Ni-Mn Alloys Research Articles

Magnetocaloric effect in ribbon samples of Heusler alloys Ni–Mn–M (M=In,Sn)

Direct measurements of the magnetocaloric effect in samples of rapidly quenched ribbons of Mn50Ni40In10 and Ni50Mn37Sn13 Heusler alloys with potential applications in magnetic refrigeration technology are carried out. The measurements were made by a precise method based on the measurement of the oscillation amplitude of the temperature in the sample while is subjected to a modulated magnetic field. In the studied compositions both direct and inverse magnetocaloric effects associated with magnetic (paramagnet-ferromagnet-antiferromagnet) and structural (austenite-martensite) phase transitions are found. Additional inverse magnetocaloric effects of small value are observed around the ferromagnetic transitions.

The Al-rich region of the Al–Mn–Ni alloy system. Part I: Ternary phases at 750–950 °C

Ternary phases in the Al-rich region of the Al–Mn–Ni alloy system were studied at 950, 850 and 750°C. Two new ternary intermetallic compounds were revealed: the φ-phase (Al5Co2-type, hP26, P63/mmc: a=0.76632(16) and c=0.78296(15)nm) and the κ-phase (κ-Al14.4Cr3.4Nil.1-type, hP227, P63/m: a=1.7625(10) and c=1.2516(10)nm). The formation of the O-phase (Pmmn; oP650; O-Al77Cr14Pd9-type; a=2.3316(16), b=1.2424(15) and c=3.2648(14)nm) was confirmed and its chemical composition as well as thermodynamic stability was specified.

The Al-rich region of the Al–Mn–Ni alloy system. Part II. Phase equilibria at 620–1000 °C

Phase equilibria in the Al-rich region of the Al–Mn–Ni alloy system were studied at 1000, 950, 850, 750, 700, 645 and 620°C. Three ternary thermodynamically stable intermetallics, the φ-phase (Al5Co2-type, hP26, P63/mmc; a=0.76632(16), c=0.78296(15)nm), the κ-phase (κ-Al14.4Cr3.4Nil.1-type, hP227, P63/m; a=1.7625(10), c=1.2516(10)nm), and the O-phase (O-Al77Cr14Pd9-type, Pmmn, oP650,: a=2.3316(16), b=1.2424(15), c=3.2648(14)nm), as well as three ternary metastable phases, the decagonal D3-phase with periodicity about 1.25nm, the Al9(Mn,Ni)2-phase (Al9Co2-type, P1121/a, mP22; a=0.8585(16), b=0.6269(9), c=0.6205(11)nm, β=95.34(10)°) and the O1-phase (base-centered orthorhombic, a≈23.8, b≈12.4, c≈32.2nm) were revealed. Their physicochemical behaviour in the Al–Mn–Ni alloy system was studied.

Growth, structure, and magnetic properties of epitaxialNixMn100−xsingle layers andCo/NixMn100−xbilayers onCu3Au(100)

The growth and structure of single-crystalline ultrathin ${\text{Ni}}_{x}{\text{Mn}}_{100\ensuremath{-}x}$ films on ${\text{Cu}}_{3}\text{Au}(100)$, and also the magnetic properties of Co ultrathin films on ${\text{Ni}}_{x}{\text{Mn}}_{100\ensuremath{-}x}/{\text{Cu}}_{3}\text{Au}(100)$ have been investigated by x-ray photoelectron and Auger electron spectroscopy, low-energy electron diffraction, reflection high-energy electron diffraction, and magneto-optical Kerr effect (MOKE). For the investigated concentration range $(10\ensuremath{\le}x\ensuremath{\le}77)$, our results reveal good epitaxial layer-by-layer growth at a substrate temperature of 300 K. A weak $c(2\ifmmode\times\else\texttimes\fi{}2)$ superstructure was observed at the surface of all NiMn films. The average perpendicular interlayer spacing of the NiMn alloy films decreases from $1.88\text{ }\text{\AA{}}$ at $x=10$ to $1.69\text{ }\text{\AA{}}$ at $x=77$. The lattice parameters of equiatomic NiMn films were determined to be $3.52\text{ }\text{\AA{}}$ perpendicular to the sample surface and $3.76\text{ }\text{\AA{}}$ in the sample plane, indicating a face-centered tetragonal (fct) structure as expected for the $L{1}_{0}$ NiMn phase with the $c$ axis along the film normal (``$c$-axis growth''). For the Co/NiMn bilayers $(23\ensuremath{\le}x\ensuremath{\le}55)$, MOKE hysteresis loops show a thickness-independent coercivity, suggesting no magnetic coupling at the Co/NiMn interface. Although the structural results indicate the formation of fct NiMn in the equiatomic concentration range, we have no indication of antiferromagnetism for the NiMn films epitaxially grown on ${\text{Cu}}_{3}\text{Au}(100)$ at room temperature. This is contrary to the observations on $\text{Co}/{\text{Ni}}_{50}{\text{Mn}}_{50}$ bilayers on Cu(100), where ``$a$-axis growth'' of NiMn occurs.

