Premium
Phase Constitution and Mechanical Properties of Carbides in the Ta–C System
Author(s) -
Hackett Kenneth,
Verhoef Shane,
Cutler Raymond A.,
Shetty Dinesh K.
Publication year - 2009
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2009.03201.x
Subject(s) - materials science , flexural strength , carbide , fracture toughness , vickers hardness test , hot pressing , phase (matter) , cleavage (geology) , tantalum , composite material , analytical chemistry (journal) , metallurgy , crystallography , microstructure , fracture (geology) , chemistry , organic chemistry , chromatography
Carbides in the Ta–C system were prepared by hot‐pressing mixed powders of TaC and Ta in C/Ta atomic ratios of 1.0, 0.9, 0.8, 0.7, and 0.6 at 1800°C for 2 h. The compositions, 1.0, 0.9, and 0.8, produced single face‐centered‐cubic (fcc) TaC y phase with C/Ta ratios essentially the same as the starting compositions and densities exceeding 96.5% of theoretical. Grain size decreased with increasing carbon deficiency with a corresponding increase in Vickers hardness from 13.5 to 20 GPa. The flexural strength, however, decreased from 650 to 500 MPa due to a decrease in fracture toughness from 5.3 to 3.8 MPa√m. The compositions 0.7 and 0.6 produced two carbide phases, fcc TaC y and rhombohedral ζ‐Ta 4 C 3− x phase in the 0.7 composition and ζ‐Ta 4 C 3− x and hexagonal‐close‐packed (hcp) α‐Ta 2 C phase in the 0.6 composition. Fracture toughness measured by single‐edge‐precracked‐beam technique was exceptionally high (12.7±0.7 MPa√m) for the 0.6 composition with a high weight percent of the ζ‐Ta 4 C 3− x phase (∼83 wt%). The fracture surface was highly faceted with multiple cleavage crack planes and steps.