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.
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•Composition-dependent interdiffusion coefficients of γ-Ni(Al), γ′-Ni3Al and β-NiAl phases.•Composition-dependent modulus and hardness of γ-Ni(Al), γ′-Ni3Al and β-NiAl phases using nanoindentation.•Martensitic transformation in β-NiAl contributes to the change in modulus and hardness.
Well-adhered nanotube arrays were produced through the anodizing technique on a Ti-25Nb-25Ta alloy and tribo-mechanically evaluated by nanoindentation and nanoscratch tests. Disregarding substrate ...effects, the hardness of the nanotube arrays layer was 0.7 ± 0.1 GPa and elastic modulus was < 12 GPa, respectively. With the load increase and nanotubes compaction, hardness reached 1.8 GPa and elastic modulus stabilized in ∼40 GPa, which features a mechanically biocompatible gradient zone for implant applications. Under scratching, plastic deformations predominated in the nanotube arrays coating, which mechanism was load-dependent: in the first stage (up to 50 mN) and the initial tubes collapsing, the coating presented low cohesive strength; under higher loads and the progressive nanotubes compaction, the cohesive strength increased, as suggested by the pattern of cracks produced. The scratch resistance for the coating failure was higher than 500 mN, consisting of an excellent bonding adhesion for a nanotube layer produced by anodization.
