The influence of ultrasonic vibration amplitude and magnetic field intensity on microstructural characteristics in laser drilling of Ti6Al4V

Abstract

Nowadays, laser drilling has found extensive medical applications such as drilling of titanium implants. However, laser drilling of such implants has encountered several restrictions such as low penetration depth, high thickness of recast layer and heat affected zone (HAZ). Therefore, various approaches such as magnetic field and/or ultrasonic vibration aided laser drilling have been proposed to overcome these limitations; among them, few studies have been conducted considering the simultaneous effect of magnetic field and ultrasonic vibrations on microstructural characteristics. Therefore, in the present paper, the effects of magnetic field intensity and ultrasonic vibration amplitude (with a frequency of 28 kHz) have been investigated on the formed phases, thickness of recast layer and thickness of HAZ in laser drilling of Ti6Al4V. According to the obtained results, adding ultrasonic vibrations to the laser drilling process will lead to an average decrease of 29.40% and 28% respectively for the thickness of HAZ and recast layer. However, with the addition of a magnetic field (0.1 Tesla), the thicknesses of HAZ and recast layer were increased by 7% and 11%, respectively. Furthermore, increasing the ultrasonic vibration amplitude was associated with the increase in the acicular alpha phase (α′) as well as more dense, and fine-grained and uniform structure. This can be attributed to the strengthening of convective heat transfer mechanism and higher cooling rate. Additionally, by increasing the intensity of the magnetic field, the structure of the acicular alpha (α′) became finer and the density of lateral branches decreased.