Dual-phase (DP) steels consisting of a ferrite matrix with dispersed martensite particles have attracted a significant interest due to their combination of high work hardening and ductility. A great deal of experimental work has been done to obtain a better comprehension of the relation of their mechanical behaviour to their microstructural characteristics. In the present work, a micromechanical study of ferrite-martensite DP steels is conducted. The deformation of ferrite is described by a rate-dependent crystal plasticity theory, which relates the stress-strain field equations on the grain level to the macroscopic behaviour of the material. The crystal plasticity theory assumes that slip is the only deformation mechanism. Martensite, on the other hand, is considered an elastic-plastic isotropic solid. The interfaces of the grains are taken into account through an idealized form of grain boundaries. A FORTRAN program was coupled with the finite element method to solve the stress equations of the crystal plasticity. Including the grain boundaries made it possible to examine the effect of ferrite grain size on the strength of the material. It is shown that by decreasing the grain size, the yield stress increases according to Hall-Petch equation. Additionally, the effects of the volume fraction of martensite (Vm) on the onset strain, i.e. the strain at which martensite deforms plastically, and of the distribution of martensite on the stress are studied. The former showed that the onset strain of the DP steel declines linearly with increasing Vm up to 36%, beyond which the onset strain becomes independent of V m. The latter revealed that when martensite particles are formed as islands in the ferrite grains, the material exhibits higher strength and hardening rate; compared to when martensite is distributed as large blocks among the ferrite grains.

No description available.

by Ng, Hiu Tung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 121-123). / by Ng, Hiu Tung. / Acknowledgement --- p.i / Abstract --- p.ii / Table of Contents --- p.iv / List of Figures --- p.viii / List of Tables --- p.xi / Chapter Chapter One --- Introduction --- p.1 / Chapter 1.1 --- Non-destructive testing techniques --- p.2 / Chapter 1.1.1 --- Liquid penetration technique --- p.2 / Chapter 1.1.2 --- Electrical methods (Eddy current testing) --- p.3 / Chapter 1.1.3 --- Ultrasonic testing --- p.4 / Chapter 1.1.4 --- Radiography --- p.5 / Chapter 1.1.5 --- Magnetic methods --- p.6 / Chapter 1.2 --- The development of Barkhausen and magnetoacoustic emissions --- p.7 / Chapter 1.2.1 --- Barkhausen emission --- p.7 / Chapter 1.2.2 --- Magnetoacoustic emission --- p.8 / Chapter 1.3 --- The advantages of using Barkhausen and magnetoacoustic emission over the other nondestructive techniques --- p.10 / Chapter Chapter Two --- Fundamental concept in ferromagnetic materials --- p.12 / Chapter 2.1 --- Ferromagnetism --- p.12 / Chapter 2.1.1 --- Curie point --- p.13 / Chapter 2.1.2 --- Hysteresis loop --- p.14 / Chapter 2.2 --- Magnetic domains --- p.17 / Chapter 2.2.1 --- Magneto static energy --- p.17 / Chapter 2.2.2 --- Structure of domain wall --- p.19 / Chapter 2.2.3 --- Domain wall motion --- p.21 / Chapter 2.2.4 --- Domain nucleation --- p.22 / Chapter 2.3 --- Magnetostriction --- p.28 / Chapter 2.3.1 --- Spontaneous magnetostriction --- p.28 / Chapter 2.3.2 --- Saturation magnetostriction --- p.29 / Chapter 2.3.3 --- Field-induced magnetostriction --- p.29 / Chapter 2.3.4 --- Magnetostriction of polycrystalline --- p.30 / Chapter 2.4 --- Effect of stress on magnetic properties --- p.36 / Chapter 2.4.1 --- Stress --- p.36 / Chapter 2.4.2 --- Effect of stress on the magnetization --- p.37 / Chapter 2.4.3 --- Effect of stress on the magnetostriction --- p.38 / Chapter 2.5 --- Eddy current shielding --- p.41 / Chapter Chapter Three --- Barkhausen emission and magnetoacoustic emission --- p.42 / Chapter 3.1 --- Barkhausen emission --- p.42 / Chapter 3.1.1 --- The wall potential energy model of Barkhausen emission --- p.43 / Chapter 3.1.2 --- Typical BE profiles --- p.45 / Chapter 3.2 --- Magnetoacoustic emission --- p.48 / Chapter 3.2.1 --- Magnetoacoustic emission model --- p.48 / Chapter 3.2.2 --- Typical MAE profiles --- p.50 / Chapter Chapter Four --- Instrumentation --- p.52 / Chapter 4.1 --- Introduction --- p.52 / Chapter 4.2 --- Experimental setup for Barkhausen emission --- p.53 / Chapter 4.3 --- Experimental setup for magnetoacoustic emission --- p.56 / Chapter 4.4 --- Specimen treatment --- p.58 / Chapter 4.4.1 --- Furnace --- p.58 / Chapter 4.4.2 --- Instron loading machine --- p.60 / Chapter 4.4.3 --- Optical microscopy --- p.60 / Chapter 4.4.4 --- Vicker's hardness tester --- p.61 / Chapter Chapter Five --- Effect of field frequency and strength on Barkhausen emission in mild steel and nickel --- p.66 / Chapter 