New X-Ray Technique to Characterize Nanoscale Precipitates in Aged Aluminum Alloys
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JMEPEG (2017) 26:4732–4737 DOI: 10.1007/s11665-017-2915-0
New X-Ray Technique to Characterize Nanoscale Precipitates in Aged Aluminum Alloys V.D. Sitdikov, M. Yu. Murashkin, and R.Z. Valiev (Submitted November 22, 2016; in revised form August 7, 2017; published online September 6, 2017) This paper puts forward a new technique for measurement of x-ray patterns, which enables to solve the problem of identification and determination of precipitates (nanoscale phases) in metallic alloys of the matrix type. The minimum detection limit of precipitates in the matrix of the base material provided by this technique constitutes as little as 1%. The identification of precipitates in x-ray patterns and their analysis are implemented through a transmission mode with a larger radiation area, longer holding time and higher diffractometer resolution as compared to the conventional reflection mode. The presented technique has been successfully employed to identify and quantitatively describe precipitates formed in the Al alloy of the Al-Mg-Si system as a result of artificial aging. For the first time, the x-ray phase analysis has been used to identify and measure precipitates formed during the alloy artificial aging. Keywords
aging, Al-Mg-Si alloy, precipitation, x-ray diffraction
1. Introduction X-ray phase analysis (XPA) is the most information rich, nondestructive integral method to determine a phase composition of metallic materials (Ref 1-3). In the context of the described technique, the identification of certain crystalline phases is based on the correlation between inherent interplanar spacing values d, the corresponding line intensities I derived from an experimental x-ray pattern and the values stored in diffractometric databases (for example, ICDD PDF-2). Thus, to perform a qualitative or quantitative phase analysis, it is necessary to identify the peaks related to the given phase or a set of phases during the measurement of x-ray patterns. Qualitative or quantitative XPA on the basis of the conventional measurement of x-ray patterns typically presents certain difficulties, if the content of observed secondary phases is below 3%, and their size constitutes less than 500 nm (Ref 47). The intensity of secondary phase peaks under these conditions is limited and cannot be seen in x-ray patterns due to a minor correlation of signal/noise peaks related to these phases. Thus, for example, retained austenite can be identified in steel only if its content is above 1%, and cementite is seen in x-ray patterns if its volume ratio equals to no less than several percent (Ref 4). In (Ref 5, 7, 8), the increase in the primary beam intensity, extension of the exposure time, the use of a parabolic monochromator have led to the identification of similar types of precipitates with a volume fraction of 1%,
V.D. Sitdikov, M.Yu. Murashkin, and R.Z. Valiev, Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, Ufa, Russia 450000; and Laboratory for Mechanics of Bulk Nanomaterials, Saint Petersburg State University, Sai
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