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A simple and robust method for fabrication of superamphiphobic surfaces by template-free chemical deposition of Cu micro-cone arrays, followed by air plasma activation and room-temperature treatment in tridecafluoro-1,1,2,2-tetrahydrooctyl trichlorosilane (FTS) is reported in this paper. After only treatment with 15 min of FTS, a water contact angle of 166.1° and an oil (diiodomethane, CH2I2) contact angle of 160.5° are reached on the Cu surfaces. The highest oil contact angle of 168.1° is achieved after 1 h treatment with FTS. Such surfaces also display enhanced corrosion resistance due to the combination of the FTS layer and air pockets which prevent ion diffusion to the internal copper.

It has been hypothesized that introduction of proper solute atoms, which preferentially segregates to grain boundaries, can stabilize the nanoscale grain size at elevated temperatures. To explore this possibility, we synthesized pure Cu and Cu-3 at. % W nanocrystalline films using magnetron sputtering. Scanning electron microscopy and x-ray diffraction showed that while grains in pure Cu coarsen rapidly when annealed at 673 K, Cu-3% W maintains a stable microstructure when annealed at the same temperature, achieving grain size of 37 nm after 120 min annealing. Nanoindentation measurements gave results consistent with the grain size evolution: upon annealing at 673 K, the hardness of the pure Cu film decreases to 40% of its initial value after 20 min, while the Cu-3% W film retains more than 90% of its initial hardness even after 120 min. Atom probe analysis shows W segregation in the Cu-3% W film. Results of this study indicate that solute segregation can be used as a method to fabricate nanocrystalline materials that are stable against grain coarsening at elevated temperatures.

In this work, we explored macroscale liquid superlubricity using glycerol as the base lubricant to form aqueous solutions with different water/glycerol weight ratios. We find that glycerol aqueous solutions with water/glycerol weight ratio of 0.2 achieves superlubricity (coefficient of friction

Electricity in many countries such as the US and China is produced by burning fossil fuels in steam-turbine-driven power plants. The efficiency of these power plants can be improved by increasing the operating temperature of the steam generator. In this work, we adopted a combined surface science and computational thermodynamics approach to the design of high-temperature, corrosion-resistant steels for this application. The result is a low-carbon ferritic steel with nanosized transition metal monocarbide precipitates that are thermally stable, as verified by atom probe tomography. High-temperature Vickers hardness measurements demonstrated that these steels maintain their strength for extended periods at 700 °C. We hypothesize that the improved strength of these steels is derived from the semi-coherent interfaces of these thermally stable, nanosized precipitates exerting drag forces on impinging dislocations, thus maintaining strength at elevated temperatures.

Boron carbide thin films were deposited on (100) silicon substrates at ambient temperature via. pulse dc magnetron sputtering. Various frequency and duty cycles were applied to the hot-pressed B 4 C target in order to understand their influence on the structure and mechanical properties of the B 4 C films. X-ray Energy dispersive spectrum, Raman spectroscopy and Transmission electronic microscopy were used to characterize the composition and microstructure of the films. Nanoindenter was employed to measure the hardness and modulus. The film toughness was evaluated by a microindentation method. The results show that both pulse frequency and duty cycle significantly affect the B/C atomic ratio and then hardness and modulus in the boron carbide films. However, the amorphous structure of the films was maintained when the frequency and duty cycle changed. The maximum hardness of 29 GPa and modulus of 247 GPa combined with relative high toughness (3.3 MPa m 1/2 ) were achieved under 50 kHz frequency and 30% duty cycle. In addition, there was no evidence to prove that the graphite phase existed in the B 4 C films although exceeded C concentration was detected.

