Net-shape Forming Research Articles

Grain Boundary Characterization in Yttria-Stabilized Zirconia by TEM Spectrum Lines

Abstract The superplasticity exhibited by some fine-grained ceramics, notably 3-mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP), offers interesting possibilities to lower manufacturing costs by near net shape forming. Both glassy and crystalline materials have been added to pure 3 Y-TZP to limit grain growth and promote grain boundary sliding during sintering and isostatic pressing. EDS spectrum lines have been used to characterize the distribution and extent of additive phases, but were not able to map some light-element components of additives (e.g., O and B in borosilicate glass). Additionally, quantification of the Si Kα peak was compromised by overlap with the Y L and Z L peaks. To both improve light element sensitivity and investigate potential changes in oxygen bonding at the grain boundaries, undoped 3 Y-TZP and 3 Y-TZP powders processed with 1 wt% barium silicate have been examined with TEM spectrum lines. Additionally, some elemental mapping has been performed. TEM specimens were examined in a 300 kV LaB6 Philips CM30T equipped with a Gatan imaging filter (GIF) at the ORNL SHaRE User Facility.

The net-shape forming of gears

Over recent years vigorous developments have been undertaken to enable the production of gears and gear forms by forming methods. The driving force behind this activity has been, in common with other areas of component manufacture, greater added value. These developments are leading to the commercial feasibility of producing gear tooth forms of high quality, ready for use. For applications where extreme high quality of tooth form is not necessary, such as automotive differentials, forged gear forms can be employed without further machining. Because the dimensional quality required of the running teeth of gears in automotive gear boxes is high as yet only machined tooth forms are sufficiently accurate. This paper describes the background to the research on the forging of spur and helical gear forms with particular attention on the production of high quality gears for land transport applications.

Nucleation control for hot-working of silicon oxynitride based ceramics

An attempt was made to develop an engineering ceramic plastically deformable at high temperatures with low flow stress at high strain rates, and without strain hardening. Dense ceramic preforms were fabricated by pressureless sintering Si3N4 + SiO2 mixed powders with an addition of MgAl2O4 at 1500 °C. A transient liquid, which occurs during the reaction sintering of Si2N2O, was utilized for subsequent net-shape forming. The ceramic (6Φ × 6 mm column) was deformed without any cracks and cavities in compression tests at high strain rates (10−2−10−3:s−1) at 1500 °C, but this was not achieved in a test at lower strain rates for a long time, because of the growth of elongated Si2N2O grains during the test. Potassium fluoride (KF) was used as a dopant for retardation of nucleation of Si2N2O during sintering and hot-working. The KF-doped preforms were successfully plastically deformed even in the test for a long time.

High strength TRIP/TWIP and superplastic steels : development, properties, application

Fine grained high carbon superplastic steels and high manganese TRIP steels with amounts of aluminium of about 7 wt-% exhibit high strength and fracture toughness at room temperature. The duplex microstructure of these superplastic steels causes uniform elongations up to 1000 % at medium and higher temperature (up to 860 °C). The TRIP effect (transformation induced plasticity) causes large elongations of about 80 % and high work hardening rates at low temperature (- 100 to 20 °C). The unique properties of the superplastic and of the TRIP steels are used for near net shape forming of machine parts and for deep drawing operations of sheets to tailored blanks in the car body manufacturing.

Net Shape Forming of Electromagnetically Elaborated Semisolid Metal Matrix Composites

Article Net Shape Forming of Electromagnetically Elaborated Semisolid Metal Matrix Composites was published on September 1, 1998 in the journal Science and Engineering of Composite Materials (volume 7, issue 3).

Processes of partial bulk metal-forming—aspects of technology and FEM simulation

This publication focuses on near-net-shape and net-shape forming of rotation-symmetrical workpieces by incremental rolling processes (cross rolling, spin extrusion). The combination of both processes is essential. The FEM simulation is compared with the model method of shape deformation (FMM), taking into account material flow and stress on the material. The flow behaviour is described in constitutive equations with respect to temperature and forming speed. The effect of the cyclic load on the material is examined. A description of the major development aims and application range in the process chain is intended.

Characterization of Intergranular Phases in Tetragonal and Cubic Yttria-Stabilized Zirconia

Abstract Achieving superplasticity in fine-grained ceramics is a potential method to lower energy costs associated with ceramic manufacturing via net shape forming. Superplasticity is intrinsic in 3-mol%- yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP), and can be enhanced by addition of glass to form intergranular phases which are thought to both limit grain growth and promote grain boundary sliding during processing (sintering and hot isostatic pressing). This permits processing at lower temperatures. However, superplasticity has not been observed in 8-mol%-yttria-stabilized cubic zirconia (8Y-CSZ), ostensibly due to its larger grain size and high grain growth rates.3,4 As part of a larger study, high-spatial-resolution energy-dispersive X-ray spectrometry (EDS) has been performed on 3Y-TZP and 8Y-CSZ specimens doped with various glassy phases to characterize intergranular compositions. Zirconia powders were mixed with glass to produce specimens having either 1 wt % lithiumaluminum- silicate, 1 wt % barium-silicate, or 1 wt % borosilicate. Some specimens were prepared without added glass.

