The structure of Ni-TiC composite coatings deposited by PPTAW method
Mariusz Bober, Jarosław Grześ
Quarterly No. 2, 2015 pages 72-77
DOI:
keywords: composite coatings Ni-TiC, plasma powder transferred arc welding method (PPTAW), fractal analysis
abstract In this paper, the structure investigations of Ni-TiC composite coatings deposited on low carbon steel (S355J0) using plasma powder transferred arc welding (PPTAW) are presented. A blend of nickel alloy powder with 40 vol% TiC was selected as the precursor material for fabricating Ni-TiC composite coatings. The obtained composite layers were characterized by macro and microstructural examination. The distribution of carbide grains in the nickel matrix was characterized by fractal analysis. In addition, the volume fraction of TiC inclusion in the nickel matrix and coating dilution as a function hardfacing parameters were calculated. Metallographic examination revealed that the coatings obtained within the range of a 60÷80 A welding current have discontinuities in the interface layer - substrate and a number of large air bubbles. The composite coatings obtained with a welding current higher than 80 A were correctly formed. The microstructure of the composite coatings contains large and small irregular titanium carbide particles. As a result of the interaction between the nickel alloy matrix and high energy plasma arc with titanium carbide during the surfacing process, small particles are formed. Both the dilution coefficient and volume fraction of TiC increase with an increase in welding current. The last part of the paper includes the results of the fractal dimension measurements of coating cross-sections. For the analyzed structures, the percentage of TiC and linear fractal dimension were determined using the line counting dimension method (LCD), which is a modification of the box counting dimension method (BCD).