A Comparative Evaluation of Third-Generation Advanced High-Strength Steels for Automotive Forming and Crash Applications.

While the third generation of advanced high-strength steels (3rd Gen AHSS) have increasingly gained attention for automotive lightweighting, it remains unclear to what extent the developed methodologies for the conventional dual-phase (DP) steels are applicable to this new class of steels. The present paper provides a comprehensive study on the constitutive, formability, tribology, and fracture behavior of three commercial 3rd Gen AHSS with an ultimate strength level ranging from 980 to 1180 MPa which are contrasted with two DP steels of the same strength levels and the 590R AHSS. The hardening response to large strain levels was determined experimentally using tensile and shear tests and then evaluated in 3D simulations of tensile tests. In general, the strain rate sensitivity of the two 3rd Gen 1180 AHSS was significantly different as one grade exhibited larger transformation-induced behavior. The in-plane formability of the three 1180 MPa steels was similar but with a stark contrast in the local formability whereas the opposite trend was observed for the 3rd Gen 980 and the DP980 steel. The forming limit curves could be accurately predicted using the experimentally measured hardening behavior and the deterministic modified Bressan-Williams through-thickness shear model or the linearized Modified Maximum Force Criterion. The resistance to sliding of the three 3rd Gen AHSS in the Twist Compression Test revealed a comparable coefficient of friction to the 590R except for the electro-galvanized 3rd Gen 1180 V1. An efficient experimental approach to fracture characterization for AHSS was developed that exploits tool contact and bending to obtain fracture strains on the surface of the specimen by suppressing necking. Miniature conical hole expansion, biaxial punch tests, and the VDA 238-100 bend test were performed to construct stress-state dependent fracture loci for use in forming and crash simulations. It is demonstrated that, the 3rd Gen 1180 V2 can potentially replace the DP980 steel in terms of both the global and local formability.

High magnetization FeCo nanoparticles for magnetorheological fluids with enhanced response.

We present results concerning the fabrication of a new magnetorheological fluid with FeCo magnetic nanoparticles (NPs) as magnetic fillers. These NPs have been fabricated by using the chemical reduction technique and show a pure crystalline phase with size ranging among 30-50 nm and high magnetization, 212 ± 2 A m2 kg-1. They agglomerate due to the strong magnetic dipolar interaction among them. These FeCo nanoparticles were used to synthesize a magnetorheological fluid by using oleic acid as surfactant, mineral oil as carrier liquid and Aerosil 300 as additive to control the viscosity of the fluid. The synthesized fluid showed a strong magnetorheological response with increasing shear stress values as the magnetic field intensity increases. Thus, we have measured a superior performance up to 616.7 kA m-1, with a yield stress value of 2729 Pa, and good reversibility after demagnetization process. This value competes with the best ones reported in the most recent literature. We have compared the obtained results with our previous reported ones by using high magnetization Fe NPs fabricated by the electrical explosion of wire method (Fe-EEW).

Improved Determination of Q Quality Factor and Resonance Frequency in Sensors Based on the Magnetoelastic Resonance Through the Fitting to Analytical Expressions.

The resonance quality factor Q is a key parameter that describes the performance of magnetoelastic sensors. Its value can be easily quantified from the width and the peak position of the resonance curve but, when the resonance signals are small, for instance when a lot of damping is present (low quality factor), this and other simple methods to determine this parameter are highly inaccurate. In these cases, numerical fittings of the resonance curves allow to accurately obtain the value of the quality factor. We present a study of the use of different expressions to numerically fit the resonance curves of a magnetoelastic sensor that is designed to monitor the precipitation reaction of calcium oxalate. The study compares the performance of both fittings and the equivalence of the parameters obtained in each of them. Through these numerical fittings, the evolution of the different parameters that define the resonance curve of these sensors is studied, and their accuracy in determining the quality factor is compared.

Real Time Monitoring of Calcium Oxalate Precipitation Reaction by Using Corrosion Resistant Magnetoelastic Resonance Sensors.

