Influence of HiPIMS pulse widths on the deposition behaviour and properties of CuAgZr compositionally graded films

In this work, the influence of different pulse widths (25, 50 and 100 μs) during high power impulse magnetron sputtering (HiPIMS) of copper, silver and zirconium was investigated in terms of plasma properties and properties of combinatorial composition gradient CuAgZr film libraries. In situ plasma diagnostics via optical emission spectroscopy (OES), time-of-flight mass spectrometry (TOFMS), and modified quartz crystal microbalance (m-QCM), followed by film ex situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) investigations allowed to determine the effect of deposition parameters on the thin films' microstructural changes. Changing the pulse width, while keeping the duty cycle constant, modified the discharge composition in the target region and the ionised fraction of the sputtered species in the substrate region. The maximum Cu ionised fraction (19 %) was found for 50 μs, resulting in compact and smooth morphology for Cu-rich films, whereas short 25 μs pulses provided porous columnar films with rough surfaces, as the result from Ar+ bombardment. For Ag-rich films, Ag segregation allowed the deposition of dense layers, regardless of the used pulse width. Furthermore, low Ag (<10 at.%) CuAgZr films produced via HiPIMS and direct-current magnetron sputtering (DCMS) were compared in terms of structural and mechanical property changes as a function of Zr contents. For the studied chemical composition range, a linear relationship between Zr content, XRD phase shift and mechanical properties was observed for HiPIMS films, in contrast to DCMS's more abrupt transitions. An increase in hardness and elastic modulus (up to 44 % and 22 %, respectively) was found for the HiPIMS films compared to DCMS ones. The obtained results highlight HiPIMS's flexibility in providing a wide range of tailoring possibilities to meet specific application requirements, such as crystalline microstructure, density and associated mechanical properties

Chemical ligation methods in the synthesis of peptides and proteins. Part 1

Proteins are biological macromolecules affecting very important functions in the body. They are involved in many biochemical processes. They can perform catalytic functions acting as enzymes. They also participate in the transport of many small molecules and ions – for example one molecule of hemoglobin carries four molecules of oxygen. In addition, proteins serve as antibodies and are involved in transmission of nerve impulses as receptor proteins. Because peptides and proteins perform so important functions, to study them it is essential to obtain these compounds in the greatest possible amounts. The compounds can be obtained generally by three main methods: • by isolation of the native peptides and proteins • by expression in microorganisms • by chemical synthesis. Each of the above methods has its advantages and disadvantages, but only the chemical synthesis gives the possibility to introduce modifications to the structure of the resulting protein, such as the insertion of new functional groups, to give the product in the final form and with satisfactory yield. In this review we present the application of chemical ligation methods in the synthesis of peptides and proteins. We describe in details mechanism of native chemical ligation method and the conditions necessary to carry the reaction [1]. The synthesis of long polypeptide chains by kinetically controlled ligation (KCL) is also depicted [2]. This part of the paper also details a number of approaches to noncysteine containing peptides by chemical ligation methods

Chemical ligation methods in the synthesis of peptides and proteins. Part 2

Proteins are synthesized only by living organisms. Today, we are able to receive them by recombinant protein expression in bacterial cells. This technique is very useful and gives satisfactory amount of desirable material but it precludes the possibility of introduction of some chemical modifications that are often obligatory. For this reason, chemical synthesis of longer peptide chains is still important and is the object of scientists attention. Over the last century, notion of peptide synthesis took a new meaning. Nowadays, we know a number of innovative methods and also automated devices which help us to make progress in this area. Nevertheless, the synthesis of longer, more complicated peptide chains and proteins still constitutes a problem. Native chemical ligation (NCL) has facilitated the synthesis of numerous complex peptide and protein targets. Expansion of ligation techniques has allowed the entry of peptides into the world of therapeutic drugs [1]. NCL reactions are carried out in aqueous solution and give good yields. Due to mild conditions, NCL overcomes racemic and solubility problems encountered in classical peptide synthesis using protected fragments. The challenge is to synthesize the C-terminal thioester-containing peptide necessary for the transesterification reaction, which is the first step of linking the peptide fragments [2]. In this review we discuss the evolution, advantages and potential applications of chemical ligation reactions. In the first part of this article we described the utility of native chemical ligation approach to non-cysteine containing peptides. This part details a number of important approaches to the synthesis of peptides bearing a C-terminal thioester. Contemporary applications of these techniques to the total chemical synthesis of proteins are also presented

Crystalline or amorphous? A critical evaluation of phenomenological phase selection rules

In this work, we reviewed the available phase selection rules comprising atomic size and topological aspects, entropies, enthalpies, melting points, valence and itinerant electron concentrations, as well as electronegativity, and validated them using a carefully prepared database of CuTiZr alloys, to assess their strengths and weaknesses. Substantially increasing interest over the last two decades in high-entropy alloys and metallic glasses motivated the search for phase selection rules that could support the designing of new alloys. These rules are most often based on phenomenological correlation between structure and topological-, thermodynamic- and/or electronic structure-related properties of alloy systems. The available phase selection criteria are, therefore, not scientifically derived, but rather statistically constructed from available experimental data. Thus, they contain potential pitfalls, hindering the rational interpretation of obtained results. With this in mind, this work discusses the importance of defining the influence of phase transformation kinetics and synthesis method on an alloy’s final structure, while highlighting the challenges of using phenomenological alloying guidelines. Furthermore, we show that the interpretation of available phase selection criteria without caution may lead to the designing and fabrication of alloys with undesired phases

