This study assesses the effect of laser melting on MCrAlY-coated copper substrates. CoNiCrAlY, NiCoCrAlY, and NiCrAlY powders were applied to copper alloy substrates by atmospheric plasma and HVOF spraying. Sample surfaces were then laser melted and coating properties were determined and correlated with coating composition, surface morphology, and cross-sectional microstructure. Laser melting not only caused the coatings to fuse to the substrate, but also precipitated the formation of an aluminum oxide surface layer that reduced the oxygen content in the coating. As a result of this finding, the coating samples were heat treated in order to measure their high-temperature oxidation resistance.

This study employs numerical simulations to investigate the effect of pulsed electron-beam treatments on the porosity of plasma-sprayed cermet coatings. Simulations show that heat flux density and pulse duration control both the degree of melting in the metal binder and volume heating in the base. With optimized parameters, a single high-energy pulse can reduce porosity and increase bonding strength without melting carbide inclusions.

In this paper, a new treatment method, flame remelt spheroidization, is used to improve the crystallinity of hydroxyapatite (HA) powders. Based on SEM and XRD analysis, the treated powder is more crystalline than spray-dried and sintered HA powder and has higher density and a smoother surface morphology as well. In addition, coatings produced by plasma spraying the treated powder are shown to have better surface microstructure than coatings synthesized from untreated powder.

In this investigation, flame spraying is used to deposit polyether ether ketone (PEEK) layers on stainless steel substrates and CO 2 and Nd:YAG laser remelting treatments are performed to densify the deposited material. Microstructural analysis of the as-sprayed and remelted coatings shows that both lasers are suitable for densifying PEEK polymer layers on stainless steel and that the resulting crystalline structure depends on laser processing parameters. Hardness measurements and tribological and scratch tests are also carried out and the results are correlated with microstructure.

This study analyzes the effects of laser remelting on the morphological structure and adherence of flame-sprayed PEEK coatings on stainless steel. Different types of lasers were used with wavelengths of 1.064 mm (Nd:YAG), 10.6 mm (CO 2 ), and 0.88 mm (diode). It was found that the longer the wavelength, the more compact the coating, but the less well-adhered. By making adjustments to compensate for the wavelength-dependent absorption coefficient of PEEK, both coating properties were improved.

WC-based cermet coatings were deposited by HVOF spraying in order to study the effects of laser remelting on coating microstructure, hardness, and dry sliding wear behavior. It was found that the laser treatment eliminates porosity and contributes to increased hardness and enforced metallurgical fusion between the coating and substrate, effectively improving adhesion and wear resistance.

The implementation of magnesium alloys for automotive, aeronautic and other applications is of the great importance due to their especial properties. Magnesium offers greater weight saving capacity than aluminium, as its density, 1.7 g/cm -3 , is two thirds the density of aluminium, 2.7 g/cm -3 , without significant loss of strength and magnesium alloys show high specific strength. On the other hand surface properties of magnesium alloys like wear and corrosion resistance are rather poor. A large amount of methods are intensively elaborated to overcome this problem from developing of new alloys, different surface treatment methods and a great variety of coating systems. In present work the results concerning improvement of corrosion and wear resistance of magnesium alloys by means of zinc based coatings are presented. Coatings are deposited on magnesium substrates (AM20, AZ31, AZ91) by arc spraying with Zn, ZnAl4 and ZnAl15 solid wires as well as by electroplating of zinc. Nevertheless the onset of bimetallic corrosion between Zn and Mg significantly increases corrosion current density. In order to provide longer protection, two main technological solutions are taken into consideration. First relies upon a modification of the main electroplating technology, second is based on the selection of an effective post treatment. For the first approach a consecutive process is elaborated based on the two-step electrodeposition. The first is from alkaline bath followed by the second step in acidic chloride bath. A dense and compact complex layer is obtained. The second approach is based on the post treatment of deposited coatings and provides a formation of thick and uniform reaction layer in magnesium on the interface between zinc or zinc based coating and substrate. These layers have fine eutectic structure with microhardness 3-4 times higher than that of the base material. Heat treatment is carried out with focused irradiation of tungsten halogen lamp line heater in atmosphere. Microstructure of deposited coatings as well as that of modified surface layers is investigated by metallographic methods. Corrosion properties are estimated by electrochemical measurements. Abrasion wear resistance of the modified layers is determined by scratch test and oscillating wear tests. It is shown that the both applied methods improve corrosion properties of magnesium alloys. Electrolytic zinc coatings deposited by electroplating in the elaborated two- step process demonstrate good barrier properties. Durability increases about three times in comparison with a single coat obtained from alkaline bath. Infra red heat treatment of thermal spray coatings results in formation of modified layers in magnesium substrates that prevent the galvanic corrosion of investigated systems. Wear resistance of reaction layers is up to 4 times higher to compare with the base material.

