Stress-strain behavior and shape memory effect in powder metallurgy TiNi alloys

Kato, Hiroyuki; Koyari, T.; Tokizane, Masaharu; Miura, S.

doi:10.1016/0956-7151(94)90152-x

Cited by 28 publications

(13 citation statements)

References 17 publications

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“…Even if low fracture strain suggests brittle failure modes, the fracture surface shows amounts of ductile fracture. Mixed brittle and ductile fracture modes were also found by Kato [17] where the first mode is described as a result of oxides on the particle boundaries.…”

mentioning

confidence: 71%

“…[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.…”

mentioning

confidence: 99%

“…3.1 % with a fracture strain of 2.2 % before the end of the pseudoplastic plateau was reached and elastic deformation of stress-induced martensite starts. It is well known from the literature, [17,25] stress plateau level will increase. Crack formation at the oxide phases is expected to cause the failure which will be investigated in subsequent studies.…”

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confidence: 99%

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

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“…Using sufficient temperatures and pressures, a densification to more than 98 % of the theoretical density is observed. The semi-finished parts can be machined like cast alloys (turning, spark erosion) [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Porous Metal Sheets of NiTi made by Wet Powder Spraying

Schüller

Krone²,

Bram

et al. 2004

Materialwissenschaft Werkst

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As a promising method to produce thin porous NiTi sheets, Wet Powder Spraying (WPS) is applied for NiTi powders. Layers with a thickness of 150 lm are obtained from pre-alloyed NiTi powders with a particle size of < 12 lm. Optimized process control for spraying and sintering was used. Microstructure and phase formation is characterized. The sheets with a porosity of 15 % show a high pseudoelastic flexibility at room temperature.

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“…The critical stress corresponding to the horizontal yield plateau (due to rearrangement of the orientation of martensitic variants) increases with the As temperature (except for Pl). This can be related to the mobility of the martensite-martensite interfaces which is assumed to be enhanced for temperatures close to the martensite => austenite transformation temperature range [8] [9]. Moreover, the total elongation to failure is greater for PM products (elongations of over 45%).…”

Section: Thermomechanical Propertiesmentioning

confidence: 99%

Microstructure and Thermomechanical Properties of Shape Memory Alloys TI₅₀-NI₅₀ Elaborated by Arc Melting and by Powder Metallurgy

Olier¹,

Brachet²,

Guénin

1995

J. Phys. IV France

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-This study was focussed on the elaboration and transformation of Ti50Ni50 shape memory alloys in relation to structural and thermomechanical properties. An original method for producing TiNi alloys by powder metallurgy (PM), through combustion synthesis, was developed. After hot extrusion, intermetallic rods without porosity were obtained. Microstructural and thermomechanical properties of products obtained by this method were systematically compared to those of some alloys elaborated by the more conventionnal method of arc melting (AM). For comparison, cast products were hot rolled at different temperatures; for all the transformation conditions used, the grain size remained coarser and more heterogeneous compared to PM products. Investigation of the thermomechanical behaviour was conducted by tensile and flexion tests. It was found that : -The ultimate tensile strength and the recovery stress were in the same range for PM and AM products but the ductility of P M products was enhanced.-The better one way shape memory recovery is obtained for a PM product with an oxygen content of about I200ppm. Also, too low content of oxygen (~600ppm) seems to decrease the stress and strain recovery during thermomechanical cycling.

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Stress-strain behavior and shape memory effect in powder metallurgy TiNi alloys

Cited by 28 publications

References 17 publications

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

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

Porous Metal Sheets of NiTi made by Wet Powder Spraying

Microstructure and Thermomechanical Properties of Shape Memory Alloys TI₅₀-NI₅₀ Elaborated by Arc Melting and by Powder Metallurgy

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Stress-strain behavior and shape memory effect in powder metallurgy TiNi alloys

Cited by 28 publications

References 17 publications

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

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

Porous Metal Sheets of NiTi made by Wet Powder Spraying

Microstructure and Thermomechanical Properties of Shape Memory Alloys TI50-NI50 Elaborated by Arc Melting and by Powder Metallurgy

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Product

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Microstructure and Thermomechanical Properties of Shape Memory Alloys TI₅₀-NI₅₀ Elaborated by Arc Melting and by Powder Metallurgy