A comparison study of microstructure and mechanical properties of Ti-24Al-14Nb-3V-0.5Mo with and without Si

Abstract

A comparative study has been made of the room-and elevated-temperature tensile properties, roomtemperature fracture toughness, fatigue-crack propagation rates, and 650 ЊC creep properties of Ti24Al-14Nb-3V-0.5Mo with and without 0.9 at. pct Si. Both alloys have microstructures consisting of the ␣ 2 , B2, and the orthorhombic O phase, with different proportions of the ␣ 2 phase relative to the (O ϩ B2) mixtures, depending on solution-treatment temperature. The alloy with a Si addition contains additional primary -Ti 5 Si 3 particles distributed in the (O ϩ B2) matrix. Tests of mechanical properties showed that the incorporation of a small fraction (about 0.03 by volume) of the Ti 5 Si 3 phase leads to greater room-temperature and elevated-temperature strengths, but lower room-temperature elongations and fracture toughness as compared with the base alloy. Alloys containing greater volume fractions of the ␣ 2 phase exhibited better tensile ductility, and this was attributed to the concurrent stabilization of the B2 phase. Examination of tensile-tested and fatigued specimens indicates that the primary failure mode of the alloys, regardless of Si addition, was due to the brittleness of the ␣ 2 phase; the silicide particles that debonded from the matrix also contribute to cracking in the monotonic loading mode. Up to a 20 pct improvement in creep-rupture life was observed in the Si-containing alloys, and this was interpreted in terms of the solute-strengthening effect of Si. While the incorporated Ti 5 Si 3 phase has an unfavorable effect on ductility and room-temperature fracture toughness, the difference in fatigue-crack propagation rates between the alloys with and without Si is minimal. It is concluded that the controlling factor for the fatigue failure in orthorhombic alloys is related to the (␣ 2 ϩ O ϩ B2) microstructure, instead of the Ti 5 Si 3 particles.

Influence of alloying elements on the microstructure and properties of Ti2AlNb

“…Al2O3 oxide film is formed after the addition of Si. Lu et al [39] added Si to Ti-24Al-14Nb-3V-0.5Mo alloys, and the creep properties of the alloys increased by 20% after the addition of Si compared to the alloys without the addition of Si, which is related to the strengthening of the Ti5Si3 exfoliation phase and the solid solution strengthening of Si. Chen et al [40] added 0.85% Y to Ti-17Al-27Nb alloy, Y exists in the form of the Y2Al phase in the alloy, which in the position of GBs, and the Y2Al phase can not only pinch the GBs to inhibit the growth of grains but also strengthen the GBs to promote the strength.…”

Effect of Si Content on the Creep Properties of Ti-6Al-4Fe-xSi Alloys

“…Recently, new low-cost titanium alloys, Ti-(4~6)Al-4Fe-(0.5~1)Si, of which the tensile properties are superior to those of Ti-6Al-4V alloy at both room and elevated temperature were developed [1,2]. It has been reported that silicon addition in titanium alloys enhances the tensile strength and creep properties by silicide precipitation and that the silicon content should be controlled as low as 0.1~0.2 wt.% to avoid coarsening of titanium silicides [3][4][5][6][7][8][9][10].…”