Fracture Of Oxide Films Research Articles

Study on the high temperature wear behavior of TiAlSiN coatings deposited on WC-TaC-Co cemented carbides

This study investigated the high-temperature wear behavior and the failure mechanism of TiAlSiN coating under thermal-mechanical coupling. The results indicate that increased temperature significantly promotes coating oxidation, forming a complete wear-resistant layer. However, coating hardness decreases significantly at elevated temperatures, deteriorating the wear property. Increased load generates higher friction heat and intensifies coating oxidation, but it accelerates oxide film fracture and spalling. Mechanical stress causes oxide film fracture, spalling and removal, while high-temperature oxidation triggers cracks healing, debris connection and oxide film re-formation. Oxide film exhibits a dynamic cycle of formation-breaking-formation in high-temperature wear.

Effect of ambient temperature on the ignition and combustion process of single aluminium particles

This experimental work aims to examine the effects of ambient temperature on the ignition and combustion process of single aluminium particles (40–170 μm). Ambient temperatures considerably influence the particle ignition delay time, but the influence on the combustion time is limited. Particle ignition probability is very sensitive to the ambient temperature. The particle ignition probability can be improved by approximately 6.7 times by increasing the ambient temperature by approximately 300 K. As the diameter increases, the ignition probability increases firstly and then decreases in the experimental conditions of Cases 02–06. The diameter ranges for the particle ignition probability of >90% in the experimental conditions of Cases 03–06 can be extended by the high ambient temperature. Moreover, the aluminium particles with high unevenness level can be ignited easily, which should be resulted from the local flame near the raised part. The characteristic particle temperature is measured using the method of two-colour pyrometry. Experimental results show that the aluminium particle in these experimental conditions can barely burn in a pure diffusion-limited regime. The structure and components of the oxide film on the unignited particle show that the oxide film fracture is a key process for particle ignition.

Rapid ultrasound-induced transient-liquid-phase bonding of Al-50Si alloys with Zn interlayer in air for electrical packaging application

Al-50Si alloys were joined by rapid ultrasound-induced transient-liquid-phase bonding method using Zn foil as interlayer at 390°C in air, below the melt point of interlayer. The fracture of oxide films along the edge of Si particles led to contact and inter-diffusion between aluminum substrate and Zn interlayer, and liquefied Zn-Al alloys were developed. The width of Zn-Al alloys gradually decreased with increasing the ultrasonic vibration time due to liquid squeezing out and accelerated diffusion. A stage of isothermal solidification existed, and the completion time was significantly shortened. In the liquid metal, the acoustic streaming and ultrasonic cavitations were induced. As the process developed, much more Si particles, which were particulate-reinforced phases of Al-50Si, gradually migrated to the center of soldering seam. The highest average shear strength of joints reached to 94.2MPa, and the fracture mainly occurred at the base metal.

Solid State Recycling of Aluminium Sheet Scrap by Means of Spark Plasma Sintering

Various solid state or ‘meltless’ recycling techniques have recently been developed for light metal scrap in form of chips. Main objective of all approaches is to bypass the need for remelting in order to reduce the overall required energy, and to avoid the material losses that occur during this step. Within this paper, the use of Spark Plasma Sintering (SPS) is proposed as a novel solid state recycling/welding technique for sheet metal scrap. Aluminium 5182 alloy scrap, derived from sheet metal, was successfully consolidated into a fully dense billet via SPS. The use of pulsed electric current heating, in temperatures well below the alloy melting point, combined with mechanical pressure, enchased the densification process resulting into a void-less material. The recycled SPS sample was fully densified and microstructural investigation has been performed in order to confirm effective oxide film breakage. The results illustrate the effectiveness of SPS in aluminium scrap consolidation, also in form of sheet scrap, providing additional means in solid state recycling. The involved mechanisms that contribute to oxide film fracture and scrap consolidation in SPS are being discussed.Keywords: Aluminium, recycling, spark plasma sintering (SPS)

Action of Displacement Control on Vacuum Free Aluminum/Copper Diffusion Liquefaction Bonding

Quickness of fracture of Al oxide film is important especially for vacuum free Al/Cu bonding. Displacement amount and rate relate closely with fracture of oxide film and create clean surface. Displacement history during bonding process under static bonding load was measured for displacement control systematically. Displacement history under static load consists of three stages with creep and liquefaction. Higher bonding load increased displacement rate of each stage and decreased the thickness of Al oxide film grown by air heating. Suitable hearing time for bond also was shortened by increment of bonding load. Two types of displacement control were designed from these experimental results. One was the accelerated displacement rate control, another was the cyclic displacement control. Fracture of Al oxide film and liquefaction of bonding surface occurred at lower displacement than static load by each displacement control.

