Mechanical strength evaluation for Nd-YAG laser and electric resistance spot weld (ERSW) joint under multiaxial loading

This work presents a comparison between laser weld (LBW) and electric resistance spot weld (ERSW) processes used for assemblies of components in a body-in-white (BIW) at a world class automotive industry. It is carried out by evaluating the mechanical strength modeled both by experimental and numerical methods. An ""Arcan"" multiaxial test was designed and manufactured in order to enable 0 degrees, 45 degrees and 90 degrees directional loadings. The welded specimens were uncoated low carbon steel sheets (S-y = 170 MPa) used currently at the automotive industry, with two different thicknesses: 0.80 and 1.20 mm. A numerical analysis was carried out using the finite element method (FEM) through LS-DYNA code. (c) 2007 Elsevier B.V. All rights reserved.

Selective corrosion of 550 degrees C aged Cu10Ni-3Al-1.3Fe alloy in NaCl aqueous solution

This work studied the electrochemical behavior of a solution treated or 550 degrees C aged Cu10Ni-3Al-1.3Fe alloy, in 0.01 M NaCl aqueous solution, through potentiodynamic polarization in both stagnant condition or under erosion process. Results showed the occurrence of a passivity break potential (E(pb)), related to the beginning of the denickelification process, which occurred as a localized attack under stagnant electrolyte. Under erosion conditions localized denickelification was not observed, despite of the presence of E(pb). This could indicate that selective corrosion of Ni, which caused the observed E(pb), occurred as a dissolution-redeposition process, with removal of the Cu deposits during erosion process. (C) 2011 Elsevier Ltd. All rights reserved.

Improvement of the cavitation erosion resistance of UNS S31803 stainless steel by duplex treatment

A duplex surface treatment consisting of High Temperature Gas Nitriding (HTGN) followed by Low Temperature Plasma Nitriding (LTPN) was carried out in an UNS S31803 duplex stainless steel. The HTGN treatment was intended to produce a relatively thick and hard fully austenitic layer giving mechanical support to the thinner and much harder expanded austenite layer. HTGN was performed at 1200 degrees C for 3 h, in a 0.1 MPa N(2) atmosphere while LTPN, was carried out in a 75% N(2) + 25% H(2) atmosphere, at 400 degrees C for 12 h, under a 250 Pa pressure, and 450 V. An expanded austenite gamma(N) layer, 2.3 mu m thick, 1500 HVO.025 hard, was formed on top of a 100 mu m thick, 330 HV 0.1 hard, fully austenitic layer, containing 0.9 wt% N. For comparison purposes LTPN was carried out with UNS S30403 stainless steel specimens obtaining a 4.0 mu m thick, 1500 HV 0.025 hard, expanded austenite layer formed on top of a fully austenitic matrix having 190 HV 0.1. The nitrided specimens were tested in a 20 kHz vibratory cavitation-erosion testing equipment. Comparison between the duplex treated UNS S31803 steel and the low temperature plasma nitrided UNS S30403 steel, resulted in incubation times almost 9 times greater. The maximum cavitation wear rate of the LTPN UNS S30403 was 5.5 g/m(2)h, 180 times greater than the one measured for the duplex treated UNS S31803 steel. The greater cavitation wear resistance of the duplex treated UNS S31803 steel, compared to the LTPN treated UNS S30403 steel was explained by the greater mechanical support the fully austenitic, 330 HV 0.1 hard, 100 mu m layer gives to the expanded austenite layer formed on top of the specimen after LTPN. A strong crystallographic textured surface, inherited from the fully austenitic layer formed during HTGN, with the expanded austenite layer showing {101} crystallographic planes//surface contributed also to improve the cavitation resistance of the duplex treated steel. (C) 2010 Elsevier B.V. All rights reserved.

Three-dimensional analysis of fracture, corrosion and wear surfaces

A brief look at the history of fractography has shown a recent trend in the quantification of topographic parameters through the use of three-dimensional reconstruction techniques, which associate SEM stereoscopy and stereophotogrammetry software, allowing the calculation of the elevation measurement at numerous points of the topography due to the parallax that takes place during the tilting of the sample along the microscope eucentric plane. Several investigators have used reconstruction techniques to correlate some fractographic parameters, such as fractal dimension and fractured to projected area ratio, to the mechanical properties of materials, such as fracture toughness and tensile strength. So far, the search for a clear relationship between the fracture topography and mechanical properties has provided ambiguous results. The present work applied a surface metrology software to reconstruct three-dimensionally fracture surfaces (transgranular cleavage, intergranular and dimple fracture), corrosion pits and tribo-surfaces in order to explore the potential of this stereophotogrammetry technique. The existence of a variation in the calculated topographic parameters with the conditions of SEM image acquisition reinforces the importance of both good image acquisition and accurate calibration methods in order to validate this 3D reconstruction technique in metrological terms. Preliminary results did not indicate the existence of a clear relationship between either the true to project area ratio and CVN absorbed energy or the fractal dimension and CVN absorbed energy. It is likely that each fracture mechanism presents a proper relationship between the fractographic parameters and mechanical properties. (C) 2009 Elsevier Ltd. All rights reserved.

