Crystal Preparation of Ni-Mn-Ga Alloys.
Abstract
Partial evaluation of the liquidus diagram of Ni-Mn-Ga by thermal analysis and microstructural evaluation has determined that the primary solidification surface for the Heusler alloy phase exists over a wide range of compositions. The primary solidification surface falls modestly in temperature with either increasing Mn or Ga concentrations. The composition, Ni50Mn25Ga25, melts incongruently over a temperature range of approximately 18 deg C. The small temperature range of solidification allows for the conditions suitable for crystal growth to be easily established and maintained throughout the crystal growth process for a wide variety of compositions. In general, the Mn composition increases as the solid grows with an associated decrease in Ni composition. Analysis of the composition profiles indicated that the compositional changes, and hence, the solidification process, is dominated by convective mixing in the liquid during growth and evaporative losses of Mn. Finally, preliminary experiments were conducted that demonstrated the feasibility of using the Czochralski technique for the preparation of Ni-Mn-Ga alloys. Additional process optimization is required to gain confidence in applying the Czochralski method to the routine preparation of Ni50Mn25Ga25 and its alloys.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 31, 1999
- Accession Number
- ADA373527
Entities
People
- Thomas A. Lograsso
Organizations
- Iowa State University