Sam Allen

• Professor Emeritus at Massachusetts Institute of Technology

Textured Ni51Mn28.5Ga20.5 polycrystalline ribbons were prepared by melt spinning method with different spinning speeds. The effect of spinning speed on microstructure, phase transformation and magnetization behavior were investigated. The martensitic transformation temperatures were hardly affected by the spinning speed. The Curie temperature was s...

Determination of the mobilities for ordering transformation in Fe3Al has been attempted by comparing the rates of experimentally observed antiphase boundary (APB) migration with that simulated by a phase filed method (PFM). The simulated boundary mobility of DO3-APB was sensitive to the ordering mobility. This allowed us to determine the ordering m...

The effects of segregation of solute atoms and vacancies on migration of a/4〈1 1 1〉 and a/2〈1 0 0〉 antiphase domain boundaries (APDBs) in stoichiometric Fe3Al at various temperatures are studied using a phase-field model [Koizumi Y, Allen SM, Minamino Y, Acta Mater 2008;56:5861] based on the Bragg–Williams approximation and kinetic parameters deter...

Three-Dimensional Printing is a Solid-Freeform Fabrication process that creates parts out of powder by spreading layers into which binder is ink-jet printed to define the part geometry of that layer. By repetition of the process layer-by-layer, three-dimensional components of very complex geometry can be created. This paper describes key aspects of...

The prospect of using ferromagnetic shape memory alloys (FSMAs) is promising for a resonant actuator that requires large strain output and a drive frequency below 1 kHz. In this investigation, three FSMA actuators, equipped with tetragonal off-stoichiometric Ni 2 MnGa single crystals, were developed to study their frequency response and resonant ch...

Segregation of solute atoms and vacancies to migrating D03–type antiphase boundaries (APBs) in Fe3Al of the stoichirometric and an Al-rich compositions has been investigated in detail by a phase-field method developed in the previous study [Koizumi et al. Acta Mater 2009;57:3039] focusing on the quantitative relationship among the segregation, APB...

In this work, three joints of a X11CrMoWVNb9-1-1 (P911) pipe were welded with three filler metals by conventional arc welding. The filler metals varied in creep strength level, so that one overmatched, one undermatched, and one matched the creep strength of the P911 grade pipe base material. The long-term objective of this work was to study the inf...

Systematic studies of alloys based on TiCr, have been performed in order to improve the toughness of Laves phase intermetallics. The extent to which alloy compositions and annealing treatments influence the toughness was quantified by Vickers indentation. The single-phase Laves behavior was first established by studying stoichiometric and nonstoich...

The morphologies and defect structures of TiCrâ in several Ti-Cr alloys have been examined by optical metallography, x-ray diffraction, and transmission electron microscopy (TEM), in order to explore the room-temperature deformability of the Laves phase TiCrâ. The morphology of the Laves phase was found to be dependent upon alloy composition and an...

The results of computer simulations on the effect of elastic energy on APB anisotropy are presented. The model used treats composition and order parameter as local variables defined at crystal planes parallel to the APB. The set that minimizes the free energy, including elastic energy terms, defines the equilibrium APB structure. It was found that,...

This work reports on the densification of iron nanoparticles heated at moderate rates without applied pressure as observed by TEM imaging, gas adsorption pore size measurement, and X-ray diffraction. Despite a low packing density, the small pore size is amenable to significant densification by pressureless sintering. Carbon residues from the stabil...

The effects of solute and vacancy segregation on APB migration in Ti3Al, and their dependence on composition, have been investigated by using a phase-field simulation in which vacancy distribution is taken into account. Al-atoms are depleted and vacancies segregate at APB in stoichiometric Ti3Al (Ti-25Al), whereas Al-atoms segregate and vacancies a...

Single crystals of nickel-manganese-gallium, a ferromagnetic shape memory alloy (FSMA), show up to 10% elongation in response to an applied magnetic field or mechanical stress. The change in dimension is not a result of magnetostriction but of twin boundary motion through the material. The field-induced extension has previously been reversed only b...

Ti-Cr alloys near the TiCr2 composition have been studied to determine the single-phase Laves field and the associated defects accompanying off-stoichiometry. A combination of metallography, x-ray diffraction, lattice parameter measurements, density measurements and electron microprobe analysis have been used to establish a narrow single-phase regi...

Ferritic 9-12 wt.% chromium steels are favored grades for thick-walled high-temperature components in thermal power plants. These steel grades have two major limitations in high temperature service. First, a drop in creep strength observed after about 10.000 hours of creep exposure at service temperatures around 600°C is observed and attributed to...

