[pt] Neste trabalho foram estudadas as modificações na resistência à fratura do aço grau R4, largamente adotado na fabricação de componentes estruturais para sistemas de ancoragem de unidades offshore, através de variações microestruturais. Após a fabricação industrial de elos de amarras, corpos de prova para ensaios de tração e CTOD foram usinados do material. A primeira etapa do procedimento experimental consistiu em tratamentos térmicos de têmpera e revenido, com diferentes temperaturas de austenitização (860, 880, 900, 920 e 940(graus)C) e mantendo-se fixa a temperatura de revenido (680(graus)C). Com base nos resultados de CTOD de carga máxima apresentados pelo material, passou-se para a segunda etapa experimental, na qual foi adotada a temperatura de austenitização admitida como ótima na primeira etapa (900(graus)C) e variando-se as temperaturas de revenido (650, 660, 670, 680, 690 e 700(graus)C). Na primeira etapa, os resultados demonstraram que, com o aumento da temperatura de austenitização (860, 880 e 900(graus)C), houve um aumento da resistência à fratura do material. No entanto, os valores praticamente não variaram a partir das temperaturas mais altas (920 e 940(graus)C). Na segunda etapa, os valores do CTOD aumentaram com o aumento da temperatura de revenido, atingindo um valor máximo a 680 (graus)C. Para temperaturas superiores (690 e 700(graus)C) a tenacidade do material sofreu uma pequena redução. As variações da tenacidade do aço grau R4, em ambas as etapas experimentais, foram associadas com as microestruturas obtidas nos respectivos tratamentos térmicos. / [en] A study has been made concerning changes in the fracture resistance of the grade R4 steel, largely used for manufacturing offshore mooring structural components, due to microstrutural variations. After the industrial manufacturing of chain links, specimens for tensile and CTOD tests were machined from the material. The first part of the experimental procedure was related to quenching and tempering heat treatments making use of different austenizing temperatures (860, 880, 900, 920 and 940(Degrees)C) and tempering at a given temperature (680(Degrees)C). On the basis of the CTOD at the maximum load presented by the material, the second experimental part was started, in which the optimal austenitizing temperature obtained in the first part (900(Degrees)C) was adopted and different tempering temperatures (650, 660, 670, 680, 690 and 700(Degrees)C) were selected. According to the CTOD testing carried out during the first experimental part, the fracture resistance of the material has increased when increasing the austenitizing temperature (860, 880 and 900(Degrees)C). However, the material`s toughness did not change significantly when quenching from the highest temperatures (920 and 940(Degrees)C). In the second experimental part, the CTOD values increased when increasing the tempering temperature, reaching a maximum value for 680(Degrees)C. Concerning the highest temperatures (690 and 700(Degrees) C) the fracture resistance of the material presented a slight reduction. The changes in the fracture resistance of the grade R4 steel, in both experimental parts, were associated with the microstrutural characteristics of the heat treatments.

