Modular high-throughput test stand for versatile screening of thin-film materials libraries

Versatile high-throughput characterization tools are required for the development of new materials using combinatorial techniques. Here, we describe a modular, high-throughput test stand for the screening of thin-film materials libraries, which can carry out automated electrical, magnetic and magnetoresistance measurements in the temperature range of −40 to 300 °C. As a proof of concept, we measured the temperature-dependent resistance of Fe–Pd–Mn ferromagnetic shape-memory alloy materials libraries, revealing reversible martensitic transformations and the associated transformation temperatures. Magneto-optical screening measurements of a materials library identify ferromagnetic samples, whereas resistivity maps support the discovery of new phases. A distance sensor in the same setup allows stress measurements in materials libraries deposited on cantilever arrays. A combination of these methods offers a fast and reliable high-throughput characterization technology for searching for new materials. Using this approach, a composition region has been identified in the Fe–Pd–Mn system that combines ferromagnetism and martensitic transformation.     

Combinatorial Synthesis and High-Throughput Characterization of Microstructure and Phase Transformation in Ni–Ti–Cu–V Quaternary Thin-Film Library

Ni–Ti–based shape memory alloys (SMAs) have found widespread use in the last 70 years, but improving their functional stability remains a key quest for more robust and advanced applications. Named for their ability to retain their processed shape as a result of a reversible martensitic transformation, SMAs are highly sensitive to compositional variations. Alloying with ternary and quaternary elements to fine-tune the lattice parameters and the thermal hysteresis of an SMA, therefore, becomes a challenge in materials exploration. Combinatorial materials science allows streamlining of the synthesis process and data management from multiple characterization techniques. In this study, a composition spread of Ni–Ti–Cu–V thin-film library was synthesized by magnetron co-sputtering on a thermally oxidized Si wafer. Composition-dependent phase transformation temperature and microstructure were investigated and determined using high-throughput wavelength dispersive spectroscopy, synchrotron X-ray diffraction, and temperature-dependent resistance measurements. Of the 177 compositions in the materials library, 32 were observed to have shape memory effect, of which five had zero or near-zero thermal hysteresis. These compositions provide flexibility in the operating temperature regimes that they can be used in. A phase map for the quaternary system and correlations of functional properties are discussed with respect to the local microstructure and composition of the thin-film library.     

Ferromagnetic shape memory alloys: synthesis,characterisation and biocompatibility of Fe–Pd for mechanical coupling to cells

Abstract

Yielding magnetically switchable strains of several percentage, ferromagnetic shape memory alloys (FSMAs) constitute a highly attractive materials class for engineering and biomedical applications. The Fe–Pd alloy is considered as a promising candidate to fulfil this goal, yet synthesis in the desirable martensite phase poses a major challenge, particularly when miniaturised as thin films. The present contribution reviews recent progress in synthesis via the splat-quenching and molecular beam epitaxy routes and reports on the physical picture that emerges from systematic characterisation. Moreover, since no cell damaging temperature variations are required to induce shape changes of FSMAs, Fe–Pd bears great potential for medical devices if good biocompatibility is ensured. Here we review studies on cellular response in contact with Fe–Pd, as well as morphological changes on roughness graded surfaces. We end with a summary how polymer coatings can enhance bioactive properties of Fe–Pd to promote cell adhesion and viability for future applications.     

Kinetics of martensitic transformations in magnetic field or under hydrostatic pressure

Abstract

We have recently constructed a phenomenological theory that provides a unified explanation for athermal and isothermal martensitic transformation processes. On the basis of this theory, we predict some properties of martensitic transformation and confirm them experimentally using some Fe-based alloys and a Ni–Co–Mn–In magnetic shape memory alloy.     

Time–dependent nature and origin of displacive transformation

We have investigated athermal and isothermal martensitic transformations (typical displacive transformations) in Fe–Ni and Fe–Ni–Cr alloys under pulsed and static magnetic fields and hydrostatic pressures in order to understand the time-dependent nature of martensitic transformation, that is, the kinetics of martensitic transformation. Also, we have calculated electronic structures of B₂ and ζ′₂ phases in AuCd by FLAPW and/or LAPW methods in order to understand the origin of B₂–ζ′₂ transformation. The following results were obtained. (i) The two transformation processes are closely related to each other, that is, the athermal process changes to the isothermal process under a hydrostatic pressure and the isothermal process changes to the athermal one under a magnetic field. (ii) These findings of (i) can be explained by the phenomenological theory, which gives a unified explanation for the two transformation processes previously proposed by our group. (iii) The calculation of the generalized susceptibility, x(q), for the B2 phase of AuCd shows that there exists a nesting vector of near 1/3<110>2Π/a as in the B2 phase of TiNi calculated previously. The density of states at the Fermi energy of the ζ′₂ phase is lower than that of the B2 phase, which is similar to the case of B2–R transformation in TiNi previously calculated.     

