Embedded Ni-Ti particles for the detection of fatigue crack growth in AA7050

A multi-functional aluminium alloy 7050 (AA7050) containing embedded Ni-Ti shape memory alloy particles to detect fatigue crack growth is proposed. The regions of intense strain near the tip of a growing fatigue crack cause nearby Ni-Ti particles to undergo a solid-state phase transformation from austenite to martensite, releasing a detectable acoustic emission signal that can be used to locate the crack in the monitored component. The AA7050/Ni-Ti composite was made by vacuum hot pressing Ni-Ti powder between rolled AA7050 plates. The effect of hot pressing temperature and subsequent heat treatments (solutionizing and peak ageing) on the Ni-Ti particles was studied. A successful proof-of-concept was demonstrated for AA7050 with embedded particles that emit a measureable and repeatable acoustic emission signal in the presence of a fatigue crack, allowing for quick diagnosis of fatigue crack damage in this material.