Materials Development Research (original) (raw)
2015
The advantages of gamma TiAl-based alloys including their specific modulus, specific high-temperature strength and oxidation resistance make them attractive candidates as high-temperature structural materials in the automotive, aerospace and power industries. Currently most attention is paid to the alloys of the third and fourth generations. However, this type of alloys contains relatively high amounts of refractory metals such as Nb and Ta. The high melting points of these metals (2477 and 3017) °C are problematic for the preparation of these products with the conventional casting, because it is necessary to use higher temperatures and thus, generally, longer total melting times. This may result in increased oxygen amounts in the products and in decreased mechanical properties. The use of Nb-Al and Ta-Al master alloys for the preparation of the resulting Ti-Al-Nb and Ti-Al-Ta alloys is highly suitable because of the reduction in the temperature during melting. This article describes the preparation of selected master alloys Nb-60Al and Ta-80Al (x/%) with the melting points of about 1600-1650 °C using plasma melting. The optimum conditions for the preparation of these master alloys (current density, feed speed, distribution and size of charge) were characterised in order to maximise the purity and homogeneity. The prepared alloys were studied with light microscopy (LM), backscattered scanning electron microscopy (BSE), energy-dispersive spectrometry (EDS), and the melting temperature was evaluated with a differential thermal analysis (DTA). Keywords: intermetallics, plasma melting, microstructure, differential thermal analysis (DTA) Prednost zlitin na osnovi gama Ti-Al je v specifi~nem modulu, specifi~ni visokotemperaturni trdnosti in odpornosti proti oksidaciji, kar jih dela zanimive za izdelavo visokotemperaturnih komponent v avtomobilski industriji, letalstvu in energetiki. Sedaj se najve~pozornosti namenja zlitinam tretje ali ~etrte generacije. Ta vrsta zlitin vsebuje relativno veliko koli~ino ognjevarnih kovin, kot sta Nb in Ta. Visoko tali{~e teh materialov (2477 in 3017) °C ote`uje izdelavo teh zlitin s klasi~nim ulivanjem, ker je treba uporabiti vi{je temperature in s tem dalj{e ~ase taljenja. To lahko povzro~i pove~anje vsebnosti kisika v proizvodih in poslab{anje mehanskih lastnosti. Uporaba predzlitin Nb-Al in Ta-Al za izdelavo zlitin Ti-Al-Nb in Ti-Al-Ta je zelo primerna zaradi zni`anja temperature pri taljenju. ^lanek opisuje pripravo izbranih predzlitin Nb-60Al in Ta-80Al (x/%) s tali{~em okrog 1600-1650 °C s taljenjem v plazmi. Za maksimiranje ~istosti in homogenosti so bili dolo~eni optimalni pogoji za pripravo teh predzlitin (gostota, hitrost dodajanja, razporeditev in velikost zatehte). Pripravljene zlitine so bile preiskane s svetlobno mikroskopijo (LM), vrsti~no elektronsko mikroskopijo s povratno sipanimi elektroni (BSE), energijsko disperzijsko spektroskopijo (EDS), temperatura taljenja pa je bila dolo~ena z diferen~no termi~no analizo (DTA). Klju~ne besede: intermetalne zlitine, taljenje s plazmo, mikrostruktura, diferen~na termi~na analiza (DTA)
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.
