Kazuhiro Hongo

The effect of second phase on the creep deformation of 6061Al matrix composites.

Abstract Creep behaviour of two types of 6061Al matrix composites, which were reinforced with 10 and 20 vol.% of alumina particles or 11 and 18 vol.% of alumina short fibers, have been investigated at temperatures ranging from 573 to 773 K. Creep curves, stress dependences of the minimum creep rate and the microstructure after creep deformation were examined. A quantitative analysis of creep curves was also carried out by the θ-projection method. The difference in the volume fraction of the reinforcing second phases does not affect the creep strength in both types of composites. Creep strength of the fiber reinforced composites is higher than that of the particle reinforced ones at 673 and 773 K. Parameters determined by θ-projection method are able to describe the creep curves of the composites quantitatively. It has been shown that the precipitation of the solute atoms influences the creep behaviour at 573 K in both composites. The existence of the soft regions around the second phase is suggested in the particle reinforced composite crept under low stress at 773 K.

Collaborative sintering of the amorphous alloy and ceramic powders for nanocrystalline composite materials

This article reports some process controls to optimize the collaborative sintering of the amorphous powder mixture as blended by mechanical alloying for the synthesis of nanocrystalline composite materials. The pulse electric current pressure sintering combined with high pressure and high heating rate techniques can be used to obtain the fully dense nanocrystalline Ti 50 Al 50 alloy having a spatial dispersion of finely divided (Zr02-3mol%Y203)55(Al 2 O 3 ) 45 particle with the crystallite size of 21 nm at the relatively low temperature of 1423 K. The sub-μm sized ceramic particle dispersed Ti 50 Al 50 composite shows the yielding event in compression; its proof stress increases up to approximately 3 GPa with an increase up to 0.2 in particle volume fraction of nanocrystalline (Zr02-3mol%Y203)55(Al 2 O 3 )4s. The instrumented spark pressure sintering with temperature slope control using specially designed graphite dies makes it possible to provide an overall powder densification and superplastic compressive forming along the gradient composition consisting of amorphous and/or nanocrystalline Ti 52 Al 48 and (Zr02-3mol%Y 2 O 3 ) 80 (Al 2 O 3 ) 20 phases.