THE EFFECT OF MATRIX MICROSTRUCTURE ON CYCLIC RESPONSE AND FATIGUE BEHAVIOR OF PARTICLE-REINFORCED 2219-ALUMINUM .2. BEHAVIOR AT 150-DEGREES-C

The 150 degrees C cyclic response of peak-aged and overaged 2219/TiC/1 5p and 2219 Al was examined using fully reversed plastic strain-contro lled testing. The cyclic response of peak-aged and overaged particle-r einforced materials showed extensive cyclic softening. This softening began at the commencement of cycling and continued until failure. At a plastic strain below 5 x 10(-3), the unreinforced materials did not s how evidence of cyclic softening until approximately 30 pct of the lif e was consumed. In addition, the degree of cyclic softening (Delta sig ma) was significantly lower in the unreinforced microstructures. The c yclic softening in both reinforced and unreinforced materials was attr ibuted to the decomposition of the theta' strengthening precipitates. The extent of the precipitate decomposition was much greater in the co mposite materials due to the increased levels of local plastic strain in the matrix caused by constrained deformation near the TiC particles .