Predicting the Austenite Fraction After Intercritical Annealing in Lean Steels as a Function of the Initial Microstructure

The final fractions of austenite after the isothermal austenite-to-ferrite transformation and its reverse transformations (including the martensite-to-austenite and the pearlite + ferrite-to-austenite transformations) in the intercritical annealing region have been studied using full equilibrium (FE), paraequilibrium (PE), and local equilibrium (LE) calculations and experiments. The LE model predictions are in a very good agreement with the experimental results, while the FE and PE model predictions deviate significantly. It is also found that the LEP/LENP transition for the austenite-to-ferrite transformation deviates from those of its reverse transformations. The magnitude of deviation increases with the increasing Mn concentration.     

Analysis of transformation stasis during the isothermal bainitic ferrite formation in Fe–C–Mn and Fe–C–Mn–Si alloys

The “transformation stasis” phenomenon during the isothermal bainitic ferrite formation has been investigated in a series of Fe–C–Mn and Fe–C–Mn–Si alloys. The Gibbs energy balance (GEB) approach is applied to model the transformation stasis phenomenon, and theoretical predictions are compared with experimental observations. The good agreement over several alloy systems demonstrates that the transformation stasis is caused by diffusion of alloying elements into the migrating austenite/bainitic ferrite interfaces. It is found that the occurrence of transformation stasis in the Fe–C–Mn and Fe–C–Mn–Si alloys depends on the concentration of Mn, while the addition of Si has a negligible effect on transformation stasis. The GEB model clearly outperforms the diffusionless T₀ model.     

Flexible Piezoelectric Touch Sensor by Alignment of Lead‐Free Alkaline Niobate Microcubes in PDMS

A highly sensitive, lead‐free, and flexible piezoelectric touch sensor is reported based on composite films of alkaline niobate K_0.485Na_0.485Li_0.03NbO₃ (KNLN) powders aligned in a polydimethylsiloxane (PDMS) matrix. KNLN powder is fabricated by solid‐state sintering and consists of microcubes. The particles are dispersed in uncured PDMS and oriented by application of an oscillating dielectrophoretic alignment field. The dielectric constant of the composite film is almost independent of the microstructure, while upon alignment the piezoelectric charge coefficient increases more than tenfold up to 17 pC N^?1. A quantitative analysis shows that the origin is a reduction of the interparticle distance to under 1.0 µm in the aligned bicontinuous KNLN chains. The temperature stable piezoelectric voltage coefficient exhibits a maximum value of 220 mV m N^?1, at a volume fraction of only 10%. This state‐of‐the‐art value outperforms bulk piezoelectric ceramics and composites with randomly dispersed particles, and is comparable to the values reported for the piezoelectric polymers polyvinylidenefluoride and its random copolymer with trifluoroethylene. Optimized composite films are incorporated in flexible piezoelectric touch sensors. The high sensitivity is analyzed and discussed. As the fabrication technology is straightforward and easy to implement, applications are foreseen in flexible electronics such as wireless sensor networks and biodiagnostics.     

An Overview of the Cyclic Partial Austenite-Ferrite Transformation Concept and Its Potential

Over the past decades, the mechanism of interface migration during the austenite-ferrite transformation in steels has attracted significant attention from physical metallurgists. There are two challenging research questions in this field: (i) What is the effect of (substitutional) alloying elements on migrating interfaces? and (ii) How to accurately determine the value of interface mobility?. Recently, a cyclic partial phase transformation approach has been proposed to study interface migration, and new insights into the above two questions have been provided. An overview of the cyclic partial phase transformation concept is given, and pathways for future research are suggested.     

Experimental Evidence of the Effect of Alloying Additions on the Stagnant Stage Length During Cyclic Partial Phase Transformations

Cyclic phase transformation experiments are performed in a series of Fe-C-xMn, Fe-C-Mn-xNi, and Fe-C-Mn-xCo alloys to study the effect of alloying elements on the length of the stagnant stage during a cyclic partial phase transformation in the austenite–ferrite two-phase region. The length of stagnant stage increases linearly with the increasing Mn or Ni concentration, while Co has no effect. It was experimentally proven that the effects of alloying elements on the length of stagnant stage are additive, and the experimental results matched the predictions of the local equilibrium model very well.     

Explaining national road fatalities

The purpose of this paper is to report on a model that can be used to explain the differences in road fatalities of individual countries. National infrastructure, transportation and socio-economic variables from international databases were considered as possible variables. The model was developed by means of stepwise regression analyses. It was found that the passenger car ownership is a better predictor of fatalities per 100000 passenger cars than vehicle ownership as a predictor of fatalities per 100000 vehicles. Many individual infrastructure and socio-economic variables have a significant effect on the fatality rate. The final model includes passenger car ownership, the Human Development Index (HDI), and the percentage of other vehicles as explanatory variables.     

Phaselock system for millimeter-wave Gunn oscillators used in radio astronomy and laboratory spectroscopy

A frequency-agile heterodyne phaselock loop (PLL) system for millimeter-wave Gunn-effect oscillators between 40 and 110 GHz is described. The Gunn oscillators are phase-locked via the bias in an active second-order servo loop. A facility for fast frequency switching with a maximum rate of 10 kHz and a frequency separation up to 80 MHz is provided. Measurements on the spectral characteristics of a phase-locked Gunn oscillator are presented. The described PLL system is used in radio astronomy and laboratory molecular spectroscopy.     

In situ observations on the austenite stability in TRIP‐steel during tensile testing

In‐situ deformation tests have been performed on a steel displaying the transformation‐induced plasticity (TRIP) effect, while monitoring the phase transformation by means of X‐ray diffraction. A tensile stress is applied to 0.4 mm thick samples of this steel with mass contents of 0.26 % Si, 1.5 % Mn, and 1.8 % Al in a transmission geometry for a synchrotron‐radiation beam of 25 μm · 25 μm. On the diffraction patterns every grain appears as a discrete spot. The austenite {200} reflections are analysed during this investigation. The diffraction patterns are treated like a powder pattern for five different η‐angles, with η representing the angle between the tensile direction and the normal direction of the diffracting {200} planes. The results of the analysis show that η = 0° and η = 90° are the preferential orientations for the transformation to martensite. The Ludwigson and Burger model [9] is used to gain more information about the stress dependence of the deformation induced martensite formation. The microdiffraction patterns also reveal the changes in carbon concentration in austenite at each retained austenite fraction.     

Characterization of the adhesion of single-walled carbon nanotubes in poly(p-phenylene terephthalamide) composite fibres

Poly(p-phenylene terephthalamide)/single-walled carbon (PPTA/SWNT) composite fibres with different draw ratios have been spun using a dry-jet wet spinning process and their structure and deformation behaviour analysed using Raman spectroscopy. The dispersion of nanotube has been examined by Raman scattering intensity mapping along the fibre. The nanotubes improved the polymer orientation in composite fibre with a draw ratio of 2 but degraded the orientation at higher draw ratios. The mechanical reinforcing effect by nanotubes is related to the change of polymer orientation, suggesting a dominant role of polymer orientation in mechanical performance of the composite fibre. High efficiency of stress transfer within the strain range of 0-0.35% and breakdown of the interface at higher strains has been found in the composite fibres through an in situ Raman spectroscopic study during fibre deformation. Cyclic loading applied on the fibre has indicated reversible deformation behaviour at low strain and gradual damage of the interface at high strains.