Ni-Mn Alloys Research Articles

Selective laser remelting of an additively manufactured Cu-Al-Ni-Mn shape-memory alloy

Selective laser melting (SLM) was used to manufacture fully martensitic (β′1) samples of the shape-memory alloy 81.95Cu-11.85Al-3.2Ni-3Mn (wt%). Crack-free specimens with a high relative density of about 98.9 ± 0.1% were produced. Immediate remelting of already processed layers during SLM enhances the relative density (99.5 ± 0.3%). Primarily by varying the scanning speed in the remelting step, the thickness of the remelted zone can be adjusted. Moreover, remelting alters the microstructure as well as the transformation temperatures, which tend to rise with the volumetric energy input. In this way, the shape-memory properties can be modified without compromising the relative density and the considerable plasticity of the samples. Thus, the remelting procedure proves to be an interesting tool for 81.95Cu-11.85Al-3.2Ni-3Mn and related alloys in order to optimize and tailor their performance already during SLM processing and without applying additional post-processing steps.

Integratable magnetic shape memory micropump for high-pressure, precision microfluidic applications

Precisely controlling the flow of fluids on a microscopic scale has been a technological challenge in the field of microfluidics. Active microfluidics, where a defined manipulation of the working fluid is necessary, requires active components such as micropumps or microvalves. We report on an optimized design of an integratable, wireless micropump made from the magnetic shape memory (MSM) alloy Ni–Mn–Ga. An external magnetic field generates a shape change in the MSM material, which drives the fluid in a similar fashion as a peristaltic pump. Thus, the pump does not need electrical contacts and avoids the mechanical parts found in traditional pumping technologies, decreasing the complexity of the micropump. With a discrete pumping resolution of 50–150 nL per pumping cycle, which is further scalable, and a pumping pressure well exceeding 2 bar, the MSM micropump is capable of accurately delivering the fluids needed for microfluidic devices. The MSM micropump is self-priming, pumping both liquid and gas, and demonstrates repeatable performance across a range of pumping frequencies. Furthermore, it operates simultaneously as both a valve and reversible micropump, offering superior possibilities compared to existing technologies within the flow rate range of 0–2000 µL/min. Due to its simplicity, this technology can be scaled down easily, which lends itself for future integration into lab-on-a-chips and microreactors for life science and chemistry applications.

Thermodynamic study of fcc-fct-fco multi-step structural transformation in Mn-Ni antiferromagnetic shape memory alloys

Shape memory effect in Mn-Ni antiferromagnetic alloys is closely related to the structural transformations that happen in this system, especially the fcc→fct→fco multi-step structural transformation. In order to discuss the change of Gibbs free energy of this alloy system during the multi-step transformation process, thus study the mechanism of shape memory effect from the standpoint of thermodynamics of fcc→fct→fco transformation, the unknown thermodynamic parameters of fct and fco phases in Mn-Ni alloys must be determined. In this work, based on the application of subregular solution model of the binary system and equilibrium relationships between different phases given in the Mn-Ni phase diagram, these unknown thermodynamic parameters were determined by solving overdetermined equation systems, and dependencies of Gibbs free energies of every phase in Mn-Ni antiferromagnetic alloys on temperature were obtained. The results of calculations show that the critical driving force of fcc→fct martensitic transformation is about 10 J/mol and higher than that of fct→fco transformation (about 1 J/mol), while the enthalpy, entropy and heat capacity of fcc→fct transformation are several times higher than the equivalent parameters for the fct→fco transformation. The dependences of critical chemical driving force, enthalpy, entropy and heat capacity on the alloy composition and temperature were calculated and discussed for the fcc→fct→fco multistep structural transformation. Based on these results, the orders of the two transformations in the fcc→fct→fco multi-step transformation happening in this system were compared with that of the single-step phase transformation, and were found to be all of first-order and to be weakened during the multi-step transformations.

