Defects in high entropy alloy HfNbTaTiZr prepared by spark plasma sintering

High entropy alloys exhibit various combinations of interesting physical properties due to the formation of solid solution stabilized by high configurational entropy. High entropy alloy HfNbTaTiZr exhibits single phase solid solution with BCC structure when prepared by arc melting [1]. Grain refinement achieved in cold rolled samples after recrystallization remarkably enhanced ductility of this alloy [2]. Mechanical alloying by milling and subsequent sintering is a frequent production way of preparing fine grained alloys from chemical elements with high melting temperature. In addition, spark plasma sintering (SPS) method with applied pressure serves as a unique tool of powder metallurgy thanks to fast heating rates and low time of exposition to elevated temperatures. Therefore, the deformation energy introduced during mechanical alloying may be effectively consumed during short sintering process and presents the additional parameter for grain refinement. The present work presents characterization of HfNbTaTiZr alloy prepared by SPS.
Microstructure of samples prepared by SPS was compared with as cast ingots. The samples were characterized by X-ray diffraction and scanning electron microscopy. Positron annihilation spectroscopy was employed for characterization of defects introduced by SPS and their thermal stability.
[1] O.N. Senkov, J.M. Scott, S.V. Senkova. D.B. Miracle, C.F. Woodward: Journal of Alloys and Compounds 509, 6043-6048 (2011).
[2] O.N. Senkov, S.L. Semiatin; Journal of Alloys and Compounds 649, 1110-1123 (2015).