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Due to its service background, the thermal behavior of Ta films is substantially concerning to researchers, especially the heat-induced β-Ta to α-Ta phase transformation. In this work, the nanocrystalline Ta films with varying β/α phase ratios (0.85–0) were deposited and vacuum annealed at 200–800 °C to study the phase transformation behavior and mechanical properties. Partial phase transformation of β-Ta to α-Ta occurred at low temperature (200 °C) and complete transformation when the annealing temperature was raised to 800 °C. Moreover, an orientation relationship of β-<110>//α-<111> and β-{330}//α-{110} was concluded, and a hypothesis theory about the low-temperature phase transformation was proposed. Annealing hardening took place at 200–600 °C and softening at 800 °C in all the samples. The hardening is mostly due to the ordering of intergranular amorphous phases with the temperature increased, simultaneously bringing the increase of modulus. The annealing softening is governed by both grain coarsening and phase transformation, where the latter is dominated in high β fraction samples. • High-temperature induced grain boundary structure ordering promotes the hardening of Ta films at 200 °C–600 °C. • β-Ta to α-Ta phase transformation was found at a wide temperature range, which partially governs the softening of Ta at 800 °C. • A preferred orientation relationship of β-<110>{330}//α-<111>{110} was concluded • The influence of phase transformation on mechanical properties was independently quantified using a simple comparative method. [ABSTRACT FROM AUTHOR]

Abstract: The extruded Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt%) alloy were subjected to large-strain hot rolling with different final rolling temperatures. The microstructural evolution and mechanical properties of the sheets were investigated. The microstructure became homogeneous after hot rolling process and long period stacking ordered (LPSO) phase distributed at grain boundaries along rolling direction. The sheet rolled at 300°C was composed of deformed grains, substructures and excessive dislocations. With increasing final rolling temperatures from 300°C to 400°C, the volume fraction of recrystallized grains with relatively random orientations increased significantly. The strength of the rolled sheets was improved while the ductility was deteriorated with decreasing final rolling temperatures. The tensile yield strength and ultimate tensile strength of the sheet rolled at 300°C reached 320MPa and 416MPa, respectively with the elongation to failure of 5.3%. The mechanical anisotropy of the rolling sheet became unity when rolled at higher temperature of 400°C due to the formation of weaker basal texture. [Copyright &y& Elsevier]

Abstract: Different cooling processes, such as quenching in warm water and cooling in furnace, were introduced to homogenize Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt%) alloy. Microstructure evolution and mechanical properties of the homogenized alloy were investigated. The as-quenched sample was comprised of α-Mg matrix, Mg5RE phase and 18R LPSO phase distributed at the grain boundaries and a few of RE-rich particles distributed randomly. During the process of cooling in furnace, Mg5RE and 18R LPSO phases were transformed into block-shaped 14H LPSO phase and lamellar-shaped 14H LPSO phase, respectively, due to the diffusion of solute atoms into the α-Mg matrix. Furthermore, the lamellar-shaped 14H LPSO phase grew and ran through the whole grains. The as-quenched sample exhibits tensile yield strength of 130MPa, ultimate tensile strength of 206MPa and elongation to failure of 5.5%, while the sample cooled in the furnace exhibits higher tensile yield strength but lower ultimate tensile strength and ductility due to the coarse grains and formation of block-shaped 14H LPSO phase. [Copyright &y& Elsevier]

Abstract: Magnesium matrix nanocomposites reinforced by SiC nanoparticles were fabricated by ultrasonic vibration with SiC nanoparticle size of 60nm and volume fractions of 0.5%, 1% and 2%, respectively. With increasing the volume fraction of the SiC nanoparticles, grain size of matrix in the SiCp/AZ91 nanocomposites was gradually decreased and morphology of the phase Mg17Al12 was refined compared with as-cast AZ91 alloy. Most of the SiC nanoparticles exhibited a homogeneous distribution in the 0.5 and 1vol.% SiCp/AZ91 nanocomposites. The ultimate tensile strength, yield strength and elongation to fracture of the 0.5 and 1vol.% SiCp/AZ91 nanocomposites were simultaneously improved. However, agglomerates of SiC nanoparticles along the grain boundaries were evidently increased when the volume fraction of nanoparticles was increased to 2, which caused the decrease of ultimate tensile strength and elongation to fracture. [Copyright &y& Elsevier]

A new ultrahigh-strength W phase (Mg 3 Y 2 Zn 3 ) containing Mg–10.3Zn–6.4Y–0.4Zr–0.5Ca (wt.%) alloy with medium RE content has been fabricated through conventional casting and indirect extrusion. The as-extruded alloy exhibits ultimate tensile strength of 466 MPa, tensile yield stress of 447 MPa and elongation to failure of 4.7%. The as-cast Mg–10.3Zn–6.4Y–0.4Zr–0.5Ca (wt.%) alloy is mainly composed of α-Mg and lamellar eutectic α-Mg and W phase distributed at grain boundaries. After extrusion, the coarse lamellar W phases in the as-cast alloy are broken into fine particles of about 0.5 μm, dispersing in the particle bands along the extrusion direction. The as-extruded alloy exhibits a bimodal microstructure consisting of ultrafine dynamic recrystallized (DRXed) grains with fine broken W phase particles at the DRXed grain boundaries and coarse un-DRXed regions. Large number of nano W phase and small amount of nano β 2 ′ phase are dynamically precipitated in the coarse unDRXed regions during extrusion, which contribute to the ultrahigh strength of the as-extruded alloy. [ABSTRACT FROM AUTHOR]

