Sintering ceramics have been widely used in industries which require electrical and mechanical properties. Thermal sprayed ceramics coatings are also applied for the industries, however the coating which has micron size pores are limited their applications due to inferior electrical and mechanical properties compared with sintering bulk. To expand thermal sprayed ceramics coating applications, dense coatings prepared by suspension plasma spraying are widely studied. Dense Al 2 O 3 coatings are applicable to fabricating equipment for electronics devices, such as ESC. There are no reports regarding electric properties of plasma sprayed dense Al 2 O 3 coating with different spray conditions. In this study to achieve a electric properties of dense Al 2 O 3 coating, spray parameters such as plasma power, gas flow rate and spray distance are investigated. Suspension materials prepared with three microns Al 2 O 3 powder are sprayed by high power suspension plasma spraying system. Spray conditions, plasma power, gas flow rate, and stand-off distance affect the coating density, crystal phase, and mechanical and electrical properties. Mechanism of coating formation by plasma spraying with fine powder suspensions will be discussed based on the findings. Al 2 O 3 coatings obtained by the plasma spraying is applied for application to application utilizing the electrical insulation properties of such electronics devise manufacturing equipment components is proceeding.

Metal and polymer additive manufacturing is advancing on several applications. On the other hand, materials cermet such as WC/Co for functional structure molding by additive manufacturing are under studying. There are few reports for WC cemented carbide additive manufacturing process by forming with polymer binder then sintering. This indirect process has difficulties to make high precision functional parts due to shape control during additional sintering process. Direct forming is desired for high precision parts. However, factors and/or mechanism to achieve direct formed functional structure have been unclear in many aspects. In this study, the process conditions of the direct selective laser melting were investigated to achieve dense and hard WC cemented carbide mold parts. The optimization of laser melting conditions for WC/Co agglomerated and sintered powder was examined. In order to forming a dense and high hardness parts, the optimum conditions between powder preparation and laser energy density which related with laser power, scan speed and spot diameter were appeared by this experiments. Moldings more than 1500HV are achieved at low laser energy density. However, some of pores were observed in moldings. In addition, the dense molding could be obtained by high laser energy density. This means optimum dense functional WC cemented carbide molding is available by optimization of the molding condition. It is applicable for growing industries like automotive, aviation and cutting tool.

Since 2008, Japanese boiler, turbine and valve manufacturers, research institutes and utility companies have been working together to develop 700V A·USC technology, with support from the Japanese government. The key areas of discussion are technology development of high temperature materials such as nickel-based alloys and advanced 9Cr steels, and their application to actual power plants. At the EPRI conference in 2013, our report mainly focused on the development of fundamental material and manufacturing technology during the first five years of the project, and the preparation status of the boiler component test and turbine rotor test for the latter four years of the project. The boiler component test, using a commercially-operating boiler, began in May 2015 and is scheduled to be finished by the end of 2016. The turbine rotor test at 700°C with actual speed will be carried out from September 2016 to March 2017. At this year’s conference, we will: l) briefly summarize the development of fundamental material and manufacturing technology and 2) provide an update on the progress of the boiler component test and the turbine rotor test.

Lowering the thermal energy and increasing the kinetic energy of sprayed particles by newly developed HVAF systems can significantly reduce material decarburization, and increases sliding wear and corrosion resistance of hard metal coatings, making HVAF coatings attractive both economically and environmentally over its HVOFs predecessors. Two agglomerated and sintered feedstock powder chemistries, respectively WC-Co (88/12) and WC-CoCr (86/10/4), with increasing primary carbides grain size from 0.2 to 4.0 microns, have been deposited by the latest HVAF-M3 process onto carbon steel substrates. Respective dry sliding wear behaviours and friction coefficients were evaluated at room temperature via Ball-on-disk (ASTM G99-90) wear tests against Al 2 O 3 counterparts, and via Pin-on-disk (ASTM G77-05) wear tests against modified martensitic steel counterparts in both dry and lubricated conditions. Sliding wear mechanisms, with formation of wavy surface morphology and brittle cracking, are discussed regarding the distribution and size of primary carbides. Corrosion behaviours were evaluated via standard Neutral Salt Spray (NSS), Acetic Acid Salt Spray (AASS), accelerated corrosion test and electrochemical polarization test at room temperature. Optimization of coating tribological properties are discussed regarding the suitable selection of primary carbide size for different working load applications.

Two agglomerated and sintered powders, WC-Co and WC-Co-Cr, were deposited by HVAF spraying and evaluated based on material decarburization, coating porosity, and microhardness. The role of carbide grain size, contiguity, and binder mean free path is investigated with respect to coating microstructure and wear and corrosion resistance.

This paper presents the results of a study on the tribological properties of TiC-based coatings deposited by HVOF spraying. Four powder feedstocks consisting of (Ti,Mo)(C,N) hardmetal with Ni and Co binders were prepared by agglomeration and sintering. The feedstocks differ in composition and particle size distribution, the latter being optimized for fuel type and equipment requirements. Coating specimens are evaluated based on microstructure, hardness, bonding strength, and friction and wear behavior. The results are presented and correlated with spray parameters, equipment differences, and feedstock characteristics.

