Search

This study presents the experimental results of structural analysis of the phase composition, grain size, plasticity, and hardness of the elinvar Ni-span-C alloy 902 after various heat treatment modes (quenching and quenching with subsequent aging). A thermal treatment mode has been selected to obtain higher physical and mechanical properties of the elinvar alloy. It is shown that the improvement of the alloy structure under thermal treatment occurs due to the thermal stresses, as well as the formation and dissolution of intermetallides.

We tailor the temperature dependence of elastic modulus (TDEM) of polycrystalline NiTi plates by cold rolling up to 60% thickness reduction. In-plane Elinvar property is obtained with a low elastic modulus temperature coefficient of 6.0 × 10−5 K−1 over a temperature range of 192 K. The microstructure mainly consists of approximately equal volume fractions of {111} -oriented B2 and {102} -oriented B19′ nanocrystals of high thermal stability due to defect pinning and grain refinement. The opposite TDEMs of the two phases can compensate each other and cause the Elinvar behavior. Such mechanism can also be used to obtain Elinvar property for other shape memory alloys.

As a new ferroelastic state, strain glass, has attracted a lot of recent attentions and, most importantly, strain glass transitions (SGTs) could underpin many phenomena that have puzzled the physics community for decades, including the quasi-linear superelasticity and Invar and Elinvar anomalies. However, there has been a lack of fundamental understanding at the atomistic level beyond the phenomenological Landau theory. In this paper, we propose a way to obtain quantitatively the continuous strain/stress fields distribution caused by doped point defects through molecular statics calculations by incorporating a Gaussian probability distribution function. By using the quantitative strain/stress fields distribution to inform phase field simulations, we reproduce quantitatively the experimentally observed critical defect concentrations separating the normal martensitic phase transition from strain glass transition at different temperatures and critical temperatures for spontaneous strain glass to martensitic transition at different defect concentrations. Based on percolation theory, we demonstrate how the strain network created by point defects with a critical concentration regulates nucleation and growth of martensitic domains, suppresses autocatalysis by strain frustration, and changes the sharp first-order martensitic transformation into a continuous SGT. A general temperature- and defect-concentration-dependent percolation criterion is formulated for accurate prediction of SGT, which could enable high throughput computations for systematic search of new strain glass systems using simply molecular static calculations.

The structure and phase composition of biocompatible titanium alloys of composition (wt %) Ti–10Zr–1.2Nb–1.5Al, Ti–6Al–4V (ELI), Ti–15Mo, and Ti–36.1Nb–3.8Zr–2.4Ta–1.9Sn have been studied in a hot-deformed state using scanning electron microscopy and X-ray diffraction analysis. The analysis of mechanical tensile properties has been performed depending on the structure and the aluminum strength equivalent of the alloys. The elasticity moduli of the alloys have been determined using tensile tests, dynamic mechanical analysis, and microindentation; the comparability of values within the error of 3–7% has been established. The nonmonotonic character of the change of the elasticity modulus upon heating to 550°C is explained in terms of the occurrence of processes of stress relaxation and recovery in the Ti–10Zr–1.2Nb–1.5Al, and Ti–6Al–4V ELI alloys and based on the precipitation of the high-modulus ω phase in the Ti–15Mo alloy. For the Ti–36.1Nb–3.8Zr–2.4Ta–1.9Sn alloy, the realization of the elinvar effect has been demonstrated. A correlation of the rate of change in the elasticity modulus with the heating temperature and the ratio of α and β phases in the structure of the alloys has been established.

