Quantitative in-situ nanomechanical characterization of metallic nanowires

This paper reviews recent studies on in-situ quantitative mechanical characterization of metallic nanowires with diameters from a few nanometers to hundreds of nanometers, with particular emphasis placed on tensile loading geometry. Critical challenges and pitfalls in manipulating, clamping, and quantitatively testing nanowire specimens, with drastically different dimensions, are discussed. Two general experimental strategies are employed: microelectrochemical systems-based technology for testing of larger-diameter metal nanowires (D ∼ 30–300 nm), and insitu transmission electron microscopyatomic force microscopy platform for testing of ultrathin metallic nanowires (D < 20 nm). Size-dependent mechanical behaviors of gold nanowires, as well as the transition of different deformation mechanisms at corresponding length scales, are clearly revealed.     

Novel techniques for selective diamond growth on various substrates

There is a need for selective diamond growth in microelectronic and tool industries. This research was di-rected towards novel approaches in the selective diamond growth on non- diamond substrates. Diamond film was selectively deposited on the copper substrate by laser- hydrocarbon liquid (benzene C₆H₆) inter-action at room temperature which was used as seed for subsequent growth of diamond by the hot filament chemical vapor deposition (HFCVD). Diamond was also selectively grown on the gold patterned alumina substrate by manipulating HFCVD processing conditions. Diamond was selectively grown on the pat-terned silicon wafer (without having any scratches).     

Gorsky damping in nanomechanical structures

The critical frequency of Gorsky damping coincides with the structural resonant frequencies of nanomechanical structures over a wide range of solute diffusivities. A lower bound of 1 at.% hydrogen in silicon is estimated for Gorsky damping to attain values comparable to previously measured loss coefficients of single-crystal silicon nanomechanical cantilever-beam resonators.     

Coating optimisation for high speed machining with advanced nanomechanical test methods

Advanced nanomechanical testing has been used to evaluate key factors influencing tool life (1) a plasticity index (PI, the plastic work done/total work done during indentation), at room and elevated temperature (2) hot hardness and (3) fatigue fracture resistance, and determine their relative importance in different cutting applications. The optimum combination of hardness and toughness/plasticity to minimise wear and extend the life of coated WC-Co cutting tools was found to vary with the severity and nature of the cutting conditions. For interrupted cutting the plasticity index is critical, with high values (i.e. not extremely high H/E) resulting in extended tool life. Elevated temperature nanoindentation showed decreasing hardness and increasing PI with temperature. In high-speed turning hot hardness is the dominant factor whilst for interrupted cutting high hot hardness should be combined with improved plasticity for longer tool life. A novel test technique nano-impact, was used to simulate the interrupted contact (and cyclic loading) conditions occurring in milling applications and evaluate the fatigue fracture resistance of coated tools. It was able to successfully rank coatings in terms of tool life in end milling and reproduce the evolution of tool wear in the cutting test. In elevated temperature nano-impact testing the probability and extent of fracture during the test decreased at elevated temperature, consistent with the higher PI. Results from the advanced nanomechanical tests can be used in combination to predict which coatings have longer life in severe cutting conditions.     

Novel routes to nanocrystalline mechanical characterization

The use of nanoindentation techniques to measure nanoscale mechanical behavior is a new path of interest to researchers today. Load drops and displacement excursions can be utilized to measure activation volumes for dislocation events in single crystals, thin films, and nanoposts. Through the introduction of a new length-scale parameter, the dislocation wall spacing, a mechanism describing staircase yielding, is presented. The dislocation wall spacing can also be used to estimate activation volumes. Molecular dynamics simulations of nickel film indentation have been used to validate the origin of staircase yielding and also show consistent dislocation wall spacings. Additionally, stress relaxation experiments have been used to estimate activation volumes.     

Creep damage characterization using non-linear ultrasonic techniques

This paper describes the use of non-linear ultrasonic techniques for the characterization of material degradation in 99.98% pure copper due to high-temperature creep. Flat dog-bone-shaped specimens were subjected to constant load creep testing at different stress and temperature levels. Creep damage progression was monitored by conducting continuous and interrupted mode creep tests. In the case of continuous loading non-linear ultrasonic (NLU) measurements were conducted after fracture at different locations along the gage length of the sample. For interrupted tests the NLU measurements were conducted on different creep life fractions, through periodic interruption of the creep test. In all cases a through transmission NLU measurement technique was employed. Three different non-linear measurements, namely static displacement, second harmonic and third harmonic, were taken and their responses compared. The NLU measurements were found to be significantly sensitive to the extent of creep damage (～200–2500% of base level), while the linear ultrasonic measurements, representing the change in longitudinal velocities, were only in the range 10–30% for a comparable creep damage level. NLU measurements carried out on fractured samples suggest that the NLU response was locally high at locations where the creep damage was concentrated, compared with other locations, even within the gage length of the specimen. This was confirmed using micrograph observations. Of the three non-linear measurements, the third harmonic data was most sensitive to creep damage.     

