X-ray powder diffraction analysis of the phase composition of α- and near-α-titanium alloys

Titanium alloys are widely used as materials for the elements of nuclear power plants, which are subject to high reliability requirements. The goal of the study is to develop X-ray diffraction analysis of the phase composition of α - and near- α -titanium alloys. Surface treatment of the samples of titanium alloys PT-3V, PT-7M and VT1-0 was carried out by mechanical, electrochemical polishing and chemical etching. It is shown that PT-3V and PT-7M alloys are characterized by a mixed structure consisting of α - and α ’-phases with precipitation of submicron particles of the β -phase along the grain boundaries. The results of X-ray diffraction analysis of the samples obtained on an X-ray diffractometer Shimadzu XRD-7000 (Cu K α radiation) were compared with the data of metallography and electron microscopy. It is shown that the results of X-ray diffraction analysis strongly depend on the method, quality and duration of the surface treatment of the samples. Electrochemical polishing and acid treatment reduce the width of diffraction peaks and lead to a more pronounced manifestation of their «fine» structure thus demonstrating the presence of at least two crystalline phases in the alloys. «Splitting» of the main X-ray peaks of titanium is a consequence of the fine structure of primary X-ray radiation ( K α 1,2 -doublet). Presence of «fine» structure of X-ray peaks and correlation between the intensities of different peaks appears to depend essentially on the mode and quality of surface treatment of the titanium alloy thus reducing the reliability of quantitative analysis of the phase composition of titanium alloys without verification of the results by direct methods of studying alloy structure.