Nickel aluminide intermetallic compounds possess attractive properties that make them good candidates for high temperature structural applications. The production of these materials in short processing times and low energy via reaction synthesis routes has been reviewed in this article including most recent novel reactive methods applied to Ni–Al intermetallics (e.g. microwave combustion synthesis and hot extrusion reaction synthesis). Future directions in this field have been suggested.

Review: reaction synthesis processing of Ni–Al intermetallic materials

Titanium diboride (TiB2) based materials have received wide attention because of their high hardness and elastic modulus, good abrasion resistance, and superior thermal and electrical conductivity. Potential applications include high temperature structural materials, cutting tools, armour, electrodes in metal smelting and wear parts. Despite its useful properties, the application of monolithic TiB2 is limited by poor sinterability, exaggerated grain growth at high temperature and poor oxidation resistance above 1000°C. Pure TiB2 can be densified only at high temperatures (∼2000°C), with an applied pressure generally being necessary during sintering. However, these high sintering temperatures cause abnormal grain growth and microcracks, which are detrimental to the mechanical properties. Various sinter additives are commonly added to obtain dense TiB2 with optimised mechanical properties at lower sintering temperature. The present review surveys the current state of knowledge on development of bulk...

Processing and properties of monolithic TiB2 based materials

Ceramic-matrix composites (CMCs) based on TiC–TiB2 have attracted enormous interest during recent years because, in comparison to single-phase ceramics, they exhibit superior properties including high hardness, good wear resistance and high fracture toughness. This paper begins with a review of the TiC–TiB2 equilibrium system and its possible influence on the processing and properties of the composite. The application of TiC–TiB2 composites has been limited due to the fact that they have been difficult to process. Much of the research effort has therefore focused on the synthesis, processing and fabrication of TiC–TiB2 and is based primarily on self-propagating high-temperature synthesis (SHS) and its derivatives, high-energy milling and sintering. The performance of SHS under the application of pressure has been the subject of particular investigation. These developments are the main subject of this review that also takes into account the resulting effects on the microstructure and the mechanical properties of TiC–TiB2. The influence of the reaction parameters like reactant composition, reactant particle size and green density on the microstructure and properties is also reported.

TiC-TiB2 composites : A review of phase relationships, processing and properties

Titanium and its alloys are attractive materials due to their unique high strength-weight ratio that is maintained at elevated temperatures and their exceptional corrosion resistance. The major application of titanium has been in the aerospace industry. However, the focus shift of market trends from military to commercial and aerospace to industry has also been reported. On the Other hand, titanium and its alloys are notorious for their poor thermal properties and are classified as difficult-to-machine materials. These properties limit the use of these materials especially in the commercial markets where cost is much more of a factor than in aerospace. Machining is an important manufacturing process because it is almost always involved if precision is required and is the most cost effective process for small volume production. This paper reviews the machining of titanium and its alloys and proposes potential research issues.

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Machining titanium and its alloys

An experimental investigation of effects of cooling/lubrication conditions on tool wear in high-speed end milling of Ti-6Al-4V

TiB2 and TiB2x2013;TiC composite compacts with 98x2013;99% density are prepared by high-pressure sintering (HPS) of premixed powders and by high-pressure self-combustion synthesis (HPCS) from the elemental constituents. The sintering and synthesis experiments are carried out at 3 GPa in the temperature and time ranges 2250x2013;2750 K and 5x2013;300 s, respectively. A high sintering temperature (2750 K) is required to obtain dense monolithic TiB2 compacts (98% density) by HPS. Compacts with a similar density are obtained at lower sintering temperature (2250 K) when 15 mol% TiC is added to TiB2. The composite compacts have marginally better fracture toughness than that of monolithic compacts. TiB2 and TiB2x2013;TiC compacts (99% density) are also prepared by HPCS from elemental constituents. A minimum ignition temperature of 2250 K is required to make the reaction self-sustaining.The compacts prepared by HPCS have superior fracture toughness to those prepared by HPS. The microstructures and the properties of the compacts prepared by HPS and HPCS are compared. A possible sequence of reaction during the HPCS of TiB2x2013;TiC is proposed.

Synthesis and sintering of TiB2 and TiB2–TiC composite under high pressure

Machining Ti6Al4V alloy with a wBN-cBN composite tool

Synthesis and densification of monolithic zirconium carbide (ZrC) has been carried out by reactive hot pressing of zirconium (Zr) and graphite (C) powders in the molar ratios 1:1, 1.25:1, 1.5:1, and 2:1 at 40 MPa, 1200 degrees-1600 degrees C. Monolithic ZrC could be synthesized with a C/Zr ratio similar to 0.5-1.0 and the post heat-treated samples have the lattice parameter in the range 4.665 to 4.698 A. Densification improves with an increasing deviation from the stoichiometry. Fine-grained (similar to 1 mu m) and nearly fully dense material (99% RD) could be obtained at a temperature as low as 1200 degrees C with C/Zr similar to 0.67. Microstructural and XRD observations suggest that densification occurred at low temperatures with nonstoichiometric Zr-C powder mixtures.

Synthesis and Densification of Monolithic Zirconium Carbide by Reactive Hot Pressing

Dense ZrB2–SiC (25–30 vol%) composites have been produced by reactive hot pressing using stoichiometric Zr, B4C, C and Si powder mixtures with and without Ni addition at 40 MPa, 1600 °C for 60 min. Nickel, a common additive to promote densification, is shown not to be essential; the presence of an ultra-fine microstructure containing a transient plastic ZrC phase is suggested to play a key role at low temperatures, while a transient liquid phase may be responsible at temperatures above 1350 °C. Hot Pressing of non-stoichiometric mixture of Zr, B4C and Si at 40 MPa, 1600 °C for 30 min resulted in ZrB2–ZrCx–SiC (15 vol%) composites of ∼98% RD.

Fabrication and mechanisms of densification of ZrB2-based ultra high temperature ceramics by reactive hot pressing

Dense ZrB2-ZrC and ZrB2-ZrCx∼0.67 composites have been produced by reactive hot pressing (RHP) of stoichiometric and nonstoichiometric mixtures of Zr and B4C powders at 40 MPa and temperatures up to 1600 °C for 30 minutes. The role of Ni addition on reaction kinetics and densification of the composites has been studied. Composites of ∼97 pct relative density (RD) have been produced with the stoichiometric mixture at 1600 °C, while the composite with ∼99 pct RD has been obtained with excess Zr at 1200 °C, suggesting the formation of carbon deficient ZrC
 x
 that significantly aids densification by plastic flow and vacancy diffusion mechanism. Stoichiometric and nonstoichiometric composites have a hardness of ∼20 GPa. The grain sizes of ZrB2 and ZrCx∼0.67 are ∼0.6 and 0.4 μm, respectively, which are finer than those reported in the literature.

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C Divakar

Papers

Synthesis and sintering of TiB2 and TiB2–TiC composite under high pressure

Machining Ti6Al4V alloy with a wBN-cBN composite tool

Synthesis and Densification of Monolithic Zirconium Carbide by Reactive Hot Pressing

Fabrication and mechanisms of densification of ZrB2-based ultra high temperature ceramics by reactive hot pressing

Low-Temperature Processing of ZrB2-ZrC Composites by Reactive Hot Pressing