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 degrees C for 1, 3, 5, and 7 hours and in an argon atmosphere at 1350 degrees 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 degrees C is softened by annealing at 1150 degrees 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 degrees C for 5 hours increases hardness and yield strength increases to 343 Hv and 581 MPa respectively.