Near net-shape forming of ceramics by absorbing dewax with fibrous absorbers

The possibility of absorbing dewax with fibrous absorbers (papers, cloths, etc.) is examined in order to make ceramic articles in near net-shape. In this new process, a low melting point wax: 75 wt.% paraffin wax, 25 wt.% microcrystalline wax and a small amount of additives, is used for a solvent. Chamotte powder is used as an example of a ceramic. The consolidated bodies containing the wax have plasticity at the proper temperature. After the wax content of the consolidated bodies has been reduced to the desired content by absorbing a part of the wax at a controlled temperature, the consolidated bodies are extruded into the desired shapes at the proper temperature. Secondary working processes such as forging can be used to make near net-shape articles. The extruded articles are further dewaxed by fibrous absorbers, followed by an evaporating dewax prior to sintering. Machining of the consolidated bodies at the proper residual wax content is also possible to make complex shaped articles. This method is successful for reducing the manufacturing cost of ceramic articles.

Near net shape forming of aluminium matrix composites by thermal plasma spray forming : F. Ajersch et al. J. of Metals, vol 48, no 6, 1996, 56–59

Near net shape forming of aluminium matrix composites by thermal plasma spray forming : F. Ajersch et al. J. of Metals, vol 48, no 6, 1996, 56–59

Semi-solid processing of novel MMCs based on hypereutectic aluminium-silicon alloys

This paper reports on the semi-solid processing (thixoforming) of spray-formed Al Si metal matrix composites (MMCs). In these novel MMCs, silicon—in quantities of up to 45 vol.%—was the reinforcing phase, rather than a ceramic. The project investigated all steps in the processing of the materials; mechanical tests on the products were carried out and demonstrator components were manufactured. It was shown that cylindrical billets of the MMCs could be formed in one step into intricate shapes at temperatures well below the liquidus. This confirmed that thixoforming is a safe, clean and practical method for the near net shape forming of components from materials that could be shaped only with difficulty by other techniques. The thixoformed MMCs exhibited very high specific stiffness, low thermal expansion, high specific strengths and high wear resistance.

Industrial scale spray forming of copper alloys : D. Stock, H.R. Müller (Wieland-Werke AG, Ulm, Germany)

This paper reports on the semi-solid processing (thixoforming) of spray-formed AlSi metal matrix composites (MMCs). In these novel MMCs, silicon—in quantities of up to 45 vol.%—was the reinforcing phase, rather than a ceramic. The project investigated all steps in the processing of the materials; mechanical tests on the products were carried out and demonstrator components were manufactured. It was shown that cylindrical billets of the MMCs could be formed in one step into intricate shapes at temperatures well below the liquidus. This confirmed that thixoforming is a safe, clean and practical method for the near net shape forming of components from materials that could be shaped only with difficulty by other techniques. The thixoformed MMCs exhibited very high specific stiffness, low thermal expansion, high specific strengths and high wear resistance.

Dislocation creep controlled superplasticity in the high carbon steel 140NiCr16-6

superplasticity in the alloyed high carbon-steel 140NiCr16-6 with phosphorus additions and a fine grained microduplex structure-containing cementite in volume fractions of 22 % (Fe,Cr,Ni) 3 C, particle size of about 1 μm and with a medium ferrite grain size of about 2 μm - has been investigated in the temperature regime of 550 to 675°C and in the strain rate range of 10 -5 to 5.10 -2 s -1 . Maximum strain rate exponents of m = 0.45 at 675°C with strain rates of the order of 10 4 s -1 have been determined. Maximum superplastic elongations of about 700 % were detected. At higher strain rates of 10 3 s -1 superplastic elongations of about 570 % were achieved. At relatively low test temperatures of 550°C elongations up to 230 % were recorded. The activation analysis in the temperature regime of 550 to 650°C show an activation energy for superplastic flow of 250 ± 20 kJ/mol. This is in agreement with the activation energy for lattice self diffusion of iron in α-iron. Above 650°C the activation energy decreases to 70 kJ/mol. This is due to a stress induced decrease in the eutectoid o-'/-transformation temperature from 685°C to somewhat lower temperatures during superplastic deformation. The superplastic deformability (m > 0.3) of this steel in a wide strain rate range at relatively low temperatures above 550°C allows near net shape forming of complex parts applying low flow stresses.

