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.
The traditional technique of titanium production is via the Kroll process which involves chlorination of TiO2 ore in the presence of carbon and reacting the resulting TiCl4 with magnesium to produce titanium sponge. These processes take place at temperatures as high as 1040 °C. The sponge particle range in size from 45 to 180 μm, with particles ~150 μm termed 'sponge fines'. These fines are irregularly shaped and porous with a sponge-like morphology. The fines are then blended with alloy additions; cold compacted into a green compact at up to 415 MPa then vacuum sintered at 1260 °C to produce a 99.5% dense component. Hot isostatic pressing (HIP) can further increase the density of these parts and produce components more economically than cast or wrought parts, but the porosity present in the material degrades fatigue and fracture properties. The BE approach has been used to produce valves for the Toyota Altezza, golf club heads and softball bats. More recently, close to 100% dense Ti Grade 5 parts has been achieved using a hydrided powder along with 60:40 Al:V master alloy. The mechanical properties compare well with those exhibited by cast-and-wrought products. A cost estimate of less than $3.00 for a 0.320 g automotive connection link has been made.
Several techniques exist to produce pre-alloyed powder, such as Grade 5. In the hydride-dehydride process feedstock such as solid scrap, billet or machined turnings are processed to remove contaminants, hydrogenated to produce brittle material then ground under argon in a vibratory ball mill, typically at 400 °C for 4 hours at a pressure of 1 psi for Ti Grade 5. The resulting particles are angular and measure between 50 and 300 μm. Cold compaction after dehydrogenation of the powder, followed by either vacuum hot pressing (in this case the dehydrogenation process can be bypassed as hydrogen is removed under vacuum) or HIP and a final vacuum anneal, produces powders with hydrogen below 125 ppm. The possible presence of contaminants makes these powders unsuitable for use in critical aircraft applications.
In the plasma rotating electrode process (PREP), the feedstock, such as Ti Grade 5, is in the form of a rotating bar which is arced with gas plasma. The molten metal is centrifugally flung off the bar, cools down and is collected. The powders produced are spherical; between 100 and 300 μm is size, with good packing and flow characteristics, making the powder ideal for high quality, near net shapes produced by HIP, such as aviation parts and porous coatings on hip prostheses.
In the titanium gas atomisation (TGA) process, titanium is vacuum induction skull melted in a water cooled copper crucible, the metal tapped and the molten metal stream atomized with a stream of high pressure inert gas. The tiny droplets are spherical and measure between 50 and 350 μm. The TGA process has been used to produce a wide variety of materials such as commercially pure (CP) titanium, conventional alpha-beta and beta alloys.
In plasma atomization (PA) process, a titanium wire is atomized by 3 inert gas plasma jets to form spherical metal powders. The distribution of diameter obtained in the PA process ranges between 0–200 μm and the powders obtained is very pure. The PA process specializes in the production of high temperature melting material as titanium (CP-Ti, Ti-6Al-4V), niobium, molybdenum, tantalum and many more.
Several metal consolidation techniques are used to produce the final product. Metal injection moulding (MIM) otherwise known as powder injection moulding is a well-established and cost-effective method of fabricating small-to-moderate size metal components in large quantities. It is derived from the method plastic injection moulding, whereby mixing of a metal powder with a polymer binder forms the feedstock, which is then injected into a mould, after which the binder is removed via heat treatment under vacuum before final sintering. With titanium however, the binders used in MIM results in the introduction of carbon into the matrix due to insufficient binder removal prior to sintering and/or deleterious reactions between the decomposing binder, the debinding atmosphere, and the metal phase. This results in titanium parts with mechanical properties unsuited for critical aerospace applications, but suitable for parts where tensile and impact properties are less important. Recently, work has been carried out to reduce the binder to < 8% volume fraction, resulting in the complete removal of the binder from the moulded component during heat treatment.
In the direct powder rolling (DPR) process BE powder is used to produce sheet and plate and composite multilayered sheet and plates. Sheets between 1.27 and 2.54 mm and 50 to 99+% dense of single layer CP titanium, Ti Grade 5, TiAl (Ti-48Al-2Cr-2Nb) and composite Ti/Grade 5/Ti and Grade 5/TiAl/Grade 5 have been produced by DPR and sintering.
Laser engineered net shaping (LENS) is an additive manufacturing technique for rapidly fabricating, enhancing and repairing metal components directly from CAD data. The processes use a high power solid state laser focused onto a metal substrate to create a ~1 mm diameter melt pool. Metal powder is then injected into the melt pool to increase the material volume and build up the component layer by layer. Experimental gas thrusters (build time 8 hours) and automotive brackets have been manufactured in Ti-Grade 5. Selective Laser Sintering (SLS) is similar, except that the laser selectively fuses powdered material by scanning on the surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed.
In hot isostatic pressing high temperature and pressure are used to consolidate powders to close to their maximum theoretical densities.
Electric current assisted sintering, also known as spark plasma sintering (SPS) relies on fast application of resistive heating and pressure to consolidate powders close to their maximum theoretical densities, without the undesired grain growth effect, thereby retaining close to original grain size and achieving improved mechanical properties in the final product.
