Development of Directionally Solidified Eutectic Nickel and Cobalt Alloys.

摘要

Investigations to develop an isotropically ductile high temperature eutectic alloy first focused on identifying the cubic (gamma +alpha) phase field and the cubic plus (gamma +sigma) phase field within the quaternary systems,Ni-Cr-W-Al. Nickel alloys containing O-15 w/o W, 2 w/o Al,and nominally 40 w/o Cr were shown to consist of a nickel-rich lamellar solid solution matrix saturated with tungsten and chromium,and aligned chromium rich lamellae containing nickel-rich Widmanstatten precipitate. Alloys containing 18 w/o W however consisted of a nickel-rich lamellar matrix and aligned sigma phase,identified by X-ray diffraction as approximately Cr8Ni5W. The attainment of significant low temperature ductility was found to be limited by the low ductility of sigma phase as previously observed for all multicomponent Ni-Cr-W-Al and Ni-Co-Cr-W-Al alloys containing 18 w/o W. Directionally solidified alloys with fully aligned gamma +alpha and gamma +sigma microstructures exhibited respectively either insufficient values of strength or ductility compared with conventional superalloys to be worthy of further development in this program. To meet the program objectives,alloys derived from the Ni3Al-Mo (gamma' -alpha) eutectic identified by us previously were selected for further investigation and optimization. Aluminum modifications of the pseudo-binary eutectic,gamma' -alpha,yielded ductile/ductile,gamma'/gamma -alpha aligned composite microstructures.