The critical resolved smear stress of peak-aged aluminium-lithium single crystals

The critical resolved shear stress (CRSS) of single crystals of aluminium-r ich aluminium-lithium alloys has been measured at 283 K. These alloys are s trengthened by coherent precipitates of the metastable Ll(2) long-range-ord ered delta' phase. The specimens had been subjected to long aging treatment s such that they were in the peak-aged state. This contrasts with the earli er investigation (Schlesier and Nembach, Acta metall. mater., 1995, 43, 398 3) in which underaged AI-LI single crystals have been studied. The contribu tion tau(p) of the delta' precipitates to the present peak-aged specimens' total CRSS has been found to be a function only of the delta' volume fracti on f, i.e. tau(p) was independent of the radius of the delta' precipitates. The experimental data tau(p)(f) are well represented by a relation which h ad been developed for the description of peak-aged gamma'-strengthened nick el-base superalloys. These latter materials are isomorphous to delta'-stren gthened Al-rich Al-Li alloys: coherent Lit long-range-ordered particles are embedded in a disordered f.c.c. matrix. (C) 1999 Acta Metallurgica Inc. Pu blished by Elsevier Science Ltd. All lights reserved.