Microstructural evolution and sintering kinetics during spark plasma sintering of pure tantalum powder

Abstract

Spark plasma sintering (SPS) technology can significantly inhibit grain coarsening due to its characteristics of rapid sintering and densification, and obtain a material with high density and uniform microstructure. We completed the SPS sintering of tantalum powder, and characterized the microstructure and mechanical properties of the samples at different sintering temperatures. The results show that during the pure tantalum sintering process, the rapid densification temperature range is 800 °C–1300 °C, and the maximum shrinkage rate of the sample is 1100 °C. A creep model was applied to determine the densification mechanisms involved in the densification stage, which can be elucidated by evaluating the stress exponent (n) and the apparent activation energy (Qd) from the densification rate law. It shows that a series of interfacial reactions and grain boundary diffusions govern the densification process at low effective compaction stresses (n = 1.6, Qd = 107.01 kJ/mol), while dislocation climbing operate at higher effective compaction stresses (n = 3.1 and n = 4.1), which is confirmed by TEM. When the sintering temperature of tantalum powder increased from 1500 °C to 1700 °C, the density and grain size of the sample increase gradually, the tensile strength and flexural strength also increase. The surface hardness of the sample increases gradually. Moreover, surface hardness is much higher than core hardness. The fracture mode of the specimen changes from brittle fracture to ductile fracture. This study has enabled the selection of high quality tantalum alloy sintering routes and optimization of the sintering process.