Laser surface modification of AZ31B Mg alloy for bio-wettability

Abstract

Laser surface modification of AZ31B Magnesium alloy changes surface composition and roughness to provide improved surface bio-wettability. Laser processing resulted in phase transformation and grain refinement due to rapid quenching effect. Furthermore, instantaneous heating and vaporization resulted in removal of material, leading the textured surface generation. A study was conducted on a continuum-wave diode-pumped ytterbium laser to create multiple tracks for determining the resulting bio-wettability. Five different laser input powers were processed on Mg alloy, and then examined by XRD, SEM, optical profilometer, and contact angle measurement. A finite element based heat transfer model was developed using COMSOL multi-physics package to predict the temperature evolution during laser processing. The thermal histories predicted by the model are used to evaluate the cooling rates and solidification rate and the associated changes in the microstructure. The surface energy of laser surface modification samples can be calculated by measuring the contact angle Santhanakrishnan, whose work demonstrated to me that how to concern the matters of research and always inspirited me to pursue to an advanced quality in experimentation and research. Comparing to the conventional metallic biomaterials such as Ti-6Al-4V, stainless steel, and Co-Cr based materials, using Mg implants can provide several benefits which other metallic implants lack. Hence high biocompatibility and the ability to degrade after bone regrowth are the significant reasons to develop Mg implants. (4) capillary rise, and (5) tilted drop. Static, or sessile drop method is the most commonly used technique, because it is easy to conduct. In this case, a droplet is placed on the testing surface by using a contact angle goniometer. The contact angle is defined as an angle formed between the solid-liquid interface and the liquid-vapor interface and which has its vertex where the three interfaces meet as shown in Fig 1.1(a). Young's equation shows the relation of interfacial tensions of solid-vapor (γ sv ), liquid-vapor (γ lv ), solid-liquid (γ sl ), and contact angle (θ) as follows:If the contact angle is greater than 90°, the surface can be considered as a hydrophobic surface (Fig 1.1(b)). On the contrary, the small contact angle on the testing surface refers to the wetting or hydrophilic surface (Fig 1.1(c)). Although it has been broadly accepted that the biological response of the surface can be influenced by hydrophobicity/hydrophilicity, the wetting effects to cell behavior are still in controversy and inconsistency. Many researchers described that it is necessary to improve surface from hydrophobicity to hydrophilicity for supporting cell adherence and, in particular, growth. On the contrary, other researchers presented that the hydrophobic surface performed better cell response [13]. However, it is now well accepted in biomaterial community both overly hydrophobic and overly hydrophilic surface are not ideal for cell attachment, rather, surfaces wi...

Laser surface processing of magnesium alloys

“…This indicated that with sufficient laser power in melting the surface, the surface roughness increased with a further increase in the laser power. Ho et al [129] mentioned that the surface roughness of laser treated samples increased with an increase in the laser energy density, which is in agreement with our observations.…”

“…It has been reported that the higher surface roughness with smaller grain size provides poor wettability [129]. The optimal combination of surface roughness, grain size and homogenous chemical composition of surface improves the wettability.…”

Effect of droplet size on wetting behavior on laser textured SiC surface

“…But, Wenzel and Cassie models cannot give the correlation of droplet size and surface morphology size according to the Eqs. (1) and (2). The phenomenon may be caused by the correlation between morphology feature size and droplets size.…”

“…Surface texturing technology has been widely used to enhance wettability by controlling the surface morphology on the substrates especially with rapid development of laser processing method (Dahotre et al [1,2], Luo et al [3], Noh et al [4], Wang et al [5]). Generally, research of surface wetting behavior has been always single, hydrophilicity or hydrophobicity, even superhydrophilicity or superhydrophobicity.…”

Thermal-induced transformation of wetting behaviors on laser-textured SiC surfaces

“…Laser processing is a method to modify surface morphology by melting and recrystallization, and the history temperature is over 300°C, even more than 1000°C during the processing [22]. Therefore, the thermal residual stress will exist after rapid cooling of the textured surface, and this stress will be released over time.…”