In-situ X-ray diffraction (XRD) measurements using high energy synchrotron radiation were performed to monitor in real time the formation of delta ferrite in a martensitic 9 wt pct chromium steel under simulated weld thermal cycles. Volume fractions of martensite, austenite, and delta ferrite were measured as a function of temperature at a 10 K/s h...

Ferritic 9-12 wt.% chromium steels are commonly used for thick-walled high-temperature components in thermal power plants, but they face two major limitations in high-temperature service. Firstly, a reduction in creep strength occurs after approximately 10,000 hours at service temperatures around 600°C, due to the dissolution of finely dispersed V-...

Effects of segregation of solute atoms and vacancies on migration of antiphase boundaries (APBs) in stoichiometric (Fe-25 at%Al) and Al-rich (Fe-28 at%Al) Fe3Al at 673 K have been studied using a phase-field method in which local vacancy concentration is taken into account [Koizumi Y, Allen SM, Minamino Y. Acta Mater 2008;56:5861, ibid. 2009;57:303...

The structural and magnetic characteristics were studied for martensitic and austenitic Ni–Mn–Ga melt-spun ribbons of as quenched and as annealed at different temperatures. No essential structure change was found before and after annealing, but there are some anomalies in the magnetization process. In the austenite state the M(T) curves measured in...

A prototype of Ni–Mn–Ga based ferromagnetic-shape-memory-alloy (FSMA) actuator was designed and built; an acoustic-assist technique was applied to the actuator to enhance its performance. A piezoelectric stack actuator was attached to the Ni–Mn–Ga sample to generate acoustic energy to enhance twin-boundary mobility and, hence, reduce the magnetic t...

The effects of segregation of solute atoms and vacancies on migration of a/4〈111〉 and a/2〈100〉 antiphase domain boundaries (APDBs) in stoichiometric Fe3Al at various temperatures are studied using a phase-field model [Koizumi Y, Allen SM, Minamino Y, Acta Mater 2008;56:5861] based on the Bragg–Williams approximation and kinetic parameters determine...

Segregation of solute atoms and vacancies to antiphase domain boundaries (APDBs) in Fe–Al alloys near the stoichiometry Fe3Al (Fe–22–28 at.% Al) was studied using a phase-field model based on the Bragg–Williams approximation. Local equilibrium vacancy concentration was determined from experimental data for vacancy formation enthalpy and the configu...

Ni–Mn–Ga based ferromagnetic shape memory alloys (FSMAs) have been shown to exhibit large magnetic-field-induced strain (MFIS) up to 10% for frequencies up to 1 kHz. However, a magnetic threshold field of 150–300 kA/m is typically required to achieve MFIS, which will require a large electromagnet. The application of a small acoustic signal to the F...

A small amplitude acoustic signal was applied to a Ni-Mn-Ga single crystal. The effect of the acoustic signal in enhancing the magnetic-field-induced strain was measured as a function of temperature over the range of 1-35°C below the austenite-start temperature. Strain output was found to decrease with decreasing temperature as a result of lowered...

Ni–Mn–Ga based ferromagnetic shape memory alloys (FSMAs) have emerged as a promising class of active materials capable of producing a large (up to 10%) magnetic-field-induced strain (MFIS). This large strain is not the familiar anisotropic magnetostriction; it results from field-induced twin-boundary motion and has appropriately been referred to as...

Composites of Ni–Mn–Ga particles in a polyurethane matrix can be made by mixing the particles with the polymer, and allowing them to cure under a magnetic field to texture the composites. These composites show large hysteresis and mechanical losses, when subjected to a cyclic stress, that were far larger than the matrix polymer ones. The additional...

Structural and magnetic transition temperatures of ferromagnetic shape memory alloys present a strong dependence on slight departures from the stoichiometry, as does the mobility of twin boundaries responsible for the large magnetic field induced strains. In this work we study four non stoichiometric Ni-Mn-Ga polycrystalline alloys with composition...

The use of ferromagnetic shape memory alloy (FSMA) particles as fillers in polymeric matrix composites has been proposed for vibration damping. The large pseudo-plastic recoverable deformation of the FSMA particles due to the rearrangement of twin variants can dissipate a large amount of energy, both under compression and tension. The composites st...

The application of acoustic energy input from a piezoelectric actuator is observed to increase the magnetic-field-induced strain (MFIS) and decrease the threshold field in Ni–Mn–Ga ferromagnetic shape memory alloys (FSMAs). To appreciate better the benefit of the acoustic assistance, the stress and strain outputs of the quasistatic FSMA actuation u...

