Numerical Simulation of Effect of Different Initial Morphologies on Melt Hydrodynamics in Laser Polishing of Ti6Al4V.

Kai Li,Zhenyu Zhao,Jie Yin,Wei Zhang,Houming Zhou,Hao Zhou,Guiyao Zhou

doi:10.3390/mi12050581

Abstract

As a surface finishing technique for rapid remelting and re-solidification, laser polishing can effectively eliminate the asperities so as to approach the feature size. Nevertheless, the polished surface quality is significantly sensitive to the processing parameters, especially with respect to melt hydrodynamics. In this paper, a transient two-dimensional model was developed to demonstrate the molten flow behavior for different surface morphologies of the Ti6Al4V alloy. It is illustrated that the complex evolution of the melt hydrodynamics involving heat conduction, thermal convection, thermal radiation, melting and solidification during laser polishing. Results show that the uniformity of the distribution of surface peaks and valleys can improve the molten flow stability and obtain better smoothing effect. The high cooling rate of the molten pool resulting in a shortening of the molten lifetime, which prevents the peaks from being removed by capillary and thermocapillary forces. It is revealed that the mechanism of secondary roughness formation on polished surface. Moreover, the double spiral nest Marangoni convection extrudes the molten to the outsides. It results in the formation of expansion and depression, corresponding to nearby the starting position and at the edges of the polished surface. It is further found that the difference between the simulation and experimental depression depths is only about 2 μm. Correspondingly, the errors are approximately 8.3%, 14.3% and 13.3%, corresponding to Models 1, 2 and 3, respectively. The aforementioned results illustrated that the predicted surface profiles agree reasonably well with the experimentally measured surface height data.

Highlights

Ti6Al4V alloy has been widely used in aerospace [1], chemical industries [2] and medical sector [3] due to its low density [4], high strength [5] and excellent biocompatibility [6].the surface quality, such as surface roughness, of the devices fabricated fromTi64 is posed in a great challenge
We developed a transient 2D model coupled of heat transfer and fluid fields based on moving heat source
It is illustrated that the effect of different initial morphologies on the evolution of the melt hydrodynamics during Laser polishing (LP)

Summary

Introduction

Ti6Al4V alloy has been widely used in aerospace [1], chemical industries [2] and medical sector [3] due to its low density [4], high strength [5] and excellent biocompatibility [6].the surface quality, such as surface roughness, of the devices fabricated fromTi64 is posed in a great challenge. Ti6Al4V alloy has been widely used in aerospace [1], chemical industries [2] and medical sector [3] due to its low density [4], high strength [5] and excellent biocompatibility [6]. The surface quality, such as surface roughness, of the devices fabricated from. Ti64 is posed in a great challenge. It is difficult to polish the complex surface. LP can effectively surface roughness, and the polished surface can be secondary strengthening such as hardness [7,8], wear and corrosion resistance [9,10]. Polishing on Ti6Al4V is a real challenge, which can modify the surface and becoming fragile and Widmanstätten patterns during PAM process [11,12]. This work can prevent the realization of such damage or wrong patterns

Methods

Results

Conclusion