Presently one of the most important tendencies is the use of tungsten (W) monoblock material for the first wall and other plasma facing components (PFCs) in tokamak. The use of low Z materials such as B 4 C for protection of PFCs is a conventional method to decrease heavy impurity influx into tokamak plasma. This study involves the fabrication and characterization of inductively coupled plasma (ICP) thermal sprayed B 4 C coating on tungsten monoblock. Thickness of the coating was about 120μm. Surface morphology of the coating is presented with scanning electron microscope and metallographic microscope analyses. X-ray diffraction analysis and X-ray photoelectron spectroscopy showed that the main phase and chemical composition of the coatings were preserved when compared with that of the initial B 4 C powder. Adhesion test result revealed that the adhesion/cohesion strength of the coating was above 13.1 MPa. This work is innovative not only for the ICP thermal sprayed method for the B 4 C coating fabrication but for the plasma sprayed B 4 C on tungsten substrate.

This study evaluates the possibility of depositing hard B 4 C and TiC reinforcing particles in a Ni matrix using low-pressure cold spraying. It also investigates the effect of particle velocity and kinetic energy on deposition efficiency, microstructure, hardness, and wear resistance. B 4 C and TiC powders were blended at 50, 75, and 92 wt% carbide content with Ni powder comprising the remainder of the mixture. The impact velocity of sprayed carbide particles was calculated using a mathematical model based on the thermodynamics of compressible fluid flow through a converging-diverging nozzle. The model showed that the kinetic energy of TiC particles prior to impact was three times smaller than that of B 4 C, resulting in a higher carbide content (18 wt% compared to 8 wt%) due to reduced fracture and rebound of the TiC particles. Although the hardness values of both coatings are within the range of cold-sprayed WC-Co-Ni, wear rates were found to be high.

B 4 C-Ni powders ranging in content from 5-60 wt% Ni were fabricated by pressurized hydrogen reduction and deposited on mild carbon steel substrates by air plasma spraying. The microstructure, morphology, and phase composition of the powders and coatings were evaluated by means of SEM and XRD analysis. The influence of Ni content on coating microstructure, fretting wear resistance, hardness, and adhesive strength was investigated in detail. The results show that Ni affects fretting wear resistance, which was found to be highest in the coating with 40 wt% nickel. The B 4 C-40Ni coating also proved superior in terms hardness, porosity, and friction coefficient, although its adhesive strength was the lowest.

This paper describes the development of detonation-sprayed aluminum-matrix composite coatings reinforced with boron carbide. The goal is to achieve a homogeneous coating structure with low porosity, low oxide content, and high concentration of embedded carbides. Tensile tests of various types were conducted and different stages of deformation were analyzed using micro computed tomography, a 3D imaging technique that reveals the formation of cracks in real time.

This study investigates the potential of external powder injection for producing functionally graded coatings by twin wire arc spraying. In spray trials, the position of the injection port was altered along the spray axis and perpendicular to the arc and different powders and carrier gases were used. Real-time images were captured by a high-speed camera during spraying to detect correlations between gas flow rates, hard particle wetting, and atomization of the molten pool. The optimal location for injection was found to be dependent on the size and density of the powder and the flow rate of the carrier gas. In the case of embedding B 4 C in a Fe-based matrix, a strong metallurgical bond was formed, confirming that powder injection is a viable approach for controlling the composition of twin wire arc sprayed coatings.

In the oil industry, logging systems involving geological sensors are designed to operate under increasing severe service conditions of deep and horizontal boreholes. Under these conditions, metal matrix composites (MMCs) with ceramic reinforcement are applied on components to achieve wear and corrosion resistant systems. The ‘cold spray’ could be described as a cold and inert process to form coating layers through severe plastic deformation of a ductile metal. Ceramic/metal MMC coating could be achieved by co-deposition of a ceramic with a ductile material. In this work, it was it was investigated the use of MMC B 4 C-Ni coating from both mechanically milled blends or B 4 CNi CVD coated batches. Powder blends involving Ni powder with fine or coarse B 4 C powders were prepared by mechanical milling. Three CVD coated B 4 C-Ni powder batches were synthesized with 30, 40 and 50 Ni wt% respectively. Cold spray coatings were achieved with 1 pass and 5 passes to investigate the building-up mechanisms and interfaces with AISI316L. Powders and cold sprayed coatings microstructures were observed by optical and scanning electron microscopies and further quantitative image analysis were carried out to determine the content of B 4 C embedded in the Ni matrix of B 4 C-Ni cold spray coatings. The highest B 4 C vol.%, up to 45%, could be reached in the case of B 4 C-Ni coated powder. Micro-hardness values of such MMC coatings were also determined through Vickers micro-indentation. The beneficial role of the Ni surrounding layer on coating formation is discussed in relation to the unique features of the microstructures obtained by cold spray of B 4 C-Ni coated powders.

