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Orientadores: Ana Maria Martinez Nazar, Ricardo E. Medrano

Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica

Resumo: Não informado

Abstract: Superplasticity is the ability of certain materials to deform homogeneously with high elongations (several hundreds or thousands percent) at elevated temperatures and low strain rates. This subject of scientific and teclinological interest is not well slablished yet. The purpose of present work is to characterize and to study the superplastic behavior of a 22.5%Cr-6.4%Ni-3.0%Mo-0.16%N duplex stainless steel. Therefore, samples from sheets of the material were examined at 950°C and 98CFC by means of tensile, strain rate change and stress relaxation tests. Moreover, microstructures and cavitation process under main conditions were also analyzed. Tensile tests provided informations about elongation and deformation homogeneity. On the other hand, the strain rate change and stress relaxation tests were more suitable to determine the strain rate sensitivity. The superplastic behavior analysis was based on whole results from elongation, strain rate sensitivity and deformation uniformity. According to these criteria, the material exhibits superplastic deformation at 980X with strain rates ranging from 10 s" to ! 0' s". Under these conditions the deformation was homogeneous (without necking), the strain rate sensitivity coefficient attained 0.7 and elongation achieved 900%. During deformation: (i) the initial microstructure composed of oriented phases change to an equiaxed stable structure and (ii) cavitation process occurs. These observations suggest the grain boundary sliding as the main superplastic deformation mechanism. Key Words: super-plasticity, duplex stainless steel, tensile test, strain rate change test, stress relaxation

Doutorado

Materiais e Processos de Fabricação

Doutor em Engenharia Mecânica