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Alloys developed for high temperature applications
2017
Alloys used for high temperatures applications require combinations of mechanical strength, microstructural stability and corrosion/oxidation resistance. Nickel base superalloys have been traditionally the prime materials utilized for hot section components of aircraft turbine engines. Nevertheless, due to their limited melting temperatures, alloys based on intermetallic compounds, such as TiAl base alloys, have emerged as high temperature materials and intensively developed with the main aim to replace nickel based superalloys. For applications in steam power plants operated at lower temperatures, ferritic high temperature alloys still attract high attention, and therefore, development of these alloys is in progress. This paper highlights the important metallurgical parameters of high temperature alloys and describes few efforts in the development of Fe-Ni-Al based alloys containing B2-(Fe,Ni)Al precipitates, oxide dispersion strengthening (ODS) ferritic steels and titanium aluminide based alloys include important protection system of aluminide coatings.
Review of high temperature materials
Heritage and Sustainable Development
High-temperature materials play a significant role in sustainable engineering across various industries and applications. Sustainable engineering aims to design, develop, and implement solutions that minimize environmental impact, enhance resource efficiency, and promote long-term sustainability. The availability of substances that can be used efficiently at high temperatures allows pushing the limits of possible measurable demands. These substances include ceramics, polymers and metals. It is used in elevated temperature materials, aircraft and space structures, and space exploration. In this study, high temperature metals are classified including superalloys, platinum and refractory metals, refractory metals such as W, Nb, Mo, Ta. Also, ceramic materials are high temperature materials. Ceramics are criticized to use in elevated temperature due to their high hardness, extraordinary strength in compression, excellent thermal stability, short-term thermal extension and tremendously g...
SN Applied Sciences
Hot deformation behavior of a high-Nb-containing cast γ-TiAl-based Ti-45Al-8Nb (at.%) alloy has been investigated in the temperature range of 1000-1200 °C and the strain rate range of 0.5-0.005 s −1. The alloy shows an initial microstructure of coarse lamellar ((α 2 + γ) and (γ + γ)) colonies. The effect of strain rate and temperature domain on hot deformability of the alloy has been analyzed through a correlation between the apparent activation energy, deformation process maps, and associated microtextural development. The relatively higher apparent activation energy (Q = 553.8 kJ/mol) could be correlated with the fully lamellar α 2 + γ microstructure which posses greater resistance to the mobile dislocation. The results are further corroborated by the "instability-dominated" processing maps indicating poor hot deformability of the alloy in the studied temperature-strain rate range. Detailed electron microscopy of the deformed samples indicates that poor workability exhibited as cracks that are predominantly found at the coarse γ-TiAl grains situated at the lamellar boundaries. The crack initiation and propagation mechanisms during hot compression have further been discussed with reference to concurrent dynamic recrystallization. It has been found that "wedge-type" cavitation damage is prevalent during compressive deformation in the temperature range studied here. Such cracking behavior is elucidated in light of the "Semiatin-Seetharaman criterion.
Future Landscape of Structural Materials in India
Advanced high-temperature structural materials are expected to play an important role in realizing the aspirations related to the next-generation aerospace propulsion devices, thermal protection system of reusable launch vehicles and thermal/nuclear power reactors. Despite considerable amount of research conducted for developing new and more efficient high-temperature structural materials, the advancement is inadequate and warrants continued efforts to address several unresolved issues concerning synthesis and processing of new materials, related characterization and testing to evaluate and ensure desired performance, durability, reproducibility and reliability in simulated experiments and real-life condition and finally, upscaling the operation for large-scale commercially viable production. In this article, an attempt has been made to review the latest status and trend in developing high-temperature structural materials for aerospace and thermal/nuclear sectors and highlight the challenges associated with development and processing of such advanced structural materials. Keywords High-temperature structural material Á Thermal protection system Á Strength Á Microstructure Á Ceramic matrix composite Á Creep Á Oxidation Á Fatigue Á Sintering
Solidification of high Nb containing TiAl based alloys
International Journal of Cast Metals Research, 2009
Casting of titanium aluminides is an attractive processing route for production of near net shape components: turbocharger wheels, valves and aero-engine components are presently at the heart of casting developments. Among the casting alloys under consideration are a number of niobium rich TiAl based alloys that contain low boron additions for grain refinement and minor additions of other elements to enhance creep resistance. An essential condition that must be met to achieve grain refinement is a solidification pathway competed via b-(Ti), e.g. a pathway that avoids peritectic growth of a-Ti. In this contribution we describe the microsegregation analysis of a unidirectionally solidified sample from the ternary alloy Ti-45Al-8Nb. The corresponding solidification path is discussed on the basis of thermodynamic calculations and is shown to closely follow Scheil predictions with some amount of back-diffusion for aluminium. The analysis indicates that the nucleation undercooling for peritectic a (Ti) in the deep mushy zone is significant.
In and ex situ investigations of the β-phase in a Nb and Mo containing γ-TiAl based alloy
Intermetallics, 2008
In a -stabilised Ti-43Al-4Nb-1Mo-0.1B alloy (composition in atomic percent) the correlation between the occurrence of -phase and temperature was analyzed experimentally and compared to thermodynamic calculations. Results from in-situ high-energy X-ray diffraction, Manuscript texture measurements, heat-treatments, scanning electron microscopy, and temperaturedependent flow stress measurements were used to study the evolution of the -phase with temperature. Thermodynamic calculations based on the CALPHAD method were applied to correlate the phases developed in the -solidifying TiAl based alloy under investigation. This alloy is characterized by an adjustable -phase volume fraction at temperatures where hotwork processes such as forging and rolling are conducted. Due to a high volume fraction of phase at elevated temperatures the hot-extruded alloy can be forged under near conventional conditions.
Development of TiAl–Si Alloys—A Review
Materials, 2021
This paper describes the effect of silicon on the manufacturing process, structure, phase composition, and selected properties of titanium aluminide alloys. The experimental generation of TiAl–Si alloys is composed of titanium aluminide (TiAl, Ti3Al or TiAl3) matrix reinforced by hard and heat-resistant titanium silicides (especially Ti5Si3). The alloys are characterized by wear resistance comparable with tool steels, high hardness, and very good resistance to oxidation at high temperatures (up to 1000 °C), but also low room-temperature ductility, as is typical also for other intermetallic materials. These alloys had been successfully prepared by the means of powder metallurgical routes and melting metallurgy methods.
A review of very-high-temperature Nb-silicide-based composites
… Materials Transactions A, 2003
The temperatures of airfoil surfaces in advanced turbine engines are approaching the limits of nickelbased superalloys. Innovations in refractory metal-intermetallic composites (RMICs) are being pursued, with particular emphasis on systems based on Nb-Si and Mo-Si-B alloys. These systems have the potential for service at surface temperatures .1350 °C. The present article will review the most recent progress in the development of Nb-silicide-based in-situ composites for very-high-temperature applications. Nb-silicide-based composites contain high-strength silicides that are toughened by a ductile Nb-based solid solution. Simple composites are based on binary Nb-Si alloys; more complex systems are alloyed with Ti, Hf, Cr, and Al. In higher-order silicide-based systems, alloying elements have been added to stabilize intermetallics, such as Laves phases, for additional oxidation resistance. Alloying schemes have been developed to achieve an excellent balance of room-temperature toughness, high-temperature creep performance, and oxidation resistance. Recent progress in the development of composite processing-structure-property relationships in Nb-silicide-based in-situ composites will be described, with emphasis on rupture resistance and oxidation performance. The Nb-silicide composite properties will be compared with those of advanced Ni-based superalloys.