High Temperature Oxidation Protection of Multi-Phase Mo-Containing TiAl-Alloys by the Fluorine Effect

2012 ◽  
Vol 1516 ◽  
pp. 95-100 ◽  
Author(s):  
Alexander Donchev ◽  
Raluca Pflumm ◽  
Svea Mayer ◽  
Helmut Clemens ◽  
Michael Schütze
Keyword(s):  
High Temperature ◽  
Oxidation Resistance ◽  
Titanium Aluminides ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Temperature Oxidation ◽  
Tial Alloys ◽  
Β Phase ◽  
Multi Phase ◽  
The Impact

ABSTRACTIntermetallic titanium aluminides are potential materials for application in high temperature components. In particular, alloys solidifying via the β-phase are of great interest because they possess a significant volume fraction of the disordered body-centered cubic β-phase at elevated temperatures ensuring good processing characteristics during hot-working. Nevertheless, their practical use at temperatures as high as 800°C requires improvements of the oxidation resistance. This paper reports on the fluorine effect on a multi-phase TiAl-alloy in the cast and hot-isostatically pressed condition at 800°C in air. The behavior of the so-called TNM material (Ti-43.5Al-4Nb-1Mo-0.1B, in at %) was compared with that of two other TiAl-alloys which are Nb-free and contain different amounts of Mo (3 and 7 at%, respectively). The oxidation resistance of the fluorine treated samples was significantly improved compared to the untreated samples. After fluorine treatment all alloys exhibit slow alumina kinetics indicating a positive fluorine effect. Results of isothermal and thermocyclic oxidation tests at 800°C in air are presented and discussed in the view of composition and microstructure of the TiAl-alloys investigated, along with the impact of the fluorine effect on the oxidation resistance of these materials.

Comparison of Fluorination Treatments to Improve the High Temperature Oxidation Resistance of TiAl Alloys in SO2 Containing Environments

2010 ◽  
Vol 638-642 ◽  
pp. 1374-1378 ◽  
Author(s):  
Patrick J. Masset ◽  
Rossen Yankov ◽  
Andreas Kolitsch ◽  
Michael Schütze
Keyword(s):  
High Temperature ◽  
Sulfur Dioxide ◽  
Ion Implantation ◽  
Oxide Scale ◽  
Oxidation Resistance ◽  
High Temperature Oxidation ◽  
Titanium Aluminides ◽  
Temperature Oxidation ◽  
Tial Alloys ◽  
Plasma Immersion Ion Implantation

Surfaces of titanium aluminides were treated by fluorine either physically using Plasma Immersion Ion Implantation (PI³) or chemically with a F-based polymer. By controlling the fluorination parameters, both treatments improve the oxidation resistance even in the presence of sulfur dioxide (0.1 vol%). No sulfur was detected in the oxide scale although thermodynamic calculations predict the formation of sulfides. The inward diffusion of oxygen and nitrogen in the alloy was found to be reduced in the presence of SO2.

Comparison of Different Fluorine-treatments for Improved High Temperature Oxidation Resistance of TiAl-alloys

2011 ◽  
Vol 1295 ◽  
Author(s):  
A. Donchev ◽  
M. Schütze ◽  
A. Kolitsch ◽  
R. Yankov
Keyword(s):  
High Temperature ◽  
Oxidation Resistance ◽  
Elevated Temperatures ◽  
Fluorine Content ◽  
Intermediate Formation ◽  
Experimental Investigations ◽  
Alumina Layer ◽  
Temperature Oxidation ◽  
Tial Alloys ◽  
Al Content