Near net shape forming of titanium by metal injection moulding : A. Smolders, R. Gilissen, (VITO Structural Materials, Mol, Belgium)

Near net shape forming of titanium by metal injection moulding : A. Smolders, R. Gilissen, (VITO Structural Materials, Mol, Belgium)

A new method for net-shape forming of large, single-domain YBa 2Cu 3O 6 + x

A new process has been developed for the net-shape fabrication of bulk, single-domain YBa 2Cu 3O 6 + x (123) specimens. To date, transport critical currents in excess of 10 000 A cm −2 have been obtained. This process, designated the seeded preform (SPF) technique, involves the permeation of peritectic liquid through a preform of pressed Y 2BaCuO 5 (211) powder. The use of a single-crystal seed of Nd 1 + x Ba 2 − x Cu 3O y ensures that only a single 123 domain is nucleated during the subsequent transformation: liquid + 211 → 123. The SPF process enjoys several important advantages over the melt-texturing techniques which are currently available. In particular, it offers the potential of net-shape forming of bulk 123 samples with complex geometries, and circumvents problems such as sagging, and substrate reaction. Also unique to the SPF process is that it produces large, single domain 123, with essentially no encapsulated liquid phase. Finally, relative to conventional melt-texturing, there is a refinement of the size of the 211 inclusions in the final microstructure, and the particles are more uniformly distributed.

Selective Doping of 3Y-TZP with CuO for Near Net Shape Forming

Selective Doping of 3Y-TZP with CuO for Near Net Shape Forming

Near net shape forming of particulate reinforced al-alloys by isothermal forming compared to semi solid forming

Particulate reinforced aluminium alloys produced by powder metallurgy are relatively expensive and difficult to shape by cutting or milling. Therefore near net shape forming of complex shapes is of high economic and technical interest. However, the formability of these MMC's under conventional forming conditions is limited. The potential of isothermal forging under various conditions as well as semi solid forming has been evaluated as a method for component production. Initially the suitable processing window and the flow stress of the material have been determined by isothermal compression tests at various temperatures and strain rates. Furtheron in a number of forming trials an end fitting has been produced by both routes, isothermal as well as semi solid forming.

Numerical analysis and design of industrial superplastic forming

In the aerospace industry, the production of structural shell components with a prescribed thickness distribution by superplastic forming requires the specification of the initial thickness profile in the undeformed sheet. To this purpose, a finite element simulation methodology developed previously for the analysis of superplastic deformation processes a long with the optimum monitoring of the forming pressure is extended to the determination of the initial thickness profile. The utilization of the procedure is shown for the pre-contouring of the blank for the industrial production of a satellite tank. The examination of the produced part confirms that the requested thickness distribution is achieved fairly well and thus proves the appropriateness of the proposed computational approach as a tool for the process design in superplastic net-shape forming

Model based process design and control for net shape forming of PM products : C.J. Coe et al. (BDM International Inc., Arlington, Virginia, USA.)

Model based process design and control for net shape forming of PM products : C.J. Coe et al. (BDM International Inc., Arlington, Virginia, USA.)

Towards net-shape forming

Net-shape forming or forming a part ready, at least partially, to be ground or assembled is presented as the key technology in the metal-working field to meeting the growing economical, technical and human needs of all industrial nations. It is analysed in this paper by showing examples of how imprecision in the quality of the formed part is effected by what elements or sources, such as the geometrical, mechanical or chemical properties of the stock material, billet or blank, the lubricant, the tool and machine, the design of the as-formed product, the plan and practice of the operational sequence including the ejection of the product from the tool, finish machining and heat treatment. Different types of occurrence of impreciseness are mentioned briefly in relation to the kind of these elements and sources. The means of attaining the net-shape product are then described for each element mentioned above, by showing practical examples. Because of the critical nature of net-shape forming technology, the necessity is stressed of optimization (based on the advanced science and technology of each item of hardware and software and of each operation which constitutes the total manufacturing system to be attended to) by a workforce that is conscious of quality control, in the attaining of the required properties and function of the product at minimum total manufacturing cost.

Nanocrystalline ceramics: Possible candidates for net-shape forming

It is shown that compacts of nanocrystalline ( n-)TiO 2− x powder can be formed at temperatures below 900°C. This processing yields, in one step, a final ceramic product with a desired shape. The n-compacts and dense ceramics are characterized by X-ray diffraction, BET- and density measurements as well as by scanning electron microscopy. The fracture toughness of n-ceramics is found to be increased by a factor of 2 in comparison to conventional polycrystalline ceramics.