract

Due to the inherent brittleness of lightweight NiAl alloys, conventional manufacturing methods are inadequate for producing large-sized NiAl sheets with excellent mechanical properties. This paper presents an alternative approach, employing Ni nets and Al foils as raw materials to fabricate a NiAl sheet via hot-press sintering in a vacuum furnace. The sheet exhibited a three-dimensional network structure, wherein small-sized grains enveloping larger grains within the net. The network structure is controlled by Ni nets used and the sintering parameters. A nearly fully dense sheet with a density of 99.98 % and a thickness of 1 mm was achieved under sintering conditions of 1400 ℃/20 MPa/0 min. The hardness distribution within the NiAl sheet exhibited a three-dimensional wavy surface profile with distinct peaks and valleys. The hardness in the high-hardness regions exceeded 600 HV0.05, while the hardness in the low-hardness regions ranged from 500 to 550 HV0.05. Tensile test results indicate that, at an initial strain rate of 0.001, the NiAl sheet exhibits brittle fracture at 900 °C, while displaying ductile fracture behavior at 950 °C and 1000 °C. The ultimate tensile strength exceeds 100 MPa at 900 °C but declines sharply as the deformation temperature increases. During tensile testing, cracks propagate along the fine-grain regions, and the fracture surface exhibits a multi-peak morphology. The study provides a new method for the preparation of heterogeneous NiAl alloy sheets and provides new ideas for the microstructure design and performance optimization of NiAl alloys.