Product Code: ICA12_1603

A Novel Method of Pulsed Laser-Cladding for Effective Control of Melting of WC Particulates in Nicr-WC Composite Coatings
Authors:
Manish Tak, International Advanced Research Centre for Power Metallurgy and New Materials (ARCI); Hyderabad India
S. M. Shariff, International Advanced Research Centre for Power Metallurgy and New Materials (ARCI); Hyderabad India
Vikram Sake, International Advanced Research Centre for Power Metallurgy and New Materials (ARCI); Hyderabad India
G. Padmanabham, International Advanced Research Centre for Power Metallurgy and New Materials (ARCI); Hyderabad India
Presented at ICALEO 2012

In cermet coatings such as WC reinforced Ni-Cr metal matrix, distribution of WC particles with effective bonding at particle-matrix interface plays an important role in retention of high hardness and toughness. Although techniques such as PTA, thermal spray, plasma spray etc. with controlled processing is possible for obtaining defect-free coatings but at expense of loss of hardness on account of substantial melting of WC. Formation of secondary carbide phases are found to be detrimental in reducing hardness and there by rendering low wear and erosion resistance of the coating. Laser cladding in continuous-energy mode can be utilized to control heat input to reduce melting of WC particles in NiCr matrix as compared to other conventional methods, however the problem of melting of these particles still persists. A method of laser-cladding under pulsed mode was found to provide a better alternative to effectively control heat-input leading to controlled melting of WC in NiCr matrix with reduction in formation of deleterious secondary carbides. In the present work, laser cladding of NiCrBSi with various percentages of WC on SS310 steel substrate has been carried out using a 6kW fiber-coupled high power diode laser integrated with an 8-axis robotic workstation and an off-axis powder feeding subsystem under argon atmosphere. Coatings were produced in both pulsed and continuous mode at a similar average laser power. Coatings were characterized for microstructure, hardness and also analyzed for erosive wear resistance. Clads produced under pulsed-mode of processing showed relatively higher amount of unmelted WC particles in g-Ni+Ni3B lamellar eutectic matrix as compared to continuous-mode of processing. Relatively higher amounts of secondary carbides and meta-stable phases were observed in CW mode as compared to Pulsed counterparts. Hardness as well as erosion resistance was found to be superior in case of pulsed-clad coating.