Three-dimensional molecular dynamics (MD) simulation is used to study the atomic-scale indentation process of a spherical diamond tip in contact with a copper substrate. In the indentation simulations, the force-displacement curve is obtained and compared with a modified elastic solution of Hertz. The contact area under different indentation depths is also investigated. The force-displacement curve under different maximum indentation depths is obtained to investigate elastic-plastic deformation during the loading and unloading processes.

Impact of a single copper particle in cold gas dynamic spray is simulated by finite element method by including the effects of high strain rates and temperature on material plasticity and failure. In order to predict stick behavior of the particle, cohesive forces that act between the particle and the substrate are included in the model by defining an interfacial cohesive strength parameter. Effect of this parameter on the deformation and stick/rebound behavior of the particle is studied. It is found that significant particle deformation, large area of contact between particle and substrate is needed to generate enough cohesive force to absorb the rebound energy of the particle and achieve sticking. As the impact velocity and assumed interfacial cohesive strength increases, particle is more likely to stick on to the substrate. Critical velocities in the same range with experimental results are predicted.

Three-dimensional molecular dynamics (MD) simulations have been performed to investigate behaviors of nanoindentation and nano-scratch. The first case concerns the effects of material defect on the nanoindentation of nickel thin film. The defect is modeled by a spherical void embedded in the substrate and located under the surface of indentation. The simulation results reveal that compared to the case without defect, the presence of the void softens the material and allows for larger indentation depth at a given load. MD simulations are then performed for nano-scratch of single crystal copper, with emphasis on the effect of indenter shape (sharp and blunt) on the substrate deformation. The results show that the blunt indenter causes larger deformation region and much more dislocations at both the indentation and scratch stages. It is also found that during the scratching stage the blunt indenter results in larger chip volume in front of the indenter and gives rise to more friction than the sharp indenter. The scope of the simulations has been extended by introducing a multiscale model which couples MD simulations with Finite Element Method (FEM), and multiscale simulations are performed for two-dimensional nanoindentation of copper. The model has been validated by well-consistent load-depth curves obtained from both multiscale and full MD simulations, and by good continuity of deformation observed in the handshake region. The simulations also reveal that indenter radius and indentation velocity significantly affect the nanoindentation behavior. By use of multiscale method, the system size to be explored can be greatly expanded without increasing much computational cost.

The tribological and electrical conduction behaviors of copper under dry sliding against copper-chromium alloys were investigated on the basis of simulation tests. The experimental results show that electrical current and trbological parameters have combined effects on both electrical conduction ability and trological properties. High sliding velocity and electrical current density deteriorate both the tribological and electrical conduction properties in tribo-electrical sliding system. In the end, Worn surface analysis suggests frictional and electrical resistance heating, electrical arc spoiling are the main factors to influence the tribological and electrical conduction properties.

The contact area, friction force and relative displacement evolution at the very early stage of fretting are investigated experimentally. Copper and steel spheres of various diameters are loaded against a hard sapphire flat by a range of normal loads deep into the elastic-plastic regime of deformation. A reciprocating tangential loading is then applied with a maximum loading below the static friction to avoid gross slip. Real-time and in situ direct measurements of the contact area, along with accurate measurements of the friction force and relative displacement, reveal substantial junction growth and energy dissipation mainly in the first loading cycle. The so called “slip amplitude” is found to be attributed to residual tangential plastic deformation rather than to interfacial slip. Elastic shake-down is observed for the 2.5% hardening steel spheres while plastic shake-down is observed in the case of the elastic perfectly plastic copper spheres.

Nanofluids, a term proposed by Choi in 1995 [1], are composites consisting of solid nanoparticles with sizes varying generally from 1 to 100 nm dispersed in a liquid. Numerous nanoparticles used as oil additives have been investigated in recent years [2–7]. Results show that they deposit on the rubbing surface and improve the tribological properties of the base oil, displaying good friction and wear reduction characteristics even at concentrations below 2%wt.

This work presents the results of a finite element study of the sliding contact of interfering cylindrical asperities. One asperity is modeled as elastic with steel properties, while the other asperity is modeled as elastic-plastic copper. The simulations were run using two different plasticity models for copper, conventional J 2 plasticity describing an initially homogeneous material and a continuum crystal plasticity model that can capture the influence of crystallographic orientation on the deformation response. The use of the crystal plasticity model and frictionless contact enables us to study the dependence of plastic deformation and energy dissipation as a function of crystal orientation and vertical interference. The relative trends predicted using crystal plasticity are consistent with classical experiments showing the dependence of friction with crystal orientation when plastic deformation is the primary energy dissipation mechanism.

