Metal-ceramic Mixtures Research Articles

CFD modelling of the powder segregation in multi-material laser directed energy deposition

One of the prevailing challenges in multi-material laser Directed Energy Deposition is the segregation of the constituents during the delivery of the feedstock into the melt pool. This phenomenon is of particular concern when metal-ceramic mixtures are involved, as the differences in the inertial properties of the powders are higher and segregation is aggravated. This issue affects the reliability of the process; indeed, powder segregation can influence the composition of the melt pool and, thus, that of the final part or coating. In this work, Computational Fluid Dynamics modelling is adopted to study this phenomenon and to explore strategies to overcome it. Firstly, a base multi-material CFD model is built. Secondly, a simplified algorithm is proposed to reduce the computational cost of simulating multiple scenarios. This model is first validated numerically against the base model. Then the simplified multi-material CFD model is experimentally validated. Thirdly, the developed tool is implemented to elaborate two strategies to minimise powder segregation in a Co-WC powder mixture. The first one is quite straightforward and little development is necessary to incorporate it to the industry. Conversely, the second one, though promising, needs further development and its practicality needs to be evaluated before being ready for industrial implementation.

An efficient model for wave propagation of temperature-dependent E-FGM plates resting on viscoelastic foundation

The present work shows the plate's wave propagation behavior made of exponent-law-based functionally graded materials (E-FGM) supported by viscoelastic foundations. In extreme thermal environments, where the E-FGMs are considered highly effective, the temperature influences the composite plate's properties. Therefore, this present study aims to investigate the wave propagation of the E-FGM plates by considering the temperature-dependent effective properties as functions of the position across the thickness and the thermal increase. The governing equations of the E-FGM plate are obtained by employing a simple higher-order shear deformation theory (HSDT) and utilizing the Hamilton principle. An eigenvalue problem is formulated to determine the principal wave propagation frequency. The effects of viscoelastic parameters on E-FGM plates' phase velocities under uniform thermal changes are investigated in detail. The results indicate that introducing metal-ceramic mixtures in the plate would lower the phase velocity in the plate. Furthermore, increasing a uniform temperature in the plate would deteriorate the foundation and plates and, therefore, result in lower velocity and less stiffness.

Advanced Functional Metal-Ceramic and Ceramic Coatings Deposited by Low-Pressure Cold Spraying: A Review

Based on the recent analysis of various databases, cold spray (CS), the newest method among thermal spraying technologies, has received the unabated attention of hundreds of researchers continuously since its invention in the 1980s. The significance of CS lies in the low process temperature, which usually ensures compressive residual stresses and allows for the formation of coatings on a thermally sensitive substrate. This paper concerns the low-pressure cold spray (LPCS) variant employed for forming metal matrix composites (MMCs) with high ceramic contents and all-ceramic coatings. At the very beginning, the influence of LPCS process parameters on deposition efficiency (DE) is analysed. In the next part, the most useful feedstock powder preparation techniques for LCPS are presented. Due to the combination of bottom-up powder production methods (e.g., sol-gel (SG)) with LCPS, the metal matrix that works as a binder for ceramic particles in MMC coatings can be removed, resulting in all-ceramic coatings. Furthermore, with optimization of spraying parameters, it is possible to predict and control phase transformation in the feedstock material. Further in the paper, differences in the bonding mechanism of metal–ceramic mixtures and ceramic particles are presented. The properties and applications of various MMC and ceramic coatings are also discussed. Finally, the exemplary direction of CS development is suggested.

Powder metallurgy process towards functional gradation of Al-Al2O3 metal ceramic mixture samples

Functionally graded materials (FGM) belong to the class of advanced materials whose properties vary along one or more coordinate. In the present study, an attempt has been made to manufacture FGM beams using a powder metallurgy process. The Al and Al2O3 in powder form are mixed to different volume fraction according to the rule of mixture. These samples are ball milled to form a proper blended mixture and to reduce the particle size for 1 hour at 250 rpm with tungsten carbide balls. A cold compacted die made of AISI D2 steel is used for preparing the sample. Different composition of Al and Al2O3 with Al2O3 varying from 0 to 10% is laid in the die using ethanol as the binder. This sample is compressed using hydraulic press with a load varying from 50-70 ton. The compressed sample is removed using a compression moulding machine, then it is sintered to a temperature of 650°C using a muffle furnace to form a smooth graded Al-Al2O3 FGM beam. Various defects such as surface cracks and bending were experienced during the preparation of samples; these defects were overcome by varying the parameters such as loading and sintering temperature.

