Search Results for improvement

To improve wear resistance of the atmospheric thermal plasma sprayed molybdenum coating, diamond deposition on the molybdenum plate and the atmospheric plasma sprayed molybdenum coating by the combustion flame chemical vapor deposition (CVD) was carried out. Diamond has excellent properties such as low surface energy, hardness, chemical corrosion resistance ability and so on. Besides, since the combustion flame CVD is the process carried out in the air, diamond/ molybdenum complex coating can be deposited without any vacuum facilities by using this technique if molybdenum coating is deposited by atmospheric thermal spray. In this study, acetylene welding torch was used as diamond synthesis apparatus and mass flow ratio C 2 H 2 /O 2 was varied from 0.9 to 1.3. Consequently, many diamond particles which were 10 micrometer in diameter respectively were deposited on the molybdenum plate by only 20 minutes combustion flame irradiation in the case of 1.2 in mass flow ratio of C 2 H 2 /O 2 . Especially, the molybdenum coating was covered with diamond films consists of 10 micrometer diameter particles in the case of over 1373K in deposition temperature. Besides, according to the results of wear testing, wear mass loss of diamond deposited coatings were much lower than that of original thermal sprayed molybdenum coatings. From these results, this process was found to have a high potential in order to improve wear resistance of thermal sprayed coating.

This study evaluates the erosion-corrosion performance of thermal spray hardcoats on bronze-coated gray cast iron. In the experiments, gray cast iron plates are coated with a bronze powder by PTA welding and the coatings are characterized based on microstructure and corrosion and wear testing. The bronze coatings provide good corrosion protection, but are shown to be susceptible to cavitation and erosion wear. To compensate, thermal spray hardcoats, including atmospheric plasma sprayed Al 2 O 3 and Cr 2 O 3 and HVOF sprayed WC-Co, were applied over bronze-coated cast iron and corrosion and wear tests were performed. It is shown that the thermal spray hardcoats greatly improve wear resistance, but despite their interconnected porosities, do not affect the corrosion performance of the underlying bronze.

This paper reviews the results of thermal spraying on the magnesium alloy AZ 91. By plasma, arc and HVOF spraying various metal based alloys were used as coating materials. The layers were investigated with regard to microstructure, bonding and corrosion resistance. Paper text in German.

Despite their light weight, 2.3 times lighter than Al, polymers are limited to application with low thermal, wear, and abrasion demands. The enhancement of the functional surfaces of the polymers using thermal spraying techniques is a challenging task due to the thermal degradation of polymers, the low wettability, and the disparate atomic properties. The twin-wire arc spraying (TWAS) process comprises two contradictory features. Almost all spraying particles are in a molten state on the one hand, and on the other hand, the spray plume has the lowest heat output among the different thermal spraying techniques. Therefore, it is a promising spraying technique for the required surface improvement. The surface of the 3D-printed parts was metalized using two successive layers. The first layer is a TWAS coating made of low-melting ZnAl 4 to avoid thermal degradation and provide a bond coat. The topcoat is also applied using a TWAS process and was made out of Ni-WC-Co as cored wires. The top hard coating has improved the wear resistance of the polymers by 14.6 times. The erosion of the coated and uncoated specimens was determined using a low-pressure cold gas spray gun. Ni-WC-Co coating led to more than five times higher erosion resistance.

Conventional processes of gas shielded metal arc welding (GMAW) do not offer directly the possibility for cladding heat sensitive materials such as aluminum with iron-based materials due to intermetallic Al/Fe phases form. This paper deals with the first evaluated cladding results of aluminum components with iron-based nanocrystalline solidifying materials by controlled shielded metal arc welding processes to improve wear resistance. In the present work, the design of experiments and data evaluations are systematically applied to get the first results about the dependence between controlled arc welding process parameters and the iron-based coatings of aluminum substrate. In particular, the effect of the chosen parameters such as wire feed speed, welding speed, frequency and further factors on the heat input, welding penetration, micro hardness, rate of welding penetration and width of intermetallic phases in the interface zone are investigated. Optical and scanning electron spectroscopy provide input for further statistical evaluation. The experiments were carried out using various controlled arc technologies which offer different control over the heat input to the substrates. Different power supplies were used.