5.1 --- Introduction --- p.66 / Chapter 5.2 --- Experiments --- p.67 / Chapter 5.3 --- Results and discussions --- p.68 / Chapter 5.4 --- Conclusions --- p.76 / Chapter Chapter Six --- Effect of residual stress on Barkhausen and magnetoacoustic emissions in steel bar --- p.77 / Chapter 6.1 --- Introduction --- p.77 / Chapter 6.2 --- Experiments --- p.81 / Chapter 6.3 --- Results and discussions --- p.84 / Chapter 6.3.1 --- BE profiles --- p.84 / Chapter 6.3.2 --- MAE profiles --- p.85 / Chapter 6.3.3 --- Optical microscopy and hardness measurements --- p.85 / Chapter 6.4 --- Conclusions --- p.92 / Chapter Chapter Seven --- Effect of residual stress on Barkhausen and magnetoacoustic emissions in a nickel bar --- p.93 / Chapter 7.1 --- Introduction --- p.93 / Chapter 7.2 --- Experiments --- p.96 / Chapter 7.3 --- Results and discussions --- p.97 / Chapter 7.3.1 --- Hardness and optical microscopy measurement --- p.97 / Chapter 7.3.2 --- BE profiles --- p.98 / Chapter 7.3.3 --- MAE profiles --- p.99 / Chapter 7.4 --- Comparison of nickel and mild steel --- p.106 / Chapter 7.5 --- Conclusions --- p.108 / Chapter Chapter Eight --- Effect of dynamic stress on Barkhausen emission in mild steel --- p.109 / Chapter 8.1 --- Introduction --- p.109 / Chapter 8.2 --- Experiments --- p.110 / Chapter 8.3 --- Results and discussions --- p.112 / Chapter 8.4 --- Conclusions --- p.118 / Chapter Chapter Nine --- Conclusions --- p.119 / References --- p.121

Orientador: Itamar Ferreira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-07-23T02:11:36Z (GMT). No. of bitstreams: 1 Martins_JairoAparecido_M.pdf: 6076848 bytes, checksum: 742363d8456eadb728338e42b630e9bd (MD5) Previous issue date: 1997 / Resumo: Atualmente, grandes esforços tem sido direcionados no sentido de se obter aços de baixo custo, com rnicroestruturas que proporcionem as melhores combinações de propriedades mecânicas, sobretudo aquelas relacionadas com fadiga em alto ciclo. Este trabalho tem como objetivos analisar as propriedades mecânicas monotônicas e cíclicas do aço API 5L X65 ¿ aço de baixo teor de carbono e microligado com titânio e nióbio-, em duas condições microestruturais distintas; a primeira na condição como fornecida (CF) e a segunda na condição tratada termicamente (T77) (normalizada a 1193K + tratada na região intercrítica a 1043 K e resfriado em óleo a uma taxa de 30 'Ks POT. ¿1¿). A primeira condição analisada, como fornecida (CF) apresentou microestrutura ferrítico-perlítica (84,9% de ferrita para 15,1% de perlita) enquanto a segunda condição (T77) apresentou microestrutura ferrítico-martensítica (82,7% de ferrita para 17,3% de martensita). Foram analisadas as propriedades de tração ('sigma¿ IND. t ), limite de escoamento ('sigma¿ IND. e) redução de área (RA) e o limite de resistência à fadiga ('S IND. f¿) para as duas condições. Verificou-se um aumento do limite de resistência à tração em 14% (de 615 MPa para 800 MPa),uma diminuição de 38% no limite de escoamento (de 530 MPa para 328 MPa), um alongamento de 8,6%, uma redução de área de 17,6% e uma diminuição do limite de resistência à fadiga de 20% (de 372 MPa para 300 MPa) com o tratamento térmico realizado. As fractografias das superfícies de fratura dos corpos de prova ensaiados à fadiga apresentaram-se muito similares, sendo que as estrias de fadiga foram mais evidentes para a condição T77 / Abstract: Nowadays, there is a significantresearch efforts in terms of obtaining economical steels with microstructure resulting in good mechanical property combinations, chief1yhigh fatigue properties. The purpose of this work is to analyze the monotonic and mechanical properties of the API 5L X65 steel, a titanium and niobium microalloyed low carbon steel, in two different microstructural conditions. The first in as received condition (CF) and the second heat treated (T77) (normalized in 1193K+ treated in intercritical region to 1043K and cooled in oil, a rate of 30 'Ks POT. ¿1¿). The CF condition presented a ferritic- perlitic microstruture (84.9% offerrite and 15% of perlite) while the T77 condition presented a ferritic-martensitic microstuture (82,7% of ferrite and 17,3% of martensite). The properties as tensile strength (S IND. u), reduction in area (RA), yield strength ('S IND.y¿) and endurance limit ('S IND. f¿) were analyzed for both conditions CF and T77. There were an increase in tensile strength of 14% (from 615 MPa to 800 MPa), a decrease in yield strength of 38% (from 530 MPa to 328 MPa), an elongation of 8.6%, a reduction in area of 17,6% and a decrease in endurance limit of 20% (from 372 MPa to 300 MPa) with the heat treatment applied. The fractografies of fracture surface were so similars, mean while in T77 condition the fatigue striations were more visible / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Orientador: Rezende Gomes dos