This thesis aims to reveal the correlation between stress corrosion cracking propagation behavior and Schmid and Taylor factor mismatch using EBSD analysis. <div><br></div><div>Chloride induced stress corrosion cracking (CISCC) is one of the most vulnerable weaknesses for the widely used austenitic stainless steel in many industries. The complex nature of CISCC involves mechanical, electrochemical, and microstructural perspectives. The objective of this thesis is to assess CISCC phenomenon in austenitic stainless steel from the mechanical and crystallographic perspective, specifically on the effect of local strain and stress and anisotropic plastic deformation. Austenitic stainless steel 304L test coupons are bent in four-point bending fixtures to obtain tensile stress for CISCC, followed by corrosion experiment in boiling magnesium chloride solution. Stress state of the sample is evaluated by finite element analysis (FEA) and X-ray Diffraction Crystallography (XRD) prior corrosion test. Cross section of the cracked region are analyzed with Electron Backscatter Diffraction (EBSD) to analyze the relationship between CISCC behaviors and crystallographic features in the sample. Schmid factor and Taylor factor are used to quantitatively evaluate CISCC initiation and propagation behavior. It is learned that in polycrystalline FCC stainless steel, mismatch of Schmid factor and Taylor factor values in adjacent grains along crack path governs CISCC propagation susceptibility and path selection. Crack propagation factor competition model is proposed based on observations from EBSD maps, incorporating Schmid factor and Taylor factor mismatch, electrochemical condition of crack tip, and anisotropic properties. <br></div>

Detta examensarbete utfördes på Scania CV AB och behandlar delar i lastbilens avgassystem som utsätts för korrosion och nötning. Huvudmålet med detta arbete är att utveckla en provmetod för livslängdsundersökning av flexibla slangar. En serie tester utfördes för att förstå grundorsakerna till brott och en FE-analys utfördes för att verifiera resultaten till dessa prov. En stor del av den flexibla slangen blir stel på grund av höga avgastemperaturer och som leder till plastisk deformation av slangen. Men de tre första lindningarna som ligger närmast motorn behåller sin flexibilitet på grund av kontinuerliga motorvibrationer. Slutsatsen är att huvudorsaken som gör att de flexibla slangarna går av, är slitage som leder till sprickinitiering. Den sprickan sprider sig i form av lågcykelutmattning d.v.s att det tar ganska kort tid tills brott sker i den flexibla slangen. Korrosion initierar mellan de icke-flexibla delar av slangen Korrosionshastigheten ökar med tiden och det orsakar små hål på ytorna. Baserat på testresultaten är den mest lämpliga stället för livslängdsundersökningar Scanias komponentprovceller. Genom att mäta slitagedjupet under repeterbara förhållanden som rekommenderas i rapporten och med hjälp av data från kundutfall, kan en livslängd uppskattas. För att kunna förbättra livslängden för de flexibla slangarna, rekommenderas att använda rostfritt stål typ 1.4828 vid tillverkning av dessa slangar bör varmformning användas, samt att avståndet mellan lagrena respektive tjockleken ökas. Flera tester med olika teststidsintervall behöver göras för att ta reda på nötningshastigheten. / This thesis was conducted at Scania CV AB with information based on corrosion and wear. The main goal of this work is to develop a test method to investigate the stripwounded hose’s lifetime. A series of tests were performed to understand the reasons of their failure and a FE analysis was performed to verify the results obtained from these tests. It was observed that a large part of stripwounded hose becomes stiff due to high temperatures of the exhaust gas. The high temperature leads to plastic deformation of the hose. In contrast, the three first windings closest to the engine keep their flexibility due to continuously engine vibrations while there is sign of wear between the layers in these three windings more than other parts of the stripwounded hose. Hence, it is concluded that the main reason for stripwounded hose’s unpredictable failures is wear which leads to crack initiation. The crack propagation is in type of low cycle fatigue which means that it takes a short time until the stripewounded hose breaks. Corrosion is initiated between the non-flexible parts of the hose. The rate of corrosion is increased by time and causes small holes on the surfaces. According to results from the experiments the most suitable location for the lifetime investigation is Scania’s component test cells . Several tests with different time spans needs to be performed. By measuring the wear depth rate under repeatable test conditions and bycomparing with stripwounded hoses from customer trucks, a lifetime can be estimated. To improve the fatigue lifetime of the stripwounded hoses, it is recommended to use stainless steel of type 1.4828, manufactured through hot-forming with larger distance between layers and thicker layers to find out the wear rate.

