X-ray measurements of faulting in Ag-Pd alloys

Abstract

A detailed study of X-ray line broadening has been made in severely cold-worked filings of pure Pd and five Ag-Pd alloys containing 20, 40, 60, 75, and 80 wt.% Pd. Debye-Scherrer line shapes recorded in a proportional counter diffractometer have been analyzed both by Fourier and integral breadth methods for the evaluation of effective particle sizes (D_e)_hkl and rms strains (<ε²>_hkl^½). It has been found that both (D_e)_hkl and <ε²>_hkl^½ are anisotropic and vary little with composition. The importance of faulting in the particle-size broadening could also be clearly observed. The intrinsic fault densities (α) estimated from peak shifts, although small, show a marked variation with solute content. Following Otte's analysis, intrinsic fault energies (γ) have been deduced using measured α, <ε²>_hkl^½, and available shear modulus values. γ values thus arrived at have been compared with those obtained for these alloys by Harris et al. using a texture method. It was concluded that interaction of d electrons has a marked influence in enhancing the fault energy values and consequently on the stability of the fcc structure. The increase in the number of s electrons from 0.6 to 1 per atom in alloys ranging in composition from 40% Pd to 0% Pd does not appear to affect γ value.