The chemical order of three off-stoichiometry Ni–Mn–Ga compositions has been measured in the austenitic phase using powder and single-crystal neutron diffraction. The compositions studied, 48–52 at.% nickel, having excess manganese and deficient in gallium, are of technical interest due to the observed large room-temperature, magnetic-field-induced...

The crystal structure of Ni-Mn-Ga ferromagnetic shape-memory alloys is extremely sensitive to composition. Several martensitic structures including tetragonal (five-layered), orthorhombic (seven-layered), and nonmodulated tetragonal have been observed. Temperature-dependent X-ray diffraction measurements and calorimetry have revealed markedly diffe...

Magnetic field-induced twin-boundary motion in Ni–Mn–Ga and other magnetic shape memory alloys is typically observed over a limited range of temperature, 10–120 K below the martensite transformation. Twin-boundary motion requires shuffling of atoms between two stable minima in {1 0 1} planes, a process that occurs only above a threshold yield stres...

Purpose Solid freeform fabrication processes such as three‐dimensional printing (3DP) and selective laser sintering (SLS) produce porous parts. Metal parts produced by these processes must be densified by sintering or infiltration to achieve maximum material performance. New steel infiltration methods can produce parts of standard alloy composition...

of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

From beginning to end I have been a simple metallurgist using metals and their structure as a kind of inverted touchstone to assay all things.

The crystal structure of the martensitic phase Ni–Mn–Ga ferromagnetic shape memory alloys has been found to be extremely sensitive to composition. A systematic exploration of the composition–structure relationship has been performed using X-ray diffraction on several single crystals having large composition gradients. Also, temperature-dependent ma...

Thermodynamics of Interface Motion Motion of Crystal/Vapor Interfaces Interface Motion during Solidification Bibliography Exercises

Specification of Space Curves and Interfaces Isotropic Interfaces and Mean Curvature Anisotropic Interfaces and Weighted Mean Curvature Equilibrium at a Curved Interface Bibliography

General Formulation Solving the Diffusion Equations Measurement of Diffusivities Bibliography Exercises

Free-Volume Model for Liquids Diffusion in Amorphous Metals Small Atoms (Molecules) in Glassy Polymers Alkali Ions in Network Oxide Glasses Diffusion of Polymer Chains Bibliography

Homogeneous Nucleation Heterogeneous Nucleation Bibliography Exercises

Concentration Gradients and Diffusion Electrical Potential Gradients and Diffusion Thermal Gradients and Diffusion Capillarity and Diffusion Stress and Diffusion Bibliography Exercises

Thermally Activated Atomic Jumping Diffusion as a Series of Discrete Jumps Bibliography Exercises

Half Title Title Copyright Contents Preface Acknowledgements Notation Symbols—Roman Symbols—Greek

Morphological Evolution for simple Geometries Diffusional Creep Sintering Bibliography Exercises

Growth of Planner Layers Growth of articles Morphological stability of Moving Interfaces Bibliography Exercises

Geometrical Degrees of Freedom Sharp and Diffuse Interfaces Singular, Vicinal, and General Interfaces Homophase and Heterophase Interfaces Grain Boundaries Coherent, Semicoherent, and Incoherent Interfaces Line Defects in Ctystal/Ctystal Interfaces Bibliography

The Diffusion Spectrum Grain Boundaries Dislocations Free Surfaces Bibliography Exercises

Entropy and Entropy Production Linear Irreversible Thermdynamics Bibliography Exercises

Atomic Mechanisms Atomic Models for Diffusivities Diffusional Anelasticity (Internal Friction) Bibliography Exercises

One-Dimensional Solidification Cellular and Dendritic Solidification Structure of Castings and Ingosts Bibliography Exercises

Fick' Second Law Constant Diffusivity Diffusivity as a Function of Concentration Diffusivity as a Function of Time Diffusivity as a Function of Direction Bibliography Exercises

Thermodynamics of Crystalline Interface Motion Conservative and Nonconservative Motion Conservative Motion Nonconservative Motion Bibliography Exercises

Isotropic Surfaces Anisotropic Surfaces Bibliography Exercises

General Features Nucleus Morphology and Energy Coherency Loss during Growth Two Example System Bibliography

General Features Crystallography Glissile Interface Nucleation of Martensitie Example of Martensitic Transformations Bibliography Exercises

Concentration Variables Atomic Volume

Overall Rate of Discontinuous Transformation Time–Temperature–Transformation (TTT) Diagrams Bibliography Exercises

Steady-State Solutions Non-Steady-State Diffusion Bibliography Exercises

Glide and Climb Driving Forces on Dislocations Dislocation Glide Dislocation Climb Bibliography Exercises

Order Parameters Molar Free-Energy Changes Continuous and Discontinuous Transformations Bibliography

The direct manufacture of metal parts by rapid prototyping (RP) often involves using a metal powder. Densification of the powder can be done either by sintering or infiltration. Infiltration avoids the shrinkage and distortion that typically accompanies sintering. However, in steels, the use of copper or bronze infiltrants limits the usefulness of...

