Effect of c/a-ratio on Crystallographic Texture and Mechanical Anisotropy of Hexagonal Close Packed Metals

摘要

Hexagonal close packed metals exhibit highly anisotropic mechanical properties, a thorough knowledge of which is a primary requisite for predictability of the dimensional changes in service as well as formability characteristics. We summarize our work on the effects of c/a-ratio on preferred orientations and the resulting anisotropic mechanical properties. Zr and Ti alloys are considered to represent low c/a-ratio while Mg alloy (AZ31B) was chosen as ideal; these materials were available in tubing form. Pure zinc sheet was used to represent high c/a-ratio. Distinct differences are noted in the basal pole distributions, and crystallite orientation distribution functions derived from the pole distributions were combined with crystal slip models to predict the mechanical anisotropy parameters. While in all cases the uniaxial yield stresses were evaluated along the RD and TD, the contractile strain ratios (CSR) were determined using grided tensile samples fabricated from sheets of Zircaloy and Zinc. The experimental results correlated with slip predictions based on predominant prism and basal slip modes respectively in Zicaloy and Zn. For Mg alloy, either pyramidal slip or a combination of basal and prism slip modes exhibited good agreement with the experimental results. In addition, the anisotropic creep behavior of thin-walled Zircaloy tubing is considered. Excellent agreement is noted, in recrystallized Zircaloy tubing, between the experimental creep locus and model predictions based on prism slip dominance. However, distinct deviations are noted in Ti3Al2.5V alloy albeit election microscopy of deformed tubing revealed dislocations on prism ({10.0}) planes with Burgers vectors along <11.0>.