IRANIAN JOURNAL OF SURFACE SCIENCE AND ENGINEERING
Year:2012 | Volume:- | Issue:13|Papers Count:10

The purpose of the present paper was evaluation and comparison of Ti 6Al 4V alloy structural surface characteristics after both surface engineering processes comprised of plasma nitriding (PN) and a PN process followed by TiN PVD deposition, duplex process. PN treatment performed under gas mixture of N2/H2=4; at temperatures of 700, 750, 800 and 850°C for 10 h. To perform duplex process, a TiN layer deposited by catholic were plasma PVD on the surface of pre plasma nitrided samples. Structural characterization of surface and cross section performed by scanning electron microscopy (SEM), atomic force microscopy (AFM), Energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and microhardness testing methods. While TiN deposition was led to formation of only d-TiN phase, three distinguished structure including of compound layer (constituted of d-TiN and e-Ti2N), aluminum-rich region and a diffusion zone, interstitial solid solution of nitrogen in titanium, were detected at the surface of plasma nitrided Ti 6Al 4V alloy. XRD patterns of duplex treated samples were indicated the simultaneous present of phases which formed during both processes. Although the structures obtained from each one of the processes alone were increased surface hardness, the hardness of outer surface produced by duplex process was significantly higher than plasma nitrided samples. Interdiffused interface of TiN layer (resulted of PVD process) with compound layer (caused by PN process) has been a significant role on the duplex coating performance. Increasing of plasma nitriding temperature, not only increased growth rate of TiN deposition by PVD process, but also improved homogeneity and continuity of TiN with compound layer.

The aim of this study is to investigate the effect of increasing deposition time and thus increasing thickness on the properties of created titanium films on 316L stainless steel substrated by using physical vapor deposition (PVD) method. To achieve this, deposition operation in various duration times of 5, 10, 15 and 20 minutes were set to obtain films with different thicknesses. Then, thickness of the titanium films were measured by using the profilometer set up and their chemical composition were determined by energy dispersive X-ray (EDX) technique. morphology of the films were investigated by using field emission scanning electron microscopy (FESEM) and their topography by atomic force microscopy (AFM). Structure of the titanium films were determined by using X-ray diffraction (XRD) technique and their adhesion strength to substrate were investigated by heat and quench quality test. The results of these tests showed that by increasing deposition time, thickness of titanium films increases from 88 nm to 298 nm. Average titanium particles size increased from 12 nm to 65 nm and structure becames more dense and uniform. average surface roughness of titanium films increased from 2.108 nm to 3.767 nm. Titanium films had a preferred orientation of (002) and showed good adhesion strength to the substrate.

In this study, hydroxyapatite powders as a bioceramic were coated on NiTi shape memory alloy by electrophoretic method. Suspension solution used as a mixture of n -butanol and tri ethanol amine (TEA). Deposition was carried out at different applied voltages of 20, 30 and 40 volts in different times from 1 to 5 minutes and constant voltage on the cathode. After deposition, the samples were dried at room temperature for 24 hours. Then weight and thickness of coating were measured. Ultimately the samples were sintered at 800oC in argon atmosphere for 2 hours. X-ray diffraction (XRD) and SEM were used for phase identification and morphological examining of coating consecutively. Composition of coating was analysied by Energy Dispersive X-ray (EDX). The results showed that a uniform, continuous and crack-free coating can be achieved at 30 volt and at shorter time after sintering. Moreover an increase in the deposition period, caused an increase in the weight and thickness of the deposition. The technique presented in this research can be a replacement technique for bioactive coatings in comparison with other techniques such as sol-gel and plasma spray coating.

This paper deals with the investigation of microstructure, phase structure and microhardness of steal substrate coated with WC- (Co/FeAl) powders by HVOF spray system. For this purpose, samples were evaluated by metallographic studies, microhardness measurements and X-ray diffraction analysis. The results indicated that both coating structures are uniform and the porosity was low. The microhardness of WC-FeAl coating is higher than WC-Co, which is caused by the higher hardness of Iron Aluminide in comparison to cobalt. Evaluation of the coatings showed that the binder has a significant impact on mechanical properties.