Assessment of the cavitation erosion resistance in high nitrogen austenitic stainless steels: study of the wear mechanisms

Specimens of a UNS S31803 steel were submitted to high temperature gas nitriding and then to vibratory pitting wear tests. Nitrided samples displayed fully austenitic microstructures and 0.9 wt. % nitrogen contents. Prior to pitting tests, sample texture was characterized by electron backscattering diffraction, EBSD. Later on, the samples were tested in a vibratory pit testing equipment using distilled water Pitting tests were periodically interrupted to evaluate mass loss and to characterize the surface wear by SEM observations. At earlier pit erosion, stages intense and highly heterogeneous plastic deformation inside individual grains was observed. Later on, after the incubation period, mass loss by debris detachment was observed. Initial debris micro fracturing was addressed to low cycle fatigue. Damage started at both sites, inside the grains and grain boundaries. The twin boundaries were the most prone to mass-loss incubation. Grains with (101) planes oriented near parallel to the sample surface displayed higher wear resistance than grains with other textures. This was attributed to lower resolved stresses for plastic deformation inside the grains with (101)

EROSION-CORROSION SYNERGISM OF AN AISI 410 MARTENSITIC STAINLESS STEEL

In this work, the behavior of an AISI 410 martensitic stainless steel under corrosion-erosion conditions is evaluated. Quenched and tempered samples were used for the wear test, using a low velocity jet-like device connected to a potentiostat. Potentiodynamic polarization curves were obtained with the electrolyte in static state, with flow conditions and under corrosion-erosion, adding quartz particles to the electrolyte. In addition, mass loss measurements under erosion and corrosion-erosion conditions were carried out. The topography of the surfaces was examined after the wear tests, using optical and scanning electron microscopy. This information, together with the results of mass losses and the electrochemical tests were used to establish the degradation mechanisms of the stainless steels under different testing conditions. The results showed that synergism is a significant part of the degradation process of this steel (66.5%) and that the mass removal process of steel was controlled by corrosion assisted by erosion.

Chemical characterization and anticorrosion properties of corrosion products formed on pure copper in synthetic rainwater of Rio de Janeiro and Sao Paulo

This work aims to characterize corrosion products formed on copper samples exposed to synthetic rainwater of Rio Janeiro and Sao Paulo. XRD and XPS were employed to determine their composition, while electrochemical techniques were used to evaluate their protective properties. XRD and XPS indicated the thickening of the corrosion layer with time. Electrochemical results showed that the protectiveness of the corrosion layer depends on the solution composition. Based on our findings a corrosion mechanism for copper in simulated rainwater is proposed where the role of NH(4)(+) ions in the cuprite layer partial regeneration is taken into account. (C) 2009 Elsevier Ltd. All rights reserved.

Dodigen 213-N as corrosion inhibitor for ASTM 1010 mild steel in 10% HCL

This article describes a study of the behavior of a mixture of amines and amides, commercially known as Dodigen 213-N (D-213 N), as a corrosion inhibitor for ASTM 1010 mild steel in 10% w/w HCl solution. The concentration range used was 1 x 10(-5) M to 8 x 10(-4) M. The weight loss and electrochemical techniques used were corrosion potential measurement, anodic and cathodic polarization curves, and electrochemical impedance spectroscopy (EIS). The solution temperature was 50 +/- A 1 A degrees C and it was naturally aerated. The corrosion potential values shifted to slightly more positive values, thus indicating mixed inhibitor behavior. The anodic and cathodic polarization curves showed that D-213 N is an effective corrosion inhibitor, since both the anodic and the cathodic reactions were polarized in comparison with those obtained without inhibitor. For all concentrations the cathodic polarization curves were more polarized than the anodic ones. The inhibition efficiency was in the range 75-98%, calculated from values of weight loss and corrosion current density, i (corr), obtained by extrapolation of Tafel cathodic linear region.

