Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films.
Powder metallurgy (PM) is a term covering a wide range of ways in which materials or components are made from metal powders. PM processes can reduce or eliminate the need for subtractive processes in manufacturing, lowering material losses and reducing the cost of the final product.
A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films is a fundamental step in many applications. A familiar example is the household mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as sputtering. Advances in thin film deposition techniques during the 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media, electronic semiconductor devices, integrated passive devices, LEDs, optical coatings, hard coatings on cutting tools, and for both energy generation and storage. It is also being applied to pharmaceuticals, via thin-film drug delivery. A stack of thin films is called a multilayer.
Plasma arc welding (PAW) is an arc welding process similar to gas tungsten arc welding (GTAW). The electric arc is formed between an electrode and the workpiece. The key difference from GTAW is that in PAW, the electrode is positioned within the body of the torch, so the plasma arc is separated from the shielding gas envelope. The plasma is then forced through a fine-bore copper nozzle which constricts the arc and the plasma exits the orifice at high velocities and a temperature approaching 28,000 °C (50,000 °F) or higher.
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Key characteristics of a superalloy include mechanical strength, thermal creep deformation resistance, surface stability, and corrosion and oxidation resistance.
Powder coating is a type of coating that is applied as a free-flowing, dry powder. Unlike conventional liquid paint which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as household appliances, aluminium extrusions, drum hardware, automobiles, and bicycle frames. Advancements in powder coating technology like UV-curable powder coatings allow for other materials such as plastics, composites, carbon fiber, and MDF to be powder coated due to the minimum heat and oven dwell time required to process these components.
Titanium powder metallurgy (P/M) offers the possibility of creating net shape or near net shape parts without the material loss and cost associated with having to machine intricate components from wrought billet. Powders can be produced by the blended elemental technique or by pre-alloying and then consolidated by metal injection moulding, hot isostatic pressing, direct powder rolling or laser engineered net shaping.
Spray forming, also known as spray casting, spray deposition and in-situ compaction, is a method of casting near net shape metal components with homogeneous microstructures via the deposition of semi-solid sprayed droplets onto a shaped substrate. In spray forming an alloy is melted, normally in an induction furnace, then the molten metal is slowly poured through a conical tundish into a small-bore ceramic nozzle. The molten metal exits the furnace as a thin free-falling stream and is broken up into droplets by an annular array of gas jets, and these droplets then proceed downwards, accelerated by the gas jets to impact onto a substrate. The process is arranged such that the droplets strike the substrate whilst in the semi-solid condition, this provides sufficient liquid fraction to 'stick' the solid fraction together. Deposition continues, gradually building up a spray formed billet of metal on the substrate.
Thermal barrier coatings (TBCs) are advanced materials systems usually applied to metallic surfaces on parts operating at elevated temperatures, such as gas turbine combustors and turbines, and in automotive exhaust heat management. These 100 μm to 2 mm thick coatings of thermally insulating materials serve to insulate components from large and prolonged heat loads and can sustain an appreciable temperature difference between the load-bearing alloys and the coating surface. In doing so, these coatings can allow for higher operating temperatures while limiting the thermal exposure of structural components, extending part life by reducing oxidation and thermal fatigue. In conjunction with active film cooling, TBCs permit working fluid temperatures higher than the melting point of the metal airfoil in some turbine applications. Due to increasing demand for more efficient engines running at higher temperatures with better durability/lifetime and thinner coatings to reduce parasitic mass for rotating/moving components, there is significant motivation to develop new and advanced TBCs. The material requirements of TBCs are similar to those of heat shields, although in the latter application emissivity tends to be of greater importance.
Gas dynamic cold spraying or cold spraying (CS) is a coating deposition method. Solid powders are accelerated in a supersonic gas jet to velocities up to ca. 1200 m/s. During impact with the substrate, particles undergo plastic deformation and adhere to the surface. To achieve a uniform thickness the spraying nozzle is scanned along the substrate. Metals, polymers, ceramics, composite materials and nanocrystalline powders can be deposited using cold spraying. The kinetic energy of the particles, supplied by the expansion of the gas, is converted to plastic deformation energy during bonding. Unlike thermal spraying techniques, e.g., plasma spraying, arc spraying, flame spraying, or high velocity oxygen fuel (HVOF), the powders are not melted during the spraying process.
Plasma activation is a method of surface modification employing plasma processing, which improves surface adhesion properties of many materials including metals, glass, ceramics, a broad range of polymers and textiles and even natural materials such as wood and seeds. Plasma functionalization also refers to the introduction of functional groups on the surface of exposed materials. It is widely used in industrial processes to prepare surfaces for bonding, gluing, coating and painting. Plasma processing achieves this effect through a combination of reduction of metal oxides, ultra-fine surface cleaning from organic contaminants, modification of the surface topography and deposition of functional chemical groups. Importantly, the plasma activation can be performed at atmospheric pressure using air or typical industrial gases including hydrogen, nitrogen and oxygen. Thus, the surface functionalization is achieved without expensive vacuum equipment or wet chemistry, which positively affects its costs, safety and environmental impact. Fast processing speeds further facilitate numerous industrial applications.