Wear and friction in sliding electrical contacts is affected by a multitude of factors such as contact load, current density, sliding speed, sliding distance and materials in contact [1], [2]. Very limited studies have been done to investigate the effect of current polarity on wear and coefficient of friction. In the present study, the authors investigate the effect of current polarity on the frictional response and wear of copper-aluminum interface. Copper wire mounted on a fixture is slid on aluminum flat under different current levels. Large scale melting at the interface was observed when slider (copper) was maintained as anode. Observations of the slider and flat surface made under microscope reveal material transfer of aluminum on copper even at low current levels of 60 Amperes. The results of the study can be used in the light of applying different coatings or surface design for anode and cathode in order to minimize their wear or degradation.

This work presents the results from a three dimensional (3D) finite element analysis (FEA) of an elastic-plastic asperity contact model for two spherical bodies sliding across each other with various preset vertical interferences. Stresses, forces, contact areas, deformations, and net energy loss are presented for steel-on-steel and aluminum-on-copper contact.

Intercalation compound of polyoxymethylene into molybdenum disulfide nanoparticles (POM/MoS 2 -IC) were prepared from trioxane, dioxolane and restacked exfoliated-MoS 2 . The so prepared nanocomposite was used as the plastic layer of self-lubrication bearing materials of steel-copper-POM. Pure POM was also selected as a comparative sample. Tribological behaviors of the obtained samples were studied on an end-face tribometer. Wear scar surfaces of the two plastic layers were characterized by a field emission scanning electron microscope. The elements of the counterpart steel surface were investigated by X-ray photoelectron spectroscopy. Results showed the wear surface of steel-copper-pure polyoxymethylene consisted of deep furrows, large-area scars and obvious flow marks. However, self-lubrication bearing materials of steel-copper-polyoxymethylene containing MoS 2 -IC nanoparticles presented excellent friction reduction and wear resistance especially under high loads. POM/MoS 2 -IC nanoparticles and its tribochemical resultants restrained the plowing effect of the counterpart steel on the plastic layer through forming a transferred film on the counterpart friction surface.

Chemical mechanical polishing (CMP) is a critical nanomanufacturing process used to remove or planarize ultrathin metallic, dielectric, or barrier layers on silicon wafers. The CMP process is a vital interim fabrication step for integrated circuits and data storage devices. One of the major shortcomings of existing CMP models is that they do not account for crystallographic effects of the thin film metal materials when predicting material removal rates. This work investigates the effect of the microstructure on the CMP of copper and metal thin films on silicon wafer. Nanoindentation tests were conducted to measure the hardness variations across a wafer surface due to the crystallography of the metal films. Spatial variation of mechanical properties was also input into an existing multi-scale CMP model. Nano-characterization and CMP experimental results are presented and compared to an existing CMP wear model.

The contact area evolution during pre-sliding (junction growth) of copper spheres loaded against a hard sapphire flat is investigated experimentally. Tests are performed with a recently developed test rig for real-time and in situ direct measurements. The results provide a new insight of the junction growth mechanism showing new points of the sphere surface that are coming into contact with the flat. It is found that junction growth at sliding inception can cause up to 45 percent increase in the initial contact area that is formed under normal preload alone. Good correlation is found between the present experimental results and a theoretical model for medium and high normal preloads.

This work presents the results of a Finite Element Analysis (FEA) used to simulate two-dimensional (2D) sliding between two interfering elasto-plastic cylinders, one with material properties of a tougher material (copper alloy Glidcop) and the other of a relatively weaker material (aluminum alloy Al 6061-T651). Trends in the deformations, reaction forces, stresses, and net energy losses as a function of sliding distance are established. Results for both frictionless and frictional sliding are presented and comparisons are drawn. The effects of plasticity and friction on energy loss during sliding are isolated.

The main purpose of the present investigation is to analyze a novel, green, and petroleum-free lubricant that is produced by mixing two environmentally benign components—canola oil and boric acid powder. To study the influence of boric acid crystal size and volume ratio on the proposed lubricants performance, computerized pin on disk experiments were conducted with spherical copper pins (radius 6.5 mm) and aluminum disks (Ra = 1.35μm). Friction coefficient measurements were taken at more than twenty distinct operating conditions while varying the lubrication condition (unlubricated, boric acid, canola oil, boric acid/canola oil mixture), boric acid volume fraction (3.5%, 7%, 10.5 and 21%), and boric acid crystal size (0–100 microns, 100–150 microns, 150–180 microns, 180–350 microns and 350–710 microns). Based on the experiments, it was determined that a 7% by volume boric acid powder in canola oil with 350–700 micron particles was the optimum green lubricant for minimizing the friction at the conditions tested. In addition, the results indicated that the boric acid/canola oil lubricant demonstrated excellent potential for use in industrial applications such as sheet metal stamping.

