NiCrBSi is a material generally used in wear-resistant coatings. In order to improve the tribological properties of atmospheric plasma-sprayed NiCrBSi coatings, Molybdenum (Mo) was incorporated into the NiCrBSi coatings to reduce the friction coefficient and wear rate under dry and oil-lubricated conditions. In this paper, Mo-NiCrBSi composite coatings with Mo content of 5, 10, 20 and 30 wt.% were deposited on stainless steel substrates respectively by atmospheric plasma spray. X-ray diffraction, optical microscopy and scanning electron microscopy equipped with energy dispersive spectroscopy were utilized to investigate the phase structure and surface morphology of the composite coatings. Reciprocating friction tests were conducted to measure the friction coefficients and 3D optical microscopy was used to depict the wear track profiles. The results showed that the 30 wt.% Mo-NiCrBSi coating exhibits the best tribological performance. In addition, MoO 2 and MoS 2 films were formed in the friction process under dry condition and oil-lubricated condition respectively.

Tungsten carbide (WC) is a well-known material used to increase the wear resistance of iron-based composite materials that exhibit a favorable wettability with iron alloy particles. In this work, two different additive manufacturing technologies, i.e., cold-spray additive-manufacturing (CSAM) and selective laser melting (SLM), were used to fabricate WC/maraging steel 300 (WC/MS300) composites. An investigation comparing the microstructure and tribological behaviors of the composites was carried out. In addition, the evolution of the reinforcement phase during these two processes was characterized by SEM and EDS methods.

TiAl 3 -Al composite coatings are believed to hold promise for extending the service temperature range of titanium alloys used as structural materials. In this study, 0.6 x 40 mm Ti-6Al-4V specimens are coated with a 30 μm thick layer of TiAl 3 -Al by low-temperature HVOF spraying. Cross-sectional imaging shows that the as-sprayed coatings have a dense laminar microstructure and are well bonded to the substrate. Following the initial examination, the coating samples were placed in a muffle furnace, where they were held at 700 °C for up to 1000 h. Mass gain was detected starting at 200 h and remained nearly constant for the remainder of the test. This is an indication of excellent corrosion resistance, which is verified by SEM cross-sectioning and elemental EDS analysis. A brief explanation of the protective mechanism of the coating is provided.

In this study, dense multicomponent NiCoCrAlTaY bond coats and feather-structured YSZ topcoats are deposited on DZ40M alloy vane surfaces by the PS-PVD method. Based on thickness measurements and microstructure examination, it is shown that the double vane surface was completely covered by both layers. The thickest portion of the coating was found close to the leading and trailing edges of the vane. The results show that it is possible to manufacture TBCs, including the bond coat and topcoat, on first-stage turbine blades by a single PS-PVD process.

This work evaluates the high-temperature oxidation behavior of thermal barrier coatings by means of impedance spectroscopy. TBCs consisting of YSZ topcoats and NiCoCrAlYTa bond coats were deposited on Ni-based superalloy substrates by atmospheric plasma spraying. Test specimens were heated in air at 1000 °C for different periods of time from 5 h to 250 h. SEM-EDS analysis of the thermally grown oxide (TGO) shows that it mainly contains alumina and grew at a parabolic rate with increasing oxidation time. The resistance of the TGO, as determined by impedance spectroscopy, was found to increase at similar rate. Impedance spectroscopy also revealed an increase in YSZ grain boundary resistance corresponding to grain boundary cracking that occurred in the first 50 h of heating. The YSZ grain boundary resistance remained relatively constant over the interval of 50 to 150 h, but showed a slight decrease beyond 150 h mainly due to sintering effects.

Tubular asymmetric LSCF oxygen transport membranes (OTMs) were prepared on stainless steel substrates by PS-PVD and supersonic air-gas plasma spraying (SAPS). The microstructure of the thermally sprayed OTMs is examined by cross-sectional imaging and oxygen permeability is assessed via oxygen permeation flux measurements carried out at atmospheric pressure in an air-helium gradient. The findings from the cross-sectional analysis and oxygen permeation tests are reported and discussed.

In plasma spray-physical vapor deposition (PS-PVD), deposition takes place not only from liquid splats, but also from nanosized clusters as well as the vapor phase. As a result, thin, dense, and porous ceramic coatings can be produced for special applications using this method. In this study, columnar-structured YSZ coatings were deposited by PS-PVD on graphite and zirconia substrates and the effect of substrate temperature on coating microstructure was investigated. A deposition mechanism of heterogeneous nucleation is presented based on the observations and findings of the study.