Effect of impact assembly on the fretting corrosion of modular hip tapers

The goal of this study was to determine the effect of assembly load and local assembly environmental conditions on the fretting corrosion of modular femoral stem tapers. Femoral head/taper assemblies in both similar (CoCrMo/CoCrMo) and mixed (CoCrMo/Ti-6Al-4V) alloy combinations were evaluated using an electrochemical test method. Specimens were assembled under impact loading and by hand, in both wet and dry conditions. Incremental cyclic loads ranging from 89 to 5,340 N were applied at a frequency of 3 Hz in Ringer's solution at ambient temperature. During the test, both the open circuit potential (OCP) and fretting current (i(fret)) were measured using a saturated calomel electrode (SCE) and counter electrode, respectively. The results were comparable for both mixed and similar alloy couples. Decreases in OCP and increases in i(fret) (indicators of oxide film fracture and repassivation) were seen with increasing load magnitude, often occurring at loads well below those expected clinically. OCP at the 5,340 N cyclic load ranged from -30.4 to -103.7 mV versus SCE for similar alloy couples, and -19.1 to -181.4 mV versus SCE for mixed alloy couples. Mean peak fretting currents ranged from 0.84 to 1.42 microA and 1.06 to 3.12 microA for similar and mixed alloy couples, respectively. The larger current magnitudes and more negative shifts in OCP for mixed alloy couples indicate the difference in oxide film fracture behavior between titanium and cobalt alloys. The load at which OCP began to drop (onset of fretting) was dependent upon the assembly conditions for both material couples. Specimens assembled with impact loads in air showed the highest resistance to fretting. The results of this study indicate that the assembly load and the environment both play a role in the initial stability of modular hip taper connections.

Nanomechanical Testing for Fracture of Oxide Films

The mechanical properties of thermally grown oxide films on various aluminum substrates were tested using nanoindentation. A sudden discontinuity, indicative of film fracture, was observed upon loading portion of the load–depth curve. The 63-nm-thick films were determined to have ultimate strengths between 4.8 and 8.9 GPa. The ultimate stress is a superposition of the bending and membrane stress. The stress intensity at fracture for each of the films was developed by approximating the resulting bending moment and various cracks sizes. At a constant ratio of crack size to oxide thickness of 0.3, the applied stress intensity at fracture of these aluminum oxide films were between 0.46 and 1.20 MPa m1/2. The residual stress in the film was assumed to be negligible in the stress intensity calculation.

A boundary constraint energy balance criterion for small volume deformation

A concept for the deformation resistance of small volumes under contact subjected to displacements in the 2–100 nm regime is proposed. In terms of an energy balance criterion, the external work minus stored elastic energy is consumed by surface energy and plastic energy absorption. The surface energy is interpreted in terms of new area of contact or new area created by slip step emergence or oxide film fracture. The plastic energy absorption is interpreted in terms of dislocation work. As such, this is analogous to a contact mechanics Griffith criterion for the hardness or flow strength of crystalline metals, semiconductors or oxides. Derivations of supporting loads and stresses provided for nanoindenter tips, nanospheres, nanocubes and thin-walled nanoboxes are presented. For comparison, measured hardness and flow strengths of Al, Au, Fe–3%Si, Ti, W and Si nanostructures are reported in the 2–100 nm length scale regime. It is proposed that Si and Ti nanospheres experience a minimum in contact resistance as dictated by a balance in surface energy dominance at small contact and dislocation hardening dominance at large contact. The variation of a strength controlling coefficient, α, with material suggests a length scale dependence on shear and/or pressure activation volumes.

