On the effect of TiC particles on the tensile properties and on the intrinsic two way effect of NiTi shape memory alloys produced by powder metallurgy

Johansen, Kerstin; Voggenreiter, Heinz; Eggeler, Gunther

doi:10.1016/s0921-5093(99)00308-1

Cited by 34 publications

(17 citation statements)

References 7 publications

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“…Tensile test results obtained on materials from the same ingots and reported in Refs. [9,10] are reproduced in Fig. 4.…”

Section: Resultsmentioning

confidence: 91%

“…The NiTi-TiC system's thermal transformation behavior [3,4], bulk mechanical properties in compression [5], and subsequent shape-memory recovery [6], and the study by neutron diffraction of twinning deformation and shape-memory recovery have been investigated [7,8]. More recently, their behavior in tension and two-way shape-memory response (wherein the transformation to martensite on cooling is biased) have been studied [9,10]. These studies show that the TiC reinforcements can be successfully utilized to tailor the mechanical properties of NiTi in a cost-effective manner.…”

Section: Introductionmentioning

confidence: 99%

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Fatigue crack-growth in shape-memory NiTi and NiTi–TiC composites

Vaidyanathan

Dunand

Ramamurty

2000

Materials Science and Engineering: A

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“…Tensile test results obtained on materials from the same ingots and reported in Refs. [9,10] are reproduced in Fig. 4.…”

Section: Resultsmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Fatigue crack-growth in shape-memory NiTi and NiTi–TiC composites

Vaidyanathan

Dunand

Ramamurty

2000

Materials Science and Engineering: A

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“…Recent attention has been given to HIP due to the achievement of near theoretical densities [10,13] and to MIM for its promising attribute of near net-shape production. [10,13,16] Although the work done by Johansen et al [9] showed promising results, demonstrating tensile strains larger than 10 % for HIPed NiTi, the majority of the remaining studies demonstrate lower fracture strains under tensile loading (0.6 %±5.1 % [10,13,16] ). The study by McNeese et al [15] revealed HIPed NiTi with recoverable tensile strains of up to 2 % and recoverable compressive strains of 4.5 %.…”

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confidence: 99%

Cast NiTi Shape‐Memory Alloys

et al. 2005

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Shape-memory alloys, such as nickel-titanium (NiTi), have the unique ability to recover an applied inelastic strain either through the removal of the applied stress (pseudoelasticity) or the application of heat (shape-memory). This capacity has made NiTi a desirable material for many applications including MEMS, [1] biomedical devices, [2,3] and civil infrastructure. [4±6] One of the first mainstream uses of NiTi was in orthodontics, in which drawn NiTi wires were used as arc wires to apply a constant force to a patient's teeth. [2,3] To date, nearly all applications of NiTi employ a deformation processed and machined material. However, due to NiTi's poor workability, especially at higher Ni content, [7] and machinability, [8] fabrication of NiTi is expensive. High cost can make the selection of NiTi an unreasonable choice for many promising applications. Although direct casting could eliminate these costly steps, little work has been done to examine the structure and properties of NiTi in its cast state, limiting the possibility of its use in potential applications.The desire for a method of near net-shape production of NiTi parts has motivated the research of powder metallurgy as a fabrication technique. [9,10] Several methods, including self propagating high temperature synthesis (SHS), [11,12] Hot Isostatic Pressing (HIP), [9,10,13±16] and Metal Injection Molding (MIM) [10,16] are being considered for the production of shapememory materials. Recent attention has been given to HIP due to the achievement of near theoretical densities [10,13] and to MIM for its promising attribute of near net-shape production. [10,13,16] Although the work done by Johansen et al. [9] showed promising results, demonstrating tensile strains larger than 10 % for HIPed NiTi, the majority of the remaining studies demonstrate lower fracture strains under tensile loading (0.6 %±5.1 % [10,13,16] ). The study by McNeese et al. [15] revealed HIPed NiTi with recoverable tensile strains of up to 2 % and recoverable compressive strains of 4.5 %. However, despite progress being made in powder metallurgy, the search for an ideal method for net-shape processing of NiTi that would maintain its unique shape-memory properties is still underway. This was the driving motivation of this study, which aims to correlate processing, structure, and properties of cast NiTi. The link between structure and properties of cast NiTi builds a foundation for the design of net-shape NiTi castings.In general, net-shape casting is a good method for producing parts with complex geometries and is one of the simplest and most direct ways to fabricate a metal component. [17] Typical problems that can arise with a cast material include compositional segregation, porosity, inclusions (oxides, sulfides and nitrides), and shrinkage. [18±21] The solidification of a metal is a thermodynamically driven process that is dependent on such things as initial compositions, temperature, and pressure. [22] For cast alloys, thermodynamics drives the solidification path and co...

