Reaction Processing of Ultra‐High Temperature W/Ta₂C‐Based Cermets

Abstract

A reactive processing method was used to produce dense (499.5% relative density) W/Ta 2 C/Ta 2 WO 8 cermets from Ta 2 O 5 , WC, TaC, and phenolic resin. The powder compacts were reacted under vacuum at 14501C and then densified at 18501C. The microstructure of the cermets was examined using scanning electron microscopy and found to contain fine grains on the order of 1-3 lm in diameter. X-ray diffraction, transmission electron microscopy, and parallel energy electron loss spectroscopy were used to identify the composition and structure of the phases in the composites. The composites were found to contain approximately 47.5 wt% W, 47.3 wt% Ta 2 C, and 5.2 wt% Ta 2 WO 8 . Crack-free and dense W/Ta 2 C-based cermets were prepared by an in situ reactive sintering process without the application of pressure during densification.

Mechanical properties of reactively processed W/Ta2C-based composites

“…1) revealed a predominantly intergranular fracture pattern, which is to be expected based on the clean interface observed between the grains. 24 Other researchers have similarly reported a correlation between the clean interface between the ceramic particles and tungsten and a resultant intergranular fracture mode. 22 In W/ZrC and W/TiC cermets containing 30 vol% ceramic phase, the fracture surface was found to be primarily intergranular with some transgranular rupture in the tungsten grains.…”

“…24 The tungsten was found to contain 31.2 at% Ta in solid solution, while the Ta 2 C was found to contain 13.4 at% W in solid solution. 24 The measured bulk density of the W/Ta 2 C cermets was thus calculated to be 99.5% of its theoretical density after sintering at 1850 • C.…”

“…The powder processing, sintering process, and chemistry of the reactions have been described in more detail previously. 24 The samples produced from the reactive processing were nominally 28 mm by 18 mm by 5 mm.…”

“…Details regarding phase identification and microstructure characterization were reported in a previous paper. 24 Specimens for mechanical testing were sectioned from the as-processed billets by surface grinding and cutting. Twenty bars were fabricated (ASTM C1162 type "A" bars with nominal dimensions of 1.5 mm by 2.0 mm by 25 mm) for mechanical testing.…”

Chemically produced tungsten–praseodymium oxide composite sintered by spark plasma sintering

“…Second-phase particles (La 2 O 3 , Y 2 O 3 , TiC, HfC, Ta 2 C, TiN, etc.) [14][15][16] dispersoids can play a major role in mitigating these problems. Rare-earth oxide particles are particularly effective, because they can gather solutes owing to strong rare-earth-oxygen interactions.…”