Highly wear resistant overlays for abrasive environments can be provided by welding technologies such as Plasma Transferred Arc Welding (PTAW) or Laser Cladding. Therefore, these overlays can contain higher amounts of hard particles with a desired homogeneous distribution through the weld overlay, all embedded in a metal matrix. Depending on the welding technology, the dissolution of the hard particles has to be considered as result of heat input and chemical reaction between hard particles and metal matrix while welding. Cast Tungsten Carbides (CTC) in self-fluxing Ni based alloys are widely used and accepted compositions and allow to target requirements such as hardness, impact toughness and/or corrosion resistance if required. This investigation compares CTC with Macroline Tungsten Carbide regarding abrasive wear resistance in Ni, Co and Fe based alloys applied by PTAW and Laser cladding and gives an outlook on potential new solutions for wear resistance in abrasive conditions. Beside the relative wear resistance, this investigation also focusses on the seam thickness as reaction zone between the carbide particles and the metal matrices. A first SEM and EDX analysis of a worn surface and precipitated phases provides an explanation regarding wear behavior in abrasive conditions.

Fiber-reinforced polymer composites (CFRP) are increasingly used in aerospace for weight-sensitive applications. However, they are subjected to degradation from the erosive forces of solid particles and water droplets. This degradation results in a decreased service life of composite components and increased repair costs. A coating can protect the CFRP surface against wear and plasma spraying could be a candidate technique to achieve this coating. However, an issue is the thermal and mechanical damage to the composite surface by the plasma-sprayed particles. Another issue is the coating adhesion, because of the low wettability of polymer surface to liquid metal and ceramic and different atomistic properties between substrate and coating material. A possible solution to both issues is the use of a primary layer deposited by a “softer” technique than thermal spraying. This study deals with the deposition of this primary layer by three methods (magnetron sputtering, air gun spraying and sol-gel) and the deposition of topcoat layer by plasma spraying. The effectiveness of the protection of the CRFP by the primary layer during topcoat plasma spraying is investigated as well as the interfaces of the duplex coatings.

For more than two decades researchers have been working on thermal barrier coatings to improve the performance of diesel engines. However, these coatings have still not achieved widespread application in conventional diesel engines. The original motivation for this work was the improvement of fuel economy, since even a few percent improvement would result in huge savings in the transportation industries, but the coatings also effect exhaust emissions, component wear, and the sensitivity of engines to fuel quality. Wear at high temperatures, where conventional lubricants are not effective, is a serious problem in low heat rejection engines. Ceramic materials such as thermal barrier coatings in cylinder liners must have an acceptable wear rate and coefficient of friction. In this work we compare the wear behaviour of nanostructured thermal spray zirconia coatings with conventional zirconia coatings. First, process parameters that allowed the nanoparticles present in the feedstock powder to be retained in the coating were found. Then pin on disc wear tests of the two types of coatings were carried out at room temperature. The coating containing retained nanoparticles exhibited a lower coefficient of friction and less wear loss under discontinuous testing than the conventional coating.

Nanostructured and conventional ZrO 2 coatings were deposited by plasma spraying. The wear and friction properties of these coatings against stainless steel under dry and water lubricated conditions were comparatively studied respectively. The results obtained showed that the wear resistance of the coating produced using the nanostructured zirconia powder is greatly improved compared with the coating produced using the conventional powder. The wear rates of the nanostructured zirconia coatings are two-fifths and half of those of conventional zirconia coating under dry and water lubricated conditions. It is explained in terms of the optimization of microstructure and higher microhardness of the nanostructured coating. In comparison with the dry condition, the water lubrication improved the tribological properties of both nanostructured and conventional zirconia coatings, which could be attributed to the formation of a smooth surface mainly consisting of zirconia and Fe 3 O 4 .

