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High and ultra-mild wear of Al–Si alloys under lubrication is measured (a) by comparison of initial and retained gold concentration in surfaces, (b) by tracking gold in the effluent lubricant or (c) alloy specific elements, and (d) by stylus profilometry. Wear >1 μm is best captured by method (d). However, (d) fails when both tribologically induced films have formed and wear is below 100 nm. Method (c) is efficient in a broad range of wear if element concentrations can be determined precisely. Methods (a) and (b) satisfy this requirement but they are only efficient for ultra-mild wear.

A novel method for the quantitative determination of the wear of materials at very low wear rates is introduced here. The main concept involves implanting gold as a trace marker into the tested materials, and measuring the gold concentration and depth profile before and after the wear tests by Rutherford backscattering (RBS). The amount of gold loss is related to the material loss under the tested conditions. The background concentration of gold in AISI 1095 and 52100 steels has been determined by neutron activation analysis (NAA; ~3 and 33 wt. ppb, respectively). Several fluences (1 × 1015–1 × 1016 atoms/cm2) of gold were implanted into AISI 52100 steel samples in order to evaluate the changes in the mechanical and tribological properties induced by implantation. The new method shows the relative effectiveness for wear prevention of the different tested lubricants with and without antiwear additives. Even the thickness of the antiwear film and the amount of zinc (from zinc dialkyldithiophosphates used as antiwear additives) can be measured by this method.

X-ray absorption near edge structure (XANES) spectroscopy has been used to characterize the chemistry of thermal films on steel samples, which were generated from a mineral base oil containing a zinc dialkyl dithiophosphate (ZDDP) additive. These films were formed at 150 °C by immersing steel coupons in ZDDP oil solutions. The phosphorus L-edge XANES spectra show that these films are composed of polyphosphates, unreacted ZDDP and other thiophosphate intermediates. Phosphorus K-edge FY XANES was used to monitor the thickness of these films, and the data are consistent with thickness derived by focussed ion beam (FIB) milling and SEM imaging. The sulphur K-edge TEY and FY XANES spectra show that these films are composed of different sulphur components, which depend upon the formation times. The surface morphology of these films was investigated using atomic force microscopy (AFM). These images show that the surface morphology of the thermal films changes with the formation time. 31P NMR spectra show that both primary and secondary ZDDP decomposes gradually at 150 °C.

X-ray absorption near-edge structure (XANES) spectroscopy has been used to characterize the chemistry of antiwear (AW) films generated from mineral base oil containing a zinc dialkyl dithiophosphate additive. These films were formed on rubbed steel surfaces with a reciprocating boundary contact using different sliding frequencies. The phosphorus L-edge XANES spectra show that these films have slightly different chemical natures. Longer chain polyphosphates were present on the steel surface prepared at the higher sliding frequencies. The surface morphology of these films was investigated using atomic force microscopy. These images show that the surface morphology of the AW films changes with the sliding frequency. Round and bigger antiwear pads were formed at a lower frequency while higher frequencies resulted in thinner films and flattened surfaces. Nanomechanical properties of these antiwear films were investigated by nanoindentation measurement and the elastic moduli extracted from force–displacement (f–d) curves are similar for all antiwear films, 100 ± 10 GPa.

The interactions of a commercially available fully formulated oil on an Al–Si alloy have been studied, and a chemical and mechanical characterisation of the resulting surface films has been undertaken to compare with the results found on 52100 steel. ZnS and Ca phosphate are the primary species found. No Mo species were found in the film, but B was detected; the latter observation contrasts with the results found for 52100 steel. A surprisingly consistent indentation modulus was found for the films formed on A383, considering the complex microstructure of the alloy, which has been shown previously to influence the mechanical response of the film produced from zinc dialkyl dithiophosphates (ZDDPs) in oil. The stiffness of the films on A383 is statistically indistinguishable from that found on 52100 steel, and the topography of the film also looks unchanged compared to the steel study.