In this work, tungsten carbide coatings are deposited by low-pressure cold spraying in order to assess the influence of powder compressive strength and binder materials on coating properties. Powder compressive strength was measured with a micro-compression tester, and cobalt and FeCr in different proportions were used as the metal binder. It was found that compressive strength affects coating hardness as well as deposition efficiency and that the optimum value for deposition efficiency is about 200 MPa. The results also indicate that dense coatings can be produced with either binder material, although coatings with an FeCr binder are the hardest.

This paper presents the results of a preliminary study comparing high-velocity oxyfuel and airfuel spraying for the deposition of tungsten carbide coatings as an alternative to electrolytic hard chrome plating. Two tungsten carbide powders with a Co matrix and two with a Co-Cr matrix were sprayed on steel substrates using commercial HVOF and HVAF equipment. The coatings obtained are evaluated by means of SEM and XRD analysis, microhardness and adhesion measurements, and corrosion and wear resistance testing. Detailed results are presented and discussed with emphasis on the role of carbide grain size, carbide contiguity, and binder mean free path. In general, HVOF coatings show significantly higher dry wear resistance, owing to the presence of coarser primary carbides from the initial coarser powder. HVAF coatings, on the other hand, exhibit lower porosity and finer well-distributed primary carbides, giving them an advantage in terms of sliding wear resistance.

From the appearance of high velocity oxygen fuel (HVOF) thermal spray system in the 1980s, WC cermet coatings have been used as anti-wear coatings in many industrial manufacturing applications. Recently, WC cermet spray materials were applied using new thermal spray methods such as warm spray and cold spray, which are still in the research phase. In HVOF spraying, WC-Co and WC-Ni powders are regularly used as coating materials. On the other hand, using cold spray, WC-Fe alloy series can be deposited as dense and thick coatings, better than WC-Co. In this study, WC-Fe alloy powders were sprayed by cold spray to investigate the influence of binder metal on the coating properties and compared with those of HVOF WC-CoCr coatings. It was observed that the lower metal ratio and FeCrNi chemical composition exhibited improved results.

Iron based coatings have recently gained much attention as they have favorable mechanical, frictional, and corrosion properties. The coatings possessed a high content of iron borides are particularly valuable for satisfying engineering needs. Boron and iron form two major boride phases, FeB and Fe2B, with different mechanical and thermal properties. Orthorhombic boride FeB is considered to be viable candidate to enhance the surface hardness and wear resistance of components, since it has high hardness. Producing of such coating by cold spray method is considered to be an alternative for boronizing method which is a conventional thermochemical surface hardening process. In this work, the crushed ferroboron (FeB) powders of Fe-17.9B-0.4C-1.6Si-0.3Al (wt. %) were deposited onto low carbon steel substrate by cold spraying. However, low and high pressure cold spraying allowed depositing very thin and single layer on the substrate, due to the intrinsic brittleness of the powder. Therefore, several contents of Al, Ni and Fe metallic powder and their combinations were added to FeB powder to obtain thick coating via cold spray processes. Post heat treated coatings at a temperature of 700 °C resulted in increase of the hardness, possibly the formation of hard phases such as intermetallic compound.

Cold spraying is well known as an attractive coating process that prevents degradation of materials, such as oxidation, decomposition and undesirable reaction due to overheating. High velocity oxy-fuel (HVOF) spraying has been recognized as the most popular technique in particular to produce tungsten carbide (WC) cermet coatings in industrial fields. However, the degradation of WC cermet occurs using HVOF that is quite different from sintered hard metal, which can be defined as an ideal material. Thus, low temperature processes, such as cold and warm spraying, are actively researched to achieve WC cermet coatings, similar to sintered one. In this study, influence of gas conditions in cold spraying on WC cermet coatings has been investigated, where WC-Co, WC-CrC-Ni and WC-Fe alloy are selected. The study reveals that nitrogen gas is effective to form thick, dense and hard coatings of WC-CrC-Ni and WC-Fe alloy compared to helium gas. This suggests optimal temperature and velocity of powder jet has been formed when using nitrogen gas.

From the appearance of high velocity oxygen fuel (HVOF) thermal spray system on 1980s, WC cermet coatings have been used as an anti-wear coating in many industrial manufacturing. Recently, WC cermet spray materials were applied to new thermal spray methods such as warm spray and cold spray under research phase. In HVOF spraying, WC-Co or WC-Ni series powder are used as standard contents. Ni and Co are binder metals for WC because of good wettability and suitable melting point. On the other hand, warm spray and cold spray are lower temperature process than HVOF. It is considered that any other factors of metal material such as hardness, toughness and crystal phase should be investigated in warm spray and cold spray. In this study, WC with Co or Fe alloy powders were sprayed by cold spray and HVOF to investigate the influence of binder metal for spray efficiency and coating property. It is cleared that Ni and Fe were superior to Co in spray efficiency and coating property in cold spray. The detail of above reason was under investigation, however, plastic deformability of binder metal is expected to be an important factor for WC cermet cold spraying.

