双峰结构Mo-Si-B基体表面多层硅化物涂层的表征和抗氧化性能

Characterization and Oxidation Resistance of Multilayered Silicide Coating on Bimodal Mo-Si-B Substrate

摘要:

由于在细晶Mo-Si-B合金中制备双峰分布的α-Mo晶粒能够在不显著降低合金强度的前提下大幅提高其断裂韧性，为了加强双峰结构合金的表面防护，同时保持其优异的力学性能，通过包埋渗在合金表面上制备了一个具有多层结构（MoSi₂，Mo₅Si₃和Mo₅SiB₂/MoB）的涂层。研究结果表明，相比在细晶结构基体上制备的涂层，双峰结构基体上的涂层表面较为粗糙，并且也表现出双峰分布的微观组织。此外，覆盖涂层后的双峰结构合金的断裂韧性依然良好，并且分布在涂层中的La₂O₃颗粒能够增韧涂层。具有涂层的双峰结构合金在1100~1300 ℃下展现出了卓越的抗氧化性，这是由于氧化过程中在涂层表面快速形成了一个薄且能自愈合的SiO₂-B₂O₃膜。随着氧化温度升高，SiO₂-B₂O₃膜的粘度降低，使得SiO₂-B₂O₃膜的厚度和氧化产物Mo₅Si₃均增加。并且，升高温度促进了Si和B的互扩散，加速了Mo₅Si₃和Mo₅SiB₂/MoB层的增长。在1300 ℃下，由于单峰结构的MoSi₂涂层拥有更多的晶界，使得含涂层的细晶合金相比含涂层的双峰结构合金表现出更多的氧化增重。

Abstract:

To enhance the surface protection of the bimodal Mo-Si-B alloy and simultaneously maintain its superior mechanical properties, a multilayered coating (MoSi₂, Mo₅Si₃ and Mo₅SiB₂/MoB) was synthesized on its surface via pack cementation. Results show that, compared to the coating on the fine-grained substrate, the coating surface on the bimodal substrate is rougher and exhibits bimodal microstructure. Additionally, the fracture toughness of bimodal alloy after coating is acceptable. The distributed La₂O₃ particles toughen the coating. Besides, the coated bimodal specimens show excellent oxidation resistance at 1100~1300 °C, which is attributed to the quick formation of a thin and self-healing SiO₂-B₂O₃ film on the coating surface. With increasing the temperature, the thickness of SiO₂-B₂O₃ film and the oxidation product Mo₅Si₃ increase because the viscosity of SiO₂-B₂O₃ film decreases. Also, improving temperature promotes the interdiffusion of Si and B, accelerating the growth of Mo₅Si₃ and Mo₅SiB₂/MoB layers. Compared to the coated bimodal alloy, the coated fine-grained alloy exhibits more oxidation mass gain at 1300 °C since the unimodal MoSi₂ coating has more grain boundaries.