Santos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-19T02:19:58Z (GMT). No. of bitstreams: 1 Zuppo_RicardoModesto_M.pdf: 3596508 bytes, checksum: bf0ebfecc1342011718b632b2d65c250 (MD5) Previous issue date: 2011 / Resumo: O objetivo deste trabalho é analisar a possibilidade de substituição do tratamento térmico de têmpera e revenimento pelo tratamento térmico de austêmpera, seguido ou não de conformação plástica a frio, na fabricação de barras laminadas do aço SAE 4140H. A temperatura de austenitização, para ambos os tratamentos, foi de 850ºC, com tempo de encharque de uma hora e quarenta e cinco minutos. Foram utilizados, para o tratamento térmico de austêmpera, temperaturas de 420; 360 e 340ºC, com tempo de encharque de uma hora, com o objetivo de se obter transformação de fase completa da austenita em bainita. Para a etapa de revenimento, das amostras inicialmente temperadas, foram utilizadas as mesmas temperaturas da austêmpera. Foram estudados aspectos microestruturais por meio de análise micrográfica (microscopia óptica) e microscopia eletrônica de varredura (MEV). As propriedades mecânicas foram analisadas por meio de ensaios de dureza, tração e impacto sendo, também, estudado o micromecanismo de fratura dos corpos-de-prova de impacto. Foi realizada uma análise comparativa dos resultados obtidos visando estabelecer os procedimentos que levam a um melhor conjunto de propriedades para determinadas aplicações / Abstract: The purpose of this work is to analyse the possibility of substitution of the heat treatment of quench followed by tempering by the austempering, followed or not by cold forming, to produce rolled bars of SAE 4140H. The temperature of austenitizing, for both treatments, was 850ºC, with soaking time of one hour and forty-five minutes. For the heat treatment of austempering, temperatures of 420, 360 and 340ºC have been used, with the soaking time of one hour, with the purpose of obtaining the complete phase transformation of the austenite in bainite. For the tempering, the same temperatures of austempering have been used. Microstructure aspects based on micrographic analysis (optic microscopy) and scanning electronic microscopy (SEM) have been studied. The mechanical properties have been analysed based on tests of hardness, tension and impact and the fracture micromechanism of the impact test specimen was also studied. A comparative analysis of the obtained results was done in order to establish the proceedings that lead to a better group of properties for determined applications / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

The mechanical behavior of structural materials used in nuclear applications is significantly degraded as a result of irradiation, typically characterized by an increase in yield stress, localization of inelastic deformation along narrow dislocation channels, and considerably reduced strains to failure. Further, creep rates are accelerated under irradiation. These changes in mechanical properties can be traced back to the irradiated microstructure which shows the formation of a large number of material defects, e.g., point defect clusters, dislocation loops, and complex dislocation networks. Interaction of dislocations with the irradiation-induced defects governs the mechanical behavior of irradiated metals. However, the mechanical properties are seldom systematically correlated to the underlying irradiated microstructure. Further, the current state of modeling of deformation behavior is mostly phenomenological and typically does not incorporate the effects of microstructure or defect densities. The present research develops a continuum constitutive crystal plasticity framework to model the mechanical behavior and deformed microstructure of bcc ferritic/martensitic steels exposed to irradiation. Physically-based constitutive models for various plasticity-induced dislocation migration processes such as climb and cross-slip are developed. We have also developed models for the interaction of dislocations with the irradiation-induced defects. A rate theory based approach is used to model the evolution of point defects generated due to irradiation, and coupled to the mechanical behavior. A void nucleation and growth based damage framework is also developed to model failure initiation in these irradiated materials. The framework is used to simulate the following major features of inelastic deformation in bcc ferritic/martensitic steels: irradiation hardening, flow localization due to dislocation channel formation, failure initiation at the interfaces of these dislocation channels and grain boundaries, irradiation creep deformation, and temperature-dependent non-Schmid yield behavior. Model results are compared to available experimental data. This framework represents the state-of-the-art in constitutive modeling of the deformation behavior of irradiated materials.