Novel application of radiotracer techniques for corrosion studies of zinc and aluminium in acidic medium

The adsorption of sulphate ions on Zn and Al was studied in 0.5 M NaClO₄ supporting electrolyte at various pH values in the range of pH=2-7 by radiotracer techniques. It was found in both cases that the adsorption of sulphate passes over maximum in the pH range studied.The phenomena observed are interpreted by the assumption that the main component of the overall process is anion adsorption on the protonated oxides/hydroxides formed as a result of corrosion. At low pH values the steady state coverage with respect to these products should be very low owing to their dissolution; consequently the extent of anion adsorption induced must also be very low. At higher pH values where no protonation occurs the adsorption of anions decreases significantly.     

The practice and characterization of historic fire gilding techniques

Fire gilding was the predominant technique for the gilding of metalwork from 300 b.c. in China and 200 a.d. in Europe until the invention of electroplating in the 19th century. This article investigates its metallurgical aspects based on studies of original objects, gilding replication experiments, and literary evidence. Author’s Note: All compositions are in weight percent. The artifact appearing on this page is a 6th–7th century Anglo-Saxon cruciform brooch of fire-gilded low-tin bronze. A fire-gilded copper Chinese garment hook with a turquoise inlay from c. 200 b.c. is shown on page 60; three Chinese garment hooks of fire-gilded and silvered copper with turquoise in lay appear on page 61. Fore more information, contact K. Anheuser, Staatliche Museen Berlin, Schlosstr. la, D-14059, Berlin, Germany, telephone 49-30-320-91-298; fax +49-30-322-16-14.     

Experimental characterization of granite damage using nonlinear ultrasonic techniques

In this paper, a nondestructive evaluation (NDE) technique based on the nonlinear second harmonic wave theory is developed and used to characterize damage of granite samples subjected to compressive loadings. The nonlinear parameter defined in the new NDE technique is measured and compared with two traditional parameters including ultrasonic pulse velocity and dynamic modulus. The nonlinear parameter is found to be much more sensitive to the damage development in granites than traditional parameters. It is shown that the increase of nonlinear parameter is close to an exponential trend with respect to the increased loading level, which also indicates a faster increase rate of the nonlinear parameter corresponding to the internal damage of granite samples. A practical damage index is thus defined based on the exponential increasing trend of the nonlinear parameter. The new damage index based on nonlinear parameter is found to have a positive correlation with the loading level. This observation suggests that the new damage index may become a valuable indicator of loading level (or correspondingly material degradation) of granites in the in situ NDE tests.     

Correlation between dislocation density and nanomechanical response during nanoindentation

The crucial role of dislocations in the nanomechanical response of high-purity aluminum was studied. The dislocation density in cold-worked aluminum is characterized by means of electron channeling contrast and post-image processing. Further in situ heat treatment inside the chamber of a scanning electron microscope was performed to reduce the dislocation density through controlled heat treatment while continuously observing the structure evolution. The effect of dislocation density on both the pure elastic regime before pop-in as well as elastoplastic deformation after the pop-in were examined. Increasing the dislocation density and tip radius, i.e. the region with maximum shear stress below the tip, resulted in a reduction in the pop-in probability. Since the oxide film does not change with dislocation density, it is therefore clear that pop-ins in aluminum are due to the onset of plasticity by homogeneous dislocation nucleation and not oxide film breakdown. Hertzian contact and the indentation size effect based on geometrically necessary dislocations are used to model the load-displacement curves of nanoindentation and to predict the behavior of the material as a function of the statistically stored and geometrically necessary dislocation density.     

The nanomechanical and nanoscratch properties of MWNT-reinforced ultrahigh-molecular-weight polyethylene coatings

Ultrahigh-molecular-weightpolyethylene (UHMWPE) and 5 wt.% multiwalled-carbon-nanotube-(MWNT) reinforced UHMWPE coatings were prepared on a steel substrate by electrostatic spraying. Nanoindentation and nanoscratch tests were performed on the coatings to evaluate the mechanical and wear properties at small length scales. The mean values of elastic modulus and hardness were higher for the MWNT-reinforced coating, while the plasticity index of the coatings was unaffected. The lateral force and coefficient of friction was considerably higher in the case of the MWNT-reinforced coating, indicating an increase in resistance to wear due to the addition of MWNT.     