Fe/VC multilayer coatings with a fixed bilayer period (Λ = 8 nm) and variable Fe fraction (ΛFe/Λ ranging from 0.6 to 0.9) were deposited on Si substrates via dc magnetron sputtering. X-Ray diffraction and transmission electron microscopy showed the nanoscale layer structure of these coatings. High-resolution transmission electron microscopy imaging revealed the formation of coherent interfaces between Fe and VC (100). Throughout the entire range of Fe fractions investigated in this study, the hardness was enhanced over the rule-of-mixture trend line. Even at Fe fraction of 0.9, the hardness value was 16.3 GPa, enhanced by about 80% over the rule-of-mixture value of 9 GPa. While all Fe/VC coatings investigated in this work have statistically the same hardness, Fe/VC coating with Fe fraction of 90% has almost twice the fracture toughness of the other Fe/VC coatings. We attribute this enhanced toughness to the favorable generation of dislocations in the Fe layers and their activation by coherency strain emanating from Fe/VC interfaces. This study also demonstrates that H/E and H3/E2 are not good proxies for the toughness of these coatings.

Two experimental bcc -Cu- and B2–NiAl-precipitation-strengthened ferritic steels with 6.3 at. % and 12.4 at. % Cu + Mn + Ni + Al, 950 MPa and 1600 MPa yield strength respectively, were studied. Atom probe tomography showed that the volume fraction and number density of NiAl-type precipitates in the heavier alloyed steel (designated as CF-9 ) is ∼60–70 times greater than those in the lighter alloyed steel (designated as CF -2). This is attributed to the smaller lattice misfit between these NiAl-type precipitates and the ferritic matrix in CF- 9 due to more incorporation of Mn atoms on the Al sub-lattice in the B2 NiAl unit cell. Loading rate sensitivity of hardness was measured for CF -2, CF -9 and SAE -1090, which does not have bcc -Cu precipitates. Results show that even though CF -2 and CF -9 have double and triple the strength of SAE -1090 respectively, their hardness shows weaker dependence on loading rate. This is attributed to the presence of bcc -Cu precipitates in CF -2 and CF -9 providing athermal activation of nearby screw dislocation motion. Auger electron spectroscopy studies of CF -9 samples reveal Cu segregation on grain boundaries. The observed Cu segregation is believed to be partly responsible for the lower elongation-to-failure of CF -9 compared with CF -2.

It is desirable to increase the hardness of protective coatings for reduced abrasive wear and to increase the toughness for improved wear performance due to fatigue and formation of flaws or cracks. Unfortunately, there is an inverse relationship between hardness and toughness: the harder the coating, the lower the toughness. Using W/VC multilayer coatings, we demonstrated that it is possible to reverse this hardness–toughness trend. These coatings were synthesized by DC magnetron sputtering with bilayer periods of about 10 nm and different thickness fractions of W. They are crystalline, with hardness and toughness exceeding that of pure VC (25 GPa and 1.0 MPa-m 1/2 ). In particular, the W/VC multilayer coating with thickness fraction of 90% W achieves hardness of 28.5 GPa, comparable to many ceramics-based hard coatings, and toughness of 7.5 MPa-m 1/2 , similar to many nanocrystalline metals. This investigation shows that one can synthesize coatings as hard as ceramics and as tough as metals. These results also indicate that H / E and H 3 / E 2 ( H = hardness and E = elastic modulus) are not good proxies for coating toughness.

Reported in this paper is a novel and facile room-temperature surface-hardening technique, capable of providing five-fold increase in the hardness of an aluminum alloy, by utilizing a cavitating waterjet laden with hard nanoparticles. Microstructural and composition analyses reveal several mechanisms responsible for surface hardening: strain hardening, grain refinement, and dispersion strengthening. The hardened alloy surface also exhibits about 50% reduction in friction in a series of microscale friction measurements. Without the need to treat the alloy at elevated temperatures, this technique obviates such problems as additional energy usage, part distortion, microstructural and composition changes, and thermal shock-induced cracking. Equally important, this new method could be further tailored to impart metals, polymers, composites, etc. with different surface functional properties.

