Search Results for (self-fluxing alloys AND nickel)

In order to improve the wear resistance and service life of the copper, the composite coating consisting of a Ni-base self-fluxing alloy (NiCrWB+50%Al 2 O 3 ) and WC (WC-12%Co) alloy were sprayed on a copper substrate using High Velocity Air Fuel(HVAF). The coating could meet the operating requirements including high hardness, good wear resistance and low cost. The Ni-base composite coating was analyzed by means of optical microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The results indicated that the structure of coating was composed of melted particles and partly unmelted round particles of Ni-base alloy, and WC particle. Only a small proportion of the Al 2 O 3 particles were retained in the coating. The phases in the coating consisted of γ-Ni, WC and a little Ni 3 B. Amorphous structures appeared and some Al 2 O 3 phase existed. The adhesion strength between coating and copper substrate was more than 50MPa. Wear results showed that the Ni-base composite coating exhibited better wear resistance than the coating with no WC particles.

The results of low stress, pin-on-disc and high stress grinding abrasive wear tests on coatings produced by plasma and oxy-acetylene flame spraywelding are presented. FNil5A and FNiWC35 Ni-based self-fluxing alloys were selected as typical spraywelding materials for abrasive wear resistance. The abrasive wear resistance mechanisms of welded overlays produced by various materials and processes were also characterized by hardness tests, microstructural and compositional analyses, and through analysis of the effect of different kinds of abrasive on the wear resistant of Ni-base self-fluxing spraywelding overlays. Results showed that FNiWC35 overlays exhibited improved resistance under low stress abrasion, but the relative wear resistances of FNiWC35 and FNil5A still depended primarily on the type and hardness of the abrasive medium used. For the same material, the abrasive wear resistance of oxyacetylene flame sprayed overlays was higher than that produced by plasma spraywelding. The wear resistance of the plasma spraywelding overlays depended not only on the material, but also strongly on the spraywelding process parameters.

Effects of diffusion treatment were investigated on the interface microstructure between a Co-based self-fluxing alloy coating and a mild steel substrate to improve the adhesion strength. Diffusion treatments were carried out at 1373 K to 1418 K for 600 s to 7200 s in an Ar atmosphere. Diffusion treatment improves the metallurgical bonding at the interface due to the diffusion of Co, Cr, W, Ni, and Si from the sprayed coating layer to the substrate and that of Fe and Mn from the substrate to the coating. This mutual diffusion forms a precipitate-free diffusion layer at the interface, and the width of this layer increases in a parabolic manner as temperature and holding time increase. The apparent activation energy for the formation of precipitate-free diffusion layer was evaluated as about 360 kJ/mol. The shearing adhesion strength of the diffusion-treated coating has been remarkably improved to 200 – 400 N/mm 2 in proportion to the width of the precipitate-free diffusion layer formed along the interface, although the shearing adhesion strength of the as-sprayed coating was only 30 N/mm 2 .

This paper describes microstructure control aimed for wear-resistance improvement of Co-based (Co-Cr-W-B-Si) self-fluxing alloy coating by diffusion treatment. The diffusion treatments of thermally sprayed Co-based self-fluxing alloy coating on steel substrate were carried out at 1370K to 1450K for 600s to 6000s under an Ar gas atmosphere. Microstructural variations of the coating and the interface between the substrate and the coating were investigated in detail. A proper diffusion treatment precipitates two kinds of fine compounds in Co-based matrix. XRD and EPMA analysis revealed these precipitates to be a chromium boride dissolving cobalt and a wolfram boride containing cobalt and chromium. The size of each precipitate became larger with increasing treatment temperature and time. A coating with the proper size borides showed a superior wear-resistance.

Self-fluxing alloys are an established thermal spray system in case of superimposed tribological and corrosive loads. A dense coating with high bonding strength can be formed by fusing. Such coating system represent the state of the art in valve technology. Diamond-like carbon (DLC) top coatings are used for friction-reduction. As an alternative approach, this study focuses on the possibility of incorporating solid lubricants in self-fluxing alloy coatings. This allows for higher local stress and failure tolerance as well as a reduced process chain. Molybdenum disulfide (MoS 2 ) was studied as solid lubricant in the self-fluxing alloy NiCrBSiFe. In this preliminary study, the optimization of the MoS 2 content with up to 10.0 wt% was performed in spark plasma sintered (SPS) bulk materials. The wear behavior under oscillating wear conditions was investigated. Besides the decrease in coefficient of friction (COF), the wear resistance was increased by incorporating MoS 2 . Furthermore, the distribution of the solid lubricants within the SPS bulk material and the influence of the production route were analyzed.

