Chemical ordering in Ni-Mn-Ga Heusler alloys
- Univ. of Maryland, College Park, MD (United States). Dept. of Materials and Nuclear Engineering
- National Inst. of Standards and Technology, Gaithersburg, MD (United States). NIST Center for Neutron Research
A good deal is known about the martensitic and ferromagnetic phase transitions in Ni{sub 2}MnGa. To understand the coupling of the phase transitions, it is necessary to characterize the chemical order-disorder transition, since the physical properties of the ordered and disordered phases are different. However, little experimental data exists regarding the A2{r_arrow}B2{prime}{r_arrow}L2{sub 1} chemical ordering sequence in Ni{sub 50}Mn{sub x}Ga{sub 50{minus}x} during cooling. Hence, the purpose of this investigation is to characterize the chemical ordering transition in Ni{sub 50}Mn{sub x}Ga{sub 50{minus}x} over a composition range of 15 {le} x {le} 35 by performing in situ neutron diffraction measurements. Experimental results are compared to the predictions of a model based on the Bragg-Williams-Gorski (BWG) approximation. Long range order parameter {eta} vs. temperature T and a quasibinary temperature-composition diagram are considered. The T-c diagram, with a composition range of 15 {le} x {le} 35, is presented to describe the A2{r_arrow}B2{prime}{r_arrow}L2{sub 1} ordering transition and the alloy melting transition. Phase transitions in selected Ni{sub 50}Mn{sub x}Ga{sub 50{minus}x} alloys are verified using differential thermal analysis (DTA).
- OSTI ID:
- 361730
- Journal Information:
- Scripta Materialia, Journal Name: Scripta Materialia Journal Issue: 10 Vol. 40; ISSN 1359-6462; ISSN SCMAF7
- Country of Publication:
- United States
- Language:
- English
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