The research objectives of this thesis are as follows: (1) Investigate the effects of carbon content, alloying, and heat treatment of steels on white layer formation, (2) Prove/disprove that the temperature for phase transformation in machining is the same as the nominal phase transformation temperature of the steel, (3) Quantify the contributions of thermal and mechanical effects to white layer generation in machining, (4) Develop a semi-empirical procedure for prediction of white layer formation that accounts for both thermal and mechanical effects. These research objectives are realized through experimental and modeling efforts on steels. Depth and hardness measurements of the white layers formed in steels show the importance of heat treatment and carbon content on white layer formation. Measurements of workpiece surface temperature and X-Ray Diffraction characterization of the machined surfaces show that phase transformation occurs below the nominal As temperature suggesting that mechanical effects play an important role in white layer formation. The maximum workpiece surface temperature, the effective stress, and plastic strain on the workpiece surface are measured and/or calculated and shown to affect the white layer depth and amount of retained austenite. A semi-empirical procedure is developed by correlating the maximum workpiece temperature and the unit thrust force increase with white layer formation.

Capes / Neste trabalho estudou-se a influência de parâmetros de rugosidade e propriedades mecânicas de um aço AISI H13 no coeficiente de atrito estático, ensaiado no sistema plano inclinado. Como contra corpo foi utilizado um recobrimento de cromo duro, considerado idealmente liso. O coeficiente de atrito foi relacionado com a área real de contato, tendo como dados de entrada parâmetros de rugosidade bidimensionais. A rotina de cálculo proposta por McCool (1987) foi aplicada para obtenção de uma estimativa de área de contato, utilizando os parâmetros Rq (rugosidade média quadrática) e RDq (inclinação média quadrática). Foram estudados três conjuntos de amostras, com acabamento superficial produzido por retificação plana e durezas distintas, produzidas por tratamentos térmicos aos corpos de prova. A variação da dureza foi obtida por meio de diferentes temperaturas de duplo revenimento: 540, 600 e 640 °C. Os ensaios de plano inclinado foram conduzidos em uma velocidade de 0,33°/s e uma carga aplicada produzida pelo peso próprio da amostra. Um sensor de movimento é acoplado ao equipamento para detectar o início do deslizamento e permitir a medida de ângulo neste instante. Para análise dos resultados, cada conjunto de amostras foi considerado como sendo diferente em função do tratamento térmico. Além disso, subconjuntos de amostras foram distinguidos em função do parâmetro Rq, por se tratar de um parâmetro médio e que é utilizado diretamente no cálculo da área real de contato. Dessa forma, para cada condição metalúrgica, pode-se verificar a variação do coeficiente de atrito estático com as propriedades mecânicas e superficiais. Foi verificado que, a dureza não apresentou influência no coeficiente de atrito estático, porem, a combinação das propriedades mecânicas e superficiais representada pelo índice de plasticidade apresenta uma relação direta. / In this work was studied the influence of roughness parameters and mechanical properties of the steel AISI H13 in the coefficient of static friction tested in the inclined plane method. The counterbody used was a coating of hard chrome, considered ideally smooth. The coefficient of friction was related to the real area of contact, taking as input bi-dimensional roughness parameters. The routine calculation proposed by McCool (1987) was applied to obtain an estimate of contact area, using the parameters Rq (root mean square roughness) and Rdq (mean square slope). Three sets of samples were studied, with surface finish produced by grinding flat and different hardness, produced by heat treatments to the samples. The variation of hardness was obtained by different double tempering temperatures: 540, 600 and 640 ° C. The inclined plane tests were conducted at a speed of 0.33 °/s and an applied load produced by the self weight of the body. A motion sensor is attached to the equipment to detect the onset of slip and allow the measure of angle instantly. To analyze the results, each set of samples was considered different depending on the heat treatment. In addition, subsets of samples were distinguished in accordance with Rq parameter, because it is an average parameter and it is used directly to calculate the real area of contact. Thus, for each metallurgical condition was possible to see, the variation of the coefficient of static friction with mechanical and surface properties. It was verified that the hardness had no effect on the coefficient of static friction, however, the combination of mechanical and surface properties represented by the plasticity index has a direct relationship.

