The invar problem

Nakamura, Yoji

doi:10.1109/tmag.1976.1059049

Cited by 163 publications

(44 citation statements)

References 76 publications

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“…Ϫ6 K Ϫ1 over a temperature range of 100 to 500 K but shows a dramatic increase from about 600 K. The cold-worked alloy exhibits the Invar property over a wider temperature range than do conventional Invar alloys (7)(8)(9). A similar abnormality in thermal expansion behavior by cold working of shape memory alloys has recently been reported by Kainuma et al (10).…”

Section: ϫ 10supporting

confidence: 70%

Multifunctional Alloys Obtained via a Dislocation-Free Plastic Deformation Mechanism

Saito

Furuta

Hwang

et al. 2003

Science

836

357

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We describe a group of alloys that exhibit "super" properties, such as ultralow elastic modulus, ultrahigh strength, super elasticity, and super plasticity, at room temperature and that show Elinvar and Invar behavior. These "super" properties are attributable to a dislocation-free plastic deformation mechanism. In cold-worked alloys, this mechanism forms elastic strain fields of hierarchical structure that range in size from the nanometer scale to several tens of micrometers. The resultant elastic strain energy leads to a number of enhanced material properties.Mechanical properties, such as strength, of metallic materials are strongly affected by metallurgical processes such as heat treatment and plastic working, which bring modifications in the microstructure. On the other hand, these processes have no substantial effect on physical properties such as elastic modulus and thermal expansion. The reason for this is that the changes that can be affected by plastic working and heat treatment do not extend to interatomic bonds or electronic states.We present a group of alloys that exhibit multiple "super" properties and drastic changes in physical properties after plastic working at room temperature. These alloys simultaneously offer super elasticity, super strength, super coldworkability, and Invar and Elinvar properties. The alloys consist of Group IVa and Va elements and oxygen and share the following three electronic magic numbers: (i) a compositional average valence electron number [electron/atom (e/a) ratio] of about 4.24; (ii) a bond order (Bo value) of about 2.87 based on the DV-X␣ cluster method, which represents the bonding strength (1-3); and (iii) a "d" electron-orbital energy level (Md value) of about 2.45 eV, representing electronegativity. The properties emerge only when all three of these magic numbers are satisfied simultaneously. Various alloy composition combinations meet these criteria, such as Ti-12Ta-9Nb-3V-6Zr-O and Ti23Nb-0.7Ta-2Zr-O [mole percent (mol %)], wherein each alloy has a simple body-centered cubic (bcc) crystal structure. In order to exhibit these properties, each alloy system requires substantial cold working and the presence of a certain amount of oxygen, restricted to an oxygen concentration of 0.7 to 3.0 mol %.Typical properties of the alloys are shown in Fig. 1 for samples before and after cold swaging with 90% reduction in area (4). Tensile stress-strain curves shown in Fig. 1A indicate that cold working substantially decreases the elastic modulus and increases the yield strength and confirm nonlinearity in the elastic range, with the gradient of each curve decreasing continuously to about 1/3 its original value near the elastic limit. As a result of this decrease in elastic modulus and nonlinearity, elastic deformability after cold working reaches 2.5%, which is at least double the value before cold working. Generally, large elastic deformations that occur in so-called "super-elastic alloys" are known to be reversible martensitic transformations resulting from deformation, d...

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Section: ϫ 10supporting

confidence: 70%

Multifunctional Alloys Obtained via a Dislocation-Free Plastic Deformation Mechanism

Saito

Furuta

Hwang

et al. 2003

Science

836

357

View full text Add to dashboard Cite

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“…A lower concentration of magnetostrictive phase in the polycrystalline alloy is also expected since the highest magnetostriction is usually found on the fcc side of the phase diagram. 32 In fact, the magnetostriction coefficient of the polycrystalline alloy was lower (20 ppm) than the measured in the amorphous alloy (30 ppm) (see Fig. 2).…”

