MICROSTRUCTURES OF HYDROGEN ABSORBING ZR0 .5TI0.5MNV MULTIPHASE ALLOYS

AB(2) type Laves phase and BCC solid solution have been investigated a s the next generation hydrogen absorbing alloys with high capacity. We have proposed a new concept of alloy design named ''Laves-phase relat ed BCC solid solution'' in the previous work. The observations of micr ostructure show that Zr0.5Ti0.5VMn consisted of three phases; matrix C 14, gray colony BCC and black particle Zr in the previous report. In t his work we investigated each phase in detail by the combination of tr ansmission electron microscopy and X-ray Rietveld analysis. The compos ition of the matrix Laves phase is found to be Zr0.5Ti0.4V1.1Mn0.9 by TEM-EDX. The bright field image of this region is homogeneous and the electron diffraction pattern shows only the C14 structure. We consider that this phase is the Laves phase in which the A site is occupied by Zr and Ti and the B site is occupied by Mn and V. This atomic ratio o f matrix is a stable composition of the phase which is contained in Zr -Ti-Mn-V alloys and is made by are melt casting process. The gray colo ny BCC phase in Zr0.5Ti0.5MnV decomposes into two nano scale phases th at are Mn solute Ti-rich and V-rich phases. The lattice strain of two coherent phases show the satellite spots in electron diffraction and a symmetric peak broadening in X-ray diffraction patterns. Black particl e Zr phase is found to be alpha-ZrO2 by analysis of the electron diffr action. This oxide particle consists of two regions which have the sam e zone axis.