Kazuaki Nishino

Phase-stability dependence of plastic deformation behavior in Ti-Nb-Ta-Zr-O alloys

The authors investigated the effects of alloy content on mechanical properties to make clear a correlation between plastic deformation behavior and β-phase stability in Ti-Nb-Ta-Zr-O alloys. It was realized that there was specific compositional area in which the alloy exhibited little work hardening and minimum Young’s modulus value. The specific area was expressed by the bond order (Bo), based on theDV-Xα method, of 2.87 and the averaged electron/atom ratio (e/a) of 4.24, which corresponded to those of a multifunctional β titanium alloy, “Gum Metal.” These electronic conditions also minimized ideal strength required for plastic deformation without any dislocation activity. The deformation behavior of alloys in the specific compositional area revealed that the unique behavior could be characterized by a “giant fault.” It was also confirmed that such a compositional area corresponded to the phase boundary between the α″ martensite and β phases at room temperature.

New surface treatment using shot blast for improving oxidation resistance of TiAl-base alloys

Abstract A new surface treatment using shot blasts with WO 3 powder has been developed. This has been most effective in improving the cyclic oxidation resistance of TiAl-base alloy in air and in a diesel engine exhaust gas atmosphere of up to 1223 K. This effect is attributed to the formation of an Al 2 O 3 layer in an oxidation atmosphere. The above layer is supposed to be formed as follows: Since the WO 3 powder is shot repeatedly during the surface treatment, a WO 3 layer adhering to the substrate is formed on the surface. This layer causes the preferential oxidation of aluminum at the early stage of oxidation, resulting in the formation of a sound and continuous Al 2 O 3 layer. The developed surface treatment gives the same oxidation resistance as that of nickel-base superalloy Inconel 713C up to 1223 K, and is applicable to complex-shape parts with as-cast skin surfaces, such as turbocharger wheels.

The Characteristics of Dispersion-Strengthened Copper Alloys Made by Hot Repressing

In order to clarify various properties of DS copper alloys made by hot repressed of internally oxidized Cu-0.33%Al powder, effects of forging temperature, attritor grinding and atomic ratios of O/Al on mechanical properties and electrical conductivity were investigated. Mean density was increased with increasing of forging temperature, and mechanical properties were also improved. About 99.7% of theoretical density was obtained when the forging temperature was above 900°C. Mechanical properties, especially elongation, of the specimens were improved by using attrited powder. The optimum mechanical properties and electrical conductivity were obtained when the atomic ratio of O/Al was nearly equal to 2.2. The anisotropy of strength at elevated temperatures was negligibly small compared with that of the commercial extruded DS copper alloys.