Reaction behavior, microstructure and application in coating of in situ ZrC-ZrB_2 ceramic composites powders from a Co-Zr-B_4C system

摘要

Reaction behavior and microstructure of products in a Co-Zr-B_4C 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 ZrB_2 and minor phases of ZrCo_3B_2 and BCo_2. The ZrCo_3B_2 was formed at the cooling stage of SHS due to the reaction between resultant ZrB_2 and Co, which inevitably led to the presence of ZrCo_3B_2 in the products regardless of Co content, preheating and Zr/B_4C mole ratio. The grain size of ZrC and ZrB_2 particles decreased to less than 0.5 μm with Co content increasing to 40-50 wt.%. The in situ ZrC-ZrB_2 ceramic composites powders synthesized by the SHS reactions in the Co-Zr-B_4C system have attractive application in the wear resistant coatings. Magnesium alloy substrate was successfully plasma sprayed with the ZrC-ZrB_2 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.