Abstract
Significant debate has been noted in the α-ω and ω-β phase transformations of zirconium. The initial pressure of the α-to-ω transformation at room temperature has been reported to vary from 0.25 to 7.0 GPa, while the hydrostatic transformation is believed to occur at approximately 2.2 GPa. Shear stress is commonly considered as a key factor leading to the discrepancy. However, the principal mechanisms previously proposed concluded that the phase transformation pressure would be decreased in the presence of shear stress. The experimental results of the α-ω transformation in zirconium are contrary to this conclusion. In the ω-β phase diagram of zirconium, the dT/dP along the phase boundary near the α-ω-β triple-point was reported to be either positive or negative, but no theoretical explanation, especially a quantitative one, has been proposed. This article aimed to quantitatively investigate and explain the controversies reported in the α-ω and ω-β phase transformations of zirconium by applying a new nonhydrostatic thermodynamic formalism for solid medium, which has recently been proposed and is capable of quantitatively estimating the impact of shear stress on phase transformations in solids.
Highlights
ZLC formalism is an approximate approach for nonhydrostatic thermodynamics which is applicable for phase equilibrium, phase diagram and phase transformation problems under nonhydrostatic situations from a macroscopic view, and is based on the following assumptions that are widely adopted in solid mechanics: (1) The object system could be regarded as a homogenous continuum, and the heterogeneities in meso- and micro-scales could be ignored or managed based on the average
The σ(P, T) relationships and the shear stress levels assumed in the six situations are valid in actual experiments. This means that the results predicted though our calculations are reasonable, it is understandable that the large scatter of the experimental measured transition pressure of the α-ω phase transformation of zirconium might be attributed to the difference in shear stress in different experiments
Significant debate has been noted in previous experiments for the α-ω and ω-β phase transformations in zirconium
Summary
This article aimed to quantitatively investigate and explain the controversies reported in the α-ω and ω-β phase transformations of zirconium by applying a new nonhydrostatic thermodynamic formalism for solid medium, which has recently been proposed and is capable of quantitatively estimating the impact of shear stress on phase transformations in solids. We aimed to explain the controversies observed in the α-ω and ω-β transformations in zirconium by applying the formalism
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