Page 25 - Annual Report_21-22

Fig. 3: Compression (left) and Bulk hardness measurements (right) of WHAs.

Structural stability and thermal expansion of TiTaNbMoZr refractory high entropy alloy

Refractory High Entropy Alloys (RHEAs) exhibit excellent B-major phase is observed until 1273 K, whereas the
room temperature as well as high-temperature mechanical B-minor phase is present up to 1173 K. Above 1173 K, the
properties, structural and microstructural stability. For formation of B′ phase is observed. As cast microstructure
these reasons, RHEAs are being considered promising is shown in (Fig. 5), which shows dendritic (DR, enriched
candidates for high-temperature structural applications with Ta, Nb, Mo) and interdendritic (IDR, enriched with
beyond Ni-based superalloys. Ti and Zr) morphology. The current work demonstrates
the profound structural stability and thermal stability of
In the present work, a near-equiatomic TiTaNbMoZr TiTaNbMoZr RHEA until 1173 K and 1000 K, respectively.
refractory high entropy alloy (RHEA) was prepared by We find that a large concentration of vacancies forms above
vacuum arc melting. It consists of two BCC solid solution 1000 K (Fig. 6). We have derived empirical expressions for
phases (predominant and minor phases are named as the lattice and dilatometric (bulk) coefficient of thermal
B-major and B- minor, respectively) at room temperature expansion (CTE) as a function of temperature. These
(Fig. 4). Structural stability and thermal expansion were derived expressions can be helpful in the design of high-
investigated using in-situ synchrotron XRD (P-07 beamline, temperature structural components for engineering
PETRA III of DESY, Hamburg, Germany) and dilatometry. applications.

Fig. 4: SXRD patterns of as-cast TiTaNbMoZr RHEA during heating from RT to 1273 K.

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