Reaction behavior, microstructure and application in coating of in situ ZrC–ZrB2 ceramic composites powders from a Co–Zr–B4C system

• ZrC–ZrB2 ceramic composites powders were successfully produced by SHS.
• Proper addition of Co in the Zr–B4C mixture promoted the ignition of SHS.
• SHS products consisted mainly of ZrC and ZrB2 besides ZrCo3B2 and/or BCo2.
• ZrCo3B2 was produced by the reaction between ZrB2 and Co at the cooling stage.
• ZrC–ZrB2 composites coatings were fabricated by APS using the SHS powders.

Reaction behavior and microstructure of products in a Co–Zr–B4C system during self-propagating high-temperature synthesis (SHS) were investigated. With an increase in Co content, the combustion temperature decreased monotonically, the ignition delay time first decreased and then increased. The final products consisted of the major phases of ZrC and ZrB2 and minor phases of ZrCo3B2 and BCo2. The ZrCo3B2 was formed at the cooling stage of SHS due to the reaction between resultant ZrB2 and Co, which inevitably led to the presence of ZrCo3B2 in the products regardless of Co content, preheating and Zr/B4C mole ratio. The grain size of ZrC and ZrB2 particles decreased to less than 0.5 μm with Co content increasing to 40–50 wt.%. The in situ ZrC–ZrB2 ceramic composites powders synthesized by the SHS reactions in the Co–Zr–B4C system have attractive application in the wear resistant coatings. Magnesium alloy substrate was successfully plasma sprayed with the ZrC–ZrB2 ceramic composites coatings using the SHS synthesized powders. The produced coatings provided superior wear resistance for magnesium alloy substrate and bonded well with the substrate.

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