Ductility enhancement in ultrafine-grained Fe–Ni–Mn martensitic steel by stress-induced reverse transformation

The effect of large strain deformation on the mechanical properties was investigated in a martensitic Fe–Ni–Mn alloy. After a combined deformation route (cold rolling plus wire drawing), the mechanical properties improved. The tensile strength of alloy in this study reaches to 2540 MPa and total tensile strain to 7% which are much higher than our previous study which after cold rolling and aging tensile strength was 1840 MPa with total tensile strain of 2.8%, although in both cases the improvement are significant for this brittle alloy. The enhancement of ductility after aging might be attributed to the effective role of grain refining down to nanoscale and the formation of austenite during deformation process and stabilization of that austenite in the aged wire. The austenite transforms to ɛ-martensite during tensile testing because of its low stacking fault energy (SFE) and increases the total measured tensile strain more. X-ray diffraction (XRD) analyses and transmission electron microscopic (TEM) images clarified the suggested reason for this ductility enhancement.

Transformation twinning of Ni–Mn–Ga characterized with temperature-controlled atomic force microscopy

The magnetomechanical properties of ferromagnetic shape memory alloy Ni-Mn-Ga single crystals depend strongly on the twin microstructure, which can be modified through thermomagnetomechanical training. Atomic force microscopy (AFM) and magnetic force microscopy (MFM) were used to characterize the evolution of twin microstructures during thermomechanical training of a Ni-Mn-Ga single crystal. Experiments were performed in the martensite phase at 25 degrees C and in the austenite phase at 55 degrees C. Two distinct twinning surface reliefs were observed at room temperature. At elevated temperature (55 degrees C), the surface relief of one twinning mode disappeared while the other relief remained unchanged. When cooled back to 25 degrees C, the twin surface relief recovered. The relief persisting at elevated temperature specifies the positions of twin boundaries that were present when the sample was polished prior to surface characterization. AFM and MFM following thermomechanical treatment provide a nondestructive method to identify the crystallographic orientation of each twin and of each twin boundary plane. Temperature dependent AFM and MFM experiments reveal the twinning history thereby establishing the technique as a unique predictive tool for revealing the path of the martensitic and reverse transformations of magnetic shape memory alloys.

Fe and Co selective substitution in Ni2MnGa: Effect of magnetism on relative phase stability

We studied the effect of selective substitution in Fe and Co 3d elements on the structural and magnetic phase transitions in the prototypical magnetic shape memory alloy Ni–Mn–Ga. We determined the phase diagram for each elemental doping substitution by means of calorimetry and ac susceptibility measurements. An effort was made to substitute each constituent element by the same amounts of doping and to study the role of parameters other than electronic concentration in controlling phase stability. Specifically, selective doping with atoms of similar atomic radii but different magnetic properties allowed us to investigate the role of magnetic interactions on the relative phase stability of the ternary compound. We determined the entropy change associated with the martensitic transition for each quaternary alloy to obtain further information on the effect of magnetism on the relative stability of the involved phases exhibited by these compounds.

New Mg–Mn–Ni alloys as efficient hydrogen storage materials

New ternary Mg–Mn–Ni alloys synthesised by high energy ball milling have been studied as hydrogen storage materials. A new Mg 3MnNi 2 ternary intermetallic compound of the Ti 2Ni type has been identified, its structure was studied by neutron diffraction. It has been shown that in the Mg–Mn–Ni system this intermetallic coexists with Mg, forming two-phase Mg–Mg 3MnNi 2 alloys. The Mg 3MnNi 2 compound reversibly absorbs about 1 wt.% of hydrogen already at room temperature and forms interstitial type Mg 3MnNi 2H ∼3 hydride. Substantially higher hydrogenation capacity has been observed in Mg–Mg 3MnNi 2 alloys with high Mg content, e.g. 5.4 wt.% for the Mg 88Mn 4Ni 8 alloy at 250–350 °C. Hydrogen absorption–desorption kinetics of these alloys are drastically improved compared to undoped magnesium due to catalytic effect of the Mg 3MnNi 2 phase.

