After almost three decades of intensive fundamental research and development activities, intermetallic titanium aluminides based on the ordered γ-TiAl phase have found applications in automotive and aircraft engine industry. The advantages of this class of innovative high-temperature materials are their low density and their good strength and creep properties up to 750 °C as well as their good oxidation and burn resistance. Advanced TiAl alloys are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments. The background of these heat treatments is at least twofold, i.e., concurrent increase of ductility at room temperature and creep strength at elevated temperature. This review gives a general survey of engineering γ-TiAl based alloys, but concentrates on β-solidifying γ-TiAl based alloys which show excellent hot-workability and balanced mechanical properties when subjected to adapted heat treatments. The content of this paper comprises alloy design strategies, progress in processing, evolution of microstructure, mechanical properties as well as application-oriented aspects, but also shows how sophisticated ex situ and in situ methods can be employed to establish phase diagrams and to investigate the evolution of the micro- and nanostructure during hot-working and subsequent heat treatments.

Design, Processing, Microstructure, Properties, and Applications of Advanced Intermetallic TiAl Alloys†

Despite the fact that additive manufacturing (AM) techniques allow to manufacture complex porous parts with a controlled architecture, differences can occur between designed and as-produced morphological properties. Therefore this study aimed at optimizing the robustness and controllability of the production of porous Ti6Al4V structures using selective laser melting (SLM) by reducing the mismatch between designed and as-produced morphological and mechanical properties in two runs. In the first run, porous Ti6Al4V structures with different pore sizes were designed, manufactured by SLM, analyzed by microfocus X-ray computed tomography (micro-CT) image analysis and compared to the original design. The comparison was based on the following morphological parameters: pore size, strut thickness, porosity, surface area and structure volume. Integration of the mismatch between designed and measured properties into a second run enabled a decrease of the mismatch. For example, for the average pore size the mismatch decreased from 45% to 5%. The demonstrated protocol is furthermore applicable to other 3D structures, properties and production techniques, powder metallurgy, titanium alloys, porous materials, mechanical characterization, tomography.

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Micro-CT-based improvement of geometrical and mechanical controllability of selective laser melted Ti6Al4V porous structures

Fe-based bulk metallic glasses: Glass formation, fabrication, properties and applications

Microstructures and mechanical properties of TiAl alloys consolidated by spark plasma sintering

Chemical composition, microstructure and sintering temperature modifications on mechanical properties of TiC-based cermet – A review

Influence of Mo2C and TaC additions on the microstructure and mechanical properties of Ti(C, N)-based cermets

In this work, the effects of 1.0 wt.% additions of Mo and Co on the microstructure and properties of WC-TiC-Ni cemented carbides were investigated using scanning electron microscope, mechanical properties tests, corrosion resistance and abrasion resistance tests. The results show that 1.0 wt.% Mo addition can refine the WC grains and increase the hardness. Moreover, with the addition of minor Mo, the corrosion resistance and abrasion resistance of alloys improved significantly. The addition of 1.0 wt.% Co can inhibit the growth of WC grains, improve the density and hardness slightly, and enhance the abrasion resistance of cemented carbides. However, the minor Co has negative effect for the corrosion resistance.

Effect of Mo and Co additions on the microstructure and properties of WC-TiC-Ni cemented carbides

Fabrication and SPS microstructures of Ti–45Al–8.5Nb–(W,B,Y) alloying powders

Effects of LaB6 addition on the microstructure and mechanical properties of ultrafine grained WC–10Co alloys

Ti–45Al–8.5Nb–(W,B,Y) alloy with industrial scale was fabricated successfully using plasma arc furnace. Microstructure and compression properties of the alloy were investigated. The results showed that a uniform fully lamellar (FL) microstructure was observed in the center and the rim of the different parts for the ingot after heat treatment. There are three microsegregations in the FL microstructure, i.e. β (B2) phase, borides and yttrium oxide. The alloy exhibits excellent compression properties at elevated temperatures. When compression temperature is higher than 1100 °C, high quality compressed samples without cracks can be obtained even engineering compression strain up to 80% for the strain rates of 1 × 10−1 to 10−3 S−1.

Y.H. He

Papers

Influence of Mo2C and TaC additions on the microstructure and mechanical properties of Ti(C, N)-based cermets

Effect of Mo and Co additions on the microstructure and properties of WC-TiC-Ni cemented carbides

Fabrication and SPS microstructures of Ti–45Al–8.5Nb–(W,B,Y) alloying powders

Effects of LaB6 addition on the microstructure and mechanical properties of ultrafine grained WC–10Co alloys

Microstructure and mechanical properties of as-cast Ti–45Al–8.5Nb–(W,B,Y) alloy with industrial scale