Synthesis of nanostructured Cr3C2-25(Ni20Cr) coatings

On the basis of the nanocrystalline Cr3C2-25 (Ni20Cr) feedstock powders pro duced by mechanical milling, a nanostructured coating has been synthesized using high velocity oxygen fuel (HVOF) thermal spraying. The properties of the nanostructured coating were compared to those of the conventional coati ng of the same composition using scanning electron microscope (SEM), transm ission electron microscope (TEM), and microhardness tests. The nanostructur ed Cr3C2-25 (Ni20Cr) coating synthesized in this study had an average carbi de particle size of 24 nm. Discontinuous elongated amorphous phases were ob served in the nanostructured coating. The conventional Cr3C2-25 (Ni20Cr) co atings produced using blended elemental powders exhibited an inhomogeneous microstructure. The observed homogeneity of the nanostructured coating is a ttributed, in part, to the microstructural improvement of the starting powd er. The nanostructured Cr3C2-25 (Ni20Cr) coating yielded an average microha rdness value of 1020 DPH300, which corresponds to a 20 pct increase in micr ohardness over that of the conventional coating. The nanostructured Cr3C2-2 5 (Ni20Cr) coating also exhibited a higher apparent fracture toughness rela tive to that of the conventional coating. The apparent mechanical property improvements in the nanostructured coating were thought to result from the uniformity of the microstructure and the high performance associated with a nanostructured structure. In addition, the mechanism that is present durin g the milling of a system containing nondeformable particles is discussed i n light of the TEM observations.