Fatigue and fracture behavior of nickel–titanium shape-memory alloy reinforced aluminum composites

A shape-memory alloy, nickel–titanium (NiTi), has been distributed throughout an aluminum matrix, using powder-metallurgy processing, in the hope of using the shape-memory effect to achieve strengthening and improve the fatigue resistance, as compared with the aluminum matrix. The shape-memory effect was activated by cold rolling the samples at −30°C. Upon reheating to the austenite phase, the NiTi was expected to return to its original shape, while embedded in the aluminum matrix. This action created residual, internal stresses around each particle, which strengthened the material. The yield and ultimate strengths, and fatigue lives of the NiTi reinforced aluminum composites, have been improved considerably, as compared with the unreinforced material. The cross-sectional microstructures of the composites, as well as, the modes of crack growth, have been examined with scanning electron microscopy (SEM) to identify fatigue and fracture mechanisms.