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Stainless steel 316 was coated with CeO₂ and Y₂O₃ modified aluminide and titanium aluminide coatings. The coatings were prepared by the pack cementation method and the high temperature oxidation behaviour of the coatings was investigated in an atmosphere containing a limited supply of air. The performance of the coatings was studied by measuring oxidation kinetics, and by scanning electron microscopic techniques. The oxidation rates of these coatings were reduced in the presence of CeO₂ and Y₂O₃ due to better adherence of their oxide scales.

A US company, Seattle Aviation Partners Inc., is developing advanced winglet designs for air transports that will cut fuel consumption from 6 per cent to more than 10 per cent during cruise phases of flight.

Gamma titanium aluminide is a material essential for meeting military and civil engine performance targets in the future and potentially it could be used throughout the engine from compressor to combustor to turbine. The current alloy being used within Rolls‐Royce is the established Ti‐45‐2‐2‐XD. This is competing for lower temperature applications such as stators and structural components which take advantage of the lower costs arising from the casting route. Rigorous design criteria are required to compensate for the risks in using these relatively new materials in components and this requires investigation into the effects of manufactured surface conditions, of microstructures local to load bearing regions and of compositional variations. For the future, Rolls‐Royce has patented a next generation gamma titanium resulting from alloy development programmes undertaken by the University of Birmingham. The aim is to optimise castability with strength and creep resistance and their potential for commercial use within the aero‐engine is discussed.

The purpose of this paper is to investigate improving high‐temperature oxidation resistance of titanium by developing new coatings based on aluminum and its combination with the substrate. Nanocrystalline plasma electrolytic saturations were applied on the surface of commercially pure titanium in an aqueous bath. The aim was to obtain good corrosion and oxidation resistances of the differently treated samples by investigation of their nanostructures. The advantages of developed new coatings and the necessity of their use in modern gas turbine engines allow the metals to be used safely at high temperatures, which in turn can enhance the efficiency of gas‐turbine engine‐compressor sections.

The electrolytic saturation process was done in an aqueous bath with different effective parameters such as frequency, peak of applied pulsed voltage, etc. to obtain the desired nanostructures. Systematic characterization was carried out on as‐prepared as well as oxidized coatings and these results are presented. The performance of new coatings was evaluated by generating weight‐gain data as a function of time, followed by detailed characterization in order to confirm the ability of the coatings to prevent oxidation and alpha‐case formation. Potentiodynamic polarization and SEM nanograph analysis were undertaken to study corrosion resistance and the nanostructure of obtained layers.

The results showed that the corrosion and oxidation resistance of the obtained layers depended strongly to the average size of nanocrystallites and their nanomorphology. All coated samples had better electrochemical and oxidation behavior compared to the untreated substrate.

The results obtained in this research into nanocrystalline plasma electrolytic saturation can be used wherever good corrosion and oxidation resistances with high efficiency are required.

The speed of treatment by this technique makes this method very suitable for industrial surface treatment of different components.

Aerospace engineers investigating new high‐performance heat‐resistant alloys for further gas turbine engines are optimistic about titanium aluminides. If the alloys can be made stronger, titanium aluminides are prime candidates to replace conventional titanium and lower temperature nickel‐base superalloys, which researchers believe lack the heat‐resistant properties that will be required from the next generation of hypersonic aerospace vehicles.

Electron beam melting (EBM) is one of the potential additive manufacturing technologies to fabricate aero-engine components from gamma titanium aluminide (γ-TiAl) alloys. When a new material system has to be taken in to the fold of EBM, which is a highly complex process, it is essential to understand the effect of process parameters on the final quality of parts. This paper aims to understand the effect of melting parameters on top surface quality and density of EBM manufactured parts. This investigation would accelerate EBM process development for newer alloys.

Central composite design approach was used to design the experiments. In total, 50 specimens were built in EBM with different melt theme settings. The parameters varied were surface temperature, beam current, beam focus offset, line offset and beam speed. Density and surface roughness were selected as responses in the qualifying step of the parts. After identifying the parameters which were statistically significant, possible reasons were analyzed from the perspective of the EBM process.

The internal porosity and surface roughness were correlated to the process settings. Important ones among the parameters are beam focus offset, line offset and beam speed. By jointly deciding the total amount of energy input for each layer, these three parameters played a critical role in internal flaw generation and surface evolution.

The range selected for each parameter is applicable, in particular, to γ-TiAl alloy. For any other alloy, the settings range has to be suitably adapted depending on physical properties such as melting point, thermal conductivity and thermal expansion co-efficient.

This paper demonstrates how melt theme parameters have to be understood in the EBM process. By adopting a similar strategy, an optimum window of settings that give best consolidation of powder and better surface characteristics can be identified whenever a new material is being investigated for EBM. This work gives researchers insights into EBM process and speeds up EBM adoption by aerospace industry to produce critical engine parts from γ-TiAl alloy.

This work is one of the first attempts to systematically carry out a number of experiments and to evaluate the effect of melt parameters for producing γ-TiAl parts by the EBM process. Its conclusions would be of value to additive manufacturing researchers working on γ-TiAl by EBM process.

The aim of this paper is to investigate the effect of cathodic charging and corrosion behavior of Ti‐48Al‐2Cr‐2Nb alloy in hydrochloric acid solutions.

TiAl alloy specimens of thickness 0.5 mm were cathodically charged in 0.1 M HCl solution at room temperature. The prominent current densities selected for this investigation were 25 and 50 mA cm⁻² for durations of 24‐120 h. The change in weight of the specimen after charging was measured by a microbalance with an accuracy of ±1 μg.

The nature of the specimen surfaces was characterized by X‐ray diffraction (XRD), auger electron spectroscopy (AES) and scanning electron microscopy (SEM) equipped with energy dispersive X‐ray spectroscopy (EDS). XRD revealed the phase transformation from microcrystalline to nano‐crystalline, particularly after high charging times (120 h) and high current density (50 mA cm⁻²). AES and EDS further assessed the compositional fluctuations on both cathodically charged and potentiodynamically polarized specimens. Surface corrosion leading to the generation of microcracks throughout the surface region was observed by SEM. Cathodic charging and the polarization process were responsible for embrittlement and pitting. Decreases in both weight and Vickers hardness values with an increase in charging time revealed that surface erosion depended strongly upon charging density.

The results presented in this work shed light on the role of alloying elements the passive behavior and their implications on their stability in hydrochloric acid environments.

Comprehensive knowledge of the complicated physical behavior of the induction furnace with cold crucible (IFCC) is required to utilize the advantages of this melting aggregate in melting and casting chemically high‐reactive materials, like titanium‐aluminides (TiAl). Practical experiences show that the overheating temperature of the melt is decisive for the quality of the cast products. Therefore, a systematic analysis of the electromagnetic and in particular, the hydrodynamic and thermal behavior of the IFCC is carried out. The examinations of the influence of the construction elements as well as the process parameters on the temperature field and finally the overheating temperature in the IFCC are performed using specifically developed numerical models. The evaluation of the numerical results is done by experimental investigations, where aluminum serves as a model melt for the experimental determination of the thermal and hydrodynamic field of the melt. The analysis of the influence of construction‐elements on the overheating temperature is focused on the design of the crucible wall and the crucible bottom, on the height‐diameter ratio of the crucible and on the axial inductor position. The inductor current, the operation frequency and the crucible filling level are found to be very important for reaching a high overheating temperature.