The unprecedented properties of multi-functional metastable β-Ti alloys, including superelasticity over a wide temperature range, ultra-low modulus, and Invar and Elinvar anomalies, have attracted a great deal of attention. Persistent research efforts have been made towards the understanding of the origins of these unique properties. In this article we report a novel shuffle-nanodomain regulated strain glass transition in a metastable β-Ti alloy, Ti-24Nb-4Zr-8Sn (wt.%, Ti2448), which could be the dominant transformation pathway that offers these unique properties. Using the ex-situ aberration-corrected scanning transmission electron microscopy and in-situ cooling transmission electron microscopy, we find that randomly distributed {011} 〈 0 1 ¯ 1 〉 β O′ phase (orthorhombic, shuffle only) nanodomains embedded in the β phase (BCC) matrix at room temperature transform to α″ phase (orthorhombic) with a continuous increase in the amount of {2 1 ¯ 1 } 〈 1 ¯ 1 ¯ 1 〉 β shear upon cooling or loading. Crystallographic analysis shows that the shuffle of the O′ phase will restrain the twelve possible shears that transform a BCC lattice to α″ martensite to only two. Thus, the randomly distributed O′ nanodomains prevent the formation of long-range-ordered, self-accommodating transformation-strain domain patterns seen in normal martensitic transformations and suppress completely the sharp first-order, auto-catalytic and avalanche-like martensitic transformation into a high-order-like (continuous) strain glass transition. Such a continuous β → O′ → α″ strain glass transition has been confirmed by dynamic mechanical analysis, resistivity and differential scanning calorimetric measurement. This unique transition pathway allows us to offer new insights into the unique properties found in this alloy.

Strain glass, a conjugate state to martensite, is emerging as an important concept in our understanding of martensitic materials. It resolves many puzzling phenomena, and potentially provides a mechanism for novel properties that are absent in conventional martensitic alloys. This article reviews the progress of strain glass research from its fundamental characterization to the interesting properties to which it leads. We first give a brief introduction of the origin and evidence of strain glass, showing nano-domains as the microscopic basis for understanding its properties. Then we demonstrate that the strain glass state can exhibit many unexpected properties such as a shape-memory effect, superelasticity with a narrow hysteresis over a wide temperature range, high damping and low modulus over a wide temperature, Invar and Elinvar effects, elastocaloric effects, and low-field-triggered large magnetostriction. Lastly, some remaining challenges and opportunities, as well as some ongoing works about the strain glass are discussed.

We discovered Elinvar effect in a severely cold worked Ti-50.8(at%)Ni thin belt that showed a modulus variation of less than 0.54GPa(∼1%) over a wide temperature range (−50 to 100 °C). Microstructural analysis showed an unraveled amorphous matrix dotted with nanosized crystallites, which demonstrated that the softening of the nanodomains in the retained nanosized crystallites and hardening of the amorphous matrix during cooling over wide temperature range can trigger the Elinvar effect.

The temperature-dependent elasticity of the B19′ NiTi is unknown today. To gain insights into the lattice-level temperature-dependent elasticity of the B19′ crystal, we present results of in-situ neutron diffraction experiments performed on polycrystalline martensitic specimens in the temperature range of 300 down to 50 K. The experimental results are compared with the density functional theory molecular dynamics (DFT-MD) and Quasi Harmonic Approximation (QHA) calculations. The results confirm that the temperature-dependent Young's modulus (TDYM) of the B19′ crystal is strongly anisotropic. For different crystallographic orientations, the change in Young's modulus over the temperature range of 300–50 K ( Δ E ( h k l ) = E ( h k l ) 50 K − E ( h k l ) 300 K ), ranges from Δ E ( 10 2 ¯ ) = 2.8 ± 3.5 GPa (extremely weak dependence) to Δ E ( 103 ) = 59.6 ± 9.1 GPa (strong dependence). Moreover, it is found that the orientation-specific TDYM and thermal expansion (TE) of the B19′ crystal are correlated. The crystallographic orientations with weak and negative TE responses exhibit a weaker TDYM than the orientations with positive TE. The DFT-MD and QHA results capture qualitatively the above experimental observations and further show that there are orientations in a B19′ crystal exhibiting elastic softening ( Δ E ( h k l ) Δ E ( h k l ) = 0) with cooling. This is found to originate from the strong negative temperature dependence of c35 stiffness constant. The experimental results along with the first-principles calculations confirm that the Elinvar and Invar are two confluent properties in NiTi SMAs and can be tailored by texturing B19′ crystallographic orientations.

