EVALUATION OF THE INTERMETALLIC COMPOUND AL2TI FOR ELEVATED-TEMPERATURE APPLICATIONS

Al2Ti is a stable intermetallic phase being investigated for elevated- temperature applications. The density of Al2Ti measured by helium pycn ometry is 3.53-3.54 g cm(-3), in excellent agreement with the density of 3.530 g cm(-3) calculated from X-ray diffraction data. Compression testing was performed on samples of as-cast, cast and hot isostaticall y pressed (cast and HIPed), and powder-processed materials in argon be tween 25 and 1000 degrees C. The yield strength of powder-processed Al 2Ti at 400 degrees C is approximately 1000 MPa, decreasing to about 50 0 MPa at 800 degrees C, over six times greater than the yield strength of cast Al2Ti over this same temperature range. Oxidation testing was performed on samples of Al2Ti in the same three material conditions a t 815 degrees C (1500 degrees F) and 982 degrees C (1800 degrees F) us ing thermogravimetric analysis (TGA). The weight gain after 100 h at 8 15 degrees C was about 1.0 mg cm(-2) for the cast and cast and HIPed m aterial conditions, comparable to those reported for TiAl and Al2Ti at this temperature. The weight gain for powder-processed Al2Ti was only 0.15 mg cm(-2) after 100 h at 815 degrees C. The thermal expansion of A1,Ti was measured by thermomechanical analysis. The coefficient of t hermal expansion varied from approximately 12 x 10(-6) degrees C-1 at 200 degrees C to 16 x 10(-6) degrees C-1 at 900 degrees C.