The cermet materials have been developed to protect surfaces against wear and corrosion. In cutting tools technology as well as chromium replacement, WC coatings have been used to improve life and performance at higher temperatures. This work compares the abrasion and adhesion resistance of a WC-Co mixed in a x:y relation with a NiCrBSiW alloy deposited by High Velocity Oxy-Fuel (HVOF) process using a JP-5000 gun in two conditions: as sprayed and thermally treated. Abrasion and adhesion tests were performed according to ASTM G-65 and ASTM C-633 respectively. The microstructure and composition of the coatings, failure and worn surface were evaluated using Optical (OM) and Scanning Electron Microscopy (SEM) as well as X-Ray energy Dispersive Spectroscopy (EDX) and X-Ray diffraction (XRD). Vickers microhardness under a 500g load has been averaged from 8 indentations per sample. The results showed that the coatings studied presented a similar microhardness as well as good abrasion resistance. The best behavior of the post-heated coating could be attributed to a lower porosity, better distributions and effective cohesion between hard phases. Partial recrystallization of the amorphous phase produced during the thermal spray process into sub-carbides could be related to the improvement in abrasion resistance of the post-treated coating.

WC-Co thermal sprayed coatings are mainly used for wear protecting functions in various industries, for which high velocity oxy fuel (HVOF) spray is considered to be the best suited process. However, WC-Co HVOF coatings still have some defects as compared with sintered bulk, such as decarburization of WC and porous structure. Recently, experiments of WC-Co coatings using warm spray (WS) and cold spray processes have demonstrated some improvements in reduction of these defects. In particular, WS process seems to be a more promising process for WC-Co coatings from the previous work. In this study, wear resistant functions of WC-12%Co coatings prepared by HVOF and WS were investigated by abrasion and erosion tests. In addition, in-flight particles were captured and their characteristics such as the amount of decarburization, crystal phase, particle strength and particle size distribution were investigated to clarify the difference between HVOF and WS processes. The result shows that the wear resistances of the WC-Co WS coatings are comparable or superior to those of the HVOF coatings, which can be attributed to the difference in the amount of W 2 C and coatings porosity revealed by the in-flight particles and the coating microstructure. The result of the in-flight particle analysis also indicates that wear resistance of WS coatings can be further improved by optimizing the powder shape and chemical composition.

The purpose of this study is to investigate the microstructure and wear resistance of plasma sprayed WC-Co-Ni coatings. WC-Co-Ni composite powders were prepared by mixing of WC powder, Co powder and a Ni-P alloy powder, followed by sintering and crushing to improve the properties of plasma sprayed WC-Co coatings. In this study, their coatings were deposited by the atmospheric plasma spraying. The evaluation of their coatings were carried out by the observation of microstructure, measuring of microhardness values, adhesion strength values and an abrasive wear test. The abrasive wear resistance of the as-sprayed WC-Co-Ni coatings was comparable with that of WC-Co coatings deposited by HVOF spraying, and besides, the properties of the post-treated WC-Co-Ni coating were comparable with those of cemented carbides.

Due to its easy handling and low operating costs, wire arc spraying has become one of the most established processes for applying protective coatings to components used in waste incineration plants. This paper discusses the development of relatively low-cost Fe-Cr-Si coating materials for incinerator applications and the corrosion and wear properties that have been achieved using conventional arc spraying methods.

Extensive laboratory testing and field usage have shown that innovative surfacing techniques have produced cost effective maintenance systems and are providing long-term benefits. Self-fusing (sometimes known as self-fluxing) alloys containing tungsten carbide (WC), applied by PTAW, HVOF and SF (Spray Fusion) brazing processes are investigated. The process used and the effect of process parameters on the wear resistance of these coatings is evaluated. The test results show that the same self-fusing alloy applied by SF compared to PTAW have proven superior in severe erosive and abrasive applications. The case histories presented will cover a variety of applications including the use of HVOF versus hard chrome plating and the improvement in wear resistance of SF applied self-fused coatings versus PTAW. These comparisons are useful in providing new, higher performance solutions, in helping to overcome today's tougher surfacing and environmental requirements

