Papers by Keyword: Solid Solution Strengthening

Abstract: With an aim of clarifying the strength of rapidly solidified P/M materials strengthened by solid solution of Mg and dispersion of transition metal compounds at elevated temperature, Al-2mass%Mn, Al-4mass%Mn and Al-6mass%Mn alloys with varied Mg additions of 0, 1 and 3 mass% were prepared by rapid solidification techniques. Rapidly solidified (RS) flakes were produced by remelting alloy ingots in a graphite crucible, atomizing the alloy melt and subsequent splat-quenching on a rotating water-cooled copper roll under argon atmosphere.　The RS flakes were consolidated to the P/M materials by hot extrusion after vacuum degassing. Cast ingots of these alloys were also hot-extruded under the same conditions to the I/M as reference materials. Metallographic structures and constituent phases were studied for the P/M and I/M materials by optical microscope and X-ray diffraction. Mechanical properties of as-extruded and annealed P/M materials and as-extruded I/M materials were examined by tensile test at room and elevated temperatures under various strain rates. Uniform dispersion of fine intermetallic compounds (Al6Mn) was observed in all the as-extruded P/M materials. Added Mg was present as the solute in I/M and P/M materials alloy even after annealing. The P/M materials containing Mg exhibited higher hardness and strength at room temperature, than those without Mg. It was considered that both solid solution of Mg and dispersion of intermetallic compounds were contributing the hardness and strength increase in the rapidly solidified Al-Mn-Mg alloys. Tensile strength increases with increasing amount of Mg in I/M materials at all testing temperatures. However, strength of as-extruded P/M materials decreases with addition of Mg at 573K and 673K. Thus the positive effects of Mg additions on tensile strength of as-extruded P/M materials disappeared at higher testing temperature. Tensile strength of annealed P/M materials in which dislocation density decreased and compound particle coarsened increased with addition of Mg at elevated temperatures.

Abstract: We investigated the contribution to the high yield strength due to the solid solution strengthening in nanocrystalline Al-Ti alloys produced by a vapor quench method. The misfit strain due to solute Ti atom in aluminum was obtained from the first principles calculation. Then, the theoretical result of the contribution to the yield strength due to the solid solution strengthening was estimated from the misfit strain using the Friedel’s theory. In dilute Al-Ti alloy, the theoretical results of the solid solution strengthening from the misfit strain was in good agreement with the analytical result using the measured grain size and yield stress.

Abstract: Solution nitriding and aging treatment were applied to Ti-4mass%Cr alloy in order to fabricate a ductile high-nitrogen titanium alloy with fine (α + β) structure. The solution-nitrided specimen with
α’ martensitic structure was significantly hardened by solid solution strengthening by the absorbed nitrogen. During the aging treatment, fine β grains with a size of 1 microns in thickness precipitated along the martensite-plate boundaries. Although the specimen was softened to some extent after the aging treatment, the hardness is kept much higher than that of the aged Ti-4mass%Cr alloy without solution nitriding. This indicates that the nitrogen is still in solid solution of α phase even after the aging treatment, and contributes to strengthening of the fine-structured Ti-4mass%Cr-N alloy.

Abstract: Recently nanocrystalline Al-Fe alloys produced by a vapor quench method have been reported. These alloys are supersaturated solid solution and exhibit high strength with good ductility. It is postulated that the high strength of the Al-Fe alloys could be achieved by both the nano-grained structures and the solid solution strengthening. The contribution to the yield strength due to both the grain size strengthening and the solid solution strengthening were analyzed from the experimental data. Then the contribution to the yield strength due to the solid solution strengthening was estimated from the misfit strain calculated from the first principles in order to compare with analytical results estimated from the experimental data.

Abstract: The applications of ab initio calculations for deformation mechanisms of Mg-based alloys are discussed. First, Peierls stress of pure magnesium is calculated from generalized stacking fault (GSF) energies obtained by ab initio calculations. Second, materials design is applied to develop new Mg-based alloys exhibiting high strength. The atomic size factors of some Mg-based solid solutions are calculated by ab initio calculations as a first step of searching most effective solute element for the solid-solution strengthening.