The powder of HSS (HSS23, AISI M3:2) was deposited by pulsed-PTA method on to low alloyed steel substrate. The influence of pulsation frequency was evaluated on the surface of deposits and on their cross sections by both light microscope and by Vickers hardness measurement apparatus and extreme properties mapping (XPS). Surfacing parameters at current frequency from 0 to 200Hz were tested during deposition of single weld bead. Dilution and heat affected zone were evaluated and compared for all tested parameters. The presence of retained austenite after deposition was determined by X-ray diffraction. The beads deposited with different frequencies differ in their shape, dilution degree, microhardness and penetration depth. It was found that the microhardness increases with current frequency.

The Cold spray method of material deposition is widely used for surface enhancement, to improve properties such as corrosion and wear. A detailed microstructural analysis of cold sprayed Ni based coatings (IN625 (Inconel 625 is a Trademark of Huntington alloys corporation) using the transmission electron microscope, revealed the occurrence of three distinct types of microstructures in the as sprayed condition, adjacent to each other. These include the occurrence of large (> 1 μm) grains having a high dislocation density, along with regions comprising shear bands (20-30 nm wide) and twins with a large aspect ratio (> 1000), along with locations having a very fine grained structure (20-30 nm). The crystallite size, using a Hall-Williamson plot measures an average 50 nm. The substrate deformation indicates a bilayer dynamic recrystallization, as a means to accommodate the strain. The microscopy studies will serve to correlate the bonding mechanism of cold sprayed IN625 on 4130 steel.

The thermal cycle test of Al 2 O 3 sprayed 1%Cr-0.5%Mo steel and 18%Cr-8%Ni steel was performed, and the failure type of thermally sprayed coating on both steels was compared. The results obtained are follows. (1)The thermal cycle fatigue life of thermal sprayed 1%Cr- 0.5%Mo steel was shorter than that of thermal sprayed 18%Cr-8%Ni steel. (2)In the case of thermally sprayed 18%Cr-8%Ni steel that is difficult to oxidize at high temperature, during thermal cycle, a tensile stress occurs in a sprayed coating and a compressive stress occurs in a substrate. Thus the thermal strain occurs at the interface of sprayed coating and substrate. The sprayed coating delaminates when the thermal cycles reach the limit value. (3)In the case of thermal sprayed 1%Cr-0.5%Mo steel that is easy to oxidize at high temperature, during thermally cycle, dense oxide film forms at the interface between the sprayed coating and substrate, and adhesive strength in the interface becomes low. Thus the sprayed coating delaminates under the lower thermal strain.

WC-CoCr coatings are deposited by HVOF process for improving surface resistance of low alloyed steels. In this study we examined the wear characteristics of WC-CoCr coatings on low alloyed steel substrate under different test conditions, using a sliding wear test unit with abrasive ball. In experimental studies discussed the effects of test load, temperature, work medium and sliding distance on the wear characteristics of coatings. Weight loss, wear track depth and width were observed . It was found that the weight loss of coatings increased in dry medium conditions. Wear weight loss was significantly reduced in lubricated condition due to decreasing friction. The wear track surface profile changed with lubrication and increasing temperature in test conditions. Under the base oil lubricated conditions the WC-CoCr coating performed well.

The aim of this investigation is to show that it is possible to inject powder into a wire arc spray process as an alternative to using cored wire to produce particle-reinforced coatings. The equipment, materials, and procedures used are described in the paper along with the microstructure and properties of the coatings obtained. By changing the feedrate of CrC particles injected into a stream of chromium steel droplets, particle-reinforced graded layers were produced by wire arc spraying on the fly without having to stop the process.

High production rate and feed powder efficiency are critical in the HVOF hardfacing of aircraft landing gear, turbine, and actuator components traditionally electroplated with carcinogenic hard chromium. Desired improvements are hindered by rapid heat build-up in substrate component and thermal expansion mismatch between the carbide coating and steel, titanium or aluminum substrate. A new, cryogenic nitrogen gas (-195°C) cooling system has been developed which limits the thermal expansion and substrate softening problems, and enables a non-stop, gun-on-target spraying. Fully automated, the operation of the new AP LIN-Cooling System is based on thermal imaging of the entire substrate and multi-zone cooling with novel, cryofluidic nozzles. Thermal logs and images of components processed are saved by the system for quality auditing purposes. This paper presents results of industrial tests of the system during WC-10Co4Cr coating of Boeing 737 landing gear, demonstrating a 50% reduction in spraying time, corresponding reductions in the consumption of powder and HVOF gases, and additional labor savings due to the use of flexible masking, unfeasible with the traditional cooling methods. Analysis of residual stresses, structures and properties of the coating and AISI 4340 steel substrate shows that the cryogenic nitrogen cooling results in high-quality products.

