Evolution of crystallographic texture and mechanical properties of single- and polycrystalline Mg (99.85 wt.%) subjected to high-pressure torsion (HPT) deformation

Die plastische Verformung mittels Hochdrucktorsion („High Pressure Torsion – HPT“) ist eine Methode, mit der man nanostrukturierte Materialien mit außergewöhnlichen physikalischen Eigenschaften in massiver Form herstellen kann. Die Methode steht derzeit im Zentrum der internationalen wenden. Nur wenig ist von den Merkmalen der HPT Verformung hexagonaler Metalle und Legierungen bekannt, auf die die vorliegende Dissertation abzielt, indem sie die Entwicklung der kristallografischen Textur während und nach der HPT Verformung von ein- und vielkristallinem Mg mit Reinheit 99.85 Gew.% untersuchte und mit Messungen der mechanischen Eigenschaften korrelierte. Die Analysen zeigten zunächst, dass sowohl beim einkristallinen wie auch beim polykristallinem Material die Strukturparameter der Ausgangsmaterialien, wie z.B. die Orientierung und die Größe der Kristallite, auf die Charakteristik der Endtextur bzw. Mikrostruktur auch von höchsten HPT Verformungsgraden keinen Einfluss haben. Diese sind einerseits gekennzeichnet von Komponenten der Scherung, die von der HPT Verformung stammen, andererseits aber auch von Komponenten, die vom hydrostatischen Druck bzw. der der Entlastung folgenden Lagerung bei Raumtemperatur abhängen. Diese Abhängigkeiten können durch spezifische Beiträge der dynamischen (“DRX”, während der HPT Verformung) und der statischen (“SRX”, nach HPT Verformung) Erholung bzw. Rekristallisation erklärt werden. Um zwischen diesen Beiträgen zu unterscheiden, wurden spezielle Experimente durchgeführt, bei denen die Proben unmittelbar nach HPT Verformung bzw. vor den Untersuchungen in Flüssig-Stickstoff “eingefroren” wurden (Proben Typ „F“); diese wurden mit Proben verglichen (Proben Typ “RX”), die nach der HPT Verformung bei Raumtemperatur gelagert und erst dann untersucht wurden. Außer den speziellen Merkmalen der Textur zeigten die “RX” Proben eine höhere Festigkeit, während dagegen die “F” Proben eine höhere Plastizität aufwiesen. Intensive Untersuchungen mit verschiedenen Methoden der Elektronenmikroskopie zeigten eine bimodale Mikrostruktur, bestehend sowohl aus kleinen, verformungsinduzierten Kristalliten (Korngrösse unter 0.3μm), als auch aus rekristallisierten, wesentlich größeren Kristalliten (Korngröße über 5 μm). Analog zu den Texturuntersuchungen nahm der Anteil an erholten bzw. rekristallisierten Kristalliten mit zunehmendem hydrostatischem Druck bzw. zunehmender Auslagerungszeit bei Raumtemperatur zu.High Pressure Torsion (“HPT”) deformation is a processing mode which achieves nanostructured materials with outstanding physical properties in bulk shape. Therefore this method is in focus of international materials research in order to fully understand and control the processes governing the nanocrystallization of materials. A great lack in knowledge is about the HPT deformation of hexagonal metals and alloys at which the current PhD. Thesis aimed, by studying the evolution of the crystallographic texture occurring during and after HPT deformation of single- and polycrystalline magnesium of 99.85 wt.% purity, and by correlating this evolution with measurements of mechanical properties. The analyses showed that – with both the single as well as the polycrystalline materials – there was no influence of the initial material parameters – like the orientation or the size of crystallites – on the final texture and microstructure even with the very high plastic strains induced by HPT. The final texture and its intensities consisted of components which arose from shear of the HPT deformation but also from others which depend on the hydrostatic pressure as well as on the annealing time at ambient temperature after release of pressure. These dependences can be explained by the specific contributions of dynamic (“DRX”, during HPT deformation) and static (“SRX”, after HPT deformation) recovery/recrystallization processes. In order to distinguish between these processes, especially designed experiments were carried out where samples have been “frozen” at liquid nitrogen temperature before the investigations (samples type “F”), and compared with those which have been stored at ambient temperature after HPT deformation and investigated afterwards (samples type “RX”). In addition to the special effects to texture, the “RX” samples revealed the higher increase in strength, whereas the “F” samples exhibited a higher plasticity. As a result of thorough investigations of microstructure by different methods of electron microscopy, a bimodal structure consisting of both small, deformation-induced crystallites (grain size below 0.3 μm) and of much larger crystallites (grain size beyond 5 μm) arising from the recovery/recrystallization processes, was found. In analogy to the texture results, the fraction of recovered/recrystallized crystallites increased with increasing annealing time and with increasing HPT pressure

