ABSTRACT The resonant absorption of recoilless g-rays, known as Mössbauer Spectroscopy, is an efficient nuclear prospecting technique to structural and magnetic analysis. When studying steels, it is possible to accurately analyze the surface of materials using the Conversion Electron Mössbauer Spectroscopy technique (CEMS) that evaluates the sample’s surface to a depth of 200 nm, and by Conversion X-ray Mössbauer Spectroscopy by (CXMS), which can go deeper and investigate inner layers of steel samples (10 mm). In this work, this technique was employed to study the crystallographic reversion (f.c.c.àh.c.p.) of stainless steel shape memory. A hexagonal martensitic phase was induced mechanically through the compression test and the reversion to austenite phase was observed using heat treatment. Mössbauer spectroscopy measurements were carried out using the conversion of electrons, and X-ray with a 57Co source in a rhodium matrix at room temperature and without the external fields. Spectra were analyzed using specific adjustment software. The results indicated great reversal of e-martensite. Rietveld refinement analysis was obtained using the XRD data to evaluate possible structural changes occurring during the thermo-mechanical treatment (cycles of deformation followed by heating). Comparison of the Mössbauer spectra and Rietveld refinement are important for understanding the reversal of the martensitic phase. In this case, the crystal structure changes resulted in a shape recovery material, which was deformed beyond its elastic limit.

ABSTRACT Doping polymers with metallic materials can improve significantly its use. Ultra high molecular weight polyethylene is known for its high resistance to abrasion and impact, and also for its friction coefficient, which is significantly lower than that of commercial steel and most polymeric materials. Therefore, this material presents high industrial demand despite its processing difficulty due to its high viscosity. One kind of polymer processing which has been widely used recently is the high energy mechanical alloying. This method provokes significant changes in the material, such as crystalline structure transformation, amorphization, formation of metastable phases, and nanostructuring, among others. In order to investigate the influence of iron dopant in structural characteristics of polymeric matrix, ultra high molecular weight polyethylene were doped with low concentrations (between 0.1 at.% and 1 at.%) of iron using the method of high energy mechanical alloying. The samples composition was characterized by X-Ray Diffraction Mössbauer Spectroscopy. A theoretical molecular modeling was carried out to simulate the iron presence in polymeric cell, which is in good agreement with the experimental results. Therefore, there is evidence that part of the iron promotes a crossed bond between the polymeric chains.

O aço inoxidável superasutenítico apresenta diversas aplicações tecnológicas, principalmente em ambientes corrosivos. A precipitação de diferentes fases pode alterar algumas de suas propriedades mecânicas. Tais alterações afetam vários fatores, incluindo a vida útil do material diante de condições de trabalho adversas. Neste estudo, medidas de Indentação Instrumentada, Tribologia e Difração de Raios X (DRX) foram utilizadas para avaliar possíveis alterações em regiões próximas à superfície em amostras tratadas termicamente. Os parâmetros analisados foram: dureza e módulo de elasticidade, coeficiente de atrito e alterações estruturais na célula unitária nas fases identificadas. Os resultados foram comparados com aço austenítico comum da família AISI 304. A presença das fases σ (grupo espacial P42mnm) e austenita-γ (grupo espacial Fm3m) foram detectadas. Os dados analisados indicaram que a presença da fase intermetálica σ contribuiu para pequenas alterações na dureza em regiões próximas à superfície e no coeficiente de atrito. Para regiões mais profundas (bulk) as propriedades analisadas foram semelhantes aos aços inoxidáveis comerciais.

The superaustenitic stainless steel presents several technological applications, mainly in corrosive environments. The different phase precipitation might alter some of its mechanical properties. Such alterations affect several factors, including the working life of the material under adverse working conditions. In this study, Instrumented Indentation techniques, Tribology and X-ray diffraction (XRD) were used to evaluate alterations in regions close to the surface. The parameters analyzed were: hardness and elastic modulus (instrumented indentation), friction coefficient (tribology) and structural alterations of the unit cell of the identified phases (XRD - Rietveld Refinement). All properties analyzed were compared with those of common austenitic steel. The presence of σ-phase (space group P42mnm) and γ-austenite (space group Fm3m) were detected. Data analyzed indicated that the presence of σ-phase caused small alteration in properties such as hardness in regions close to the surface. In the regions farther from the surface (material bulk) data can be compared to that of conventional austenitic steel.