Effects of annealing on the magnetic entropy change and exchange bias behavior in melt-spun Ni–Mn–In ribbons

Heusler alloy Ni(48)Mn(37)In(13) ribbons were prepared by melt-spinning. Post-annealing increases the martensitic transformation temperature T(M) and the Curie temperature T(C) of the austenitic phase. The maximum magnetic entropy changes Delta S(M)(max) in the annealed ribbons are 30.1 and -6.5 J kg(-1) K(-1) in the vicinity of T(M) and T(C), respectively, for a field change of 3980 kA m(-1). Exchange bias effects are also found in the ribbons. The effects of annealing on the physical properties are discussed. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Comparing properties of substrate-constrained and freestanding epitaxial Ni–Mn–Ga films

In order to use the magnetic shape memory alloy Ni–Mn–Ga with its high achievable strain of up to 10% for microactuators, freestanding epitaxial films are required. Here we show that these conditions can be fulfilled when using chromium as a sacrificial layer. The low misfit towards Ni–Mn–Ga enables epitaxial growth. Furthermore, Cr can afterwards be removed selectively by wet-chemical etching and during deposition no significant interdiffusion is observed. The structure, microstructure and magnetic properties of micrometer thick films are not affected by the etching process. Films are ferromagnetic at room temperature and we observe the coexistence of non-modulated (NM) and seven layered modulated (14 M) martensite. Tensile stress–strain measurement of a freestanding bridge reveals a broad strain plateau of 12% at a twinning stress of 25 MPa, indicating reorientation of NM variants.

Temperature-minimum line in the Cu-Ni-Mn phase diagram

225 The phase diagram of the Cu–Ni–Mn system has been studied for a long time. In Fig. 1, we show iso therms on the liquidus and solidus surfaces of the dia gram established by Parravano in 1913 [1]. Note the temperature minima in the diagrams of the Cu–Mn and Ni–Mn systems, where there are general regions corresponding to solid solutions with a bcc structure on the copper and nickel sides, and the unlimited solubility in the Cu–Ni system. This raises the question of whether there is a contact line of the liquidus and soli dus surfaces in the ternary Cu–Ni–Mn diagram, con necting the minima in the binary Cu–Mn and Ni–Mn diagrams. On that line, there should be a continuous series of ternary alloys solidifying at constant tempera ture, with values ranging from 1020°C (the minimum on the Ni–Mn diagram) to 870°C (the minimum on the Cu–Mn diagram). Nothing has been reported regarding the existence of such a line in metallic systems as yet. Ternary Cu–Ni–Mn alloys with a small control lable temperature range of solidification are encoun tered as solder for use up to 800°C. According to the fundamental texts on physico chemical analysis [1, 2], the isotherms on the ternary Cu–Ni–Mn diagram indicate that the minima in the binary Cu–Mn and Ni–Mn systems are connected along a line running along the liquidus and solidus sur faces of the ternary system. This, in turn, indicates that those surfaces touch along this line. The liquidus and solidus surfaces do not touch in the ternary Cu–Ni–Mn diagram presented in [3]. Verification of the data in [3]—by plotting three dimensional diagrams using 3D Studio Max 9.0 soft ware—indicates that the diagrams and isotherms in [3] are not consistent and, in fact, the liquidus and solidus surfaces do meet along the line connecting the minima in the binary Cu–Mn and Ni–Mn diagrams. It is not a straight line. There are depressions on the liquidus and solidus sur faces of the ternary Cu–Ni–Mn diagram determined by the minima in the binary Cu–Mn and Ni–Mn systems, according to [4]. We conclude that the liquidus and solidus surfaces do not touch on the basis of the ter Temperature Minimum Line in the Cu–Ni–Mn Phase Diagram

Production and characterization of large single crystals made of ferromagnetic shape memory alloys Ni–Mn–Ga