Most hard coatings are based on ceramic materials and are generally brittle. It is desirable to have coatings that are both hard and tough. Here, we review several strategies that can be employed to increase coating toughness while maintaining hardness. Various nanocomposite and multilayer coatings (Ti/TiB 2 , FeMn/TiB 2 , Fe/VC and W/VC) were synthesized to explore three such toughening strategies: coherency strain, transformation toughening, and nanograined metals. Practical methods used to measure coating toughness in this work were presented: scratch testing, nanoindentation, and modified Vickers. Results demonstrate that coating systems that exploit these strategies show significantly enhanced toughness compared with those that do not. In particular, the strategy of using nanolayers of a metal with high elastic modulus alternating with spacer layers much thinner than the metal appears to be the most effective. In principle, one can reach hardness values up to 10% of the elastic modulus, while attaining toughness comparable to most nanocrystalline metals. Given that most metals with high elastic moduli are refractory materials, such coatings may also be useful for high-temperature applications.

High-strength low-carbon ferritic steels attaining a maximum yield strength of 1600 MPa by combined Cu and NiAl precipitation-strengthening were developed. The yield strength of the alloys increases monotonically with the total concentration of the principal alloying elements i.e. Mn, Cu, Ni and Al. At 12.40 at.%, a 1600 MPa yield strength is achieved after solution treatment at 950 °C followed by aging at 550 °C for 2 h. For all three alloys investigated, the hardness reached a maximum after 1–2 h aging at 500–550 °C. At peak hardness, the combined precipitation of the body-centered cubic (bcc) Cu-alloy and B2-ordered NiAl-type intermetallic precipitates is observed by atom probe tomography (APT). The morphology, composition and structure of the Cu-alloy and NiAl-type precipitates were characterized using APT and transmission electron microscopy, as a function of aging time at 550 °C. In peak hardness conditions, the equiaxed bcc Cu-alloyed precipitates contain substantial amounts of Fe and are enriched in Ni, Al and Mn. Ni and Mn segregate at the Cu-alloy precipitate/ferrite matrix interface. In addition to the segregation, B2 NiAl-type precipitates nucleate at the Cu-alloy precipitates. After aging for 2 h, most Cu-alloy precipitates have a NiAl-type precipitate attached to their side. On subsequent further aging, the Cu-alloyed precipitates enrich progressively with Cu and elongate, indicating a transformation to the 9R or face centered cubic structure. The Cu-alloyed precipitates coarsen slower than the NiAl-type precipitates due to interfacial energy differences between the two types of precipitates, slower diffusion kinetics of Cu through the NiAl precipitates, different matrix equilibrium solubility and solute transfer from Cu-alloyed precipitates to NiAl-type precipitates. The relatively slow growth and coarsening of Cu-alloyed precipitates are consistent with the observation of an only modest decrease of hardness with extended aging.

While positive correlation between fracture toughness and H/E and H3/E2 has been reported for some ceramic coatings, we outline an argument that such correlation cannot be true in general, especially for nanolayer and nanocomposite coatings that present multiple interfaces to impede crack growth. Literature data are presented to support this argument.

The objective of this research is to characterize the elastic modulus, hardness, fracture toughness, and structure of multilayer coatings consisting of alternating nanolayers of Fe 1 − x Mn x and TiB 2 coatings ( x = 0, 0.18, and 0.35). These coatings were synthesized by dc magnetron sputtering. X-ray diffraction showed that Fe 0.82 Mn 0.18 contains 79% bcc and 21% fcc phases, while Fe 0.65 Mn 0.35 contains close to 100% fcc phase. The hardness of these multilayer coatings was found to exhibit a small enhancement (~ 2 GPa) over the rule-of-mixture values. The most striking finding is that the fracture toughness of Fe 0.82 Mn 0.18 /TiB 2 is about twice of that for Fe 0.65 Mn 0.35 /TiB 2 and Fe/TiB 2 with comparable hardness. In addition, Fe 0.82 Mn 0.18 /TiB 2 exhibits a quasi-elastic response in nanoindentation experiments. Given that Mn addition to Fe is known to result in the formation of metastable fcc phases at room temperature (with the degree of metastability controlled by the Mn content) and that the fcc phase may transform to the bcc phase under stress, such a transformation is likely to play a role in the increased toughness and quasi-elastic nanoindentation response observed in these coatings and may provide a strategy in the synthesis of hard coatings with improved toughness.

