A contamination-free electron-transparent metallic sample preparation method for MEMS experiments with in situ S/TEM

Microelectromechanical systems (MEMS) are currently supporting ground-breaking basic research in materials science and metallurgy as they allow in situ experiments on materials at the nanoscale within electron-microscopes in a wide variety of different conditions such as extreme materials dynamics under ultrafast heating and quenching rates as well as in complex electro-chemical environments. Electron-transparent sample preparation for MEMS e-chips remains a challenge for this technology as the existing methodologies can introduce contaminants, thus disrupting the experiments and the analysis of results. Herein we introduce a methodology for simple and fast electron-transparent sample preparation for MEMS e-chips without significant contamination. The quality of the samples as well as their performance during a MEMS e-chip experiment in situ within an electron-microscope are evaluated during a heat treatment of a crossover AlMgZn(Cu) alloy.Comment: Preprint submitted to Microscopy and Microanalysi

Mg-Alloys for Forging Applications - A Review

Interest in magnesium alloys and their applications has risen in recent years. This trend is mainly evident in casting applications, but wrought alloys are also increasingly coming into focus. Among the most common forming processes, forging is a promising candidate for the industrial production of magnesium wrought products. This review is intended to give a general introduction into the forging of magnesium alloys and to help in the practical realization of forged products. The basics of magnesium forging practice are described and possible problems as well as material properties are discussed. Several alloy systems containing aluminum, zinc or rare earth elements as well as biodegradable alloys are evaluated. Overall, the focus of the review is on the process control and processing parameters, from stock material to finished parts. A discussion of the mechanical properties is included. These data have been comprehensively reviewed and are listed for a variety of magnesium forging alloys.ISSN:1996-194

Modeling the concurrent growth of inter- and intragranular Si precipitates during slow cooling of the alloy AA6016

AbstractThis work combines two established models for precipitate growth in the bulk and at the grain boundary to investigate the growth of pure Si precipitates in the alloy AA6016 during slow cooling after hot rolling. Despite the simplicity of the approach, the predicted phase fractions and the predicted width of the precipitate-free zone are in agreement with the measured values. The model predictions suggest that ­raising the Si content and increasing the density of primary Fe-based particles reduces the fraction of grain boundary precipitates. The model correctly reproduces the technologically important effect of the cooling rate on intra- and intergranular growth. The model predictions can be used to optimize hot rolling schedules and the alloy design

Effect of Compositional and Processing Variations in New 5182-Type AlMgMn Alloys on Mechanical Properties and Deformation Surface Quality

Laboratory-scale sheets of 5182-type AlMgMn alloys with varying Mg and Mn contents and additions of different amounts of Zn, Cu, Zr and Er were studied. The sheets were produced using two different cold-rolling degrees and two soft-annealing treatment procedures: air-circulated furnace annealing at 370 °C with subsequent furnace cooling, and salt-bath annealing with subsequent water quenching. Mechanical properties and deformation surface quality were studied via tensile tests with simultaneous visual surface characterization. The influence of the chemical composition and the processing route on grain size, mechanical properties, and surface quality is discussed in the study. A reduction in the Mg content improves the surface quality after plastic deformation, but at the expense of the mechanical properties. The results suggest the presence of an optimum Mn content in terms of optical appearance and mechanical properties. Adding Zr largely inhibits recrystallization, which is reflected in a textured microstructure. Adding Er affects neither the surface quality nor the mechanical properties. Specific combinations of Zn or Cu addition, cold-rolling degree, and heat treatment generate significant improvements in the mechanical and optical properties. In general, annealing at high temperature with subsequent quenching leads to enhanced surface quality and mechanical properties, and adding Zn enables further noteworthy improvements

Fast differential scanning calorimetry to mimic additive manufacturing processing: specific heat capacity analysis of aluminium alloys