ABSTRACTIntermetallic TiAl-alloys can replace the heavier Ni-based superalloys in several high temperature applications with regards to their mechanical properties, however they can not be used at temperatures above 800°C in oxidizing environments for longer times because of insufficient oxidation resistance. Despite an Al-content of about 45 at.% in technical alloys, no protective alumina layer is formed because the thermodynamic stabilities of titanium oxide and aluminum oxide are of the same order of magnitude. Therefore a mixed TiO2/Al2O3-scale is formed which is fast growing so that the metal consumption rate is quite high. On the other hand the formation of a slow growing alumina layer is promoted by a fluorine treatment. This so called fluorine effect leads to the preferential intermediate formation of gaseous aluminum fluorides at elevated temperatures if the fluorine content at the surface stays within a defined concentration range. These fluorides are converted into solid Al2O3 due to the high oxygen partial pressure of the high temperature service environment forming a protective pure Al2O3 surface scale. In this paper results of high temperature oxidations tests of several technical TiAl-alloys will be presented. Different F-treatments e.g. dipping or spaying which are easy to apply have been used and their results will be compared. The mass change data of the F-treated specimens are always lower than those of the untreated ones. Post experimental investigations such as light microscopy, scanning electron microscopy and energy dispersive X-ray analysis reveal the formation of a thin alumina layer on the F-treated samples after optimization of the process while a thick mixed scale is found on the untreated samples. The results will be discussed in view of an optimized procedure and the future use of TiAl-components in high temperature environments.

scholarly journals Phase Transition and Ordering Temperatures of TiAl-Mo Alloys Investigated by In Situ Diffraction Experiments

2010 ◽  
Vol 654-656 ◽  
pp. 456-459 ◽  
Author(s):  
Thomas Schmoelzer ◽  
Svea Mayer ◽  
Frank Haupt ◽  
Gerald A. Zickler ◽  
Christian Sailer ◽  
...  
Keyword(s):  
Ternary Phase ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Ternary Phase Diagram ◽  
High Energy ◽  
The Body ◽  
Alloying Element ◽  
Tial Alloys ◽  
Β Phase

Intermetallic TiAl alloys with a significant volume fraction of the body-centered cubic β-phase at elevated temperatures have proven to exhibit good processing characteristics during hot-working. Being a strong β stabilizer, Mo has gained importance as an alloying element for so-called β/γ-TiAl alloys. Unfortunately, the effect of Mo on the appearing phases and their temperature dependence is not well known. In this work, two sections of the Ti-Al-Mo ternary phase diagram derived from experimental data are shown. These diagrams are compared with the results of in-situ high-temperature diffraction experiments using high-energy synchrotron radiation.

The effect of thermal exposure on precipitation of Ti3Al(C,N) in Ti-48Al-IV-0.2C

1992 ◽  
Vol 50 (1) ◽  
pp. 22-23
Author(s):  
W.T. Donlon ◽  
W.E. Dowling ◽  
C.E. Cambell ◽  
J.E. Allison
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Titanium Aluminides ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Weight Ratio ◽  
Thermal Exposure ◽  
Treatment Temperature ◽  
Field Samples ◽  
Structural Applications

Titanium aluminides are attractive candidates for high temperature structural applications because of their high strength to weight ratio at elevated temperatures. The microstructure of these alloys consists of γ-TiAl (distorted L10 structure) , plus α2-Ti3Al (ordered DO19 structure). Varying the heat treatment temperature and cooling rate of these alloys alters the volume fraction and distribution of the γ and α2 phases. This has significant effects on the room temperature ductility. In addition, precipitation of carbides has been observed during high temperature exposure. The effect of these precipitates on the mechanical properties has yet to be determined.Figure 1 shows the general microstructure that was used for this investigation. TEM foils were prepared by electropolishing using 5% perchloric, 35% 1-butanol, 60% methanol at -40°C. No precipitates were found following heat treatment in the γ+α phase field. Samples approximately 20 mm square were thermally exposed to temperatures between 625° and 1000°C for times between 1 and 2000 hours.