Fe-Ni based Elinvar alloys performing temperature-independent elastic modulus over a wide temperature range have found wide and significant applications. Although numerous models involved with magnetism have been proposed to explain the Elinvar anomaly, some of the puzzles concerning the anomaly have not been fully understood. In this work, a remarkable discrepancy between the inflection temperature of modulus and the Curie temperature in a typical Fe-Ni-Cr Elinvar alloy was found, challenging the magnetic mechanism for Elinvar anomaly. Microstructural characterization and dynamic mechanical analysis demonstrate the occurrence of a strain glass transition with continuous formation of nanodomains. Accompanying such a transition, the gradual softening in the elastic modulus of austenite offsets the modulus hardening due to the vibrational anharmonicity of nanodomains upon cooling, leading to the Elinvar effect. As a result, the inflection temperature of modulus corresponds to the initiation of nanodomains’ formation instead of magnetic transition. Our findings specify the association of Elinvar anomaly with structural aspects, and provide new insights into the mechanism of Elinvar anomaly in Fe-Ni based alloy.

Intensive microstructural characterizations were conducted on the γ′ precipitates in Ni-Span C, a typical precipitation hardened Fe-Ni-Cr based Elinvar alloy. The impact of precipitates on the physical and mechanical properties of the alloy was investigated. The results indicate that the aging generated nano-sized γ′ precipitates are coherent and coplanar with the matrix, and prolonging aging time leads to the increase in mismatch between γ′ and parent phase. It was found that the γ′ precipitates play key roles in promoting Elinvar behavior, reducing paramagnetic-ferromagnetic transition temperature and reinforcing the alloy.

An active learning approach to train machine-learning interatomic potentials (moment tensor potentials) for multicomponent alloys to ab initio data is presented. Employing this approach, the disordered body-centered cubic (bcc) TiZrHfTax system with varying Ta concentration is investigated via molecular dynamics simulations. Our results show a strong interplay between elastic properties and the structural ω phase stability, strongly affecting the mechanical properties. Based on these insights we systematically screen composition space for regimes where elastic constants show little or no temperature dependence (elinvar effect).

Background The atomizers of electronic cigarettes (ECs) contain metals that transfer to the aerosol upon heating and may present health hazards. This study analyzed 4th-generation EC pod atomizer design features and characterized their elemental/metal composition. Methods Eleven EC pods from six brands/manufacturers were purchased at local shops and online. Pods were dissected and imaged using a Canon EOS Rebel SL2 camera. Elemental analysis and mapping of atomizer components was done using a scanning electron microscope coupled with an energy dispersive x-ray spectrometer. Results EC pods varied in size and design. The internal atomizer components were similar across brands except for variations occurring mainly in the wicks and filaments of some products. The filaments were either Elinvar (nickel, iron, and chromium) (36.4%), nichrome (36.4%), iron-chromium (18.2%), or nickel (9%). Thick wires present in 55% of the atomizers were mainly nickel and were joined to filaments by brazing. Wire-connector joints were Elinvar. Metal air tubes were made of Elinvar (50%), nickel, zinc, copper, and tin (37.5%), and nickel and copper (12.5%). Most of the wick components were silica, except for two pods (PHIX and Mico), which were mainly ceramic. Connectors contained gold-plated nickel, iron-chromium multiple alloys of nickel, zinc, gold, iron, and copper. Wick chambers were made of Elinvar. Outer casings were either nickel, copper-tin, or nickel-copper alloys. Magnets were nickel with minor iron, copper, and sulfur. Some frequently occurring elements were high in relative abundance in atomizer components. Conclusions The atomizers of pods are similar to previous generations, with the introduction of ceramic wicks and magnets in the newer generations. The elements in EC atomizers may transfer into aerosols and adversely affect health and accumulate in the environment.

The experimental results of structure analysis, such as phase composition, grain size, strength and hardness of elinvar Ni-SPAN-C alloy 902 after different modes of heat treatment (quenching and ageing for stress relaxation) are presented in this study. It is made possible to obtain improved physical and mechanical properties than those acquired by conventional heat treatment. Heat treatment mode was selected that allowed to obtaining higher physical and mechanical properties of elinvar alloy compared to standard technology. It was shown that the improvement of alloy structure during thermal treatment is due to thermal stresses, as well as formation and dissolution of intermetallides.