Crystallographic orientation inhomogeneity and crystal splitting in biogenic calcite

The calcitic prismatic units forming the outer shell of the bivalve Pinctada margaritifera have been analysed using scanning electron microscopy–electron back-scatter diffraction, transmission electron microscopy and atomic force microscopy. In the initial stages of growth, the individual prismatic units are single crystals. Their crystalline orientation is not consistent but rather changes gradually during growth. The gradients in crystallographic orientation occur mainly in a direction parallel to the long axis of the prism, i.e. perpendicular to the shell surface and do not show preferential tilting along any of the calcite lattice axes. At a certain growth stage, gradients begin to spread and diverge, implying that the prismatic units split into several crystalline domains. In this way, a branched crystal, in which the ends of the branches are independent crystalline domains, is formed. At the nanometre scale, the material is composed of slightly misoriented domains, which are separated by planes approximately perpendicular to the c-axis. Orientational gradients and splitting processes are described in biocrystals for the first time and are undoubtedly related to the high content of intracrystalline organic molecules, although the way in which these act to induce the observed crystalline patterns is a matter of future research

Struktura fazowa oraz tekstura osadzonych elektrolitycznie stopów InSn na podłożu miedzianym

Stopy In-Sn są interesujące jako materiały dla technologii połączeń bezołowiowych oraz jako materiały zastępujące toksyczne warstwy kadmowe. W pracy badano warstwy indowo-cynowe osadzone z kompleksowych roztworów cytrynianowych. Kąpiele cytrynianowe są szczególnie atrakcyjne jako nietoksyczne kąpiele dla elektrolitycznego osadzania stopów. Osadzanie prowadzono w różnych warunkach hydrodynamicznych przy zastosowaniu wirującej elektrody dyskowej (WED). Stosowany potencjał, warunki hydrodynamiczne, pH, skład roztworu i dodatki składników organicznych miały silny wpływ na skład chemiczny, strukturę fazową i teksturę osadzonych warstw. Obliczono równowagi fazowe w układzie Cu-In-Sn i przedstawiono izoplety diagramu fazowego. W zakresie 25 do 400° C przeprowadzono badania termicznej stabilności osadów na podkładzie miedzianym przy zastosowaniu strukturalnej analizy rentgenowskiej.The In-Sn alloys are interesting as the materials used in the lead-free interconnection technology and as the replacement materials for toxic cadmium layers. This work investigated the indium-tin layers electrodeposited from the complex citrate solutions. The citrate electrolytic baths are especially attractive as the non-toxic baths for the electrodeposition of alloys. The depositions were conducted in various hydrodynamic conditions by means of the rotating disc electrode technique (RDE). It was observed that the applied potential, hydrodynamic conditions, pH, composition of solution and additional organic compounds have a strong effect on the chemical composition, the phase structure and the texture of the electrodeposited layers. The phase equilibria in the Cu-In-Sn ternary system were calculated and the isopleths of the phase diagram were presented. The X-ray structural investigations of the thermal stability of the deposits on the copper substrate were carried out in the temperature range from 25 to 400° C

