Experimental Investigation on the Phase Equilibria of the Nb-Ti-Si-B System at 1500 °C

Abstract

The phase equilibria at 1500°C of the Nb-Ti-Si-B quaternary at the Nb-rich region were carefully studied. Seven alloys were arc-melted and subsequently annealed at 1500°C for 150 h. BSE image, XRD and EPMA results show that Nbss + T2 + Nb 3 B 2 , Nbss + T2 + Nb 3 Si and Nbss + T2 + Nb 3 B 2 + Nb 3 Si were present in these alloys. Extensive solubility of Ti and Si were found in the Nb 3 B 2 phase. The experimental findings were compared favorably with the calculated phase equilibria. The phase equilibria in the Nb-rich region of the Nb-Ti-Si-B system have Nbss + T2, Nbss + T2 + Nb 3 B 2 , Nbss + T2 + Nb 3 Si and Nbss + T2 + Nb 3 B 2 + Nb 3 Si. This work provides important guide lines on the effect of B addition to the microstructure of the Nb-rich Nb-Ti-Si alloys.

Effects of B and Si on the fracture toughness of the Nb–Si alloys

“…However, the addition of 4.5B to NbeTieSi could suppress the primary solidification of Nb 3 Si and inhibit (Nb) þ Nb 3 Si eutectic, it promotes direct eutectic solidification between (Nb) and T2 in Nb-rich corner of NbeTieSieB liquidus projection, so 4.5B would be an optimal amount to observe this critical transition, as shown in the calculated 2D liquidus projections in Fig. 1(b) [9,10]. The (Nb) þ T2 eutectic valley as well as large (Nb) þ T2 two-phase region in the isothermal tetrahedron space is of practical importance to fabricate the desirable in-situ (Nb) þ T2 composites.…”

“…(a) Calculated liquidus projection of the NbeSieTi ternary system[8] (b) Calculated 2D liquidus section of NbeTieSieB (X B ¼ 4.5 at%)[9,10]. The symbols denote the experimentally investigated alloy compositions.…”

Boron site preference in ternary Ta and Nb boron silicides

“…In contrast to the Ta-Si-B system, extended efforts focused on phase equilibria in the Nb-Si-B system [6][7][8][9][10], for which a critical assessment was presented by Korniyenko et al [11]. A recent thermodynamic modeling of the Nb-rich part of Nb-Si-B system includes a liquidus projection [12]. The ternary compounds or solution phases involved crystallize essentially in three structure types: Cr 5 B 3 , W 5 Si 3 and Mn 5 Si 3 -type, which all three are characteristic for binary transition metal silicides TM 5 Si 3 .…”

Liquid–solid phase equilibria in Nb-rich corner of the Nb–Ti–Si–B system

“…In order to improve the design of new engineering materials and understand the relationship between microstructure and properties, the knowledge of the phase equilibria of the Nb-Ti-Si-B quaternary system is prerequisite. Detail information on the phase equilibria at 1500 • C in the Nb-rich region of the Nb-Ti-Si-B system has been reported elsewhere [6]. The objective of this study is to understand the effect of B addition on the liquid-solid phase equilibria in the Nb-rich Nb-Ti-Si-B alloys.…”

“…Only the ingots with a weight loss of less than 0.5 wt.% were chosen for further investigations, and the actual compositions were considered very close to the nominal compositions. The microstructure analysis procedures for the as-cast samples are similar as for the annealed samples, which have been described in more detail previously [6].…”