The influence of powder characteristics on the sintering behaviour and impurity content of spark-plasma-sintered zirconium

Abstract

At present, most zirconium products as well as its alloys are obtained by foundry methods. New technologies used to manufacture high-quality components, such as direct laser sintering or microwave sintering, require spherical powders of a narrow particle size distribution, as this affects the packing density and sintering mechanism. The powders also have to be chemically pure, as impurities such as H, O, C, N and S cause brittleness and problems with corrosion. Commercially procured, high purity zirconium powders from three different sources were characterised for their particle size and phase composition. Dilatometer studies have shown the effect of powder contamination at the beginning and at end of the sintering process. For powders of 99.9% purity, the start of sintering takes place at a temperature of about 700 °C. For powders of 98.8% purity, the sintering starts at 500 °C. In the studies presented in this paper, the SPS/FAST (Spark Plasma Sintering/Field Assisted Sintering Technique) method was chosen for densification processes. Sintered materials were characterised for their density using the Archimedes principle, relative density and Vickers hardness. A determination of the oxygen, nitrogen and hydrogen content in zirconium powders and sintered samples was carried out. The studies confirmed that SPS of zirconium powders in an argon atmosphere slightly decreases the content of oxygen and nitrogen. At 1000 °C, at pressure of 35 MPa, in argon, there is no decomposition of zirconium hydrides in sintered materials.