Investigation of the corrosion behaviour of AA 2024-T3 in low concentrated chloride media

Aluminium alloy (AA) 2024-T3 is an important engineering material due to its widespread use in the aerospace industry. However, it is very prone to localized corrosion attack in chloride containing media, which has been mainly associated to the presence of coarse intermetallics (IMs) in its microstructure. In this work the corrosion behaviour of AA 2024-T3 in low concentrated chloride media was investigated using microscopy and electrochemical methods. TEM/EDS observations on non-corroded samples evidenced the heterogeneous composition within the IMs. In addition, SEM observations showed that intermetallics with the same nominal composition present different reactivity, and that both types of coarse IMs normally found in the alloy microstructure are prone to corrosion. Moreover, EDS analyses showed important compositional changes in corroded IMs, evidencing a selective dissolution of their more active constituents, and the onset of an intense oxygen peak, irrespective to the IM nature, indicating the formation of corrosion products. On the other hand, the results of the electrochemical investigations, in accordance with the SEM/EDS observations, evidenced that IMs corrosion dominates the electrochemical response of the alloy during the first hours of immersion in the test electrolyte. (c) 2008 Elsevier Ltd. All rights reserved.

Electrochemical study of modified non-functional bis-silane layers on Al alloy 2024-T3

In the last few years great efforts have been made in order to find and to develop environmentally friendly substitutes for Cr6+ pre-treatments applied on aluminium alloys used in the aircraft industry. Among the potential substitutes, silane layers have attracted considerable interest from researchers and from the industry. The present work investigates the anti-corrosion behaviour of (bis-1, 2-(triethoxysilyl) ethane (BTSE)) silane layers modified with Ce ions and/or silica nanoparticles applied on Al alloy 2024-T3 substrates. The corrosion behaviour was investigated in 0.1 M NaCl solution via d.c. polarization and electrochemical impedance spectroscopy (EIS). Contact angle measurements and XPS were used to assess information on the chemistry of the silane pre-treated surfaces. The results have shown that the introduction of additives improves the corrosion protection properties of the silane layer. (c) 2008 Elsevier Ltd. All rights reserved.

Improved moisture and hydrocarbons barrier of epoxy resin-based coating

To improve the surface characteristics of epoxy resin coatings, a treatment by fluorine-containing plasma was used to develop a coating with low surface free energy and improved chemical resistance. Through the coating analysis it was possible to verify information about the CF(n) bond formation and the fluorination depth. The best plasma process parameters presented the best fluorination depth, 90 nm, and fluorine concentration was nearly 30%. The improvement in contact angle of water was 50% and of raw petroleum was 130%. Salt spray test proves that the coating fluorination decreases the chance of substrate corrosion.

Novel sources of witches` broom resistance (causal agent Moniliophthora perniciosa) from natural populations of Theobroma cacao from the Brazilian Amazon

Witches` broom is a severe disease of Theobroma cacao L. (cacao), caused by the basidiomycete Moniliophthora perniciosa. The use of resistant cultivars is the ultimate method of control, but there are limited sources of resistance. Further, resistance from the most widely used source (`Scavina 6`) has been overcome after a few years of deployment. New sources of resistance have been intensively searched for in the Amazon basin. Here, we evaluated for witches` broom resistance, cacao accessions from various natural cacao populations originally collected in the Brazilian Amazon. Resistance of 43 families was evaluated under nursery and/or field conditions by artificial or natural infection, respectively, based on disease incidence. Screening for resistance by artificial inoculation under nursery conditions appeared to be efficient in identifying these novel resistance sources, confirmed by natural field evaluation over a nine-year period. The increase in natural field infection of `Scavina 6` was clearly demonstrated. Among the evaluated families with the least witches` broom incidence, there were accessions originally collected from distinct river basins, including the Jamari river (`CAB 0371`; `CAB 0388`; `CAB 0392`; and `CAB 0410`); Acre (`CAB 0169`); Javari (`CAB 0352`); Solimes (`CAB 0270`); and from the Purus river basin, the two most outstanding resistant accessions, `CAB 0208` and `CAB 0214`. The large genetic diversity found in cacao populations occurring at river basins from Acre and Amazonas states, Brazil, increased the chance that the selected resistant accessions would be genetically more dissimilar, and represent distinct sources of resistance to M. perniciosa from `Scavina 6`.