Section: B Macroscopic Magnetostriction In Polycrystalline Fecobmentioning

confidence: 71%

“…When passing from the crystalline to the amorphous state with increasing boron, only an fcc-like local structure is retained, confirming previous observations 22 on similar alloys. This is a common behavior in Invar and magnetostrictive alloys, 32 FeCo included and might indicate that such a transformation originates an intermediate metastable phase with magnetostrictive properties.…”

Section: Introductionmentioning

confidence: 77%

Determination of the magnetostrictive atomic environments in FeCoB alloys

et al. 2012

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The atomic environments of Fe and Co involved in the magnetostriction effect in FeCoB alloys have been identified by differential extended x-ray fine structure (DiffEXAFS) spectroscopy. The study, done in amorphous and polycrystalline FeCoB films, demonstrates that the alloys are heterogeneous and that boron plays a crucial role in the origin of their magnetostrictive properties. The analysis of DiffEXAFS in the polycrystalline and amorphous alloys indicates that boron activates magnetostriction when entering as an impurity into octahedral interstitial sites of the Fe bcc lattice, causing its tetragonal distortion. Magnetostriction would be explained then by the relative change in volume when the tetragonal axis of the site is reoriented under an externally applied magnetic field. The experiment demonstrates the extreme sensitivity of DiffEXAFS to characterize magnetostrictive environments that are undetectable in their related EXAFS spectra.

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“…3,[6][7][8] On the other hand, the origin of the Invar effect, whereby these materials exhibit a low or near zero thermal expansion ͑LTE͒ coefficients below the magnetic ordering temperature has remained an issue of controversial debate for a long time. [9][10][11][12][13][14][15] A microscopic explanation of the Invar effect in iron-nickel alloys has been given considering that the magnetic structure is characterized by a continuous transition from the ferromagnetic state at high volumes to a disordered noncollinear arrangement at low volumes. 10 In simple words, there must be a negative contribution to the thermal expansion, which is related to the magnetic ordering, and which cancels out the ever-present positive contribution coming from the anharmonicity of the lattice vibrations.…”

Section: Introductionmentioning

confidence: 99%

“…3,16 Therefore, this effective temperature invariant thermal expansion can be exploited in a number of technological applications such as precision measurements for standards, large size cryogenic liquid containers, etc. 15,17 Furthermore, the Invar effect is not limited to being a property of only Fe-Ni alloys, but it is also found in many other crystalline three dimensional ͑3D͒ systems such as Fe-Pt, Pd 3 Fe, Fe 3 C, or Fe-Cu, [18][19][20][21][22] amorphous Fe alloys, [23][24][25] as well as intermetallic systems such as R-Fe ͑R = Rare Earth͒. 26,27 Hence, these alloys can be structurally ordered or disordered, ferromagnetic or antiferromagnetic.…”

Section: Introductionmentioning

confidence: 99%

Stress-induced large Curie temperature enhancement inFe64Ni36Invar alloy

et al. 2009

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We have succeeded in increasing up to 150 K the Curie temperature in the Fe 64 Ni 36 invar alloy by means of a severe mechanical treatment followed by a heating up to 1073 K. The invar behavior is still present as revealed by the combination of magnetic measurements with neutron and x-ray techniques under extreme conditions, such as high temperature and high pressure. The proposed explanation is based in a selective induced microstrain around the Fe atoms, which causes a slight increase in the Fe-Fe interatomic distances, thus reinforcing ferromagnetic interactions due to the strong magnetoelastic coupling in these invar compounds.

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The invar problem

Cited by 163 publications

References 76 publications

Multifunctional Alloys Obtained via a Dislocation-Free Plastic Deformation Mechanism

Multifunctional Alloys Obtained via a Dislocation-Free Plastic Deformation Mechanism

Determination of the magnetostrictive atomic environments in FeCoB alloys

Stress-induced large Curie temperature enhancement inFe64Ni36Invar alloy

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