Crystallography and morphology of chromium rich eutectic carbides in an As-Cast Fe-Cr-C alloy crystallized in non-equilibrium conditions

The crystallography and microstructure of eutectic carbides crystallizing in non-equilibrium conditions in hypoeutectic Fe24Cr0.8C have been studied by light microscopy, scanning electron microscopy, and transmission electron microscopy. The alloy was synthesized in an arc furnace in high purity argon atmosphere and crystallized on water-cooled copper mould. Greater thermal gradient in regions close to water-cooled, copper mould in comparison with top of the ingot gives a formation of eutectic carbides with two morphologies: large polygonal carbides and surrounding them much smaller, plate-like carbides instead of rod-like carbides, observed in top of the ingot. There was no evidence for influence of non-equilibrium crystallization to the formation of types of carbides different than M₂₃C₆

The Characterization Of Cast Fe-Cr-C Alloy

The paper presents the results of the characterization of alloy from Fe-Cr-C (carbon content 0.79 wt.%) system including the microstructure, phase analysis, morphology and hardness in as cast state. The chemical composition was designed to create chromium-rich ferritic matrix with high volume fraction of carbides in form of interdendritic eutectics. The research was carried out on the cross section of the ingot, synthesized in an arc furnace under high purity argon atmosphere and crystallized on water-cooled copper mould. Microstructural characterization was carried out by light microscopy and scanning electron microscopy (SEM). Phase identification was performed by X-Ray diffraction (XRD). The microstructure of the investigated alloy is composed of primary and secondary dendrites Fe-Cr solid solution and complex M23C6 and M7C3 carbides in interdendritic areas. Segregation of Cr and C during crystallization causes precipitation of M7C3 carbides. The average hardness of the alloy is 205±12 HV10

Charakterystyka stopu Fe-Cr-C w stanie lanym

The paper presents the results of the characterization of alloy from Fe-Cr-C (carbon content 0.79 wt.%) system including the microstructure, phase analysis, morphology and hardness in as cast state. The chemical composition was designed to create chromium-rich ferritic matrix with high volume fraction of carbides in form of interdendritic eutectics. The research was carried out on the cross section of the ingot, synthesized in an arc furnace under high purity argon atmosphere and crystallized on water-cooled copper mould. Microstructural characterization was carried out by light microscopy and scanning electron microscopy (SEM). Phase identification was performed by X-Ray diffraction (XRD). The microstructure of the investigated alloy is composed of primary and secondary dendrites Fe-Cr solid solution and complex M23C6 and M7C3 carbides in interdendritic areas. Segregation of Cr and C during crystallization causes precipitation of M7C3 carbides. The average hardness of the alloy is 205±12 HV10.W pracy dokonano analizy mikrostruktury, faz oraz wybranych właściwości stopu w stanie lanym z układu Fe-Cr-C (stężenie węgla 0,79% mas.). Skład chemiczny zaprojektowano tak, aby uzyskać osnowę ferrytyczną bogatą w chrom z dużym udziałem objętościowym węglików eutektycznych. Badania przeprowadzono na przekroju poprzecznym wlewka wykonanego w piecu łukowym w atmosferze ochronnej argonu, krystalizującego na miedzianym łożu, chłodzonym wodą. Obserwacje mikrostruktury przeprowadzono z wykorzystaniem mikroskopii świetlnej oraz skaningowej mikroskopii elektronowej (SEM). Identyfikację faz wykonano za pomocą rentgenowskiej analizy fazowej. Mikrostruktura badanego stopu składa się z dendrytów pierwszo i drugorzędowych roztworu stałego chromu w żelazie α oraz węglików złożonych M23C6 i M7C3, powstałych w obszarach międzydendrytycznych. Segregacja Cr i C podczas krystalizacji, sprzyja wydzielaniu węglików typu M7C3. Średnia twardość stopu wynosi 205±12 HV10

Experimental and Thermodynamic Study of Selected in-Situ Composites from the Fe-Cr-Ni-Mo-C System

The aim of the study was to synthesize and characterize the selected in-situ composites from the Fe-Cr-Ni-Mo-C system, additionally strengthened by intermetallic compounds. The project of the alloys was supported by thermodynamic simulations using Calculation of Phase Diagram approach via Thermo-Calc. Selected alloys were synthesized in an arc furnace in a high purity argon atmosphere using a suction casting unit. The studies involved a range of experimental techniques to characterize the alloys in the as-cast state, including optical emission spectrometry, light microscopy, scanning electron microscopy, electron microprobe analysis, X-ray diffraction and microhardness tests. These experimental studies were compared with the Thermo-Calc data and high resolution dilatometry. The results of investigations presented in this paper showed that there is a possibility to introduce intermetallic compounds, such as χ and σ, through modification of the chemical composition of the alloy with respect to Nieq and Creq. It was found that the place of intermetallic compounds precipitation strongly depends on matrix nature. Results presented in this paper may be successfully used to build a systematic knowledge about the group of alloys with a high volume fraction of complex carbides, and high physicochemical properties, additionally strengthened by intermetallic compounds