The conditions needed to design gum metal were reconsidered based on the equivalent β stabilizer content required to obtain compositional/microstructural variability in a Ti-24(Nb + Ta + V)-(Zr, Hf)-O system. It was found that 90% cold-worked Ti-23Nb-1Ta-2Hf-O alloy exhibits gum-metal-like superproperties such as ultrahigh strength, ultralow elastic modulus, superelasticity, superplasticity, and Elinvar behavior. These multi-functions can be achieved even with the deformation-induced ω phase if nanodomains and giant faults exist. This suggests that not only the three electronic magic numbers, but also the equivalent β stabilizer content should be considered to attain the superproperties.

Behaviors of displacive phase-transforming materials above the temperature of transformation, where abnormal thermal, elastic, magnetic properties are often observed, are mostly explained by intrinsic peculiarities in electronic/atomic structure. Here, we show these properties may also be attributed to extrinsic effects caused by a thermoelastic equilibrium in highly defected pretransitional materials. We demonstrate that the stress concentration near stress-generating defects such as dislocations and coherent precipitates could result in the stress-induced transformation within nanoscale regions, producing equilibrium embryos of the product phase. These nanoembryos in thermoelastic equilibrium could anhysteretically change their equilibrium size in response to changes in applied stress or magnetic fields leading to superelasticity or supermagnetostriction. Similar response to cooling may explain the observed diffuse phase transformation, changes in the coefficient of thermal expansion and effective elastic modulus, which, in turn, may explain the invar and elinvar behaviors. Defects that generate stress in a metallic atomic lattice can lead to phase transformations in nanoscale regions under external stimuli. Research led by Wei-Feng Rao at Nanjing University of Information Science and Technology in China used phase field microelasticity simulations to examine local stress around defects (such as dislocations and nanoprecipitates) in materials that undergo displacive martensitic transformations at a certain temperature. They found that stress fields around defects promoted the formation of stable nano-embryos of the product phase even above the transformation temperature. The size of the nano-embryos only depended on the strained lattice and not on temperature, enhancing their sensitivity to external changes in applied stress or magnetic field. The behavior of these nano-embryos can help better understand the superelastic effect in gum metals, supermagnetostriction in iron-based shape memory alloys, and the invar and elinvar effects.

In this work, two sets of selective laser melting (SLM) process parameters were used alternately to produce a layer-structured NiTi sample. The transformation behavior of the sample shows that austenite transforms gradually into martensite over a wide temperature range (~ 130 K) during cooling. A microstructure composed of alternating layers of austenite and martensite is observed at room temperature. The sample shows excellent damping performance and the Elinvar effect, which originates from the gradual formation of martensite. This work suggests that SLM could serve as an effective way to directly fabricate functionally graded materials.

A homogeneous fine-grained structure that provides required strength characteristics has been shown to form in the (44NKhTYu alloy) elinvar for the considered thermal processing mode. Experimental data are provided that demonstrate elasticity characteristics to remain constant within a temperature range from–70 to +70°С. The persistence of the propagation velocities of elastic waves in this temperature range makes it possible to use this regularity in the development of techniques for thermal-processing quality evaluation. The ratio of the velocities of longitudinal and shear elastic waves has been proposed as a “diagnostic parameter.” The possibility has been studied for using elastic waves to inspect 44NKhTYu-alloy characteristics after various thermal-processing modes.

Recent experimental and theoretical investigations suggested that doping sufficient point defects into a normal ferroelastic/martensitic alloy systems could lead to a frozen disordered state of local lattice strains (nanomartensite domains), thereby suppressing the long-range strain-ordering martensitic transition. In this study, we attempt to explore the possibility of developing novel ferrous Elinvar alloys by replacing nickel with carbon and manganese as dopant species. A nominal Fe89Ni5Mn4.6C1.4 alloy was prepared by argon arc melting, and XRD, DSC, DMA and TEM techniques were employed to characterize the strain glass transition signatures, such as invariance in average structure, frequency dispersion in dynamic mechanical properties (storage modulus and internal friction) and the formation of nanosized strain domains. It is indicated that doping of Ni, Mn and C suppresses γ→α long-range strain-ordering martensitic transformation in Fe89Ni5Mn4.6C1.4 alloy, generating randomly distributed nanosized domains by strain glass transition. Keywords: Strain glass transition, Elinvar alloys, Point defects, Nanosized domains

