Tribological properties for unlubricated sliding wear of electroless Ni-P/diamond composite films with different ceramic contents were evaluated by the pin-on-disk method with different applied loads ...with Al
2O
3 countermaterial. As-plated amorphous and heat-treated crystalline matrices were considered. Hardness, Young modulus, Milman plasticity parameter, and crack-arrest fracture toughness were evaluated by diamond pyramid indentation methods. Correlations among mechanical properties and tribological behavior were evaluated quantitatively. The wear resistance of as-plated samples with an amorphous matrix can be correlated with hardness. The wear resistance of heat-treated samples with crystalline two-phase matrix can be correlated with fracture toughness.
In this paper a model for the fatigue strength prediction of rope wires is presented and discussed. Within this method the fatigue process of wires is described in terms of propagation of the surface ...defects caused by cold drawing. In particular, the fatigue limit is related to the population of extreme defects and to the material properties expressed by cyclic yield strength and by crack propagation thresholds.
The model has been successfully applied for the prediction of fatigue strength of two different eutectoid steel wires, one of them being zinc coated, used in ropeway applications.
Failure Analysis of Tuna Cans BARELLA, S; CINCERA, S; BONIARDI, M ...
Journal of failure analysis and prevention,
08/2011, Letnik:
11, Številka:
4
Journal Article
Recenzirano
A metal container used for food packaging must preserve the food's edibility characteristics for a long period of time. Lacquered tinplate is suitable for canning food provided that the cans are ...airtight. This article details a root cause failure analysis that was conducted utilizing a sample of tuna cans taken from an affected batch of one million units. Several examinations were carried out to identify the failure's root cause: visual examination, SEM fractography, micro-hardness measurement, and microstructural characterization. The cracks are located in the HAZ of the welded zone. As a result of the examinations carried out, the authors were able to identify the cause of the primary failure. The identified fracture mechanism is that of stress corrosion cracking (SCC), due to both the aggressive environment (high water content in the oil) and the low lacquer adhesion caused by superficial welding irregularities.
A certain number of motorbike disc brakes, made of stainless steel, shown the presence of small cracks only after a few thousands miles. These cracks were mainly located nearby the holes placed on ...flange to ventilate and refresh pads.
According to results, the deterioration can be led back to thermal cyclic strain (related with the heating–cooling cycles developed during the brake action) superimposed to the mechanical strain caused by braking torque.
This work analyses the aforesaid disc brakes investigating both the main causes and the evolution of its deterioration in order to find out possible solutions. The short lifespan of such discs has to be ascribed to the rapid decay of the mechanical properties of the manufacturing material. Material decay is liable for starting cracks.
Several actions could be chosen to face this problem. The choice of a particular chemical composition, which will be demonstrated to be unfit for the purpose, produced an extreme tempering of the steel as a direct result of its protracted exposure to high temperatures (a situation which can be considered usual referring to disc brakes).
In this work, we present the effect of choosing a different kind of steel, characterized by a greater resistance to the tempering processes.
The phase-change memory technology is based on a chalcogenide compound able to reversibly switch between two stable states, namely, an amorphous high-resistive state and a crystalline low-resistive ...one, enabling the storage of the logical bit. Such phase transition is made by electrical pulses delivered to the memory cell, able to force a temperature raise within the material and to allow the temperature conditions required for the phase change. The cell internal temperature needs accurate control, and the evaluation of the thermal resistance of the memory cell represents a milestone to develop thermally efficient cell architectures and to gain insights into the thermal properties of the phase-change material. An experimental method for cell internal temperature evaluation has been developed and then supported by the electrothermal simulation of the cell behavior during the program operation, allowing for scaling predictions.
Fatigue crack propagation in Duplex Stainless Steels (DSSs) is strongly affected by microstructure and therefore by the choice of the steel grade or by the heat treatment conditions. In the present ...work fatigue behaviour of 22 Cr 5 Ni DSS has been investigated both after solution annealing and after different embrittling thermal cycles. Fatigue tests have been done in air considering the influence of both the stress ratio and the loading direction. Roughness analysis has been performed to point out a relationship between fracture morphology and fatigue crack propagation data and it shows that fracture surface roughness influence on fatigue crack advancing depends on loading conditions. A scanning electron microscope (SEM) fracture surface analysis has been performed to investigate the fatigue crack propagation micro mechanisms in 22 Cr 5 Ni duplex stainless steel.
