Application of High-Pressure Torsion to WC–Co Ceramic-Based Composites for Improvement of Consolidation, Microstructure and Hardness

Abstract

This study shows that ultrafine-grained composites of WC11 mass% Co are successfully consolidated by high-pressure torsion (HPT) followed by sintering at lower sintering temperatures or shorter sintering time than hot isostatic pressing (HIP) and compression and sintering. For the samples processed by HPT and successive sintering, the grain size (³700 nm) is smaller and the hardness (³1700 Hv) is higher when compared to those consolidated by compression and sintering and HIP. A heterogeneous microstructure consisting of nanograins of Co and WC and coarse grains of WC ceramics with high dislocation density, 2 © 10 16 m ¹2, is formed during HPT, but the average grain size is slightly increased by subsequent sintering. A W 3 Co 3 C carbide forms by sintering, while its fraction increases with increasing the shear strain or with increasing the sintering temperature.

Review on Recent Advancements in Severe Plastic Deformation of Oxides by High‐Pressure Torsion (HPT)

“…After compression, the lower HPT anvil is rotated against the upper anvil under pressure and large shear strain is induced in the material ( γ = 2 πrN / h ; γ : shear strain; r : radial distance from disc center, N : number of HPT turns, h : thickness of disc). The high pressure in this method significantly suppresses the failure of material and provides a unique condition to process hard and/or brittle materials such as high‐melting‐temperature metals, intermetallics, glasses, ceramics, silicon, carbon polymorphs, and polymers …”

Plastic Deformation of BaTiO3Ceramics by High-pressure Torsion and Changes in Phase Transformations, Optical and Dielectric Properties

“…These results are consistent with the earlier reports on the improvement of consolidation of ceramics by HPT processing. [32,33] Figure 5(c) shows that the sintered samples exhibit similar dielectric loss, especially at temperatures in the range of 70-140°C. Therefore, the increase in dielectric constant is not due to the effect of dielectric loss.…”

“…[32,33] Earlier papers reported that the optimum grain size to achieve high dielectric constants was in the range of 700-1,300 nm. [2,3,5] However, this present work suggests that the optimum grain size can shift even to the nanometer level after severe straining.…”

“…However, some researchers reported that the high-pressure torsion (HPT) method, which is mainly used for metal processing, [25][26][27][28] is an effective technique for introducing plastic strain in ceramics. [29][30][31][32][33] In this work, intense plastic strain is imposed on BTO ceramic powders using the HPT method and the evolution of microstructure, phase transformations, PL and dielectric properties are investigated.…”

High-pressure torsion of thick Cu and Al–Mg–Sc ring samples

“…It is applicable to hard and less ductile materials [5,6] even to intermetallics [7][8][9], ceramics [10][11][12][13], and semiconductors [14][15][16][17]. The samples for the HPT are used in the form of disk or ring and [18,19], because the shear strain is introduced in proportion to the distance from the rotation center [1], the ring sample is preferable to achieve a homogeneous structure throughout the sample [18,19].…”