Enhancing the High Temperature Capability of Ti-Alloys (original) (raw)
Related papers
Combined Al- plus F-treatment of Ti-alloys for improved behaviour at elevated temperatures
Materials and Corrosion-werkstoffe Und Korrosion, 2011
Titanium is a widely used structural material because of its low specific weight, good mechanical properties and excellent corrosion resistance at ambient temperature. As a result of increased oxidation at elevated temperatures and environmental embrittlement the maximum operation temperature of standard Ti-alloys is only about 600 8C. The oxidation behaviour can be improved by different methods, e.g. coatings. This leads to an improvement which is, however, often limited. The combination of Al-enrichment in the sub surface zone, so that a TiAl-layer is formed, plus F-treatment gives impressively good results because a protective alumina scale is formed due to the fluorine effect. This alumina scale prevents oxygen inward diffusion which causes embrittlement and protects the material against environmental attack. The procedure is applied to alloys with a very low Al-content or even no Al at all. In the paper results of oxidation tests of a-Ti without any treatment, with Al-treatment and with a combination of Al-þ F-treatment are presented. Aluminium was diffused into the samples by a powder pack process. Fluorine was applied by a liquid phase process. The formation of an alumina scale on treated samples was revealed by post experimental investigations. The results are discussed referring to the fluorine effect model for TiAl-alloys.
Properties of Novel High Temperature Titanium Alloys for Aerospace Applications
MATEC Web of Conferences
The attractive combination of strength and low density has resulted in titanium alloys covering 15 to 25% of the weight of a modern jet engine, with titanium currently being used in fan, compressor and nozzle components. Typically, titanium alloys used in jet engine applications are selected from the group of near alpha and alpha-beta titanium alloys, which exhibit superior elevated temperature strength, creep resistance and fatigue life compared to typical titanium alloys such as Ti-6Al-4V. Legacy titanium alloys for elevated temperature jet engine applications include Ti-5Al-2Sn-2Zr-4Mo-4Cr, Ti-6Al-2Sn-4Zr-2Mo-0.1Si and Ti-4Al-4Mo-2Sn-0.5Si. Improving the mechanical behavior of these alloys enables improved component performance, which is crucial to advancing jet engine performance. As a world leader in supplying advanced alloys of titanium, nickel, cobalt, and specialty stainless steels, ATI is developing new titanium alloys with improved elevated temperature properties. These im...
Suppressing the oxygen ingress into Ti-alloys by a one-step Al- plus F-treatment
MATEC Web of Conferences, 2020
Oxygen ingress into technical Ti-alloys during high temperature exposure in oxygen containing environments leads to an enriched surface zone due to the high oxygen solubility in titanium. This affected zone is known as alpha case and is embrittled compared to the substrate material. Therefore, the operating temperature of these alloys is limited. An enrichment of Al in the surface zone of Ti-alloys leads to an improvement by the formation of intermetallic TixAly-phases with decreased oxygen solubility. This one-step Al-enrichment plus a F-treatment is proposed for the formation of a continuous stable alumina scale which prevents oxygen inward diffusion. In this paper the results of high temperature exposure tests in air of technical Ti-alloys are presented without any treatment and treated with Al-enrichment including fluorination. Post experimental investigations such as SEM reveal the formation of thin alumina layers on treated samples. Hardness measurements confirm that no embrit...
Intermetallics, 2021
Current limitations to a wider use of intermetallic TiAl alloys in aircraft and automotive engines arise from an insufficient oxidation resistance at temperatures above approximately 800°C. In this paper, the high temperature oxidation behavior of three engineering -TiAl-based alloys at 900°C in air is reported. The performance of the TNM alloy (Ti-43.5Al-4Nb-1Mo-0.1B), the 4822 alloy (Ti-48Al-2Cr-2Nb), and the Nb-free IRIS alloy (Ti-48Al-2W-0.08B) is compared (all chemical compositions are given in at.%). During testing in air non-protective mixed oxide scales developed on all untreated samples, but with different compositions and thicknesses. These different oxide layers are characterized and their formation mechanisms are discussed. The presence of W in the IRIS alloy leads to a better oxidation behavior compared to untreated TNM and 4822. This behavior was changed in the direction of a protective alumina layer formation via the so-called "fluorine effect". The above-mentioned alloys were treated with fluorine via a liquid phase process by evenly spraying a fluorine containing polymer on all faces of the specimens. The oxidation resistance of the fluorine treated samples was significantly improved compared to the untreated specimens. Due to the fluorination all treated test coupons exhibited slow oxidation kinetics. The results of isothermal as well as thermocyclic exposure tests are presented and discussed in the view of the chemical composition and processing conditioned microstructure of the three investigated γ-TiAl-based alloys. Keywords A. intermetallics (aluminides, silicides) B. oxidation C. coatings F. microscopy, various G. aero-engine components; automotive uses, including engines (and other transportation uses) Highlights Comparison of the engineering γ-TiAl-based alloys TNM, 4822 and IRIS with regard to their oxidation resistance Positive effect of W in the IRIS alloy is leading to reduced spallation Improvement of the oxidation resistance for all tested technical γ-TiAl-based alloys via the fluorine effect No effect of the different microstructures and chemical compositions on the fluorine effect efficiency Possible application at high temperatures above 800°C after a fluorine treatment
Origin of high temperature oxidation resistance of Ti–Al–Ta–N coatings
Surface and Coatings Technology, 2014
Alloying Ti-Al-N coatings with Ta has proven to enhance their hardness, thermal stability, and oxidation resistance. However, especially for arc-evaporated Ti-Al-TaN coatings only limited information on the detailed influence of the elements on various properties is available. Therefore, we have developed arc-evaporated Ti 1-x-y Al x Ta y N coatings with various Al (x = 0.50-0.65) and Ta (y = 0.00-0.15) contents. While the thermal stability of our coatings during annealing in inert He atmosphere increases with increasing Ta content, best results are obtained for specific Ta-Al ratios during oxidation. Single phase cubic Ti 0.32 Al 0.60 Ta 0.08 N yields a mass-gain of only ~5 % after 5 h at 950 °C in synthetic air, whereas Ti 0.35 Al 0.65 N is completely oxidized after 15 min. This is in part based on the suppressed anatase and direct rutile TiO 2 formation at a defined Ta-Al content. Consequently, the anatase-to-rutile transformation, generally observed for Ti 1-x Al x N, is absent. This reduces the generation of pores and cracks within the oxide scale and especially at the nitride-oxide interface, leading to the formation of a protective rutile and corundum based oxide scale. This is also reflected in the pronounced decrease in activation energy for the protective scale formation from 232 kJ/mol for Ti 0.35 Al 0.65 N down to 14.5 kJ/mol for Ti 0.32 Al 0.60 Ta 0.08 N. Based on our results we can conclude that especially phase transformations within the oxide scale need to be suppressed, as the connected volume changes lead to the formation of cracks and pores.