Evaporation is a common method of thin-film deposition. The source material is evaporated in a vacuum. The vacuum allows vapor particles to travel directly to the target object (substrate), where they condense back to a solid state. Evaporation is used in microfabrication, and to make macro-scale products such as metallized plastic film.
Solution precursor plasma spray (SPPS) is a thermal spray process where a feedstock solution is heated and then deposited onto a substrate. Basic properties of the process are fundamentally similar to other plasma spraying processes. However, instead of injecting a powder into the plasma plume, a liquid precursor is used. The benefits of utilizing the SPPS process include the ability to create unique nanometer sized microstructures without the injection feed problems normally associated with powder systems and flexible, rapid exploration of novel precursor compositions.
Electrostatic spray-assisted vapour deposition (ESAVD) is a technique to deposit both thin and thick layers of a coating onto various substrates. In simple terms chemical precursors are sprayed across an electrostatic field towards a heated substrate, the chemicals undergo a controlled chemical reaction and are deposited on the substrate as the required coating. Electrostatic spraying techniques were developed in the 1950s for the spraying of ionised particles on to charged or heated substrates.
Hardfacing is a metalworking process where harder or tougher material is applied to a base metal. It is welded to the base material, and generally takes the form of specialized electrodes for arc welding or filler rod for oxyacetylene and gas tungsten arc welding. Powder metal alloys are used in plasma-transferred arc (PTA), also called powder plasma welding, and thermal spray processes like high-velocity oxygen fuel coating, plasma spray, spray and fuse, etc. Submerged arc welding, flux core arc welding (FCAW) and metal inert gas (MIG) / metal active gas (MAG) use continuously fed wire varying in diameter depending on the process and current. The strip cladding process uses strips from 50 mm wide to 125 mm with a thickness of 0.5mm. Open arc welding uses a continuously fed tubular electrode which may or may not contain flux.
Plasma transferred wire arc (PTWA)thermal spraying is a thermal spraying process that deposits a coating on the internal surface of a cylindrical surface, or external surface of any geometry. It is predominantly known for its use in coating the cylinder bores of an internal combustion engine, enabling the construction of aluminium engine blocks without cast iron cylinder sleeves.
Cladding is the bonding together of dissimilar metals. It is different from fusion welding or gluing as a method to fasten the metals together. Cladding is often achieved by extruding two metals through a die as well as pressing or rolling sheets together under high pressure.
Detonation spraying is one of the many forms of thermal spraying techniques that are used to apply a protective coating at supersonic velocities to a material in order to change its surface characteristics. This is primarily to improve the durability of a component. It was first invented in 1955 by H.B. Sargent, R.M. Poorman and H. Lamprey and is applied to a component using a specifically designed detonation gun (D-gun). The component being sprayed must be prepared correctly by removing all surface oils, greases, debris and roughing up the surface in order to achieve a strongly bonded detonation spray coating. This process involves the highest velocities and temperatures (≈4000 °C) of coating materials compared to all other forms of thermal spraying techniques. Which means detonation spraying is able to apply low porous and low oxygen content protective coatings that protect against corrosion, abrasion and adhesion under low load.
Cold spray additive manufacturing (CSAM) is a particular application of cold spraying, able to fabricate freestanding parts or to build features on existing components. During the process, fine powder particles are accelerated in a high-velocity compressed gas stream, and upon the impact on a substrate or backing plate, deform and bond together creating a layer. Moving the nozzle over a substrate repeatedly, a deposit is building up layer-by-layer, to form a part or component. If an industrial robot or computer controlled manipulator controls the spray gun movements, complex shapes can be created. To achieve 3D shape, there are two different approaches. First to fix the substrate and move the cold spray gun/nozzle using a robotic arm, the second one is to move the substrate with a robotic arm, and keep the spray-gun nozzle fixed. There is also a possibility to combine these two approaches either using two robotic arms or other manipulators. The process always requires a substrate and uses only powder as raw material.
Laser metal deposition (LMD) is an additive manufacturing process in which a feedstock material is melted with a laser and then deposited onto a substrate. A variety of pure metals and alloys can be used as the feedstock, as well as composite materials such as metal matrix composites. Laser sources with a wide variety of intensities, wavelengths, and optical configurations can be used. While LMD is typically a melt-based process, this is not a requirement, as discussed below. Melt-based processes typically have a strength advantage, due to achieving a full metallurgical fusion.