Development of 3rd generation Medium Mn duplex steels for automotive applications

The mechanical behaviour and fracture were studied in a Fe–5Mn–2.5Al–0.2C (in wt-%) Medium Mn steel. Metallographic and magnetic measurements confirm the significant influence of the transformation kinetics of the strain-induced martensite on the mechanical properties and strain heterogeneities (Lüders and Portevin-Le Chatelier-like phenomena). An accurate study of isothermal evolutions of the microstructure, associated with atomistic calculations, complements current thermodynamic databases to quantify the nature and volume fraction of phases at different temperatures. A kinetic approach then predicts the influence of annealing conditions on the composition of retained austenite, key parameter for the martensitic transformation kinetics. This supports quantitative modelling of the influence of the intercritical annealing temperature on the ultimate tensile strength for industrial developments of these new grades.     

Martensitic transformation and microstructure of polycrystalline Ni–Mn–Ga and C-doped Ni–Mn–Ga Heusler alloys

Abstract

The martensitic transformations of Ni–21·7Mn–23·8Ga (at.-%) (NiMnGa) and Ni–19·4Mn–22·7Ga–1·6C (at.-%) (NiMnGaC) alloys were investigated by the measurement of resistivity. Two kinds of martensitic transformations occur in NiMnGa alloy. The first martensitic transformation is thermoelastic, which exhibits a steep increasing in resistivity. The second transformation exhibits a larger thermal hysteresis compared with the first transformation. NiMnGaC alloy only shows a single martensitic transformation and the C addition increases the first martensitic transformation temperatures. The first martensitic phase of NiMnGa alloy is of five layered structure while the martensitic phase of NiMnGaC alloy is of non-modulated structure. Combined with the observation of optical microscopy and TEM, NiMnGa alloy exhibits much wider martensite twins than NiMnGaC alloy does.     

Guest Editorial: Personal perspective on microstructure of steels: 25th anniversary of MST and collection of papers in honour of Sir Robert Honeycombe

Abstract

The shape memory properties and microstructure associated with γ(fcc) → ?(hcp) martensitic transformation in an Fe–14Ru alloy have been investigated. The degree of shape recovery was measured via a bending test, and the microstructure was examined using X-ray diffractometry, optical microscopy, and transmission electron microscopy. The Fe–14Ru alloy showed shape recovery to some extent, but to a lower degree than in Fe–Mn–Si based shape memory alloys. The lower strength of the matrix, the presence of ? and α′ martensites at room temperature, and the higher stacking fault energy in the Fe–14Ru alloy are thought to be responsible for the weaker shape memory effect.     

A current perspective on high-throughput polymer science

Recent years (2000–2003) have witnessed an upsurge in the application of combinatorial and high-throughput experimental methods to polymers. This review highlights the most recent developments in high-throughput polymer science, in order to put into perspective the articles selected for this special section of The Journal of Materials Science. This article begins by defining the unique challenges in polymer (and materials) high-throughput screening (HTS), with respect to other applications of combinatorial and high-throughput methods in drug discovery and catalyst development. Advances in the preparation of HTS libraries are then discussed, with a distinction made between libraries for synthetic investigation and libraries for formulation and characterization. Then, the recent applications of HTS to polymer analytical methods (for chemical characterization of synthetic libraries) and physical characterization methods (for formulation libraries) are presented.     

Effect of enhanced interfacial reaction on the microstructure,phase transformation and mechanical property of Ni–Mn–Ga particles/Mg composites

This study investigated the microstructure, phase transformation and mechanical property of Ni–Mn–Ga particles/Mg composites with a strong interfacial reaction between the particles and the matrix. The strong interfacial reaction was related to the large surface area and energy per unit volume of the flaky shape Ni–Mn–Ga particles that favors the reaction between the particles and matrix. The martensitic transformation behavior was largely weakened due to the interfacial reactions and thus the reduced volume fraction of Ni–Mn–Ga particles. The composites exhibited a much improved compressive strength and ductility in comparison with that of the Ni–Mn–Ga alloy. The compressive plasticity of the composites was decreased when the Ni–Mn–Ga particle content exceeded 40 wt%. In comparison with the Mg-composites with large size Ni–Mn–Ga particles, the composites with small size particles would have a much stronger interfacial reactions, which was detrimental to the phase transformation and mechanical ductility of the composites. The investigation results in this article could provide a reference for the design and preparation of the particles reinforced metal matrix functional composites.     

