CONTINUUM PREDICTIONS OF DEFORMATION IN COMPOSITES WITH 2 CREEPING PHASES .2. NB5SI3 NB COMPOSITES/

The primary and steady-state creep behavior of ductile-phase toughened Nb5Si3/Nb in situ composites has been simulated using the analytical and finite element (FE) continuum techniques described in Part I of th is paper. The material constants in the creep constitutive law have be en fitted to experimentally measured creep properties of the bulk Nb5S i3 and Nb solid-solution phases. The composite microstructure has been idealized to facilitate the modeling, with a variety of microstructur al idealizations resulting in very similar predicted composite creep r ates. The models somewhat underpredict the steady-state strain rates a nd over predict the primary creep strains for the Nb-10 at.% Si compos ite studied experimentally. Several potential causes for these discrep ancies have been identified, including internal damage effects and a p ossible increase in the Nb5Si3 stress exponent at high stress. However , the models correctly make the important prediction that the creep st rength of the Nb-rich composite is dominated by the strong Nb5Si3 phas e. FE predictions of large internal tensile stresses in the matrix are consistent with experimental observations of creep damage.