We have synthesized Ti–TiB 2 nanocomposite coatings by dual-cathode magnetron sputtering in argon onto polished titanium and silicon substrates with the TiB 2 volume fraction varying between 6 and 45%. Over this volume fraction range, TiB 2 is present as nanoparticles with diameter ~ 3 to 5 nm. When deposited on titanium substrates, the coatings are relatively stress-free. Through most of the composition range, the coating hardness is enhanced over the rule-of-mixture value by 5 to 10 GPa. We used two methods to determine coating fracture toughness: nanoindentation and nanoscratch. Results from these two methods are consistent and demonstrate that Ti–TiB 2 nanocomposite coatings exhibit a “flatter” hardness–toughness relationship compared with metal carbide/DLC and TiN/ a –Si 3 N 4 nanocomposite coatings, i.e. , the hardness decreases slower with increasing toughness. We speculate that the improved toughness of Ti–TiB 2 nanocomposite coatings is due to the formation of coherent Ti–TiB 2 interfaces, which in turn produce stress fields activating the motion of nearby dislocations within the Ti matrix and hence improved fracture toughness.

Advanced ultra-high strength steels are highly desirable for a wide range of engineering applications. Nanoscale co-precipitation strengthening in steels has received increasing attention in recent years and has become a new cornerstone for the development of advanced steels with superior combination of mechanical, welding, and irradiation properties for a new era. In this review, we highlight recent advances in computation-aided alloy design, nanostructural characterization, and unique properties of newly developed nanoscale co-precipitation-strengthened steels. In particular, our emphasis is on elucidating alloy design strategies, the co-precipitation mechanism, and cooperative evolution of multiple types of nanoparticles, and the correlation between nanostructures and bulk steel properties. Finally, future research areas for this class of nanostructured steels are critically discussed.

This work examines the thermal behavior and failure mechanisms of TiN/CNx multilayer coatings deposited by DC magnetron sputtering. The samples were examined by transmission electron microscopy before thermal analysis. During thermal analysis, the samples were heated up to 1070 K at a constant rate of 10 K min−1 in a N2 atmosphere and their thermal stability was evaluated by thermo gravimetric (TGA) and differential thermal analyses (DTA). These analyses indicate that the multilayer coating is thermally stable up to 950 K, followed by stress relaxation when the temperature exceeds 950 K. After this thermal treatment, coating surfaces were observed by scanning electron microscopy. Buckling and fractured surface were seen for multilayers deposited with and without substrate bias voltage applied during growth process, although samples deposited with substrate bias are more resistant to crack formation and propagation.

Because of the high residual compressive stress normally accompanying the growth of diamond-like carbon (DLC) coatings and the large mismatch in the thermal expansion coefficient between DLC and steel, it is difficult to grow DLC coatings much thicker than 0.25 μm on steels. This paper describes our attempt to overcome this thickness limitation by a sequence of carbonitriding, carburizing and equilibration pre-treatments of the steel surface, followed by DLC coating deposition, all conducted within the same deposition system without breaking vacuum. These pre-treatments resulted in a surface with a graded composition and hardness profile. Such a graded interface is expected to reduce the interfacial energy, decrease thermal mismatch between the coating and the substrate, and thus improve coating adhesion. X-ray diffraction revealed the formation of various hard carbide and nitride phases. Raman spectroscopy showed that the modified steel surface just before DLC deposition exhibits local carbon bonding characteristics similar to DLC. Pulsed dc plasma-enhanced chemical vapor deposition was used to deposit one-micron thick DLC on these steel surfaces. The coating hardness was ~ 18–19 GPa. Its adhesion on the steel substrate was measured by scratch testing and was found to be comparable to thick, adherent DLC coatings deposited by other methods.

