Monitoramento da corrosão do aço de baixo carbono em sistema com fluxo turbulento de NaCl 3%: uma investigação eletroquímica

Em dutos que operam em regime turbulento, o processo corrosivo é acelerado e diretamente responsável por inúmeros prejuízos em plantas industriais, tais como paradas nas linhas de produção, falhas em equipamentos e elevados custos de manutenção. Embora haja poucos estudos laboratoriais nesta condição de escoamento, há um consenso entre inúmeros pesquisadores que o monitoramento e investigações nesta condição são essenciais, uma vez que simulam condições representativas da realidade industrial. Este trabalho investigou a influência do fluxo do meio eletrolítico sobre os parâmetros eletroquímicos do aço ABNT 1020 em solução NaCl 3% submetido a diferentes velocidades (0,21, 0,42, 0,62 e 0,84 m.s-1), relacionando os resultados obtidos por Espectroscopia de Impedância Eletroquímica (EIE) e Polarização Potenciodinâmica Linear (PPL). Os ensaios eletroquímicos foram realizados a partir de uma plataforma experimental construída para tal finalidade e acoplada às conexões do potenciostato, a fim de se obter curvas experimentais enquanto o eletrólito fluía dentro da célula e interagia com a superfície do metal. Os resultados mostraram que a variação da velocidade provoca mudanças notáveis nos principais parâmetros do ensaio e que as técnicas eletroquímicas corroboraram entre si mesmo em condições turbulentas de escoamento na plataforma de testes.Palavras-chave: Corrosão. Aço carbono. Fluxo turbulento. Eletroquímica.

Prediction of hot flow plastic curves of ISO 5832-9 steel used as orthopedic implants

An austenitic stainless steel ISO 5832-9 used as a biomaterial was torsion-deformed over the temperature range of 1000-1200 °C and strain rates of 0.05, 0.1, 1.0 and 5.0 s- 1. The flow stress curves obtained showed two regions where firstly there is a rising on stress characterized as work hardening mechanism acting and secondly a decreasing in work-softening after a peak stress. The flow curves were modeled by adjusting the experimental data with Zener-Hollomom parameter to construct the constitutive equations that describe the plastic behavior in both regions. The first region was described until the peak stress, taking into consideration the competition between work hardening and recovery while the second one was described applying the softening time of 50% and the Avrami equation. In some hot deformation conditions the simulated curves showed good agreement with the experimental ones while in others conditions the simulated showed differences to experimental curves that was discussed and associated with other mechanisms that acted during hot deformation

Dispersion Diagram of Trigonal Piezoelectric Phononic Structures with Langasite Inclusions

The dispersion relation of elastic Bloch waves in 1-3 piezoelectric phononic structures (PPnSs) with Langasite (La3Ga5SiO14) inclusions in a polymeric matrix is reported. Langasite presents promising material properties, for instance good temperature behaviour, high piezoelectric coupling, low acoustic loss and high quality factor. Furthermore, Langasite belongs to the point group 32 and has a trigonal structure. Thus, the 2-D bulk wave propagation in periodic systems with Langasite inclusions cannot be decoupled into XY and Z modes. The improved plane wave expansion (IPWE) is used to obtain the dispersion diagram of the bulk Bloch waves in 1-3 PPnSs considering the classical elasticity theory and D3 symmetry. Full band gaps are obtained for a broad range of frequency. The piezoelectricity enhances significantly the band gap widths and opens up a narrow band gap in lower frequencies for a filling fraction of 0.5. This study should be useful for surface acoustic wave (SAW) filter and 1-3 piezocomposite transducer design using PPnSs with Langasite

Dynamic Phase Transformation Behavior of a Nb-microalloyed Steel during Roughing Passes at Temperatures above the Ae3

A five-pass torsion simulation of the roughing passes applied during hot plate rolling was performed in the single-phase austenite region of a Nb-microalloyed steel under continuous cooling conditions. The deformation temperatures were approximately half-way between the Ae3 and the delta ferrite formation temperature (i.e., 250 °C above the Ae3) in which the free energy difference of austenite and ferrite is at maximum. The microstructures in-between passes were analyzed to characterize and quantify the occurrence of deformation-induced dynamic phase transformation. It was observed that about 7% of austenite transforms into ferrite right after the final pass. The results are consistent with the calculated critical strains and driving forces which indicate that dynamic transformation (DT) can take place at any temperature above the Ae3. This mechanism occurs even with the presence of high Nb in the material, which is known to retard and hinder the occurrence of DT by means of pinning and solute drag effects. The calculated cooling rate during quenching and the time–temperature–transformation curves of the present material further verified the existence of dynamically transformed ferrite