The authors report, for the first time, a comprehensive chemical and mechanical characterisation of antiwear films prepared from a fully formulated oil that is commercially available. Wear increases substantially when using the fully formulated oil compared to using ZDDP alone. X-ray absorption near edge structure (XANES) spectroscopy at the P K- and L-edges, S K-edge, Mo L-edge, B K-edge, Ca L-edge, O K-edge and Fe and Zn L-edges permits chemical characterisation of the major elements in the thin films. Ca phosphates, ZnS and MoS2 are the main P and S species formed, contrary to previous studies involving only ZDDPs, whereby Zn phosphates are the dominant species. These findings can be accounted for by using the hard and soft acid and bases (HSAB) principle. Small amounts of CaCO3 are present, but no B was detected, implying it does not become incorporated into the film. Atomic force microscopy (AFM) reveals continuous pads with a relatively uniform indentation moduli (125 ± 10 GPa), separated by...

The interaction of a friction modifier and a calcium phenate detergent additive, with zinc dialkyl dithiophosphates (ZDDPs) in the formation of antiwear films on A383, has been studied using synchrotron radiation and nanoindentation techniques. X-ray absorption near edge structure (XANES) spectroscopy has shown that films prepared from oils containing both ZDDP and detergent, and ZDDP and molybdenum dithiocarbamate (MoDTC), are chemically similar to, but thicker than those made from oils containing only ZDDP. In addition, wear was greatly reduced in the presence of the detergent which was correlated with the basicity and the presence of the friction modifier. The phosphorus K and L edge XANES spectra show that the tribofilms are polyphosphate glasses of similar nature to those found on steel, but characterised by a shorter chain length. The sulphur K edge shows a MoS2 like film and under certain conditions, the presence of a sulphate species is detected. High resolution topographic images and mech...

The simulation of the lubrication of aluminum–silicon (Al–Si) alloy cylinder-bore conditions is an important goal in automotive tribology. This study describes the use of X-ray absorption near edge structure (XANES) to determine the macro-chemistry of zinc-dialkyl-dithiophosphates (ZDDPs) antiwear (AW) films formed on A383, an Al-Si alloy. The temperature dependence of the chemistry and mechanical properties were examined using X-ray photoelectron emission microscopy (X-PEEM), and imaging indentation techniques. Our findings suggest that ZDDPs break down to form polyphosphate glasses, which have different chemical natures and depend on the underlying substrate. Furthermore, the chemical nature of the films appears temperature dependent on both the macro- and micro-scale. Not only are the chemical species different, but the mechanical properties also differ, depending on the region upon which an AW pad is formed. Through the use of focused ion beam (FIB) milling, we can determine the film thickness, which was previously estimated from the P K-edge XANES areal density of samples with known thicknesses.

The nanomechanical properties of antiwear films formed from zinc dialkyl-dithiophosphates (ZDDPs) on steel have been studied by nanoindentation techniques as a function of temperature. X-ray absorption P K- and L- near edge structure (XANES) spectroscopy has shown that films prepared from oils containing ZDDPs on 52100 steel (pin on flat coupons) consist primarily of medium chain polyphosphates with sulphur (S K-edge) predominantly present as sulphide. Using various scanning probe techniques, high-resolution topographic images and mechanical properties can be extracted at the same length scale. Using focused ion beam (FIB) milling we have compared real cross-sectional film thickness with a value estimated from the P K-edge XANES. We report the first measurements of the elastic modulus of the antiwear films at elevated temperatures relevant to the automobile operating conditions (T ≤ 200 °C). The antiwear films demonstrated a relatively constant indentation modulus over a wide range of temperatures consistent with their efficacy in reducing wear by preventing asperity contact.

Phosphorus L-edge and oxygen K-edge X-ray PhotoEmission Electron Microscopy (XPEEM) have been used to characterize the chemical nature of the cation present in tribochemical films via comparison with model Fe2+ and Zn2+ compounds. The results are contrasted to the P L-edge, P K-edge and S K-edge XANES data. The findings suggest that antiwear pads containing long chain zinc polyphosphate glass are formed at the points of asperity contact, and a thin, short chain zinc polyphosphate film is formed where no asperity contact is made. SEM/EDX measurements helped to elucidate the distribution of the elements, and strong spatial correlations were observed between P, O, Zn and S in the pads, indicating that they are composed mostly of zinc polyphosphates, especially near the surface. The zinc polyphosphate antiwear pads are characterized by a much lower modulus than that observed on the thin film regions, the latter being characteristic of the substrate steel.

Subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) was applied to determine the acid dissociation constant for bisulfate adsorbed at the Pt(111) electrode surface. The experiments were carried out in NaF+HF buffer solutions with pH varying between 0.4 and 6.1. The SNIFTIR spectra were used to identify adsorbed bisulfate and sulfate ions and to monitor changes in the concentration of the adsorbed species with pH. The pKa for the adsorbed bisulfate was determined from the changes of the intensity of IR bands assigned to sulfate and bisulfate with pH. The values of pKa depend on the electrode potential and their values range between 3.3 and 4.7. They are significantly higher than the value of pKa in the bulk of the solution. The magnitude of pKa indicates that bisulfate is the predominantly adsorbed species at pH 4.7.

A study of the electrodeposition and electrochemical dissolution of ultrathin Ni films on Ag(111) electrodes in Watts electrolyte by in situ scanning tunneling microscopy (STM), electrochemical quartz microbalance (EQCM), and cyclic voltammetry (CV) is presented. Ni deposition starts at potentials negative of − 0.72 V s. SCE (i.e., overpotentials η160 mV), where an incommensurate, (111)-oriented film with an in-plane lattice rotation of 0.5° relative to the Ag substrate lattice is formed. The lateral nearest neighbor spacing is as in bulk Ni (2.49 A) for a film thickness 3 ML and expanded for monolayer (2.54 A) and bilayer (2.52 A) films. Depending on the deposition potential, three growth regimes, resulting in different deposit morphologies, are observed: At low overpotentials (160⩽η/mV⩽200) a smooth Ni film is formed ia a 2D step-flow growth process, commencing at steps of the Ag substrate. At medium overpotentials (200η/mV300) a transformation from 2D step-flow to 3D growth occurs, resulting in the selective formation of Ni multilayer islands along the Ag steps. At even higher overpotentials (η300 mV) 3D islands are formed at the steps and on the substrate terraces. The size of the Ni multilayer islands is independent of the terrace widths, indicating that Ni growth proceeds ia direct discharge at step sites (“direct deposition”). The transition from 2D to 3D growth as well as the change in island shape with overpotential can be rationalized by a different potential dependence of the various microscopic nucleation and growth processes. The multilayer growth at steps is attributed to next-layer nucleation at the structural defect induced by the Ag–Ni boundary and can be described quantitatively as a function of deposition time by a simple 2D model. In addition, place-exchange of Ni with Ag surface atoms and encapsulation of Ni islands by Ag is observed. Dissolution of the electrodeposited multilayer Ni films proceeds ia step-flow etching, with a higher dissolution rate for the Ni monolayer as compared to higher Ni layers.

The electrodeposition of nickel on (111)-oriented gold films has been studied in electrolytes with different Ni2+ concentrations and/or pH values using the electrochemical quartz crystal microbalan...

Based on time-dependent in situ scanning tunneling microscopy (STM) studies, we demonstrate that for Ni on Ag(111) and Ru on Au(111), electrochemical metal-on-metal deposition can result in pronounced substrate surface restructuring. For Ni/Ag(111), we observe that at low deposition flux and low coverage, Ni submonolayer islands at steps are partly embedded in the Ag terraces, whereas at higher deposition flux and higher coverage, substrate restructuring results in the formation of monolayer bays in the Ag terraces. We suggest that this restructuring process proceeds predominantly via step edge diffusion of Ag atoms. For Ru/Au(111), the formation of fjords and monolayer holes in the Au terraces is observed at low and high Ru coverage, respectively. The importance of the Au surface mobility for the restructuring process is demonstrated by comparing experiments in H 2 SO 4 and HCl solutions, in which Au exhibits strongly different surface mobilities. For this system, restructuring involves Au diffusion along Au steps, Au atom detachment from the Au steps, and upward exchange diffusion. According to these observations and their comparison with similar findings for vacuum deposition, we conclude that this restructuring requires (i) a high substrate surface mobility and (ii) a stronger bonding of substrate atoms to deposit islands than to the substrate.

