3D ATOM PROBE INVESTIGATION OF PRECIPITATION IN THE Al-Sc-Zr SYSTEM

摘要

Three dimensional atom probe has been applied to investigate the non-isothermal nucleation and growth of Sc- and Zr-containing dispersoids in Al-Zr-Sc ternary alloys. A non-isothermal approach of diffusion has been developed in order to account for the diffusion of solute elements during the heating ramp. In the early stages of precipitation (at 560K), a high number density of Sc-rich clusters first form. Then, these clusters transform to Al_3Sc spherical shaped particles, which exhibit a L1_2 structure already at 623K. At the end of the heating ramp, Al_3Sc particles display a cuboiedal morphology. When Zr diffusion is activated (i.e. above 623K), Zr atoms are found to segregate to Al_3Sc/α-Al matrix interfaces. Finally, isothermal annealing at 748K induces the formation of an Al_3Zr_(0.4)Sc_(0.6) compound around former Al_3Sc particles, therefore giving a duplex core/shell structure to the dispersoids. These experimental observations are discussed based on thermodynamical and diffusion aspects.