Microarc Molybdenum Steel Saturation Using Ammonium Molybdate

Introduction. One of the most significant challenges in modern materials science is increasing the reliability and durability of tools and machine parts. To address this issue, it is essential to develop high-hardness coatings with enhanced properties. Typically, high-energy techniques are employed for this purpose, but they require complex and costly equipment, limiting their widespread use. Therefore, problem of creating such coatings remains a significant challenge. An effective and affordable approach to creating these coatings on steel products is microarc surface alloying from a coating pre-applied to the surface of the hardened products. The aim of the work was to assess the potential of diffusion molybdenum saturation for creating such coatings. Ammonium molybdate was used as the diffusant agent.
Materials and Methods. To achieve the aim of this study, we used thermodynamic analysis of chemical reactions that can occur within the temperature range of the microarc heating process. For each reaction, we calculated the change in standard Gibbs energy, which allowed us to determine the feasibility and range of occurrence. An experimental study of the microarc molybdenum saturation process was conducted using ammonium molybdate on steel 20 samples using a laboratory setup. The surface current density was set at 0.53 A/cm², and the duration of the process was 6 minutes.
Results. The Gibbs free energy changes for chemical reactions that can occur during the thermal decomposition of ammonium molybdate have been calculated. An experimental study has shown the formation of a molybdenum coating, and the concentration of molybdenum in the diffusion layer has been determined. On the surface of the samples, carbides Mo2C and Fe3Mo3C have been found. The dependence of the coating depth on the content of diffusant in the coating and its thickness has been determined.
Discussion and Conclusion. Thermodynamic analysis has shown that atomic molybdenum can be formed through direct reduction or with the intermediate formation of molybdenum dioxide. The research has confirmed the formation of a diffusion coating on steel after microarc saturation with molybdenum, and the depth of this coating depends on the amount of diffusant in the coating and its thickness. These findings will be used to develop technological processes for microarc molybdenum plating of steel products.

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