Ferromagnetic shape memory alloys (MSMA) are well-known smart materials for actuation applications, due to their large shape change in applied magnetic fields. Off-stoichiometric Ni–Mn–Ga single crystals of MSMA exhibit a magnetic-field induced strain of about 10%. In the past decade a lot of effort has been put into understanding and optimizing the properties of Ni-Mn-Ga alloys in terms of the magnetic shape memory effect, starting with the production of single crystals and going all the way to heat treatment and magneto-mechanical training.Here we focus on and present the production and characterization of single crystal Ni–Mn–Ga alloys with off-stoichiometric composition. The molten material was cast into preheated ceramic shells and directionally solidified in a Bridgman-type process. Cylindrical single crystal bars of diameters up to 48 mm and a length of 110 mm were obtained by using suitable grain selectors. Only small misorientations between the single crystal c-axis and the bar axis were found in these bars. The crystals were characterized in terms of composition, segregation, crystal orientation and microstructural features by means of SEM/EDS, EBSD and light microscopy.

Electrooxidation of methanol on NiMn alloy modified graphite electrode

Nickel and nickel–manganese alloy modified graphite electrodes (G/Ni and G/NiMn) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol in alkaline solutions. The methods of cyclic voltammetery (CV), chronoamperometry (CA) and impedance spectroscopy (EIS) were employed. In CV studies, in the presence of methanol NiMn alloy modified electrode shows a significantly higher response for methanol oxidation. The peak current of the oxidation of nickel hydroxide increase is followed by a decrease in the corresponding cathodic current in presence of methanol. The anodic peak currents show linear dependency upon the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of methanol was found to be 4 × 10 −6 cm 2 s −1. A mechanism based on the electro-chemical generation of Ni 3+ active sites and their subsequent consumptions by methanol have been discussed and the corresponding rate law under the control of charge transfer has been developed and kinetic parameters have been derived. The charge transfer resistance accessible both theoretically and through the EIS have been used as criteria for derivation of the rate constant.

Research on Ni–Mn alloy electroforming process for revolving parts

The quality control of the electrodeposit is one of the keys to extending the application of electroforming technology. In this paper, experimental equipment was developed to electroform revolving parts. The conformal anode, high frequency pulse current and well chosen electrolyte were employed to carry out Ni–Mn alloy electroforming for a model of the rocket nozzle. The reasons why the electrodeposits broke and pores existed in the deposits were found. By adding additives to the electrolyte and improving agitation of the electrolyte, the break and pore of the deposits were eliminated. Finally, the acceptable electroforms were obtained.

Effect of the introduction of H atoms on magnetic properties and magnetic entropy change in metamagnetic Heusler alloys Ni–Mn–In

By hydrogen insertion into Ni51Mn49−xInx (x=16.2,16.6) Heusler alloys, the interstitial compounds Ni51Mn49−xInxHδ were fabricated. The introduction of H atoms does not change the L21 structure of the alloys but shifts martensitic temperature (TM) to lower temperature. Magnetic measurements indicated the hydrogenated Ni51Mn49−xInxHδ compounds retain the metamagnetic properties although the ferromagnetic behavior of martensitic phases is slightly enhanced due to the introduction of H atoms. The strong metamagnetic behaviors result in large magnetocaloric effect (MCE). By controlling H content an extended temperature range having large MCE can be achieved.

미세 용접된 BLU CCFL 전극의 유리비딩 열처리 온도에 따른 접합부 특성

Characterization of the microweld CCFL electrode for the TFT-LCD backlight unit was carried out in terms of the glass beading heat treatment conditions. We evaluate the weld zone and parent metal of the microweld CCFL electrodes that were exposed to simulated glass beading heat treatment. The CCFL electrode was composed of the cup made with pure Ni, the pin made with pure Mo and the lead wire made with Ni-Mn alloy. Each part of the electrode was assembled together by micro spot welding process and then the assembled electrodes were exposed to simulated glass beading temperatures of <TEX>$700^{\circ}C,\;750^{\circ}C$</TEX> and <TEX>$800^{\circ}C$</TEX>. The microstructures of the microweld CCFL electrode were observed by using optical microscope, scanning electron microscope and EDS. Micro-tensile and microhardness test were also carried out. The results indicated that the grain coarsening in the HAZs(heat affected zones) for both the cup-pin weld and pin-lead wire were exhibited and the grain coarsening of the HAZ for the cup and the lead wire was more obvious than the HAZ of the pin. The micro-tensile test revealed that the fracture occurred at the cup-pin weld zone for all test conditions. The fracture surface could be classified into two parts such as pin portion and cup portion including weld nugget. The failure was seemed to be initiated from the boundary between nugget and pin through the weld joint. The result of the microhardness measurement exhibited that the relatively low hardness value, about 105HV was recorded at the HAZ of the cup. This value was about 50% less than that of the original value of the cup. The reduction of the microhardness was considered as the cause of the grain coarsening due to welding process. It was also appeared that there was no change in electric resistance for the standard electrodes and heat treated electrodes.

