فصلنامه علوم و مهندسی سطح ایران
پیاپی 22 (زمستان 1393)

In this paper Al doped ZnO (AZO) thin films with 0, 3, 6 and 12% Al molar concentration were prepared by sol-gel process on glass substrates. The deposited films were annealed at different temperatures of 300-500 ˚C for 1 h in air. X-ray diffraction (XRD) showed wurtzite crystalline structure for the films annealed above 400 ˚C. Then the films were irradiated by beams of excimer (KrF, λ=248 nm) laser. The evolution of crystal structure and surface morphology were studied using XRD and filed emission scanning electron microscope (FE-SEM). The real-time measurement of electrical conductivity during laser irradiation showed a transient or persistent photoconductivity depending on sample type. The effect of laser energy on photoconductivity was also investigated. Using photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) spectra, the laser induced photoconductivity effect was discussed.

The purpose of this study is investigation of hot corrosion behavior of plasma-sprayed yttria stabilized zirconia (YSZ) thermal barrier coatings in the presence of molten sulfate-vanadate salt. For this intention, NiCoCrAlY bond coat and followed by YSZ top coat were deposited on Inconel 738LC substrates by atmospheric plasma spraying (APS). Hot corrosion test was carried out on the surface of YSZ coating in the presence of salt mixture of Na2SO4 + V2O5 at 1000 °C for 30 h. To investigate hot corrosion behavior, microstructural characterization by scanning electron microscope (SEM), elemental analysis by energy dispersive spectroscopy (EDS) and phasic analysis by x-ray diffractometry (XRD) were done. Based on the results, reaction between molten salt and stabilizer of zirconia (Y2O3) and formation of YVO4 crystals, the detrimental phase transformation of zirconia from tetragonal to monoclinic due to depletion of stabilizer and finally creation of thermal and physical stresses was recognized to degradation mechanism of YSZ ceramic coatings in the presence of molten sulfate-vanadate salt.

In the present research, cast iron cladding of low carbon steel was carried out. Filler metals were cut from as-casting cast iron block and cladding was carried out by using gas tungsten arc welding (GTAW) process. Effect of welding parameters on the cladding characteristics was studied experimentally. Microstructural investigation accompanied with XRD analysis indicated that fine pearlitic structure with inter-dendritical cementite was formed in the clad layer. Microhardness and wear resistance investigation of clad layer illustrated that the cast iron overlayer on low carbon steel could improve the surface properties of the cladded samples significantly. Microstructural observations of worn surface indicate that the mechanism of wear was predominantly abrasive one.

In this study copper coatings were deposited by cold spraying, under different spraying conditions. Microstructure of the coatings was investigated by optical and scanning electron microscopy. Additionally, differential scanning calorimetry (DSC) and thermal gravimetric analysis were used to examine the quality of the coatings, especially with regards to the extent of the bonded area between the particles. As shown in SEM results, the electrolytic-powder exhibited a much higher population of internal boundaries, as compared to the spherical powder sample. This means that even for identical values of FBA for both types of sample, the electrolytic sample would contain a larger amount of non-bonded areas per unit volume. The results of DSC indicated exothermic reactions at certain temperatures that maybe related to spray conditions and microstructural properties. The samples sprayed at higher pressures, have lower non bonded areas. TGA also has confirmed this result. Moreover, it can be concluded, the spherical powders cause more compact coatings. So, thermal analysis can be utilized reliably to examine the fraction of bonded areas in cold-sprayed deposits.

In this research paper the crystallinity-index and physical-mechanical properties of Co-based self-fluxing thermal spray coatings produced using APS and HVOF on low-carbon steel substrates were investigated. Advanced characterization methods such as XRD, SEM and TEM as well as DSC thermal analysis were used to evaluate the evolution of phase transformation during thermal spraying processes. The phase analysis results show that the main phase of the thermal spray coatings was α-Co solid solution with FCC crystal structure as well as amorphous phase that produced during rapid solidification of particles over the course of flying on impacting to the substrate. The Crystallinity-index for APS and HVOF coatings was computed around 75% and 80% respectively. The existence of amorphous phase in the matrix was yielded to increase the hardness of the coatings. The average microhardness was estimated around 800 and 500 Vickers for HVOF and APS coatings respectively. In addition the porosity content percentage was calculated about 2.12±0.11 for HVOF and 5.52±0.73 for APS coatings. The adhesion strength test showed that for the APS coating fracture was happened in the interface of the coating / substrate in the form of adhesive, however, for HVOF coating fracture was occurred in glue or the interface of the glue / substrate.

Co-P electrodeposites are appropriate substitute for hard chromium coatings due to their suitable properties. In this study, nano-crystalline and amorphous Co-P coatings were deposited on plain carbon steel substrates using a direct current and their morphology was examined. The effect of pH on morphology, current efficiency, phosphorus content, hardness and preferred orientation of the coatings were investigated. Moreover, the effect of heat treatment on microstructure and hardness of the nano-crystalline and the amorphous coatings was studied. The results showed that, phosphorus content and hardness of the coatings were decreased by increasing the pH from 1 to 4 in spite of an enhancement in the current efficiency up to 98%. Preferred orientation and morphology of the coatings were also changed by increasing of pH values. Hardness numbers of the amorphous and the nano-crystalline coatings, deposited at the optimum condition, were about 750 and 600 HV, respectively. These values were increased and reached 1090 and 760 HV by heat treatment.

This work represents a simple method for production of bilayer Au/Ag nanostructures used in localized surface Plasmon resonance sensors. Different thickness of Au and Ag were sputter-deposited on cleaned glass slides and annealed at 150°C and 300°C using an electrical furnace in ambient air for 2, 3 and 4 h. The analysis of the surface topology and optical property was performed by AFM apparatus and UV-visible spectrometer. Annealing changed appearance color of samples and red shifted the resonance wavelength. By increasment of annealing time and temperature, the resonance wavelength and the mean size of produced particles on the surface increased.

In this study, the surface of the samples were hardened by pulsed Nd:YAG laser. After determination of optimal parameters of laser transformation hardening of mentioned steel and improving in hardness compared to previous studies by pulsed Nd:YAG laser, the pitting corrosion behavior of hardened and as received surfaces were compared. SEM and Optical microscopic studies were done to study the microstructure. Cyclic polarization tests were used to study the electrochemical corrosion behavior. The result showed that in the result of solid- state transformation and refining of carbides in the steel matrix, improvement in the depth and surface hardness was obtained and the hardness of about 700 Vickers in the surface was gained. The polarization curves showed increased 113mV in potential. It was observed that this steel didn’t have repassivation capability even after laser surface hardening.

In recent years, electroless Ni-B coatings have attracted much attention because of their wear-resistance and having high hardness. In the present research, using a two-level factorial design with three center points, the effect of ethylenediamine, ammonia and stabilizer solutions concentration on microhardness of the coatings in heat-treated condition was studied. The results showed that ethylenediamine concentration had no effect on the microhardness, but it made the electroless plating solution more stabilized. The stabilizer solution had the highest main-effect in increasing the microhardness. Also the interaction between ammonia and stabilizer solutions was significant. The maximum achieved microhardness for the coatings was 1358 HV which had been achieved when the ethylenediamine and ammonia concentrations were at their highest level. Scanning electron microscopy revealed that the microstructure was granular. Also the X-Ray diffraction analysis showed that the microstructure of the coating is nano-scaled and consisted of Ni3B, Ni2B and probably crystalline Ni grains.