Delaminated areas beneath organic coating: A local electrochemical impedance approach

Local electrochemical impedance mapping was used to investigate delamination phenomena at the steel/epoxy-vinyl primer interface. The delamination occurred from an artificial defect(cutter scribing) and from ageing in a salt spray chamber. The samples were taken from the salt spray chamber after 20, 30 and 50 days of exposure. To observe delamination after ageing, the corrosion product layers were removed by a cathodic polarization at −1.5 V/SCE for 4 h. A non-aged reference sample was tested for comparison. Mapping was performed at 5 kHz. Initiation and propagation of the delamination were clearly observed. The delaminated surface areas measured by visual observations after the removal of the coating were lower than those determined by local electrochemical impedance mapping. The delamination mechanisms were discussed with reference to literature data

Detection and Removal of Long Scratch Lines in Aged Films

[[abstract]]Historical films usually have defects. We study the type of defects, and propose a series of solutions to detect defects before they are repaired by our inpainting algorithms. This paper focuses on a difficult issue to locate long vertical line defects in aged films. A progressive detection algorithm is proposed. We are able to detect more than 86% (recall rate) of effective line defects. These line defects are then removed step by step. The experiments use real historical video collected from national museum and public channel, instead of using computer generated noise. The results are visually pleasant based on our subjective evaluation by volunteers[[conferencetype]]國際[[conferencedate]]20060709~20060712[[iscallforpapers]]Y[[conferencelocation]]Toronto, Ont., Canad

Effects of Chromate and Chromate Conversion Coatings on Corrosion of Aluminum Alloy 2024-T3

Various effects of chromate conversion coatings (CCCs) and chromate in solution on the corrosion of AA2024-T3 and pure Al are studied in this work. Raman spectroscopy was used to investigate the nature of chromate in CCCs through a comparison with the spectra of known standards and artificial Cr(III)/Cr(VI) mixed oxides. Chromate was shown to be released from CCCs and to migrate to and protect a nearby, uncoated area in the artificial scratch cell. However, experiments investigating the effect of chromate in solution on anodic dissolution kinetics under potentiostatic control indicated that large chromate concentrations were needed to have an effect.This work was supported by Major H. DeLong at the United States Air Force Office of Scientific Research under contracts F49620-96-1-0479 and F49620-96-0042

Towards an improved understanding of plasticity, friction and wear mechanisms in precipitate containing AZ91 Mg alloy

This work reports a combined experimental and atomistic simulation study on continuous precipitates (CPs) and discontinuous precipitates (DPs) affecting the scratch induced wear in AZ91 magnesium alloy. Nanoscratching experiments complemented by atomic simulations were performed to understand the directional dependence and origins of plasticity, friction and wear mechanisms as benchmarked to nanocrystalline HCP magnesium. Post scratch deformation analysis was performed using electron back scattering diffraction, scanning electron microscope and molecular dynamics (MD) simulation. The direction of orientation of the precipitates was observed to make a significant influence on the deformation behaviour. For example, regardless of the precipitates type (CP or DP), a ductile-brittle transition becomes pronounced while scratching along the direction (orientation) of precipitates, whilst a fully ductile response was obtained while scratching along the direction normal to the precipitates. However, regardless of the direction of orientation, DPs showed a higher wear resistance and coefficient of friction compared to the CPs. These observations were supported by the quantitative analysis of the planar defects such as coherent twins, extrinsic and intrinsic stacking faults in the deformation zone as well as 1/3〈11¯00〉" role="presentation"> ( and 1/3〈12¯10〉" role="presentation"> dislocations type extracted from the MD analysis.These observations will facilitate an improved design of AZ91 alloys in particular and intermetallic precipitate containing alloys in general

Tribo-Mechanical Investigation of the Functional Components used in Flexible Energy Harvesting Devices

During the previous decade, the development of energy harvesting devices based on piezoelectric materials has garnered great interest. The ability to capture ambient mechanical energy and convert it to useable electricity is a potential solution to the ever-growing energy crisis. One of the most attractive functional materials used in these devices is zinc oxide (ZnO). This material\u27s relative low cost and ease of large-area processing has spurred numerous device designs based around it. The ability to grow ZnO nanostructures of various geometries with low-temperature chemical methods makes this material even more attractive for flexible devices. Although numerous device architectures have been developed, the long-term mechanical reliability has not been addressed.;This work focuses on the fabrication and mechanical failure analysis of the flexible components typically used in piezoelectric energy harvesting devices. A three-phase iterative design process was used to fabricate prototypical piezoelectric nanogenerators, based on ZnO nanowires. An output of several millivolts was achieved under normal contact and microtensile loading, but device failure occurred after only a few loading cycles, in all cases. Ex situ failure analysis confirmed the primary sources of failure, which became the focus of further, component-level studies. Failure was primarily seen in the flexible electrodes of the nanogenerating devices, but was also observed in the functional piezoelectric layer itself.;Flexible electrodes comprised of polyester substrates with transparent conductive oxide (TCO) coatings were extensively investigated under various loading scenarios to mimic tribo-mechanical stresses applied during fabrication and use in flexible contact-based devices. The durability of these films was explored using microtensile testing, spherical nanoindentation, controlled mechanical buckling, stress corrosion cracking, and shear-contact reciprocating wear. The electro-mechanical performance and reliability of functional ZnO films and nanostructures were also studied. ZnO was deposited on rigid and flexible substrates for investigations including controlled buckling, and contact-based rolling/sliding scenarios. Numerous in situ and ex situ analytical techniques were used to characterize component-level failure mechanisms, including two-probe electrical resistance, optical microscopy, SEM, AFM, and stylus profilometry.;Experimental results show that there is a strong relation between crack onset strain values, during microtensile and controlled bucking loading, and coating thickness. Relatively high crack onset values were observed for both thinner coatings and those patterned using photolithography and wet chemical etching techniques. Tribological experiments show that although piezoelectric ZnO films produce a measurable electrical output during combined rolling/sliding contact, cohesive wear of the oxide and adhesive wear between oxide and substrate is present and detrimental to sustained film functionality