The development of heterogeneous materials based on Ni and B4C powders using a cold spray and stratified selective laser melting technologies

The work is dedicated to the creation of new ceramic-composite materials based on boron carbide, nickel and using a laser welding in order to obtain three dimensional objects henceforth. The perspective way of obtaining which has been suggested by the authors combined two methods: cold spray technology and subsequent laser post-treatment. At this stage, the authors focused on the interaction of the laser with the substance, regardless of the multi-layer object development. The investigated material of this work was the metal–ceramic mixture based on boron carbide, which has high physical and mechanical characteristics, such as hardness, elastic modulus, and chemical resistance. The nickel powder as a binder and different types of boron carbide were used. The ceramic content varied from 30 to 70% by mass. Thin ceramic layers were obtained by the combined method and cross-sections of different seams were studied. It was shown that the most perspective layers for additive manufacturing could be obtained from cold spray coatings with ceramic concentrations more than 50% by weight treated when laser beam was defocused (thermal-conductive laser mode).

On the mechanical behavior of a functionally graded micro-beam subjected to a thermal moment and nonlinear electrostatic pressure

Abstract In the present work, mechanical behavior of a functionally graded cantilever micro-beam subjected to a nonlinear electrostatic pressure and temperature changes has been studied. It has been assumed that the top surface is made of pure metal and the bottom surface from a metal–ceramic mixture. The ceramic constituent percent of the bottom surface varies from 0% to 100%. In addition to the Volume Fractional Rule of material, exponential function has been used for representation of continuous gradation of the material properties through micro-beam thickness. Attention being paid to the ceramic constituent percent of the bottom surface, five different types of FGM micro-beams have been investigated. Nonlinear integro-differential thermo-electro mechanical equation based on Euler–Bernoulli beam theory has been derived and solved using Step-by-Step Linearization Method and Finite Difference Method. The effects of temperature changes and the electrostatic pressure on the deflection and stability of FGM micro-beams having various amounts of the ceramic constituent have been studied and normal stress distributions in the cross section along the beam thickness have been given and compared with a classic metal beam.

Calculation of Particle Parameters for Cold Spraying of Metal-Ceramic Mixtures

Formation of metal-ceramic composite coatings by cold spray is one of the major directions in the development and application of the technology. As experiments showed, addition of a hard ceramic component into the mixture can shift the transition from substrate erosion to particles adhesion closer to adhesion. This effect may be induced by ceramic particles which not only erode, but also activate the target surface. Velocity and temperature of particles at their high-velocity impact onto the substrate are governing parameters in particles/substrate interaction. These parameters influence both the process of metal particles deposition and the process of erosion/activation of the substrate surface by ceramic particles. Metallic and ceramic particles collide with each other in the gas stream. These collisions can produce preactivation effect on metal particles by cleaning their surface. The level of activation depends on a typical velocity of collision which is the difference between velocities of metal and ceramic particles. Parameters of metallic and ceramic particles in the gas stream are estimated. Calculations show that components of mixtures with fine abrasive particles have greatly different velocities that influences preactivation of metal particles. At the same time, the substrate surface is activated by fine abrasive particles characterized by a high-impact velocity.

Hydrodynamic compressibility of silicon carbide through shock compression of metal-ceramic mixtures

Shock-compression experiments were performed on 50% by volume ceramic-metal mixtures of silicon carbide and copper at pressures of 15–30 GPa. The objective of these experiments was to determine the hydrodynamic compressibility (dynamic pressure-volume response) of silicon carbide through shock measurements on the ceramic-metal composite and the application of analytic mixture theory. Compression states inferred for silicon carbide above 20 GPa appear consistent with hydrodynamic behavior and are in agreement with compression curves extrapolated from ultrasonic data. Dynamic strength or viscosity effects apparently complicate shock compression of the ceramic-metal composite at the lower shock pressures. Shock release experiments on the composites provide further high-pressure equation-of-state data for the ceramic-metal mixture.

Chromium Oxide – Chromium Cermets

THE preparation and properties of chromic oxide–chromium cermets have been examined as part of a general investigation into the possibility of preparing metal–ceramic mixtures (‘cermets’) by partial reduction of refractory oxides. The method consists of pressing a mixture of chromic oxide and carbon, both in the finely divided state, into compacts and sintering to temperatures in the range 1,400°–1,600° C in a vacuum of circa 10−4 mm mercury. The amount of carbon is calculated to give 1–10 per cent metallic chromium in the sintered body.