THE EFFECT OF MATRIX MICROSTRUCTURE ON CYCLIC RESPONSE AND FATIGUE BEHAVIOR OF PARTICLE-REINFORCED 2219-ALUMINUM .1. ROOM-TEMPERATURE BEHAVIOR

The low-cycle and high-cycle fatigue behavior and cyclic response of n aturally aged and overaged 2219/TiC/15p and unreinforced 2219 Al were investigated using plastic strain-controlled and stress controlled tes ting. In addition, the influence of grain size on the particle-reinfor ced materials was examined. In both reinforced and unreinforced materi als, the naturally aged conditions were cyclically unstable, exhibitin g an initial hardening behavior followed by an extended region of cycl ic stability and ultimately a softening region. The overaged reinforce d material was cyclically stable for the plastic strains examined, whi le the overaged unreinforced material exhibited cyclic hardening at pl astic strains greater than 2.5 X 10(-4). Decreasing grain size of part icle-reinforced materials modestly increased the cyclic flow stress of both naturally aged and overaged materials. Reinforced and unreinforc ed materials exhibited similar fatigue life behaviors; however, the re inforced and unreinforced naturally aged materials had superior fatigu e lives in comparison to the overaged materials. Grain size had no eff ect on the fatigue life behavior of the particle-reinforced materials. The fatigue lives were strongly influenced by the presence of cluster s of TiC particles and exogenous Al3Ti intermetallics.