N. P. Korzhova

New Light-weight Eutectic Alloys Based on L12 Cubic Aluminum Intermetallics with Enhanced Heat Resistance

The influence of the eutectic (Ll 2+ß) concentration on mechanical properties of as-cast eutectic alloys with the participation of L l 2 intermetallic phase of ternary Al-Ti-Cr system has been studied. The contour map of hardness values was constructed in the region of existence the eutectic L ^ L l i + ß transformation. The likeness of isohardness lines and the line of the univarianl eutectic transformation indicates that the eutectic structure formation essentially determines the level of as-cast alloys mechanical properties. It has been confirmed by mechanical tests at room and high temperatures for alloys with a various volume fraction of eutectic. For the alloy with the best combination of properties the temperature dependence of yield stress was determined in short-term compression tests. It was shown that the weakening of this alloy begins at temperatures higher than 700 °C, and at 1000 °C the yield stress equals 150 MPa. The high-temperature tests show that the thermal stability of as-cast alloys properties increases with increasing of eutectic (Ll 2 +ß) volume part. The investigations carried out showed that the eutectic (Ll 2+ß) alloy with optimum chemical composition has high heat resistance up to 1000 °C, that considerably exceeds the heat resistance of TiAl alloy. This testifies to the possibility of using the new eutectic (l . l2+ß) alloy of ternary system Al-Ti-Cr as a heatresistant material. In view of the high thermal stability of the structure and mechanical properties of eutectic alloy and also the good compatibility of its chemical composition with TiAl, it may be recommended for use as a material for coatings of alloys on the TiAl base and for practical application in condition;, of elevated

High-Purity Chromium Targets

A procedure for producing large-scale chromium ingots by means of induction-arc melting was developed. From the high-purity, low-alloyed chromium ingots obtained, chromium targets were produced by of thermoplastic treatment techniques. The method of electron-beam evaporation of high-purity chromium was also used for production of targets.

Mechanism of fracture of dispersion-strenghthened tungsten

ConclusionsIn a dispersion-strengthened tungsten alloy fracture mechanisms change with rise in temperature in the same sequence as in unalloyed tungsten: quasibrittle cleavage at low temperatures is succeeded by partly tough fracture at 400°C (TBru1), tough fracture through the body of the grain is observed in the range from 1000 (TBru2) to 1600°C, and at 1800°C tough intergranular fracture commences. The cold-brittleness points of the dispersion-strengthened tungsten alloy are lower (TBru1 by 100 and TBru1 by 200°C) then those of unalloyed tungsten, while the temperature of transition to tough intergranular fracture is higher. As a result, the dispersion-strengthened alloy has a wider temperature range of tough transgranular fracture, with a larger value ofψ. The wider range of tough transgranular fracture in the dispersion-strengthened tungsten alloy may be linked with a tendency for microvoids to form in the material on the second-phase particles, as a consequence of which subsequent fracture occurs by a microvoid coalescence mechanism.