X-Ray Diffraction of Nonmetallic Phases Chemically Extracted from Columbium Alloys

The identification of non-metallic phases occurring in a metallic matrix cannot always be accomplished by standard methods of X-ray diffraction analysis. Separation of the nonmetallic phases from the matrix by chemical extraction, with subsequent X-ray diffraction analysis allows identification of the nonmetallic phases without the problems associated with X-ray analysis of bulk samples.In one study of alloy carbide dispersions in columbium, X-ray diffraction of the bulk samples could adequately identify the carbides present, but it was only by studying the chemically extracted residues that an important oxygen gettering effect of one of the alloy additions was discovered. In another study, X-ray diffraction work on extraction residues of Cb-Zr alloys showed evidence of a double oxygen gettering effect producing two distinct oxides. In the built sample, some of the diffraction lines produced by one of these oxides were masked by the tines of the columbiurn matrix. Therefore, only by use of an extraction technique were these two oxides identifiable by X-ray diffraction. In a Cb–10Ti–10Mo alloy, X-ray diffraction was used to study the nature of the sub scale formed during oxidation of the alloy. At least two nonmetallic phases were found. By using chemical extraction techniques, the phase responsible for the formation of the subscale was identified as TiO.These studies demonstrate some of the advantages of the chemical extraction techniques for obtaining samples of nonmetallic phases for study by X-ray diffraction.