Effects of grain-shape anisotropy and texture on balanced-biaxial creep of Ti and Zr alloys

Abstract

Biaxial creep behaviors of stress-relieved and recrystallized thin-walled tubing of Ti-3AI-2.SV and Zircaloy-4 are considered under equal hoop and axial stresses by internal pressurization superimposed with axial load. Both hoop and axial strains were monitored and the ratio of the strain rate along the hoop to that along the axial directions is considered to represent the degree of anisotropy.In both of these alloys, relatively weak hoop direction in cold-worked stress-relieved (CWSR) materials became slightly stronger following recrystallization. Crystallographic texture was considered in terms of x-ray pole figures from which the crystallite orientation distribution functions (CODFs) were derived and crystal plasticity model with slip dominant on prism planes was combined with the CODFs to predict the creep anisotropy. While good correlation was noted for recrystallized materials, distinct deviations are observed for CWSR that are believed to arise from grain shape anisotropy. The relatively small (equiaxed) grain size along the hoop and radial directions results in grain boundary sliding leading to stress enhancements along these directions. This anisotropy in grain boundary sliding is shown to explain the observed deviations.

Deformation Microstructures and Creep Mechanisms in Advanced ZR-Based Cladding Under Biazal Loading

“…Similar trend has also been noticed in Zirlo [6]. Murty et al [16,17] showed that a good correlation for the CWSR Zircaloy can be obtained by considering stress enhancement occurring in the hoop direction during grain boundary sliding. …”

Experimental creep behaviour determination of cladding tube materials under multi-axial loadings

“…The distinctive feature of this device is the simultaneous use of a radiative furnace, laser extensometers, an open pressuring system and a tensile and compression electromechanical device. Indeed, radiative furnace have already been used by Kaddour [11,12]. Laser extensometers have been used by Ferrer or Onimus [13,14].…”

“…In Ref. [12], Earthman and Murty studied the creep of Zycraloy-4 with specimens made of open tubes pressurized by an inert gas to submit the sample to a hoop stress controlled by the pressure level. But as they used static load to impose the axial load to the sample, they were not able to control precisely the load path.…”

The internal pressurization creep of Zr alloys for spent-fuel dry storage feasibility

“…In class-A alloys, only normal transients are expected (i.e., decreasing strain rate with boundaries vs. distinct subboundaries, respectively. 42,43 Offsets of grain boundaries are usually observed during GBS.…”