Selective electron beam melting (SEBM) belongs to the additive manufacturing technologies which are believed to revolutionise future industrial production. Starting from computer-aided designed data, components are built layer by layer within a powder bed by selectively melting the powder with a high power electron beam. In contrast to selective laser melting (SLM), which can be used for metals, polymers and ceramics, the application field of the electron beam is restricted to metallic components since electric conductivity is required. On the other hand, the electron beam works under vacuum conditions, can be moved at extremely high velocities and a high beam power is available. These features make SEBM especially interesting for the processing of high-performance alloys. The present review describes SEBM with special focus on the relationship between process characteristics, material consolidation and the resulting materials and component properties.

Additive manufacturing of metallic components by selective electron beam melting — a review

Imbalances between metal supply and demand, real or anticipated, have inspired the concept of metal criticality We here characterize the criticality of 62 metals and metalloids in a 3D “criticality space” consisting of supply risk, environmental implications, and vulnerability to supply restriction Contributing factors that lead to extreme values include high geopolitical concentration of primary production, lack of available suitable substitutes, and political instability The results show that the limitations for many metals important in emerging electronics (eg, gallium and selenium) are largely those related to supply risk; those of platinum group metals, gold, and mercury, to environmental implications; and steel alloying elements (eg, chromium and niobium) as well as elements used in high-temperature alloys (eg, tungsten and molybdenum), to vulnerability to supply restriction The metals of most concern tend to be those available largely or entirely as byproducts, used in small quantities for highly specialized applications, and possessing no effective substitutes

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Criticality of metals and metalloids.

Increasing the temperature of jet engines requires materials that are stable against degradation. Towards this goal, growth of TiAl alloys with high strength and ductility, as well as superior creep resistance, is reported at high temperatures.

Polysynthetic twinned TiAl single crystals for high-temperature applications

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

After more than 30 years of fundamental research and development activities intermetallic titanium aluminides based on the ordered γ-TiAl phase have found applications in aerospace and automotive industries. The advantages of this class of innovative high-temperature lightweight materials are their low density, their good strength and creep properties, as well as their oxidation resistance up to 750 °C. A drawback, however, is their limited ductility at room temperature, which is reflected by a low plastic strain at fracture. Advanced engineering TiAl alloys, such as the β-solidifying so-called TNM alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in atomic percent), are complex multi-phase materials which can be processed by ingot or powder metallurgy, precision casting methods as well as additive manufacturing. Each production process leads to specific microstructures which can be altered and optimised by thermomechanical processing and/or subsequent heat treatments, whereby the knowledge of t...

Intermetallic titanium aluminides in aerospace applications – processing, microstructure and properties

The present article will describe the science and technology of titanium aluminide (TiAl) alloys and the engineering development of TiAl for commercial aircraft engine applications. The GEnxTM engine is the first commercial aircraft engine that is flying titanium aluminide (alloy 4822) blades and it represents a major advance in propulsion efficiency, realizing a 20% reduction in fuel consumption, a 50% reduction in noise, and an 80% reduction in NOx emissions compared with prior engines in its class. The GEnxTM uses the latest materials and design processes to reduce weight, improve performance, and reduce maintenance costs. GE’s TiAl low-pressure turbine blade production status will be discussed along with the history of implementation. In 2006, GE began to explore near net shape casting as an alternative to the initial overstock conventional gravity casting plus machining approach. To date, more than 40,000 TiAl low-pressure turbine blades have been manufactured for the GEnxTM 1B (Boeing 787) and the GEnxTM 2B (Boeing 747-8) applications. The implementation of TiAl in other GE and non-GE engines will also be discussed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427413000444

M. J. Weimer

Papers

TiAl alloys in commercial aircraft engines

The Science, Technology, and Implementation of TiAl Alloys in Commercial Aircraft Engines