A Process for Production of a Niobium-containing TiAl Based Alloy
Canadian Metallurgical Quarterly, 2010
A new generation of turbine engines based on titanium aluminides may be commercially manufactured if these materials could be produced more cheaply and more easily. In the present work, challenges faced during the production of a g-TiAl-based alloy (Ti-48Al-2Cr-2Nb-1B (at%) including the evaporation of aluminum and the formation of niobium-rich inclusions were studied and a set of recommendations has been proposed to overcome them. It was found that TiAl and Nb 3 Al are appropriate master alloys to produce an alloy with a controllable chemical composition and a microstructure free from inclusions without a need for any extra melting processes. A two stage mechanism was found to be responsible for chemical composition variation during the production of the alloy using elemental raw materials: a sharp aluminum loss in the first melting and a moderate one in the second and third melting processes. The first stage can be avoided by using master alloys. It was demonstrated that mechanical properties of an alloy produced after an appropriate heat treatment is comparable to alloys produced by other methods. Prevention of extra melting times has a strong impact on economics and commercialization of these materials. Résumé-On pourrait fabriquer de façon commerciale une nouvelle génération de moteurs à turbine basés sur les aluminures de titane si l'on pouvait produire ces matériaux plus économiquement et plus facilement. Dans le présent travail, on a étudié les défis rencontrés lors de la production d'un alliage basé sur le g-TiAl (Ti-48Al-2Cr-2Nb-1B at%), incluant l'évaporation de l'aluminium et la formation d'inclusions riches en niobium et l'on a proposé une série de recommandations pour les surmonter. On a trouvé que le TiAl et le Nb 3 Al étaient des alliages maîtres appropriés pour la production d'un alliage à composition chimique contrôlable et à microstructure libre d'inclusions sans le besoin de procédés supplémentaires de fusion. On a trouvé qu'un mécanisme à deux étapes était responsable de la variation de la composition chimique lors de la production de l'alliage utilisant des matériaux élémentaires, bruts: une perte élevée d'aluminium lors de la première fusion et une perte modérée lors du deuxième et du troisième procédé de fusion. On peut éviter la première étape en utilisant des alliages maîtres. On a démontré que les propriétés mécaniques d'un alliage fabriqué après un traitement thermique approprié étaient comparables aux alliages produits par d'autres méthodes. L'absence de temps supplémentaire de fusion a un impact important sur l'économie et la commercialisation de ces matériaux.
High temperature materials: properties, demands and applications
Chemical Industry
High-temperature materials are used in a wide range of industries and applications such as gas turbine engines for aircrafts, power and nuclear power plants, different types of furnaces, including blast furnaces, some fuel cells, industrial gas turbines, different types of reactors, engines, electronic and lighting devices, and many others. Demands for high-temperature materials are becoming more and more challenging every year. To perform efficiently, effectively and at the same time to be economically viable, the materials used at high temperatures must have certain characteristics that are particularly expected for applying under such extreme conditions, for example, the strength and thermal resistance. In the present review, some important requirements that should be satisfied by high temperature materials will be discussed. Furthermore, the focus is put on refractory concretes, ceramics, intermetallic alloys, and composites as four different categories of these materials, which...
Cold-pressing and vacuum arc melting of γ-TiAl based alloys
Advanced Powder Technology, 2019
Beta (b) solidifying c-TiAl intermetallic alloys of nominal composition Ti-48Al, Ti-48Al-2Nb, Ti-48Al-2Nb-0.7Cr alloys have been cold pressed and vacuum arc melted. The Al loss was due to compaction method used prior to the melting technique, since it was evident after compaction that Al particles migrated to the surface in contact with the die facets after cold pressing. Electron backscatter diffraction (EBSD)orientation mapping demonstrated that the a-precipitation from the parent b-phase follows the Blackburn orientation relationship (BOR). Microstructural characterization of the alloys was studied by scanning electron microscopy (SEM) equipped with energy dispersion spectroscopy (EDS) for microanalysis. X-ray diffraction (XRD) technique was used to detect phase compositions.
Processing and Properties of Nb-Ti-Based Alloys
Superalloys 1992 (Seventh International Symposium), 1992
The processing characteristics, tensile properties, and oxidation response of two Nb-Ti-Al-Cr alloys were investigated. One creep test at 650°C and 172 MPa was conducted on the base alloy which contained 40Nb-40Ti-lOAl-1OCr. A second alloy was modified with 0.11 at. % carbon and 0.07 at. % yttrium. Alloys were arc melted in a chamber backfilled with argon, drop cast into a water-cooled copper mold, and cold rolled to obtain a 0.8~mm sheet. The sheet was annealed at 1100°C for 0.5 h. Longitudinal tensile specimens and oxidation specimens were obtained for both the base alloy and the modified alloy. Tensile properties were obtained for the base alloy at room temperature, 400, 600, 700, 800, 900, and 1000°C, and for the modified alloy at room temperature, 400, 600, 700, and 8OOOC. Oxidation tests on the base alloy and modified alloy, as measured by weight change, were carried out at 600, 700, 800, and 900°C. Both the base alloy and the modified alloy were extremely ductile and were cold rolled to the final sheet thickness of 0.8 mm without an intermediate anneal. The modified alloy exhibited some edge cracking during cold rolling. Both alloys recrystallized at the end of a 0.5-h annealing treatment. The alloys exhibited moderate strength and oxidation resistance below 600°C, similar to the results of alloys reported in the literature. The addition of carbon produced almost no change in either the yield strength or ductility as measured by total elongation. A small increase in the ultimate tensile strength and a corresponding decrease in the reduction of area below 600°C were observed. Carbon addition also served to marginally refine the grain size after annealing. The results of this study and those of similar alloys reported in the literature suggest that 40Nb-40Ti-lOAl-1OCr forms a good base alloy suitable for alloying for improvement in its oxidation and high-temperature strength properties.