In this study, NiCoCrAlYTa-10%Al 2 O 3 powder was deposited on heat-resistant steel substrates by supersonic atmospheric plasma spraying. Coating microstructure, adhesion strength, porosity, oxygen content, microhardness, and wear resistance were systematically evaluated. The results show that the coatings are dense and well adhered and exhibit excellent wear resistance.

Low-temperature HVOF spraying finds its potential applications in the preparation of high-performance metallic coatings with low oxygen content and porosity. In this study, the spraying method is used to deposit fine WC-10Co4Cr powders on stainless steel substrates at different spraying distances and the effects on microstructure, microhardness, fracture toughness, splat morphology, and surface roughness are investigated and discussed.

Advanced materials are the crucial factors determining the successful application of future nuclear fusion energy. Plasma facing materials (PFMs) are one of the most important armor materials in nuclear fusion experiment devices for direct facing with the extremely high thermal load, thermal shock and strong irradiation of high energy particles. W coated CuCrZr substrate has been considered as one of the candidates to the armor materials due to its high melting point, chemical stability and good thermal conductivity. However it was a challenge to obtain high strength thick W coatings because of the major difference of CTE between the W and CuCrZr substrate. In this paper, graded W/Cu layers were deposited as the bond layer via Low Pressure Plasma Spraying (LPPS) on the CuCrZr substrate. Subsequently, thick LPPS W coatings over 1.5 mm were prepared as the top layer. The adhesive and cohesive strengths for thick W coatings on CuCrZr substrates were evaluated according to the standard of ASTM C633. The results showed that the oxide formation on the W coating surface rapidly deteriorated the coating microstructure and properties.

Fundamental properties of Titanium coating prepared by low temperature HVOF process aided by injection of water had been published by our research group. The results showed that low temperature HVOF process provided as a good means for the deposition of comparatively dense Ti coating, however the interconnected pores observed in Ti coating degraded corrosion resistance of Ti coating, therefore it was necessary to manufacture denser Ti coating. Two processes were respectively applied for the densification of Ti coating. One process was to perform post heat treatment for as-sprayed Ti coating with conventional Ti powder as feedstock. The other process was to modify thermal spray powder. Ti powder mixing with spherical glass powder was used to deposit denser Ti coating as a result of shot peening effect of hard glass powder. Finally the corrosion resistance for densified Ti coatings was evaluated by electrochemical characterization.

In order to explore wear properties of Ni-based coating on the copper substrate, the coatings with different composition were designed. Ni-based coating, Ni-based/Al 2 O 3 and Ni-based/Al 2 O 3 /WC coatings were sprayed by HVAF on the copper substrates. Wear properties of different composite coating were measured at different loads at room temperature. The experimental results indicate that all the coatings have high wear resistance. Adding Al 2 O 3 in sprayed powders has little effect on the microstructures and wear properties of coating. The wear resistant is improved by the addition WC-12Co obviously. The best wear resistant is obtained when optimum WC-12Co content is added.

A conventional GTV K2 kerosene fuel HVOF spraying system has been modified with the aim to expand the applicable range of process conditions in order to also cover the presently existing gap between conventional HVOF and cold gas spraying. Different measures have been applied in order to reduce heat transfer and increase momentum transfer to spray particles. Increase of momentum transfer results both in reduced particle temperature as a consequence of reduced dwell time in the hot flame area and high particle velocities. In detail expansion nozzles with conical shape that provide improved expansion of combustion gases, combustion chambers with reduced critical diameters that provide increased combustion chamber pressures and the injection of coolant media water and / or nitrogen into the combustion chamber are applied. The effect of modified spraying conditions on the process characteristics and coating properties have been studied for a variety of materials. Besides copper, titanium alloys and MCrAlYs also WC/Co(Cr) and Cr 3 C 2 /Ni20Cr have been sprayed and respective coatings have been analysed concerning their microstructure, gas content, microhardness and wear resistance. In particular a moderate increase of oxygen content in dense titanium alloy coatings compared to the powder feedstock from 0.41 to 0.59 wt.-% proves the high potential of the undertaken measures to expand the application field of HVOF spraying. Thereby existing systems only need relatively small modifications to achieve this expansion.