The magnetoelastic resonance is used to monitor the precipitation reaction of calcium oxalate () crystals in real-time, by measuring the shift of the resonance frequency caused by the mass increase on the resonator. With respect to previous work on the same matter, the novelty lies in the adoption of an amorphous ferromagnetic alloy, of composition , as resonator, that replaces the commercial Metglas® 2826 alloy (composition ). The enhanced corrosion resistance of this material allows it to be used in biological environments without any pre-treatment of its surface. Additionally, the measurement method, which has been specifically adapted to this application, allows quick registration of the whole resonance curve as a function of the excitation frequency, and thus enhances the resolution and decreases the detection noise. The frequency shift is calibrated by the static deposition of well-known masses of . The resonator dimensions have been selected to improve sensitivity. A 20 mm long, 2 mm wide and 25 m thick magnetoelastic resonator has been used to monitor the precipitation reaction of calcium oxalate in a 500 s time interval. The results of the detected precipitated mass when oxalic acid and calcium chloride are mixed in different concentrations (30 mM, 50 mM and 100 mM) are presented as a function of time. The results show that the sensor is capable of monitoring the precipitation reaction. The mass sensitivity obtained, and the corrosion resistance of the material, suggest that this material can perform excellently in monitoring this type of reaction.

Magnetic, Magnetoelastic and Corrosion Resistant Properties of (Fe-Ni)-Based Metallic Glasses for Structural Health Monitoring Applications.

We have performed a study of the magnetic, magnetoelastic, and corrosion resistance properties of seven different composition magnetoelastic-resonant platforms. For some applications, such as structural health monitoring, these materials must have not only good magnetomechanical properties, but also a high corrosion resistance. In the fabricated metallic glasses of composition Fe73-xNixCr5Si10B12, the Fe/Ni ratio was varied (Fe+Ni=73% at.) thus changing the magnetic and magnetoelastic properties. A small amount of chromium (Cr5) was added in order to achieve the desired good corrosion resistance. As expected, all the studied properties change with the composition of the samples. Alloys containing a higher amount of Ni than Fe do not show magnetic behavior at room temperature, while iron-rich alloys have demonstrated not only good magnetic properties, but also good magnetoelastic ones, with magnetoelastic coupling coefficient as high as 0.41 for x=0 in the Fe73Ni0Cr5Si10B12 (the sample containing only Fe but not Ni). Concerning corrosion resistance, we have found a continuous degradation of these properties as the Ni content increases in the composition. Thus, the corrosion potential decreases monotonously from 46.74 mV for the x=0, composition Fe73Ni0Cr5Si10B12 to -239.47 mV for the x=73, composition Fe0Ni73Cr5Si10B12.

Size Dependence of the Magnetoelastic Properties of Metallic Glasses for Actuation Applications.

We present an exhaustive study of the magnetoelastic properties of 24 strips with different rectangular dimensions, cut from a long ribbon of Metglas® 2826MB3. The strips have a length-to-width ratio R = L/w ranging from 2 to over 20. Significant variations of the apparent saturation Young's modulus and the ΔE effect with strip geometry, changing from 160 GPa and 4% for L = 10 mm, w = 5 mm and R = 2, to 164 GPa and 9.6% for L = 35 mm, w = 1.7 mm and R = 20.6, have been observed. In order to obtain the highest values of the ΔE effect, the magnetomechanical coupling coefficient, k, and the quality factor of the resonance, Q, a value R > 14 is needed. The effective anisotropy field Hk*, taken as the minimum of the E(H) curve, and its width ΔH, are not as strongly influenced by the R value, and a value of R > 7 is enough to reach the lowest value. From our measurements we infer that the formerly predicted value of R > 5 needed for a good magnetic and magnetoelastic response of the material must be actually regarded as the lowest limit for this parameter. In fact, we show that the demagnetizing factor N, rather than the length-to-width ratio R, is the parameter that governs the magnetoelastic performance of these strips.

Accurate Determination of the Q Quality Factor in Magnetoelastic Resonant Platforms for Advanced Biological Detection.

The main parameters of magnetoelastic resonators in the detection of chemical (i.e., salts, gases, etc.) or biological (i.e., bacteria, phages, etc.) agents are the sensitivity S (or external agent change magnitude per Hz change in the resonance frequency) and the quality factor Q of the resonance. We present an extensive study on the experimental determination of the Q factor in such magnetoelastic resonant platforms, using three different strategies: (a) analyzing the real and imaginary components of the susceptibility at resonance; (b) numerical fitting of the modulus of the susceptibility; (c) using an exact mathematical expression for the real part of the susceptibility. Q values obtained by the three methods are analyzed and discussed, aiming to establish the most adequate one to accurately determine the quality factor of the magnetoelastic resonance.

Nanostructured ZnO in a Metglas/ZnO/Hemoglobin Modified Electrode to Detect the Oxidation of the Hemoglobin Simultaneously by Cyclic Voltammetry and Magnetoelastic Resonance.