Integration of Hot Isostatic Pressing and Heat Treatment for Advanced Modified γ-TiAl TNM Alloys
Materials
The conventional processing route of TNM (Ti-Nb-Mo) alloys combines casting and Hot Isostatic Pressing (HIP) followed by forging and multiple heat treatments to establish optimum properties. This is a time-consuming and costly process. In this study we present an advanced alternative TNM alloy processing route combining HIP and heat treatments into a single process, which we refer to as IHT (integrated HIP heat treatment), applied to a modified TNM alloy with 1.5B. A Quintus HIP lab unit with a quenching module was used, achieving fast and controlled cooling, which differs from the slow cooling rates of conventional HIP units. A Ti-42.5Al-3.5Nb-1Mo-1.5B (at.%) was subjected to an integrated two HIP steps at 200 MPa, one at 1250 °C for 3 h and another at 1260 °C for 1 h, both under a protective Ar atmosphere and followed by cooling at 30 K/min down to room temperature. The results were compared against the Ti-43.5Al-3.5Nb-1Mo-0.8B (at.%) thermomechanically processed in a conventional...
Materials, 2019
Intermetallic γ-TiAl based alloys are innovative lightweight structural high-temperature materials used in aerospace and automotive applications due to already established industrial-scale processing routes, like casting and hot-working, i.e., forging. A promising alternative method of production, regarding manufacturing of near net-shape components, goes over the powder metallurgy route, more precisely by densification of TiAl powder via spark plasma sintering. In this study, gas atomized powder from the 4th generation TNM alloy, Ti-43.5Al-4Nb-1Mo-0.1B (in at.%), was densified and the microstructure was investigated by means of electron microscopy and X-ray diffraction. The sintered microstructure exhibits lamellar α2-Ti3Al /γ-TiAl colonies surrounded by globular γ- and ordered βo-TiAl phase. The coarse lamellar spacing stems from the low cooling rate after densification at sintering temperature. Against this background, subsequent heat treatments were designed to decrease the lame...
Hot-working behavior of an advanced intermetallic multi-phase γ-TiAl based alloy
Materials Science and Engineering: A, 2014
Microstructure and phase evolution of a β-solidifying Ti-43Al-4Nb-1Mo-0.1B alloy with minor C and Si Deformation study within a temperature range of 1150-1300 °C and a strain rate regime of 0.005-0.5 s -1 Strain-resolved constitutive modeling of the flow behavior up to a true deformation of 0.9 Surface fitting approach of flow curve data via a hyperbolic-sine law Processing maps in correlation with metallographic post-analysis Complementary information, i.e. phase fractions and texture, from in situ HEXRD experiments Critical discussion of experimental difficulties in performing hot-deformation tests -2 / 18 -ABSTRACT New high-performance engine concepts for aerospace and automotive application enforce the development of lightweight γ-TiAl based alloys with increased high-temperature capability above 750 °C. Besides an increased creep resistance, the alloy system must exhibit sufficient hot-workability. Therefore, a refined βsolidifying TNM alloy with an alloy composition of Ti-43Al-4Nb-1Mo-0.1B (in at.%) and minor additions of C and Si is investigated by means of uniaxial compressive hot-deformation tests. The occurring mechanisms during hot-working were decoded by ensuing constitutive modeling of the flow curves by a phase field region-specific surface fitting approach via a hyperbolic-sine law as well as by evaluation via processing maps combined with microstructural post-analysis. Furthermore, complementary in situ high energy X-ray diffraction experiments give a deeper insight about the deformation behavior of the alloy, i.e. phase fractions and texture evolution during isothermal and non-isothermal compression.
Intermetallics, 2008
Microstructure and mechanical properties of gas-tungsten-arc (GTA)-welded Ti-15V-3Cr-3Sn-3Al alloy in direct current electrode negative mode are characterized. The thermal profile was measured during welding with continuous current (CC) and pulsed current (PC) at different frequencies. A single-step postweld aging of the welded samples at subtransus temperature was attempted to study precipitation of alpha phase. Two different morphologies of alpha phase are observed along with a partitioning of alloying elements into the two phases. Processing conditions for higher strength are identified and correlated with the thermal profile. Microstructure changes due to postweld heat treatment were characterized.