No description available.

Two magnesium alloys (Mg-4Y-4Gd-2Ca and Mg-2Y-2Gd-1Ca) with high ignition tem- perature were successfully processed by extrusion. Mg-2Y-2Gd-1Ca alloy was addition- ally processed by equal channel angular pressing (ECAP) to achieve ultrafine-grained microstructure. The effect of extrusion parameters on fraction of recrystallized grains, grain size, and texture was revealed by EBSD analysis. The presence of Mg2Ca, REH2 and Mg5RE secondary phases was proven by SEM and TEM. Microstructural condition including distribution and morphology of secondary phase par- ticles directly affected the mechanical properties. Yield tensile stress exceeding 200 MPa was achieved in each condition. Large non-recrystallized grains with strong {10̄10} tex- ture resulted in a significant anisotropy in mechanical properties. Processing by ECAP led to a homogeneous microstructure with a mean grain size below 1 µm. ECAP condition showed superior mechanical properties with a low anisotropy. The developed and analysed microstructural condition resulted in favourable mechanical properties. The studied alloys are therefore promising for the application in aerospace industry. 1

No description available.

Title: Investigation of titanium alloys using neutron diffraction Author: Gergely Németh Department / Institute: Department of Physics of Materials Supervisor of the master thesis: prof. RNDr. Kristián Mathis, Ph.D., DrSc., Department of Physics of Materials Abstract: Titanium grade 2 was treated by multiple passes of the continuous equal- channel angular pressing technique (CONFORM ECAP) and, after each pass, additionally by rotary swaging. The residual strain field in samples processed by only CONFORM ECAP was studied by neutron diffraction strain scanning. In order to elucidate the microscopic background and calculate the related residual stress field, the local microstructure was thoroughly investigated by various experimental techniques. The microstructure and the deformation behavior of the rotary swaged samples was studied by transmission electron microscopy and by in-situ neutron diffraction during compression. The results of the analyses indicated that microstructural gradients were present in the material as the result of the inhomogeneous deformation during the CONFORM ECAP treatment. These gradients were identified as the main reason of the presence of residual stress fields. The distributions of stress fields calculated based on microstructural parameters were in correlation with simulation...

Предметом исследования является производство сортового проката высокого качества. Приведен литературный обзор, включающий в себя некоторые особенности производства сортового проката без дополнительных продольных усилий, описание влияния натяжения и/ил подпора на качество получаемого проката. Выполнена постановка задачи по моделированию прокатки полосы одновременно в трех клетях. Адекватность представленной модели показана путем сравнения результатов моделирования и показаний с действующего стана. Погрешность по формоизменению не превысила 0,4%, по моменту прокатки 11%, что является удовлетворительной сходимостью. На основе разработанной модели спланирован и выполнен расчетный эксперимент по влиянию рассогласования скоростей непрерывной прокатки на технологические параметры процесса. Получены уравнения регрессия описывающие закономерности влияния рассогласования скоростей прокатки на технологические параметры процесса. / The subject of the research is the production of high quality long products. A literature review is presented, which includes some features of the production of bars without additional longitudinal forces, a description of the effect of tension and/or back dam on the quality of the rolled products. The formulation of the problem of modeling rolling bar simultaneously in three stands is completed. The adequacy of the presented model is shown by comparing the simulation results and indications from the rolling mill. The error in the spreading did not exceed 0.4%, at the torque of rolling 11%, which is satisfactory convergence. Based on the developed model, a design experiment was planned and performed on the effect of the mismatch of continuous rolling speeds on the process parameters. The regression equations are obtained that describe the patterns of the influence of mismatch of rolling speeds on the technological parameters of the process.