In this work, a metastable face-centered cubic High Entropy Alloy (HEA) Fe35.0Co28.7Ni24.8Cr1.1Al1.3V4.5Ti1.2Nb2.8Si0.6 was found to exhibit significantly suppressed thermal expansion coefficient (6.0 ppm/K) and stable Young's modulus over a wide temperature range. Experimental and theoretical analyses suggest that both Invar and Elinvar effects were present; in addition, the metastability of this alloy with respect to the first-order phase transition and the magnetic second-order phase transition led to abrupt changes in thermal expansion behavior. The first-order phase transition was associated with the formation of a plate-like D019 phase. The magnetic second-order phase transition decreased the Invar effect and the Elinvar effect and resulted in a significant magnetic entropy difference (−3.12 J kg−1 K−1) in this HEA of interest.

This work reports the existence of the strain glass state in Ni-rich Ni-Ti-Zr shape memory alloys induced by the precursor stages of the H-phase precipitation, typical of this alloy system. The strain glass is detected from dynamic mechanical testing and microstructural observations by electron diffraction and Transmission Electron Microscopy (TEM). The elastic modulus measurements also suggest the elinvar effect in these alloys. The strain glass state of this material exhibits superelastic effect in compression with recoverable strain levels over 4% and very little temperature dependence of the stress-strain curves over a temperature range of 230 to 300 K.

Ferromagnetic strain glass is a glassy phenomenon reported in the defects of doped Ni-Mn-Ga, Fe-Pd, and Fe-Ni-Cr ferromagnetic martensitic alloy systems recently. It is essentially a frozen state with coexisting short-range lattice strain order and long-range magnetic order. The basic structural unit of the ferromagnetic strain glass is the magnetic martensitic nanodomain. The reorientation energy barrier of these nanodomains is insignificant. They grow slowly across a wide temperature region in the parent phase matrix, and the modulus of the parent phase matrix and nanodomains shows an opposite temperature-dependent tendency. These transforming properties lead to the low-field-driven large magnetostriction and Elinvar effect. Therefore, ferromagnetic strain glass alloys have potentially important applications in microactuators or sensors and precision apparatuses. This paper introduces the macroscopic physical properties, microstructural characteristics, and functional effects of ferromagnetic strain glass. Through the phase diagram of the Ni- X -Mn-Ga ( X =Co, Fe) system, the formation of a ferromagnetic strain glass and its relationship with martensitic and premartensitic phases are clarified. Furthermore, the novel transformation behavior, i.e., the spontaneous martensitic transition of ferromagnetic strain glass in the phase boundary region between ferromagnetic martensite and ferromagnetic strain glass, is also introduced. The material design based on ferromagnetic strain glass is expected to bring new opportunities for the performance breakthrough and functionality development of magnetic materials.

A combination of quantum mechanics calculations with machine learning (ML) techniques can lead to a paradigm shift in our ability to predict materials properties from first principles. Here we show that on-the-fly training of an interatomic potential described through moment tensors provides the same accuracy as state-of-the-art {\it ab inito} molecular dynamics in predicting high-temperature elastic properties of materials with two orders of magnitude less computational effort. Using the technique, we investigate high-temperature bcc phase of titanium and predict very weak, Elinvar, temperature dependence of its elastic moduli, similar to the behavior of the so-called GUM Ti-based alloys [T. Sato {\ it et al.}, Science {\bf 300}, 464 (2003)]. Given the fact that GUM alloys have complex chemical compositions and operate at room temperature, Elinvar properties of elemental bcc-Ti observed in the wide temperature interval 1100--1700 K is unique., Comment: 15 pages, 4 figures

