Spark plasma sintering of novel ZrB2-SiC-TiSi2 composites with better mechanical properties

We report here the development of ultrafine grained ZrB2-SiC composites using TiSi2 as the sintering aid and spark plasma sintering (SPS) as the processing technique. It was observed that the presence of TiSi2 improved the sinterability of the composites, such that near theoretical densification (99.9%) could be achieved for ZrB2-18 wt.% SiC-5 wt.% TiSi2 composites after SPS at 1600 degrees C for 10 min at 50 MPa. Use of innovative multi stage sintering (MSS) route, which involved holding the samples at lower (intermediate) temperatures for some time before holding at the final temperature, while keeping the net holding time to 10 min, allowed attainment of full densification of ZrB2-18 wt.% SiC-2.5 wt.% TiSi2 at a still lower final temperature of 1500 degrees C at 30 MPa. TEM observations, which revealed the presence of anisotropic ZrB2 grains with faceted grain boundaries and TiSi2 at the intergranular regions, suggested the occurrence of liquid phase sintering in the presence of TiSi2. No additional phase was detected in XRD as well as TEM, which confirmed the absence of any sintering reaction. The as developed composites possessed an excellent combination of Vickers hardness and indentation toughness, both of which increased with increase in TiSi2 content, such that the ZrBi2-18 wt.% SiC-5 wt.% TiSi2 (SPS processed at 1600 degrees C) possessed hardness of similar to 20 GPa and indentation toughness of similar to 5 MPa m(1/2). The use of MSS SPS at 1500 degrees C for ZrBi2-18 wt.% SiC-2.5 wt.% TiSi2 composite resulted in improvement in hardness of up to similar to 27 GPa and attainment of high flexural strength of similar to 455 MPa. (C) 2011 Elsevier B.V. All rights reserved.

Hot-pressed TiB2-10 wt.% TiSi2 ceramic with extremely good thermal transport properties at elevated temperatures (up to 1273 K)

This contribution reports and analyses the high thermal transport property of hot-pressed TiB2-10 wt.% TiSi2 ceramics. Depending on the test temperature, the thermal conductivity values of the TiB2 composite (which range from 89 to 122W m(-1) K-1) are determined to be 18-25% higher than that of monolithic TiB2. The thermal transport properties are analyzed in terms of electronic and phonon contributions. The electronic contribution is the major component of the thermal conductivity of TiB2 and comparable contributions from both electronic and phonon components are observed for the TiB2-TiSi2 composite. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A TEM study on TiB2-20%MoSi2 composite: Microstructure development and densification mechanism

We report the results of transmission electron microscopy (TEM) study, carried out on a hot-pressed TiB2-20 wt.%MoSi2 composite. One of the important microstructural observations includes the detection of crystalline TiSi2 at triple grain junctions. The densification mechanism is discussed, based on experimental observations and thermodynamic analysis

Reactive diffusion in the Ti-Si system and the significance of the parabolic growth constant

Solid diffusion couple experiments are conducted to analyse the growth mechanism of the phases and the diffusion mechanism of the components in the Ti-Si system. The calculation of the parabolic growth constants and the integrated diffusion coefficients substantiates that the analysis is intrinsically prone to erroneous conclusions if it is based on just the parabolic growth constants determined for a multiphase interdiffusion zone. The location of the marker plane is detected based on the uniform grain morphology in the TiSi2 phase, which indicates that this phase grows mainly because of Si diffusion. The growth mechanism of the phases and morphological evolution in the interdiffusion zone are explained with the help of imaginary diffusion couples. The activation enthalpies for the integrated diffusion coefficient of TiSi2 and the Si tracer diffusion are calculated as 190 +/- 9 and 197 +/- 8 kJ/mol, respectively. The crystal structure, details on the nearest neighbours of the components, and their relative mobilities indicate that the vacancies are mainly present on the Si sublattice.