This article summarizes the discussions and deliberations on transformative research issues and opportunities in energy efficiency identified by a panel of experts assembled for the Civil, Mechanical, and Manufacturing Innovation Division of the US National Science Foundation. The discussions were confined to two areas – reducing energy consumption in buildings and improving energy efficiency in transportation. While these represent only a very small segment of important areas in energy efficiency, the panel considered them to be the most promising in terms of return on investment in research efforts. In the area of reducing energy consumption in buildings, high-priority research topics include information technology infrastructure for fundamental data gathering, processing and management, whole system and process integration for design and operation of smart buildings, and high-performance building components and sub-systems. In the area of energy efficiency in transportation, high-priority research topics include development of high-temperature high-performance ferrous alloys, systems design of protective coatings, fundamental understanding of surface texturing effects on friction and wear, and development of oxidatively stable bio-based lubricants. The energy challenge is serious. We need sustained investment in renewable energy, energy efficiency, and talent development in these new technologies for the future of our civilization.

This article presents a summary of research issues and opportunities in alternative energy source research identified by panels of experts assembled by the Engineering Directorate of the US National Science Foundation. The objective was to identify transformative research issues and opportunities to make alternative energy sources viable. The article presents motivations for energy research, grand challenges, and specific challenges in the research areas covered. The grand challenges identified for the United States include supplying 30% of US electricity from photovoltaics by 2030, supplying 25% of US electricity from wind by 2025, displacing 30% of US hydrocarbon use by 2030 with bio-based products, and providing a practical 250–300 W h/kg energy storage system by 2025. Similar challenges could be outlined along the same lines for the remainder of the world. Examples of specific areas of research focus identified as promising include high performance p-type transparent conductors, multijunction thin-film photovoltaic devices, defects in chalcogenide semiconductors, experimental study and numerical modeling of the fluid mechanics of airflow as applied to wind turbines, improved materials for wind turbines, methods for creating high energy density transportable biological feedstocks, biorefinery processes yielding infrastructure-compatible biofuels and biochemicals directly, and improved electrodes and electrolytes for Li ion batteries. Arguments for each of these as research priorities are given.

The mechanical properties of Cu-rich nano-cluster-strengthened ferritic steels with and without boron doping were investigated. Tensile tests at room temperature in air showed that the B-doped ferritic steel has similar yield strength but a larger elongation than that without boron doping after extended aging at 500 degrees C. There are three mechanisms affecting the ductility and fracture of these steels: brittle cleavage fracture, week grain boundaries, and moisture-induced hydrogen embrittlement. Our study reveals that boron strengthens the grain boundary and suppresses the intergranular fracture. Furthermore, the moisture-induced embrittlement can be alleviated by surface coating with vacuum oil. (C) 2010 Elsevier B.V. All rights reserved.

Titanium dioxide (TiO 2 ) films with varying concentrations of gold particles were synthesized using pulsed DC magnetron sputtering, with the intent to develop infrared reflecting films for use on cars and planes to reduce solar heat load. Under our deposition conditions, the films are smooth (RMS roughness on the order of 1.0–2.0 nm) and consist of rutile TiO 2 with embedded gold. The average gold particle diameter on the sample surface was found to change from 60 to 200 nm as the volume fraction of gold in the films increased from 1.9 to 4.3% (3.5 to 7.9 mol% Au). The maximum reflectance of these films in the infrared region (800–2500 nm) is > 50%, compared with 30% for pure TiO 2 . The Maxwell–Garnett equation does not model the reflectance data very well, due to the relatively large gold particle size. Instead, by assuming that the contribution of gold particles to the reflectance response is proportional to their projected areal fraction in an effective medium approximation, we were able to fit the observed reflectance data quite well.

Multilayer oxide coatings consisting of amorphous Al 2 O 3 and crystalline TiO 2 nanolayers have been deposited using reactive pulsed d.c. magnetron sputtering at different partial pressures of oxygen. Hardness enhancement has been observed in oxide multilayer coatings with amorphous Al 2 O 3 as the majority component. These coatings had greater hardness-to-modulus ratios and showed greater resistance to wear over monolithic Al 2 O 3 and TiO 2 majority phase multilayers. Multilayer films retain their high hardness up to ~ 800 °C in air; some hardness enhancement in the Al 2 O 3 majority phase multilayer coating remains even after 1 h of air annealing at 1000 °C. The hardness decrease at elevated temperatures is due to the roughening of interfaces between nanolayers, which can be attributed to the annealing-driven change of crystallographic texture of TiO 2 layers.

