Alloy design of Nb₅Si₃ composite with a fine lamellar structure for ultra-high temperature application

Ultra-high temperature material with both high temperature strength and room temperature toughness is pursued by controlling microstructure of an alloy based on a niobium silicide. The alloy of interest consists of an intermetallic Nb₅Si₃ phase as the matrix, having excellent high temperature strength, and ductile Nb primary solid solution phase being dispersed in the matrix to impart some room temperature toughness. A fine lamellar microstructure consisting of these two phases can be obtained by utilizing the eutectoid decomposition of high-temperature phase Nb₃Si, the control of lamellar spacing is attempted by selection of heat treatment condition by which overall mechanical properties can be chosen as desired. It is found that a coarser lamellar microstructure shows better room temperature compressive plastic deformability as well as higher elevated temperature strength. The alloys investigated in this study show superior compressive strength at over 1300 K as compared with some commercial Ni-base superalloys.