Powder Preparation Process For Reactive Sprayed Ti-B-C-N Ceramic Coatings

Ti-B-C-N ceramic coatings were prepared on Q235 steel by reactive plasma spraying. Ti, B4 C and graphite powders were chosen as reaction system. Two kinds of powders(Ti:B4C:C=4:1:1 and Ti:B4C:C=14:3:5) were used as spraying powder, and 10wt% Co powder was added as metal binder. Two powders preparation methods(milling, sintering and crushing) were used to treat spraying powder. The phases, cross-section morphologies, microhardness and corrosion resistance of reactive plasma sprayed Ti-B-C-N coatings were researched by X-ray diffraction technology(XRD), optical and scanning electron microscope(SEM), microhardness and electro-chemical analyzer.The results are as follows: the flowability of sintered and crushed powders is better than that of milled powder, and the flowability of powders sintered at 600℃ and crushed is better than that of powders sintered at 900℃ and crushed. Coatings with 150 μm- 200 μm thickness were successfully prepared by reactive plasma spraying for milled powder of both formulations; the main phases of the coating include: TiN, C0.3N0.7Ti and little amount of TiB2; the self-corrosion potential of coating is about 100 mV more positive than that of the substrate; the microhardness of the coatings for both formulations are about 740 HV. Coatings with 200 μm and 400 μm thickness were respectively prepared by reactive plasma spraying for the formulation(Ti:B4C:C=4:1:1) with powders sintered at 900℃ and crushed under the conditions of 70V/600 A and 70V/650A; the average microhardness of the coatings were about 864 HV(70V/600A) and 768 HV(70V/650A); the main phases of two coatings include: TiN, TiB2, C0.7N0.3Ti and some oxides of Co and Ti; the corrosion resistance of two coatings were harder than that of the substrate. The corrosion resistance of coating prepared under the conditions of 70V/600 A is better. Coatings about 200 μm thickness were successfully prepared by reactive plasma spraying with two formulations(Ti:B4C:C=4:1:1 and Ti:B4C:C=14:3:5) of powders sintered at 600℃ and crushed; the main phases of two coatings include: TiN, TiB2 and C0.3N0.7Ti, and the superhard-phase of BN was generated for Ti: B4C: C=14:3:5 formulation; the average microhardness(1 268.83HV) of the coating for Ti:B4C:C=14:3:5 formulation was higher than that(787.63HV) of coating for Ti:B4C:C=4:1:1formulation, and the corrosion resistance of the coating with Ti:B4C:C=4:1:1 formulation was better.