Thermally sprayed coatings of self-fluxing alloys are mainly fused using an autogenous flame. This subsequent fusing step reduces the porosity of the coating and achieves a pronounced metallurgical bonding. Therefore, an enhancement of the coating adhesion and intersplat cohesion as well as the corrosion and wear resistance are achieved. During this non-automated fusing step, the coating quality is significantly influenced by the operator's handling of the flame fusing process. By means of an alternative fusing using laser, can improve the reproducibility and automatability. In this work, the effect of different laser parameter settings and structural defects on fusing depth, microstructure evolution and tribological properties of thermally sprayed self-fluxing coatings and bulk materials is discussed. Gas atomized powder of conventional NiCrBSiFe self-fluxing alloy was processed by powder flame spraying and by spark-plasma sintering (SPS) as reference state. The findings reveal the potential of laser fusing to achieve a significant improvement in the coating quality and property profile of a wide variety of initial structures related to the process conditions.

Fusible Ni-B-Si alloys with a variety of alloy additions (Cr, Mo, Cu etc.) have been in service for many years as fused coatings with moderate corrosion resistance. Both gas- and water-atomised powders have been used with the spray and fuse and with the plasma transferred arc process to produce coatings. As the severity of corrosive industrial environments has increased, for example in waste burning boilers, existing alloys have not provided the desired service performance. This study was undertaken to develop a new family of alloys with improved corrosion resistance without sacrificing usability, wear resistance or cost effectiveness. A range of compositions was prepared and evaluated for deposition characteristic, microstructure, hardness, wear resistance and corrosion resistance in various media. The resulting alloy has an exceptional combination of wear and corrosion resistance in comparison to conventional alloys, when tested under comparable conditions.

Atmospheric plasma spraying of alloys often results in their composition changes. The main source of the changes is usually preferential oxidation of some elements composing the alloy. As a rule, these are the alloying elements whose affinity to oxygen is high. Changes due to this effect are well known from metallurgy; however, they were scarcely studied from the point of view of plasma spraying. Preferential evaporation of some elements may also contribute to the alloy composition changes. The aim of the present paper is to give quantitative data on composition changes of selected alloys sprayed by a water-stabilized plasma gun. Two Ni-base alloys and one high-alloy Cr-Ni-steel were studied. The main tool for determining the sample composition was electron probe X-ray microanalysis. To quantify the results and to eliminate the systematic errors, the data obtained by this method were calibrated by repeated chemical analysis of feedstock powders. The alloy composition was determined after both stages of plasma spraying, i.e. after the inflight stage of molten particles and after the stage comprising particle impact, solidification, coating formation and cooling. To study the situation after the former stage, the flying particles were trapped and quenched in liquid nitrogen. In the Ni-Cr alloy containing 20%Cr, strong Cr depletion was observed. The Fe depletion in the Ni-Fe alloy (47%Fe), though unambiguous, was less significant. The high-alloy steel (Czech equivalent of AISI 316) was also Cr depleted, whereas the concentrations of other alloying elements (Mo, Ni) remained effectively unchanged. In all cases, the depletion occurred at the first spraying stage and became more pronounced during the second stage. Strong air entrainment occurs not only in a plasma jet produced by a water-stabilized plasma gun, but also if gas-stabilized plasma guns are used in atmospheric plasma spraying. It follows that the dominant mechanisms of composition changes during plasma spraying by both techniques are similar.

This study investigates the effect of alloying additions on the oxidation behavior of iron (Fe) and nickel-chromium (NiCr) powders during atmosphere plasma spraying. The chemical composition and phases of oxides in the particles as well as in the coatings are assessed for different powder mixtures and spraying parameters. The results show that oxygen content can be significantly reduced by adding silicon (Si) and boron (B) to iron powders and Si, B, and carbon (C) to NiCr. The preferential oxidation and subsequent vaporization of Si, B, and C from the surface of the sprayed particles are believed to play a major role in controlling oxidation in the APS process.