Capes / Neste trabalho estudou-se a influência de parâmetros de rugosidade e propriedades mecânicas de um aço AISI H13 no coeficiente de atrito estático, ensaiado no sistema plano inclinado. Como contra corpo foi utilizado um recobrimento de cromo duro, considerado idealmente liso. O coeficiente de atrito foi relacionado com a área real de contato, tendo como dados de entrada parâmetros de rugosidade bidimensionais. A rotina de cálculo proposta por McCool (1987) foi aplicada para obtenção de uma estimativa de área de contato, utilizando os parâmetros Rq (rugosidade média quadrática) e RDq (inclinação média quadrática). Foram estudados três conjuntos de amostras, com acabamento superficial produzido por retificação plana e durezas distintas, produzidas por tratamentos térmicos aos corpos de prova. A variação da dureza foi obtida por meio de diferentes temperaturas de duplo revenimento: 540, 600 e 640 °C. Os ensaios de plano inclinado foram conduzidos em uma velocidade de 0,33°/s e uma carga aplicada produzida pelo peso próprio da amostra. Um sensor de movimento é acoplado ao equipamento para detectar o início do deslizamento e permitir a medida de ângulo neste instante. Para análise dos resultados, cada conjunto de amostras foi considerado como sendo diferente em função do tratamento térmico. Além disso, subconjuntos de amostras foram distinguidos em função do parâmetro Rq, por se tratar de um parâmetro médio e que é utilizado diretamente no cálculo da área real de contato. Dessa forma, para cada condição metalúrgica, pode-se verificar a variação do coeficiente de atrito estático com as propriedades mecânicas e superficiais. Foi verificado que, a dureza não apresentou influência no coeficiente de atrito estático, porem, a combinação das propriedades mecânicas e superficiais representada pelo índice de plasticidade apresenta uma relação direta. / In this work was studied the influence of roughness parameters and mechanical properties of the steel AISI H13 in the coefficient of static friction tested in the inclined plane method. The counterbody used was a coating of hard chrome, considered ideally smooth. The coefficient of friction was related to the real area of contact, taking as input bi-dimensional roughness parameters. The routine calculation proposed by McCool (1987) was applied to obtain an estimate of contact area, using the parameters Rq (root mean square roughness) and Rdq (mean square slope). Three sets of samples were studied, with surface finish produced by grinding flat and different hardness, produced by heat treatments to the samples. The variation of hardness was obtained by different double tempering temperatures: 540, 600 and 640 ° C. The inclined plane tests were conducted at a speed of 0.33 °/s and an applied load produced by the self weight of the body. A motion sensor is attached to the equipment to detect the onset of slip and allow the measure of angle instantly. To analyze the results, each set of samples was considered different depending on the heat treatment. In addition, subsets of samples were distinguished in accordance with Rq parameter, because it is an average parameter and it is used directly to calculate the real area of contact. Thus, for each metallurgical condition was possible to see, the variation of the coefficient of static friction with mechanical and surface properties. It was verified that the hardness had no effect on the coefficient of static friction, however, the combination of mechanical and surface properties represented by the plasticity index has a direct relationship.

