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Massive transformation, as a non-conventional solid-state phase transformation mode, is scarcely observed in metals with hexagonal closed packed (HCP) structure, especially in Zr and its alloys. In this study, however, we report the massive transformation in a Zr-1.0Cr-0.4Fe alloy after conventional β-quenching. It is shown that the necessary condition to induce the occurrence of massive transformation requires an appropriate composition and cooling rate of the alloy to be simultaneously within reasonable ranges. We combine the electron backscatter diffraction (EBSD) and crystallographic reconstruction techniques to systematically assess the orientation relationship between massive grain (αm) and its β parent grain. It is demonstrated that, similar to martensitic transformation, the orientation between αm and β parent grain during massive transformation satisfies Burgers orientation relationship, i.e. and. Furthermore, a statistical analysis of EBSD data shows that variant selection occurs during massive transformation due to pre-existing β-β grain boundary. Based on mathematical theory and crystallographic calculations, we further explore the detailed mechanisms of variant selection during massive transformation. [ABSTRACT FROM AUTHOR]

In this paper, we report the formation of an atypical double twinning sequence in Zircaloy-4 during rolling at room temperature. The grain orientation analysis based on electron backscattering diffraction (EBSD) data reveals that this double twinning mode is of the 11 2 ̅ 1 - 10 1 ̅ 2 type, namely, the secondary 10 1 ̅ 2 twin generated within the primary 11 2 ̅ 1 twin. Based on the combinative analysis of Schmid factor and local strain accommodation, the formation and variant selection mechanism of this double twinning are discussed. [ABSTRACT FROM AUTHOR]

Abstract: The adiabatic shear bands formed in the zirconium alloy impacted by split Hopkinson pressure bar at a strain rate of about 6000s−1 were characterized systemically by means of a high resolution field emission scanning electron microscope equipped with electron backscatter diffraction probe. The results show that the transformed bands were distinguished on the cross-section view of the impacted specimens, and the ultrafine and equiaxed grains formed in the transformed bands were confirmed. The gradient variation of the grains across the transformed bands from the boundary to the center of the bands was observed, and the grains at the center of the transformed bands were finer than other zones. Based on the characterization of the deformed microstructure adjacent to the transformed bands, the formation mechanism of the ultrafine and equiaxed grains in the transformed bands was revealed, and the rotational dynamic recrystallization mechanism should be responsible for the formation of the ultrafine and equiaxed grains in the transformed bands. According to the collection of the cumulative misorientation at different strain levels, the formation and evolution process of the ultrafine and equiaxed grains in the transformed bands were speculated. The microhardness measurements show that high microhardness value in the transformed bands was obtained because of the grain refining, and the large standard deviation of the microhardness at the center of the transformed bands was confirmed due to the gradient microstructural distribution in the bands. [Copyright &y& Elsevier]

Twinning is frequently reported in Zr alloys during deformation and martensitic phase transformation. In the present work, however, we report and twinning after furnace cooling form β phase domain to room temperature in a Zr alloy. Intergranular thermal residual stresses produced during cooling due to anisotropic coefficients of thermal expansion, combined with the extraordinarily large grain size of the transformed α-Zr, are believed to be the reasons accounting for the formation of these twins. [ABSTRACT FROM AUTHOR]

Abstract: Composite aluminium alloys reinforced with Al2O3p particles have been produced by squeeze casting followed by hot extrusion and a precipitation hardening treatment. Good mechanical properties can be achieved, and in this paper we describe an optimization of the key processing parameters. The parameters investigated are the extrusion temperature, the extrusion rate and the extrusion ratio. The materials chosen are AA 2024 and AA 6061, each reinforced with 30vol.% Al2O3 particles of diameter typically in the range from 0.15 to 0.3μm. The extruded composites have been evaluated based on an investigation of their mechanical properties and microstructure, as well as on the surface quality of the extruded samples. The evaluation shows that material with good strength, though with limited ductility, can be reliably obtained using a production route of squeeze casting, followed by hot extrusion and a precipitation hardening treatment. For the extrusion step optimized processing parameters have been determined as: (i) extrusion temperature=500°C–560°C; (ii) extrusion rate=5mm/s; (iii) extrusion ratio=10:1. [Copyright &y& Elsevier]