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

Tungsten carbide in nickel based self-fluxing alloy overlays has been dominating hardfacing applications due to its excellent properties, namely extremely high wear resistance. Nevertheless, there are still applications and limits which tungsten carbide has not conquered. This study focuses on (TiW)C 1-x which was deposited with several matrix materials and tested in wear, corrosion and impact resistance and benchmarked against tungsten carbide. Results for several other carbides such as (NbW)C 1-x , (VW)C 1-x , NbC 1-x and TiC 1-x overlays deposited by plasma transferred arc (PTA) and laser cladding (LC) will be presented and discussed. As a result of deposition trials and overlay testing, it was found that better thermodynamic stability of alloyed carbides allows them to be used in an iron based matrix and/or a matrix with a high chromium content, in applications requiring improved corrosion and oxidation resistance, better impact resistance and lower weight.

Deposition of a dense coating with solid particles by cold spraying requires sufficient deformation of impacting particles and previously deposited underlying particles. The cermet particles and subsequent coating with a high hardness are difficult to deform upon impact. To increase the ability of deformation, the cermet spray particles with a porous structure design is proposed to fulfill the requirements of deformation on impact. To understand the deposition mechanism, the deposition behavior of single WC-Co spray particles impacting on the substrates with different hardnesses during cold spraying were examined using WC-12Co powders with different porosity. The substrates include stainless steel, nickel-based self-fluxing alloy coatings were employed to examine the effect of substrate deformation on the cermet particle deposition. It was found that using two porous powder of the porosity of 30% and 44% the WC-Co cermet particles were deposited on the substrate of different hardness from 200Hv to 800Hv. The deposition of the particles is mainly attributed to the deformation of powders themselves. The properly designed porous cermet powder with certain hardness is necessary condition to deposit hard WC-Co cermet coating.

Nickel based self-fluxing alloy coating extends the service life of furnace wall tubes at waste incineration plants due to its excellent corrosion resistance and heat resistance. With our system, fusing of such coatings is performed by induction heating, which offers improved efficiency and reliability of products. Compared with conventional plasma, flame, and HVOF thermal-sprayed coatings, induction-fused coatings provide a far stronger metallurgical bond at the interface, while minimizing the inclusion of pores. In addition, the tubes are less costly than those with welded coatings, and the process reduces the distortion of the products, facilitating easier final assembly. A successful experimental application of 11 units (four, six-meter pipes per unit) revealed virtually no corrosion on the exposed surfaces, and showed an improved water heating efficiency over that of the original mortar-coated tubes. Over 200 such units are now being employed in four incinerators in Taiwan, and further installations are in progress.

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.

High Velocity Oxygen Fuel (HVOF) spraying established itself as an effective method in addition to the conventional thermal spray processes within a very short period. Self fluxing nickel alloys, cermets (e.g. WC-Co / Cr3C2-NiCr) as well as oxide ceramic coatings have proved themselves suitable for wear protection applications. Weight reduction, the care of resources and the increase of efficiency for structural components leads to the substitution of customary hard particles. Titanium carbide (TiC) characterizes itself on account of the material features such as the high hardness, the high melting point, the high strength and the low density for the substitution of conventional carbides. The Self Propagating High Temperature Synthesis (SHS) is a suitable process for the production of composite powders. The powders produced by SHS show a high carbide content, which is finely distributed with an almost stoichiometric composition of the TiC inside the powder particles. The carbides are protected against dissociation and oxidation during the thermal spray process by a complete velum of matrix alloy. The current investigations deal with the wear resistance of TiC-composite coatings produced by HVOF compared to conventional wear resistant coatings. The investigations contain the analysis of the microstructure by optical and scanning electron microscope (SEM) and the measurement of the microhardness of the deposited coatings. Special attention is drawn to the interface between the hard particles and the matrix alloy. The optimized coatings are tested with different wear tests, such as Taber-Abraser test, sliding and oscillating wear test and are compared with common wear resistant coatings in order to underline the high potential for different wear applications. Moreover an additional corrosion test (salt fog test) is carried out with regard to the corrosion resistance of the different matrix alloys.

