Publication Date

8-17-2018

Department

Ames Laboratory

Campus Units

Ames Laboratory

OSTI ID+

1483366

Report Number

IS-J 9801

DOI

10.1016/j.tca.2018.08.011

Journal Title

Thermochimica Acta

Volume Number

668

First Page

142

Last Page

151

Abstract

Hf-Ni is an important binary system for high temperature alloys and shape memory alloys which has been investigated several times in the literature but often using samples of Hf contaminated by Zr. The thermodynamics of this system are remodeled in this work based on first-principles calculations and additional experiments using Hf with relatively low Zr contamination (0.25 wt. %). Diffusion couples in the Ni-rich portion of the Hf-Ni system heat treated at 1173, 1273 and 1373 K are used to measure phase stability and Hf solubility in the fcc phase. The solubility observed in fcc Ni from Ni/Ni50Hf50 (at.%) diffusion couples is larger than that observed in previous experiments. These results are the only source fit to during modeling of the fcc solubility to mitigate effects from Zr contamination. Data in the literature suggests that the high temperature crystal structure of the B33 NiHf phase is, in fact, the B2 structure. High temperature synchrotron measurements provide confirmation of this crystal structure. Modeling of the B2 phase was aided by first-principles calculations using special quasi-random structures (SQS). The present CALPHAD model will prove useful when designing shape memory alloys containing Hf and when modeling the Hf activity in Ni-base high temperature alloys.

DOE Contract Number(s)

AC02-07CH11358

Language

en

Department of Energy Subject Categories

36 MATERIALS SCIENCE

Publisher

Iowa State University Digital Repository, Ames IA (United States)

Available for download on Saturday, August 17, 2019

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