A classroom-tested textbook providing a fundamental understanding of basic kinetic processes in materials This textbook, reflecting the hands-on teaching experience of its three authors, evolved from Massachusetts Institute of Technology's first-year graduate curriculum in the Department of Materials Science and Engineering. It discusses key topics...

Active materials have long been used in the construction of sensors and devices. Examples are piezo-electric ceramics and shape memory alloys. The more recently developed ferromagnetic shape-memory alloys (FSMAs) have received considerable attention due to their large magnetic field-induced, reversible strains (up to 10%).In this article, we review...

Ferromagnetic shape memory alloys can respond to a magnetic field or applied stress by the motion of twin boundaries and hence they show large hysteresis or energy loss. Ni-Mn-Ga particles made by spark erosion have been dispersed and oriented in a polymer matrix to form pseudo 3:1 composites which are studied under applied stress. Loss ratios have...

Internal friction and the elastic modulus of Ni–Mn–Ga single crystals have been simultaneously measured as a function of the temperature during cooling and heating at 3 °C/min between 140 and 20 or 0 °C. The measurements were done in single cantilever mode. Two distinct internal friction peaks indicate martensitic and reverse transformation, respec...

The twin-boundary motion in Ni–Mn–Ga single crystals has been studied with 620 μs magnetic-field pulses on samples of 5  mm ×5  mm cross section and 10 mm in length. A sequence of pulses applied on a single variant induces an extension. It is close to linear with the pulse’s peak generated driving forces, for peaks in excess of 0.68×K_u,...

A technique has been developed that uses acoustic energy to assist a magnetic field in driving twin boundary motion in a NiMnGa single crystal. Acoustic assisted magnetic-field-induced strain has been observed to increase the magnetic-field-induced strain response by up to one order of magnitude. This effect is most pronounced for magnetic field dr...

The motion of twin boundaries in Ni–Mn–Ga ferromagnetic shape memory alloy (FSMA) particles embedded in a polymer matrix has been proposed as an effective mechanism for the dissipation of vibration energy. Indirect evidence of the motion of these boundaries through vibrating sample magnetometer measurements on FSMA/polyurethane matrix composite is...

Ni-Mn-Ga ferromagnetic shape memory alloys (FSMA) are a potential new class of actuator materials able to respond at higher frequencies (at least 300 Hz) with comparable strains (up to 6 %) in a moderate field (below 1 T)[1]. Magnitude of the strain depends on the values of several critical material parameters, most importantly the martensitic tran...

Transient liquid-phase infiltration (TLI) involves a powder-metal skeleton and an infiltrant with similar composition containing a melting-point depressant (MPD). Upon infiltration, the MPD diffuses into the skeleton, causing isothermal solidification and allowing a homogeneous final-part composition. Diffusional solidification of the infiltrant ca...

The effects of alloying elements on the stacking fault energy in Fe-Mn-Si based shape memory alloys were investigated by a new generation solution model. Gibbs free energy change for tetragonal(t) to monoclinic(m) martensitic transformation in ZrO2 based ceramics containing CeO2 and Y2O3 was calculated by the regular solution model. The martensitic...

The field-induced actuation of Ni–Mn–Ga single crystals through twin-boundary motion has been demonstrated with magnetic fieldpulses of various intensities lasting 620 μs. It is shown that the complete field-induced strain can be obtained in 250 μs, which implies the possibility of full 6% cycling of Ni–Mn–Ga at 2 kHz, for crystals having dimension...

Evidence of relaxation has been observed in ferromagnetic Ni–Mn–Ga single crystals. The relaxation may be explained by a change in symmetry-conforming short-range ordering according to Ren and Otsuka in this off-stoichimetric ordered alloy. Martensite stabilization has also been found after martensite ageing.

