The Effect of Silicide Volume Fraction on the Creep Behavior of Nb-Silicide Based In-Situ Composites

Abstract

This paper will describe the creep behavior of high-temperature Nb-silicide in-situ composites based on quaternary Nb-Hf-Ti-Si alloys. The effect of volume fraction of silicide on creep behavior, and the effects of Hf and Ti additions, will be described. The composites were tested in compression at temperatures up to 1200 o C and stress levels in the range 70 to 280 MPa. At high (Nb) phase volume fractions the creep behavior is controlled by deformation of the (Nb) and, as the volume fraction of silicide is increased, the creep rate is reduced. However, at large silicide volume fractions (>0.7) damage in the silicide begins to degrade the creep performance. The creep rate has a minimum at a volume fraction of ~0.6 silicide. The creep performance of the monolithic and silicide phases will also be discussed.

The effects of Ti and Mo additions on the microstructure of Nb-silicide based in situ composites

“…The Si content of the alloys was set to 18 at.% for optimum oxidation resistance and creep behaviour [13]. The Ti addition was set at 24 at.% in order to maintain an eutectic temperature of O1700 8C and to avoid the formation of the Ti 5 Si 3 phase, which has been reported to be detrimental to the creep-rupture strength of the composites [14].…”

A study of the microstructures and oxidation of Nb–Si–Cr–Al–Mo in situ composites alloyed with Ti, Hf and Sn

“…In this study, the Si content was set to 18 at% for optimum oxidation resistance and creep behaviour [25]. The Cr content was kept at 5 at% in order to balance the oxidation resistance, creep resistance, fracture toughness and melting point.…”

Solid-state phase equilibria in metal-rich Hf–Ti–Si system at 1350°C

“…Ti and Hf are added to these composites to improve room temperature fracture toughness and high temperature oxidation resistance [2,4]. However, high Ti and high Hf concentrations can have adverse effects on creep performance [5,6]. In order to improve the design of new engineering materials and understand the relationship between microstructure and properties, it is essential to have accurate knowledge of phase equilibria of the NbeTieHfeSi quaternary system, especially in the metal-rich region.…”

“…b(Hf,Ti,Si) þ (Hf,Ti)5 Si 3 The microstructure of the Hfe60Tie10Si and Hfe85Tie 5Si alloys consisted of two phases: b(Hf,Ti,Si) and (Hf,Ti) 5 Si 3 .Fig. 8(a) and (b) show low and high magnification images of the Hfe60Tie10Si alloy, in which the light gray phase is (Hf,Ti) 5 Si 3 and the b(Hf,Ti,Si) has transformed to a(Hf,Ti,Si) and b(Hf,Ti,Si).…”