Application of multireflection grazing incidence method for stress measurements in polished Al–Mg alloy and CrN coating

Multi-reflection grazing incidence geometry, referred to as MGIXD, characterized by a small and constant incidence angle, was applied to measure low surface stresses in very thin layers of Al–Mg alloy and CrN coating. These two materials were selected in order to deal with the low and high levels of residual stress, respectively. The influence of different mechanical treatments on residual stresses was studied for Al–Mg samples. It was found that both rolling and mechanical polishing influence the distribution and amplitude of residual stress in surface layers. In the case of CrN coating, a very high compressive stress was generated during the deposition process. The stress distributions determined by the MGIXD method is in good agreement with the classic sin2 technique results for all studied samples. In performing stress measurements for a powder sample, it was found that the application of the Göbel mirror in the incident beam strongly reduces statistical and misalignment errors. Additionally, the root mean square values of the third order lattice strain within diffracting grains were determined

Structural evolution of near-surface layers in NiTi alloy caused by an ion implantation

The results of X-ray diffraction studies on structural changes in the near-surface layers in the NiTi alloy caused by nitrogen-ion implantation with the energy E = 50 keV and the fluence D = 1018 cm-2 are presented. X-ray diffractometry, using the Philips diffractometer type X'Pert in the Bragg-Brentano geometry, was used to identify the phase composition of NiTi alloy. For layer by layer analysis of structural changes in the near-surface layers, the D8 Discover Bruker diffractometer with polycapilar beam optics was used. The ion-implanted NiTi alloy in the near-surface layer exhibits five phases: the dominating austenite phase, two martensitic phases and a small amount of the Ni4Ti3 and NTi phases. Along with the decreasing thickness of the near-surface layer investigated in material an increasing fraction of the Ni4Ti3 and NTi phases was observed. With the thickness of this layer about 340 nm, besides still existing the austenite, Ni4Ti3 and NTi phases, only one martensitic phase is present in the alloy. Further decrease of the thickness of the near-surface layer to about 170 nm leads to the increasing fraction of the Ni4Ti3 and NTi phases

Digital standardization of lean manufacturing tools according to Industry 4.0 concept

Standardization is a key element in the effective use of lean manufacturing methodologies and tools for achieving process sustainability. Their combination is conducive to eliminating waste and improving the efficiency of production processes and guarantees the company that employees use the most efficient tools and do not waste time on unnecessary activities. These activities can be further improved by using digital solutions, in accordance with the concept of Industry 4.0. Therefore, the authors have developed the e-Lean system, whose task is to digitize selected lean manufacturing tools. The subject of this work is analysis of the functionality and effectiveness of the essential part of the e-Lean system in the form of specialized TPM (Total Productive Maintenance) software as an application. During implementation in a construction production company, the TPM application was tested by lean manufacturing and maintenance specialists. The research consisted of assessing the functionality and efficiency of processes in relation to conventional TPM solutions. Additional functionalities of the e-Lean system have been confirmed, such as systemic approval of machinery inspection, which requires passing all necessary steps at individual inspection points, direct access for supervisors to the results of inspection activities and their status, direct and easy access to photographic documentation of machines added during inspection both in optimization of working time and its course (e.g., the optimal number of steps taken by the employee during the inspection), as well as an efficient system of motivating employees (collecting points). The improvement in the effectiveness of processes was determined by measuring the control times for three control points (polymerization furnace, packing area, and defibering machines). The average control time was reduced from 16,200 to 13,923 s. Thus, thanks to the use of the application, it was found that the efficiency of using the TPM tool was increased by approx. 15% compared to previously used non-digital solutions.The authors are grateful to FCT (Fundação para a Ciência e Tecnologia, Portugal) who partially financially supported this work through the RD Units Project Scope UIDP/04077/2020 and UIDB/04077/2020