X-Ray diffraction line profile analysis on the microstructure of cold-worked face-centered cubic Cu-Ge-Si alloys: Effect
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S.K. P R A D H A N , Senior Research Fellow, and M. DE, Senior Lecturer, are with the Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Calcutta 700032, India. Manuscript submitted September 6, 1988. METALLURGICAL TRANSACTIONS A
were characterized by evaluating different defect parameters, namely, intrinsic ( a ' ) , extrinsic (a"), and twin or growth (/3) fault probabilities, change in lattice parameter (Aa/ao), dislocation densities (p), domain sizes (D), stacking fault energy (30, etc. from peak shift, peak asymmetry, and peak broadening analyses of the recorded profiles for all the alloy compositions investigated. The accuracies of these parameters lie within the respective ranges, as evaluated earlier, tSj Peak shift, peak asymmetry, and peak broadening analyses have been done following the same procedure as adopted earlier, t4,51and the results are shown in Figure 1 and Tables I and II. From a comparative study of the values of change in lattice parameter A a / a o and net deformation stacking fault density (a} obtained from peak shift analysis (Table I) and the plots of lattice parameter ahu VS extrapolation function cos 0 cot 0, it reveals, as in the earlier cases, [~-SJ that (a) is primarily responsible for shifting the peaks. The asymmetry parameters, (4.5 a" + /3), are found to increase with increasing solute concentration (Table I), contrary to the earlier observation with the Cu-Mn-Si system, t4J Figure 1, showing the plots of (a) against electron atom ratio ( e / a ) for Cu-lGe-Si, Cu-lSi-Ge, Cu-Ge, ~91Cu-Si, I1~ and Cu-Ge-Si t6] alloys, depicts the effects of dilute solutes Si and Ge compared to the other binary and ternary alloy systems, as shown in Figure 1. Notable observations are (1) addition of 1 wt pct Si to binary Cu-Ge t91 enhances the fault concentration (a} to a considerable extent, with a decreasing tendency at higher Ge concentration, and (2) addition of 1 wt pct Ge to binary Cu-Si t~~ influences (a) less significantly, which closely resembles the a variations of Cu-Si ~1~and concentrated Cu-Ge-Si t61 alloys. The results of the present investigation have also been studied in light of the observations of Foley et al.t6~ on the occurrence of (t~) values for the concentrated ternary Cu-Ge-Si alloys. The present alloy compositions approach the curved mixed-phase boundary lying close and parallel to Si-rich or Ge-rich edges of the isothermal diagram. [6] The alloys investigated have average solute contents of 5.5, 7.4, and 9.5 at. pct. O f these, the ct values for the alloys with 5.5 and 7.4 at. pct of total solute vary with increasing Ge concentration, in accordance with the observation of Foley et al., t61 showing peaks at about 50/50 S i / G e ratio, which is associated with the curved mixed-phase (fcc a phase and hcp ~"phase) boundary and the related influence of the free energy difference, t6] However, for the Cu-lGe-Si alloy with total solute content of 9.5 at. pet and a higher S i / G e ratio (Si 9.6 at. pct, Ge - 0.8 at. pct), the a value f
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