Structural, electronic, mechanical and thermodynamic properties of Cr–Si binary silicides from first-principles investigations

The structural, mechanical and thermodynamic properties of the orthorhombic TMAl (TM=Ti, Y, Zr and Hf) aluminides from first-principles calculations

Effects of solid solution elements on damping capacities of four Mg-1at%X binary alloys (X = Zn, Sn, Ga, Al) with similar grain sizes are carefully investigated with pure Mg as comparison. The strain-amplitude-independent damping capacity of the solid solution alloy decreases with the higher lattice distortion caused by solute atoms, while the yield strength is just the opposite. The strain-amplitude-dependent damping capacity is affected by the lattice distortion, the stacking fault energy and the mixing enthalpy between solute atoms and Mg atoms, while the stacking fault energy is the dominant. The Mg-1at%Sn alloy exhibits the highest strain-amplitude-independent damping capacity, while the Mg-1at%Al alloy has the best strain-amplitude-dependent damping capacity at room temperature. When the temperature rises to about 100 °C, the Mg-1at%Zn alloy with the largest lattice distortion degree has the best strain-amplitude-independent damping. This may be related to the increase of the dynamic force for dislocation bowing caused by thermal activation.

Effects of solid solution elements on damping capacities of binary magnesium alloys

Hot compression tests of Mg-Gd-Y-Zr alloy at different deformation temperatures and strains were carried out with Gleeble-1500 simulator at strain rate of 0.002 s−1. The microstructure evolution of 400 °C/0.002 s−1 sample under different strain was analyzed emphatically by transmission electron microscopy and electron backscatter diffraction technology. Dynamic precipitation characteristics and nucleation-expansion mechanism of dynamic recrystallization (DRX) were discussed in detail. The results indicated that the dynamic precipitation takes place prior to DRX, and the morphology, size and distribution of precipitates change with increasing strain. At the later stage of deformation, the large-size hard phase β-Mg5(Gd,Y) can induce the particle-stimulated nucleation (PSN) mechanism under large strain and act as an effective nucleation site for DRX. In addition, we constructed a schematic diagram of the DRX nucleation-expansion mechanism of Mg-Gd-Y-Zr alloy under high temperature deformation. The first layer of DRX grains is formed by discontinuous dynamic recrystallization (DDRX) mechanism characterized by grain boundary bulge out, and the precipitates distributed at the original grain boundary promote DDRX nucleation; The expansion of necklace structure depends on continuous dynamic recrystallization (CDRX) mechanism; Subgrain division can further refine DRX grains.

Dynamic precipitation and recrystallization mechanism during hot compression of Mg-Gd-Y-Zr alloy

We have studied the microstructure evolution and deformation behavior of Mg-5Gd-3Y-(1Sn)-0.5Zr alloys during hot compression (T = 350 °C, 400 °C, 450 °C and 500 °C, e ˙  = 0.002 s−1, 0.01 s−1, 0.1 s−1 and 1 s−1) by transmission electron microscopy and electron backscattering technology. Sn can promote dynamic precipitation to activate the particle-stimulated nucleation (PSN) mechanism induced by the cluster precipitates and promote and dynamic recrystallization (DRX); in addition, Sn can inhibit the formation of high-angle grain boundaries (HAGBs) by reducing the activation of pyramidal and slip and delaying DRX. The two processes are in a competitive relationship with each other in the hot deformation of Mg-Gd-Y-Sn-Zr alloys. At low temperatures (350 °C–400 °C) and high strain rates, the former dominates: DRX is promoted, accompanied by a decrease in flow stress. At high temperatures (450 °C–500 °C) and low strain rates, the latter is dominant due to the absence of dynamic precipitation: DRX is delayed, and flow stress is increased accordingly. Flow stress between the two extreme deformation conditions is determined by the competitive relationship between them. We also found that the addition of Sn could increase the thermal deformation activation energy of Mg-Gd-Y-Zr alloys, weaken the texture and inhibit twin growth. Finally, we constructed a schematic diagram of the DRX mechanism during the thermal deformation process to illustrate the effects of PSN, CDRX, and DDRX on the evolution of the microstructure in detail.

Effect of Sn addition on the deformation behavior and microstructural evolution of Mg-Gd-Y-Zr alloy during hot compression

Microstructure and mechanical properties of Mg-Gd-Y-Sm-Al alloy and analysis of grain refinement and strengthening mechanism

Abnormal temperature effect on tensile strength of Mg-13Gd-2Y-0.5Zr alloy

Dynamic precipitation of Mg–8.08Gd–2.41Sm–0.30Zr (wt %) alloy during hot compression was studied in the present work. The effects of temperature and strain rate on dynamic precipitation, and the effects of dynamic precipitation on dynamic recrystallization (DRX) and microhardness, were systematically analyzed. For this purpose, hot compression tests were conducted at the strain rates of 0.002~1 s−1 and temperatures of 350~500 °C, with the compaction strain of 70% (emax = 0.7). The obtained results revealed that dynamic precipitation occurred during hot compression at 350~400 °C, but did not occur for T ≥ 450 °C. The precipitates were demonstrated to be β-Mg5Gd with a size of 200~400 nm, and they were distributed in the DRXed region. Dynamic precipitation occurred at strain rates in the 0.002~0.01 s−1 range, but did not occur when the strain rates were in the 0.1~1 s−1 range for the hot compression temperature of 350 °C. The relationships between the hot compression temperature (T) and DRXed grain size (lnd), microhardness (Hv), and DRXed grain size (d−1/2) of Mg–8.08Gd–2.41Sm–0.30Zr alloy were obtained.

Dynamic Precipitation in Mg–8.08Gd–2.41Sm–0.30Zr Alloy during Hot Compression

Tensile creep behavior and microstructure evolution of Mg-11Gd-2Y-0.5Zr alloy

Mg–11Gd–2Y–xSm–0.6Al (x = 0, 1, 3, 5) alloys were prepared in electromagnetic induction furnace by gas protection. The crystal structure, microstructure and mechanical properties of as-cast Mg–11Gd–2Y–xSm–0.6Al alloys were studied by X-ray diffraction, metallographic microscope, scanning electron microscopy and tensile testing. The results show that the main phases of Mg–11Gd–2Y–xSm–0.6Al alloys are α-Mg matrix, Mg5Gd, Mg24Y5 and Mg41Sm5. The addition of Sm refines the microstructure and increases the number of second phase in the grain boundary. The diffraction peaks of the cylindrical plane (100)α-Mg, base plane (002)α-Mg and conical plane (101)α-Mg are shifted to a low angle. The offset of diffraction peak and the lattice constant of α-Mg increase with the increase in Sm content. The crystal axis ratio decreases with the increase in Sm content. When the addition of Sm is 3%, the ultimate tensile strength reaches to 240 MPa, which increases by 17.07%. The improvement in mechanical properties is mainly attributed to the grain refinement and the decrease in the crystal axis ratio of α-Mg.

Quanan Li

Papers

Microstructure and mechanical properties of Mg-Gd-Y-Sm-Al alloy and analysis of grain refinement and strengthening mechanism

Abnormal temperature effect on tensile strength of Mg-13Gd-2Y-0.5Zr alloy

Dynamic Precipitation in Mg–8.08Gd–2.41Sm–0.30Zr Alloy during Hot Compression

Tensile creep behavior and microstructure evolution of Mg-11Gd-2Y-0.5Zr alloy

Effect of Sm on Microstructure, Mechanical Property and Lattice Constant of As-Cast Mg–11Gd–2Y–0.6Al Alloy