A novel growth effect, the potential-controlled transition from 2D step-flow growth $(\ensuremath{-}0.69\phantom{\rule{0ex}{0ex}}{\mathrm{V}}_{\mathrm{A}\mathrm{g}/\mathrm{A}\mathrm{g}\mathrm{C}\mathrm{l}})$ to (i) selective growth of 3D admetal islands at substrate steps $(\ensuremath{-}0.73\phantom{\rule{0ex}{0ex}}\mathrm{V})$ and (ii) 3D island growth on steps and substrate terraces $(\ensuremath{-}0.85\phantom{\rule{0ex}{0ex}}\mathrm{V})$, is demonstrated for Ni electrodeposition on Ag(111). The nucleation and growth process apparently proceeds via direct deposition from the solution at step sites and can be rationalized by a kinetically controlled multilayer growth process, where the higher layer nucleation rate increases more with overpotential than does the 2D growth rate.

Results of an in situ scanning-tunneling microscopy (STM) study on the initial stages of Ni electrodeposition on Ag(111) are presented and compared with previous results on Au(111). In the submonolayer range the STM results indicate substantial place exchange of Ni with Ag surface atoms. Submonolayer Ni islands are formed almost exclusively at the step edges, they are partly embedded into the upper terrace. In contrast, on Au(111) place exchange of Ni adatoms with the Au substrate occurs exclusively at the elbow sites of the herringbone reconstruction, and adlayer nickel islands nucleate selectively on top of the embedded Ni atoms (low overpotential) or also at steps (high overpotential). At multilayer coverages atomically smooth Ni deposits are found on both metal substrates with a lattice constant similar to that in metallic Ni. On Ag(111) large, quasi-two-dimensional Ni islands are observed, contrasting the almost perfect layer-by-layer growth on Ni/Au(1 11). The density of structural defects within the Ni islands on Ag( 111) is significantly lower than for the Ni film on Au( 111 ).

An in-situ scanning tunneling microscopy (STM) study of Cu(100) electrode surfaces in sulfuric and hydrochloric acid solutions in the potential range −0.6 to −0.1 V versus Ag AgCl (KClsat) is presented, revealing the surface structure and dynamics in the double-layer region and providing detailed structural data on the initial stages of anodic Cu dissolution. After preparation by electropolishing in phosphoric acid, large, atomically flat terraces, separated by frizzy, almost randomly oriented steps are observed in H2SO4 solution in the double-layer region. Atomic-scale observations reveal a (1 × 1) surface lattice in the entire potential range, even during Cu dissolution. In HCl solution this surface morphology and atomic structure are visible only at potentials negative of −0.4 V, whereas above −0.4 V a c(2 × 2) Cl adlattice is observed, together with strong faceting of the steps along the [010] and [001] directions. At low etch rates, the dissolution of clean Cu surfaces proceeds solely by step-flow etching in both electrolytes. In H2SO4 solution the dissolution process is accompanied by strong fluctuations in the step positions and by an increase in step roughness. In HCl solution the [010]- and [001]-oriented steps are stabilized by the c(2 × 2) Cl adlayer and Cu dissolution proceeds by the subsequent removal of complete atomic rows consisting of primitive (√a × √2)R45° units of the (2 × 2) adlattice along these steps. A mechanism is proposed where the dissolution of Cu atoms occurs at two slightly different, structurally well-defined kink sites in the c(2 × 2) lattice, which rapidly travel along the step edge (i.e. along [010] or [001]) during the dissolution process. Adsorbed impurities can locally pin Cu terraces, resulting in the formation of highly anisotropic islands, peninsulas and troughs, or induce the formation of monoatomic etch pits.