Mechanical properties of WC-Co coatings prepared by cold spraying (CS) and warm spraying (WS) have been studied with changing material parameters of Co content (12~25%), powder size (-45+15 and -20+5 µm) and WC particle size (0.2 and 1.8 µm) in this paper. The study reveals that a formation of undesirable phases such as W 2 C, W, and amorphous or nanocrystalline Co-W-C (eta) phase has been suppressed in the CS and WS coatings. Both coatings have high hardness, which is comparable to or superior to HVOF coatings as well as higher density (low porosity) than the HVOF. Abrasion wear test has shown that WS coatings has higher resistance than CS coatings within this study. As for powder properties, smaller powder and smaller WC particle sizes are effective to produce hard and dense coatings leading to higher wear resistance.

Warm Spray (WS) process, which can control the temperature of a combustion gas jet used to propel powder, has been successfully applied to deposit WC-Co coatings. Detrimental reactions resulting from dissolution of WC into Co binder and decarburization were suppressed effectively by keeping the WC-Co particles’ temperature below the m.p. of the binder phase. In this study, three nano-structured WC-12Co powders with different particle strength were prepared by changing the sintering conditions of spray-dried powder and were deposited by WS. The deposition efficiency and porosity of the coatings decreased with increasing the particle strength. The coating deposited from the powder with very low particle strength showed significant phase changes, while those deposited from the higher particle strengths showed almost no change. Particle Image Velocimetry revealed significant disintegration of the weakest powder, which explains the changes observed. The hardness and wear properties of the former coating, therefore, were inferior to the other two.

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.

Yttrium oxide (Y 2 O 3 ) coatings have been prepared with high power axial injection plasma spraying using fine powder slurries. It is clarified that the coatings have high hardness, low porosity and high erosion resistance against CF4 contained plasma in the previous study. This suggests that the plasma spraying of Y 2 O 3 with slurry injection techniques is applicable to fabricating equipments for semiconductor devices, such as dry etching. Surface morphologies of the slurry coatings with splats are almost similar to conventional plasma-sprayed Y 2 O 3 coatings, identified from microstructural analysis by field emission SEM in this study. However, no lamellar structure has been seen from cross sectional analysis, which is apparently different from the conventional coatings. It has also been found that crystal structure of the slurry Y 2 O 3 coatings mainly composed of metastable phase of monoclinic structure, whereas the powders and the conventional plasma spray coatings have stable phase of cubic structure. Mechanism of coating formation by plasma spraying with fine powder slurries will be discussed based on the findings.

WC-Co cermet coatings were fabricated by using Warm Spraying, which is a modification of HVOF spraying to lower the temperature of the propellant gas below the melting point of Co. By changing the processing parameters, specimens were prepared for hardness, abrasion wear and particle erosion tests. Their microstructures were examined by SEM and XRD. The microstructure clearly showed the effects of suppression of the dissolution of WC into the Co phase, which is the major cause of embrittlement of the conventional HVOF sprayed WC-Co coatings. By combinations of adequate feedstock powder and processing parameters, it was possible to take advantage of fine WC grain size to prepare coatings with higher hardness (HV > 1400), smoother surface (Ra < 2 μm), and moderately improved wear performances compared with conventional HVOF coatings.

This paper describes tribological properties of WC cermet coating layers which are thermally sprayed with HVOF. On the assumption of the severe sliding condition in which large compress and tensile stress are applied to a surface layer simultaneously, relatively hard material is chosen as counter parts and additional tensile stress is applied. WC/12%Co, WC/10%Co/4%Cr and WC/20%CrC/7%Ni are employed as coating material. From the experimental results, it is found that the WC cermet spray coatings by the HVOF are inferior to sintered WC/Co with regard to fracture toughness near the surface and pseudo plastic deformation which are main wear behavior in severe sliding condition. It is also found that a heat treatment has certain effect to eliminate the wear caused by the surface fracture, while, for the pseudo plastic deformation, it does not exhibit much effect.

This study investigates the influence of plasma spray conditions on the structural, mechanical, and plasma-erosion properties of yttrium oxide coatings. Powder feed rate, plasma power, and primary particle size appear to have little effect on plasma erosion properties, hardness, surface morphology, and coating structure. However, a Y 2 O 3 coating produced with fine powder retained a smooth erosion surface despite its porosity and relatively low hardness.

In this present work, WC-Co coatings with different Co contents were deposited by warm spraying using two different powder sizes and their microstructure, hardness, fracture resistance, and wear properties were investigated. The coatings produced from fine powders showed higher hardness and better wear behavior for all Co contents than those deposited from coarse powders, which is attributed to improved splat-splat bonding and a reduction in porosity that comes with using fine powder.