The critical driving force for martensitic transformation, the stacking fault energy of parent phase at the start martensite start temperature Ms and the influence of anti-ferromagnetic transition on the Gibbs energy of Fe-Mn-Si alloys have been reviewed. The Gibbs energies of the fcc(γ) and hcp(\varepsilon) phases as a function of temperature have...

An analytic model is described that accounts for thc nanoscale strain field that defines the twin-boundary width and energy density as well as the interaction of a 90° domain wall with such a twin boundary. These parameters are being used as input to micromagnetic calculations of the domain-wall profile perturbed by the twin-boundary strain field....

Ferromagnetic Shape Memory Alloy Ni-Mn-Ga has twin boundaries in the martensitic phase that move when a suitable magnetic field is applied. In this fashion strains of up to 6% have been observed for static fields in single crystals [1]. Recently 2.5% strain has been demonstrated [2] in Ni-Mn-Ga single crystals for oscillating fields up to frequenci...

Magnetic-field-induced strains in Ni-Mn-Ga alloys have shown promise since their recent discovery. Large, free strains and moderate AC strains that provide mechanical work have already been demonstrated by this author and others. If the development of this ferromagnetic shape memory alloy (FSMA) is to continue towards application, its preparation a...

Martensitic Ni-Mn-Ga single crystals evidence twin boundaries that can be displaced by applying a mechanical stress. Twin boundary motion is a form of plastic deformation. Thus, Ni-Mn-Ga alloys are very good candidates for passive vibration damping, because relatively large amounts of energy can be dissipated in this way. However, research in to th...

Field-induced strains up to 10% at room temperature have been observed in magnetic shaep memory alloys based on off-stoichiometric compositions of the intermetallic compound Ni2MnGa. This occurs by the motion of twin boundaries in the ferromagnetic martensitic state under magnetic fields of a few kOe. Some data illustrating the interdependence of s...

Field-induced strains up to 10% at room temperature have been observed in magnetic shaep memory alloys based on off-stoichiometric compositions of the intermetallic compound Ni2MnGa. This occurs by the motion of twin boundaries in the ferromagnetic martensitic state under magnetic fields of a few kOe. Some data illustrating the interdependence of s...

Magnetic-field-induced strain in single crystals of Ni-Mn-Ga magnetic shape memory alloys were studied under cyclic field conditions using a compression spring to reset the sample as H-->0. Low frequency actuation strain of 2.5% degraded to about 1.5% at an actuation frequency of 500 Hz. Two resonant-like features appaer in the ε(f) data, which app...

Ferromagentic shape memory alloy composites exhibit good qualities as vibration absorbers. Loss ratios in excess of 25% have been measured in polymer samples containing 20 vol% Ni-Mn-Ga. The ability to dissipate large amounts of energy is due to the same mechanism that is also responsible for the large strains observed in single crystals used as ac...

Effects of 1 T external magnetic field on the transformation strains and resistivity changes associated with martensitic transformation in Ni2MnGa single crystals have been investigated by simultaneously monitoring the variations in strain and electrical resistivity with temperature. The results show that the strains on transforming from austenite...

Martensitic Ni-Mn-Ga single crystals are easily twinned and the twin boundaries can be displaced by applying a mechanical stress or magnetic field. Twin boundary motion is a highly dissipative process. Composites of aligned Ni-Mn-Ga particles in a polymer matrix show evidence of stress-induced twin boundary motion that results in stress-strain curv...

In this paper, ferromagnetic shape memory alloys, most notably NiMnGa have received considerable attention because of the remarkable 6% to 10% field induced strains they have exhibited at room temperature in the magnetic fields of order 0.5 T. In order to address this question, the important technical properties that these materials exhibit will be...

For years it was speculated that the large strains associated with the thermoelastic shape‐memory effect, such as in NiTi alloys, could be captured by application of a magnetic field in certain martensites that are also ferromagnetic. Ferromagnetic shape‐memory alloys (FSMAs) moved from a hypothetical new class of active materials, to join piezoele...

The dynamic field-induced strain response at 2Hz is reported for a ferromagnetic shape memory alloy (FSMA), Ni49.8Mn28.5Ga21.7. For the d31 actuation mode, longitudinal strain response was measured as a function of longitudinally applied bias stress and transverse applied field. Under a 1.5MPa compressive bias stress, dynamic strains of 2.6% were a...

Micro magnetic and analytic models have been sued to describe the equilibrium twin structure and quasistatic actuation behavior of ferromagnetic shape memory alloys. However, these models do not incorporate microscopic aspects of the twin-boundary strain field, interactions with defects or non-equilibrium behavior. A model is described that account...