O aço SAE/AISI 52100 é utilizado para a fabricação de rolamentos como também na fabricação de outras peças e dispositivos como cames de eixo comando de válvulas. Um dos problemas desta liga é a necessidade de revenimentos em temperaturas muito baixas para obtenção de alta dureza e para evitar o fenômeno da fragilização da martensita revenida (FMR), em detrimento da tenacidade. Foi projetada uma nova liga Fe-C-Mn-Si-Cr (AISI/SAE 52100 modificado com 1,74% de Si e 0,96% de Mn) baseada na mesma ideia do aço 300M em relação ao SAE/AISI 4340. O efeito do Si na cinética de precipitação da cementita retarda a fragilização da martensita revenida (FMR), além de aumentar a dureza e mantê-la com valores relativamente altos mesmo quando do revenimento em temperaturas mais altas. A proposta do presente trabalho foi comprovar a resistência desta nova liga frente à FMR e demonstrar a resistência ao amolecimento perante o revenimento (curvas de revenimento). Com o intuito de estudar o efeito do Si na dureza do novo aço, foram elaboradas curvas de revenimento medindo-se essa propriedade em amostras do novo aço e do aço comercial após têmpera em temperaturas de austenitização na faixa de 825ºC e 960ºC, seguida por tratamento criogênico em nitrogênio líquido (-196ºC) durante doze horas e revenidas em temperaturas na faixa de 250ºC a 500ºC. Foram obtidas durezas acima de 60HRC, sendo que o aço modificado chegou a tingir 68HRC, no estado temperado. Foi estudada também a resistência ao amolecimento da nova liga e do aço comercial submetendo amostras em temperaturas constantes na faixa de 350ºC a 450ºC, variando-se o tempo na faixa de uma a dez horas. O aço modificado, após 10 horas em 450ºC, apresentou ainda, dureza de 58HRC. Para determinação das propriedades mecânicas desta nova liga foram realizados ensaios de tração em amostras temperadas e revenidas, comparativamente ao aço SAE/AISI 52100 comercial. Para a realização do estudo da FMR, foram comparados resultados dos ensaios de impacto para o aço SAE/AISI 52100 comercial (0,25%Si) e modificado (1,74%Si). O aço modificado não apresentou o fenômeno da FMR. Foram analisados aspectos microestruturais por meio de microscopia eletrônica de varredura (MEV) e difração de raios-x. / The SAE/AISI 52100 steel is used for bearing manufacturing and automotive parts like camshafts lobes. A problem with this alloy is the need for low tempering temperature in order to obtain high hardness and to avoid the tempered martensite embrittlement phenomena, compromising the toughness. Based on the same idea as 300M steel regarding SAE/AISI 4340 steel, a new Fe-C-Mn-Si-Cr bearing alloy (AISI 52100 steel, modified with 1.74% Si and 0.96%Mn) was developed. The effect of Si on the kinetics of cementite precipitation leads to a higher temperature of tempered martensite embrittlement (TME) occurrence and keep high hardness values even when the steel is submitted to a higher temperatures tempering or for long time. The purpose of this work was to confirm the new alloy tempered martensite embrittlement (TME) resistance and to verify its softening resistance (tempering curves). Intending to investigate the Si effect on new steel hardness, hardness measurements were performed on modified and commercial steels samples after 825ºC 960ºC austenitization, twelve hours -196ºC cryogenic treatment and 250ºC 500ºC tempering. It was obtained hardness values over 60HRC and the modified steel presented 68HRC as quenched. The new alloy and commercial alloy softening resistance was studied by hardness measurement on samples submitted to 350ºC 450ºC constant temperature tempering in periods of time from one to ten hours. The Si alloyed steel presented 58HRC after 10 hours at 450ºC. For the mechanical characterization of the new alloy, tensile tests were performed in quenched and tempered samples. In the tempered martensite embrittlement study, impact tests results for commercial SAE/AISI 52100 (0.25%Si) and modified (1.74%Si) were compared. The modified steel presented no tempered martensite embrittlement. Microstructural aspects were studied by scanning electron microscopy and x-ray diffraction analysis.

The Diploma thesis deals with the verification of Jominy end-quench test when analysis of hardenability of aluminium alloys is considered. The problem was solved experimentally, by developing end-quench curves of selected grades of aluminium alloys. Degree of hardenability of alloy is hardness after complete strengthening heat treatment. Samples of aluminium alloys commonly used for aircraft structures were prepared and then subjected to end-quench tests in various quenchants. On the basis of performed experiments, suitability of Jominy end-quench test for comparison of hardenability of alloys was found. Part of the thesis deals with the creation of equivalent cooling rate diagrams using the developed end-quench curves.

The aim of this thesis is influence of precipitation hardening regime, specifically quench rate, on mechanical properties of aluminium alloy A356 (AlSi7Mg0.3). Samples were after solution treatment quenched into water with different temperatures and age hardened. Tensile strength tests, hardness tests and microstructure observations were done after heat tretment.