Screening of the Interactions Between Mg‐PSZ and TRIP‐Steel and Its Alloys During Sintering

Ceramic–steel compound materials are used in a wide range of applications up to date. Major advantages are the mechanical properties due to the combination of brittle ceramic with tough steel. This study deals with effects of the sintering process on austenitic TRIP‐steel/Mg‐PSZ composite materials for mechanical load applications. Both, the Fe? Cr? Ni? steel and partially stabilized zirconia offer their special mechanical behavior only in a metastable state. The ability of phase transformation depends mainly on the chemical composition. Mutual interactions of the alloying metals (Cr, Ni, Mn, and Fe) and the ceramic stabilizer (MgO) during sintering may prevent the martensitic phase transformation. This may cause disadvantageous mechanical behavior on mechanical load in use.     

High-throughput characterization of film thickness in thin film materials libraries by digital holographic microscopy

Abstract

A high-throughput characterization technique based on digital holography for mapping film thickness in thin-film materials libraries was developed. Digital holographic microscopy is used for fully automatic measurements of the thickness of patterned films with nanometer resolution. The method has several significant advantages over conventional stylus profilometry: it is contactless and fast, substrate bending is compensated, and the experimental setup is simple. Patterned films prepared by different combinatorial thin-film approaches were characterized to investigate and demonstrate this method. The results show that this technique is valuable for the quick, reliable and high-throughput determination of the film thickness distribution in combinatorial materials research. Importantly, it can also be applied to thin films that have been structured by shadow masking.     

Identification of novel compositions of ferromagnetic shape-memory alloys using composition spreads

Exploration of new ferroic (ferroelectric, ferromagnetic or ferroelastic) materials continues to be a central theme in condensed matter physics and to drive advances in key areas of technology. Here, using thin-film composition spreads, we have mapped the functional phase diagram of the Ni-Mn-Ga system whose Heusler composition Ni(2)MnGa is a well known ferromagnetic shape-memory alloy. A characterization technique that allows detection of martensitic transitions by visual inspection was combined with quantitative magnetization mapping using scanning SQUID (superconducting quantum interference device) microscopy. We find that a large, previously unexplored region outside the Heusler composition contains reversible martensites that are also ferromagnetic. A clear relationship between magnetization and the martensitic transition temperature is observed, revealing a strong thermodynamical coupling between magnetism and martensitic instability across a large fraction of the phase diagram.     

Degradation of Fe–Cr–Al–RE and Ni–Cr–Al–RE foils in air and combustion gas atmospheres

Abstract

In the continuing drive to increase gas turbine operating efficiencies (and reduce environmental emissions), it is necessary to consider ways of improving the temperature capabilities of hot gas path sealing materials. One potential route is to investigate the possibility of using alternative materials within the traditional honeycomb structure.

This paper presents the results of investigations into the high temperature oxidation performance of a range of commercial Fe–20wt%Cr–5wt%Al–RE and Ni–16wt%Cr–5wt%Al–RE foil materials in air and simulated combusted natural gas environments. The effects of exposures for periods of up to 1500 hours have been studied in the temperature range 950–1300°C. During each series of tests the foils were subjected to regular thermal cycles (to room temperature) with dwell periods at the target exposure temperatures ranging from 20 hours at the higher temperatures to 100 hours at the lower temperatures.

The degradation kinetics of each foil sample were monitored using mass change measurements at each thermal cycle. In addition, samples were periodically removed for destructive examinations to enable more meaningful metal loss measurements to be made and degradation mechanisms to be established. In this way the principal parameters governing the oxidation performance were established, as well as times to the onset of breakaway oxidation (when these fell within the exposure periods studied at each temperature). Earlier models for the performance of Fe–Cr–Al–RE materials have been adapted to describe the performances of the foils observed in this study.     

Subsecond thermophysics research at the Boris Kidrich Institute Vincha

In the early eighties, at the Boris Kidrich Institute Vincha, a method for measuring specific heat and electrical resistivity of electrical conductors in the millisecond resolution range was developed for measurements from room temperature to 1900 K. Over a period of nearly 10 years, the method was applied to different materials, including pure metals, ferrous, and nickel/ chromium alloys, and to the characterization of candidate materials for thermophysical property reference standards. This paper describes the method and reviews the results obtained in specific heat and electrical resistivity studies of ferromagnetic and other materials. The paper also demonstrates capabilities of the method for describing phase transitions or anomalies in pure metals (Fe, Co, Ni) or alloys (Nichrome, austenitic stainless steel).Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