In order to improve the efficiency of gas turbines, thermal barrier coatings (TBCs) have been applied to components in the hot sections of advanced gas turbines. During service, thermally grown oxide (TGO), which consists of an Al 2 O 3 layer and a mixed oxide layer, forms at the interface between the top coating and bond coating. It is supposed that the reason for failures of TBCs, such as cracking, delamination or spalling, is due to decreased bond strength caused by TGO growth or due to the formation of stress concentration sites caused by porosities in the mixed oxide. In this study, to inhibit the growth of TGO, plasma sprayed CoNiCrAlY bond coating was remelted with a YAG laser prior to spraying the top coating. A thin Al 2 O 3 layer formed at the top coating/bond coating interface, and the formation of porous mixed oxide during thermal aging tests was inhibited. Four-point bending tests showed that the bond strength of TBC with remelted CoNiCrAlY was superior to standard TBC.

The morphologies of Y-PSZ coatings remelted after (i.e., post-treated) or simultaneously (i.e., in situ) with their deposition were observed by optical and scanning electron microscopy in order to study the behavior of the coatings during laser irradiation. A change in the microstructure, from lamellar to dendritic, was observed in both cases. Moreover, cracks and delaminations are less emphasized for the coatings treated during deposition than for those treated after deposition. Finally, the pore connectivity was evaluated implementing an electrochemical test. Results clearly indicate that the coatings obtained by in situ laser remelting are significantly more impervious than as-sprayed coatings.

The aim of this study is to show how electron beam remelting affects the structure and properties of CoCrW coatings. As described in the paper, CoCrW powders are plasma sprayed onto nickel substrates and a modified electron beam welder is used to remelt the deposits. The effects of the treatment are assessed via SEM and XRD analysis, wear testing, and hardness measurements. In summary, electron beam remelting improves a number of coating properties including adhesion strength and fretting wear resistance. It also eliminates oxide inclusions and lamellar structures and reduces layer porosity. Paper includes a German-language abstract.

This paper assesses the effect of laser remelting on nickel-base coatings produced by thermal spraying. NiAl, NiCr, and NiCrAlMoFe layers are deposited on steel substrates via flame and plasma spraying and treated with a CO 2 laser operated at different power levels. The treated layers are evaluated based on microstructure, hardness profile, and wear resistance. Plasma-sprayed NiCrAlMoFe layers treated at a power of 1000 W exhibited the highest wear resistance. Paper includes a German-language abstract.

This paper reports on a structural characterisation of the nickel alloy coatings, before and after the fuse process is done and the main phases in each case, showing important differences between the nickel alloy coatings. Spray and fuse process involves thermal spraying to apply a coating of special self-fluxing alloys and a post thermal treatment at temperature between the solidus and liquidus of the alloy, when important diffusion processes take place. An improvement of the hardness and tribological properties is observed with the addition of tungsten carbide-cobalt to the nickel alloy powder. The results show the excellent tribological properties of the spray and fused coatings, better than the obtained for the as-sprayed coatings. The adhesion strength of the nickel alloy coating after the thermal treatment achieve a value above 80 MPa. Paper includes a German-language abstract.

This paper investigates the effect of laser treatment on alumina-TiO 2 coatings deposited by detonation spraying. It describes the changes observed in the microstructure and hardness of the remelted layers. The originally lamellar structure is transformed into a fine, pore-free columnar structure in which the grains are oriented perpendicular to the interface between the layer and substrate. The remelted zones contain alpha-aluminum oxide as the main phase and are characterized by high microhardness, although a few defects were observed on the periphery. Paper includes a German-language abstract.

Thermal spray processes are widely used to deposit high-chromium nickel-chromium coatings to improve high temperature oxidation and corrosion behaviour. However, in spite of the efforts made to improve the present spraying techniques, such as HVOF and plasma spraying, these coatings may still exhibit certain defects such as unmelted particles, oxide layers at splat boundaries, porosity and cracks, which are detrimental to corrosion performance in severe operation conditions. Due to low process temperature only mechanical bonding is obtained between the coating and substrate. Laser remelting of the sprayed coatings was studied in order to overcome the drawbacks of sprayed structures and to markedly improve the coating properties. The coating material was high-chromium nickel-chromium alloy, which contains small amounts of molybdenum and boron (53.3%Cr- 42.5%Ni - 2.5%Mo - 0.5%B). The coatings were prepared by high-velocity oxy-fuel spraying onto mild steel substrates. High power fiber coupled continuous wave Nd-YAG laser equipped with large beam optics was used to remelt the HVOF sprayed coating using different levels of scanning speed and beam width (10 mm and 20 mm). Coating remelted with the highest traverse speed tended to suffer cracking during rapid solidification inherent to laser processing. However, choosing appropriate laser parameters, non-porous, crack-free coatings with minimal dilution between coating and substrate were produced. Laser remelting resulted in the formation of dense oxide layer on top of the coatings and full homogenization of the sprayed structure. The coatings as-sprayed and after laser remelting were characterized by optical and electron microscopy (OPM, SEM). Dilution between coating and substrate was studied with EDS. The properties of the laser remelted coatings were directly compared with properties of as-sprayed HVOF coatings.