High temperature corrosion is a serious problem on tlie heat exchanger tubes of recuperators because they encounter an corrosive environment at maximum temperature around 900°C. These tubes were found to be corroded via oxidation, sulfidation and molten salt corrosion. Particularly molten salt corrosion could be the most severe corrosion mechanism. As a protective coating for recuperators, nickel and cobalt based self-fluxing alloys, iron based amorphous alloy and chromium carbide cermet coatings were considered. These coatings were prepared by an arc spray and or/not fusing or a HVOF spray. Their molten salt corrosion resistance was tested, and the high temperature corrosion resistance in a SO2 containing atmosphere was examined. Also microstructures of the coatings were studied after corrosion tests.

Characterization of coatings made with the help of Computer Controlled Detonation Spraying (CCDS) was performed. The applied coatings include hard alloys (WC/Co -75/25, WC/Co - 88/12, WC/Co/Cr - 86/10/4, and Cr 2 C 3 / NiCr), aluminum oxide, nickel-chromium self-fluxing alloy, titanium, bronze, and stainless steel. Tribological investigations of coatings were provided using abrasion test (ASTM standard G65), erosion test (ASTM standard G76), and hydro-abrasive test. To make hydro-abrasive tests special device and method were elaborated based on the interaction of water jet saturated with corundum particles with a coating surface.

This study assesses the wear performance of HVOF-sprayed nanostructured TiB 2 composite coatings and the use of mechanical alloying for powder preparation. In order to prevent the formation of undesired secondary borides, TiB 2 particles are processed with a nickel-base self-fluxing matrix alloy. XRD analysis shows that the minimum average TiB 2 crystal size is 22 nm after high-energy milling and only slightly larger and uniformly distributed after HVOF spraying. The resulting TiB 2 layers are characterized based on morphology and wear behavior and are shown to hold promise for abrasive wear applications. Paper includes a German-language abstract.

For deposition of protective coatings different coating techniques are available. Usually, detailed evaluation of various deposit types and materials is necessary for selection of the best suited coating for specific application fields and demands. Subject of this work are thermally sprayed functional coatings applied as wear (and corrosion) protective layers. Examination of different optimized thermal spray coatings, i.e. HVOF sprayed WC/Co(Cr) and Cr 3 C 2 /NiCr coatings, conventional flame sprayed and fused self fluxing alloy coatings reinforced by hardmetal and APS sprayed oxide Al 2 O 3 /TiO 2 and Cr 2 O 3 coatings, is done in comparison to thick hard chromium platings. Two abrasive wear tests featuring wear by lose abrasive particles are carried out. These impart dry wear conditions according to ASTM G65 (Rubber Wheel test) and wear by abrasive suspensions according to ASTM G75 (Miller test). The work also contains evaluation of newly developed HVOF torch components permitting increased combustion gas, and therefore also particle, velocities concerning the benefit in terms of coating properties. Exemplary evaluation of the new components influence on velocity and temperature of spray particles is carried out by comparative SprayWatch analyses. Both the influence on the coatings microstructure and the wear performance are studied. Coating microstructure is evaluated qualitatively by optical and scanning electron microscopy and the micro hardness HV0.3 is measured. Worn surfaces are studied by SEM in order to deduce wear mechanisms.

This paper gives an account of pin-on-disc low stress abrasive wear and erosion wear tests on the specimens made by oxy-acetylene flame spray-fusing technology to explores the effect of WC content on the wear resistance of oxy-acetylene flame spray-fusing overlays. In the test, Ni60, NiWC25 and NiWC35 three kinds of various WC content Ni-base self-fluxing alloys were used as the typical wear resistance materials compared with 16Mn material and high Cr cast iron arc surfacing overlay. In pin-on-disc wear tests, SiC, Al 2 O 3 and SiO 2 different abrasive were used, and in erosion wear tests 30° and 90° erosion wear tests were performed. This paper also analyzed the wear mechanisms of spray-fusing overlays that possess different WC content by means of hardness tests and overlay's structure analysis. The results show that WC content influences the wear resistance of spray-fusing overlays greatly, but in various wear type and conditions, its effect's degree and tendency are quite different.