Local thermal expansions and lattice strains in the Elinvar alloy ${\mathrm{Fe}}_{49.66}{\mathrm{Ni}}_{42.38}{\mathrm{Cr}}_{5.49}{\mathrm{Ti}}_{2.47}$ (Ni Span C) and the stainless steel $\text{SUS}304{\mathrm{Fe}}_{71.98}{\mathrm{Ni}}_{9.07}{\mathrm{Cr}}_{18.09}{\mathrm{Mn}}_{0.86}$ (AISI304) were investigated by the temperature-dependent Cr, Fe, and Ni $K$-edge extended x-ray absorption fine-structure (EXAFS) measurements, combined with the path-integral effective classical potential Monte Carlo (PIECP MC) theoretical simulations. From the EXAFS analysis of the Elinvar alloy, the local thermal expansion around Fe is found to be considerably smaller than the ones around Ni and Cr. This observation can be understood simply because Fe in the Elinvar alloy exhibit an incomplete Invar-like effect. Moreover, in both the Elinvar and SUS304 alloys, the local thermal expansions and the lattice strains around Cr are found to be larger than those around Fe and Ni. From the PIECP MC simulations of both the alloys, the first-nearest neighbor Cr-Fe pair shows extraordinarily large thermal expansion, while the Cr-Cr pair exhibits quite small or even negative thermal expansion. These findings consequently indicate that the lattice strains in both the Elinvar and SUS304 alloys are concentrated predominantly on the Cr atoms. Although the role of Cr in stainless steel has been known to inhibit corrosion by the formation of surface chromium oxide, the present investigation may interestingly suggest that the Cr atoms in the bulk play a hidden new role of absorbing inevitable lattice strains in the alloys.

Strain glass is a new structural state in ferroelastic materials, which offers unique transition behavior and properties. In this chapter, we introduce a phase field model of strain glass systems and study their transition behavior and the associated properties by computer simulations. Local stresses associated with randomly distributed defects, including point defects and extended defects (dislocations and concentration modulations), are found to play the most important role in the formation of strain glass, by suppressing autocatalysis in nucleation and confining the growth of martensitic domains. A broad distribution of defect strength leads to continued nucleation and growth of martensitic domains in a broad temperature or stress range and renders the otherwise sharp first-order martensitic transformation into a broadly smeared “diffuse” strain glass transition with slim hysteresis, nearly linear superelasticity, ultralow elastic modulus and Invar and Elinvar anomalies. New strategies for designing strain glass systems with large recoverable strain are discussed.

Doping point defects into shape memory alloys (SMAs) influences their transformation behavior and mechanical properties. We propose a general Landau free energy model to study doping effects, which only assume that point defects produce local dilatational stresses coupled to the non-order parameter volumetric strain. Different dopants can be represented by their range of interaction and potency of dilatational stress. Time-dependent simulations based on our model successfully reproduce experimentally observed doping effects in SMAs, including the elevation or suppression of the transformation temperature, the modification of mechanical properties, the appearance of a cross-hatched tweed structure and the emergence of a frozen glassy state with local strain order. We predict that the temperature range for superelasticity will be enhanced in the crossover regime between martensite and strain glass. In addition, an Elinvar effect appears most likely in alloys with dopants tending to increase the transformation temperature, which needs to be verified experimentally. Moreover, the two dopant parameters in the Landau model, the interaction range and potency of the dilatational stress, inspire us to identify three material descriptors with which we can construct an empirical machine learning model. The model predicts the transformation temperature, and the slope of the change in transformation temperature as a function of doping composition, enabling an effective search for doped SMAs with targeted properties via machine learning.

The present article serves as a concise review of strain glass and its broader concept – ferroic glass. Strain glass is a frozen disordered strain state composed of nano-sized strain domains, which is formed due to the frustration created by point defects or dopants. Such frustration creates glassy nano-sized martensite-like domains that do not grow into a macroscopic martensite during cooling and instead show typical glass-freezing dynamics. Strain glass bears much resemblance with the glass phenomena found in other two types of ferroic systems, relaxor ferroelectric, and spin glass. These three ferroics-based glasses are thus called ferroic glasses. Characteristics of strain glass, including recent in situ high-resolution TEM images, are shown. Unusual properties associated with strain glass, such as superelasticity with narrow hysteresis, high-damping, and low modulus, as well as Invar and Elinvar effect in cold-rolled β-Ti alloys are demonstrated.

