Papers by Keyword: Thermal Spray Coating

Abstract: In recent years, Al-5Mg alloy thermal spray coatings have been used as an anti-corrosion coating applied for various components of steel structures, in some cases it was covered by the conventional heavy-duty coating. However, the deterioration characteristics of overlapping layers between thermal spray layer and heavy-duty paint coating still not clear. In this study, to compare the anti-corrosion characteristics of the single thermal spray coating and overlapping layers, the accelerated cyclic exposure tests were carried out on specimens with three types of coating layers. To clarify the deterioration characteristics, the cross-cut defect were introduced into specimens, and the EIS measurements, glossiness test, EPMA elemental analyses were conducted on test specimens. The test results indicated that the deterioration of the overlapping layer at the steel base-exposed portion occurs earlier than the case of Al-5Mg thermal spray coating. In addition, the deterioration of thermal spray coating was accelerated by the sealing treatment in specimen with overlapping layers.

Abstract: In scientific work has been developed a thickness calculation procedure of an aluminum thermal spray coating, sprayed on the low-alloyed steel surfaces in order to provide its effective protection at hight temperatures. The method is based on the calculations of the diffusion layer thickness with consideration of temperature change on the blank`s surface and on the dependence of the parameter (directly proportional to the diffusional coefficient) on the temperature.

Abstract: The objective of this study is to clarify the deterioration behaviors of overlapping layers between Al-5Mg alloy thermal spray coating and heavy-duty paint coating. Combined cyclic corrosion tests were carried out on common carbon steel plates with overlapping layers. To evaluate the effective area of the sacrificial anode reaction caused by the thermal spray coating, machined straight-line defects with widths of 0.2, 6 and 12 mm were introduced in the overlapping layer. The experimental results indicated that the layers began to deteriorate from the lower part of the thermal spray coating along the defects. The deterioration of the thermal spray coating was accelerated by the sealing treatment. The blister area and height at the overlapping layer were significantly different depending on the sealing treatment.

Abstract: The aim of this paper is to evaluate the microstructural and nanohardness characteristics of tungsten carbide-cobalt (WC-Co) cermet coatings deposited by liquid suspension spraying. Commercially available WC-Co coating powder was milled and water based suspension was produced as feedstock for the thermal spray coating process. Microstructural evaluations of WC-Co cermet coatings included XRD (X-Ray Diffraction) and SEM (Scanning Electron Microscopy). Post spraying nanomechanical evaluations were conducted using a Berkovich nanoindenter. Results indicated relatively higher modulus but lower hardness of suspension coatings. The load displacement curves during nanoindentation were characteristic of the complex coating microstructure showing signs of microcracking and pile-up.

Abstract: An addition of cerium oxide to NiCrAiY coatings could boost the high temperature properties of the coatings in the actual service condition due to the purification of its microstructures. High temperature oxidation studies of D-Gun sprayed MCrAlY coatings with minor addition of CeO₂ is inadequate in the literature. Therefore, the present work was focused to study the effect of cerium oxide on the high temperature oxidation behavior coatings on superalloys. Cyclic oxidation tests were carried out for 100 cycles at 900 °C to study the oxidation kinetics of un-coated and bare superalloys. The corroded products obtained during cyclic oxidation of coatings were subjected to XRD, FE-SEM/EDAX and X-ray mapping analysis to reveal the high temperature oxidation mechanisms.

Abstract: Detonation gun spray coating method (D-Spray) [1] is one of the effective method of thermal spray coating process. The surface of material or substrate will be enhanced by deposition of coating powders such as metal oxides and ceramics like aluminium oxides, tungsten carbide ,nickel chromium etc by D-spray method that prevents the metal from corrosion and to increase the wear resistance. This coating process had wide applications in different engineering sectors such as aviation industry, marine industry, biomedical industry etc., In this Experimental study the Process parameter optimization of D-spray coating process which is one of the Thermal spray Coating process was done by Taguchi method, [3] in order to find the best processing conditions and to get higher quality of coating. [6] Microhardness was estimated for various combinations of parameters and the optimum process parameters were obtained. Best combination of process parameters has been predicted which results that the thickness of the coating has got a major effect.

Abstract: Identification of failure mechanisms of thermal spray coatings by means of traditional fractography of failed parts is often troublesome. Reason for this is a highly inhomogeneous character of the coating microstructure and harsh in-service conditions which may hinder evidentiary fractographic marks. In this study, failure evolution of advanced thermal barrier coating (TBC) prepared by plasma spraying was studied in-situ at high magnification in a scanning electron microscope under well-defined laboratory conditions of three-point bending (3PB).

Abstract: Effects of h-BN particles on mechanical properties and adhesion of semi-crystalline poly (ether-ether-ketone) (PEEK) coatings were studied. PEEK powder was mixed with various contents of h-BN nanoparticle in ethanol under ultrasonic mixing. As-mixed powders were sprayed onto low carbon steel substrate with thermal spray technique. The hardness, scratch hardness, specific scratch wear rate, prevailing deformation mechanisms and adhesion were obtained from scratch tests by varying the applied load. The damage geometry on scratched polymer surfaces and scratch wear volume loss were examined using scanning electron microscope (SEM) and surface profilometer, respectively. The results indicated that the addition of h-BN content improved the hardness of the composite. In addition, the specific scratch wear rate and the adhesion between PEEK coatings and substrate decreased with increasing h-BN content. The poor adhesion resulted from the reductions of flow-ability and viscosity between PEEK and substrate caused by heat dissipation from the h-BN particles.

Abstract: In the cylinder of a sleeveless engine, molten iron-based alloy is directly sprayed onto the aluminum engine block instead of the previously used cast iron cylinder liner. However, a thermal spraying cylinder liner exhibits poor machining performance during the finish boring process because of severe tool wear. This research investigates the finish boring performance of a thermal spraying cylinder liner to clarify the root cause of tool wear. The results show that mechanical wear is a dominant effect.

Abstract: Diffusion treatments of TiAl-based alloys (49.1 at% Al) aluminum coated by thermal spray were carried out at the temperature range of 700°C-1100°C. The influence of the diffusion condition for the formation of intermetallic phases in the coating has been investigated. In the initial stage of diffusion treatment, TiAl₃ was formed on the outermost surface by the diffusion between liquid aluminum and the substrate. In addition, an intermediate layer comprised of Ti₂Al₅ (at 1100°C), TiAl₂ and Al diffused layer (Al-rich TiAl) was confirmed under the outermost layer. The maximum thickness of TiAl₃ during the initial stage increases as the diffusion temperature decreases. In addition, the shape of TiAl₃ layer was dependent on the diffusion temperature; the outermost layer without pores was confirmed at the temperature of 700°C. TiAl₂ and Al-rich TiAl developed by solid-state diffusion from TiAl₃ layer following a parabolic low. The activation energies for growth have been calculated to be 194 kJ/mol for TiAl₂ and 292 kJ/mol for Al-rich TiAl.