THE SPECTRUM OF RATE CONTROLLING DEFORMATION MECHANISMS OPERATING IN CREEP IN AN Al-8.5Fe-1.3V-1.7Si-l5SiC_p COMPOSITE AT TEMPERATURES RANGING FROM 623 TO 948 K

摘要

Creep in an Al-8.5Fe-1.3V-1.7Si alloy reinforced with silicon carbide particulates - an Al-8.5Fe-1.3V-1.7Si-15SiC_p composite - is investigated at temperatures ranging from 623 to 948 K. At temperatures 623, 673 and 723 K the creep is associated with a true threshold stress decreasing with increasing temperature more strongly than the shear modulus of the composite matrix. The true activation energy of creep is close to the activation enthalpy of lattice diffusion in the composite matrix and the true stress exponent of minimum creep strain rate is close to 5. The creep is interpreted in terms of athermal detachment of dislocations from incoherent Al_(12)(Fe,V)_3Si phase particles in the matrix.At temperatures 773, 798 and 823 K the true threshold stress is not observed. The true stress exponent of minimum creep strain rate increases with increasing stress and the true activation energy of creep is higher than the activation enthalpy of lattice diffusion in the matrix. The creep is interpreted in terms of thermally activated detachment of dislocations from the incoherent Al_(12)(Fe,V)_3Si phase particles.At temperatures ranging from 873 to 948 K the true threshold stress reappears. However, its origin is different from that at temperatures 623-723 K. The true activation energy is close to the activation enthalpy of grain boundary diffusion and the true stress exponent of minimum creep strain rate is close to 2.5. The creep at these temperatures is interpreted in terms of superplastic flow.