Microstructure and low temperature oxidation of pack Si-B co-deposition coating on pure Mo

B-modified MoSi₂ coatings on pure Mo surface were prepared by pack Si-B co-deposition process. The phase structure and composition of the coatings were studied by means of XRD, EDS and WDS techniques. Coating formation mechanism was investigated based on thermodynamics calculation. The results show that the Si-B co-deposition coatings prepared at 1100~1400 ℃ in the pack 16Si-4B-4NaF-76Al₂O₃ have a 5-layer structure. From surface to substrate, the coating can be divided into the MoSi₂ out layer, the MoSi₂+MoB second layer, the Mo₅Si₃ third layer, the MoB fourth layer and the Mo₂B inner layer. The growth of the coating is dominated by the inward diffusion of Si and B. The deposition of Si mainly forms MoSi₂ phase, and the inward diffusing B either diffuses into the substrate to form Mo-B composite layers or develops MoB dispersions in MoSi₂. Oxidation behavior of the Si-B co-deposition coating at 600 ℃ reveals that B atoms can diffuse outward to the coating surface and oxidize to B₂O₃.