Recent experimental studies showed that the ductility of NiTi is not affected by moisture, while addition of iron beyond 9 a/o in NiTi leads to moisture-induced embrittlement. To explore the nature of this embrittlement, we studied the chemical interaction between water vapor and (Ni,Fe)Ti(110) surfaces with 5 a/o and 10 a/o Fe. Temperature-programmed desorption and X-ray photoelectron spectroscopy show that decomposition of water to produce atomic hydrogen occurs on both surfaces. Activation energy for surface diffusion was calculated by density functional theory, showing that addition of Fe decreases H surface diffusivity, in agreement with experiment. Together with the observation that addition of 9 a/o Fe increases the strength of NiTi, this indicates that moisture-induced embrittlement in higher strength NiTi alloys is not due to faster H surface diffusion, but lower critical hydrogen concentration required for embrittlement.

Using pulsed dc magnetron sputtering, we synthesized hydrogenated amorphous carbon films with and without sulfur doping. These films were smooth and amorphous, with low compressive stress (

Ultrathin CN x overcoats were grown using pulsed dc magnetron sputtering. Substrates were mounted on a holder that allowed 45° tilt angle and rotation. Effects of process parameters on film growth were reviewed. AFM scans over large sampling areas show that thin CN x films obtained at -100 V substrate bias with 45° substrate tilt and 20-25 rpm rotation have r.m.s. roughness about 0.2-0.3 nm when sampled over 20 × 20 μm 2 areas, increasing to ∼0.45 nm when sampled over ∼0.05 × 3 cm 2 using X-ray reflectivity measurements. These 1-2 nm thick ultrasmooth coatings reduced corrosion damage compared with coatings of the same thickness grown without substrate tilt and rotation. This improved performance is likely a result of more efficient and uniform momentum transfer parallel to the surface during deposition in this configuration. In addition, detailed X-ray reflectivity measurements showed that the mass density of these CN x films is ∼2.0 g/cm 3 , independent of film thickness from ∼1 to 10 nm, consistent with ion beam analysis.

Boron carbide (B4C) and boron carbon nitride (BxCyNz) thin films were synthesized by pulsed DC magnetron sputtering. Effects of target power, target pulse frequency, substrate bias and pulse frequency on surface roughness were studied by AFM over sampling areas of 20 μm × 20 μm. For B4C, the combination of target power of 75 W/50 kHz and substrate bias of −100 V/2 kHz results in the smallest surface roughness. Compressive stress in these films is around 2.5 GPa. These B4C films have a hardness of 30 ± 5 GPa and reduced modulus of 250 ± 50 GPa. Nitrogen incorporation into B4C films, which gives BxCyNz thin films, has a beneficial effect. When deposited under similar conditions with substrate bias pulsed at −100 V / 20 kHz, the root-mean-square surface roughness decreases to 0.19 nm, compared with 0.28 nm for B4C. The hardness of BxCyNz is 20 ± 3 GPa, and reduced modulus is 210 ± 30 GPa. Auger electron spectroscopy was used to characterize the film composition. High-resolution cross-sectioned TEM images and diffraction show that both films are amorphous. Corrosion studies indicate that BxCyNz is a better protective coating for hard disk substrates than B4C and CNx films. This is attributed mainly to the smoother morphology of BxCyNz films.

TiB 2 /TiC multilayer coatings were synthesized in a dual-cathode unbalanced magnetron sputter–deposition system with substrate rotation. Our previous research has demonstrated that all coatings on M2 steel are polycrystalline with TiB 2 (001) preferred orientation and have a layer structure. Compressive stress in these coatings is less than 2 GPa, with hardness up to 60 GPa, which corresponds to 100% hardness enhancement over the rule-of-mixture value. This paper concentrates on the tribological and dry machining evaluation of these coatings. Coatings were deposited on Si(001), polished M2 steel, and C3 WC cutting tool inserts. From dry block-on-ring tribotesting, the 3:0.5 multilayer (i.e., the layer thickness is 3.0 nm for TiB 2 and 0.5 nm for TiC) coating provides four times improvement in wear resistance over the uncoated M2 steel substrate. In addition, dry machining was performed using AISI 1018 steel and 319 aluminum alloy cylindrical workpieces. Monolithic TiB 2 and 3:1 multilayer coatings (i.e., the layer thickness is 3.0 nm for TiB 2 and 1.0 nm for TiC) have the best performance: the flank wear was reduced by about a factor of ten compared with the uncoated tool after a cutting distance of 600 m. Results from cutting force measurements demonstrate that as far as dry machining is concerned, there is no direct correlation among cutting forces, room-temperature hardness, and flank wear. In dry machining of aluminum, the carbide tool deposited with the 3:1 multilayer, unlike other tools, has negligible buildup on the rake face. This results in better and more consistent surface finish of the final workpiece and less likelihood for premature tool breakage.

