Fatigue Crack Propagation Behavior of Nickel-Foam Reinforced Aluminum Alloy.

Nickel-foam reinforced aluminum alloy (NFRA) has recently attracted special interest as one of the metal matrix composites. Nickel-foam is easily integrated with aluminum alloy because of high porosity, and its specific surface area is large enough to improve the wetability and adhesion and to form a Ni-Al intermetallic compound which is helpful in improving wear resistance.The aim of this investigation is to clarify the fatigue behavior of this new material. Fatigue crack propagation behavior of NFRA was studied using compact tension specimens under a testing frequency of 10Hz in air and stress ratio of 0.05, 0.5 and 0.7. Three types of NFRA with Ni-form squeeze casted with AC8A aluminum alloy were prepared and were heat treated with T6 processing.Fatigue crack propagation rate of NFRA decreased significantly as compared with that of AC8A-T6 aluminum alloy for low values of ΔK. The crack propagation rate was affected by the shape and size of nickel-foam. Acceleration and retardation of propagation rate was observed around the Ni-skelton because of propagation along the Ni-foam/matrix interface and in Ni-foam. The mechanism of crack propagation for NFRA was indicated by the equation of da/dN=A(Kmax)α(ΔK)β, where A, α and β are constant.