Electrodeposition Mechanism of Zn‒Ni‒Mn Alloy at Different Time Intervals

Mechanism of electrodeposition and stripping of Zn‒Ni‒Mn alloys deposited at different time intervals from aqueous sulfate media were investigated. The corrosion properties of coatings on steel substrate were studied by using different techniques. It might have been established that the attained Zn‒Ni‒Mn alloy exhibits a superior corrosion resistance at low plating times. Also, the ternary Zn‒Ni‒Mn alloy shows finer-grain size, more homogeneous, more uniformity, adherence, hardness, and compactness with respect to the alloy electrodeposited at high plating times. Alloys of the high content of Ni have been obtained at very low deposition times indicating that the initial layer of alloy plating is nickel, as the more noble metal than Zn or Mn, which deposits preferably during the first few seconds. As a result, the coatings obtained at low deposition times have more noble corrosion potentials than those obtained at high deposition times.

Substitution of Ni for Zn on microstructure and mechanical properties of Mg–Gd–Y–Zn–Mn alloy

Abstract This study analyzes the effect of substitution of Ni for Zn on microstructure and mechanical properties of Mg–Gd–Y–Zn–Mn alloy. Our results show that the volume fraction of Mg5(Gd, Y) and (Mg, Zn)3RE phase decreased and LPSO phase increased with more substitution of Ni. After homogenization, only α-Mg and LPSO phase existed. In Mg–Gd–Y–Zn–Mn alloys, the LPSO phases mainly consisted of the 14H type. While in Mg–Gd–Y–Ni–Mn alloy, the LPSO phases consisted of the 18R type. In addition, compared with Mg–Gd–Y–Zn–Mn alloy, the mechanical properties of as-extruded Ni-substitution alloys were improved due to the better refinement of the size of grains and LPSO phases. The tensile strength in as-extruded Mg–Gd–Y–Ni–Mn alloy could reach up to 400 MPa with 18% of the elongation to failure.

Microstructure evolution and mechanical properties of spark plasma sintered W–Ni–Mn alloy

Tungsten heavy alloys (90W–6Ni–4Mn) were prepared through spark plasma sintering (SPS) using micron-sized W, Ni, and Mn powders without ball milling as raw materials. The effects of sintering temperature on the microstructure and mechanical properties of the 90W–6Ni–4Mn alloys were investigated. SPS technology was used to prepare 90W–6Ni–4Mn alloys with relatively high density and excellent comprehensive performance at 1150–1250 °C for 3 min. The 90W–6Ni–4Mn alloys consisted of the W phase and the γ-(Ni, Mn, and W) binding phase, and the aγerage grain size was less than 10 µm. The Rockwell hardness and bending strength of alloys first increased and then decreased with increasing sintering temperature. The best comprehensiγe performance was obtained at 1200 °C, its hardness and bending strength were HRA 68.7 and 1162.72 MPa, respectiγely.

Electrodeposition of multicomponent Co–Cr–Fe–Mn–Ni alloy

Abstract This work is focused on the initial realization of a multi-component coating deposition from the aqueous solution. The Coating composed of the elements Co-Cr-Fe-Mn-Ni was prepared by electroplating process. The chosen substrate was copper. The purpose of the work was to apply the high entropy alloy, which is defined as alloy with structure of a solid solution containing five or more elements in an approximately equal atomic ratio. The use of electrodeposition in this area is rare. The conditions of the plating process, the percentage of the metal ions and cohesion of the layers were studied. The morphology of the excluded coatings was monitored by scanning electron microscopy and their elemental composition was verified by the EDS analysis. The wear resistant features were examined approximately before and consequently also after the thermal resistance testing.

Intrinsic Micromechanism of Multi-step Structural Transformation in MnNi Shape Memory Alloys

Simulation of the multi-step transformation of cubic matrix → multi-variant tetragonal domain → orthorhombic domain was realized by phase-field method. The intrinsic micromechanism of the second-step transformation in MnNi alloys was studied. It was found that the orthorhombic variant originated from the tetragonal variant with similar orientation, and bar-shaped orthorhombic phase firstly occurred around the interface of twinning bands. The second-step transformation resulted in localized variation of internal stress.

