The present work is focused on investigating the effect of SiC addition (0, 15, 20, 25 and 30 vol.%) on microstructural features, phase evolution and mechanical properties of the vacuum hot pressed TiB 2 at 1850 °C/2 h/20 MPa. Hardness measurements revealed an initial increase in hardness from 14.2 GPa for nominally pure TiB 2 to 20.8 GPa for TiB 2 –15 vol.% SiC and a subsequent decrease with further increase in the SiC addition. Also the TiB 2 –30 vol.% SiC showed an improved indentation fracture toughness of 5.76 MPa m 1/2 which was mostly attributed to the addition of the SiC particles that could activate toughening mechanisms such as crack deflection, crack branching and grain breaking. The microstructure of the sintered samples was characterized by XRD and FESEM, which indicated that SiC reacted with and removed oxide impurities (TiO 2 and B 2 O 3 ) that were present on the particle surfaces. Elimination of such impurities promoted densification by minimizing grain coarsening and in composite contain 30 vol.% SiC the reaction led to in situ formation of TiC. Hence, the results indicated that sinterability of TiB 2 -based composites was remarkably improved by addition of SiC compared to the single phase TiB 2 ceramic.

Microstructural development and mechanical properties of hot pressed SiC reinforced TiB2 based composite

The effects of adding SiC as a reinforcement and TiN as an additive on TiB2-based composites fabricated by the spark plasma sintering (SPS) technique were investigated. SPS was implemented at the sintering conditions of 1900 °C temperature, 7 min holding time and 40 MPa pressure. Adding these two secondary phases had noticeable effects on the microstructure of TiB2-based composites. A relative densities of 99.9% was obtained for TiB2–SiC–TiN composite. Detection of in-situ formed phases and investigation on them were done using SEM, XRD, EDS and thermodynamic assessment. These evaluations proved the formation of in-situ phases of TiC, BN nano-platelets, TiSi and B4C in the TiB2-based composite codoped with SiC and TiN. Formation of these in-situ phases had fascinating effects on the sinterability and ultimate microstructure of titanium diboride.

Reactive spark plasma sintering of TiB2–SiC–TiN novel composite

ZrB2-TiB2-based ceramics with varying amount of TiB2 (up to 30 wt%) were hot pressed at 2200 °C in Ar atmosphere, and the effect of the TiB2 addition on mechanical properties like hardness, fracture toughness, scratch resistance, wear resistance and thermal conductivity of the system was compared to monolithic ZrB2 ceramic. It was found from X-ray diffraction that TiB2 completely entered into the structure and formed solid solution with ZrB2. Addition of TiB2 in ZrB2 system improves the mechanical and wear resistance properties. ZrB2-TiB2 (30 wt%) ceramic, for example, showed highest hardness of 22.34 GPa, fracture toughness 3.01 MPa(m)1/2 and lowest coefficient of friction (0.398 at 10 N load). The addition of TiB2 in ZrB2 system showed lower thermal conductivity than monolithic ZrB2 by increasing grain boundary thermal resistance.

Mechanical and thermal properties of hot pressed ZrB2 system with TiB2

Spark plasma sintering of TiB2–boron ceramics using commercially available raw powders is reported. The B4C phase developed during reaction-driven consolidation at 1900 °C. The newly formed grains were located at the grain junctions and the triple point of TiB2 grains, forming a covalent and stiff skeleton of B4C. The flexural strength of the TiB2–10 wt.% boron ceramic composites reached 910 MPa at room temperature and 1105 MPa at 1600 °С. Which is the highest strength reported for non-oxide ceramics at 1600 °C. This was followed by a rapid decrease at 1800 °C to 480–620 MPa, which was confirmed by increased number of cavitated titanium diboride grains observed after flexural strength tests.

Ultra-high elevated temperature strength of TiB2-based ceramics consolidated by spark plasma sintering

Like most carbide-based composites, the two main characteristics of alumina–tungsten carbide (Al2O3–WC) composites are high hardness and high wear resistance. These features confer the composites important engineering applications, in particular when they are used as cutting tools. The present research involved a study of Al2O3–WC nanometric powders obtained through reactive milling. In this process, high-energy milling promotes the reaction in a mixture of reactive powders. The material was milled in a high-energy SPEX 8000 Mixer/Mill, using WO3 ,A l and C precursor powders. The highly exothermic self-propagating high-temperature synthesis (SHS) type reaction was self-sustained, producing a temperature peak that was detected by a thermocouple attached to the external surface of the vessel. Using stoichiometric proportions of the reagents to reduce the WO3 and to obtain WC, and adding Al2O3 as diluent, the SHS reaction occurred up to a limit of 0.8 mols of diluent, forming not only alumina but also a W2C mixture with little WC. To obtain only WC it was required the addition of more than 0.8 mols of C, which indicates that the reaction may have occurred through a gaseous phase reaction mechanism. © 2007 Elsevier B.V. All rights reserved.

Xiao Chuanchun

Papers

In-situ HIP synthesis of TiB2/SiC ceramic composites