In twin wire arc spraying process it is possible to use feedstock wires of two different compositions at the same time. As a result of this procedure it can be achieved composite coatings called also as pseudo alloys with modified physical properties. In this study nickel and cobalt based super alloy materials were arc sprayed with pure molybdenum wire to tailor corrosion and wear resistance of the coatings. Coatings for the tests were sprayed using two different twin wire Sulzer Metco arc-spraying units, Smart Arc and OSU 300, operating with suitable spray parameters to produce coatings of good quality. It was already known that these twin wire configurations are producing coatings with differing microstructures. Coating sprayed with the OSU system was clearly finer in structure and one purpose of this study was to measure the effect of the micro structural size on the corrosion and wear properties of the final coatings. Microstructures of the coating materials were studied and analyzed from cross-sectional specimens. Volume fraction of pure molybdenum in the coating matrices was evaluated with simple line method and according to the results volume fraction of pure molybdenum metal is over 50 volume-% in all of these tested composite coatings and higher in materials sprayed with OSU unit. Also the microstructure of the coatings was seen to be finer when OSU was used as was expected. Wear resistance was measured with modified ASTM G65 rubber wheel sand abrasion wear test and corrosion resistance was tested in low pH values and chlorine containing environment according to the ASTM G48 corrosion testing standard. Corrosion testing was carried out at room temperature 22°C and also at higher 50°C temperature. Molybdenum addition is clearly improving the abrasion wear resistance of the tested coating systems. At room temperature also the corrosion resistance is getting better with molybdenum addition but at higher temperature this effect is not so clear.

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.

In recent years Norwegian industries together with SINTEF and NTNU have run several projects dealing with development of thermally sprayed ceramic-metallic coatings for corrosion and wear applications. The mechanisms of erosion, corrosion and combined actions have been studied. The coatings studied are of the metal-carbide / metallic binder type sprayed by the High Velocity Oxygen Fuel (HVOF) process. The influence of powder properties like carbide particle size, powder grain size distribution, chemical composition (i.e. type of carbide and composition of the metallic binder) together with the influence of spray systems and parameters have been studied. The studies have demonstrated how optimization of powder and spray parameters improve corrosion and wear behavior of the coatings. Attention has also been paid to methods used for manufacturing powders for thermal spraying. This is very important from a corrosion point of view. The manufacturing methods should make sure that metallic binders are sufficiently alloyed to achieve the necessary corrosion resistance. The results from the work done in these projects are valuable for suppliers of thermal spray powders, spray companies and end users of coatings.

Borides are promising materials with good wear and corrosion resistance properties. Boride coatings are expected to perform better where wear and corrosion resistances are simultaneously required. Zirconium diboride is an important emerging material for such applications, due to its high hardness, high melting point, good wear resistance and corrosion as well as high temperature oxidation resistance. Special properties of laser beam like beam directionality, high intensity and spatial resolution makes laser alloying a fast and efficient technique for producing improved wear resistance coatings. In the present work, mild steel was laser alloyed with ZrB2, using "two-stage" technique of laser alloying. These coatings after characterization by optical microscopy, SEM, EDAX and XRD techniques were tested on a "Pin-on-Disk" machine for determining their wear resistance.

During the last decades, improved understanding of tribological behavior of different material combinations led also to an intensified development of thermal spray applications. In the field of e.g. hard chromium replacement by thermal spraying, significant amount of work has been done and published world wide, however, the authors manly focused on only one tribological aspect like friction, abrasion, erosion, cavitation or corrosion, respectively. In real applications, often more than one of those factors influence the successful use of these coatings. Besides the bulk properties of the materials, the coating micro structure, which is strongly spray system dependent, needs to be considered and investigated. Higher functionality and reliability than conventional competitive coatings still has to be proved at laboratory scale and under field conditions for thermally sprayed coatings. This paper describes the state of the art of thermally sprayed coatings as alternatives for other coatings. Published literature data and a wide range of own tribological investigations and field tests, reveals the potential for other applications.

Conducted are investigations of powders for plasma spray of wear resistant coatings. Studied are shape, relief and particle size of NiCr-Fe+50(80)%Cr 3 C 2 , NiCr-Fe+50(80)%SiC powders using scanning electron microscopy. Investigations is supplemented by the results of X-ray structural studies. Investigations serve to develop coatings with the improved oil trap capability, increased hardness and wear resistance, sprayed by a plasma jet. The developed coatings will be used to restore and strengthen machines components