The superior mechanical properties of Boron Carbide make it very attractive for use as a wear resistant coating in tribological applications. Boron carbide is the hardest non-oxide ceramic produced in large quantities. It offers a high erosion and abrasion resistance, high chemical and outstanding heat resistance. B4C can be formed on a suitable substrate by thermal spray process as an alternative to high wear carbide coatings. The objective of this work was to investigate and to characterize the mechanical properties of a boron carbide based coating applied by HVOF spraying using a non commercial powder for corrosion and abrasion applications. The produced coatings were evaluated by metallographic procedure, microhardness, porosity and roughness measurements as well as adhesion and wear tests. The results are promising and signal good applications for such coatings.

The aim of this work is to assess the potential of HVOF-sprayed boron carbide-based coatings for protecting surfaces against abrasive wear. The results are evaluated by microstructure characterization, microhardness measurements, and adhesion and wear tests.

Functionally graded coatings with continuous changes of microstructures and properties across the material are expected to have low residual and thermal stresses and improved bonding strength between base materials and the ceramic coatings. This paper presents a technique to produce high-performance graded coatings in which the mix of components in the coating changes continuously from the base materials out. A hybrid HVOF-Arc spray gun has been employed to create such coatings. The metallic matrix material is utilized in the form of wires that are fused by arcing process. A high velocity combustion jet carrying the ceramic particles atomizes the molten material and mixes the ceramic particles with the matrix material. The feed rate of the matrix material and the reinforcing material are controlled together giving a systematic variation of the reinforcement phase. Two material systems; WC-16%Cr 3 C 2 -Ni-5%Al and B 4 C-Al(5%Si) have been investigated. The in-flight particle characteristics of the process have been characterized. The resulting microstructures and process capabilities are discussed.

Boron carbide has been successfully deposited on Ti alloy by vacuum plasma spraying (VPS). Mechanical properties of the deposited structure were assessed by micro-hardness and nano-hardness indentation. Chemical and phase compositions of the starting powder and the as-sprayed structure were characterized using hot gas extraction (LECO), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and Raman spectroscopy. The microstructure consisted of equiaxed boron carbide grains, microcrystalline boron carbide particles, and amorphous carbon regions at the grain boundaries. The amount of boron oxide and amorphous carbon increased during spraying. Carbon segregation to grain boundaries in the as-deposited B 4 C was observed. The measured micro-hardness was slightly higher than values previously reported (1033 ± 2009 HV). There was significant variation of nano-hardness from point to point in the material due to the existence of multiple phases, splat boundaries, and porosity in the deposited structure.

An investigation was conducted to assess the potential of water-stabilized plasma (WSP) spraying for applying protective boron carbide coatings to fusion reactor components. This paper describes how test samples were produced and how coating quality was determined. The authors sprayed boron carbide powder onto steel and stainless steel substrates using different powder feeding and spraying distances, substrate preheat temperatures, and carrier gases. They also investigated methods for optimizing the plasma jet and improving coating adhesion. The boron carbide coatings were characterized based on phase composition, porosity, oxygen content, and flexural strength. Paper includes a German-language abstract.

Recent developments in the field of plasma sprayed ceramic coatings at Shanghai Institute of Ceramics (SIC) are presented. Nano-titania and nano-tungsten carbide coatings were prepared. Their structure and properties were detected. The super hard B 4 C coating was deposited by APS. The physical and mechanical and anti-irradiation properties of B 4 C were measured. Wollastonite coating was deposited and its bioactivity has been tested. The results obtained indicated that (1) nano-titania coating possessed porous structure and unique electric properties; (2) nano-WC-Co coating exhibited notable wear resistance; (3) B 4 C coating was excellent irradiation resistance and (4) the carbonate-containing hydroxyapatite was formed on the surface of wollastonite coating, which indicated that this coating has excellent bioactivity.

