Celso Antonio Barbosa

Efeitos da adição de níquel em ligas ferro-cromo. Parte I: propriedades mecânicas

The aim of this work was to study the influence of Ni additions on the mechanical properties of Fe-Cr alloys. For this purpose, alloys were prepared with an 18%Cr-0.01%C-0.2%Si-0.4%Mn base composition and variable Ni content (0, 10, 20, 40 and 60 weight %). The alloys were characterized by X-Ray diffraction and thermal analyses. Their hardness was determined before and after cold deformation. Tension tests were carried out at room temperature and 350oC to verify the effect of temperature on the mechanical behavior of the alloys. The mechanical characterization aim was to use these figures to correlate mechanical properties and machinability (results originating from a parallel study).

Evolução temporal da interfase açoinoxidável P558/solução de cloreto de sódio por espectroscopia de impedânciaeletroquímica

P558 stainless steel, nickel free, has been studied by this group with the purpose of verifying its viability for use in orthopedic implants. In previous works, it has been shown by stationary electrochemical techniques that this steel presents a similar behavior of that presented by ISO 5832-9 with a corrosion resistance significantly higher when compared to ISO 5832-1 stainless steel, usually known as F138 SS. In this work the temporal evolution of the interfase P558/NaCl 0.11 mol L-1 was studied by electrochemical impedance spectroscopy, at the open circuit potential. The time intervals observed were 10 min. 1 day, 2 days and 5 days. It was observed that the passive film became more protective with the increase of time. The experimental data was modeled using the equivalent electrical circuit approach. This approach suggested an initial existence of a slightly protective passive film, which then permitted the formation of a more compact secondary film upon stabilization of the conditions.

Estudo eletroquímico comparativo do aço ISO 5832-9 em diferentes meios de interesse biológico

The electrochemical behavior of ISO 5832-9 stainless steel at 37 oC in 0.9% NaCl, Ringer Lactate and minimum essential medium (MEM) has been studied, using linear voltammetry, and surface analysis by SEM and EDS. Mechanical and toxicity tests were made. ISO 5832-9 is passivated at corrosion potential (Ecorr) and it does not present pitting corrosion on the media studied from Ecorr to 50 mV above the transpassivation potential (Ei). SEM and EDS analysis have shown that the sample previously immersed in MEM presents a different behavior at 50 mV above Ei: the manganese oxide inclusions are absent in the surface. Ecorr values and passivation current density values jpass changed according to the following. Ecorr, RL < Ecorr,NaCl < Ecorr, MEM and jMEM << jRL ≅ jNaCl. The stainless steel was characterized as non toxic in the cytotoxicity assay.

Efeitos da adição de níquel em ligas ferro-cromo. Parte II: tempo de vida da ferramenta em processo de torneamento

Abstract The aim of this work was to study the influence ofNi content on coated cemented carbide tool wear duringthe machining process of stainless alloys. For thispurpose alloys were prepared with an 18%Cr-0.01%C-0.2%Si-0.4%Mn base composition and variable Nicontent (0, 10, 20, 40 and 60 weight %). Tests werecarried out with coated cemented carbide tools; classM15 with TiC/Al2O3/TiN coating. All alloys weremachined under the same process conditions(Vc = 230 m/min, ap = 0.6 mm and f = 0.1 mm/rotation),so the only variation source was the Ni content.Preliminary results indicate that the tool life lowerswhen Ni content rises. Keywords: Stainless steels, Ni alloys, tool wear,tribology, machinability. Efeitos da adicao de niquel em ligas ferro-cromo. Parte II: tempo de vida daferramenta em processo de torneamento Daniel Cirillo Marques Faculdade de Engenharia Mecânica da Unicamp, Campinas, SP. E-mail: dcirillo@fem.unicamp.br Celia Cristina Moretti Decarli Faculdade de Engenharia Mecânica da Unicamp, Campinas, SP. E-mail: cdecarli@fem.unicamp.br