HIGH-TEMPERATURE BEHAVIOUR OF Ti-Al-Nb-Ta INTERMETALLICS (original) (raw)

Structure and High-Temperature Oxidation of Ti-Al-Nb and Ti-Al-Ta Intermetallics

Key Engineering Materials, 2011

Ti-Al based intermetallics are prospective high-temperature materials showing low weight combined with a relatively high strength, high creep resistance and good oxidation resistance at high temperatures. Beside Ti and Al, these materials commonly contain other additives modifying their properties. In the present work, structure and oxidation resistance of two Ti-Al-Nb and Ti-Al-Ta alloys are studied. The alloys are prepared by vacuum arc melting and oxidation is conducted in air at 800-1000°C. It is found that there are significant differences in the structure depending on the ternary additive. There are also differences in oxidation behavior and these differences are discussed in relation to oxidation mechanism.

Nb and B effect on mechanical properties of Ti–Al based intermetallic materials

Vacuum, 2019

Ti-TiAl 3 in-situ composites containing different percentages of Nb and B were effectively produced from Ti, Al, Nb and B powders by electric current assisted sintering (ECAS) technique which is a powder metallurgy processing method. Samples are sintered for 90 s with 2000 A current. The effect of B and Nb on the hardness, fracture toughness and wear resistance of samples were studied. The microstructure properties of the sintered samples were analysed with scanning electron microscopes (SEM), the phases in the samples were determined with XRD and their hardness and fracture toughness values were measured with a Vickers hardness tester with a load of 0.98 N and 98 N respectively. The highest fracture toughness value has been obtained with wt %10 Nb addition as 5.23 MPa m 1/2 , whereas the highest hardness was determined as 965 HV for wt%5 B reinforced in situ-Ti-TiAl 3 composite. Best wear resistance was obtained in the 47.5Ti-47.5Al-5B sample. While Nb additive had a negatory effect on wear resistance, additive B had a positive effect on wear resistance.

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

Structure of Ti–Al–Nb intermetallics produced by mechanical alloying and hot-pressing techniques

Materials Chemistry and Physics, 2003

Mechanical alloying and hot-pressing consolidation were applied for the manufacturing of γ-TiAl alloys with additions of 5, 10 and 15at.% Nb. The microstructure shows numerous twins within the γ-TiAl phase in the hot-pressed alloys. The grain size (about 0.5μm) is much smaller than in the cast alloys. Local chemical analysis indicates that Ti is preferentially replaced by Nb in all

Properties and structural characteristics of Ti–Nb–Al alloys

Materials Science and Engineering: A, 2005

The use of Al as an ␣ stabilizer in different Ti-Nb alloys has been investigated for its effect on some properties and changes in structural characteristics. Quenched alloys with 10-40% Nb and 2-15% Al were analyzed in terms of their phase transformations, as well as elastic modulus, density and internal friction. It was found that the rhombic distortion introduced in the ␣ -HCP phase transforms into another martensitic ␣ structure. Above 5% Al, metastable ␤-BCC is formed and eventually predominates. The appearance of another metastable phase, , was verified in alloys between 2 and 5% Al with less than 35% Nb. These structure transformations are a consequence of the obstructing effect of Al on the redistribution of Ti and Nb. The elastic modulus increases with Al and decreases with Nb percentage due to different developed structures, especially at lower Al content. Small fluctuations in the generally increasing variation of the density with Nb, for Al percentages, were attributed to the phase transformations. The internal friction was relatively large for the martensitic, ␣ or ␣ , structure but decreases significantly with the appearance of ␤ phase.

Hot Oxidation Resistance of an Intermetallic Nb-Ti-Al Alloy

MRS Proceedings, 1994

Structure, phase composition and air oxidation behavior in the temperature range 800 to 1400°C of a Nb-Ti-Al-based intermetallic alloy with the chemical composition (wt %): Nb-47.0; Ti-23.9; Al-21.0, V-4.4, and Cr-4.1 have been studied. The alloy structure is two-phase -σ (Nb2Al type) and γ (TiAl type). Preliminary air oxidation at 1400°C decreases the oxidation rate at 1150°C by a factor 2 to 3. It is connected with the formation of a protective scale (rutile and corundum with chromium and vanadium additions), refining of the alloy structure, and the formation of an internally oxidized underscale.

Enhancing the High Temperature Capability of Ti-Alloys

Steel Research International, 2012

Titanium is a widely used structural material for applications below approximately 5008C but right now it cannot be used at higher temperatures. Titanium forms a fast growing rutile layer under these conditions. Furthermore enhanced oxygen uptake into the metal subsurface zone leads to embrittlement which deteriorates the mechanical properties. To overcome this problem a combined Al-plus F-treatment was developed. The combination of Al-enrichment in the surface zone so that intermetallic Ti x Al y-layers are produced which form a protective alumina layer during high temperature exposure plus stabilization of the Al 2 O 3-scale by the fluorine effect led to significantly improved resistance against increased oxidation and embrittlement in high temperature exposure tests of several Ti-alloys. In this paper, the experimental procedures and achieved improvements are described. The results will be discussed for the use of Ti-alloys at elevated temperatures.

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.