Materials with Invar (Elinvar) property have a negligible temperature dependence in lattice constant (elasticity), and both pristine and hydrogenated graphene possess these two superior properties. The isotope effects on the vibrational, Invar, and Elinvar properties of them are studied using density-functional simulation. The increase in mass not only lowers the vibrational frequencies of (hydrogenated) graphene, but also influences the inter-atom and inter-branch hybridizations in hydrogenated graphene. However, the Invar and Elinvar properties have a negligible isotopic dependence, and the underlying mechanism is revealed by analyzing the isotope effects on phonon dispersions, anharmonicity, and thermodynamics. When carbon/hydrogen isotope is used to selectively engineer some properties (e.g., thermal transport and kinetic stability), such isotopic independence of the Invar and Elinvar properties can guarantee the minimized side effects on structure and stiffness.

The paper studies the density and porosity of 44NKhTYu elinvar alloy blanks produced by powder technology, jet molding, and electron-beam remelting. It is shown that jet molding and solid-phase sintering of powders over a narrow remelting temperature range are the most promising. They can be used to make blanks and products whose density and porosity are close to those of cast alloy, the metallic yield being increased.

Young's modulus-temperature and thermal expansion curves were measured in gamma-Fe-31Mn-(0.25-8.67) Si-0.77C (at%) alloys by dynamic audio resonance method and in a light dilatometer. The results show that the anomalies in Young's modulus and thermal expansion appear near the Neel temperature. The temperature coefficient of Young's modulus, (1/E(p))(dE(p)/dT), is controlled by Si content below the Neel temperature. When Si content increases to 5.31 at%, (1/E(p))(dE(p)/dT) is close to zero in temperature range from 260 to 335 K, i.e. the Fe-31Mn-5.31Si-0.67C (at%) alloy shows Elinvar character. The temperature range in which the Elinvar character appears is wider than that of gamma-Fe-Mn Elinvar alloys. The change in exchange energy and the Delta E effect result from the effect of Si on the antiferromagnetic behavior in gamma-Fe-Mn alloys since it induces or enhances localized magnetic moment. When the increase in normal Young's modulus due to lowering temperature is compensated by the Delta E effect caused by the antiferromagnetic ordering, Elinvar character appears. (C) 2011 Elsevier B.V. All rights reserved.

The microstructure, phase composition, and mechanical properties of the alloy 44NKhTYu have been studied using metallography, X-ray diffraction, and acoustic testing. The main peculiarities of the formation of intermetallic phases and their effect on the mechanical properties of the alloy have been determined.

Properties of elinvars produced by a powder technology are studied experimentally at all hierarchic structural levels. The problems of an increase in the homogeneity of the structure and a decrease in the porosity of a powder elinvar are solved by alloying with titanium hydride and 2 wt % nickel powder with a particle size of 50–70 nm. A heat treatment regime is optimized to improve the mechanical properties, namely, the hardness, strength, modulus of elasticity, and porosity. Based on the studied laws of structure formation, a powder elinvar with properties similar to the corresponding cast alloy is produced: its density is 98%, the modulus of elasticity is up to 190 GPa, the ultimate strength is 1100 MPa, and the relative elongation is up to 13%.

Analysing magnetic field recordings from a quiet period in January 2007 we find that seismometers with a sensitivity to horizontal component of magnetic field larger than 0.2 m/s/s/T would not be able to resolve the NLNM (New Low Noise Model, Peterson 1993) between 0.3 mHz and 3 mHz (i.e. in the low-frequency normal-mode band). In a previous study the sensitivity to magnetic field of stations in the GRSN (German Regional Seismic Network) was analysed. Only recently we became aware that this unwanted sensitivity can limit the resolution of some of these stations even during magnetically quiet periods. The situation will be even worse during less quiet periods and at other sites of the global network of broad-band seismometers since amplitudes of natural variations of Earth's magnetic field are likely to be larger at higher geomagnetic latitude. Vertical or oblique components of broad-band sensors which require a suspension spring can suffer from this since the springs are made from elinvar alloys. Elinvar alloys necessarily are ferromagnetic and magnetostrictive. It is thus crucial to use appropriate means (e.g. a permalloy shield) to ensure a low sensitivity to magnetic fields when designing and installing high-resolution broad-band seismometers for the observation of normal modes. Artificial sources of magnetic fields should be avoided in the vicinity of the seismometers. We demonstrate that even the small magnetic fields caused by supply currents in data acquisition systems can generate disturbances in seismic broad-band recordings. Although making use of invar and elinvar alloys too, the LaCoste Romberg earth tide gravimeter ET-19 and the invar wire strainmeters at BFO (Black Forest Observatory) are not limited due to magnetic field variations in their resolution for seismic normal modes.