Phase transformations of n-layer graphenes into diamond at high pressures and temperatures

The effect of high pressure (7.7 GPa) and temperature (1700°C) on the phase transformations of both graphene plates with a high degree of crystallinity having less than four layers and thickness not exceeding 5 nm and powders of multilayer graphenes (of 10–20 monolayers) and 8–12 nm in thickness was experimentally studied in the presence of carbon solvents (Ni–Mn alloy, iron). Factors both contributing and inhibiting the diamond synthesis from graphene in the presence of the solvents for carbon are defined. It is shown that the transformation of multilayer graphenes into diamond at high pressure and temperature by a two-stage scheme of the diamond synthesis (i.e., after three-dimensional structural ordering of graphene at the first stage) is preferable.

Long-range atomic order and grain boundary ensemble in alloys with L12 superstructure

It is found experimentally that in the Ni3Mn and Pd3Fe alloys with superstructure L12, ordered through a two-phase region A1 + L12, an increase in the degree of long range atomic order is accompanied by a reduction in the special and twin boundaries’ angle of deviation from the special boundaries in the CSL model, and by a change in the special boundaries’ spectrum and its average energy. The dependence of the proportion of Σ3 twin boundaries within the spectrum of special boundaries and the average energy of special boundaries on the degree of long range atomic order is determined by the dependence of these parameters on the mean square displacement and probability of antiphase grain boundaries being superimposed on the boundary planes, and on the presence of second phases on special boundaries.

Studies on electrochemical deposition of novel Zn–Mn–Ni ternary alloys from an ionic liquid based on choline chloride

Ternary Zn–Mn–Ni alloy coatings were electrodeposited for the first time from a choline chloride based ionic liquid with the aim of collecting properties of binary Zn–Mn and Zn–Ni alloys into one alloy system. The effect of electrodeposition potential on the composition and corrosion performance of the obtained ternary Zn–Mn–Ni deposits was investigated and contrasted with the characteristics of Zn–Mn and Zn–Ni deposits. Cyclic voltammetry revealed that the deposition of ternary Zn–Mn–Ni alloys behaved differently from the deposition of binary Zn–Mn and Zn–Sn alloys and that Mn deposition takes place at positive potentials in the Zn–Mn–Ni electrolyte than in the Zn–Mn electrolyte due to the presence of Ni2+ ions in the electrolyte. X-ray diffraction studies showed that the Zn–Mn–Ni ternary alloys consist of a lattice of Zn (with Mn and Ni imbedded inside) at low electrodeposition potentials and MnZn(with Ni imbedded inside) phase at high electrodeposition potentials. Chemical composition analysis show that the Mn content in the ternary Zn–Mn–Ni alloy increased with increase in electrodeposition potential, whereas Zn and Ni contents are suppressed. The corrosion tests results indicate that through addition of Ni into the Zn–Mn binary alloy, the Zn–Mn–Ni alloy tailored are more corrosion resistant than the Zn–Mn binary alloy whilst the passivation behavior is still preserved.

Nano-Localized Thermal Analysis and Mapping of Surface and Sub-Surface Thermal Properties Using Scanning Thermal Microscopy (SThM).

Determining and acting on thermo-physical properties at the nanoscale is essential for understanding/managing heat distribution in micro/nanostructured materials and miniaturized devices. Adequate thermal nano-characterization techniques are required to address thermal issues compromising device performance. Scanning thermal microscopy (SThM) is a probing and acting technique based on atomic force microscopy using a nano-probe designed to act as a thermometer and resistive heater, achieving high spatial resolution. Enabling direct observation and mapping of thermal properties such as thermal conductivity, SThM is becoming a powerful tool with a critical role in several fields, from material science to device thermal management. We present an overview of the different thermal probes, followed by the contribution of SThM in three currently significant research topics. First, in thermal conductivity contrast studies of graphene monolayers deposited on different substrates, SThM proves itself a reliable technique to clarify the intriguing thermal properties of graphene, which is considered an important contributor to improve the performance of downscaled devices and materials. Second, SThM's ability to perform sub-surface imaging is highlighted by thermal conductivity contrast analysis of polymeric composites. Finally, an approach to induce and study local structural transitions in ferromagnetic shape memory alloy Ni-Mn-Ga thin films using localized nano-thermal analysis is presented.

