EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Refractory complex concentrated alloys (RCCAs) are potential substitutes for nickel or TiAl alloys for high temperature application in aircraft engines, between 800°C and 1000°C. In particular, the Ti- Nb-Al ternary system with the precipitation of stable orthorhombic phase in the bcc matrix shows good mechanical properties both at both room (with good ductility) and high temperatures (with...

The internal twin-boundaries in lamellar $\gamma$-TiAl alloys, namely true-twin (TT), rotational boundary (RB), and pseudo-twin (PT), are known to be effective in strengthening the TiAl microstructures, but a better understanding of the role of these boundaries on fracture behavior is still required for designing microstructures with optimised mechanical properties. To this end, molecular...

Reducing the emissions of CO2 and NOx in aviation and automotive industry requires the usage of innovative high temperature materials. An important class of materials meeting the specific requirements are intermetallic γ-TiAl based alloys. Their properties include a low density compared to other high temperature materials, a high specific strength and a good creep resistance up to 750 °C. A...

In order to improve the efficiency of modern turbines in aviation technology with simultaneous reduction of exhaust gas emissions, intermetallic TiAl alloys are implemented as structural material for highly durable turbine blades. Fourth-generation TiAl alloys typically exhibit an excellent high-temperature behavior, promising oxidation resistance and represent a lightweight alternative for...

The capability of Ti-Al-based alloys to substitute Ni-based superalloys in high-temperature, high-strength applications has led to intensive research over the last decades. Today, such alloys based on the intermetallic phases TiAl and Ti3Al with some additions of, e.g., Cr, Nb, or Mo, have made the step into real applications for example as turbine blades. Regarding the production of parts...

Much attention has been given over the last decade to TiAl intermetallics due to their low density, high specific strength and relatively good resistance to oxidation at service conditions. These alloys are considered as structural materials in new generation energy-conversion systems that expectedly increase their power efficiency and ecological compatibility owing to reduced component...

The field of turbine blades in aeronautical jet engines is dominated by nickel-based superalloys, due to their ability to withstand highly demanding mechanical and thermal loads. From the environmental perspective, reducing weight and enhancing efficiency, the main disadvantage of nickel-based superalloys is their high density of 8 g/cm³. As an alternative, lightweight intermetallic...

Due to their low density (roughly 4 g/cm$^3$) and excellent high temperature properties, such as good creep behavior, high specific yield strength as well as good oxidation resistance, intermetallic γ-TiAl based alloys are applied in the automotive and aircraft industry, i.e. as turbocharger turbine wheels or turbine blades in the last stage of the low pressure turbine. One disadvantage of...

Fe-Al intermetallic alloys display interesting properties for applications at high temperatures, including excellent mechanical strength and good oxidation resistance. Moreover, their cost is attractive, and they present weight reduction compared to other iron-based alloys. However, their low ductility at room temperature prevents them to be implemented industrially by simple routes such as...

Wrought γ’-strengthened Ni-based superalloys are commonly used in aircraft engine disk applications. The required high strength and temperature resistance is achieved by a high alloying content and, thus, resulting complex microstructures. This high alloying content makes these alloys prone to segregation which, in combination with the high inherent strength, leads to cracking during...

Contemporary alloys for gas turbines operate at 90% of their melting point, necessitating the development of novel materials that withstand higher temperatures. Promising possibilities are alloys located in the system MoSiTiB, which have been under investigation for several years and show viable properties in terms of high-temperature mechanical properties and corrosion resistance.

The...

The excellent mechanical properties up to 650°C make Alloy 718, a Ni-based superalloy, a common material used in low-pressure turbine discs of commercial airplanes. A major contribution to the high mechanical strength is attributed to the presence of nanoscale γ' and γ" precipitates. Different ageing treatments, such as conventional or direct ageing cause variations in the volume fraction,...

The strength of superalloys is strongly influenced by gamma prime precipitates, whose size and volume fraction can be adjusted by heat treatments. According to classical precipitation strengthening models, an increasing precipitate diameter should lead to a transition from weak to strong coupling of the dislocation pairs that form superdislocations in the gamma prime phase. We show that...

This study aims to assess the fabrication route of cobalt-based superalloys using directed energy deposition (DED) process. Compared with nickel-based superalloys, the precipitation kinetics of the γ’-strengthening phase leads to moderate hardening at high cooling rate, which prevents or limits strain aged cracking during fabrication.
The DED process induces a complex oriented grain...

Additive manufacturing (AM) has long since evolved from its initial mode of use in rapid prototyping to commercial manufacturing. AM Ni-based superalloys have found use in the design of critical components in the aerospace industry due to its ability to retain its mechanical properties at elevated temperatures near its melting point. Furthermore, with advances in electron beam melting (EBM)...

Metal Dusting is a high temperature corrosion mechanism observed in industries handling carbonaceous gases. In the temperature range of 400 to 900°C, carbon-rich species of the gas decompose and carbon diffuses into the material, resulting in a catastrophic material degradation. The dissociation reactions are catalyzed by iron, nickel and cobalt. Iron and nickel are commonly used as base...

High pressure turbine blades are the most challenging parts due to severe operating conditions in a jet engine. Single crystal nickel based superalloys are extensively used for this application due to high creep and thermal fatigue resistances. Mastering directional solidification during investment casting is one of the main challenges when manufacturing them, as defects such as...

The versatility of the alloy 718 justifies its use as high-temperature components, gas turbine parts, rocket motors, storage tanks and spacer grids of nuclear reactor fuel elements, for example. However, the improvement in the performance of nickel superalloys in various application areas is a motivation for the search for continuous innovation of these materials. In this sense, the use of...

Tungsten inert gas welding (TIGW) and shielded metal arc welding (SMAW) have been used for welding SA213-T91 superheater tubes used in power plants. The optimal performance of power plant components during service entirely depends on the post-weld microstructural conditions. It is known that welding not only results in inhomogeneous microstructures and mechanical properties but as well may...

This work is focused on the oxidation behavior of an alumina-forming heat resistant steel used in steam cracking furnaces, in which a mixture of steam and ethane is heated up to 850°C in order to produce ethylene. In this application, the main problem arises from the formation of coke leading to pipe obstruction, carburization of the alloy and reduced heat exchanges. One of the possible...

Martensitic steels such as modified 9% Cr steels (P91 & P92) were developed and widely utilized in industry due to their low price and acceptable creep strength among martensitic steels. The martensitic 12% Cr steels were proposed to improve corrosion resistance of components at higher temperature to improve efficiency of power plants and reduce CO2 emission. However, all attempts to develop...

Titanium and its alloys are widely used in various areas, from aerospace to medical implants to car industry and jewellery. Titanium alloys can be divided into several groups. We study the group called metastable β titanium alloys. These alloys contain a sufficient amount of elements which stabilize the high temperature β phase (body centred cubic), so that the transition to the low...

Nowadays, the use of near-α titanium alloys in aircraft engines is limited to low pressure compressor part, since above 600°C, the mechanical properties of the conventional near-α titanium alloys are drastically reduced. For the past 20 years numerous research works have been carried out to find suitable strengthening method to improve near-α titanium alloys properties for temperatures up to...