فصلنامه علوم و مهندسی سطح ایران
پیاپی 54 (زمستان 1401)

In this study, a hierarchical coating of titanium dioxide/tungsten trioxide (TiO2/WO3) was created using the synergistic methods of plasma/hydrothermal electrolytic oxidation on the surface of pure titanium. For this purpose, TiO2 coating was first created by plasma electrolytic oxidation (PEO) process in phosphate-base electrolyte on titanium substrate. , then WO3 particles were created by hydrothermal process on TiO2 coating. The effect of the duration of the hydrothermal process (12, 18 and 24 hours) on the photocatalytic behavior of the coatings was investigated. Phase studies and microstructural characteristics were performed using X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). Photocatalytic degradation of methylene blue under visible light in the presence TiO2-WO3 coatings and TiO2 coating were compared. The pure TiO2 PEO coating showed about 47% degradation of methylene blue, while the optimal TiO2-WO3 composite coating, created by the combination of the plasma electrolytic oxidation /hydrothermal methods, resulted in 83% MB degradation. The highest photocatalytic activity of the TiO2-WO3 coating after hydrothermal for 18 h can be attributed to the presence of the visible-light-driven WO3 phase and its appropriate rod microstructure. After 12 h hydrothermal, the morphology of WO3 phase consisted of the nanoparticles and nanorods, while increasing the processing time up to 18 h led to the morphology development including the increase of nanoparticle size increment and growth of the nanorods.

In this research, pure CoNiCrAlY and composite CoNiCrAlY-2, 4 wt% Al2O3 powders were deposited by the HVOF process on IN738 nickel-based superalloy substrates. Composite powders were produced using a water-based solution method and polyvinyl alcohol adhesive to distribute oxide nanoparticles on CoNiCrAlY microparticles. An oxidation test was performed on the coatings at 1050°C and 50, 100, 150, and 200 hours in the stationary air. The microstructure and phase composition of the coatings were investigated by SEM and XRD before and after the oxidation test. The results showed that nanoparticles are present with relatively uniform distribution around the powders and the microstructure of the corresponding coatings. Porosity and surface roughness of pure and composite coatings (2, 4 wt%) were measured as 0.6, 1, and 2.7 vol.% and 4.4, 4.8, and 7.1 µm, respectively. After 200 hours of oxidation test, the thickness of the oxide layer formed on pure and composite coatings (2, 4 wt%) was measured as 5.2, 4.3, and 5.9 micrometers, respectively. CoNiCrAlY coating containing 2 wt% of Al2O3 showed the best resistance to oxidation due to the creation of diffusion barriers by nanoparticles. In contrast, the composite coating containing 4 wt% of Al2O3 had the weakest resistance to oxidation, which was caused by the rough surface morphology and the occurrence of internal oxidation in it.

Considering the growth of technology in biomaterial science, the main goal of surface coating is to increase biocompatibility and reduce adverse reactions of the body. Polyetheretherketone is a semi-crystalline thermoplastic that has outstanding mechanical and chemical properties as well as high thermal stability, and is a polymer that can be used in bone replacements. This polymer is also used with a porous structure. The modified biocompatibility of this polymer in the porous state using titanium coating has been considered in this research. At first, the porous peek samples were prepared using pure peek and sodium chloride salt as spacer, by dry mixing method and using SPS method. Then, the thin layer of titanium metal was coated on the polyetheretherketon substrate using plasma spray method and the effect of coating on the biomedical performance of polyetheretherketone was determined and evaluated. The main advantages of plasma spray titanium were the undamaged substrate and good stability of the coating layer, which were confirmed by SEM, XRD and bond strength analysis. Also, mechanical tests were taken from the porous sample, which showed that the density, compressive strength, and hardness of the produced sample are significantly high. In order to investigate the formation of apatite on the prepared samples, the bioactivity of these coated and uncoated samples was investigated by immersing them in simulated body fluid and it was concluded that polyetheretherketone coated with titanium has bioactivity properties.

In this research, additive manufacturing of IN625 on IN738 substrate was investigated by a cubic sample with dimensions of 2*2 cm2 with a unidirectional pattern. The purpose of manufacturing this sample; was to check the part microstructure, mechanical properties, and texture. To check the properties, electron and optical microscopes, and diffractometers equipped with goniometer were used. The results showed that the texture of grains is from the molten pool towards the substrate (in the direction of heat transfer). The SEM images showed that the columnar dendrites in the upper layers of the sample are larger than the columnar dendrites in the middle areas along with the secondary arm. Examination of the polfigure showed a Goss texture component ({011} >100) besides to a weak cubic component ({001} >100). The increase in length was 990, 563 MPa and 48% for the direction parallel to the tension axis.