Laser cladding of pre-placed stellite SF6 powder with a pulsed Nd:YAG laser and optical fibres

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Abstract
A series of experiments was performed to investigate the cladding of Stellite SF6 powder, pre-placed on mild steel substrates, with a pulsed Nd:YAG laser and optical fibres. The beam from a pulsed Nd:YAG laser, operating at an average output power of 300 W, was transmitted to the workpiece via a step-index glass fibre of length 10 m and core diameter 0.6 mm. A number of parameters were investigated such as the pulse energy, pulse frequency, focal length, powder depth and spot overlap to determine their effect on clad layer formation and integrity. Two different sets of experiments were performed, one involved producing single tracks and the other continuous layers.The results indicate that the laser beam profile is a critical parameter affecting most of the clad layer’s characteristics such as its thickness, dilution and cracking. The beam profile should be preferably rectangular in shape in order to produce a low-dilution clad layer. Also, the energy per unit area should be high enough to prevent crack formation and result in an appropriate bonding. The repetition rate of the laser appeared to affect only the processing speed, as higher repetition rates allow higher processing speeds for the same spot overlap.The study has demonstrated that it is feasible to produce sound Stellite SF6 clad layers on mild steel using a pulsed Nd: YAG laser and optical fibres.A series of experiments was performed to investigate the cladding of Stellite SF6 powder, pre-placed on mild steel substrates, with a pulsed Nd:YAG laser and optical fibres. The beam from a pulsed Nd:YAG laser, operating at an average output power of 300 W, was transmitted to the workpiece via a step-index glass fibre of length 10 m and core diameter 0.6 mm. A number of parameters were investigated such as the pulse energy, pulse frequency, focal length, powder depth and spot overlap to determine their effect on clad layer formation and integrity. Two different sets of experiments were performed, one involved producing single tracks and the other continuous layers.The results indicate that the laser beam profile is a critical parameter affecting most of the clad layer’s characteristics such as its thickness, dilution and cracking. The beam profile should be preferably rectangular in shape in order to produce a low-dilution clad layer. Also, the energy per unit area should be high enough to prevent crack f...

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