B4C/Ni composite coatings prepared by cold spray of blended or CVD-coated powders

Abstract : In this work, the microstructures of B4C/Ni coatings by cold spray with blends or chemical vapor deposited (CVD) Ni-coated powders were investigated and compared. Powder blends with Ni powder and fine or coarse B4C powders were prepared for various B4C content ranging from 54 to 87 vol.% (equal to 25-65 wt.%). Three CVD Ni-coated B4C powder batches were also synthesized with various B4C content using the fine B4C as core particles. Ni-coated powders and both types of cold sprayed coating microstructures with blends or coated powders were investigated by optical and scanning electron microscopy. Further quantitative image analysis was carried out on scanning electron microscopy (SEM) images to measure the B4C content within the coating regarding the influence of the nominal content in the feedstock for each coating type. Both types exhibited fine fragments and unfragmented B4C, but coatings with CVD-coated powders had many more unfragmented particles. Moreover, the higher levels for both B4C (44.0 ± 4.1 vol.%) and coating microhardness (429 ± 41 HV0.5) were obtained in case of the CVD-coated powders. However, it was assessed that the highest microhardness was not obtained for the highest B4C content. This questionable result is discussed with regard to the fully original composite microstructure obtained from CVD Ni-coated B4C powder.