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Microstructure and mechanical properties of an austenitic heat-resistant steel (12Cr18Ni12Ti) serviced in a supercritical power plant at 570 °C/25.4 MPa for 160,000 h were investigated. The results show that the hardness and the tensile strength did not decrease; however, the impact toughness was remarkably reduced. The TiC precipitate shows excellent thermostability; for example, it hardly grew up, and no big M23C6 carbides were found. However, large Fe, Cr-rich σ-phase was doomed to precipitate along grain boundary, which should be responsible for the reduced toughness. The growth of σ-phase was observed to have an interaction with the preexisted carbides.

powder thus milled was contaminated by Fe, Ni and Cr, the actual factor causing the improved sintered density To eliminate the contamination of activator elements, was not clear. Moreover, few comparative studies have such as Fe and Ni, W-15Cu compacts were prepared reported on the eVects of contamination on the electrical from mechanically alloyed powders using an attritor properties and the thermal properties. The objective of this with a zirconia tank, balls and agitator arms. Coarse work was thus to use grinding balls, agitating arms and tungsten and copper powders, 9•9 mm and 13•3 mm, a grinding tank, all made of zirconia, to produce W-Cu respectively, were milled to 1•26 mm composite powders composite powders that are free of contamination of Fe, after 145 h of milling. The milled powder contained Ni and Cr. The resulting properties are compared with little free copper and was highly combustible in air.those of materials produced using stainless steel grinding After sintering, the 50 vol.-% dense green compacts balls. attained a density of 15•8 g cm-3 or 96•2%. The microstructure consists of uniformly interdispersed tungsten and copper. When stainless steel grinding balls were EXPERIMENTAL PROCEDURE used, the powder was heavily contaminated withThe morphology and the characteristics of the raw tungsten Fe and Ni. The contamination improved the density and copper powders are shown in Fig. 1 and Table 1, slightly, but the grain size and the electrical resistivity respectively. To increase the neness of the starting powder, increased signi cantly as well. The sintering behaviours an attritor was used to further grind the powder. The of the two composite powders were similar. Most chamber size of the attritor was 750 000 mm3 and the grinddensi cation occurred during heating before reaching ing balls were 3 mm in diameter. The grinding barrel, the melting point of copper.PM1044 grinding balls and the agitating arms were all made of zirconia. The grinding shaft was made of stainless steel but Dr Hwang

Highly-aligned flake graphite (FG) reinforced Cu matrix composites with high thermal conductivity and adaptive coefficient of thermal expansion were successfully prepared via the collaborative process of tape-casting and hot-pressing sintering. To overcome the problem of fragile interface, Zr-Cu alloy powder was introduced instead of pure Zr powder to enhance the interfacial strength, ascribed to the physical-chemical bonding at the Cu-FG interface. The results indicate that the synthetic ZrC as interfacial phase affects the properties of FG/Cu composites. The thermal conductivity reaches the maximum value of 608.7 W/m∙K (52% higher than pure Cu) with 0.5 wt % Zr. Surprisingly, the negative coefficient of thermal expansion (CTE) in the Z direction is acquired from −7.61 × 10−6 to −1.1 × 10−6/K with 0 to 2 wt % Zr due to the physical mechanism of strain-engineering of the thermal expansion. Moreover, the CTE in X-Y plane with Zr addition is 8~10 × 10−6/K, meeting the requirements of semiconductor materials. Furthermore, the bending strength of the FG/Cu-2 wt % Zr composite is 42% higher than the FG/Cu composite. Combining excellent thermal conductivity with ultralow thermal expansion make the FG/Cu-Zr composites be a highly promising candidate in the electronic packaging field.