Effect of Copper Addition on the Niobium Disilicide Coatings by Pack Cementation

Abstract

NbSi 2 coatings were deposited on pure niobium by halide-activated pack cementation method. The effect of copper addition in pack mixture on the siliconizing process was investigated. After siliconizing on niobium at 1050 C for 2 h using a pack mixture composed of Si, NaF and SiC, a single phase of hexagonal NbSi 2 coating was formed. The addition of copper in pack mixture not only increased the growth rate of the coatings, but also led to form a very thin interlayer between the NbSi 2 coating and the niobium substrate.

Preparation of Niobium Disilicide Coating by Heating Niobium in a Sodium–Silicon Melt

“…No formation of Nb 5 Si 3 on Nb plates has been reported for NbSi 2 coating prepared by pack cementation at 1327 1373 K 8,9) and by electroless plating using molten salt at 1173 K. 12) On the other hand, formation of Nb 5 Si 3 was confirmed in the experiments of NbSi diffusion couples at higher temperatures (14731773 K) under an ambient pressure 22,23) and under high pressure (40 MPa) with SPS equipment.…”

“…8,9) Na acts as a solvent to dissolve Si at relatively low temperature and the Si in the NaSi melt reacts with Nb at the surface, and then diffuses into the plate, forming a NbSi 2 layer.…”

“…515) Pack cementation 711) is a conventional chemical vapor deposition method for the fabrication of NbSi 2 coating on Nb substrates. Li et al 8) and Yoon et al 9) prepared NbSi 2 layers with a thickness of around 2566 µm on Nb substrates by pack cementation where Nb substrates were embedded in a pack mixture of fine Si powder, halide activators (NaF, MgF 2 ), and inert fillers (SiC, Al 2 O 3 ), this mixture being heated at 1323 1373 K for 23 h in a vacuum or an Ar atmosphere. NbSi 2 has also been coated on Nb plates and bulks by electroless plating using molten salt 12) and by spark plasma sintering (SPS).…”

Effects of Nb-Alloying on High-Temperature Oxidation of MoSi2

“…These values correspond to a 3/2 atomic ratio of ((9/13)Mo+ (4/13)Nb)/Si or ((9/13)Mo+(4/13)Nb) 3 Si 2 . Mo 3 Si 2 and Nb 3 Si 2 are metastable phase of MoSi and NbSi systems, respectively [25,26]. These regions remained scattered in the MoSi 2 matrix thus a Si-decient phase did not form in Nb-containing samples beneath the oxide layer as it did in pure MoSi 2 .…”

High temperature behaviour of NbSi2 coating on the Nb-1Zr-0.1C alloy

“…Among various coating techniques, the molten salt method is one of the widely used deposition technique employed to develop diffusion coating on various metals like Mo, Nb [13]. A comparison of various coating methods is presented in Table 1 [14][15][16][17][18][19]. Molten salt technique offers many advantages over other techniques, such as easy coating set up, low operational temperature and shorter time period to develop coating.…”