High‐Performance Thermomagnetic Generators Based on Heusler Alloy Films

Recent developments on Heusler alloys including Ni–Mn–X and Ni–Co–Mn–X (X = Ga, In, Sn,…) demonstrate multiferroic phase transformations with large abrupt changes in lattice parameters of several percent and corresponding abrupt changes in ferromagnetic ordering near the transition temperatures. These materials enable a new generation of thermomagnetic generators that convert heat to electricity within a small temperature difference below 5 K. While thermodynamic calculations on this energy conversion method predict a power density normalized to material volume of up to 300 mW cm−3, experimental results have been in the range of µW cm−3. Challenges are related to the development of materials with bulk‐like single‐crystal properties as well as geometries with large surface‐to‐volume ratio for rapid heat exchange. This study demonstrates efficient thermomagnetic generation via resonant actuation of freely movable thin‐film devices of the Heusler alloy Ni–Mn–Ga with unprecedented power density of 118 mW cm−3 that compares favorably with the best thermoelectric generators. Due to the large temperature‐dependent change of magnetization of the films, a periodic temperature change of only 3 K is required for operation. The duration of thermomagnetic duty cycle is only about 12 ms, which matches with the period of oscillatory motion.

Experimental and computational study of diffusion mobilities for fcc Ni–Cu–Mn alloys

Based on the available thermodynamic description and experimental diffusivities, the diffusion mobilities of Ni, Cu and Mn for fcc Ni–Cu–Mn ternary alloys have been investigated in the present work. Interdiffusion coefficients for fcc Ni–Mn binary alloys with Mn content up to 60at% and for Ni-rich fcc Ni–Cu–Mn ternary alloys were measured using diffusion couple method combined with Electron Probe Micro-Analyzer (EPMA) technique. During the assessment of diffusion mobilities by means of the CALPHAD method, experimental interdiffusivities for Cu-rich fcc Cu–Mn–Ni alloys were also taken into account. Comparisons between the results calculated using the diffusion mobilities assessed in the present work and the experimental data show that a good agreement has been obtained for the diffusion data such as the diffusion coefficients, concentration profiles and diffusion paths. Thus it is believed that the diffusion mobilities for fcc Ni–Cu–Mn alloys obtained in the present work can be applied for a wide composition range.

Direct observation of fast-moving twin boundaries in magnetic shape memory alloy Ni–Mn–Ga 5 M martensite

We report a direct observation of fast Type II twin boundary motion under a pulsed magnetic field excitation in Ni–Mn–Ga 5M martensite, utilizing high-speed camera technique. Our results demonstrate saturation velocities up to ~39m/s measured along [100] direction for individual boundaries moving at RT, showing an order of magnitude larger values as compared to the earlier studies. Actuation response times of ~1μs were observed using laser vibrometry technique. The reported results show a minor role of magneto-static forces and emphasize the role of inertia and internal friction in twin boundary dynamics at the measured speeds.

Self-patterning of epitaxial Ni–Mn–Ga/MgO(001) thin films

In this work, a detailed report on the growth of elongated bar-like crystallites with a definite crystallographic orientation, forming a self-organized patterned surface layer, with a thickness of about 100 nm, onto 900 nm thick ferromagnetic shape memory alloy Ni–Mn–Ga films epitaxially grown on MgO(001) is presented. The phenomenon appears above a threshold of lattice mismatch (≈2%) between the film and substrate. The structural, magnetic and transformation properties of such films are described and analyzed. Particularly, the different magnetic states of the two film layers are discerned by ferromagnetic resonance. The feasibility of creating a ferromagnetic shape memory alloy with a nanoscale self-patterned surface, during the very same process of film deposition, can be interesting for potential applications where control of the surface architecture would be needed.

