Part I: characterization of Cr3C2-25% NiCr reactive plasma sprayed coatings produced at different pressures

The present work was performed with the aim of characterizing various plasm a sprayed Cr3C2-NiCr coatings produced by using different processing pressu res between 300 and 1200 mbars.. in a nitrogen controlled atmosphere CAPS s ystem. X-Ray diffraction was carried out on all coatings by using Bragg-Bre ntano geometry. The phases identified in the as-supplied powder Cr3C2/Ni-Cr were fcc Ni-Cr and orthorhombic Cr3C2 In contrast to the original powder, the coatings showed evidence of Cr3C2, Ni-Cr and either Cr6.2C3.35N0.35 or Cr3C1.52N0.48 carbo-nitride phases depending on the ratio of C/N in the coa ting. The presence of Cr7C3 and CrO2 was also identified in the coatings de posited at atmospheric pressure. The volume fraction of carbide plus nitrid e phase in the coating was always less than the volume fractions of the car bide phase in the original feed stock powder. The volume fraction of carbid e plus nitride phase was found to depend quite markedly on the spraying par ameters such as pressure. power input, spraying distance and substrate cool ing. The results have been presented in terms of spraying efficiency,. The highest value of xi (86.4%) was obtained for coatings produced at 1200 mbar pressure, a spraying distance of 120 mm, without N-2 cooling and the lowes t value (25.2%) was found for the coatings deposited at 300 mbar for the sa me spraying distance but with N, cooling. The presence of graphitic carbon was detected in all samples especially for specimens where the fraction of carbide plus carbo-nitride phases was the greatest. The influence of sprayi ng parameters such as pressure, power input., spraying distance and substra te cooling on the microstructure was determined. The highest microhardness value of 2296 HV50 was found for the carbide plus carbo-nitride phase conta ined in the specimens produced at 1200 mbar spraying pressure, 120-mm spray ing distance and substrate heating at 600 degreesC. (C) 2001 Elsevier Scien ce B.V. All rights reserved.