One-dimensional carbon nanotubes and two-dimensional graphene nanosheets with unique electrical, mechanical and thermal properties are attractive reinforcements for fabricating light weight, high strength and high performance metal-matrix composites. Rapid advances of nanotechnology in recent years enable the development of advanced metal matrix nanocomposites for structural engineering and functional device applications. This review focuses on the recent development in the synthesis, property characterization and application of aluminum, magnesium, and transition metal-based composites reinforced with carbon nanotubes and graphene nanosheets. These include processing strategies of carbonaceous nanomaterials and their composites, mechanical and tribological responses, corrosion, electrical and thermal properties as well as hydrogen storage and electrocatalytic behaviors. The effects of nanomaterial dispersion in the metal matrix and the formation of interfacial precipitates on these properties are also addressed. Particular attention is paid to the fundamentals and the structure–property relationships of such novel nanocomposites.

Recent progress in the development and properties of novel metal matrix nanocomposites reinforced with carbon nanotubes and graphene nanosheets

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†

Microstructurally inhomogeneous composites: Is a homogeneous reinforcement distribution optimal?

Advances in gamma titanium aluminides and their manufacturing techniques

The present article will describe aspects of the science and technology of titanium aluminide (TiAl) alloy system and summarise the low and high temperature mechanical and environmental properties exhibited by different alloy generations. In terms of processing developments, conventional gravity casting and near net shape casting would be discussed in detail. Also newer and non-conventional forging and additive manufacturing routes would be briefly highlighted. Extensive investigations of TiAl alloys have enabled their commercial implementation in aerospace and automotive industries. The GEnx™ engine is the first commercial aircraft engine that used TiAl (alloy 48–2–2) for their low pressure turbine blades. Among non GE engines, recently, new β-stabilised TiAl alloy (TNM) is being used to manufacture LPT blades for PW1100G™ engines. TiAl materials and design processes can reduce engine weight and improve engine performance.

TiAl alloys in commercial aircraft engines

Microstructure evolution and mechanical properties of a novel beta γ-TiAl alloy

The microstructure and properties of Ti–Mo–Nb alloys for biomedical application

In this paper, high temperature titanium matrix composites with different volume fraction of (TiB + TiC) reinforcements were in situ synthesized by casting route. The microstructure and tensile properties of the composites were presented and discussed. The results reveal that both the TiB whiskers and TiC particles tend to segregate at prior β boundaries. The prior β grain size and α lath width are gradually refined with increasing volume fraction of reinforcements. Evolution of tensile properties shows that enhancement in yield strength and ultimate tensile strength with addition of reinforcements is primarily attributed to microstructural refinement, while the remarkable reduction in ductility is possibly due to the cracking of TiB whiskers and TiC particles.

Evolution of microstructure and tensile properties of in situ titanium matrix composites with volume fraction of (TiB + TiC) reinforcements

Deformation behavior of high Nb containing TiAl based alloy in α + γ two phase field region

Ti–3.5Al–5Mo–6V–3Cr–2Sn–0.5Fe is a high-strength β titanium alloy that shows excellent tensile properties. This paper presents the effect of hot rolling and heat treatment on the microstructure and tensile properties of this alloy. Microstructure observation shows that the α+β rolled alloy leads to smaller β grain size than the β rolled alloy in all heat treatment conditions. Solution treatment of the alloy in the α+β field can also lead to smaller β grain than solution in the β field. Tensile results indicated that the strength of the alloy was improved greatly by aging heat treatment, which was attributed to the secondary α phase. The 790 °C rolled alloy can obtain an ultimate strength of 1744 MPa by solution at 800 °C plus aging at 440 °C. The strength decreases and ductility increases with the increase of aging temperature. Moreover, the ductility of the alloy is significantly determined by the rolling and solution procedure. Rolling and solution treated at the α+β field results in better ductility than rolling and solution at the β field. Therefore, to obtain the high ductility, the α+β rolling and α+β solution should be chosen as long as possible before aging heat treatment.

Yu Yong Chen

Papers

Microstructure evolution and mechanical properties of a novel beta γ-TiAl alloy

The microstructure and properties of Ti–Mo–Nb alloys for biomedical application

Evolution of microstructure and tensile properties of in situ titanium matrix composites with volume fraction of (TiB + TiC) reinforcements

Deformation behavior of high Nb containing TiAl based alloy in α + γ two phase field region

Effect of hot rolling and heat treatment on microstructure and tensile properties of high strength beta titanium alloy sheets