Cette thèse porte sur l'étude de systèmes quantiques à N-corps à température nulle, où le comportement du système n'est alors soumis qu'aux effets quantiques. Je vais présenter ici une approche variationnelle développée avec Tommaso Roscilde, mon directeur de thèse, et Fabio Mezzacapo, mon co-encadrant de thèse, pour étudier ces systèmes.Cette approche se base sur une parametrisation de l’état quantique (dit Ansatz) à laquelle on applique une procédure d’optimisation variationnelle lui permettant de reproduire l'évolution d'un système soumis à l'équation de Schrödinger, tout en limitant le nombre de variables considérées. En considérant une évolution en temps imaginaire, il est possible d'étudier l'état fondamental d'un système. Je me suis ainsi intéressé à un modèle de chaîne XX de spins 1/2, dont les corrélations à longue portée rendent l'étude difficile, et adapté ainsi notre approche pour reproduire au mieux les corrélations et l'intrication du système. Je me suis ensuite intéressé au modèle J1-J2 dont la structure de signe non positive des coefficients de l’état quantique pose un défi important pour les approches Monte Carlo; et dans laquelle la frustration magnétique induit une transition de phase quantique (d’un état aux corrélations à longue porté vers un état non magnétique avec formation d’un cristal de lien de valence). Je me suis enfin intéressé à l'évolution temporelle d'un système à N-corps à partir d'un état non stationnaire. J'ai pu étudier la capacité de notre approche à reproduire la croissance linéaire de l’intrication dans le temps, ce qui est un obstacle fondamental pour les approches alternatives telles que le groupe de renormalisation de la matrice densité. / This thesis presents a study of quantum many-body systems at zero temperature, where the behavior of the system is purely driven by the quantum effects. I will introduce a variationnal approach developped with Tommaso Roscilde, my PhD supervisor, and Fabio Mezzacapo, my co-supervisor, in order to study these systems.This approach is based on a parametrisation of the quantum state (named Ansatz) on which we apply a variational optimisation, allowing us reproduce the system's evolution under Schrödinger's equation with a limited number of variables.By considering an imaginary-time evolution, it is possible to reconstruct the system's ground state. I focused on S=1/2 XX spin chain, where the long-range quantum correlations complicate a variational study; and I have specifically targeted our Ansatz in order to reproduce the correlations and the entanglement of the ground state. Moreover I considered the antiferromagnetic S=1/2 J1-J2 spin chain, where the non-trivial sign structure of the coefficients of the quantum state introduces an important challenge for the quantum Monte Carlo approach; and where the magnetic frustration induces a quantum phase transition (from a state with long range correlations to a non-magnetic state in the form of a valence-bond crystal).Finally I focused on the time evolution of a quantum many-body system starting from a non-stationary state. I studied the ability of our approach to reproduce the linear increase of the entanglement during time, which is a fondamental obstacle for other approaches such as the density-matrix renormalization group.

A têmpera, que consiste no resfriamento rápido do aço, após austenitização, é um dos tratamentos térmicos mais utilizados. O objetivo desse tratamento é a obtenção da estrutura martensítica, que oferece ótimas propriedades de dureza e resistência. A água, as soluções de polímeros e os óleos minerais são os meios refrigerantes mais comuns, sendo os óleos responsáveis pelo resfriamento em 80% dos casos. Verificou-se, no Brasil, o desconhecimento, dos mercados produtor e consumidor, quanto ao universo dos óleos de têmpera comercialmente disponíveis e de suas respectivas características de resfriamento. Assim, atentou-se para a necessidade de apresentar aos mercados já descritos, uma classificação dos óleos de têmpera nacionais,relacionando-os como rápidos, intermediários e lentos, destacando ainda, aspectos importantes nos parâmetros de resfriamento. / Quenching of steels, which consist of very fast cooling from austenitizing temperatures, is the most used heat treatment. The aim of this treatment is the obtation of martensitic microstructure. This microstructure confer excellent hardness and strength properties. The most common quenchants are water, polymer solutions and mineral oils, and the oils themselves are responsible by the 80% of the quenchants used during quenching. In Brazil, it was verified consumer lack of knowledge of the oils available as quenchants and their characteristics. Therefore, in this work as attempt was made to present the quenchants available and their classification as fast, intermediary and slow quenchants.