An approach to dry friction and wear for small volumes

Abstract Fracture and contact mechanics can synergistically contribute to the fundamental understanding essential to scaling of small volumes. Consider two levels of scale in terms of contact area: (i) light wear of tribological contacts at the nanometre level; (ii) delamination of hard protective coatings or ductile metal films at the micrometre level. We first briefly address two phenomena—one showing that oxide film fracture is responsible for yield excursions during nanoindentation and the other showing that analysis of acoustic events can sort out some of the discontinuous events of yield and fracture on the nanometre scale. These concern mostly the fracture process concomitant with a localized plasticity event. However, they do not address the fundamental aspects of what controls the size of the yield event or what controls the size of a localized fracture event, for example delamination. We propose that one way of understanding these two levels of scale and their interconnectivity is through a volume-surface area concept. At present, we show two levels of understanding for contacts to single-crystal surfaces and how these provide insight and potentially quantification of light wear contact.

An approach to dry friction and wear for small volumes

Fracture and contact mechanics can synergistically contribute to the fundamental understanding essential to scaling of small volumes. Consider two levels of scale in terms of contact area: (i) light wear of tribological contacts at the nanometre level; (ii) delamination of hard protective coatings or ductile metal films at the micrometre level. We first briefly address two phenomena-one showing that oxide film fracture is responsible for yield excursions during nanoindentation and the other showing that analysis of acoustic events can sort out some of the discontinuous events of yield and fracture on the nanometre scale. These concern mostly the fracture process concomitant with a localized plasticity event. However, they do not address the fundamental aspects of what controls the size of the yield event or what controls the size of a localized fracture event, for example delamination. We propose that one way of understanding these two levels of scale and their interconnectivity is through a volume-surface area concept. At present, we show two levels of understanding for contacts to single-crystal surfaces and how these provide insight and potentially quantification of light wear contact.

Processing of Thick Dielectric Films for Power MEMS: Stress and Fracture

ABSTRACTThis paper presents residual stress characterization and fracture analysis of thick silane based PECVD oxide films. The motivation for this work is to elucidate the factors contributing to residual stress, deformation and fracture of oxide films so as to refine the fabrication process for power MEMS. It is shown that residual stress in oxide films strongly depended on thermal processing history. Dissolved gases were found to play an important role in governing intrinsic stress. The tendency to form cracks is a strong function of film thickness and annealing temperature. Mixed mode fracture mechanics was applied to predict critical cracking temperature, and there is a fairly good match between theoretical predictions and experimental observations.

The Strength and Fracture of Passive Oxide Films on Metals

AbstractPassive films have been grown electrochemically on a polycrystalline titanium alloy. By varying the applied voltages, the film thickness is varied. A testing apparatus has been constructed to allow measurements of nanomechanical properties during electrochemical testing using a Ag/AgCl reference electrode in a traditional three-electrode potentiostatic scan. The stress at which oxide film fracture occurs is correlated to the applied potential. Observations of in situ film fracture measurements on single grains during immersion show the strength of the film remains constant in environments in which the film is inert, but decreases by approximately 20% in solutions which lead to corrosion. The fracture mode of the oxide has been observed using atomic force microscopy, and is shown to qualitatively match the largest tensile stresses which develop using elastic contact mechanics. A simplified model for determining the maximum tensile stress around an indentation is presented, and is used to show the stress required for fracture increases approximately linearly with increasing applied anodic polarization, from 850 MiPa to approximately 3 GPa for applied potentials between 1 and 9 V.

