Silicide Coating Fabricated by HAPC/SAPS Combination to Protect Niobium Alloy from Oxidation

Abstract

A combined silicide coating, including inner NbSi2 layer and outer MoSi2 layer, was fabricated through a two-step method. The NbSi2 was deposited on niobium alloy by halide activated pack cementation (HAPC) in the first step. Then, supersonic atmospheric plasma spray (SAPS) was applied to obtain the outer MoSi2 layer, forming a combined silicide coating. Results show that the combined coating possessed a compact structure. The phase constitution of the combined coating prepared by HAPC and SAPS was NbSi2 and MoSi2, respectively. The adhesion strength of the combined coating increased nearly two times than that for single sprayed coating, attributing to the rougher surface of the HAPC-bond layer whose roughness increased about three times than that of the grit-blast substrate. After exposure at 1200 °C in air, the mass increasing rate for single HAPC-silicide coating was 3.5 mg/cm(2) because of the pest oxidation of niobium alloy, whereas the combined coating displayed better oxidation resistance with a mass gain of only 1.2 mg/cm(2). Even more, the combined coating could significantly improve the antioxidation ability of niobium based alloy at 1500 °C. The good oxidation resistance of the combined silicide coating was attributed to the integrity of the combined coating and the continuous SiO2 protective scale provided by the oxidation of MoSi2.

The Protection, Challenge, and Prospect of Anti-Oxidation Coating on the Surface of Niobium Alloy

“…By analyzing the advantages and disadvantages of the coating preparation process, related scholars appropriately combined different methods to make up for each other's advantages and disadvantages, thereby obtaining a composite coating with superior oxidation resistance [65,66]. Common combination categories, process conditions, coating composition, thickness, and oxidation characteristics are shown in Table 4.…”

Surface Optimization of ZrC–SiC Inner Layer to Enhance Ablation Property of SiC/ZrC–SiC Multi-Layer Coating for C/C Composites

“…However, as the ablation time extended, according to Figure 15a, the vapor pressure of Si and SiO 2 was about 700 times higher than that of ZrO 2 at 2300 • C. Meanwhile, the decomposition pressure of SiO 2 was much higher than that of ZrO 2 (Figure 15b), causing the formation of a porous ZrO 2 skeleton layer. Thanks to the jagged and porous surface of the inner layer with lower PC temperature (1450 • C), the irregular undulating surface of the CVD-SiC middle layer was inherited from the inner layer, generating the sawtooth combination between the middle and outer layer, which caused a strong interface bonding strength and restrained the spallation of the coating during ablation [25,37]. As a result, ZrO 2 could react with a small fraction of SiO 2 to form a dense ZrO 2 -SiO 2 solid solution with a low melting point and avoid the spalling of the ZrO 2 scale (Equation ( 17)).…”

Vertical grain and columnar structured Ba(Mg1/3Ta2/3)O3 thermal barrier coating deposited by solution precursor plasma spray

“…In this work, BMT is chosen as a thermal insulation material for niobium alloy. Due to the poor oxidation resistance of niobium alloy, an oxidation-resistant layer of Mo(Si, Al)2 is necessary to serve as a bond coat material [29,39]. As for the deposition sequence, a comparison of TEC should be considered first, as seen in Fig.…”