Deposition mechanisms and characteristics of nano-modified multimodal Cr3C2–NiCr coatings sprayed by HVOF

Nano-modified multimodal and conventional Cr –NiCr coatings were fabricated by high-velocity oxygen-fuel spraying deposited on CuCrZr substrates. Results showed that individual nano-modified multimodal Cr –NiCr particles were composed of nano (25−180 nm), submicron (200 nm to 0.5 μm), and micron (2–4.5 μm) Cr grains, NiCr binder phases, and a tiny amount of rare earth oxide additives. The nano-modified multimodal Cr –NiCr coatings maintained a unique structure: submicron Cr grains embedded in the voids formed by micron Cr grains, NiCr binder phases and nano Cr grains imbedded in the voids formed by submicron and micron Cr grains, and nano Cr grains are dispersed in NiCr metal binder phases. A few discontinuous elongated amorphous and nanocrystalline phases existed in them. The mechanical interlocking was the dominant bonding mechanism accompanied by local metallurgical bonds. Compared to the conventional coating, the multimodal coating was uniform and dense (porosity was 0.3 ± 0.12%) as well as not obvious lamellar structures, the adhesive strength was 75.32 ± 1.21 MPa, exhibiting a 65 pct increase, and the microhardness was increased by about 18%. The lower porosity and higher strength of nano-modified multimodal structure coating were mainly related to dispersion distribution and synergistic coupling effects of Cr hard grains with different scales.