A PROPOSED MECHANISM FOR THE STRENGTHENING OF SAP-TYPE ALLOYS

摘要

Wrought materials produced from sintered and extruded flake metal powders (SAP-type alloys) containing a finely dispersed stable second phase possess enhanced elevated temperature properties. Based upon an extension of the re?sults found previously by Ansell and Weertman of NRL in. investigating the creep properties of the MD 2100 aluminum SAP-type alloy, it is proposed that the extrusion process causes motion of the grain boundaries, sweeping dislocation sources into the vicinity of the second phase, where they are pinned in place and no longer active. Since high stresses are necessary to nucleate dislocations from other than normal dislocation sources, the observed higher yield strengths and lower ductility common to these alloys are to be expected. The SAP-type alloys therefore are not dispersion hardened alloys in the usual sense, since normal dislocation sources in these alloys would -be active, with the dispersed second phase acting only to hinder dislocation movement. If the manufacturing process of the SAP-type alloys were adjusted so that only some of the dislocation sources were pinned, it is assumed that alloys with high temperature tensile prop?erties superior to those of the normal dispersion hardened alloys could be obtained without extreme loss of ductility.