We have synthesized the amorphous silicon/carbon (Si/C) multilayer thin films on Cu substrate and investigated their applications as the anode for high rate rechargeable Li-ion batteries. X-ray diffraction and Raman spectrum revealed that the films were amorphous. The electrochemical evaluation was performed with constant current charge/discharge test under various loading currents in PC. The results showed a high first initial capacity of 3107 mAh g−1 and a high first coulombic efficiency of 83% at 15C rate (60 A/g). In the following cycles, a capacity of 2000 mAh g−1 at 30C (120 A/g) and 1500 mAh g−1 at 60C (240 A/g) were attained with a retention of 99%. The test predicted that the Si/C multilayer thin films were a promising anode material for lithium ion batteries.

The recrystallization and associated nanoindentation behavior of a Zr–10Al–5Ti–17.9Cu–14.6Ni (at.%) bulk amorphous alloy was investigated using in situ transmission electron microscopy and high-temperature nanoindentation. The onset of recrystallization occurs around 710 K, with the formation of Zr 2 Cu, Al 3 Zr 4 , and Ni 10 Zr 7 . Nanoindentation hardness and elastic modulus were obtained as a function of temperature from 298 to 723 K. The hardness was measured to be ∼7.5 GPa and found unchanged at temperatures below 673 K, but softened rapidly and decreased to 5 GPa at 723 K. These results can be correlated very well with the onset of recrystallization of this alloy at ∼700 K. The present study demonstrates that transmission electron microscopy, hot-stage nanoindentation, and X-ray diffraction are supplementary techniques for the study of glass relaxation and crystallization of metallic glasses.

Iron addition beyond 9 a/o in NiTi leads to embrittlement by water or hydrogen. To explore the nature of this embrittlement, we studied the chemical interaction between water vapor and (Ni,Fe)Ti(110) surfaces with 5 a/o and 10 a/o Fe. Temperature-programmed desorption shows that decomposition of water to produce atomic hydrogen occurs on both surfaces. X-ray photoelectron spectroscopy further demonstrates that the decomposition occurs around 190 K in both cases. A statistical model was developed to explore the effect of dopant atoms on hydrogen diffusion, assuming that diffusion depends on local composition. Dopant atoms such as boron that bind strongly to hydrogen slow down diffusion and therefore should suppress the environmental effect, consistent with atomistic simulations. Fe binds to hydrogen less strongly and therefore should result in faster diffusion. However, the present model shows that this increase in diffusivity is minimal. Therefore, this result indicates that nonchemical effects must be at work in moisture-induced embrittlement of (Ni,Fe)Ti alloys when the Fe concentration exceeds 9 a/o.

Hydrogenated carbon (CH x ) films were grown by reactive magnetron sputtering of graphite in an argon–hydrogen plasma. Pulsed d.c. bias was applied to both the carbon target and the substrate to maintain a stable process and reasonable deposition rate. The resulting films were smooth and stress-free. The influence of hydrogen concentration and relative humidity on friction properties of the films was investigated. At 5% relative humidity, the lowest friction coefficient of 0.01 was obtained at a sputter-gas composition containing 25% hydrogen. Excessive incorporation of hydrogen produces softening and degrades its friction performance at high contact stresses. Molecular dynamics simulation studies showed the reduction of friction coefficient with surface hydrogenation. These studies indicate that pulsed d.c. magnetron sputtering can produce hydrogenated carbon films with friction properties similar to those prepared by chemical vapor deposition methods.

