Growth mechanisms of grain boundary allotriomorphs in Al-4Pct Cu at high homologous temperatures: Interfacial vs direct volume diffusion

Abstract

The lengthening and thickening kinetics of θ allotriomorphs in Al-4 pet Cu were measured at 350°, 400°, and 450°C. Three different analyses all indicated that interfacial diffusion (i.e., a right angle collector plate mechanism) was the predominant growth mechanism at 350° and 400°C, but that volume diffusion directly to the growing allotriomorphs made a significant contribution to growth at 450°C. Using the data of this and previous investigations one may conclude that volume diffusion of solute directly to the allotriomorph does not contribute noticeably to growth belowT/T (solidus) = 0.78, plays a substantial but still a minority role atT/T (solidus) = 0.84 and 0.90 and becomes the major contributor atT/T (solidus) ≥ 0.91 when the matrix is fee.