"The quench sensitivity of AA7136 has been experimentally investigated using Jominy end quench and test coupons of various heat treatments. It was found that this alloy is not quench sensitive. In addition, the effects of heating rate on both solution and aging treatments on AA7136 and AA7075 were determined using a newly developed reverse Jominy heating test. It was observed that hardness was reduced after rapid heating during aging and hardness increased slightly after rapid heating during solutionizing. These results are discussed in terms of microstructural developments. "

"The effects of heat treating process parameters on the microstructure, residual stress, and distortion of a vacuum carburized, quenched and cold treated ring gear made of Pyrowear 53 has been determined using Abaqus and DANTE software. The data from these finite element method simulations was compared to measured values from physical testing. It was found that the heat treating process of the ring gear could be simulated and provide similar results to the measured and specified values for hardness, carbon content, and distortion. The simulations and distortion in this paper provide a detailed view of the mass transfer, heat transfer, and stress that occur during heat treating. These simulations suggest nonuniform cooling of a ring gear leads to greater distortion than uniform cooling. Simulations compared the retained austenite and hardness in ring gears that were oil quenched and high pressure gas quenched."

A 6061 aluminum probe was quenched with the CHTE probe-quenching system in distilled water while varying bath temperature and the level of agitation. Time vs. temperature data was collected during the quench by use of an ungrounded K-type thermocouple embedded inside the probe. Cooling rates and heat transfer coefficients, h, were calculated and Quench Factor Analysis (QFA) was also performed to quantitatively classify the quench severity. The data showed an increase in both maximum cooling rate and heat transfer coefficient and a decrease in the Quench Factor, Q, as bath temperature decreased and agitation level increased. Maximum heat transfer coefficient values ranged from 1000 W/m2K to 3900 W/m2K while maximum cooling rates of 50¡ÃƒÂ£C/s to 190¡ÃƒÂ£C/s were achieved. In addition, it was found that at higher levels of agitation, there was also an increase in the variation (i.e. standard deviation) of the cooling rate and therefore h and Q.

Phase transitions and their associated critical phenomena are of fundamental importance and play a crucial role in the development of statistical physics for both classical and quantum systems. Phase transitions embody diverse aspects of physics and also have numerous applications outside physics, e.g., in chemistry, biology, and combinatorial optimization problems in computer science. Many problems can be reduced to a system consisting of a large number of interacting agents, which under some circumstances (e.g., changes of external parameters) exhibit collective behavior; this type of scenario also underlies phase transitions. The theoretical understanding of equilibrium phase transitions was put on a solid footing with the establishment of the renormalization group. In contrast, non-equilibrium phase transition are relatively less understood and currently a very active research topic. One important milestone here is the Kibble-Zurek (KZ) mechanism, which provides a useful framework for describing a system with a transition point approached through a non-equilibrium quench process. I developed two efficient Monte Carlo techniques for studying phase transitions, one is for classical phase transition and the other is for quantum phase transitions, both are under the framework of KZ scaling. For classical phase transition, I develop a non-equilibrium quench (NEQ) simulation that can completely avoid the critical slowing down problem. For quantum phase transitions, I develop a new algorithm, named quasi-adiabatic quantum Monte Carlo (QAQMC) algorithm for studying quantum quenches. I demonstrate the utility of QAQMC quantum Ising model and obtain high-precision results at the transition point, in particular showing generalized dynamic scaling in the quantum system. To further extend the methods, I study more complex systems such as spin-glasses and random graphs. The techniques allow us to investigate the problems efficiently. From the classical perspective, using the NEQ approach I verify the universality class of the 3D Ising spin-glasses. I also investigate the random 3-regular graphs in terms of both classical and quantum phase transitions. I demonstrate that under this simulation scheme, one can extract information associated with the classical and quantum spin-glass transitions without any knowledge prior to the simulation.