High-resolution, in-situ scanning tunneling microscopy studies of the surface structure and the microscopic mechanisms of the dissolution of Cu(100) in hydrochloric and sulfuric acid solutions at low dissolution rates are presented. On clean Cu surfaces dissolution proceeds exclusively at surface defects in form of atomic steps and is strongly dependent on the anion species. Foreign metal impurities can either inhibit Cu dissolution via pinning or enhance it by inducing the formation of etch pits. In the presence of inhibiting, organic adlayers the removal of Cu atoms at the steps is significantly slower and corrosion is determined by the formation of etch pits at higher potentials.

A detailed in situ STM study of the electrodeposition and electrochemical dissolution of Ni on reconstructed Au(111) electrode surfaces in various electrolytes is presented, demonstrating the electrochemical formation of well-defined, ultrathin, epitaxial Ni films. Formation of Ni nuclei starts below the ${\mathrm{Ni}}^{0}{/\mathrm{N}\mathrm{i}}^{2+}$ Nernst potential via place exchange of Ni with Au atoms at the elbows of the herringbone reconstruction, followed by nucleation of Ni islands on top of these substitutional Ni atoms at overvoltages $\ensuremath{\eta}g~80\mathrm{mV},$ and by nucleation at step edges of the Au substrate at $\ensuremath{\eta}g~100\mathrm{mV}.$ At submonolayer coverages islands with two different growth morphologies, compact, triangularly shaped and highly anisotropic, needlelike islands, are observed. Upon further growth these islands coalesce and an almost perfect two-dimensional Ni monolayer is formed. Multilayer growth was studied up to coverages of 5 ML; it exhibits a similar layer-by-layer growth, resulting in very smooth Ni films. In atomic-scale observations a hexagonal Ni lattice with a lattice spacing of 2.5 \AA{} is resolved, similar to the (111) orientation in bulk Ni, and with the same orientation as the Au lattice. The order in the highly defective first Ni layer is considerably improved by second-layer deposition. The significant differences to vapor-deposited Ni on Au(111) indicate a structure-decisive role of coadsorbates in the electrochemical environment. Dissolution of the Ni films at potentials positive of the Nernst potential proceeds via formation of etch pits and step-flow etching.

In-situ scanning tunneling microscopy (STM) observations on the electrodeposition of nickel on Cu(100) are presented. At overpotentials of η = 30 to 100 mV formation of a disordered adlayer of a precursor species is observed. Deposition of pseudomorphic Ni monolayer islands commences at η = (145 ± 5) mV at Cu step edges and in the center of atomically smooth Cu terraces. At overpotentials in the range 145 mV to 180 mV Ni is deposited in a rather rough multilayer growth process, with nucleation of second layer islands starting at total coverages as low as 0.1 ML.

The improvement of fuel consumption is an important driving force for research and development in the automobile industry in order to minimize greenhouse gas emissions as well as improving fuel economy. Aluminum alloys are a class of alternative materials that are being used to replace cast iron in motor components due to the concomitant weight savings which result in improved fuel efficiency, and cost savings. Our research focuses on these alternative Al-based alloys as well as traditional steel interfaces, and the protective films that form on the surfaces. Currently the zinc dialkyl-dithiophosphates (ZDDPs) have been used as engine oil additives for over 60 years. They are important chemically-active additives, known for their antioxidant and antiwear characteristics. ZDDPs are known to form a protective film (tribofilms) at rubbed surfaces, typically on iron containing metals surfaces commonly used in the automotive industry; however ZDDPs and the products formed are not well suited for the environment as they can readily poison the catalytic converters and their efficacy on Al-Si alloys is not well established.Copyright © 2007 by ASME and General Motors

An in-situ STM study of the initial stages of Ni electrodeposition on Au and Cu single-crystals is presented. On reconstructed Au(111) a complex, potential-dependent nucleation and growth process is found, involving selective Ni island formation at specific surface sites and growth of two types (compact and needle-like) of Ni monolayer islands. At higher coverages (1 ML ≤ θ ≤ 5 ML) an almost perfect layer-by-layer growth of a metallic Ni(111)-film was observed. Considerably rougher films were found on Au(100) and Cu(100).