Orientador: Fernando Alvarez / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-05T23:16:31Z (GMT). No. of bitstreams: 1 Zagonel_LuizFernando_D.pdf: 13909392 bytes, checksum: 08d9ce72a7691aa00b93b053302e92d1 (MD5) Previous issue date: 2006 / Resumo: O objetivo deste trabalho é estudar processos de tratamento superficial por plasma com especial atenção às peculiaridades da técnica frente às demais práticas de nitretação, buscando compreender o processo a partir dos fenômenos observados na superficie. Dois tipos de tratamento foram realizados e três as técnicas utilizadas: nitretação por feixe de íons e por plasma pulsado e carbonitretação por deposição assistida por feixe de íons. A liga tratada foi o aço AISI-H13. As superficies das amostras foram tratadas em diversas temperaturas, de 260°C a 6000C, diversos tempos de processo, de 75 minutos a 5 horas, diversas densidades de corrente e diversas misturas gasosas, permitindo a observação de diferentes estruturas cristalinas, durezas, microestruturas e concentrações de nitrogênio na camada nitretada. Os diferentes estudos realizados dentro dessas amplas condições experimentais permitiram observar e/ou modelar o processo de tratamento superficial em condições diferenciadas. Estudos de nitretação com diferentes composições de feixe iônico de nitrogênio e hidrogênio mostraram que o hidrogênio tem um importante papel no processo, mesmo na ausência de oxigênio. A presença de hidrogênio levou ao aumento da concentração superficial de nitrogênio e à formação de fases de nitretos de ferro tipo E-Fe2-3N. Um estudo da nitretação em diversas temperaturas indicou que o processo de oferta de nitrogênio não depende da temperatura e que a 260°C nitretos de ferro de alta concentração de nitrogênio podem ser formados. A difusão de nitrogênio no aço utilizado mostrou-se ativada pela temperatura, mas efeitos de difusão por bordas de grão pareceram estar presentes, o que causou um aumento da dureza em altas profundidades. A técnica de deposição assistida por íons foi utilizada nesse estudo para o tratamento de superficie de carbonitretação. Nessa técnica, o carbono foi depositado continuamente sobre a superficie da amostra enquanto esta foi bombardeada com íons de nitrogênio. O estudo mostrou que a técnica apresenta características distintas daquelas da carbonitretação a gás ou a plasma. Em especial, foi observada a restauração da fase ferrita com altas concentrações de carbono e nitrogênio para alta deposição de carbono. Um estudo amplo sobre o papel do fluxo de íons, temperatura e tempo no processo de nitretação também foi realizado, visando clarificar as características do potencial químico na nitretação a plasma. Como demonstrado, esse potencial depende do balanço de massa entre o fluxo de íons e a difusão para o volume / Abstract: The objective of this project is to study processes of plasma surface treatment with special emphasis to the differences these techniques might show in relation to others, looking forward to understand the process from surface phenomena. Two kinds of surface treatment have been studied, including three different techniques: ion beam nitriding, pulsed plasma nitriding and carbonitriding by ion beam assisted deposition. The treated alloy was the steel AISI-H13. The samples surfaces have been treated at several different temperatures, from 260°C to 600°C, several process times, from 75 minutes to 5 hours, several ion current densities e several gas mixtures, allowing the observations of different crystalline structures, surface and profile hardness, microstructures, and nitrogen concentration at the surface and within a profile. The undergone studies over these wide conditions leaded to the observation and modeling of the surface treatments at these different situations. Studies of nitriding with different ion beam compositions of nitrogen and hydrogen showed that hydrogen play a major role even in the absence of oxygen. The hydrogen presence within the surface allowed an enhancement on the nitrogen concentration and the formation of iron nitrides 1ike E-Fe2-3N. A study of nitriding over several different temperatures indicates that the nitrogen offer at the surface is not dependent upon temperature and even at very low temperatures like 260°C, high nitrogen concentration iron nitrides can be formed. The nitrogen diffusion is shown to be activated by temperature, but grain boundary effects seam to be present, what caused a hardness increase at high depths. The ion beam assisted deposition technique was used for carbonitriding. In this set-up, carbon is continuously deposited over the surface while the sample is exposed to nitrogen ions. The study showed that the approach displays distinct characteristics with respect to gas or p1asma carbonitriding. By this new technique, high carbon deposition preserves the formation of E-Fe2-3N phase, without loss of diffusion to bulk. A wide study about the role of the ion flux, temperature and time on ion nitriding process was also performed, looking forward to clarify the behavior of the chemical potential of nitrogen at the surface. As it was understood, this quantity will depend on the mass balance between the ion flux and the diffusion to bulk / Doutorado / Física da Matéria Condensada / Doutor em Ciências