Powder Processing Effects on the Rapid Low‐Temperature Densification of ZrB2–SiC Ultra‐High Temperature Ceramic Composites Using Spark Plasma Sintering

Abstract

Investigating the powder processing effects on a ZrB2–25 vol% SiC ceramic composite densified using spark plasma sintering (SPS) allows for identification of densification mechanisms and enables a reduction in sintering temperature to a minimum of 1650°C. Attrition milling (AM) and ball milling (BM) were investigated as processing methods to produce a fine and coarse powder densified using SPS with or without a tube furnace preheat treatment. Ceramics formed from AM and BM powders contain 1.66 wt% oxygen contamination, primarily ZrO2 and SiO2, and 0.35 wt% oxygen contamination as SiO2, respectively. Heat treatment slightly reduces oxygen contamination but has significant impacts on the densification mechanisms. Without heat treatment, powder coarsening dominates the initial sintering process in the SPS inhibiting densification until ~1350°C. After heat treatment, sintering and densification is enabled at low temperature, 1000°C–1100°C. The densification of ZrB2–SiC composites can be broken into a two‐step process with phase 1 as the sintering step based on powder surface area reduction and phase 2 as a forging step where high‐temperature creep and pressure eliminate porosity after the primary grains have formed. A time–temperature‐density plot illustrates the change in densification mechanism used to fully densify ZrB2–SiC composites in SPS.