Progeny evaluation for resistance to Phaeosphaeria leaf spot in tropical maize

Maize breeding programmes in Brazil and elsewhere seek reliable methods to identify genotypes resistant to Phaeosphaeria leaf spot. The area under the disease progress curve (AUDPC) is an accurate method to evaluate the severity of foliar diseases. However, at least three data points are required to calculate the AUDPC, which is unfeasible when there are thousands of genotypes to be assessed. The aim of this work was to estimate the heritability of disease resistance, evaluate disease severity at different times using a nine-point scale in comparison to the AUDPC, and establish the most suitable phenological period for disease assessment. A repeated experiment was conducted in a 11 x 11 lattice experimental design with three replications. Disease assessments were carried out at flowering, 15 and 30 days post-anthesis for the parental lines DS95, DAS21, the F1 generation and 118 F2:3 progenies. Then, the AUDPC was obtained and results compared with the single-point evaluations used to calculate it. Individual and joint analyses of variance were conducted to obtain heritabiliy estimates. The assessments performed after the flowering stage gave higher estimates of heritability and correlation with AUDPC. We concluded that one assessment between the 15th and 30th day after flowering could provide enough information to distinguish maize genotypes for their resistance to Phaeosphaeria leaf spot under tropical conditions.

Inheritance of resistance to Puccinia psidii G. Winter in a eucalyptus interspecific hybrid progeny evaluated under conditions of natural infection

Inheritance of resistance to Puccinia psidii G. Winter in a eucalyptus interspecific hybrid progeny evaluated under conditions of natural infection Rust caused by the fungus Puccinia psidii is currently the most important disease of eucalyptus. It is widely disseminated in Brazil, and causes serious damage in nurseries and plantation areas. The identification of resistant germplasm along with knowledge of the genetic basis of resistance heredity are the first requirements for the success of breeding programs aiming to develop resistant varieties. Earlier studies carried out under controlled conditions suggested a monogenic control as well as the participation of at least two genes promoting resistance to rust. The goal of this study was to evaluate the resistance to P. psidii under field conditions in fourteen progenies from controlled crosses and self-crosses among four hybrid clones of Eucalyptus grandis Hill ex Maiden x Eucalyptus urophylla ST Blake that contrast for resistance to the fungus. Results indicated that resistance could be explained by one locus with main effects and at least three different alleles. However, loci with minor effects may influence the resistance, since variation on severity classes was observed. Differences in segregation of resistance between reciprocal crosses were not observed, indicating absence of cytoplasmic effects.

Transgenic Sweet Orange (Citrus sinensis L. Osbeck) Expressing the attacin A Gene for Resistance to Xanthomonas citri subsp citri

Genetic transformation with genes that code for antimicrobial peptides has been an important strategy used to control bacterial diseases in fruit crops, including apples, pears, and citrus. Asian citrus canker (ACC) caused by Xanthomonas citri subsp. citri Schaad et al. (Xcc) is a very destructive disease, which affects the citrus industry in most citrus-producing areas of the world. Here, we report the production of genetically transformed Natal, Pera, and Valencia sweet orange cultivars (Citrus sinensis L. Osbeck) with the insect-derived attacin A (attA) gene and the evaluation of the transgenic plants for resistance to Xcc. Agrobacterium tumefaciens Smith and Towns-mediated genetic transformation experiments involving these cultivars led to the regeneration of 23 different lines. Genetically transformed plants were identified by polymerase chain reaction, and transgene integration was confirmed by Southern blot analyses. Transcription of attA gene was detected by Northern blot analysis in all plants, except for one Natal sweet orange transformation event. Transgenic lines were multiplied by grafting onto Rangpur lime rootstock plants (Citrus limonia Osbeck) and spray-inoculated with an Xcc suspension (10(6) cfu mL(-1)). Experiments were repeated three times in a completely randomized design with seven to ten replicates. Disease severity was determined in all transgenic lines and in the control (non-transgenic) plants 30 days after inoculation. Four transgenic lines of Valencia sweet orange showed a significant reduction in disease severity caused by Xcc. These reductions ranged from 58.3% to 77.8%, corresponding to only 0.16-0.30% of leaf diseased area as opposed to 0.72% on control plants. One transgenic line of Natal sweet orange was significantly more resistant to Xcc, with a reduction of 45.2% comparing to the control plants, with only 0.14% of leaf diseased area. Genetically transformed Pera sweet orange plants expressing attA gene did not show a significant enhanced resistance to Xcc, probably due to its genetic background, which is naturally more resistant to this pathogen. The potential effect of attacin A antimicrobial peptide to control ACC may be related to the genetic background of each sweet orange cultivar regarding their natural resistance to the pathogen.