Parametric investigation of pulsed Nd: YAG laser cladding of stellite 6 on stainless steel S. Sun * , Y. Durandet, M. Brandt Industrial Laser Applications Laboratory, Industrial Research Institute Swinburne, Swinburne University of Technology, 533-545 Burwood Road, Hawthorn, VIC 3122, Australia Received 15 December 2003; accepted in revised form 4 March 2004 Available online 3 September 2004 Abstract A systematic research into the cladding of stellite 6 on stainless steel by pulsed Nd:YAG laser has been carried out. The effects of pulse energy, pulse frequency, powder mass flow rate and spot overlap on the clad layer height, dilution and heat-affected zone (HAZ) have been examined. It was found that both the clad height and penetration into the substrate increase with the pulse energy, spot overlap and pulse frequency, but the effects of these parameters on dilution are complex. The dilution reaches the lowest value (4%) at the incident energy of 18 and 25 J/ pulse, spot overlap of 89% and pulse frequency of 40 Hz. The powder mass flow rate of 22 g/min (for energy of 25 J/pulse and spot overlap of 83%) produces thick clad layer with low dilution but results in the formation of defects. The hardness of the clad layer decreases linearly with increasing dilution. No cracks have been found in single-track clad layers at a spot overlap of 89%, however, cracks occurred at lower spot overlap. These cracks were eliminated by the multi-track cladding when the track increment is less than 1/3 of the width of track, which is believed to be due to the remelting or heat treatment of the previous clad track by the subsequent track. The track bands in multi-track clad show coarser structure, higher element segregation and lower hardness. D 2004 Elsevier B.V. All rights reserved. Keywords: Pulsed laser cladding; Pulse energy; Pulse frequency; Spot overlap; Clad height; Dilution 1. Introduction Laser cladding is a laser surfacing process in which the objective is to cover a particular part of the substrate with material which has superior properties, producing a fusion bond between the two with minimal mixing (dilution) of the clad by the substrate [1]. The process has received a lot of attention over the years and is now applied commercially in a range of industries such as the automotive, mining and aerospace. In the power generation industry, the leading edge of turbine blades in a low-pressure (LP) steam turbine becomes eroded in service by the water droplets in the steam atmosphere [2,3]. Laser cladding has been demonstrated to be the optimum approach to repair turbine blades because of its ability to produce controlled dilution and fusion bonding between the clad layer and substrate and low distortion [4–6]. The laser used for this is normally a continuous wave laser, such as the CO 2 and Nd:YAG [4]. However, contrary to the continuous wave laser cladding, the pulsed laser cladding offers a number of advantages for the repair of turbine blades. While heat build up during cladding with a continuous wave laser is relatively low compared to other conventional processes, it can be too high in some situations leading to the undesirable effects of high dilution and cracking of the layer. Pulsed laser cladding is one possible solution to this problem, offering significantly lower heat build-up in the workpiece and therefore lower heat-affected zone, dilution and tendency to crack. The laser power-off period between two pulses allows the melt pool to solidify, therefore, the cooling rate is faster 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.03.058 * Corresponding author. Tel.: +61 3 92145624; fax: +61 3 92145050. E-mail address: ssun@groupwise.swin.edu.au (S. Sun). Surface & Coatings Technology 194 (2005) 225– 231 www.elsevier.com/locate/surfcoat