An X-ray determination of the thermal expansion of α-phase Ag–Al alloys at high temperatures

Abstract

The lattice expansion of four Ag-AI alloys of different composition has been determined by X-ray measurements. The alloys, which contain 5-8, 9.2, 15.8 and 18.2 at.% AI, have been investigated in the temperature range 303-928 K. ~av for the four compositions are 20-41, 19.69, 19.93 and 20-37 x 10 6 K-1Relatively few measurements of thermal expansion exist for alloys (both binary and ternary) and therefore a programme has been undertaken to study the lattice expansion of copper-and silver-based alloys (De, 1969;Halder & Sen Gupta, 1974, 1975 and semiconducting materials (De & Sen Gupta, 1982) at high temperatures by an X-ray diffraction method.Four Ag-AI alloys containing 5"8, 9.2, 15.8 and 18.2 at.% AI were prepared from spectroscopically pure Ag and AI (metals supplied by Johnson Matthey and Co., Ltd, London). Accurately weighed quantities of the constituent metals were placed in graphite crucibles which were sealed under vacuum in quartz capsules. The melting was done in a muffle furnace and the capsules were constantly shaken. The resultant ingots were then homogenised by keeping the capsules at 873 K for ten days. The lattice parameters of the ingots were determined from diffractometer tracings of the annealed powders, obtained by hand-filling the ingots and sieving the powders through a 325 mesh screen, and heat-treated at 773 K for 8 h in evacuated quartz tubes. The actual compositions of the alloys were determined by interpolating these values of lattice parameters from the lattice parametercomposition curve obtained by Foote & Jette (1940). A portion of the annealed powders was then sealed in thinwalled quartz capillaries (internal diameter --,0.3 mm) and X-ray photographs were taken with a standard Unicam 19 cm high-temperature powder camera using Cu K~t radiation. Each photograph was followed by duplicate runs to show reproducibility of the data within the range of experimental error. The temperatures of the camera and furnace were measured accurately within +_ 2 K with the help ofa Pt-PtRh thermocouple, previously calibrated by measuring the lattice parameters of pure silver (Quader & Dey, 1962). The line positions were accurately measured at least three times each from the high-angle edges of the films, using an optical device (Rich, Seifert and Co., Hamburg) with a precision of 0.1 mm. To minimize systematic errors in the measurements, lattice parameters were obtained by using the Nelson & Riley (1945) extrapolation function and the precision in the values of the lattice parameters was found to be within _+ 0.0004 A. Table 1 contains mean values of the lattice parameters obtained from two sets of photographs for each temperature for four Ag-AI alloys in the temperature range 303-928 K. The initial and final room-temperature lattice-parameter values (also shown in Table 1) show that there is no appreciable loss of solute AI during repeated heat treatment. The lattice parameters increase non-linearly with temperature and from least-squares fits of the experimental data the coefficients of line...

An X-ray determination of the thermal expansion of α-phase Cu–Al alloys at high temperature

“…Similar behaviour of lattice expansion has been observed earlier in Ag-Ga (Halder & Sen Gupta, 1974), Cu-Ga (Halder & Sen Gupta, 1975) and Ag-Al' (Pradhan & De, 1986) systems. The dependence can be expressed analytically from a leastsquares fit of the experimental data by the following relations:…”

“…1. The values of a are found to decrease almost linearly with increasing temperature for all four alloy compositions in a manner similar to the ~ vs temperature variation for the Ag-A1 alloy system (Pradhan & De, 1986). This sort of variation of ~ with temperature for binary Cu-AI and Ag-A1 (Pradhan & De, 1986) alloys appears to differ from those of pure Cu, Ag and A1 for which values increase with increasing temperature (Pathak & Vasavada, 1970).…”

“…In continuation of our earlier study on high-temperature lattice expansion of Ag-A1 alloys in the f.c.c, phase by X-ray diffraction (Pradhan & De, 1986) the present investigation is concerned with high-temperature lattice expansion of four alloys of Cu-AI in the solid-solution range in connection with its industrial importance. These measurements form part of a programme recently undertaken to study the hightemperature thermal expansion behaviour of some copperand silver-based alloys (De, 1969;Halder & Sen Gupta, 1974, 1975Pradhan & De, 1986) and semiconducting compounds (De & Sen Gupta, 1982) for which no thermal expansion data are available in the literature but which are considered to be of importance to theoreticians and also to the electronics industry.…”

“…These measurements form part of a programme recently undertaken to study the hightemperature thermal expansion behaviour of some copperand silver-based alloys (De, 1969;Halder & Sen Gupta, 1974, 1975Pradhan & De, 1986) and semiconducting compounds (De & Sen Gupta, 1982) for which no thermal expansion data are available in the literature but which are considered to be of importance to theoreticians and also to the electronics industry.…”

“…The final compositions were determined by lattice-parameter measurements from diffractometer tracings of the annealed powders and subsequently confirmed by atomic absorption spectroscopy (Varion, BD 1475). X-ray photographs at different temperatures were taken in the standard Unicam 19 cm high-temperature camera using Cu Ka radiation and the lattice parameters were determined to an accuracy of +0.0004 ,~ following the method of procedure adopted earlier (Pradhan & De, 1986). The actual values of the lattice parameters are the mean values obtained from two sets of measurements for each temperature for all four alloy compositions in the temperature range 303-923 K.…”