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8 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Oxidation Kinetics of Cast TiAl3

The isothermal oxidation kinetics of the TiAl3 compound over a wide temperature range is documented, and these rates are related to exclusive alpha-Al2O3 scale growth. The specific weight change vs time curves are shown. Two abnormalities are immediately apparent. One is that a rapid initial uptake of oxygen occurs at times less than 5 h, followed by a lower oxidation rate at longer times, for tests at 900 C and below. The other is that the final weight changes for the 700, 800, and 900 C tests are not in the sequence expected with respect to temperature. Isothermal oxidation of drop cast TiAl above 1000 C was found to exhibit parabolic oxidation controlled by protective alpha-Al2O3 scale formation. TiAl is the only phase in the binary Ti-Al system that forms exclusive scales of alpha-Al2O3 in isothermal oxidation. High anomalous rates at short times and at temperatures below 1000 C resulted from the internal oxidation of a second phase of aluminum.

Smialek, J. L.↗
DOE OSTI2020

Materials Data on TiAl3 by Materials Project

Al3Ti is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ti is bonded to twelve Al atoms to form TiAl12 cuboctahedra that share corners with four equivalent TiAl12 cuboctahedra, corners with eight equivalent AlTi4Al8 cuboctahedra, edges with eight equivalent TiAl12 cuboctahedra, edges with sixteen equivalent AlTi4Al8 cuboctahedra, faces with four equivalent TiAl12 cuboctahedra, and faces with fourteen AlTi4Al8 cuboctahedra. There are four shorter (2.72 Å) and eight longer (2.88 Å) Ti–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded to four equivalent Ti and eight equivalent Al atoms to form AlTi4Al8 cuboctahedra that share corners with four equivalent AlTi4Al8 cuboctahedra, corners with eight equivalent TiAl12 cuboctahedra, edges with twenty-four AlTi4Al8 cuboctahedra, faces with six equivalent TiAl12 cuboctahedra, and faces with twelve AlTi4Al8 cuboctahedra. All Al–Al bond lengths are 2.88 Å. In the second Al site, Al is bonded to four equivalent Ti and eight Al atoms to form AlTi4Al8 cuboctahedra that share corners with twelve equivalent AlTi4Al8 cuboctahedra, edges with eight equivalent TiAl12 cuboctahedra, edges with sixteen AlTi4Al8 cuboctahedra, faces with four equivalent TiAl12 cuboctahedra, and faces with fourteen AlTi4Al8 cuboctahedra. All Al–Al bond lengths are 2.72 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiAl3 by Materials Project

Al3Ti is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ti is bonded to twelve equivalent Al atoms to form TiAl12 cuboctahedra that share corners with twelve equivalent TiAl12 cuboctahedra, edges with twenty-four equivalent AlTi4Al8 cuboctahedra, faces with six equivalent TiAl12 cuboctahedra, and faces with twelve equivalent AlTi4Al8 cuboctahedra. All Ti–Al bond lengths are 2.81 Å. Al is bonded to four equivalent Ti and eight equivalent Al atoms to form AlTi4Al8 cuboctahedra that share corners with twelve equivalent AlTi4Al8 cuboctahedra, edges with eight equivalent TiAl12 cuboctahedra, edges with sixteen equivalent AlTi4Al8 cuboctahedra, faces with four equivalent TiAl12 cuboctahedra, and faces with fourteen equivalent AlTi4Al8 cuboctahedra. All Al–Al bond lengths are 2.81 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiAl3 by Materials Project