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“…[17] The mixture of the powders with strengthening particles is possible, also the preparation of structures with graded compositions, e.g., for cell culture tests. [18,19] For elemental powder mixtures HIPing is not often described in the literature. McNeese et al [20] show that almost homogeneous microstructures can be obtained with respect to the occurrence of undesired NiTi 2 precipitates.…”

mentioning

confidence: 99%

“…Five capsules were prepared using HIP parameters at 1065 C for 3 h at a pressure of 100 MPa according to reference. [18] After the HIP process, the capsules were mechanically removed. Investigation of phase transformation temperatures by differential scanning calorimetry (DSC) and determination of impurity levels of oxygen, nitrogen and carbon was performed on chips machined from the compacts.…”

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confidence: 99%

Hot Isostatic Pressing (HIP) of Elemental Powder Mixtures and Prealloyed Powder for NiTi Shape Memory Parts

et al. 2003

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we used. If one phase would stay or become disconnected, one would either obtain a loose powder or the etching process would stop after the particles connected to the specimen surface have been leeched out.A section through the nanoporous metal is also shown in Figure 2d. It demonstrates that the porosity is not confined to the surface but penetrates the entire specimen thickness. This result suggests, but does not prove gas permeability. Thus, gas permeability tests using hydrogen were also performed. The set up consists of a vacuum tight holder with inlet and outlet, a vacuum pump, a gas supply and a gas chromatograph. The nanoporous sheets, approximately 6 mm 20 mm wide and 0.1 mm to 0.25 mm thick, were placed in the holder. The whole system was evacuated prior to testing to a pressure of less than 1 Pa. Constant hydrogen pressure was then applied on one side of the porous membrane for 300 seconds and the permeated gas was collected at the other side. The pressure on the inlet side was varied between 20 Pa and 102 kPa. The volume of the recipient was selected such, that the pressure increase at the outlet side was always less than a tenth of the inlet pressure. In other words, the pressure difference was essentially equal to the applied pressure at the inlet. The permeated gas content was then measured by the gas chromatograph.The test results are shown in Figure 3, whereby the flow rate is related to standard conditions. They confirm gas permeability of the nanoporous material and a linear relation between pressure drop and flow rate. At Dp = 102 kPa a column of hydrogen gas, approximately 1 mm high, permeates through a given filter area per second. It should be noted that no attempts to degas the filters prior to testing were made so far. Probably this will further improve permeability as some of the aqueous electrolyte is likely to remain in the porous structure due to capillary forces. Furthermore, it is anticipated that the permeability can be widely varied, as volume fraction and size of the open channels can be influenced by chemical composition of the alloy and processing conditions. We anticipate use of the new nanoporous Ni-alloys in such diverse fields of application as medicine, mechanical engineering and chemical engineering. Filtration of bacteria is one example, where the ability to sterilize the microorganisms by resistance heating of the metallic filter is an added advantage not amenable to ceramic filters or polymer membranes. Solid oxide fuel cells are another example, where nanoporous metals exhibiting gas permeability would be highly beneficial as they would enable thin film deposition of the electrode and membrane materials, thus reducing the electrical resistance of the cell. Nanoporous metals could also aid the development of miniaturized low temperature fuel cells, believed to power laptops and cellular phones in the future, [6] as further miniaturization of the fuel processing system, requiring micro heat exchangers and reactors, becomes possible. This is just a small selection of po...

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On the effect of TiC particles on the tensile properties and on the intrinsic two way effect of NiTi shape memory alloys produced by powder metallurgy

Cited by 34 publications

References 7 publications

Fatigue crack-growth in shape-memory NiTi and NiTi–TiC composites

Fatigue crack-growth in shape-memory NiTi and NiTi–TiC composites

Cast NiTi Shape‐Memory Alloys

Hot Isostatic Pressing (HIP) of Elemental Powder Mixtures and Prealloyed Powder for NiTi Shape Memory Parts

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