An xhyphen;ray diffraction study of lattice imperfections in coldhyphen;worked facehyphen;centeredhyphen;cubic alloys. VI. Copperhyphen;aluminum (agr; phase)

摘要

Following earlier approaches in this series of work, detailed xhyphen;ray peakhyphen;shift, peakhyphen;asymmetry, and peakhyphen;broadening analyses have been performed on the xhyphen;ray diffraction line profiles obtained from coldhyphen;worked filings of five compositions of Cuhyphen;Al alloys in the fcc phase, namely, Cuhyphen;3.7, 6.7, 12.3, 14.9, and 18.4 at.thinsp;percnt; Al. The analysis reveals an increased presence of stacking faults of an intrinsic nature, primarily responsible for the observed peak shift and domain size peak broadening. A very small presence of extrinsic stacking faults accounts for the observed asymmetry in the profiles, and the twin faults are nearly absent. The effective particle sizes decrease and microstrains increase with increasing solute concentration, and these are anisotropic in nature. An estimation of dislocation density rgr; and stacking fault energy ggr; for the alloys was also made which tends to predict a reasonably good value of ggr;0(27 mJ/m2) for pure copper. Annealing experiments on three alloys with an increased concentration of solute Al do not clearly reveal any detectable evidence of solute segregation at the stacking faults, as in the earlier case with fcc Aghyphen;Al.