Titanium exhibits very good corrosion resistance property because of the formation of very dense oxide coating. Especially the good corrosion against Cl- solution for titanium material makes it wide applications in sea industry. It is very difficult to deposit titanium coating under atmospheric condition due to the strong affinity with oxygen and nitrogen especially in high temperature plume. Except the expensive LPPS process, much attention has been paid to the newly developed cold spraying. Unfortunately the stringent requirement for the starting power and low production efficiency limit the application of the cold spraying. A modified HVOF process was developed by reducing the outlet diameter of chamber and by directly introducing water into chamber, therefore lower plume temperature and higher chamber pressure than conventional HVOF process can be achieved. Attempts to deposit Titanium coating were carried out, and immersion of Titanium coated A3 steel into artificial seawater was performed in order to evaluate the density of as-sprayed Titanium coating. The results showed that dense Titanium coating could be obtained after parameter optimization and very few corrosion spot was observed on the surface of Titanium coated A3 steel after immersion into artificial seawater for 120 h.

In this study, agglomerated nanocrystalline ZrO 2 --Y 2 O 3 powder was calcinated from 900 to 1300 °C for 2 h. The calcinated nanopowder was used as feedstock and deposited by air plasma spraying on a NiCoCr bond coat applied to a nickel substrate via low pressure plasma spraying. For comparison, conventional ZrO 2 -Y 2 O 3 topcoats were also produced. Nanostructured and conventional thermal barrier coatings were calcinated from 1050 to 1250 °C for 2-20 h. Experimental results indicate that monoclinic tetragonal phases in the agglomerated nanopowder were transformed into cubic phase after calcination. The cubic phase content increased with increasing calcination temperature. High temperature calcination can make the yttria segregated at grain boundaries dissolve in zirconia. Different from the phase constituent of the as-sprayed conventional TBC, which consisted of diffusionless transformed tetragonal, the as-sprayed nanostructured TBC consisted of cubic phase containing high yttria. No phase transformations were observed in either TBC after calcination.

High velocity oxygen fuel (HVOF) sprayed WC coatings have been found wide applications as substitutions of chrome plating in the airplane industry. The wear of HVOF WC coated landing gear against Al-Ni-Bronze alloy leads to the wear or spalling of WC particles, and finally results in the degradation of sealing property for landing gear system. WC-Co coating with nano-size WC particles is expected to exhibit good wear resistance, and the weight loss of Al-Ni-Bronze alloy can also be reduced, which is beneficial to the sealing property of landing gear system. Three types of coatings are prepared using agglomerated, sintered nano-scaled WC-12Co, conventional WC- 12Co and WC-10Co4C powders, respectively. The wear behaviors of the as-sprayed coatings against Al-Ni- Bronze alloy are investigated at the different loads and linear velocities. The study is expected to provide the basis for the application of HVO/AF nano-scaled WC coating in landing gear.

Thick pure tungsten coatings were deposited on molybdenum and copper substrate by vacuum plasma spray for different purpose. The microstructures of tungsten coatings were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of preheating temperature of the substrate and introduction of gradient bond layer on the adhesive strength of the coating was investigated. High heat load was tested by high power electron beam bombardment only for tungsten coating on copper. All the results show that the properties of tungsten coating were strongly influenced by different processes, and the density of the coatings is close to 95% of theory density.

HVO/AF (High-Velocity-Oxygen/Air-Fuel) WC-17Co and WC-10Co4Cr coatings exhibit great potential in the replacement of electrolytic hard chrome (EHC) coating, and comprehensive properties of such coatings should be not worse than those of electrolytic hard chrome coating. The impingement-resistance of HVAF coatings sprayed on 300M ultra-high strength steel was studied in this paper. As an important property index, the fracture toughness of HVAF WC coatings was measured using micro-indentation method at the load of 9.8, 19.6, 24.5, 29.4 and 49.0N respectively. The cracks resulted from stress concentration in the micro-indentation were analyzed. The impingement-resistance for two HVAF WC coatings and EHC was evaluated according to the ASTM D3170 standard, and steel ball dropping experimentation was performed at the height of 0.61, 1.52, 1.83, 2.36 and 2.59m respectively. The cracks caused by both impingements were analyzed using SEM and optical microscopy in comparison with cracks in micro-indentation test.

Low pressure plasma spray (LPPS) technology has exhibited its advantage in deposition of yttria stabilized zirconia (YSZ) coating. The YSZ coatings deposited under different chamber pressures were characterized by XRD and SEM in this paper. Preliminary results showed that as-sprayed coatings contained partially-melted zone, and increased chamber pressure was beneficial to the melting of particle. It was revealed that as-sprayed coatings were mainly composed of metastable tetragonal phase except for minor content of cubic phase analyzed by XRD. Compared to air plasma spray (APS) coating, the microhardness and toughness of well-flatten LPPS coating are respectively high and excellent.

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.