# Micromachining in Powder-Mixed Micro Electrical Discharge Machining
## 4 Application of Power-mixed \(\upmu\)-EDM (PM \(\upmu\)-EDM)
### Application of PM\(\mu\)-EDM in Surface Modification  
Applications of powder-mixed dielectric fluid \(\mu\)-EDM are not only limited to obtaining high surface quality and material-removal rates. Powder material such as silver has anti-bacterial property, as well as high electrical conductivity [61; 62], which is compatible as surfactant in the dielectric fluid. [PERSON] et al. [63] utilized silver nanopowder to machine and to modify the surface of Ti-6 Al-4V for improving its antibacterial property in medical applications. The results show that the deposited silver content increases with the increase in the powder concentration, however, at similar concentrations of powder, it decreases with the increase in pulse energy. Therefore, it is recommended to have a pulse energy lower than 17.5 uJ to achieve the surface requirement of having a antibacterial properties.  
In order to improve the hard and wear resistance properties of an engine part, solid lubricating powders such as MoS\({}_{2}\) have received more special attention than other materials [64].  
[PERSON] et al. [65] utilized MoS\({}_{2}\) powder-mixed deionized water to generate a hard, wear-resistant and lubricating layer on titanium surface. The experiment results showed that the microhardness of titanium surface increased significantly up to two times more than the microhardness of base metal. This is due to the formation of an intermediate phase of titanium with molybdenum disulfide and oxides. In addition, the coefficient of friction of the modified surface decreased from 0.47 to 0.13. It can be concluded that a hard, self-lubricating and wear-resistant coated layer of MoS\({}_{2}\) was deposited over the titanium surface through a powder-mixed dielectric \(\mu\)-EDM process.  
In biomedical application, powder-mixed dielectric \(\mu\)-EDM was used to improve the hydrophilicity of the titanium surface, since a high-hydroophilicity surface is essential for dental implants as well as other biomedical applications [66; 67; 68; 69]. [PERSON] et al. [70] added pure Ti powders (35-45 \(\upmu\)m in diameter) into the deionized water at concentrations of 3 g/L and 6 g/L. Pure Ti grade 4 was used as a tool electrode and the workpiece material. Hydrophilicity examination was performed by using the sessile drop method and a contact angle goniometer. The results showed that under conventional \(\mu\)-EDM process, the water contact angle of the surface was found around 87\({}^{\circ}\). When the powder was introduced into the fluid, the surface exhibited an improvement of hydrophilicity surface, which was around 65\({}^{\circ}\). This can be explained that the introduction of titanium powder into dielectric fluid provides a thicker recast layer with a high content of TiO on the surface, resulting in the improvement of surface hydrophilicity.  
[PERSON] et al. [71] investigated the effect of using tungsten disulphide (WS\({}_{2}\)) powder-mixed dielectric fluid \(\mu\)-EDM for the surface modification of Ti-6 Al-4V. The material from the tool and the suspended powder from dielectric fluid migrated to the workpiece due to the generated high thermal energy from electrical sparks. Among other parameters, such as voltage and duty factor, the concentration of suspended WS\({}_{2}\) was the most significant parameter affecting the deposition rate, surface roughness and the microhardness. The average microhardness value was improved up to three times from the original hardness value. [PERSON] et al. [72] obtained a coated surface with solid lubrication, hard and corrosion resistance on Ti6 Al4V by mixing BN powder into a dielectric fluid of \(\mu\)-EDM. Due to the presence of the BN, TiN dan TiAlN on the coated surface, the average microhardness improved from 280 HV (parent material) to in the range of 390.1 \(\pm\) 6.2-1393.5 \(\pm\) 7 HV. The wear test showed that the wear rate was significantly improved from 0.22 mg/min to 0.05 mg/min. The friction test also showed a great improvement of the coefficient of friction (CoF) from 0.4 to 0.26.