Spark Plasma Sintering Behavior of Nb-Mo-Si Alloy Powders Fabricated by Hydrogenation-Dehydrogenation Method

Abstract

In this study, the sintering behaviors of Nb-6Mo-20Si-3Cr (at percentage) in situ composite powders were studied. The Nb alloy powder was fabricated by a hydrogenation-dehydrogenation method, and both the alloy ingot and powders consisted of two phases: An Nb metal phase and the α-Nb5Si3 phase. Consolidation of the alloy powders was performed at 1500, 1600, and 1700 °C using spark plasma sintering, and the microstructures and phases formed at various sintering temperatures were analyzed. Micropores were observed in the compact sintered at 1500 °C due to the lack of complete densification at that temperature. The densification was completed at 1600 °C and the microstructure was slightly coarsened at 1700 °C compared to the microstructure of the compact sintered at 1600 °C. The microstructures prepared by the powder metallurgy method were finer than the microstructure of the ingot prepared by the casting method. The phase formation behavior varied according to the sintering temperature. Specifically, the α-Nb5Si3 phase, which is a stable structure of the Nb5Si3 phase at a low temperature, was transformed to the β-Nb5Si3 phase (which is stable at a high temperature) with an increasing sintering temperature.

Sintering behaviour of Nb–16Si–25Ti–8Hf–2Cr–2Al alloy powder fabricated by a hydrogenation–dehydrogenation method

“…We compared the results in this study with previous study [24]. They found that no oxide was observed in the microstructure of sintered compacts even when the Nb-6Mo-20Si-3Cr (at.-%) alloy powders were produced via the HDH method and consolidated using SPS.…”

“…Nb is one such element that forms a hydride during hydrogen annealing, making it brittle and easier to pulverise. Park et al [23,24] used this property of Nb and produced Nb-Mo-Si silicide-based alloy powders via the HDH method. Based on these studies and the results of the present study in Figure 3, it would be possible to produce Nb alloy powders of various compositions using the HDH method.…”

On the Nb5Si3 Silicide in Metallic Ultra-High Temperature Materials

“…The aforementioned metallic UHTMs can be single-phase or multiphase materials. The RMICs are multiphase materials with microstructures that consist of bcc solid solution(s) and intermetallic(s) [1,2,[20][21][22][23][24][25][26][27][28], whereas the RHEAs and RCCAs can be single-phase bcc solid solution alloys or multiphase alloys with microstructures that consist of solid solution(s) and intermetallic(s), e.g., [3], or only intermetallics, e.g., [15,16]. For the said categories of metallic UHTMs, the M 5 Si 3 silicides (M = transition metal (TM), RM), in particular the Nb 5 Si 3 and Mo 5 Si 3 silicides, have attracted the interest of alloy designers and developers [1,3,13,24] owing to their creep properties and high Si content that benefits oxidation resistance [29][30][31][32][33][34][35][36][37][38][39][40].…”