Al3Ti is Magnesium-derived structured and crystallizes in the orthorhombic Pmm2 space group. The structure is three-dimensional. Ti is bonded to two equivalent Ti and ten Al atoms to form TiTi2Al10 cuboctahedra that share corners with eight equivalent AlTi4Al8 cuboctahedra, corners with ten equivalent TiTi2Al10 cuboctahedra, edges with two equivalent TiTi2Al10 cuboctahedra, edges with sixteen AlTi4Al8 cuboctahedra, faces with four equivalent TiTi2Al10 cuboctahedra, and faces with sixteen AlTi4Al8 cuboctahedra. Both Ti–Ti bond lengths are 2.84 Å. There are a spread of Ti–Al bond distances ranging from 2.83–2.85 Å. There are three inequivalent Al sites. In the first Al site, Al is bonded to four equivalent Ti and eight Al atoms to form AlTi4Al8 cuboctahedra that share corners with eight equivalent TiTi2Al10 cuboctahedra, corners with ten equivalent AlTi4Al8 cuboctahedra, edges with four equivalent TiTi2Al10 cuboctahedra, edges with fourteen AlTi4Al8 cuboctahedra, faces with four equivalent TiTi2Al10 cuboctahedra, and faces with sixteen AlTi4Al8 cuboctahedra. There are two shorter (2.84 Å) and six longer (2.86 Å) Al–Al bond lengths. In the second Al site, Al is bonded to four equivalent Ti and eight Al atoms to form AlTi4Al8 cuboctahedra that share corners with eighteen AlTi4Al8 cuboctahedra, edges with eight equivalent TiTi2Al10 cuboctahedra, edges with ten AlTi4Al8 cuboctahedra, faces with four equivalent TiTi2Al10 cuboctahedra, and faces with sixteen AlTi4Al8 cuboctahedra. There are a spread of Al–Al bond distances ranging from 2.81–2.85 Å. In the third Al site, Al is bonded to two equivalent Ti and ten Al atoms to form AlTi2Al10 cuboctahedra that share corners with eighteen AlTi4Al8 cuboctahedra, edges with four equivalent TiTi2Al10 cuboctahedra, edges with fourteen AlTi4Al8 cuboctahedra, faces with eight equivalent TiTi2Al10 cuboctahedra, and faces with twelve AlTi4Al8 cuboctahedra. Both Al–Al bond lengths are 2.84 Å.

36 MATERIALS SCIENCE↗
NASA NTRS1974

Environmental protection of titanium alloys at high temperatures

Various concepts were evaluated for protecting titanium alloys from oxygen contamination at 922 K (1200 F) and from hot-salt stress-corrosion at 755 K (900 F). It is indicated that oxygen-contamination resistance can be provided by a number of systems, but for hot-salt stress-corrosion resistance, factors such as coating integrity become very important. Titanium aluminides resist oxygen ingress at 922 K through the formation of alumina (on TiAl3) or modified TiO2 (on Ti3Al, TiAl) scales. TiAl has some resistance to attack by hot salt, but has limited ductility. Ductile Ti-Ni and Ti-Nb-Cr-Al alloys provide limited resistance to oxygen ingress, but are not greatly susceptible to hot-salt stress-corrosion cracking.

Wright, I. G.↗
NASA NTRS1982

Control of interface reactions in SIC/TI composites

The reaction between a 0.5 to 1.0 Al film and a thick Ti substrate to form TiAl3 occurs very rapidly on heating to 635 C and causes the Al to be confined to the surface region. After heating to 900 C Ti3Al is formed with little release of Al into alpha Ti. Further annealing at 900 C eventually causes the Ti3Al phase to decompose and a substantial amount of Al is released into alpha Ti. The interdiffusion coefficient for Al in alpha Ti at 900 C increases by less than one order of magnitude as Al is varied from 0 to 20 at %. These data were obtained from the (101) X-ray diffraction intensity band using polycrystalline samples. Improvements in the analysis of X-ray diffraction data for the determination of composition profiles are discussed.

Houska, C. R.↗
NASA NTRS1983

Reactions and diffusion between an Al film and a Ti substrate

The reaction between a 0.5 to 1.0 micron Al film and a thick Ti substrate to form TiAl3 occurs very rapidly on heating to 635 C and causes the Al to be confined to the surface region. After heating to 900 C, Ti3Al is formed with little release of Al into alpha-Ti. Further annealing at 900 C eventually causes the Ti3Al phase to decompose and a substantial amount of Al is released into alpha-Ti. The interdiffusion coefficient for Al in alpha-Ti at 900 C was found to increase by less than one order of magnitude as Al is varied from 0 to 20 at. pct. These data were obtained from the (101) X-ray diffraction intensity band using polycrystalline samples. Improvements in the analysis of X-ray diffraction data for the determination of composition profiles are discussed.

Rao, V. B.↗
NASA NTRS1990

Cyclic oxidation of aluminide coatings on Ti3Al+Nb

A number of pack aluminide coatings were produced on fiber-reinforced Ti3Al+Nb composites and were compared for their protection effect in cyclic oxidation at 982 C. It was found that pack aluminizing of Ti3Al+Nb can successfully produce an oxidation resistant TiAl3 coating which forms alpha-Al2O3 scales. These coatings offer a substantial improvement over the uncoated matrix material in 982 C cyclic oxidation. Coating cracks were found to contribute to degradation of thick coatings.

Smialek, James L.↗