ND-YAG LASER ALLOYING OF HIGH-SPEED STEEL TOOLS WITH BN AND TI BN ANDTHE EFFECTS ON TURNING PERFORMANCE/

A 400 W pulsed Nd:YAG laser was used to surface alloy BN and Ti/BN on AISI M2 steel using hexagonal BN powder and Ti foil (25 mum thickness) . The clearance (flank) faces of the single-point tool were laser allo yed using BN and Ti/BN. Optical metallography, scanning electron micro scope, Vicker's microhardness and X-ray diffraction were employed to c haracterize the alloyed layers. The depths of the laser-alloyed zones of BN- and Ti/BN-alloyed tools were about 140 mum and 260 gm respectiv ely. The hardness of the laser-alloyed layer with BN was about 640 HV while that of the alloyed layer with Ti/BN was about 680 HV. The alloy ed layers were free from cracks and porosity. Both the alloyed and una lloyed tools were then tested on a 14.7 kW engine lathe to turn AISI 1 045 steel workpieces. The results indicated that the tool life of BN-a lloyed tools was about 200% higher than that of the unalloyed tools, w hile the tool life of Ti/BN-alloyed tools was about 260% higher when t he tool life criterion was chosen as 0.3 mm flank wear. Also, the tool wear rate was reduced by about 30% and 50% for BN-and Ti/BN-alloyed t ools, respectively. The reduction in tool wear of the alloyed tools wa s attributed to a reduction of the chip-tool contact length (and conse quently the reduction of coefficient of friction between the tool and workpiece material) and to the different chip formation mechanisms.