Electroless Ni–P Plating on Mullite Powders and Study of the Mechanical Properties of Its Plasma-Sprayed Coating

To effectively improve the properties of a mullite coating and its interfacial bonding with the substrate, a Ni–P layer is deposited on the surface of mullite powders by electroless plating. The original mullite powders and coated mullite powders are then deposited onto stainless-steel substrates by plasma spraying. The growth mechanism of the Ni–P layer during the plating, the microstructures of the coated powders and mullite coating and the properties of the mullite coatings are characterized and analyzed. The results indicate that the Ni–P layer on the surface of the mullite powder has cell structures with a dense uniform distribution and grows in layers on the surface of the mullite powder. The crystallization behavior of Ni-P amorphous layer is induced by heat treatment. Compared to the original mullite coating, the coating prepared by the coated mullite powders has better manufacturability, stronger adhesion to the substrate, lower porosity (7.40%, 65% of that of the original coating), higher hardness (500.1 HV, 1.2 times that of the original coating), and better thermal cycle resistance (two times that of the original coating). The method of preparation of high-temperature thermal barrier coatings with coated mullite powders has a high application value.

EFFECT OF HEAT TREATMENT ON THE MICROSTRUCTURE AND PERFORMANCE OF HIGH-VELOCITY AIR-FUEL SPRAYED WC-10Co4Cr COATINGS

In this study a high-velocity air-fuel (HVAF) flame-sprayed WC-10Co4Cr coating was heat-treated at (240; 300; 400) °C for 2 h in an air atmosphere. The effect of the heat treatment on the hardness, fracture toughness, wear resistance, corrosion resistance, phase composition and microstructure behaviour of the coatings was investigated. It could be concluded from the X-ray diffraction (XRD) pattern that the phase of the coatings was mainly composed of tungsten carbide, an amorphous phase, a small amount of W2C and trace metal tungsten. However, the heat-treated coating had a small increase in W2C compared to the original coating, although the amount of amorphous phase did not decrease significantly. The results indicated that as the heat-treatment temperature increased, the hardness of the coating first increased and then decreased, while the fracture toughness increased. The polarization test confirmed that the heat-treated coating had higher corrosion resistance than the original coating. In addition, the results of the reciprocating friction and wear test indicated that small amounts of W2C strengthening phases were formed in the WC-10Co4Cr coating after heat treatment at 400 °C. This process did not eliminate many of the tougher Co and WC phases. Therefore, this coating had the best wear resistance among all the comparative coatings.

Thermochemical processes occurring in a titanium nitride coating under the effect of thermal laser pulses

The thermochemical processes in a TiN coating deposited on a steel substrate under cyclic irradiation with laser pulses are investigated. It has been established that the combustion of the coating in the irradiated regions occurs spatially inhomogeneously due to the uneven distribution of microregions in the coating, consisting of titanium nitride compounds with different stoichiometry. It is shown that dissociation reactions of various titanium nitride compounds with the release of free nitrogen occur inside the coating. As a result, the ratio of the mass fractions of titanium nitride compounds with different stoichiometry changes in comparison with the original coating. Diffusion of nitrogen into the steel substrate results in the formation of iron nitride.

Filling and retouching of losses in a Portuguese Army model 1859 clothes backpack

Two identical backpacks were treated on two occasions to be exhibited alongside at the Lisbon Military Museum. Although both backpacks are the model 1859, the treatment procedures related to the painted canvas were approached differently. The distortions and losses of canvas on the first treated backpack were easily addressed with an ultrasonic humidifier and the insertion of new canvas. Regarding the surface coating, it was consolidated with BEVA® 371, and the inserted canvas was filled with a pigmented wax paste described in a book from the late 19th century. The second backpack was in far worse condition, which, when compared with archive record, seemed likely that it was exhibited for a long period in a damp environment. There were also traces of an organic coating distinct from the original coating. These conditions resulted in a stiffer backpack, with more losses of canvas and surface coating. As a result, the distortions could not be removed, new fabric could not be properly inserted, and the consolidation of the surface coating had to be addressed in a different way. For these motives, the goal of treatment of the second treated backpack was cut short for a more realistic goal, but resulted in a good outcome, nonetheles.