Deposition Potential Influence on the Electrodeposition of Zn–Ni–Mn Alloy

The effect of deposition potential on the electrodeposition, composition, surface characteristics and corrosion resistance properties of Zn–Ni–Mn alloy coatings were investigated. During the deposition potential range from −0.500 to −1.000 V, normal codeposition of the alloy components occurred, meanwhile at deposition potentials more cathodic than −1.000 V, the anomalous codeposition took place. Shifting the deposition potentials toward the negative direction led to an increase in the thickness of the deposit, incremented the adhesion and compactness and improved the corrosion resistance properties. X-ray diffraction studies of the deposit showed the presence of hexagonal pure Zn phase, hexagonal Mn0.27Zn0.73 phase and cubic γ-Ni5Zn21 and/or tetragonal δ-Ni3Zn22 phases.

Determination of Viscosity for Liquid Fe–Cr–Mn–Ni Alloys

The determination of viscosity of liquid Cr–Mn–Ni steel (16% Cr, 7% Mn) alloyed with 3–20% nickel is of interest in the present experimental investigation. The alloys are manufactured using a cold crucible induction levitation melting. The viscosity measurement is performed using a vibrating finger viscometer for high temperatures (≥1500 °C) and viscosities below 10 mPa s. The BN–ZrO2 vibrating finger is set in a driven harmonic oscillation in its resonance frequency of ca. 26 Hz. The constant peak‐to‐peak amplitude of the oscillator is controlled using a laser micrometer and a powered field coil. The viscosity of Fe–Cr–Mn–Ni alloys is slightly decreased from 3 to 6% nickel and from 6 to 9% nickel a slight increase of the isothermal viscosity is observed. Finally, the viscosity decreased significantly from 9 to 20% nickel content in the samples. The variation in the viscosity at high temperatures can be caused by a change in the primary solidification behavior, as shown in the phase diagram of the Cr–Mn–Ni steel. The temperature function of the viscosity of the high‐alloyed steels is expressed using the Arrhenius function. A precise viscosity measurement is necessary for a mathematical modeling of the vacuum inert gas atomization of steel powder manufacturing.

Effects of solute elements on hardening and microstructural evolution in neutron-irradiated and thermally-aged reactor pressure vessel model alloys

ABSTRACTNanometer-sized Cu-enriched solute clusters containing Mn, Ni, and Si atoms are considered as the primary embrittling feature in reactor pressure vessel steels. In order to understand the effects of solute atoms Mn, Ni, and Si on hardening and cluster formation, reactor pressure vessel model alloys FeCu, FeCuSi, FeCuNi, and FeCuNiMn were irradiated at 290 °C in a research reactor. Thermal ageing at 450 °C was also carried out to compare with the results in the neutron irradiation. The addition of Mn resulted in larger hardening and higher cluster number density in both thermal ageing and neutron irradiation. In FeCu0.8NiMn alloy, the size distribution of Cu-enriched clusters formed in 62-h thermal ageing (almost peak hardening) was very similar to that formed in the neutron irradiation, indicating they are on a similar growing stage. But the average Ni and Mn composition in clusters formed in neutron irradiation was higher. A good linear relationship between hardening and the square root of cluster volume fraction for both neutron irradiation and thermal ageing data was found.

Effects of glycine and current density on the mechanism of electrodeposition, composition and properties of Ni–Mn films prepared in ionic liquid

The effects of glycine on the mechanism of electrodeposition of Ni–Mn alloy film prepared in ChCl–urea ionic liquid were studied in order to control the composition, microstructure and properties of the film. The cyclic voltammograms revealed that the presence of glycine in the ionic liquid can inhibit the reduction of Ni2+ ions but promote the reduction of Mn2+ ions in the cathodic scan. However, it promoted the dissolution of both Ni and Mn deposits in the ChCl–urea ionic liquids during the reverse scan. Glycine changed the mode of Ni–Mn film growth from Volmer–Weber mode into Stranski–Krastanov mode. The Mn content in the Ni–Mn film increased with the increase of concentration of glycine and current density. The Ni–Mn alloy film with 3.1at.% Mn exhibited the lowest corrosion current density of 3×10−7A/cm2 compared with other films prepared and exhibited better corrosion resistance than pure Ni film in 3.5wt.% NaCl solution.