MECHANISMS OF ELEVATED TEMPERATURE DEFORMATION IN SELECTED ALUMINUM ALLOYS AND RELATED INTERMETALLIC COMPOUNDS

Two studies of the mechanisms of elevated temperature deformation are included in this dissertation.; In Part I of this dissertation, a new technique for distinguishing between pure metal and alloy type creep behavior is described. Strain rate changes were performed using an Instron electromechanical testing machine. The observed variation in plastic strain rate with stress was then compared with the known variation for steady deformation. For both aluminum and Al-5.8 at.%Mg the observed transient response was successfully used to make a qualitative distinction between pure metal and alloy type behavior.; The strain rate change technique was also used to study the elevated temperature deformation behavior of the intermetallic compounds NiAl and CoAl. NiAl exhibits pure metal type behavior between 1100 and 1300 K. CoAl, however, undergoes a transition from pure metal to alloy type behavior upon decreasing the temperature from 1400 to 1200 K. Slip appears to be inherently more difficult in CoAl than in NiAl with lattice friction effects limiting the mobility of dislocations at a much higher temperature in CoAl than in NiAl.; In Part II of this dissertation, the elevated temperature deformation characteristics of a rapidly solidified Al-8.4 wt.%Fe-3.6 wt.%Ce alloy are described. Constant true strain rate compression tests show that the Al-Fe-Ce alloy is significantly stronger than ODS aluminum at temperatures below approximately 723 K. However, unlike ODS aluminum, the strength of the Al-Fe-Ce alloy falls rapidly with increasing temperature above 723 K. Particle coarsening is only partially responsible for the observed elevated temperature softening. In direct contrast to ODS alloys, which contain non-deformable particles, the true activation energy for deformation of the Al-Fe-Ce alloy between 723 and 773 K is significantly greater than that for matrix self-diffusion. Since abnormally high true activation energies for deformation are also exhibited by materials containing deformable particles, such as (gamma)' strengthened superalloys, it is concluded that elevated temperature deformation in the Al-Fe-Ce alloy involves deformation of both the matrix and the precipitates. The loss in strength of the Al-Fe-Ce alloy appears to be related to a reduction in strength of at least some of the second phase particles at temperatures above 723 K.