Papers by Keyword: Niobium Alloys

Abstract: Owing to its fairly higher melting point (2468°C) and superior thermal conductivity, Niobium alloys are rendered as candidate material for high temperature applications, where state of the art Nickel base super alloys cannot be used. Its applications possess wide range of aerospace components mainly encompassing aircraft exhaust chambers, thrust augmenters, rocket engines and other industries such as chemical and petrochemical. The only limitation with niobium alloys is their inferior oxidation resistance, which can be tackled by developing a high temperature oxidation resistant coating. In this regard, Nickel Aluminide (NiAl) having a melting point of 1638°C embraces a paramount importance amongst the coating categories. In this study, NiAl was synthesized using vacuum melting and strip casting followed by ball milling. The powder was coated on C-103 Niobium alloy specimens using air plasma technique and evaluated for high temperature stability. It was deduced that the coating was exceptionally stable up to 1234 °C in ambient conditions.

Abstract: The work reports on the phase transformation in mechanically alloyed and hot-pressed Nb-4Si-8B and Nb-8Si-16B (at-%) alloys. Elemental powder mixtures were processed in a planetary ball mill under argon atmosphere using 300 rpm, stainless steel balls (19 mm diameter) and vials (225 mL), and a ball-to-powder weight ratio of 10:1. After dry milling for 7h, wet milling with isopropyl alcohol for more 20 min was adopted to increase the recovering of previously cold-welded Nb-4Si-8B powders. To obtain the equilibrium structures the as-milled powders were hot-pressed under vacuum at 1200^oC for 1 h. The as-milled powders and hot-pressed samples were characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. XRD results revealed the presence of metastable phases in as-milled Nb-Si-B powders. The hot pressing has produced dense Nb-Si-B samples, which were formed by the Nbss, Nb₃B₂ and Fe₂Nb phases beside of other unknown Si-rich phase.

Abstract: Niobium metal is one of the promising material for hydrogen purification because of its high hydrogen permeability. In order to design and develop a new palladium-free hydrogen permeable membrane, it is important to understand the effects of alloying elements on the hydrogen permeability through metals. However, to the niobium metal, the alloying effects still remain unclear. In the present study, using a DC-polarization technique under the diffusion limiting condition, the hydrogen permeability of Nb-5mol%M alloys were investigated in high precision at 573K. Here, M’s were 4d transition metals, Zr, Mo, Ru and Pd. The permeability of niobium is found to be varied with the addition of a small amount of alloying element. For example, the hydrogen permeability of niobium increases by the addition of Zr but decreases by the addition of Ru.