High Temperature Oxidation in Multicomponent Nb Alloys

2005 ◽  
Vol 475-479 ◽  
pp. 717-720 ◽  
Author(s):  
E. Sarath K. Menon ◽  
Madan G. Mendiratta
Keyword(s):  
High Temperature ◽  
Oxidation Resistance ◽  
Elevated Temperatures ◽  
Material System ◽  
Silicon Alloys ◽  
Temperature Oxidation ◽  
Multiphase Alloys ◽  
Temperature Capability ◽  
New Generation ◽  
Poor Oxidation Resistance

Niobium-Silicon alloys offer potential as a new generation of refractory material system that could meet the high-temperature capability envisaged to exceed the application temperatures of Ni base superalloys. A serious concern in the application of Nb based alloys is their poor oxidation resistance at elevated temperatures. The ternary diagram Nb-Ti-Si system exhibits eutectic groves nearly parallel to the Nb-Ti binary and terminate in a Class II invariant reaction, L+(Nb,Ti)3Si → β+ (Ti,Nb)5Si3. A peretectic ridge from the reaction, L+(Nb,Ti)5Si3 →(Nb,Ti)3Si also exists and these reactions control the microstructures resulting from solidification of these Nb alloys. The microstructures associated with these alloys comprise a distribution of Nb5Si3 in β matrix. The effect of various alloying elements on the resulting microstructures are illustrated The effect of microstructural distribution on oxidation resistance of multiphase alloys are also discussed.

The Use of Fluorine to Protect β-Solidifying γ-TiAl-Based Alloys against High-Temperature Oxidation

MRS Advances ◽  
2017 ◽  
Vol 2 (25) ◽  
pp. 1361-1367
Author(s):  
Alexander Donchev ◽  
Mathias Galetz ◽  
Svea Mayer ◽  
Helmut Clemens ◽  
Michael Schütze
Keyword(s):  
High Temperature ◽  
Titanium Aluminides ◽  
Elevated Temperatures ◽  
Turbine Blades ◽  
Nominal Composition ◽  
Hot Workability ◽  
Two Phase ◽  
Alumina Layer ◽  
Temperature Oxidation ◽  
Al Content

ABSTRACTLight-weight alloys based on intermetallic titanium aluminides (TiAl) are structural materials considered for high-temperature applications, e.g. in aero engines or automotive engines. TiAl alloys of engineering interest consist of two phases, the γ-TiAl and the α2-Ti3Al-phase. Recent developments have led to the so-called TNM alloys (T = TiAl; N = Nb; M = Mo) with an Al-content of 43.5 at.%. These alloys also possess the disordered body centered cubic β-Ti(Al)-phase at elevated temperatures, which ensures a better hot-workability compared to conventional two-phase alloys. However, the relatively low Al content (< 45 at.%) limits the high-temperature capability due to reduced oxidation resistance. This impedes their application in a temperature range above 800°C. The present work shows how the fluorine effect counteracts this disadvantage due to the formation of a protective alumina layer. The performance of the TNM alloy with the nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (at.%) is compared with another TNM alloy variant containing additional elements, such as Si and C, and the so-called GE alloy (Ti-48Al-2Cr-2Nb; at.%), which is already in use for turbine blades. The results of isothermal and thermocyclic high-temperature exposure tests of untreated and fluorine treated specimens will be compared. The effect of composition and microstructure of the alloys on the oxidation behavior with and without fluorine treatment are discussed.

Hot-die Forging of a β-stabilized γ-TiAl Based Alloy

2008 ◽  
Vol 1128 ◽  
Author(s):  
Wilfried Wallgram ◽  
Helmut Clemens ◽  
Sascha Kremmer ◽  
Andreas Otto ◽  
Volker Güther
Keyword(s):  
Mechanical Properties ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Small Deformation ◽  
High Volume ◽  
Compression Tests ◽  
Tial Alloys ◽  
Β Phase ◽  
Heat Treated ◽  
Hot Die Forging

AbstractBecause of the small “deformation window” hot-working of γ-TiAl alloys is a complex and difficult task and, therefore, isothermal forming processes are favoured. In order to increase the deformation window a novel Nb and Mo containing γ-TiAl based alloy (TNM™ alloy) was developed. Due to a high volume fraction of β-phase at elevated temperatures the alloy can be hot-die forged under near conventional conditions, which means that conventional forging equipment with minor and inexpensive modifications can be used. With subsequent heattreatments balanced mechanical properties can be achieved. This paper summarizes our progress in establishing a “near conventional” forging route for the fabrication of γ-TiAl components. The results of lab scale compression tests and forging trials on an industrial scale are included. In addition, the mechanical properties of forged and heat-treated TNM™ material are presented.

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