B₄C-Ni Composite Coatings Prepared by Cold Spray of Blended or CVD-Coated Powders

In the oil industry, logging systems involving geological sensors are designed to operate under increasing severe service conditions of deep and horizontal boreholes. Under these conditions, metal matrix composites (MMCs) with ceramic reinforcement are applied on components to achieve wear and corrosion resistant systems. The ‘cold spray’ could be described as a cold and inert process to form coating layers through severe plastic deformation of a ductile metal. Ceramic/metal MMC coating could be achieved by co-deposition of a ceramic with a ductile material. In this work, it was it was investigated the use of MMC B₄C-Ni coating from both mechanically milled blends or B₄CNi CVD coated batches. Powder blends involving Ni powder with fine or coarse B₄C powders were prepared by mechanical milling. Three CVD coated B₄C-Ni powder batches were synthesized with 30, 40 and 50 Ni wt% respectively. Cold spray coatings were achieved with 1 pass and 5 passes to investigate the building-up mechanisms and interfaces with AISI316L. Powders and cold sprayed coatings microstructures were observed by optical and scanning electron microscopies and further quantitative image analysis were carried out to determine the content of B₄C embedded in the Ni matrix of B₄C-Ni cold spray coatings. The highest B₄C vol.%, up to 45%, could be reached in the case of B₄C-Ni coated powder. Micro-hardness values of such MMC coatings were also determined through Vickers micro-indentation. The beneficial role of the Ni surrounding layer on coating formation is discussed in relation to the unique features of the microstructures obtained by cold spray of B₄C-Ni coated powders.