Composition-dependent interdiffusion coefficient, reduced elastic modulus and hardness in γ-, γ′- and β-phases in the Ni-Al system

Abstract

A combinatorial approach using diffusion couples and advanced characterization was carried out to investigate the composition-dependent interdiffusion and mechanical properties of γ-Ni(Al) solid solution, γ′-Ni3Al and β-NiAl. The diffusion couples between pure Ni and Ni52Al48 were annealed at temperatures of 1000 °C, 1100 °C and 1200 °C for 96 h, 48 h and 24 h, respectively. The γ-Ni(Al), γ′-Ni3Al and β-NiAl have developed in the diffusion zone. The β-NiAl transformed to martensite above room temperature when Al is less than 37 at.%. The composition-dependent interdiffusion coefficients for all phases corresponded closely to previous research. A systematic composition-dependent elastic modulus and hardness for γ-Ni(Al), γ′-Ni3Al and β-NiAl phases were obtained by nanoindentation. Variation of elastic modulus and hardness in the γ-Ni(Al) solid solution is influenced by solid solution strengthening and hardening due to precipitation of γ′-Ni3Al while cooling. The evolution of elastic modulus and hardness in the β-NiAl phase exhibited a minimum value of elastic modulus and hardness near the phase boundary between martensite and austenite. Lattice softening associated with martensitic transformation was recognized to lower the value of elastic modulus and hardness.