Comparison of mechanical properties of Ni3Al thin films in disordered FCC and ordered L12 phases

Abstract We report the results of several experiments isolating the effect of long-range order on mechanical properties of intermetallic compounds. Kinetically disordered FCC Ni 3 Al (Ni 76%) thin films were produced by rapid solidification following pulsed laser melting. For comparison, compositionally and microstructurally identical films with ordered L1 2 structure were produced by subsequent annealing at 550°C for 2 h. These FCC and L1 2 Ni 3 Al thin films were tested by nanoindentation for hardness and Young's modulus, and the critical strain to fracture was measured by straining the substrate under four-point bending. Ni 3 Al thin films in the disordered phase were found to have nearly twice the critical strain to fracture, more than three times the fracture toughness, and about 20% lower hardness than in the ordered counterpart. Blunter crack tips and crack bridging observed in the disordered phase also illustrate increased ductility. The increased plasticity of Ni 3 Al due to chemical disorder is manifested both within the grains and at the grain boundaries. Young's moduli of the ordered and disordered materials were found to be indistinguishable.