In the present work, a nanostructured ZnO layer was synthesized onto a Metglas magnetoelastic ribbon to immobilize hemoglobin (Hb) on it and study the Hb's electrochemical behavior towards hydrogen peroxide. Hb oxidation by H2O2 was monitored simultaneously by two different techniques: Cyclic Voltammetry (CV) and Magnetoelastic Resonance (MR). The Metglas/ZnO/Hb system was simultaneously used as a working electrode for the CV scans and as a magnetoelastic sensor excited by external coils, which drive it to resonance and interrogate it. The ZnO nanoparticles for the ZnO layer were grown hydrothermally and fully characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and photoluminescence (PL). Additionally, the ZnO layer's elastic modulus was measured using a new method, which makes use of the Metglas substrate. For the detection experiments, the electrochemical cell was performed with a glass vial, where the three electrodes (working, counter and reference) were immersed into PBS (Phosphate Buffer Solution) solution and small H2O2 drops were added, one at a time. CV scans were taken every 30 s and 5 min after the addition of each drop and meanwhile a magnetoelastic measurement was taken by the external coils. The CV plots reveal direct electrochemical behavior of Hb and display good electrocatalytic response to the reduction of H2O2. The measured catalysis currents increase linearly with the H2O2 concentration in a wide range of 25-350 µM with a correlation coefficient 0.99. The detection limit is 25-50 µM. Moreover, the Metglas/ZnO/Hb electrode displays rapid response (30 s) to H2O2, and exhibits good stability and reproducibility of the measurements. On the other hand, the magnetoelastic measurements show a small linear mass increase versus the H2O2 concentration with a slope of 152 ng/µM, which is probably due to H2O2 adsorption in ZnO during the electrochemical reaction. No such effects were detected during the control experiment when only PBS solution was present for a long time.

Metallic Glass/PVDF Magnetoelectric Laminates for Resonant Sensors and Actuators: A Review.

Among magnetoelectric (ME) heterostructures, ME laminates of the type Metglas-like/PVDF (magnetostrictive+piezoelectric constituents) have shown the highest induced ME voltages, usually detected at the magnetoelastic resonance of the magnetostrictive constituent. This ME coupling happens because of the high cross-correlation coupling between magnetostrictive and piezoelectric material, and is usually associated with a promising application scenario for sensors or actuators. In this work we detail the basis of the operation of such devices, as well as some arising questions (as size effects) concerning their best performance. Also, some examples of their use as very sensitive magnetic fields sensors or innovative energy harvesting devices will be reviewed. At the end, the challenges, future perspectives and technical difficulties that will determine the success of ME composites for sensor applications are discussed.

Sensor applications of soft magnetic materials based on magneto-impedance, magneto-elastic resonance and magneto-electricity.

The outstanding properties of selected soft magnetic materials make them successful candidates for building high performance sensors. In this paper we present our recent work regarding different sensing technologies based on the coupling of the magnetic properties of soft magnetic materials with their electric or elastic properties. In first place we report the influence on the magneto-impedance response of the thickness of Permalloy films in multilayer-sandwiched structures. An impedance change of 270% was found in the best conditions upon the application of magnetic field, with a low field sensitivity of 140%/Oe. Second, the magneto-elastic resonance of amorphous ribbons is used to demonstrate the possibility of sensitively measuring the viscosity of fluids, aimed to develop an on-line and real-time sensor capable of assessing the state of degradation of lubricant oils in machinery. A novel analysis method is shown to sensitively reveal the changes of the damping parameter of the magnetoelastic oscillations at the resonance as a function of the oil viscosity. Finally, the properties and performance of magneto-electric laminated composites of amorphous magnetic ribbons and piezoelectric polymer films are investigated, demonstrating magnetic field detection capabilities below 2.7 nT.

XAS and XMCD study of the influence of annealing on the atomic ordering and magnetism in an NiMnGa alloy.

The proper annealing of Ni(51)Mn(28)Ga(21) ribbon alloy gives rise to an increase of the saturation magnetization and of the magnetic order T(C) (up to 20 K) and martensitic transition T(M) (up to 10 K) temperatures. The combined x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) studies indicate that the annealing treatment drives the alloy to a more ordered structure without significantly affecting the local structure in terms of interatomic distances and bonding geometry. By contrast, the annealing strongly affects the near-edge absorption at the Mn K-edge while no effect is observed at either the Ni or Ga K-edge. These results suggest that annealing leads to a modification of the electronic structure of the Mn atoms while that of Ni and Ga atoms remains unvaried. However, strong XMCD signals are detected at both Ni and Ga K-edges whose amplitude increases after annealing. These results point out that despite the change of the magnetic properties of the system being mainly associated with the modification of the electronic properties of the Mn atoms, both Ni and Ga may play a non-negligible role through the polarization of the conduction band.