Surface treatment of a low-cost beta titanium alloy to combat wear

The development of an effective ceramic conversion treatment of TIMETAL LCB (Ti-6.8Mo-4.5Fe-1.5Al) has been investigated. Various characterisation methods were used to analyse samples in order to identify the best process conditions including SEM, EDX, XRD, GDS, micro-indentation and scratch testing. A solution treatment temperature of 850°C was used as this is the appropriate temperature for the mechanism of solution treatment according to the β-transus temperature of this alloy. The results show that a solution treatment of 0.5 hours produces an acceptable thickness of oxygen hardened case, an almost equal hardness to that of a longer treatment and a far better oxide layer, than a longer treatment time did, in terms of adherence to the substrate. An aging temperature of 500°C was found to be the best as a lower temperature than this produced too thin an oxide layer and a higher temperature meant the oxide layer became exceedingly brittle. An aging time of 8 hours was found to be best as this gave good hardness, good performance in both static and dynamic loading and good wear resistance. The wear testing results show that the tribological properties of the TIMETAL LCB alloy have been significantly enhanced by the new ceramic conversion treatment specifically developed for beta alloys. The improved friction and wear properties can be attributed to the low-friction TiO$^2$ outer oxide surface layer supported by a Ti$^3$O$^5$ inner oxide layer and an oxygen diffusion hardened case up to a depth of ~70μm

PDA/PTFE Solid Lubricant Coating for 60NiTi Applications

The intermetallic alloy 60NiTi has a unique combination of high hardness and low elastic modulus, which makes it highly resistant to dents. Additionally, 60NiTi is extremely corrosion resistant and chemically inert. These properties make 60NiTi a desirable material for challenging mechanical component applications with high contact stresses and in harsh environments. However, lubrication issues have hindered the use of 60NiTi because it has poor tribological performance if it is not properly lubricated. The mechanical properties of hardened 60NiTi and its microconstituents were studied by nanoindentation. This study showed that the bulk properties of 60NiTi are driven by the properties of the NiTi + Ni4Ti3 region. The large Ni3Ti precipitates were found to have significantly higher hardness. This discovery inspired new theories for the wear behavior of 60NiTi. Despite its high hardness and extraordinary hardness-to-elasticity ratio, 60NiTi has poor tribological performance in unlubricated sliding. Since oil-based lubrication cannot be used in many applications, there is need for a suitable solid lubricant coating that can be applied to 60NiTi. A polytetrafluoroethylene (PTFE)-based solid lubricant coating that uses a polydopamine (PDA) adhesive underlayer was developed and evaluated for use on 60NiTi. PDA/PTFE coating was evaluated on 60NiTi substrate by linear-reciprocating wear tests against a Si3N4 ball. The coating reduced friction and protected the substrate surface from adhesive and abrasive wear during accelerated testing. The durability of the coating was drastically improved by grinding and polishing the substrate surface to produce a valley-dominant surface. The valleys of the substrate surface provided mechanical interlocking of the PDA/PTFE coating. Nanoindenter scratch tests and scanning electron microscopy imaging of the scratches provided a detailed understanding of the microstructural behavior and failure mechanisms of the coating. Additionally, incorporating graphite particles in the PTFE layer was shown to further enhance the coating performance. The coating was found to compact under repetitious sliding under normal loads to form a less-porous structure with enhanced cohesion. The valley-dominant substrate surface reduced tensile stresses in the coating, and the graphite particles added to the PTFE layer enhanced the coating cohesion. The combined effect was better resistance to coating tears that could lead to global coating delamination. Lastly, methods were developed to apply and test the PDA/PTFE coating as a ball bearing lubricant. A custom bearing tester was designed and built to study the effectiveness of the coating in ball bearing applications. The balls and races of hybrid R8 bearings were coated with PDA/PTFE or PDA/PTFE+GPs, and the bearing tests showed promising results. This work advanced the understanding of the unique mechanical properties of 60NiTi and developed PDA/PTFE solid lubricant coatings that are suitable solid lubricants for 60NiTi. Additionally, the microstructural behavior and failure mechanisms of PDA/PTFE-based coatings are better understood. The results are promising solutions for lubricating 60NiTi in challenging mechanical component applications

