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Mechanical Spectroscopy of MgB2 Containing SiC

Silva M. R., Silva L. B. S., Rodriques Jr. D., Grandini C. R.

Archives of Metallurgy and Materials

2015

Vol. 60, iss. 4

3083--3086

The compound magnesium diboride (MgB2) has been well-known since the 1950s; however, its superconducting properties were unknown. Intrinsic characteristics of MgB2 make this material a promising candidate for technological applications, although the low value of the irreversibility field and the decrease in critical current density with the increase in the magnetic field considerably reduce its utility. The present work aimed to study the effect of carbon-based doping on anelastic properties of MgB2 as measured by mechanical spectroscopy. The samples were prepared by using the powder-intube method. The samples were made with 5, 7.5, and 10 wt.% of silicon carbide (SiC). The results reveal complex mechanical loss spectra caused by the interaction between point defects and surface defects in the crystalline lattice of MgB2.

Dwuborek związek magnezu (MgBV) jest znany od 1950 roku; jednak jego właściwości nadprzewodzące były nieznane. Swoiste cechy MgB2 czynią ten materiał obiecującym kandydatem do zastosowań technicznych, jednak niskie wartości nieodwracalnego pola i zmniejszenie krytycznej gęstości prądu ze wzrostem pola magnetycznego znacznie zmniejszają jego użyteczność. Celem pracy było zbadanie wpływu domieszkowania związkiem węgla na anelastyczne właściwości MgB2 mierzone metodą spektroskopii mechanicznej. Próbki zostały przygotowane za pomocą metody powder-in-tube (PIT). Wytworzono próbki o zawartości 5, 7.5 i 10 % wag. węglika krzemu (SiC). Wyniki pokazują złożone widma strat mechanicznych powodowanych przez wzajemne oddziaływanie pomiędzy defektami punktowymi i defektami powierzchniowymi w sieci krystalicznej MgB2.

Effect of copper on strain-induced martensite and the parameters that simulate the stress-strain curve of an austenitic stainless steel AISI 304

Gilapa L C M, Oliveira C A S, Silva M R

Journal of Achievements in Materials and Manufacturing Engineering

2012

Vol. 55, nr 2

679--684

Purpose: This study examined the effect of copper on the phase transformation (γ → a')-induced by the deformation and in the variables of the equation that simulates the stress- equivalent strain curve. Design/methodology/approach: The phase transformation (y → a') was studied through the magnetic properties using a vibrating sample magnetometer - VSM. The simulation of the stress-equivalent strain curve was performed using the obtained results in experimental studies, using the commercial software Maple. Findings: It was observed that the addition of copper in the austenitic stainless steel (ASS) AISI 304 promotes increased stability of the austenite, slowing therefore, the formation of martensite induced by deformation. It was also observed that the addition of copper influences on the values of the variables of the equation that simulate the stress-equivalent strain curve. Research limitations/implications: The stress-equivalent strain curve was simulated satisfactorily, however it was observed that the equation that simulates the curve displays values of the variables not usually found, this may be due to the approximations made in applying the rule of mixtures. Practical implications: It was observed that with the increase of copper, the ASS tend to increase the stability of the austenitic phase, which implies a delay in hardening of the material and a probable influence on the variables of the equation that simulates the stressequivalent strain curve. Originality/value: The influence of copper on the formation of magnetic martensite (a') and consequent influence in obtaining the variables of the equation that generates the stress-equivalent strain curve.