The present research deals with the synthesizing of chromium coating by pulse and direct current from standard bath chromium in the same condition. Crystal structure, morphology, hardness, and surface roughness of fabricated coatings were controlled by varying processing parameter including on time and off time. X-ray diffraction and scanning electron microscopy were employed to evaluate the phase identification and surface morphology of coating. It was found that b-chromium with hexagonal structure forms in pulse plating; however with an increase in off time, the amount of b-chromium in the structure was increased. Finally the coating morphology was affected and varied from trigonal pyramidal like in 50% duty cycle to cubic structure in 20% and caused a decrease in coating properties.

In this paper we present the results of a study on the use of electro-catalytic coating of PbO2 on Ti/SnO2 substrate. The experiments were conducted using continuous and pulse DC electroplating innitrate type electrolyte. Electroplating parameters, such as, current density and electrolyte temperature were changed to produce a coating with a high surface roughness, small crystal size and high active surface area. The samples were studied using a number of techniques that included SEM (Scanning Electron Microscopy), roughness measurement and CV (Cyclic Voltammetry). The results showed that a combination of 65oC and 33 mAcm-2 were an optimum temperature and current density that yield a good coating of pure 5-phase. The morphology of coating that. mentioned above electroplating conditions included nano-flakes with a thickness about 45-85 nm and 0.75-10 mm length. The STM (Scanning Tunneling Microscopy) observation of the surface revealed that the coating also included PbO2 nano-particles with an average diameter in the range of 7-21 nm.

The main purpose of this work is to investigate the effects of different ions produced in plasma focus device (SBUPF1) with the specification of (8.6mF, 25 kV, 2.5kJ) on the Aluminum surface. Also the possibility of ion implantation with the use of this device has been investigated. Argon and Hydrogen+1%Krypton used as working gas. For determining optimum ion density, optimum pressure and operating voltage for Argon as operating gas have been obtained (0.45mbar and 22kV respectively). These parameters for Hydrogen+1%Krypton were 5mbar and 23kV respectively. Irradiated samples have been analyzed with SEM technique for morphological and surface study of samples. The EDX spectroscopy and the SRIM calculations have been done to determine the composition of samples and the penetration depth of the ions in the samples respectively. Melting and surface evaporation effects and generation of cracks were seen in these samples. The intensity of these effects for the samples put in different height from the anode top has been determined. Elemental analysis with EDX technique showed that copper ions penetrated into the samples due to sputtering from anode.

In this paper thermal spray nanocrystalline coatings were developed by devitrification of Fe-based amorphous phase. In this approach a new composition of Fe-Cr-Mo-P-B-C-Si amorphous powder was produced in solid state by mechanical alloying of elemental powder mixture. After optimizing the powder morphologies as well as the size distributions, some coatings were produced by high velocity oxy fuel (HVOF) on carbon steel substrates. The phase transformations of coatings during devitrification were investigated by x-ray diffractometry (XRD), and transmission electron microscopy (TEM). It was found that by carefully controlling the HVOF parameters and the rate of cooling, the amorphous phase could be crystallized in the controlled manner and the microstructures with fully amorphous and nanocrystalline phases in the range of 10-20 nm were obtained. Therefore, these coatings will have the modified mechanical and tribological properties.

A spacecraft in orbit undergoes extreme temperature cycling due to the direct sun load on one side and deep cold space on the other side. The equilibrium temperature of any subsystem of the spacecraft is controlled by the solar absorptance (as) and infrared emittance (e) of its surface. White and black thermal control coatings applied to the spacecraft components play an important role on thermal control by providing suitable optical properties. In the present paper, the thermo-optical and adhesion properties of black silicone and white silicate thermal control coatings based on taguchi design were studied. Results showed that the surface pretreatment and adhesion promoter type had important influence on the adhesion properties of the black silicone thermal control coatings. The thermo-optical testing showed that solar absorbtion and emittance coefficients of this coating were 0.955 and 0.920 respectively. The results also, indicated that the pigment type was most effective parameter on the thermo-optical properties of white silicate thermal control coatings. The solar absorbtion and infrared emittance of this coating were 0.230, 0.907 respectively. Overall conclusion indicated both of optimized coatings in this study had desirable thermo-optical and adhesion properties, therefore could use as thermal control coatings on the surfaces of spacecraft.