Investigation of the temperature behavior of the coefficient of tensoresistance π of the amorphous Fe86B14 alloy in a temperature range from room temperature to the crystallization temperature has been carried out. It has been revealed that below the Curie temperature TC, in the interval of existence of elinvar properties, π in this alloy increases only weakly, with a temperature coefficient of 4 × 10−4 K−1. At T > TC, a stronger temperature increase of π is observed. An analysis performed has shown that the most probable reason of the observed temperature changes in π was a temperature-induced change in Young’s modulus of the alloy. It has been shown that during crystallization the coefficient of tensoresistance π decreases with increasing amount of crystalline phases in the alloy.

Using both the statistical-thermodynamics methods within the scope of the selfconsistent field approximation and the diffraction data on coherent (or diffuse) scattering of X-rays (or thermal neutrons) from (dis)ordered f.c.c.-Ni–Fe alloys of various compositions, the estimation of interatomic interactions (including their magnetic contribution) and their temperature– concentration dependences were obtained. Based on the static concentration-wave representation, the expressions for configuration free energies of L12-Ni3Fe-type permalloy, L10-NiFe-type elinvar and L12-Fe3Ni-type invar were analyzed, considering explicit expressions for configuration entropies of atomic and magnetic subsystems with their configuration internal energies. Phase diagram of a system at issue was plotted within the field of the presence of f.c.c.-Ni–Fe alloys; their phase boundaries, equilibrium (static) properties near critical points (order parameter, etc.), and possible microstructures developed by composition-controlled magnetic transitions and/or order–disorder constant-composition solid–solid phase transformations were discussed. The obtained results were compared with available experimental data.

Summary C.-E. Guillaume received the Nobel Prize for Physics in 1920 for the discovery and development of a pair of alloys that had characteristics invariant with temperature: one had constant length near ambient temperature, the other had constant Young's modulus. A recent analysis expresses retrospective surprise at this award: the objective of this short paper is to justify the award retrospectively, in terms of the continuing and impressive consequences of Guillaume's discoveries.

A new beta titanium alloy group which exhibits multi functions, such as, ultra-low elastic modulus, ultra-high strength, huge elasticity, clayey plasticity at room temperature without work hardening, Elinvar and Invar properties, has been developed. These ''super'' properties are attributable to an arcane feature in relation to plastic deformation of the alloy; they result from a dislocation-free plastic deformation mechanism. In cold-worked alloy, this plastic deformation mechanism forms elastic strain fields with a hierarchical structure ranging in size from the nanometer scale to several tens of microns. This elastic strain energy produces a number of unique properties. (orig.)

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.

Two types of piezoelectric bulk acoustic wave resonators have been fabricated at various frequency ranges using zinc oxide (ZnO) piezoelectric thin films with negative temperature coefficient of frequency (TCF) and substrates with positive TCF. One is a 3.58 MHz resonator made of ZnO thin film on ELINVAR, which is known to be able to control its TCF by heat-annealing conditions. The other is a 200 MHz resonator made of ZnO thin film on a membrane of SiO2 which has positive TCF. The TCF of the 3.58 MHz resonator is controlled by heat-annealing temperature of ELINVAR alloy, and that of the 200 MHz resonator is also controlled by the thickness ratio between ZnO and SiO2. The TCFs of both resonators are optimized to about 2 ppm/°C though methods to control TCF are different. As a result of the experiments, it is clarified that TCF of piezoelectric bulk acoustic wave resonators can be controlled in the range of MHz to several hundreds of MHz range combining some kinds of materials that have different TCF values.