A simple model is proposed for the evaluation of crack-arrest fracture toughness KIc0 of thin films by Vickers indentation. This approach applies to films thinner than the penetration depth of the ...Vickers indenter. The model equations are provided in closed form, even though they are so complex that they must be integrated numerically in practical applications. The problem of the evaluation of KIc0 for thin films and substrates is derived in general form and applied to three cases: (i) evaluation of KIc0 for the film in the case that the depth of the crack in the film is smaller than the film thickness, (ii) evaluation of KIc0 for the film in the case that the crack emanating from the film either crosses the film/substrate interface or is stopped by it, (iii) evaluation of KIc0 for the substrate in the case that the crack emanating from the film crosses the film/substrate interface. The model was tested with original and literature experimental data: (i) revision KIc0 values of electroless Ni-P thin films were re-evaluated, (ii) KIc0 of electroless Ni-P thin films of various thickness with various loads were measured (original data) and computed, (iii) KIc0 of electroless Ni-P substrates coated with electrodeposited Au-Cu were measured (original data) and computed.
Phase Change Memory (PCM) operation relies on the reversible transition between two stable states (amorphous and crystalline) of a chalcogenide material, mainly of composition Ge2Sb2Te5 (GST). In ...Wall type PCM cells, cycling endurance induces a gradual change of the cell electrical parameters caused by variations in the chemical composition of the active volume. The region closer to the GST-heater contact area, becomes more Sb rich and Ge depleted. The new alloy has usually different thermal characteristics for the phase transitions that influence the electrical behavior of the cell. In this study we analyze the morphological, structural and electrical properties of two Sb-rich non-stoichiometric alloys: Ge14Sb35Te51 and Ge14Sb49Te37, at their amorphous and crystalline phase. Experiments have been performed in non-patterned blanket films and, to simulate the device size, in amorphous regions of 20nm, 50nm and 100nm diameter respectively. The amorphous Ge14Sb35Te51 film crystallizes in the meta-stable face centered cubic structure at 150°C and in the rhombohedral phase at 175°C, behavior characteristic of the Ge1Sb2Te4 composition. The average grain size is of about 100nm after an annealing at 400°C. The Ge14Sb49Te37 film crystallizes only in the hexagonal phase, with an average grain size of about 60nm after annealing at 400°C. The X-ray fluorescence analysis shows a non uniform distribution of the constituent atoms and in particular a Ge signal decrement and a Sb enrichment at grain boundaries. The in situ annealing of amorphous nano-areas (RESET state under a thermal stress) indicates a fast re-crystallization speed for Ge14Sb35Te51, 80pm/s at 90°C, and a lower speed for Ge14Sb49Te37, at 130°C a grain growth velocity of 50pm/s has been measured. The different behavior of the two alloys is discussed in terms of structural vacancies filling by the Sb atoms in excess and by their segregation at grain boundaries. The influence of the obtained results on the device characteristics is discussed.
A numerical simulation is proposed of erosion–corrosion phenomena in four-phase flows comprising two immiscible liquids, gas and particulate solid. The simulation geometry is a pipe bend and the ...evaluated quantity is the wall erosion–corrosion brought about by the flow of a fluid mixture of two liquid phases, one of which is corrosive, plus a gas phase flow and a solid phase. A computational fluid dynamic tool has been adopted for the simulation of the flow field inside the piping and for the simulation of the particle trajectories and impact rates. As far as corrosion is concerned, a passivating and an actively corroding metallic material have been considered. Erosion model parameters have been derived from experiments correlating particle impact angle and erosion rate. Corrosion model parameters have been obtained from electrochemical measurements. The effects of the key operating parameters (fluid flow velocity, particulate content and gas volume fraction) have been evaluated by a two-level design of experiments approach. The single most important effects on synergistic damaging and on the ratio of corrosive to overall damaging have been identified. Erosion-enhanced and erosion-limited effects of flow conditions have been highlighted for the passivating and for the actively corroding alloys, respectively.
NiO–YSZ films – of thicknesses in the range ca. 1–15 μm – have been fabricated by multi-step galvanostatic deposition from acidic hydroalcoholic solutions of NiCl
2, ZrOCl
2 and YCl
3, containing ...Chitosan. The crystallographic structure of the electrodeposits has been studied by XRD, their chemical composition has been evaluated by EDX analysis, their morphology has been observed by SEM and optical microscopy and their adhesion has been quantified by the scratch-test method. Deposition-rate measurements have pinpointed some kinetic factors, relevant to process optimisation and bath management. As-plated samples exhibit an X-ray amorphous structure, that can be converted to crystalline fcc-NiO/cubic-fluorite YSZ by heat treatment. The YSZ composition is Y/Zr ca. 0.2 (molar ratio) and does not depend appreciably on processing conditions; the NiO content can be tuned in the range Ni/(Zr
+
Y) ca. 0.2–2 (molar ratio) by adjusting the electrodeposition parameters.