Yield Point Phenomena and Dislocation Velocities Underneath Indentations Into BCC Crystals

AbstractIn a single material, hardnesses can range from 3σys up to the theoretical strength or approximately E/10 where σys and E are tensile yield strength and modulus. This variation results with decreasing depth of penetration. Such indentation size effects may be associated with surface contamination, passivation films and dislocation phenomena. Even where dislocation nucleation is relatively difficult as in GaAs, the hardness varies from about 1.5 to 15 GPa as the indentation depth decreased from about 100 nm to 10 nm. Similar size effects in BCC metals can give hardnesses which range from about 1 to 30 GPa as the indentations decrease from 1000 nm to 10 nm. Here, there are two types of “yield” phenomena which can be related to an organic contamination film and a dislocation pile-up induced oxide film fracture. As measured in single crystals of Fe, Mo, W, Ta and NiAl, this typically gives lower and upper “yield” points which range from 0.6 to 10 raN. When a dislocation pile-up breaks through the oxide film, velocities can be reasonably large due to the stress at the head of the pile-up. The average dislocation velocity of this avalanche is controlled, to first order, by the Peierls’ energy. A more exhaustive study of NiAl, with a B2/BCC type crystal structure shows that dislocation velocity can be related to the local pile-up stress and a Peierls’ barrier of about 2.2 eV.

Fretting Corrosion of Solder-Coated Electrical Contacts

The contact resistance of fretting solder-plated contacts may rise quickly due to the accelerated formation of insulating oxides on their surfaces. This condition becomes worse with increase in length of wipe and with reduction in normal load. The solder-plated versus gold-plated system shows a more rapid rise in contact resistance which can be explained by differences in the mechanics of oxide film fracture compared to that of all-solder-coated contacts. Many fluid lubricants are able to maintain low, stable contact resistance when applied to surfaces in thick (about 20 000 A) layers, particularly on both contacts of a mated pair. The contact resistance of solder versus gold is more difficult to stabilize with lubricants than that of solder against itself, although lubricants may be useful provided that fretting distances are small. The effectiveness of coatings is due to their ability to greatly reduce oxygen arrival at the surface. When it is impractical to employ finishes other than solder on the contacts of separable connectors and when fretting can occur, it is recommended that coatings of viscous oils or greases be used to prolong contact life. An example of a useful coating is one which is obtained by immersion and withdrawal of the contacts from a mixture by weight of 20 percent polyphenylether fluid and 1 percent of microcrystalline wax in 1,1,1- trichloroethane.

5087. Emission of electrons and positive ions upon fracture of oxide films: JT Dickinson et alJ Vac Sci Technol,18 (2), 1981, 238–241

5087. Emission of electrons and positive ions upon fracture of oxide films: JT Dickinson et alJ Vac Sci Technol,18 (2), 1981, 238–241

The Role of Defects in the Fracture of Oxide Films on Metals

The extent of fracture of anodic oxide films during tensile deformation of aluminum is shown to be controlled by the density of defects in the oxide. The density of defects was monitored by the “leakage” resistance of the film, while the extent of fracture of the oxide was obtained from measurements of reanodization current transients. Other experiments in a photoelectron microscope showed that these oxides are ruptured at emerging slip steps. This provided the basis of a simple model for oxide fracture, which requires the presence of a defect in the oxide at the site of an emerging slip step. A relationship between the leakage resistance and fracture susceptibility of the oxide was derived and confirmed by experiment, showing that both properties are controlled by the same type of defect. The density of these defects may be controlled by the surface preparation prior to anodization. If the density of defects is greatly reduced, even a thin (28 nm) oxide becomes strong enough to suppress slip step formation during tensile deformation.

Emission of electrons and positive ions upon fracture of oxide films

During tensile deformation of oxide-coated aluminum, small cracks a few hundredths of a mm in length occur in the oxide film. During and following the appearance or elongation of these cracks, electron emission (EE) and positive ion emission (PIE) are detected in the surrounding vacuum. Crack propagation in the oxide coating can be detected with an acoustic emission (AE) transducer. Correlations between charged particle emission and film fracture can then be determined. A comparison of rates of EE, PIE, and AE, the distribution of the number of electrons or ions per burst, and the time distributions relative to crack propagation of both EE and PIE are presented. The time distributions indicate distinct differences in the rate limiting steps governing EE and PIE.

Fracture of oxide films on strained aluminium

Abstract The mode of fracture of anodic film on aluminium has been examined. It is concluded that the films are reasonably elastic and that when they fail there is ‘slip’ at the film metal interface. There is no evidence of crack propagation from film to metal. The etching behaviour of strained aluminium can be explained using the present results.