Объектом исследования являются медь и малолегированные бронзы, подвергнутые интенсивной пластической деформации. Целью работы было определение текущего состояния научных исследований по использованию меди и малолегированных бронз. А также предложить состав и исследовать структуру и свойства бронзы выбранного состава после интенсивной пластической деформации методом динамического канально-углового прессования. В процессе работы проводился анализ литературных источников. В результате исследования было установлено текущее состояние по проблематике работы и определен вектор исследований. Методами оптической металлографии, дюрометрического анализа, просвечивающей электронной микроскопии и сканирующей электронной микроскопии с применением дисперсионно-энергетического анализа и анализа на основе обратного рассеяния электронов было проведено исследование сплава Cu-0,8 вес.% Hf. При различных обработках методом динамического канально-углового прессования. Эксперимент включал различное состояние бронзы перед деформированием. Также было проведено исследование термической стабильности полученных методом динамического канально-углового прессования образцов. Было установлено, что гафниевая бронза после прессования обладает высокими механическими характеристиками и ультрамелкодисперсной структурой. При этом полученная структура стабильна при комнатной температуре и при последующем отжиге вплоть до 400 °С. Что позволяет рекомендовать данный материал как основу для широкого спектра электротехнических изделий. / The object of research is copper and low-alloy bronzes after severe plastic deformation. The purpose of this work was to review scientific research on the use of copper and low-alloy bronzes. As well as the development of the composition and study of the structure and properties of bronze after severe plastic deformation by the method of dynamic channel-angular pressing had been carried out. Literature analysis was carried out. Methods of optical metallography, durometric analysis, transmission electron microscopy and scanning electron microscopy using energy dispersion analysis and analysis based on electron backscattering had been used to study the Cu-0.8 wt.% Hf alloy. Various processings had been carried out by the method of dynamic canal-angular pressing. The state of the bronze before deformation was variouse. We also studied the thermal stability of samples obtained by the method of dynamic channel-angular pressing. It was found that hafnium bronze after pressing has high mechanical characteristics and an ultrafine structure. In this case, the resulting structure is stable at room temperature and upon subsequent annealing up to 400 °C. That allows us to recommend this material as a basis for a wide range of electrical products.

Объект исследования – деформированные в результате интенсивной пластической деформации кручением под высоким давлением образцы на основе платины и алюминия. Цель работы – разработка технологии получения интерметаллида PtAl2 с последующим изучением микроструктуры и механических свойств полученных образцов. Методы исследования – проведение механосинтеза, изучение микроструктуры, измерение микротвердости. Результаты работы – методом кручения под высоким давлением из исходных металлических порошков получены образцы в виде пластин, содержащие интерметаллическую фазу. Образцы были исследованы в сканирующем электронном микроскопе и в рентгеновском дифрактометре. Произведены испытания микротвердости образцов. Рентгенофазовый анализ, показал наличие интерметаллида в продеформированных образцах. Новизна исследования состоит в способе получения интерметаллида PtAl2 путем механосинтеза при комнатной температуре (методом кручения под высоким давлением). Область применения – полученные результаты могут быть использованы при создании покрытий на основе интерметаллидов PtAl2 для авиастроения и машиностроения. / Subject of the research are samples based on platinum and aluminum and deformed by using high pressure torsion. The purpose of the work is to develop a technique to produce PtAl2 intermetallic compounds with subsequent study of the microstructure and mechanical properties of the obtained samples. Research methods: carrying out mechanical alloying, studying the microstructure, conducting mechanical hardness tests of samples. As a result of the research samples in the form of plates containing an intermetallic phase were obtained by high pressure torsion the starting metal powders. Samples were examined using a scanning electron microscope and an X-ray diffractometer. The microhardness of the samples was tested. X-ray phase analysis showed the presence of intermetallic in deformed samples. The novelty of the study is to obtain intermetallic using high pressure torsion. Application field: the obtained results can be used to create PtAl22 intermetallic compounds for aircraft and machine building.

В работе описаны процессы пластической деформации для наиболее распространённых металлов с ГПУ кристаллической решеткой, к числу которых относится титан, магний, цирконий. Рассматривается характеристика ГПУ металлов с точки зрения особенностей кристаллического строения и действующих механизмов пластической деформации, описана область применения. Описано поведение металлов с ГПУ решеткой при пластической деформации и при повышенных температурах, что накладывает требования к технологии производства изделий из данных металлов. Представлены основные условия текучести, применяемые для ортотропных металлов, отражающие различное поведение материала в разных направлениях. Методом конечных элементов выполнены расчеты и представлено сравнение параметров плоской прокатки циркониевого сплава Э125 при применении изотропного и ортотропного условий текучести. / The paper describes the processes of plastic deformation for the most common metals with an HCP crystal lattice, which include titanium, magnesium, and zirconium. The characteristics of HCP metals are considered from the point of view of the features of the crystal structure and the operating mechanisms of plastic deformation, and the scope is described. The behavior of metals with an HCP lattice under plastic deformation and at elevated temperatures is described, which imposes requirements on the technology for the production of products from these metals. The basic flow conditions used for orthotropic metals are presented, reflecting the different behavior of the material in different directions. The finite element method is used to perform calculations and compare the parameters of flat rolling of the E125 zirconium alloy using isotropic and orthotropic yield conditions.