Preparation of Extinction Free Gamma Ti-51at.%Al Alloy Powder and Characterization by X-ray Diffraction
Stoner, Troy A.
Fox, Alan G.
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The lattice parameters, structure factors, and Debye-Waller temperature factor of a homogenized, binary Ti-51at.%Al intermetallic alloy were determined using powder X-ray diffraction (XRD). Previous studies have been hampered by extinction at low Bragg angles, therefore improved powdering methods were implemented. The powder was produced by pulverizing lathe turnings taken from the sample ingot using a ceramic mortar and pestle. then the powder was passed through a U.S. Standard 400 sieve mesh (38 microns). After further grinding a new acoustical sieving procedure was performed where powder particles were passed through a 2000 line per inch sieve mesh (5-7 microns). Next the powder was annealed to relieve induced stress produced during grinding. An X-ray diffraction study was conducted for Bragg angles 10-140 deg. The L1 structured TiAl lattice parameters of a =4.002 and c=4.081 were determined using XRD peak positions. the resulting c/a ratio equalled 1.02. The measured integrated intensities of the fundamental reflections were used to determine a Debye-Waller temperature factor of B=0.65 using the Wilson method. these values were determined to be accurate based on comparison to previous research and theoretical approximations. The effects of extinction at low angles were not completely avoided with the refined powder particle size however, they were significantly reduced.
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