L. L. Rokhlin

Solid-state phase equilibria in the Mg corner of the MgGdSm phase diagram

Abstract The solid-state phase equilibria in the Mg corner of the MgGdSm phase diagram were investigated by optical and scanning electron microscopy, X-ray diffraction and electrical resistivity measurements. The experiments showed that in the Mg corner of the system there are only three solid phases in equilibrium: the Mg solid solution and the two Mg-richest compounds of the adjoining binary systems. Each of the binary compounds take into solution significant quantities of the second rare-earth metal. Gd and Sm mutually reduce their solubility in the Mg solid solution. Isothermal sections of the phase diagram at 500 and 300°C are presented.

Phase composition and recrystallization of Al-based Al-Sc-Mn-Zr alloys

The phase composition and recrystallization of Al-based alloys with small amounts (up to 4 wt %) of transition metals, such as Sc, Mn, and Zr, are studied by metallography and electrical resistivity and hardness measurements. No new phases, besides phases in equilibrium with an Al-based solid solution in the associated ternary systems, are found for the portion of the quaternary Al-Sc-Mn-Zr system under study. It is also found that the manganese and zirconium solubilities in the Al-based solid solution decrease in the presence of scandium and that zirconium additions in Al-Sc-Mn alloys increase their recrystallization temperature.

Phase equilibria in solid Mg-Rich Mg-Sm-Tb alloys

The structure of Mg-rich Mg-Sm-Tb alloys with samarium and terbium contents up to 30 at % each is studied by metallography, electron microprobe analysis, and electrical resistivity measurements. The magnesium-based solid solution is found to be in equilibrium only with the Mg41Sm5 and Mg24Tb5 phases belonging to the Mg-Sm and Mg-Tb binary systems composing the ternary system, respectively. The individual and total samarium and terbium solubilities in a magnesium-based solid solution at 500 and 300°C are determined. The terbium and samarium solubilities in the Mg41Sm5 and Mg24Tb5 phases, respectively, are also determined. Partial isothermal sections at 500 and 300°C of the Mg-Sm-Tb phase diagram in the Mg- rich region are constructed.

Effect of yttrium and chromium on the recrystallization of Al-Sc alloys

The effect of small chromium and yttrium additions (0.14–1.0 wt%) on the recrystallization of Al-Sc alloys having 0.1–0.4% Sc is studied with polarized light. The microstructure of cold-rolled samples annealed at 100–630°C for 1 h is examined. The chromium and yttrium additions are found to slightly affect the recrystallization temperature of the Al-Sc alloys: they increase or decrease it slightly depending on the scandium content.

Phase equilibria in Al-rich Al-Sc-Cr alloys

Phase equilibria in aluminum alloys containing up to 1.2 wt % Sc and 1.0 wt % Cr are studied by optical microscopy and differential thermal and electron microprobe analyses. Two vertical sections and the projection of liquidus surface have been constructed. The four-phase nonvariant equilibrium at a temperature of 656.5 ± 1°C is found to have a transition character. The Al-based solid solution is found to be in equilibrium only with the Al3Sc and Al7Cr binary phases.

Al-rich portion of the Al-Hf phase diagram

Electrical resistivity measurements, differential thermal analysis, optical microscopy, and the deposition of hafnium compound particles from a melt are used to study the Al-rich portion of the Al-Hf phase diagram. Prominence is given to the hafnium solubility in solid and liquid aluminum. The studies show a peritectic character of the invariant reaction during the solidification of alloys with sufficiently high hafnium contents and a slight difference between the peritectic and melting temperatures of pure aluminum. The hafnium solubility in solid and liquid aluminum is shown to increase with the temperature. The hafnium solubility in solid aluminum at the peritectic temperature (maximum solubility) is 1.00 wt % (0.153 at %); the hafnium solubility in liquid aluminum at this temperature is 0.43 wt % (0.065 at %).

Joint effect of scandium, manganese, and chromium on the recrystallization of aluminum alloys

The joint effect of manganese and chromium additions (0.25–0.8 wt %) on the recrystallization of Al-(0.1–0.4 wt %) Sc alloys is studied. The recrystallization is studied using changes in the microstructure of the alloys annealed in the temperature range 100–630°C. Depending on the scandium content in the alloys, combined alloying of them with manganese and chromium is found to lead to a slight increase or decrease in the recrystallization temperature of the Al-Sc alloys.

Phase equilibria in the ternary Al-Sc-Mn system

Optical microscopy, electron microprobe analysis, and electrical resistivity measurements are used to study Al-Sc-Mn alloys containing up to 3 at % Sc and to 2.5 at % Mn. The boundaries of the Al-based solid solution are determined at 640, 600, and 400°C, and the isothermal section of the Al-rich portion of the Al-Sc-Mn system at 640°C is constructed. The Al-based solid solution is found to be in equilibrium with the ScAl3 and MnAl6 phases.

Thermodynamic evaluation of the Cu-Mg-Zr system

The thermodynamic evaluation of the Cu–Mg–Zr system is presented in this paper. A literature survey was carried out first based on the most recent literature, which was scanned from the THERMET literature database. The evaluation of the thermodynamic parameters was carried out using Thermo-Calc (version H) software. The evaluation of the Cu–Mg–Zr system was carried out using the most recent experimental data from the literature and a set of DTA measurements. DTA measurements were done using alumina (Al2O3) crucibles under helium atmosphere with the niobium (Nb) reference crucible. The evaluated Cu–Mg–Zr phase diagram fitted well with experimental data with the liquidus data in a limited range of composition. There were two miscibility gaps observed in the system. New τ phase was detected using the X-ray and microscopic analysis and the data was used in this evaluation.

Effect of alloying elements on the texture and the anisotropy of the mechanical properties of magnesium alloys with REM, lithium, and aluminum

The formation of the texture and the anisotropy of the mechanical properties in extruded rods of commercial alloys MA5, MA18, MA21 and also experimental Mg-Y-based and Mg-Y-Ce-based alloys are studied by X-ray diffraction and the measurement of the hardness and the tensile and compressive properties. It is shown that the magnesium alloys can be separated into three groups according to the anisotropy of the mechanical properties. The first group consists of the alloys not containing rare-earth metals and lithium, and the second group is the alloys with yttrium for which the yield strength in the axial direction of the rods are significantly higher than those in the transverse direction. The alloys of the first group demonstrate a substantial excess of the yield strength in the axial direction in the tension tests as compared to those in compression tests, and the second group alloys do not demonstrate such a difference. The ceriumand lithium-containing alloys (the third group) exhibit a weak anisotropy of the strength properties. A method for estimating the anisotropy of the strength properties is developed on the basis of calculation of the Taylor factors for basal slip averaged over all orientations of crystallites, and a quantitative method is developed for determining the phase composition by measuring the solid solution lattice parameter.