Application of Diamond-Like Nanocomposite Tribological Coatings on LIGA Microsystem Parts

The major focus of this study was to examine the feasibility of applying diamond-like nanocomposite (DLN) coatings on the sidewalls of Ni alloy parts fabricated using lithographie, galvanoformung and abformung (LIGA: a German acronym that means lithography, electroforming, and molding) for friction and wear control. Planar test coupons were employed to understand the friction mechanisms in regimes relevant to LIGA microsytems. Friction tests were conducted on planar test coupons as well as between LIGA-fabricated test structures in planar-sidewall and sidewall-sidewall configurations. Measurements were made in dry nitrogen and air with 50% relative humidity by enclosing the friction tester in an environmental chamber. In contrast to bare metal-metal contacts, minimal wear was exhibited for the DLN-coated LIGA NiMn alloy parts and test coupons. The low friction behavior of DLN was attributed to its ability to transfer to the rubbing counterface providing low interfacial shear at the sliding contact. The coating coverage and chemistry on the sidewalls and the substrate-coating interface integrity were examined by transmission electron microscopy, Automated eXpert Spectral Image Analysis, and electron backscatter diffraction on cross sections prepared by focused ion beam microscopy. The role of novel characterization techniques to evaluate the surface coatings for LIGA microsystems technology is highlighted.

Structural state of Ni-Mn solid solutions in a wide range of concentrations based on the data of scattering and absorption of X-rays

It has been demonstrated that Ni-Mn alloys prepared from elemental powders by the method of mechanical alloying appear to be fcc solid solutions in a wide concentration range. Structural studies of samples with the amount of Ni from 50 to 95 at % were carried out by the methods of X-ray diffraction, electron microscopy, and EXAFS spectroscopy.

Epitaxial Ni–Mn–Ga films derived through high temperature in situ depositions

Epitaxial films of the magnetic shape memory alloy Ni–Mn–Ga have been deposited on(100) YSZ substrates in a previously unexplored high temperature depositionregime. The temperatures employed encouraged the development of the desiredmicrometer-size highly twinned martensitic grain structure, where the loss of manganeseand gallium at high temperatures was compensated for through enrichments tothe target material. The films show the desired shape memory alloy propertiesof having a well-defined reversible martensitic transformation, centered around85 °C, a room temperature martensitic phase with an in-plane saturation magnetization of64 emu g−1, and a magnetically induced reorientation of the martensite variants which occurs at a lowmagnetic field of 400 Oe. The films also exhibit a hysteresis loop in the magnetic transition,a feature attributed to the overlap of the magnetic and structural phase transitions. Theresults suggest that the described in situ route provides a superior pathway to theformation of Ni–Mn–Ga films.

Anisotropy of the Neutron Scattering in the Paramagnetic Phase and on the Spin Waves in the Mn0.71Ni0.29Alloy

We have confirmed the significant anisotropy of the generalised magnetic susceptibility in the paramagnetic and antiferromagnetic phase of the fcc Mn–Ni alloys. In this paper the detailed account of the experiments performed on the Mn0.71Ni0.29 alloy is given. Our main result for the paramagnetic phase is that the correlation length is larger for the direction parallel to the anisotropy axis than for the perpendicular one by a factor of 1.6. The spin-wave velocity observed at 15 K is higher for the direction parallel to the anisotropy axis than that for the perpendicular direction by a factor of 1.2. These results are similar to that for the Mn0.62Ni0.38 alloy. Our results indicate that the magnetic carriers are more localized and the magnetic interactions are less extended in alloys with higher Ni concentration.