Effect of Si Content on In-situ Formation Mechanism of Hf-Ta-Si Coating on Ta12W Alloy Surface

Abstract:

Using the slurry reaction sintering process to prepare Hf-Ta-Si composite coating on Ta12W alloy surface, the effect of Si content on the in-situ formation mechanism of the Hf-Ta-Si coating was investigated. Results show that 30Hf:70Si coatings exhibit inferior surface uniformity with some pores. The upper part of the sample displays a four-layer gradient structure: the outermost layer is primarily composed of HfSi and HfC, the middle layer consists of (Ta, Hf)₅Si₃ solid solution, the lower main-layer consists of TaSi₂, and the coating/substrate interface layer is Ta₅Si₃. However, the flow of molten Si under gravity leads to Si-enrichment on the lower part of the coating. After optimizing the Hf:Si ratio to 40:60, the gradient differences in elemental distribution on the coating surface decrease. The surface layer is dominated by HfSi/HfC, but the precipitation of HfC becomes more uniform. The continuity of the (Ta, Hf)₅Si₃ solid solution in middle layer is enhanced, whereas the lower layer and the interface transition layer remain unchanged. Overall, a denser multi-layer gradient structure is formed with improved surface uniformity. Additionally, the acid-alcohol resin in the organic solvent suffers high-temperature pyrolysis and in-situ reacts with Hf to generate the ultra-high-temperature ceramic HfC. This phenomenon is expected to enhance the oxidation resistance and high-temperature stability of coating.