Effect of ζ‐Ta4C3−xon the mechanical properties of tantalum carbide at elevated temperatures

Abstract

AbstractTantalum carbide ceramics containing at least 75‐wt% ζ‐Ta4C3−xwere synthesized and densified to ∼99% of the theoretical density. Flexural strength in four‐point bending was measured from room temperature up to 1600°C, achieving strengths of 710 ± 36.5 MPa at room temperature and decreasing to 180 ± 19.7 MPa at 1600°C. Fracture toughness was measured via the chevron notch method from room temperature up to 1600°C, with a toughness of 10.2 ± 0.4 MPa m1/2at room temperature and decreasing to 4.7 ± 0.1 MPa m1/2at 1600°C. At 1600°C, ductile behavior was observed during testing, and mixed mode fracture was observed on all fracture surfaces. Vickers indentations were used at room temperature to damage the surface of specimens and shed some light on damage mechanisms in the material. Kinking and delamination were observed around the indentations. At elevated temperatures, these deformation mechanisms may activate more often, causing a decrease in strength and resulting in ductility between 1400 and 1600°C. The Griffith analysis was also used to identify critical flaws. The long axis of high aspect ratio grains appears to be the critical flaw from room temperature up to 1400°C, prior to any ductile behavior. Overall, the nanolaminate microstructures, and the kinking and delamination deformation mechanisms that result from it, are reminiscent of MAX phase and kinking nonlinear elastic materials.