Simulation of laser surface hardening of Ti-6AL-4V

Abstract

Laser hardening aims to improve the wear behaviour of various component. The advantage of using laser as a heat source in this surface hardening method is that its region can be controlled. In laser surface hardening the source of heat is laser which is made to fall on the surface of the material. The surface layer is heated such that phase transformation occurs and the cooling rate would decide the hardness achieved. To study this, simulation of laser hardening of Ti6AL4V was carried out using ABAQUS and JMatPro software. Optimized parameters of laser were taken such as the laser power, scanning speed and beam spot diameter. Measurements of Vickers microhardness was done through simulation in ABAQUS and it was found that there was increase of surface harness after the laser hardening process, from (324 HV to 448 HV) measured on top surface of Ti6AL4V. The simulation for Vickers hardness was challenging as the properties of material which was changed due to heat interaction has to be evaluated. The change in material properties such as yield stress and corresponding strain values are calculated based on cooling rates. To find the cooling rate Rosenthal equation was used and for particular cooling rate the material properties was calculated from JMatPro software which takes account the phase transformations in it. The hardness decreases with increase of depth from surface. It was found that as we increase distance from centre of beam spot the hardness value decreases. The laser surface hardening was performed on different thickness of sheets as 1.5 mm and 3 mm. The effect of sheet thickness was also studied in this research. The main aim was to get maximum harness at top surface of Ti6AL4V. It was seen that with increase of cooling rate, the harness was enhanced. In this research, the enhancement of cooling rate was studied using the concept of heat sink. The effect on cooling rate with thermal contact resistance at the interface of Ti6AL4V and heat sink was also studied.