AZ91 alloy was subjected to multidirectional forging (MDF) and the relationship between microstructures and mechanical properties generated by MDF were investigated. The results showed that after 1 MDF pass grain size of the alloy decreased compared with as-cast alloy, and the amount of recrystallization grains increased when the MDF temperature increased from 250 °C to 400 °C. With increasing the MDF passes at 350 °C, grains of the alloy were gradually refined. A typical basal texture was obtained after 1 MDF pass, and then the basal pole scattered with the increase of MDF passes. Mg 17 Al 12 phases were precipitated along grain boundaries during MDF, which could hinder the growth of recrystallization grains. Both tensile strength and elongation to failure of the alloy were significantly enhanced till 3 MDF passes with increasing the MDF passes. [ABSTRACT FROM AUTHOR]

The present study dealt with the AZ91 alloy subjected to multidirectional forging (MDF) under decreasing temperature conditions with emphasizing on relationship between microstructures and mechanical properties generated by MDF. The obtained results showed that grains of the alloy were gradually refined while the amount of the second phase precipitated along the grain boundaries was increased with increasing the MDF passes and decreasing the MDF temperature. Compared with the as-cast alloy, yield strength, ultimate tensile strength and elongation of the AZ91 alloy after MDF under decreasing temperature conditions were simultaneously increased. As the numbers of MDF passes were gradually increased and the MDF temperature was gradually decreased, the yield strength was gradually decreased, suggesting that texture softening may overwhelm the strengthening due to the grain refinement as well as the homogeneous distribution of precipitates. [ABSTRACT FROM AUTHOR]

Highlights: [•] Friction stir processing (FSP) was applied to Mg–Gd–Y–Zn–Zr casting. [•] The grain boundary Mg3RE and LPSO phases in the casting dissolved after FSP. [•] Fine grains with LPSO phase distributed only within the grains was achieved. [•] High mechanical properties were obtained in FSP Mg–Gd–Y–Zn–Zr. [ABSTRACT FROM AUTHOR]

Abstract: A large Mg-4.50Zn-1.13Ca (wt%) alloy ingot 350mm in diameter and 1730mm long was successfully fabricated by semi-continuous casting. The microstructures and mechanical properties of the as-cast and as-extruded alloys were investigated. The as-cast alloy exhibits uniform chemical composition and microstructure from the centre to the surface of the ingot and mainly consists of α-Mg and Ca2Mg6Zn3. The coarse grains and network-like second phases that are distributed at the grain boundaries result in poor mechanical properties for the as-cast alloy. The mechanical properties of the as-extruded alloys are significantly enhanced. The high yield strengths of the as-extruded alloys mainly result from the fine DRXed grain and the stronger basal texture. [Copyright &y& Elsevier]

Abstract: The microstructure and mechanical properties of Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt%) alloy sheets produced by combined processes of extrusion, large-strain hot rolling and ageing treatment were investigated. The sheet rolled at 300°C was mainly composed of deformed grains while that rolled at 400°C was fully recrystallized, and the LPSO phase distributed at the grain boundaries in both sheets. The sheet rolled at 300°C and then peak-aged at 200°C exhibits 0.2% proof stress (PS) of 454MPa, ultimate tensile strength (UTS) of 469MPa and elongation to failure of 1.3% at ambient temperature, and 0.2% PS of 413MPa, UTS of 457MPa and elongation to failure of 6.8% at 200°C, respectively. While the sheet rolled at 400°C and peak aged at 200°C had lower 0.2% PS and superior ductility. The improvement of strength is ascribed to the fine β′ phase precipitated within the grains, the LPSO phase and dispersed cuboid Mg–Gd–Y containing phase located at the grain boundaries. [Copyright &y& Elsevier]

Abstract: Ultra high-strength Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr alloy sheet was prepared by large-strain hot rolling and subsequent ageing process. The sheet exhibits excellent tensile properties at ambient temperature with ultimate tensile strength of 517MPa, 0.2% proof stress of 426MPa and elongation to failure of 4.5%. The notable improvement in strength is attributed to the dense distribution of the fine precipitates inside the grains, scattered precipitates at the grain boundaries, bimodal grain size distribution with fine recrystallized grains and large deformed grains with intense basal texture. [Copyright &y& Elsevier]

Abstract: Mg–5.25wt.% Zn–0.6wt.% Ca alloy was subjected to equal channel angular pressing (ECAP) at 250°C using route A, Bc and C, respectively, in order to investigate the effect of shearing strain path on microstructure, texture and mechanical properties. Route Bc was the most effective in grain refinement and generating high angle grain boundaries, while route A was the least effective. Different textures were developed when a different ECAP route was applied. After ECAP using route A, the tensile yield strength (TYS) got much higher than those of the as-extruded alloy, which was primarily resulted from the strengthening due to the grain refinement. Because the Schmid factor for basal slip system was changed only a little, the texture soften effect was not obvious. After ECAP using route C, TYS of the Mg alloy was significantly decreased although the grain size was significantly refined, because the texture softening effect was dominant over the strengthening due to the grain refinement. [Copyright &y& Elsevier]