Residual stress characterization in structural materials by destructive and nondestructive techniques

Transmutation of nuclear waste is currently being considered to transform long-lived isotopes to species with relatively short half-lives and reduced radioactivity through capture and decay of minor actinides and fission products. This process is intended for geologic disposal of spent nuclear fuels for shorter durations in the proposed Yucca Mountain repository. The molten lead-bismuth-eutectic will be used as a target and coolant during transmutation, which will be contained in a subsystem vessel made from materials such as austenitic (304L) and martensitic (EP-823 and HT-9) stainless steels. The structural materials used in this vessel will be subjected to welding operations and plastic deformation during fabrication. The resultant residual stresses cannot be totally eliminated even by stress-relief operations. Destructive and nondestructive techniques have been used to evaluate residual stresses in the welded and cold-worked specimens. Results indicate that tensile residual stresses were generated at the fusion line of the welded specimens made from either austenitic or martensitic stainless steel, with reduced stresses away from this region. The magnitude of residual stress in the cold-worked specimens was enhanced at intermediate cold-reduction levels, showing tensile residual stresses in the austenitic material while exhibiting compressive stresses in the martensitic alloys. Comparative analyses of the resultant data obtained by different techniques revealed consistent stress patterns.     

Effect of bias voltage on microstructure and nanomechanical properties of Ti films

In order to investigate nanomechanical properties of nanostructured Ti metallic material, pure Ti films were prepared by magnetron sputtering at the bias voltage of 0-140 V. The microstructure of Ti films was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). It is interesting to find that the microstructure of pure Ti films was characterized by the composite structure of amorphous-like matrix embodied with nanocrystallines, and the crystallization was improved with the increase of bias voltage. The hardness of Ti films measured by nanoindentation tests shows a linear relationship with grain sizes in the scale of 6-15 nm. However, the pure Ti films exhibit a soft tendency characterized by a smaller slope of Hall-Petch relationship. In addition, the effect of bias voltage on the growth orientation of Ti films was discussed.     

Corrosion and nanomechanical properties of vanadium carbide thin film coatings of tool steel

The corrosion and nanomechanical characteristics of tool steel coated with vanadium carbide thin films deposited by DC reactive magnetron sputtering were investigated. Cyclic polarization and electrochemical impedance spectroscopy measurements in a 3.5% sodium chloride solution indicated that corrosion decreases as the C content and the substrate temperature during deposition increase. The maximum hardness is reached for VC coatings with C/V ratios around unity, decreasing for either higher or lower C/V ratios. Complementary physicochemical analyses, made here or elsewhere, are used to clarify the reasons for such behavior. The present results are discussed in terms of the optimization of the deposition parameters aiming at concomitantly good corrosion resistance and high hardness.     

New techniques for copper refining

The use of oxygen in steelmaking, now well established, points toward similar advances in copper refining with this now-inexpensive industrial gas.     

Processing techniques for bulk high-Tc

If the enormous potential of the high-critical-temperature superconductors is ever to be realized, materials processing is the key. Although remarkable strides have been made during the past few years, greater processing innovations are needed to accelerate progress toward major bulk applications. Many challenges and research opportunities remain.     

采用不同的焊接工艺方法修复管道

众所皆知，按焊缝的空间位置，可分为平焊、立焊、横焊和仰焊4种，平焊操作位置最佳，焊接电流可取上限值，焊速快，易于保证焊接质量，从而提高生产效率，所以在生产实践中被广泛的应用。立焊、横焊次之，而仰焊位置的操作是最不理想的，这是因为熔池中的液态金属受重力的作用，有滴落的趋势，因而要尽可能的避免，若不能避免，则应采用小直径的焊条，电流取下限值、短弧焊接等措施才能保证质量。     

Powder-blowing techniques for electric steelmaking

After 10 years of experimental and practical applications of its powder-blowing techniques to steelmaking, IRSID has adapted these techniques to electric-furnace steelmaking for dephosphorization, desulfurization, and dissolution of various elements.     

Recent advances on physico-chemical characterization of passive films by EIS and differential admittance techniques

Thin Nb₂O₅ anodic films (∼20 nm thick) grown in phosphoric acid solution have been characterised by EIS and differential admittance study in a large range of potential and frequency. The overall electrical behaviour has been interpreted by means of the theory of amorphous semiconductor Schottky barrier in presence of a non-constant density of states (DOS). A comparison of DOS for films grown in different electrolytes is reported.