A ceramic composite coating of a FeB alloy reinforced with cobalt-coated tungsten carbide (WC-12Co) particles and nickel-coated tungsten carbide (WC-12Ni) particles was deposited on a mild steel substrate by arc spraying cored wire, respectively. The microstructure and the worn surfaces of the coatings were analyzed by X-ray diffraction (XRD), Scanning electron microscope (SEM). And wear mechanisms of the coatings have been discussed on the basis of the observation. The results showed that adding WC powders can obviously increase the hardness and abrasive wear resistance property of the coating. The average microhardness of the coatings is about 900~1000 HV 0.1 . In the experimental conditions, the coatings have the excellent abrasive wear resistance which is 7~10 times higher than that of the Q235 mild steel. Plastic microcutting and brittle peeling play the predominant role in abrasion wear of the coating.

Nowadays wire arc spraying of chromium steel has gained an important market share for corrosion and wear protection applications. In order to optimize the process parameters and to evaluate the effect of the spray parameters DoE based experiments have been carried out as well. In this paper, the effects of the process parameters of spray current, voltage and atomizing gas pressure on the particle jet properties of mean particle velocity and mean particle temperature as well as plume width are presented. To monitor these values the AccuraSpray system was used. The properties of the coatings with regard to morphology, composition and phase formation are included as well. These investigations are part of the development of new power supplies and the enhancement of spray parameter range. As a result of these experiments the spray parameters can be adjusted according to the requirements of the chromium steel coatings.

The results for joints obtained by dynamic diffusion bonding of a 90MnCrV8 high strength steel coated with WC-Co are shown in the present work. This high strength steel substrate was coated with WC-Co, sprayed by HVOF technique (Diamond Jet Hybrid DJH-2700) using propylene as fuel gas at different conditions. The dynamic diffusion bonding was carried out in a high frequency furnace, all joints were made in air. Before doing the joints, the steel was coated with Ni and Cu by electrochemical processes in order to obtain a soft 20 m interlayer of Ni30Cu alloy. Microstructure and reacted zones in the joints were investigated by means of Scanning Electron Microscopy (SEM) and Dispersive X Ray Spectrometry (EDX). In all joints different reacted zones can be distinguished, caused by diffusion processes which take place during the joint tests. The mechanical properties of the joints were quantified in a tensile machine, using a constant load of 0.1 MPa·s -1 . All joints broke by the WC-Co coating zone by delamination processes. The fracture surface was studied by SEM-EDX in order to know the fracture mechanism of the joints. The maximum tensile strength obtained confirm a very promising technology for industrial applications.

Cr 3 C 2 -NiCr, NiCr, WC-Co and Stellite-6 alloy coatings were sprayed on ASTM SA213-T11 steel using the HVOF process. Liquid petroleum gas (LPG) was used as the fuel gas. Hot corrosion studies were conducted on the uncoated as well as HVOF sprayed specimens after exposure to molten salt at 9000C under cyclic conditions. The thermo-gravimetric technique was used to establish the kinetics of corrosion. XRD, SEM/EDAX and EPMA techniques were used to analyse the corrosion products. All these overlay coatings showed a better resistance to hot corrosion as compared to that of uncoated steel. NiCr Coating was found to be most protective followed by the Cr 3 C 2 -NiCr coating. WC-Co coating was least effective to protect the substrate steel. It is concluded that the formation of Cr 2 O 3 , NiO, NiCr 2 O 4 , and CoO in the coatings may contribute to the development of a better hot corrosion resistance. The uncoated steel suffered corrosion in the form of intense spalling and peeling of the scale, which may be due to the formation of unprotective Fe 2 O 3 oxide scale.

The influence of the high velocity air fuel (HVAF) sprayed coating on the fatigue behavior of the low alloy steel was studied at different stress levels. It was observed that only one single main crack initiator existed in the substrate after fatigue at low stress levels, but there were multi-cracks on the substrate surface at high stress level. Detailed investigations showed that the cracks in the HVAF coatings sinuously extended to the interface and deflected thereat along the interface. Consequently, free-standing coating was formed due to its limited bond strength to the substrate and the lower elastic modulus than that of the substrate. The gap between the free-standing coating and the substrate surface was found to be correlated with the stress level. The high stress can greatly degrade the adhesion to the substrate causing the delamination of the coating. The cracks in the HVAF coating had no significant effect on the fatigue life of the substrate.

Anilox rolls are ink-metering rolls used in the printing industry to transfer an exact amount of ink to the printing cylinder. The importance of high quality anilox rolls has increased with the demand for higher quality printing. Improvements of the characteristics of anilox rolls have been achieved mainly by using laser-engraved, ceramic-coated rolls rather than the common chrome-plated and mechanically engraved rolls. The best results concerning the ceramic coating of anilox rolls were achieved by Cr 2 O 3 coatings. These coatings require a bond coat for good corrosion resistance. By far the most-used technology to produce this bond coat is high velocity oxygen fuel (HVOF) spraying using NiCr material. In order to lower the cost of the anilox roll coating it has been investigated if NiCr can be replaced by the chromium steel 316L as bondcoat material. 316L was applied to the surface by HVOF. The characteristics of 316L / Cr 2 O 3 layers were compared with respect to the required quality of the coating. The results were 316L / Cr 2 O 3 coatings with good mechanical characteristics compared to NiCr / Cr 2 O 3 layers. In particular, the metallographic sections showed compact coatings having a tensile adhesive strength slightly higher than and a corrosion resistance similar to the coatings with a NiCr bond coat.