Work is progressing on bypassing the conventional route of atomising wrought feedstock or sponge and the inherent cost associated with the traditional Kroll process. Several of these processes, such as the FFC, MER Corporation, OS, Ginatta and BHP Billiton processes rely on the electrolytic reduction of TiO2 (a cheap and abundant material) to form Ti metal. So far, no material from these processes has been sold commercially on the open market, and cost models have yet to be published, but they offer the possibility of inexpensive titanium powder in the near future. The countries that have such facilities to generate Titanium Sponge are Saudi Arabia, China, Japan, Russia, Kazakhstan, the USA, Ukraine and India. The Titanium Sponge Plant in India is the only one in the world that can undertake all the different activities of manufacturing aerospace grade titanium sponge under one roof.
Sintering or frittage is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction.
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 avoid, or greatly reduce, the need to use metal removal processes, thereby drastically reducing yield losses in manufacture and often resulting in lower costs.
Selective laser sintering (SLS) is an additive manufacturing (AM) technique that uses a laser as the power source to sinter powdered material, aiming the laser automatically at points in space defined by a 3D model, binding the material together to create a solid structure. It is similar to selective laser melting; the two are instantiations of the same concept but differ in technical details. SLS is a relatively new technology that so far has mainly been used for rapid prototyping and for low-volume production of component parts. Production roles are expanding as the commercialization of AM technology improves.
Titanium diboride (TiB2) is an extremely hard ceramic which has excellent heat conductivity, oxidation stability and wear resistance. TiB2 is also a reasonable electrical conductor, so it can be used as a cathode material in aluminium smelting and can be shaped by electrical discharge machining.
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, good surface stability, and resistance to corrosion or oxidation.
Microstructure is the very small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25× magnification. The microstructure of a material can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behaviour or wear resistance. These properties in turn govern the application of these materials in industrial practice.
Ceramic forming techniques are ways of forming ceramics, which are used to make everything from tableware such as teapots to engineering ceramics such as computer parts. Pottery techniques include the potter's wheel, slip casting and many others.
Laser powder forming, also known by the proprietary name is an additive manufacturing technology developed for fabricating metal parts directly from a computer-aided design (CAD) solid model by using a metal powder injected into a molten pool created by a focused, high-powered laser beam. This technique is also equivalent to several trademarked techniques that have the monikers direct metal deposition (DMD), and laser consolidation (LC). Compared to processes that use powder beds, such as selective laser melting (SLM) objects created with this technology can be substantially larger, even up to several feet long.
Metal injection molding (MIM) is a metalworking process in which finely-powdered metal is mixed with binder material to create a "feedstock" that is then shaped and solidified using injection molding. The molding process allows high volume, complex parts to be shaped in a single step. After molding, the part undergoes conditioning operations to remove the binder (debinding) and densify the powders. Finished products are small components used in many industries and applications.
Titanium hydride normally refers to the inorganic compound TiH2 and related nonstoichiometric materials. It is commercially available as a stable grey/black powder, which is used as an additive in the production of Alnico sintered magnets, in the sintering of powdered metals, the production of metal foam, the production of powdered titanium metal and in pyrotechnics.
Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface. The "feedstock" is heated by electrical or chemical means.
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.
Electron-beam additive manufacturing, or electron-beam melting (EBM) is a type of additive manufacturing, or 3D printing, for metal parts. The raw material is placed under a vacuum and fused together from heating by an electron beam. This technique is distinct from selective laser sintering as the raw material fuses having completely melted.
Cemented carbide is a hard material used extensively as cutting tool material, as well as other industrial applications. It consists of fine particles of carbide cemented into a composite by a binder metal. Cemented carbides commonly use tungsten carbide (WC), titanium carbide (TiC), or tantalum carbide (TaC) as the aggregate. Mentions of "carbide" or "tungsten carbide" in industrial contexts usually refer to these cemented composites.
Precision glass moulding is a replicative process that allows the production of high precision optical components from glass without grinding and polishing. The process is also known as ultra-precision glass pressing. It is used to manufacture precision glass lenses for consumer products such as digital cameras, and high-end products like medical systems. The main advantage over mechanical lens production is that complex lens geometries such as aspheres can be produced cost-efficiently.
Selective laser melting (SLM) is one of many proprietary names for a metal additive manufacturing technology that uses a bed of powder with a source of heat to create metal parts. Also known as direct metal laser melting (DMLM), the ASTM standard term is powder bed fusion (PBF). PBF is a rapid prototyping, 3D printing, or additive manufacturing (AM) technique designed to use a high power-density laser to melt and fuse metallic powders together.
3D metal moulding, also referred to as metal injection moulding or (MIM), is used to manufacture components with complex geometries. The process uses a mixture of metal powders and polymer binders – also known as "feedstock" – which are then injection-moulded.
A variety of processes, equipment, and materials are used in the production of a three-dimensional object via additive manufacturing. 3D printing is also known as additive manufacturing, therefore the numerous available 3D printing process tend to be additive in nature with a few key differences in the technologies and the materials used in this process.
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.