Preparation of WC-SiC Whisker Composites by Hot Pressing and Their Mechanical Properties

Abstract

Composites of WC and SiC whisker (0-30 vol% SiC) were prepared at 1550 to 1800 C by using a resistance-heated hot pressing technique called spark plasma sintering. The composites obtained were examined for reaction products and microstructure, and were characterized for mechanical properties. The addition of small amounts of SiC induced the marked grain growth of WC, and drove the densification of WC. Above 10 vol% SiC, dispersed SiC phases impeded the grain growth of WC. Increasing sintering temperature made SiC whiskers thick and lowered the aspect ratio of whiskers. The hardness of composites decreased with increasing average grain size of WC. The Young's modulus of dense composites was decreased with the SiC content. The addition of 3 to 5 vol % SiC greatly increased the fracture toughness of WC.

Effects of Cr<SUB>3</SUB>C<SUB>2</SUB> and V<SUB>8</SUB>C<SUB>7</SUB> on the Microstructure and Mechanical Properties of WC-SiC Whisker Ceramics

“…Sintering of WC required a temperature of 1800 C to obtain a fully dense sintered body with a bulk density of 15.70 Mg m À3 , 4) which agrees with the previously determined X-ray density of 15.669 Mg m À3 . 18) However, WC-5 vol% SiC W (base ceramic) could be densely hot pressed at 1650 C. In the sintered base ceramic and Cr 3 C 2 -added ceramics, XRD analyses showed some evidence of a W 5 Si 3 phase that was not observed in the V 8 C 7 -or Cr 3 C 2 and V 8 C 7 -added ceramics.…”

“…The Young's modulus for both the 5 µm separate V 8 C 7 addition and the simultaneous Cr 3 C 2 and V 8 C 7 addition decreased with GGI content. The calculated Young's modulus, determined by the volumetric proportion of each component using 702 GPa for WC, 4) 440 GPa for hot-pressed SiC, 24) 370 GPa for Cr 3 C 2 25) and 430 GPa for V 8 C 7 , 25) remained nearly the same due to the relatively small amounts of GGI. The V 8 C 7 addition resulted in the largest decrease in Young's modulus.…”

“…1. The relative density was determined from the experimental bulk density of WC (15.70 MgÁm À3 ) 4) and the X-ray densities of -SiC (3.216 MgÁm À3 ), 19) Cr 3 C 2 (6.66 MgÁm À3 ) 20) and V 8 C 7 (5.641 MgÁm À3 ) 21) assuming that each component was insoluble in the others. The relative density was slightly over 100% in some compositions, which may have been due to the use of X-ray densities in calculations and/or the dissolution of WC in Cr 3 C 2 and V 8 C 7 .…”

“…3) Recently, new binderless carbides were developed consisting of WC-SiC whisker (SiC W ) ceramics without any metallic binders. 4) The WC-SiC W ceramics, which were manufactured by resistance-heated hot pressing, called spark plasma sintering, had relatively high fracture toughness values above 7 MPa m 1=2 and exhibited better sinterability than pure WC. The highest degree of sinterability and highest fracture toughness were obtained at 3 to 5 vol% SiC W .…”

Effects of Carbon Addition on Microstructures and Mechanical Properties of Binderless Tungsten Carbide

“…Thus, most of W 2 C found in the sintered WC must have been caused by surface oxidation of the fine WC starting powder and the decarburization reaction during sintering, as described previously. 20) Zhao et al indicated that the W 2 C phase formed during sintering due to the existence of WO 3 layers on WC particles by the following reactions:…”