Effect of Post-Annealing Process on Nb-Hf Alloy Produced by Spark Plasma Sintering.

In this study, the effect of annealing treatment on microstructure and mechanical properties of the Nb-10Hf-1Ti wt.% produced by Spark Plasma Sintering (SPS) was investigated. Scanning electron microscope (SEM), optical microscopy, X-ray diffraction analysis, hardness, and uniaxial tension test were used to characterize the samples. Annealing treatment was carried out in a vacuum of 10^-3 Pa at 1150 °C for 1, 3, 5, and 7 hours and in an argon atmosphere at 1350 °C for 5 hours. Internal oxidation and subsequent hafnium oxide formation causes the hardening of the C103 alloy and drastically increases the hardness and tensile strength. However, HfO₂ particles formed at the grain boundary cause brittleness and cleavage fracture of samples. Volume fraction, particle size, and mean inter-particle spacing of oxides significantly change by annealing which affects the mechanical properties. The SPSed sample at 1500 °C is softened by annealing at 1150 C for 5 hours and its hardness and yield strength are reduced from 303 to 230 Hv and 538 to 490 MPa respectively. While annealing at 1350 °C for 5 hours increases hardness and yield strength increases to 343 Hv and 581 MPa respectively. [ABSTRACT FROM AUTHOR]