PDA/PTFE Solid Lubricant Coating for 60NiTi Applications

The intermetallic alloy 60NiTi has a unique combination of high hardness and low elastic modulus, which makes it highly resistant to dents. Additionally, 60NiTi is extremely corrosion resistant and chemically inert. These properties make 60NiTi a desirable material for challenging mechanical component applications with high contact stresses and in harsh environments. However, lubrication issues have hindered the use of 60NiTi because it has poor tribological performance if it is not properly lubricated. The mechanical properties of hardened 60NiTi and its microconstituents were studied by nanoindentation. This study showed that the bulk properties of 60NiTi are driven by the properties of the NiTi + Ni4Ti3 region. The large Ni3Ti precipitates were found to have significantly higher hardness. This discovery inspired new theories for the wear behavior of 60NiTi. Despite its high hardness and extraordinary hardness-to-elasticity ratio, 60NiTi has poor tribological performance in unlubricated sliding. Since oil-based lubrication cannot be used in many applications, there is need for a suitable solid lubricant coating that can be applied to 60NiTi. A polytetrafluoroethylene (PTFE)-based solid lubricant coating that uses a polydopamine (PDA) adhesive underlayer was developed and evaluated for use on 60NiTi. PDA/PTFE coating was evaluated on 60NiTi substrate by linear-reciprocating wear tests against a Si3N4 ball. The coating reduced friction and protected the substrate surface from adhesive and abrasive wear during accelerated testing. The durability of the coating was drastically improved by grinding and polishing the substrate surface to produce a valley-dominant surface. The valleys of the substrate surface provided mechanical interlocking of the PDA/PTFE coating. Nanoindenter scratch tests and scanning electron microscopy imaging of the scratches provided a detailed understanding of the microstructural behavior and failure mechanisms of the coating. Additionally, incorporating graphite particles in the PTFE layer was shown to further enhance the coating performance. The coating was found to compact under repetitious sliding under normal loads to form a less-porous structure with enhanced cohesion. The valley-dominant substrate surface reduced tensile stresses in the coating, and the graphite particles added to the PTFE layer enhanced the coating cohesion. The combined effect was better resistance to coating tears that could lead to global coating delamination. Lastly, methods were developed to apply and test the PDA/PTFE coating as a ball bearing lubricant. A custom bearing tester was designed and built to study the effectiveness of the coating in ball bearing applications. The balls and races of hybrid R8 bearings were coated with PDA/PTFE or PDA/PTFE+GPs, and the bearing tests showed promising results. This work advanced the understanding of the unique mechanical properties of 60NiTi and developed PDA/PTFE solid lubricant coatings that are suitable solid lubricants for 60NiTi. Additionally, the microstructural behavior and failure mechanisms of PDA/PTFE-based coatings are better understood. The results are promising solutions for lubricating 60NiTi in challenging mechanical component applications

Rhodium Pyrazolate Complexes as Potential CVD Precursors

Reaction of 3,5-(CF3)(2)PzLi with [Rh(mu-Cl)(eta(2)-C2H4)(2)](2) or [Rh(mu-Cl)(PMe3)(2)](2) in Et2O gave the dinuclear complexes [Rh(eta(2)-C2H4)(2)(mu-3,5-(CF3)(2)-Pz)](2) (1) and [Rh-2(mu-Cl)(mu-3,5-(CF3)(2)-Pz) (PMe3)(4)] (2) respectively (3,5-(CF3)(2)Pz = bis-trifluoromethyl pyrazolate). Reaction of PMe3 with [Rh(COD)(mu-3,5-(CF3)(2)-Pz)](2) in toluene gave [Rh(3,5-(CF3)(2)-Pz)(PMe3)(3)] (3). Reaction of 1 and 3 in toluene (1 : 4) gave moderate yields of the dinuclear complex [Rh(PMe3)(2)(mu-3,5-(CF3)(2)-Pz)](2) (4). Reaction of 3,5-(CF3)(2)PzLi with [Rh(PMe3)(4)]Cl in Et2O gave the ionic complex [Rh(PMe3)(4)][3,5-(CF3)(2)-Pz] (5). Two of the complexes, 1 and 3, were studied for use as CVD precursors. Polycrystalline thin films of rhodium (fcc-Rh) and metastable-amorphous films of rhodium phosphide (Rh2P) were grown from 1 and 3 respectively at 170 and 130 degrees C, 0.3 mmHg in a hot wall reactor using Ar as the carrier gas (5 cc min(-1)). Thin films of amorphous rhodium and rhodium phosphide (Rh2P) were grown from 1 and 3 at 170 and 130 degrees C respectively at 0.3 mmHg in a hot wall reactor using H-2 as the carrier gas (7 cc min(-1)).Welch Foundation F-816Petroleum Research Fund 47014-ACSNSF 0741973Chemistr