Eutectic AlSi12, commonly used in casting and in additive manufacturing, is investigated with Fast Differential Scanning Calorimetry to determine the impact of different cooling rates from the liquid state upon the apparent specific heat capacity on subsequent heating. A heat flow correction strategy is developed and refined for the reliable and precise measurement of sample heat flow using chip sensors and assessed by the evaluation of results on pure (99.999%) aluminium. That strategy is then applied to the study of the AlSi12 eutectic alloy, and rate-dependent perturbations in the measured apparent specific heat capacity are discussed in terms of Si supersaturation and precipitation. Several cooling rates were implemented from - 100 to - 30,000 K s(-1), and subsequent heating ranged from + 1000 to + 30,000 K s(-1). After rapid cooling, a drop in AlSi12 apparent specific heat capacity is found on heating above similar to 400 degrees C; even at rates of + 10,000 K s(-1), a result which has high relevance in metal additive manufacturing where similarly fast temperature cycles are involved. The Literature data, temperature modulated DSC and CALPHAD simulations on the heat capacity of AlSi12 are used to provide comparative context to the results from Fast Differential Scanning Calorimetry.ISSN:1388-6150ISSN:1418-2874ISSN:1572-894

Influence of Zn and Sn on the Precipitation Behavior of New Al–Mg–Si Alloys

In this study, we demonstrate how Zn and Sn influence hardening behavior and cluster formation during pre-aging and paint bake treatment in Al–Mg–Si alloys via hardness tests, tensile tests, and atom probe tomography. Compared to the standard alloy, the Sn-modified variant shows reduced cluster size and yield strength in the pre-aged condition. During the paint bake cycle, the clusters start to grow very fast and the alloy exhibits the highest strength increment. This behavior is attributed to the high vacancy binding energy of Sn. Adding Zn increases the formation kinetics and the size of Mg–Si co-clusters, generating higher yield strength values for both the pre-aged and paint baked conditions. Simultaneous addition of Zn and Sn creates a synergistic effect and produces an alloy that exhibits moderate strength (and good formability) in the pre-aged condition and accelerated hardening behavior during the paint bake cycle.ISSN:1996-194

Reprint of: Characterization of bulk metallic glasses via fast differential scanning calorimetry

ISSN:0040-603

Prototypic Lightweight Alloy Design for Stellar‐Radiation Environments

The existing literature data shows that conventional aluminium alloys may not be suitable for use in stellar‐radiation environments as their hardening phases are prone to dissolve upon exposure to energetic irradiation, resulting in alloy softening which may reduce the lifetime of such materials impairing future human‐based space missions. The innovative methodology of crossover alloying is herein used to synthesize an aluminium alloy with a radiation resistant hardening phase. This alloy—a crossover of 5xxx and 7xxx series Al‐alloys—is subjected to extreme heavy ion irradiations in situ within a TEM up to a dose of 1 dpa and major experimental observations are made: the Mg32(Zn,Al)49 hardening precipitates (denoted as T‐phase) for this alloy system surprisingly survive the extreme irradiation conditions, no cavities are found to nucleate and displacement damage is observed to develop in the form of black‐spots. This discovery indicates that a high phase fraction of hardening precipitates is a crucial parameter for achieving superior radiation tolerance. Based on such observations, this current work sets new guidelines for the design of metallic alloys for space exploration.ISSN:2198-384

Differential Scanning Calorimetry and Thermodynamic Predictions—A Comparative Study of Al-Zn-Mg-Cu Alloys

Al-Zn-Mg-Cu alloys are widely used in aircraft applications because of their superior mechanical properties and strength/weight ratios. Commercial Al-Zn-Mg-Cu alloys have been intensively studied over the last few decades. However, well-considered thermodynamic calculations, via the CALPHAD approach, on a variation of alloying elements can guide the fine-tuning of known alloy systems and the development of optimized heat treatments. In this study, a comparison was made of the solidus temperatures of different Al-Zn-Mg-Cu alloys determined from thermodynamic predictions and differential scanning calorimetry (DSC) measurements. A variation of the main alloying elements Zn, Mg, and Cu generated 38 experimentally produced alloys. An experimental determination of the solidus temperature via DSC was carried out according to a user-defined method, because the broad melting interval present in Al-Zn-Mg-Cu alloys does not allow the use of the classical onset method for pure substances. The software algorithms implemented in FactSage®, Pandat™, and MatCalc with corresponding commercially available databases were deployed for thermodynamic predictions. Based on these investigations, the predictive power of the commercially available CALPHAD databases and software packages was critically reviewed