Examination of Multiphase (Zr,Ti)(V,Cr,Mn,Ni)2 Ni-MH Electrode Alloys. Part 2: Solid-State Transformation of the Interdendritic B2 Phase Phase

Published

August 15, 2010

Author(s)

Leonid A. Bendersky, Ke Wang, William J. Boettinger, Dale E. Newbury, K. Young, B. Chao

Abstract

Multi-component Zr-Ti-Ni-TM (TM=V, Cr, Mn and Co) cast alloys intended for use as negative electrodes in Ni metal hydride batteries were studied to determine the solidification microstructure and solidification path in the Part I of this paper. Part II of the paper examines by transmission electron microscopy the complex internal structure of the interdendritic regions (grains) found in Part I. The phases in these regions formed by solid-state transformation and are thought to play an important role in the improvement of electrochemical charge/discharge characteristics of the overall alloy composition. By studying one alloy from Part I, Zr20Ti24.1V1.67Cr0.65Mn1.6Co3.4Ni47.8Al0.4Sn0.1, it is shown that the interdendritic grains initially solidify as either a bcc or B2 phase close to the composition (Ti,Zr)44(Ni,TM)56). The phase then undergoes transformation to Ni10Zr7-type, Ni11Zr9-type and martensitic phases. The transformations obey crystallographic orientation relationships between the high- temperature parent bcc phase and Zr-the Ni-type intermetallics, and consequently lead to a complex multivariant structure of faceted domains. The orientation relationship for the orthorhombic Ni10Zr7-type is [011]Ni10Zr7//[001]B2; (100)Ni10Zr7//(100)B2; there is also a secondary relationship - [021]Ni10Zr7//[001]B2; (100)Ni10Zr7//(011)B2. The orientation relationship for the tetragonal Ni11Zr9-type is [001]Ni11Zr9//[001]B2; (130)Ni10Zr7//(100)B2, which is responsible for 12 orientational variants. Although the observed Ni10Zr7-type and Ni11Zr9-type phases are multicomponent structures, binary Ni- Zr and ternary Ni-Zr-Ti phase diagrams could be used to rationalize the formation of the observed domain structure.

Citation

Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science

Pub Type

Journals

Keywords

Laves phase, Ni-Zr, Hydrogen storage, TEM

Citation

Bendersky, L. , Wang, K. , Boettinger, W. , Newbury, D. , Young, K. and Chao, B. (2010), Examination of Multiphase (Zr,Ti)(V,Cr,Mn,Ni)2 Ni-MH Electrode Alloys. Part 2: Solid-State Transformation of the Interdendritic B2 Phase Phase, Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science (Accessed October 8, 2024)