Thermal spray of Al was carried out on the modified 9Cr-1Mo steel to evaluate the steam oxidation resistance of the sprayed Al coating. Atmospheric plasma spray process (APS) was used to coat aluminum on sandblasted 9Cr-1Mo steel substrate. The coating thickness was around 40 µm. The coated specimens were steam oxidized in four different temperatures, ranging from 600 to 750°C. The results show that the scale growth occurred in the interface between coating and substrate subsequently it penetrated into the coating structure. Al diffused into the alloy substrate with high solubility. The diffusion increased with increase in the steam temperature and test duration. Diffused aluminum formed the high hardness intermetallic compound in the substrate near the coating/substrate interface. With increase in the test duration, the intermetallic compound moved towards the bulk and at prolonged aging, it became dissolved. This was identified from the decrease in the micro hardness values at coating/substrate interface at prolonged duration. The scale growth at the substrate surface of Al sprayed steel was much controlled compared to the uncoated specimens.

Thermally sprayed hardmetal coatings are often used to protect valves in steam turbines against wear. Normally the valve spindles are made of CrMo steel and their bearings are made of Stellite, a cobalt-base alloy. In this investigation, a block-on-ring wear test is used with rings and blocks made of the same materials as the spindles and bearings. The rings were coated with Cr3C2-NiCr by HVOF spraying. Wear tests showed increasing weight loss up to 400°C and a sharp decline at 600°C due to a thin surface oxide layer that begins growing at 450°C. The coatings are characterized based on SEM, EDX, and hardness measurements. Paper text in German.

This paper compares the corrosion resistance of electrolytic hard chrome plating and HVOF-sprayed WC-Co-Cr on two steel alloys used in landing gears. Test samples were evaluated by means of salt spray testing and electrochemical measurements. Post-test metallographic examinations were conducted to investigate the failure mode of the coatings. Test results are presented along with relevant findings and observations. Paper includes a German-language abstract.

The processing of frozen foods places high demands on the strength and edge retention of knives, which are typically made of chromium steels due to their corrosion resistance. In meat processing, in addition to cutting, the knives also assume a transport function, where enormous bending forces can occur. A trade-off between strength and ductility is thus required when choosing a material and heat treatment. This paper describes the implementation of a path-controlled build-up welding system for complicated flat contours and the special properties of a newly developed corrosion-resistant powder optimized for knife edges. Field tests indicate that, with the plasma transferred arc welding process and new powders, service life can be extended by a factor of five. Paper text in German.

The work reported herein deals with the interaction among the thermally sprayed coatings and steel substrate in acid aqueous solutions investigated by using the electrochemical process. Thermally sprayed coatings on steel substrate for such as the tribological applications except for the sacrificial anode property have been extended. The environment of these machinery components is often utilized accompanied with the aqueous solutions. The galvanic corrosion occurred in aqueous solutions among the metals or alloys have been well known. In the actual spray process, the formation of penetrated pores or crevice defects are not generally avoided. In the aqueous solution environment, the penetrated defects cause the galvanic corrosion between coating and steel substrate, and tend to be occurred the coating spalling. In this work, the electrochemical process was employed to determine the corrosion phenomena. The preferable combination of sprayed coatings and steel substrate are discussed and the examples of design of the intermediate layers are proposed.

Lock-in thermography is a nondestructive inspection method based on modulated heat transport in combination with infrared imaging. Measurement times are relatively short, about 3 or 4 minutes, and the method is amenable to inspecting a wide range of large and small parts. This paper describes the basic principle behind the method and its application to different thermal sprayed coatings (e.g., Cr-steel, Al2O3). It explains how the test samples were prepared with artificial defects simulating delaminations, inclusions, and other types of imperfections and how the method performed in each case.

Results of macro- and microhardness investigations of newly developed coatings are presented in this paper. The coatings were produced with flame- and arc spraying technique. The coating structure and hardness is significantly influenced by the spraying method and spraying parameters. It will be shown that properties for flame sprayed coatings are more effected by parameter variations than for arc sprayed coatings. A higher hardness, a greater density and a better particle cohesion can be obtained by using the arc spraying method.

In the article the results of set of experiments concerning the changes in microstructure of plasma sprayed Al 2 O 3 , Cr 2 O 3 and W 2 C coatings of tribological test pieces obtained with use of locally applied laser beam treatment are given and discussed. The improvement of sprayed on coating layer adhesion to the steel base was ascertained and evaluated. The possibilities of the application of the described technology for development and production of slide elements of tribological joints are noticed.