EFFECTS OF GRAIN-SHAPE ANISOTROPY AND TEXTURE ON BALANCED-BIAXIAL CREEP OF TI AND ZR ALLOYS

Biaxial creep behaviors of stress-relieved and recrystallized thin-wal led tubing of Ti-3Al-2.5V and Zircaloy-4 are considered under equal ho op and axial stresses by internal pressurization superimposed with axi al load. Both hoop and axial strains were monitored and the ratio of t he strain rate along the hoop to that along the axial directions is co nsidered to represent rite degree of anisotropy. In both of these allo ys, relatively weak hoop direction in cold-worked stress-relieved (CWS R) materials became slightly stronger following recrystallization. Cry stallographic texture was considered in terms of x-ray pole figures fr om which the crystallite orientation distribution Junctions (CODFs) we re derived and crystal plasticity model with slip dominant on prism pl anes was combined with the CODFs to predict the creep anisotropy. Whil e good correlation was noted for recrystallized materials, distinct de viations ave observed for CWSR that are believed to arise from grain s hape anisotropy. The relatively small (equiaxed) grain size along the hoop and radial directions results in grain boundary sliding leading t o stress enhancements along these directions. This anisotropy in grain boundary sliding is shown to explain the observed deviations.