For faster signal propagation in integrated circuits, new materials with lower dielectric constant (low- k ) values are required with copper metal lines. Although integration of low- k materials ( k <3.0) has been demonstrated, but ultra low- k materials possess many challenges due to their poor mechanical integrity and weak adhesion to other interconnects. During chemical mechanical planarization (CMP) generation of several defects including delamination of low- k materials is severe problem in the integration of these materials. Different slurries and pad introduces different levels of defect and also batch-to-batch variation in consumables is often makes process more difficult. In this study we have investigated the tribological properties of CMP pad and wafer interface while monitoring coefficient of friction and acoustic emission data. Signals are analyzed in order to online defect monitoring, batch-to-batch consumable variations and different consumables effects.

A contact mechanics theory of static friction is presented for isotropic rough surfaces exhibiting fractal behavior. The analysis is based on a piece-wise power-law size distribution and a normal slope distribution of the asperity contacts and elastic-fully plastic deformation models. Numerical integration yields solutions for the normal and friction forces in terms of fractal parameters, elastic-plastic material properties, and interfacial shear strength. The variation of the static coefficient of friction with normal load is related to the effect of the surface topography on the dominant deformation mode at the asperity contacts. Plastic deformation of the smaller asperity contacts dominates at low loads and elastic deformation of the larger asperity contacts at high loads. The critical load signifying the transition from predominantly plastic to elastic deformation depends on the fractal parameters and material properties. In the low-load range, the static coefficient of friction decreases with the increase of the load, while in the high-load range it increases relatively faster with the load. Numerical results for copper fractal surfaces illustrate the effects of normal load, surface topography, and interfacial shear strength on the static coefficient of friction.

The effect of various process parameters like pressure, velocity and process consumable characteristics like pad properties and slurry chemistries on copper during Chemical Mechanical Planarization (CMP) process have been extensively researched. However, the thermal aspects of CMP have not been understood in detail. In this research, we present the effect of slurry temperature on the coefficient of friction and the resulting micro-structural changes in the copper material due to the polishing process. We also investigated the work hardening effect of polishing on copper thin film. From the results, it was found that temperature has an effect on the coefficient of friction but the effect of process parameters influences the effect of temperature. The effect of temperature on coefficient of friction is also dependent on the material of polishing pad. From XRD measurements more crystallinity was observed for the sample polished at 29°C as compared to other samples. The mechanical properties of copper investigated before and after CMP show improved mechanical properties with polishing. Significant change was observed among the mechanical properties of samples polished at different temperatures.

Fatigue strength is often a limiting factor for the application of babbitt to hydrodynamic bearings. Many studies address mechanical fatigue, but fewer studies address thermal fatigue. In the United States, the selection of babbitt for hydrodynamic bearings has become increasingly uniform based on the ASTM B-23 specification, with the majority of bearings using ASTM B-23, alloy #2. Alternative tin-based alloys some containing cadmium, but all with higher antimony and copper content, leading to higher compressive load capacity have been popular with European-designed bearings. In light of environmental concerns with cadmium, one significant babbitt (whitemetal) vendor, developed an alternative design alloy replacing the cadmium with silver and zinc. All of these alloys are predominantly tin, which has a non-cubic thermal structure and anisotropic thermal expansion. In equilibrium at high antimony contents, three phases of antimony compounds are present, including increasing amounts of tin-antimony cuboids. As a result thermal expansion results in stress concentration along phase and grain boundaries. Increasing temperatures can allow for alloy migration within the tin matrix. These factors can affect the application of babbitts subject to repeated thermal transients, as can occur during the typical startup of a heavily loaded thrust bearing. Accelerated thermal fatigue tests without load have been performed on six different babbitt compositions statically cast on steel plates. Measurements of thermal deformation and bond strength were made at periodic intervals, as well as visual examination of metallurgical changes. The results indicate that tin-alloys with lower alloy contents are subject to increased surface deformation, on the order of the hydrodynamic film thickness. Tin-alloys with higher alloy content show increased alloy migration and more tin-antimony intermetallic formation. Intermetallic compounds concentrated at the steel-babbitt interface grew during the testing. These phase changes reduce the toughness of the babbitt-steel interface due to embrittlement, raising the potential for bond failure. The need for testing in a loaded condition to help quantify the relevance of these indications to loaded hydrodynamic conditions is identified.

The measurements of nanomechanics have been established to study the effects of strain burst and pile-up on the hardness and elastic modulus of single crystal copper samples. For nanoindentation of the single crystal copper subjected to various loadings, the residual depths have been analyzed and compared with the cross sectional depth profile obtained by the atomic force microscope (AFM). A penetration depth around 5 to 8 nm is observed before the strain burst. It is found that the critical load to cause the first burst slightly decreases with increasing loading rate. A new graphical method based on the 3-D image of indent was proposed to eliminate the hardness and elastic modulus errors induced by the pile-up effect. The hardness and elastic modulus are not influenced by the value of maximum load and reduced to around 95% of their direct measurement values based on the Oliver-Pharr method. In comparison, the hardness decreases with increasing maximum load and shows strong dependence with the maximum load applied when the work of indentation method was employed.