Residual stresses in two laser surface melted stainless steels

Abstract

Residual stresses were studied in two laser surface melted stainless steels: one martensitic, Fe–12Cr–0·2C, and the other austenitic, Fe–17Cr–11Ni–2·5Mo (compositions in wt-%). Stresses were measured by X-ray diffractometry over a range of depths, processing conditions, and stress relieving heat treatments. The volume increase associated with the martensitic transformation develops compressive stresses in single tracks of the martensitic steel and modifies the subsurface stresses of the laser surface melted steel. However, interactions between tracks offset the compressive surface stresses at all but the slightest overlaps. Residual stresses in the martensitic steel are minimized by increasing the advance between tracks and are reduced to a lesser extent by increasing the beam diameter and decreasing the traverse velocity. The austenitic steel, undergoing no solid state phase transformation on cooling, develops tensile residual stresses of the order of the yield stress for all the processing conditions evaluated. Suitable stress relieving heat treatments were identified for each steel.

MST/422     

First-principles investigation of B2 partial disordered structure,martensitic transformation,elastic and magnetic properties of all-d-metal Ni-Mn-Ti Heusler alloys

In this work,the B2 partial disordered structure of the austenitic parent phase,martensitic transformation,elastic and magnetic properties of the Ni8 Mn4+xTi4-x(x=0,1 and 2) Heusler alloys have been systematically investigated by the first-principles calculations.The preferential atomic occupation of B2 structure is one Ti atom exchange with the nearest neighboring Mn atom from the view of lowest energy principle.This disordered exchange sites(Mn-Ti) and the excess Mn atoms occupying the Ti sites(MnTi)could reduce the nearest Mn-Mn distance,resulting in the anti ferromagnetic state in the austenitic and martensitic phases of the alloys.The total magnetic moment of the alloy decreases with the increasing Mn content;it is ascribed to the antiferromagnetic magnetic moments of the excess Mn atoms.When x=0,the alloy does not undergo martensitic transformation since the austenite has absolute phase stability.The martensitic transformation will occur during cooling process for x=1 or 2,owing to the energy difference between the austenite and the martensite could provide the driving force for the phase transformation.The elastic properties of the cubic austenitic phase for the Ni2 MnTi alloy is calculated,and the results reveal the reason why Ni-Mn-Ti alloy has excellent mechanical properties.The origin of martensitic transformation and magnetic properties was discussed based on the electronic density of states.     

Evolution of microstructure in laser clad Fe–Cr–Mn–C alloy

Abstract

The laser surface cladding technique was used to form in situ Fe–Cr–Mn–C alloys on AISI 1016 steel substrate. In this process, mixed powders containing Cr, Mn, and C in the weight ratio 10: 1 : 1 were delivered using a screw feed, gravity flow, carrier gas aided system into the melt pool generated by a 10 kW CO₂ laser. This technique produced an ultrafine microstructure in the clad alloy layer. The microstructure of the laser surface clad region was investigated by optical, scanning and transmission electron microscopy, and X-ray microanalysis techniques. Microstructural study showed a high degree of grain refinement and an increase in solid solubility of alloying elements which, in turn, produced a fine distribution of complex types of carbide precipitates in the ferrite matrix because of the high cooling rate. An alloy of this composition does not show any martensitic transformation or retained austenite phase.

MST/356     

Effect of rapid solidification on giant magnetostriction in ferromagnetic shape memory iron-based alloys

Ferromagnetic shape memory Fe–29.6 at.% Pd alloy ribbons prepared by the rapid solidification, melt-spinning method, showed a giant magnetostriction of 830 microstrain when an external magnetic field of 7 kOe was applied nearly normal to the ribbon surface at room temperature. This ribbon's magnetostriction was several times as large as conventional polycrystalline bulk's one before rapid solidification. The magnetostriction in the rolling direction depended strongly on a direction of applied magnetic field. We considered that this phenomenon is caused by a rearrangement of activated martensite twin variants just below the austenite phase transformation temperature. We investigated their basic material properties, i.e. the dependencies of magnetostriction on temperature as well as on magnetic angular orientation to the surface, magnetic properties, crystal structure, surface texture morphology and shape memory effect of Fe–29.6 at.% Pd ribbon samples by comparing with conventional bulk sample. It can be concluded that the remarkable anisotropy of giant magnetostriction of ribbon sample is caused by the unique uniaxial-oriented fine grain structure formed by the melt-spinning method. In addition, we confirmed the possibility of rapidly solidified Fe–Pt ribbon as a new kind of iron-based ferromagnetic shape memory alloys for magnetostrictive material.