Mustafa Ürgen

Preparation of zeolite coatings by direct heating of the substrates

A novel method is proposed for the preparation of zeolite coatings on substrates, which suppresses the reaction in the bulk and promotes that on the substrate by applying a temperature difference between the reaction mixture and the substrate. The substrate is heated directly, with a soldering resistance in this study, while the reaction mixture is kept at a lower temperature by means of a water bath. The method is tested for the case of zeolite 4A synthesis on stainless steel plates from a clear aluminosilicate solution. As a result of suppressed activity, the composition of the solution remains nearly constant and the solution side of the coating always experiences a lower temperature. As a result, the phase transformations of the metastable zeolites can be delayed for extremely long periods of time, depending on the volume of the reaction mixture. The deposition of crystals from the solution onto the surface of the coating is also avoided. Crystalline coatings of zeolite 4A could be prepared by the appropriate selection of the temperatures of the water bath and the substrate. A final treatment, which involves an increase in the temperature of the water bath, may be applied to the coatings at the end of their preparation, in order to remove the sparse amount of impurities observed at certain synthesis times and to increase the crystallinities when necessary. The mass of the zeolite coated on the substrate is shown to increase significantly with respect to that obtained by conventional synthesis when the proposed method is utilized. The method can thus be useful for some applications where the employment of relatively thicker zeolite coatings of metastable phases may be desired.

Microstructure and properties of nitride and diboride hard coatings deposited under intense mild-energy ion bombardment

Abstract The concept of low or mildly energetic but intense ion bombardment was applied to coatings based on the nitrides and diborides of the transition metals titanium and zirconium. Coatings were deposited using non-reactive unbalanced d.c. magnetron sputtering. Films were bombarded by means of argon ions with varying energy ( E i ) and intensity (ion/atom flux ratio J i / J a ). Fracture cross-sections revealed the existence of the transition zone (zone T) structure for all coatings. TiN and ZrN coatings, which are exposed to low energetic bombardment, revealed a preferred growth on (111) lattice planes. Mildly energetic and intense bombardment resulted in a shift of the preferred orientation to (200). TiB 2 and ZrB 2 films grow more or less randomly under low energetic and less intense bombardment. However, they displayed a preferred (001) orientation with increasing intensity of the ion irradiation. The hardness of the coatings increased by the effect of both mildly energetic and intense ion bombardment, mainly as a result of reduced film porosity and to a lesser extent due to reduced crystal size and increasing film stresses.

Characterization of molybdenum nitride coatings produced by arc-PVD technique

Abstract Molybdenum nitride coatings were deposited onto high-speed steel (HSS) substrates by the arcPVD technique. It was possible to produce coatings with Mo2N and MoN structure by varying the nitrogen partial pressure between 0.4 and 1.5 Pa. The relationships between hardness, thickness, and crystallographic structure of the coating and the deposition parameters were investigated. Hardness of the coatings increased with the increase of nitrogen content of the coating. Tribological behavior of the coatings was determined by ball-on-disk wear tests. The wear behavior of Mo-N-coated HSS samples against alumina balls was better than that of TiN-coated ones. Electrochemical polarization experiments were conducted in 1 N sulfuric acid. The porosity of the sample was determined by the copper decoration test. The coating with the lowest nitrogen content showed the best corrosion protective properties in the electrochemical tests.

Effect of nitrogen pressure, bias voltage and substrate temperature on the phase structure of Mo-N coatings produced by cathodic arc PVD

Abstract In this study, the effect of nitrogen pressure, bias voltage and the substrate temperature on the structure of Mo–N coatings produced by arc PVD was investigated. High speed steel substrates were coated at 1.9, 1.5, 1.2, 0.8 and 0.4 Pa nitrogen pressures by using −150, −250 and −350 V bias voltages. The coating procedures were performed at two temperature ranges: at 410–510 °C and at 300–380 °C. At the nitrogen pressure of 1.9 Pa and bias voltage of −150 V, δ-MoN (hexagonal) phase was obtained. When the pressure decreased to 1.5 and 1.2 Pa, mixed phases of δ-MoN and γ-Mo 2 N were produced. At lower nitrogen pressures of 0.4 and 0.8 Pa coatings consisted mainly of γ-Mo 2 N. At higher bias voltages it was impossible to produce single phase δ-MoN even at the highest nitrogen pressure (1.9 Pa). At lower nitrogen pressure and higher bias voltages cubic γ-Mo 2 N was the predominant phase. Lower substrate temperatures promoted the formation of δ-MoN phase. The hardness of the coatings changed from 3372 to 5085 kg/mm 2 depending on the ratio of phase components in the coatings.