This paper describes a novel application of OF-boride layers on steel surfaces. The plasma-sprayed boron carbide powder on steel was diffusion annealed to form a suitable iron-hemiboride intermediate layer with a coefficient of thermal expansion between the coefficients for the steels used and ceramic coatings to create. In the next step, this system was completed with a second plasma-sprayed layer on aluminum oxide o zirconium oxide. The adhesion of these samples was checked after dynamic loading as a result of alternating thermal loads at 600, 800, 1000 or 1200 deg C. The resulting values were compared both with the adhesion values of the same ceramic coatings on steel without a boride intermediate layer and with the adhesion values of these ceramic coatings on steel that were borated according to the classic method in a boron carbide pack with activators. Paper includes a German-language abstract.

The Laser Megajoule (LMJ) is designed to produce, in laboratory, fusion energy with a significant gain. Such an energy could be achieved by imploding a small capsule filled with a DT mixture. Fusion experiments produce a large emission of neutrons, x-rays, laser scattered light and debris which impose a first wall protection for the laser target chamber made of a low Z and refractory material. As boron carbide appeared to be a good candidate, among others, it was decided to evaluate the potentiality of plasma sprayed B4C coatings for this application. This paper deals with the optimization of plasma spraying conditions to build up coatings that satisfy specifications required for the first wall. Coating general properties are presented as well as outgassing performances. Specific x-ray and laser tests were performed to evaluate coating behavior close to real LMJ working conditions.

The development of nuclear fusion reactors is presently considered to be the only possible answer to the world's increasing demand for energy, while respecting the environment. Nuclear fusion devices may be broadly divided into two main groups with distinctively different characteristics: magnetic confinement fusion (MCF) and inertial confinement fusion (ICF) reactors. Although the two nuclear fusion technologies show similarities in energy levels (as high as 3 J/cm2) and type of environment (high temperature plasmas) to be contained, the materials of choice for the protective shields (first wall in the ICF and deflectors in the MCF) differ significantly. In ICF reactors, multiple laser beams are used to ignite the fuel in single pulses. This process exposes the first wall to microshrapnel, unconverted light, x-rays, and neutrons. B4C is a low Z material that offers high depth x-ray absorption to minimize surface heating, is not activated by neutrons (will not become radioactive), and offers high hardness and vapour temperature. The long term operation envisioned within MCF reactors, where a continuous nuclear fusion of the fuel is sustained within the confinement of a magnetic field, favours the use of high Z materials, such as W, to protect the plasma exposed deflectors. The reason is a lower erosion rate and a shorter ionization distance in the plasma, which favours the redeposition of the sputtered atoms, both resulting in a lower contamination of the plasma. The production of the first wall and the deflector shields using solid B4C and W materials respectively, is obviously unthinkable. However, ProTeC has developed high density coatings for both ICF and MCF nuclear fusion reactors. W coatings with less than 2% porosity have been produced for both, the Tokamac MCF reactor and its Toroid Fueler. The toroid fueler is a plasma generating device designed to accelerate particles and inject them into the centre of the operating fusion reactor in order to refuel. For the application in an ICF reactor, B4C coatings exhibiting porosity levels below 3% with a hardness above 2500 HV have been deposited directly onto Al substrate. Properties such as outgassing, resistance to erosion and shrapnel, and the influence of x-rays have been studied and showed exceptional results.

Thermally-sprayed low-Z coatings of boron carbide (B4C) on aluminum substrates were investigated as candidate materials for first-wall reactor protective surfaces. Comparisons were made to thermally-sprayed coatings of boron, MgAl204, Al2O3, and composites. Graded bond layers were applied to mitigate coefficient of thermal expansion mismatch. Microstructures, thermal diffusivity before and after thermal shock loading, steel ball impact resistance, CO2 pellet cleaning and erosion tolerance, phase content, stoichiometry by Rutherford backscattering spectroscopy (RBS), and relative tensile strengths were measured.