The Effects of the Addition of Ti3SiC2 on the Microstructure and Properties of Laser Cladding Composite Coatings

This study explored the effects of Ti3SiC2 on the microstructure and properties of laser cladding coatings using X-ray diffractometer, scanning electron microscope, electrochemical workstation, and UMT-2 wear tester analyses. It was found that with the addition of Ti3SiC2, the reinforcing phases in the composite coating were TiC, Ti(B,C)2, honeycomb-like (Cr, Fe)23C6, and a novel composite ceramic with an “eyeball” structure, which had an inside core of Al2O3 and TiC outer surrounding structure. The microhardness, wear, and corrosion resistance of the composite coating were about 1.35, 2, and 4.3 times those of the original coating, respectively. The main wear mechanisms of the original coating were severe fatigue spalling and microcutting, while the main mechanisms of the composite coating were slight microcutting and the formation of the transferred film.

Effect of Carbon Fiber Addition on the Microstructure and Wear Resistance of Laser Cladding Composite Coatings

In this study, the effect of carbon fibers (CFs) on the microstructure and wear resistance of Fe-based alloy coating produced by laser cladding was investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), and wear tester. The results indicated that with the addition of CFs, the microstructure of the composite coating mainly transformed from α-Fe cellular dendrites and γ-Fe/(Cr, Fe)7C3/CrB eutectics to bulk-like (Cr, Fe)7C3, nano-size B4C, and γ-(Fe, Ni)/(Cr, Fe)23C6 lamellar eutectics. Additionally, the microhardness and wear resistance of the composite coating compared with the original coating both increased by approximately two times. The original coating showed the dominant wear mechanisms of micro-cutting and serious brittle spalling, while the composite coating with CFs showed the main wear mechanism of slight scratching.

Surface Microstructure of Nanoaluminized CoCrAlY Coating Irradiated by HCPEB

A thermal sprayed CoCrAlY coating was prepared by air plasma spray on the surface of Ni-based superalloy GH4169; then, a nanoscale aluminum film was deposited with electron beam vacuum deposition on it. The coatings irradiated by high-current pulsed electron beam were investigated. After HCPEB treatment, the Al film was remelted into the bond coat. XRD result shows that Al and Al2O3phase were recorded in the irradiated and aluminized coatings, while Co-based oxides which originally existed in the initial samples disappeared. Microstructure observations reveal that the original coating with porosity, cavities, and inclusions was significantly changed after HCPEB treatment as compact appearance of interconnected bulged nodules. Moreover, the grains on the irradiated coating were very refined and homogeneously dispersed on the surface, which could effectively inhibit the corrosive gases and improve the coating oxidation resistance.

Research on the TiC Reinforced Steel Matrix Surface Composites Prepared by SHS Casting

In this paper, TiC reinforced steel matrix surface composites were prepared by vacuum evaporative casting infiltration process and self-propagating high-temperature synthesis. The effect of original composition, binder types and original coating density on the hardness, wear resistance and microstructure of the coating were also studied. The results showed that the Ti and C content was 80% while added 3% PVA, by pressed at 200MPa pressure leading optimal coating quality. Meanwhile the average hardness was 48HRC and the wear rate was 40%.

Effect of Different Binder on the TiC Reinforced Steel Matrix Surface Composites

In this paper, TiC reinforced steel matrix surface composites were prepared by vacuum evaporative casting infiltration process and self-propagating high-temperature synthesis. The effect of original composition, binder types and original coating density on the hardness, wear resistance and microstructure of the coating were also studied. The results showed that the Ti and C content was 80% while added 3% PVA, by pressed at 200MPa pressure leading optimal coating quality. Meanwhile the average hardness was 62.5HRC and the wear rate was 22 % of high manganese steel.

Carbon Nanotubes Improves the Tribological Properties of Ni60/Al2O3 Coatings

Carbon nanotubes (CNTs) was introduced into Ni60/Al2O3coating by flame spraying. The effect of adding CNTs on the tribological properties of the coating was studied by varying the CNTs content as 0.0, 1.5, 3.0 and 4.5 wt% in the Ni60/Al2O3powders. The microhardness tester was used to measure the microhardness of the coating. Wear tests were performed on a pin-on-disk tribometer, to evaluate the tribological properties of the Ni60/Al2O3/CNTs coatings. Microstructural characterization was performed using scanning and transmission electron microscopy. Ni60/Al2O3/CNTs coatings revealed a lower wear rate and friction coefficient compared with the original coating, and their wear rates and friction coefficients showed a decreasing trend with increasing mass fraction of CNTs within the range from 0 to 3.0 wt% due to the effects of the reinforcement and reduced friction of CNTs. The results showed that the CNTs played dual roles in improving the tribological performance of the coating, indirectly by influencing the microstructure and mechanical properties of the coating and directly by acting as a lubricating medium.