Sn and Ti influences on intermetallic phases damage in hot dip galvanizing

Protection against metallic materials corrosion is one of the most important means to reduce both maintenance costs and environmental impact. In the last years new studies on chemical baths compositions and fluxes have been performed in order to improve processes, corrosion resistance and mechanical behavior of Zn based coatings. Chemical bath composition is often improved by the Sn addition which increases the fluidity ofthe melt. Ti addition makes the coatings to change color under appropriate heat treatment. In this work a comparative microstructural analysis, in Zn-Sn and Zn-Ti coatings, is performed to evaluate intermetallic phases formation kinetics and the influence of intermetallic microstructure on coating damage under constant bending deformation

pearlitic ductile cast iron fatigue crack paths and damaging micromechanisms

Abstract The influence of the graphite nodules morphology (shape, dimension and distribution) on ductile cast irons (DCIs) mechanical properties is experimentally confirmed both in static, quasi static and cyclic loading conditions. According to the most recent results, these graphite elements cannot be merely considered as "microvoids embedded in a metal matrix", but their presence implies a modification of the damaging micromechanisms and this modification I s influenced by the metal matrix microstructure. In this works, the different damaging mechanisms that are active in the graphite nodules in a pearlitic DCI are semi-quantitatively analyzed using light optical microscope observations of the fracture surface profiles

Structural transitions in a NiTi alloy: a multistage loading-unload cycle

NiTi shape memory alloys (SMAs) are increasingly used in many engineering and medical applications, because they combine special functional properties, such as shape memory effect and pseudoelasticity, with good mechanical strength and biocompatibility. However, the microstructural changes associated with these functional properties are not yet completely known. In this work a NiTi pseudo-elastic alloy was investigated by means of X-ray diffraction in order to assess micro-structural transformations under mechanical uniaxial deformation. The structure after complete shape recovery have been compared with initial state

Integranular corrosion susceptibility analysis in austeno-ferritic (duplex) stainless steels

Abstract: Austenitic-ferritic stainless steels combine the favorable properties of ferrite and austenite, showing both high mechanical properties and very good corrosion resistance. These steels are characterized by the precipitation of many secondary phases, carbides and nitrides for tempering temperatures between 200 and 1050°C. This phenomenon implies a high susceptibility to localized corrosion, however better than austenitic and ferritic grades. In this work, the susceptibility to intergranular corrosion in of two duplex stainless steel characterized by analogous ferrite/austenite volume fraction was investigated. A "standard" duplex stainless steel SAF 2205 and a "super" duplex stainless steel SAF 2507 were investigated by means of potentiostatic reactivations tests. In addition, chronoamperometric tests and light optical microscope observations of the specimens surfaces were performed in order to analyze the evolution of the corrosion morphologies

Overload effects on fatigue cracks in ferritic-pearlitic ductile cast irons

Abstract Matrix microstructure (e.g., phases volume fraction, grains size and grain distribution) and graphite nodules morphology peculiarities (e.g., nodularity level, dimension, distribution etc.) strongly affect the mechanical behavior and damaging micromechanisms in Ductile Cast Irons (DCIs). Concerning the influence of the graphite nodules, it depends both on the matrix microstructure and the loading conditions (e.g., static, quasi-static or cyclic loadings). The influence of graphite nodules on the damaging micromechanisms is not univocally identified. Some authors proposed to consider the graphite nodules as voids embedded in a more or less ductile matrix; other authors recently proposed a more complex contribution of the graphite nodules, suggesting a mechanical properties gradient inside the graphite nodules, with the graphite elements – matrix debonding as only one of the possible damaging micromechanisms. In this work, three different ferritic-pearlitic DCIs were investigated, focusing the damaging micromechanisms due to overloads applied on fatigue cracked Compact Type specimens. Scanning Electron Microscope (SEM) and Digital Microscope (DM) observations were performed on the lateral surfaces of the overloaded specimens following a step by step procedure: SEM observations were mainly focused on the damaging mechanisms in graphite nodules; DM observations were mainly focused on the damaging mechanisms in the ferritic-pearlitic matrix

Sn and Ti influences on intermetallic phases damage in hot dip galvanizing

Protection against metallic materials corrosion is one of the most important means to reduce both  aintenance costs and environmental impact. In the last years new studies on chemical baths compositions and fluxes have been performed in order to improve processes, corrosion resistance and mechanical behavior of Zn based coatings. Chemical bath composition is often improved by the Sn addition which increases the fluidity of the melt. Ti addition makes the coatings to change color under appropriate heat treatment. In this work a comparative microstructural analysis, in Zn-Sn and Zn-Ti coatings, is performed to evaluate intermetallic phases formation kinetics and the influence of intermetallic microstructure on coating damage under constant bending deformation

bending damages in galvanized ductile cast irons

Abstract Ductile cast irons (DCIs) are characterized by mechanical properties close to low and medium carbon steels. Carbon atoms are mainly localized in graphite nodules, which are dispersed in a metallic matrix. The microstructure of metallic matrix can be ferritic, austenitic, pearlitic, martensitic or their mix, depending on chemical composition and heat treatment. Thanks to the high castability and low production costs, DCIs are used in many fields (e.g., automotive and pipes). The wide utilization of DCIs in many fields and critical application leads to particular attention to the corrosion phenomenon. Hot dip galvanizing is one of most important protection process, used to protect metallic materials (mainly steels) against corrosion in many aggressive environments. In this work, a ferritic-pearlitic DCI (GS500) was galvanized by using a pure Zn bath at 440°C to generate a zinc coating. Bending tests on galvanized specimen were performed to generate crack damage in the coating phases. The bending cracks path propagation in zinc coatings were observed using both a light optical microscope and scanning electron microscope. A damage parameter, defined as a number of radial crack for a millimeter of the deformed arc, was evaluated for each zinc coating intermetallic phases

grain size influence on fatigue behaviour in a cuznal pe sma

Abstract Due to their capability to recover the initial shape, Shape Memory Alloys (SMAs) are widely used in many applications. Different grades are commercially available and they can be classified considering either their chemical compositions (Cu based, Ni based, Fe based and so on..) or according to their mechanical behaviour. The most used SMAs are the Ni based alloys thanks to their performances both in terms of mechanical resistance and in terms of fatigue resistance, but their costs are quite high. Cu based alloys are good competitors of the Ni based alloys. The recent optimization of their chemical composition improved both the corrosion resistance in aggressive environments and their mechanical performances. In this work, the influence of the grain size on fatigue crack propagation in two Cu-Zn-Al SMAs focusing on the damaging micromechanisms

GRB Observed by IBIS/PICsIT in the MeV Energy Range

We present the preliminary results of a systematic search for GRB and other transients in the publicly available data for the IBIS/PICsIT (0.2-10 MeV) detector on board INTEGRAL. Lightcurves in 2-8 energy bands with time resolution from 1 to 62.5 ms have been collected and an analysis of spectral and temporal characteristics has been performed. This is the nucleus of a forthcoming first catalog of GRB observed by PICsIT.Comment: 6 pages, 3 figures. Poster presented at COSPAR 2008. Advaces in Space Research, accepted for publicatio