Investigations On Micro-Texture Morphology Of TC4 Surface Obtained By Millisecond Pulsed Laser

Laser texturing technology is a recently developed technology which is mainly used to improve the surface properties of metal materials.The interesting characteristics of this technology include the controllable special morphology with micro scale or nano scale structure,high efficiency,and the convenience.This technology has been regarded as an effective way to improve the wear resistance,and in turn to extend the life span of the components and parts.It is very essential for saving energy and enhancing economic performance.Up to date,more researches on laser texturing mainly focus on the technology and characterization of the properties.However,it is needed to carry on further investigations on temperature field distribution,the relationship between morphology and surface roughness,and the research on effect rule of the morphology on the wear resistance.This is beneficial for optimize the technology and realize the controllable design of textured morphology.In present work,the temperature field distribution was calculated,on the basis of the calculation results,laser texturing experiments were carried out.The influences of texturing parameters on the morphology,surface roughness,and in turn the wear resistance were investigated.In this paper,a new parameter named ratio of depth to width of the textured pit was proposed and used to represent the relation between morphology and surface roughness and wear resistance.The results indicated that the pulse width,pulse frequency,and laser scanning speed were three main factors that influence the temperature field distribution.The highest temperature during laser texturing increased with increasing of pulse width and pulse frequency.Meanwhile,the temperature gradient and the time duration to reach the highest temperature also increased.On a contrary,the highest temperature,the temperature gradient and the time duration to reach the highest temperature all decreased with increasing of scanning speed.No obvious influence of pulse width on the density of textured pit was observed.However,the ratio of the pit depth to the pit width(r)increased with increasing of pulse width.Both of the density of textured pit and the ratio of pit depth to the pit width were dependant on the pulse frequency and scanning speed.The density and the ratio increased with increasing of pulse frequency,but decreased with increasing of scanning speed.The ratio of pit depth to the pit width(r)can be used to represent the surface roughness Ra.A higher ratio results in a higher surface roughness.The relationship between the Ra and r can be expressed as Ra2=7061.31×r.The erosion of laser ablation to the substrate was reduced by using controlling technology.The textured morphology with a lower ratio of pit depth to pit width was realized using the modulated technology.A lower ratio r in turn decreased the surface roughness.The textured surfaces with different ratio r and surface roughness Ra presented different wear resistance properties.In present work,the better parameters for preparing an excellent textured surface were obtained.The pulse width was no more than 1.4 ms,the pulse frequency and the scanning speed were no less than 14 Hz and 800 mm/min,respectively.Coatings with three different textured morphologies named pit texture,linear texture and pseudoclathrate texture were fabricated on TC4 substrate.Among them,the linear texture coating presented similar wear resistance as TC4 substrate,while the pit texture coating and pseudoclathrate texture coating exhibited excellent wear resistance.Furthermore,the wear resistance of pseudoclathrate texture coating was much better than that of the pit texture coating.