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.

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.

Effective Fluorine Treatment for Improved High Temperature Oxidation Behavior of Novel Cu, Mo and Si Containing TiAl-Alloys

2014 ◽  
Vol 783-786 ◽  
pp. 1117-1122
Author(s):  
Alexander Donchev ◽  
M. Galetz ◽  
M. Schütze
Keyword(s):  
High Temperature ◽  
High Temperature Oxidation ◽  
Oxidation Behavior ◽  
Titanium Aluminides ◽  
Turbine Blades ◽  
Surface Region ◽  
Alumina Layer ◽  
Temperature Oxidation ◽  
Tial Alloys ◽  
High Temperature Oxidation Behavior

Intermetallic light weight TiAl-alloys are expected to replace the heavy Ni-based super alloys in several high temperature applications. However until now they cannot be used at temperatures above 700°C for longer times due to their insufficient oxidation resistance. The high temperature oxidation behavior can be improved drastically for the use at temperatures up to at least 1050°C by small amounts of fluorine in the surface region of TiAl-components. A thin protective alumina layer is formed after an optimized fluorine treatment during exposure in oxidizing high temperature environments. Results of isothermal and thermocyclic high temperature oxidation tests of untreated and halogen treated TiAl-samples of new types of TiAl-alloys containing Mo, Cu and Si will be presented in this paper. These results will be compared and discussed considering the beneficial effect of fluorine for a later use as e.g. turbine blades in jet engines. Key words: Titanium aluminides, high temperature oxidation, halogen effect,

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.

Microstructures and Properties of Refractory Niobium-Silicide-Based Composites

2005 ◽  
Vol 475-479 ◽  
pp. 737-740 ◽  
Author(s):  
Shi Yu Qu ◽  
Ya Fang Han ◽  
Liguo Song
Keyword(s):  
Solid Solution ◽  
High Temperature ◽  
Phase Structure ◽  
High Temperature Oxidation ◽  
Multicomponent System ◽  
Compression Tests ◽  
Two Phase ◽  
Temperature Oxidation ◽  
Al Content ◽  
Oxidation Rates

The microstructures, mechanical properties and oxidation resistance of the refractory Nb-silicide-based composites have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), compression tests and high-temperature oxidation experiments. The results showed that 1773K/100h heat-treatment was an optimum processing for acquiring equilibrium Nb solid solution and silicides microstructure. In the binary Nb-Si system, the microstructure consisted of continuous Nb5Si3 equilibrium matrix and dispersed Nb particles, while in the the Nb-Ti-Cr-Al-Si-(Hf) multicomponent system, there are two typical microstructures, i.e., a two-phase structure of β (Nb solid solution)+D81 Nb5Si3-type silicide in the alloys with the Si+Al content (15at.% and 6at.%, respectively), and a three-phase structure of β+D81 Nb5Si3-type + D88 Ti5Si3-type silicides in the alloys with lower Si+Al content (10at.% and 8at.%, respectively). The results of compression tests showed that all alloys display high strength at both room and high temperatures, only a slight decrease in compression properties occured for Nb-Ti-Cr-Al-Si alloys, comparing to the binary Nb-Si in-situ composites. This type of alloys possesses good high temperature strengths up to at least 1473K. The results of high-temperature oxidation experiments showed that the oxidation rates of the alloys with Ti, Cr, Al and Hf addition were at least one order of magnitude lower than those of the Nb-Si binary alloys.

Application of the Fluorine Effect to TiAl-Components

2008 ◽  
Vol 1128 ◽  
Author(s):  
A. Donchev ◽  
R. Pflumm ◽  
M. Schütze
Keyword(s):  
High Temperature ◽  
Oxide Scale ◽  
Mixed Oxide ◽  
Gas Flow ◽  
Turbine Blades ◽  
Oxidation Mechanism ◽  
Dynamic Resistance ◽  
Surface Zone ◽  
Alumina Layer ◽  
Temperature Oxidation

AbstractThe oxidation resistance of TiAl-alloys can be improved by several orders of magnitude by fluorine doping of the surface zone of the material. The oxidation mechanism changes from the formation of a thick mixed oxide scale to a protective alumina layer. This fluorine treatment influences only the surface region of the components so that the bulk properties are not affected. Recent results achieved with TiAl-components showed the potential of a fluorine treatment for the use of TiAl in several high temperature applications. Turbine blades for aero engines made of TiAl were treated with fluorine by different methods and their performance during high temperature oxidation tests in air is shown. Further on by selective local fluorination a structured oxide scale develops on TiAl above 800°C. A simple high temperature activation cause the formation of areas covered by a thin alumina layer alternating with a thick mixed oxide scale where no fluorine was applied before oxidation. The aim is to reproduce a shark-skin pattern (tiny parallel ridges) on the surface in order to minimize the aero dynamic resistance of turbine blades rotating in a gas flow. Different methods used for this attempt and the corresponding results are also presented.

Mechanical Properties and Oxidation Behavior of Si3N4/BN Laminated Ceramics

2007 ◽  
Vol 280-283 ◽  
pp. 1869-1872
Author(s):  
Cui Wei Li ◽  
Chang An Wang ◽  
Yong Huang
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Boron Nitride ◽  
Oxidation Behavior ◽  
Elevated Temperatures ◽  
Testing Procedure ◽  
No Oxidation ◽  
Temperature Oxidation ◽  
High Temperature Oxidation Behavior

Laminated ceramics with high mechanical properties were fabricated in the Si3N4/BN system. The mechanical properties at elevated temperatures were tested, and the oxidation behavior during tested procedure was studied at the same time. The flexure strength of the Si3N4/BN laminated ceramics changed a little below 1000°C. The displacement-load curves appeared non-linear characteristic even at high temperature. During testing procedure at high temperature, oxidation behavior of silicon nitride and silicon carbide happened, and no oxidation product of boron nitride was found. The silicon nitride layers were oxidized to form a protective silicate scale, which prevented oxidation of the boron nitride interlayers. The stability of boron nitride was beneficial to the boron nitride interlayer to partition the silicon nitride matrix layers at high temperature.

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