As-cast microstructures and solidification paths of the Nb–Si–Ti ternary alloys in Nb_5Si_3–Ti_5Si_3region

摘要

The as-cast microstructures and solidification paths of the Nb–Si–Ti ternary alloys in the Nb5Si3–Ti5Si3region were investigated.Since there exist some isomorphous compounds in the Nb5Si3–Ti5Si3region,such as aNb5Si3with B3Cr5prototype,bNb5Si3with Si3W5prototype,cNb5Si3with Mn5Si3prototype,and Ti5Si3with Mn5Si3prototype,the primary solidification areas of these compounds were not typically indentified in previous experiments.In the present paper,the microstructure observation,the phase identification,and the composition measurement were performed using scanning electron microscopy(SEM),X-ray diffraction(XRD),and electron probe microanalysis(EPMA),respectively.No ternary compound is found.There exist three primary solidification areas,bNb5-x(Ti)x Si3,aNb5-x(Ti)x Si3,and Ti5-x(Nb)x Si3in the Nb5Si3–Ti5Si3region.Together with the literaturereported experimental data and optimization results,the liquidus projection of the whole Nb–Si–Ti ternary system is constructed,and totally ten primary solidification areas—diamond-Si,Nb1-x(Ti)x Si2,Ti1-x(Nb)x Si2,Ti1-x(Nb)x Si,Ti5-x(Nb)x Si4,bNb5-x(Ti)x Si3,aNb5-x(Ti)x Si3,Ti5-x(Nb)x Si3,(Nb,Ti)3Si,and BCC—and nine transitional invariant reactions—L?Nb1-x(Ti)x Si2?Ti1-x(Nb)x Si2?Si,L?Nb1-x(Ti)x Si2?Ti1-x(Nb)x Si2?Ti5-x(Nb)x Si4,L?Ti5-x(Nb)x Si4?Ti1-x(Nb)x Si2?Ti1-x(Nb)x Si,L?bNb5-x(Ti)5Si3?Nb1-x(Ti)x Si2?Ti5-x(Nb)x Si4,L?bNb5-x(Ti)x Si3?aNb5-x(Ti)x Si3?Ti5-x(Nb)x Si4,L?aNb5-x(Ti)x Si3?Ti5-x(Nb)x Si3?Ti5-x(Nb)x Si4,L?aNb5-x(Ti)x Si3?bNb5-x(Ti)x Si3?Ti5-x(Nb)x Si3,L?bNb5-x(Ti)x Si3?Ti5-x(Nb)x Si3?(Nb,Ti)3Si,and L?(Nb,Ti)3Si?Ti5-x(Nb)x Si3?BCC—are confirmed.