Microstructures and mechanical properties of Nb/Nb-silicide in-situ composites synthesized by reactive hot pressing of ball milled powders

To develop advanced structural materials at very high temperatures, ban mil ling followed by reactive hot pressing was employed to fabricate binary Nb/ Nb-silicide in-situ composites with 3.5 to 16 mol% silicon content. Changes in morphology during milling of niobium and silicon elemental powders were studied, and microstructures and mechanical properties of reactively hot p ressed composites were evaluated by OM, SEM, XRD, DTA and EPMA. No detectab le niobium silicide was formed during milling. Reactive hot pressing of the milled powders yields two kinds of silicides, Nb3Si and Nb5Si3, through in -situ reaction between heavily deformed niobium particles and fragmented si licon particles. DTA revealed that silicide formation occurs at 940 K for N b3Si and 1050 K for Nb5Si3. Fully dense Nb/Nb-silicide in-situ composites w ith equiaxed grain microstructures are produced by the reactive hot pressin g of milled powders. All of the composites exhibit considerable compressive ductility without cracking even at room temperature. Annealing at high tem perature results in growth of equiaxed grains of niobium and silicide, ther eby increasing high temperature strength.