Optimizing gas pressure for enhanced tribological properties of DLC-coated graphite.

In this study, for the first time, the optimization of applied pressure for achieving the one of the best tribological properties of diamond-like carbon (DLC) coating on graphite surface using plasma-enhanced chemical vapor deposition (PECVD) method was investigated. Raman spectroscopy and microscopy methods were used to characterize the applied coating. Additionally, the mechanical properties of the coating were investigated through nanoindentation testing. The wear resistance of coating has been tested as functional test. The results indicated that with increasing gas pressure, the sp3 hybridization percentage decreases, while the ID/IG ratio increases. The average roughness values for the uncoated sample and the coated samples at working pressures of 25, 30, and 35 mTorr were obtained as 1.6, 5.1, 3, and 2.4 nm, respectively. The results of hardness and wear tests showed that these properties were optimized by reducing the applied gas pressure. The highest hardness was 11.59 GPa, and the best sample in terms of the mechanical properties of the coating was the sample applied at a gas pressure of 25 mTorr. Results show that the optimal sample in tribological performance is the one applied at a working pressure of 25 mTorr. Because this sample demonstrates the lowest coefficient of friction, and wear depth.

Synthesis, microstructure and mechanical properties of porous Mg--Zn scaffolds.

Magnesium alloys have been intensively studied as biodegradable implant materials, as their mechanical properties render them promising candidates for bone tissue engineering applications. In the present work, porous Mg-4wt% Zn and Mg-6wt% Zn scaffolds were prepared using a powder metallurgy process. The effects of the porosity and Zn content on the microstructure and the mechanical properties of the fabricated scaffolds were studied. The above mentioned fabrication process involved sequential stages of mixing and compression of Mg and Zn powders with carbamide materials as space-holder particles followed by sintering the green compacts at different temperatures below the melting point of Mg. The results indicate that the porous Mg--Zn specimens with a porosity and pore size of approximately 21-36% and 150-400 µm, respectively, could have enhanced mechanical properties comparable with those of cancellous bone. In addition, an increase in the amount of Zn in the applied alloy gives rise to a significant refinement of magnesium grain size and an improvement in the mechanical properties, such as the compression strength, of the porous Mg--Zn specimens. Furthermore, according to the results, the porous Mg--Zn alloy could be considered one of the most promising scaffold materials for hard tissue regeneration.