No description available.

No description available.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: properties prediction, quenchant database, TTT diagram. Includes bibliographical references (p.190-193).

Made available in DSpace on 2014-10-09T12:29:28Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:40Z (GMT). No. of bitstreams: 1 12907.pdf: 1852096 bytes, checksum: 4b1d5ce099ad8f5b1da0845dac78c66e (MD5) / Dissertacao (Mestrado) / IEA/D / Universidade Federal do Rio de Janeiro - UFRJ

Made available in DSpace on 2014-10-09T12:29:28Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:40Z (GMT). No. of bitstreams: 1 12907.pdf: 1852096 bytes, checksum: 4b1d5ce099ad8f5b1da0845dac78c66e (MD5) / Dissertacao (Mestrado) / IEA/D / Universidade Federal do Rio de Janeiro - UFRJ

No description available.

No description available.

Chemical strengthening via ion exchange is commonly used in the industry to produce ultra-thin and resistant glasses used for high-tech applications. This process results in the formation of an ion-exchanged region near the glass surface that is under significant compressive stress, which tremendously improves the mechanical strength and the scratch resistance of the glass. The aim of this thesis is to deepen our fundamental understanding of the ion-exchange mechanisms. Since the mechanical strength against brittle fracture of ion-exchanged glasses depends on the compressive stress at the surface and the depth of interdiffusion, special attention was paid to the two main parameters affecting those properties: the parent glass composition and stress relaxation processes.First, the effect of the parent glass composition on interdiffusion properties was analyzed. We focused our study on the effect of the alkali oxide:alumina ratio and the ionic potential (charge:radius) of divalent cations on the interdiffusional properties. An increase of the Al2O3 content in Na+/K+ ion-exchanged silicate glasses leads to a reduction of the depth of interdiffusion layer and an enhancement of the surface compressive stress. These trends are shown to be consistent with the compositional variation of the glass connectivity and hence, the stress relaxation occurring during the ion-exchange. It is also found that the depth of interdiffusion is higher for glasses containing divalent cations with a higher ionic potential such as Mg and Zn. This is attributed to the larger free volume available and the weaker Na-O bonds in those glasses. Second, the structural origin of stress relaxation is investigated. In the Na+/K+ ion exchanged glasses, the K+-foreign cations are introduced in the cages of the Na+-host cations. Due to stress relaxation, the size of the K-O coordination shell in ion-exchanged glasses increases. This increase is achieved by two structural adaptation mechanisms: a contraction of the Na-O, Ca-O and Mg-O coordination shell and both a shortening of the Si-NBO distances and an opening of the Q4 Si-O-Si angles. The greater knowledge developed in this thesis on the effect of parent glass composition on interdiffusion mechanisms and stress relaxation processes provides further insight into practical ways to optimize the mechanical strength of ion-exchanged glasses. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

No description available.

Este trabalho apresenta o projeto de um sistema gerador de \"set-point\" (GSP), utiliza-do na determinação dos parâmetros de trabalho de fornos industriais de têmpera contínua de aços ao carbono, cuja modelagem é baseada na lógica \"fuzzy\". O trabalho é constituído de três etapas básicas: primeiro, estudou-se os princípios metalúrgicos do aço e do processo de têmpera, necessários para o entendimento do problema, tendo como foco no aço CK75 de grande aplicação industrial. Segundo, estudou-se a funcionalidade de todas as partes constitu-intes do forno e seu modo de operação. Na terceira etapa, baseado em entrevistas com os ope-radores e técnicos em metalurgia, considerados especialistas no processo de têmpera, reali-zou-se a modelagem \"fuzzy\". Constatou-se de que forma as partes do forno afetam a trans-formação do aço, as variáveis de entrada e saída relevantes para o GSP e finalmente realizou-se o GSP com o MATLAB®. O modelo foi exaustivamente testado na produção de aço tem-perado, em um dos fornos da empresa Mangels, o que possibilitou sua validação de forma incontestável. / This work presents the project of a generating system of \"set-point\" (GSP), used in the determination of the parameters of work of a process of continuous tempering of carbon steels, whose modeling is based on the \"fuzzy\" logic. The work is made of three basic stages. First of all the principles of metallurgy for the steel and temper process, which are necessary for the understanding of the problem are studied. It is focused in the steel CK75 of great in-dustrial application. In the second stage, the functionality of all parts of the furnace and its operation way is studied. In the last stage a \"fuzzy\" modeling is accomplished, based on inter-views with the operators and technicians in metallurgy, who are considered specialists in the temper process. It is identified how the parts of the oven affect the transformation of the steel, variable input and output relevant to GSP. Finally will use the GSP with MATLAB® is car-ried out. The model was tested in exhaustive way in one of the furnace of the company Man-gels what made its incontrovertible validation possible.