Oxidation behavior of molybdenum nitride coatings

Molybdenum nitride coatings were deposited onto H13 hot working tool steel and alumina substrates by arc PVD. The coatings were characterized with respect to their mechanical and structural properties. Oxidation behavior of the coatings on alumina substrates was investigated by TG/DTA. Coated H13 substrates were oxidized in a tube furnace under atmospheric conditions at specific temperatures determined from TG/DTA tests of the same coating on alumina substrate. The oxide scale morphology was characterized by scanning electron microscopy and X-ray diffraction. Resistance to oxidation of Mo–N coatings is poor because of the non-protective nature of their oxides and the volatility of the oxides at moderately high temperatures. The oxides formed during the oxidation were determined as MoO2 and MoO3. The oxidation reaction product MoO3 is a volatile oxide and its evaporation reaction starts at after 550 °C. In addition, decomposition of Mo2N starts at 681 °C and the decomposition reaction product is metallic molybdenum, which also oxidizes to volatile MoO3.

The effect of heating on corrosion behavior of TiN- and CrN-coated steels

Abstract TiN and CrN coatings were deposited on 1040 carbon steel substrates by arc-PVD. Coated materials were then subjected to heating at 600 and 650°C in vacuum for 1 h. As-coated and heat-treated samples were characterized with respect to their hardness and thickness. Electrochemical polarization experiments were conducted on the samples in 1 N sulfuric acid. Porosity of the samples was determined by means of a copper decoration test. EDS line-scan analyses were performed on the fracture surfaces of the coatings. It was found that heating decreased the hardness, increased the number of pores extending through the coating and improved the corrosion-protective properties of the coated materials. CrN-coated samples exhibited better corrosion-protective properties than TiN-coated steels.

The effect of heat treatment on corrosion behavior of laser surface melted 304L stainless steel

Abstract Laser surface melting (LSM) improves the passivation and pitting behavior of 304L stainless steel. This improvement was attributed to microstructural modification, mainly to increased δ-ferrite content, and elimination and/or redistribution of sulfur based inclusions. In this study, in order to clarify the role of microstructural changes that took place during LSM on electrochemical behavior, laser surface melted 304L grade stainless steel was heat treated at 1050 °C. A detailed analysis of the electrochemical behavior of as-received, laser surface melted and laser surface melted + heat treated 304L in sulfuric acid and sodium chloride solutions was conducted. Effects of laser surface melting and post heat treatment on pit morphology was also investigated.

Lower temperatures for the preparation of thinner zeolite A coatings

The possibility of preparing thin zeolite 4A coatings on quartz and stainless steel substrates by direct synthesis from a clear aluminosilicate solution has been investigated. In this context, the effects that originate from the synthesis temperature on the thickness of the zeolite coatings have been determined. The nucleation curves and the crystal growth rates pertaining to the coatings prepared at different temperatures have been obtained by taking into account the variation of the numbers and sizes of the zeolite particles and the sizes of the largest crystals on the substrates, respectively, with respect to time. The apparent activation energies corresponding to nucleation and crystal growth have been estimated from these data. It has been determined that the thickness of closed zeolite 4A layers may be decreased at relatively lower synthesis temperatures in case relatively longer synthesis times are employed. The reduction obtained in the thickness of the zeolite coatings with decreasing temperature is due to the rate of nucleation being less temperature sensitive than the rate of crystal growth. The crystal growth activation energies corresponding to the synthesis of zeolite 4A coatings on stainless steel plates are noticeably higher than those obtained when quartz plates are employed while the apparent activation energies for nucleation on these two substrates are quite close. Zeolite 4A coatings of 1 and 0.7 μm thickness have been prepared on quartz and stainless steel substrates, respectively, at 45°C.

Corrosion characteristics of plain carbon steel coated with TiN and ZrN under high-flux ion bombardment

Abstract Plain carbon steel samples (Ck 35) were coated non-reactively with TiN and ZrN by means of an unbalanced magnetron sputtering technique. Ion bombardment parameters ion energy E i and ion to neutral ratio J i / J . were systematically varied within the work. Parallel to the morphological improvement in the coatings, the samples exhibited an improved corrosion performance. The application of flux dense ion bombardment reduced the coating porosity, thus improved corrosion performance. The energetic ion bombardment reduced the inherent porosity, while it increased the possibility of arcing between substrate and chamber wall resulting in surface failures. As a result, low or mild energetic ion bombardment with high flux was assessed as a useful tool for improving corrosion performance of a coated system.

Characterization of Mo2N/Ag Nanocomposite Coatings Produced by Magnetron Sputtering

In the present study, Mo2N/Ag (MeN-X type) nanocomposite coatings were produced on HSS substrates by magnetron sputtering. The silver content of the films were adjusted by changing the inserted area of silver on Mo target. The silver content of the films were between 0 and 10 at%. The effect of Ag content on the hardness and structural properties of Mo2N/Ag nanocomposite thin films were investigated.