Compression tests at temperatures down to 4.2K, and transmission electron microscopy, were used to investigate the twinning of the C15 HfV2-Nb Laves phase. Two-phase, C15 plus body-centered cubic, alloys were chosen. Transmission electron microscopy revealed that substantial mechanical twinning took place in the C15 Laves phase matrix at room temperature and 77K. A deep minimum in the flow stress, with a drop of nearly 500MPa, appeared at about 77K in C15/body-centered cubic samples. Since no such anomaly was seen in the body-centered cubic phase, it was concluded that it could be attributed to mechanical twinning in the C15 Laves phase. Twin bands observed in the C15 matrix of deformed samples at 298 and 77K could be classified into 3 categories according to their thickness: coarse twin bands (10nm to several hundred nm thick), fine twin bands (3 to 10nm-thick) and ultra-fine twin bands (average thickness 1.5nm). A high density of ultra-

fine twin bands was the characteristic feature of twinning in the C15 matrix. They belonged to the <112>(111) twinning system and commonly intersected one another.

Deformation Twinning in a HfV2-Nb Based Laves Phase Alloy. Y.Kimura, D.E.Luzzi, D.P.Pope: Materials Science and Engineering A, 2002,329-331, 241-8

 Table 8

 Diffusivity of Fe in Zr41Be20Ti16.5Cu12.5Ni10