Effect of oxidation resistant Al3Ti coating on tensile properties of a near α-Ti alloy
Surface and Coatings Technology, 2013
Near α Ti-alloys are used in compressor parts of advanced gas turbines engines at temperatures up to about 600°C. Long term high temperature exposure of these alloys in air is expected to degrade their mechanical properties and limit their life and/or performance. Therefore, an appropriate oxidation resistant coating may be necessary to protect such alloys during high temperature use. The present study examines the effect of oxidation resistant Al 3 Ti coating deposited through pack aluminizing method on the tensile properties of a near α alloy called Titan 29A. Tensile properties have been evaluated at RT and 600°C after exposing the coated tensile samples (up to 2000 h) at 650°C in air. The RT ductility of the alloy was severely affected after oxidation exposure despite the presence of the coating. However, the ductility at 600°C was much less affected. The strength of the coated alloy after the oxidation exposure largely remained unchanged at both the above temperatures. The effect of oxidation exposure on the mechanical properties of the coated near α alloy has been correlated with microstructural and fractography observations.
Oxidation protection behaviour of titanium aluminide coatings developed by TIG technique
Advances in Materials and Processing Technologies, 2015
Titanium alloys are attractive in aerospace applications for low density and good mechanical properties but they have poor in oxidation and wear resistance. A coating layer of titanium aluminide can mitigate these problems to some extent and make the alloys suitable for hot structure applications. This paper discusses the formation of titanium aluminide coatings on commercial purity titanium (CPTi) surfaces by melting a pre-placed aluminium and titanium powder mixture, using a tungsten inert gas (TIG) welding torch. Depending on powder composition and energy input, the resolidified melt layer produced a single phase 2-Ti 3 Al or a dual phase 2 and -TiAl microstructures of lamellar or columnar dendritic types. The microhardness varied from 400 to 600 Hv based on the distribution within the microstructure. Testing the resistance to oxidation, by heating and cooling through nine cycles at 750 0 C for a total of 100 h in air, gave a weight gain of 1.00 mg cm-2 for the 2-Ti 3 Al coating compared to 2.60 mgcm-2 for the CPTi specimen. The dual phase coating showed much improved oxidation resistance with a weight gain of 0.35 mg cm-2 after exposure at similar conditions.
Effect Of Nb, Cr And W On The High Temperature Oxidation Behavior Of Ti-Al Alloys
2011
This research is focused on intermetallic TiAl and their oxidation behavior for structural materials at high temperatures in automotive, aerospace and gas turbine industries. However, the commercial application of Ti-Al is currently limited by their insufficient oxidation resistance at temperature above 700-850oC. The addition of alloying elements such as Nb, Cr and W is significant in producing good Ti-Al alloys for high temperature applications. Ti-Al alloys were fabricated using arc- melting furnace. Then the phases present, microstructure evaluation and hardness test were characterized using XRD, FESEM/EDX and Vikers hardness
Intermetallics, 2013
The interest for TiAl intermetallic alloys is growing in the last years because of their excellent ratio between mechanical properties and density. However, the application is restricted at temperatures up to 873e973 K by the resistance to oxidation. For this reason it is of great importance to study protective coatings able to raise its temperature of performance above 1073 K. A TiAl 3 layer was obtained on the surface of TieAl intermetallic samples, depositing an Al coating by arc Physical Vapour Deposition, followed by a thermal treatment. The microstructure and the composition of the coating were characterised before and after the thermal treatment by Scanning Electron Microscopy, X-Ray Diffraction, Focused Ion Beam and Glow Discharge Optical Emission Spectroscopy. The mechanical behaviour of the thermal treated layer was investigated by means of scratch tests and nanoindentation. Oxidations at 1123 K were carried out on coated and uncoated samples, in order to study the effect of the coating on the oxidation resistance of the samples. The aluminide coating provides a protection against oxidation in air at the considered temperatures due to its ability to form a continuous Al 2 O 3 scale on the surface. The TiAl 3 layer phase transformations occurring during high temperature exposition were also investigated.