TiB2/TiC multilayer coatings were synthesized in a dual-cathode, non-reactive, unbalanced magnetron sputtering system with stationary and rotating substrates. All coatings are polycrystalline with TiB2(001) preferred orientation and have a multilayer structure. Coatings synthesized with stationary substrates have high compressive stress (4–7 GPa), and their hardness is slightly enhanced (∼25%) over the rule-of-mixture value. Coatings grown with substrate rotation have much lower compressive stress ( 60 GPa). Substrate rotation appears to improve mobility of surface species and allows more time for surface diffusion, thus resulting in denser films with lower void concentration. This may explain the substantial difference in hardness enhancement between these two cases. After being annealed in an inert environment (vacuum or argon) at 1273 K for 1 h, these multilayer coatings retain their layer structure. Moreover, most coatings have improved crystallinity and increased room-temperature hardness after such annealing.

A statistical model was developed to explain effects of alloying elements on moisture-induced embrittlement in intermetallics. This model shows that if alloying elements have strong binding to atomic hydrogen, they may suppress moisture-induced embrittlement by slowing hydrogen diffusion even at low alloying element concentrations. The concentration needed to effectively slow down the diffusion process decreases with temperature. Grain boundary segregation is not a necessary condition to suppress embrittlement as long as the alloying element binds to hydrogen sufficiently strongly and its concentration is above a certain level. In the other extreme, when the binding of hydrogen to the surface is so weak that hydrogen desorption occurs simultaneously as surface diffusion, the model demonstrates that above a certain desorption rate, there may be not enough hydrogen diffusing to the crack tip to cause embrittlement.

We conducted an international round-robin experiment to determine the consistency of nanoindentation hardness measurements of thin films among six different laboratories, using three different samples. These samples were chosen to present a challenge of indenting at small loads (μN range). They were: 250-nm-thick TiN x , 700-nm-thick TiC, and 500-nm-thick TiB 2 /TiC multilayer coatings (each layer being 3-nm thick), prepared at Northwestern University using magnetron sputtering on silicon (0 0 1) substrates. Each research team was free to use whatever nanoindentor and analysis methods at its disposal. This round-robin experiment demonstrates that for the hardness range of interest (15–35 GPa) and using well-documented procedures and analysis methods, the reported results from all laboratories are essentially the same, allowing for a statistical spread of approximately ±14%. For consistent hardness measurements, four precautions must be observed: (i) proper tip-area function calibration, (ii) using sharp indenters, (iii) performing nanoindentation measurements with minimal thermal drift and with drift correction, (iv) using smooth samples, and (v) measuring the full hardness–maximum penetration curve.

Single and multilayer boron nitride and boron carbide films were grown using d.c. magnetron sputtering in a single cathode deposition system. High frequency pulsed bias voltages were applied to both the target and the substrate during deposition. An external solenoid was utilized to increase the ion flux during deposition. Momentum of incident ions was found to play a key role for cubic BN:C formation. Multilayer film growth was investigated as a way to obtain thick and adherent cubic boron nitride containing coatings. Boron carbide films were found to have a hardness exceeding 40 GPa and a smooth surface morphology (r.m.s. roughness 0.1–0.15 nm), high elasticity, and high wear resistance.

We reported in an earlier study the use of amorphous SiNx to periodically interrupt the growth of TiN in order to suppress the columnar structure. X-Ray diffraction and transmission electron microscopy studies confirmed that the columnar growth was effectively suppressed. In this paper, we showed that these TiN/SiNx multilayer coatings attain lower dry friction coefficient (half of TiN) and better nanoscratch resistance than TiN coatings. Block-on-ring wear tests showed that the wear rate of optimized TiN/SiNx multilayer coatings is three times better than that of TiN coatings. Most important, the rolling-contact-fatigue life of the M50 bearing rod, coated with a 0.75 μm thick TiN/SiNx multilayer coating, is more than 10 times (test stopped manually before failure) better than that of uncoated ones and five times better than rods coated with conventional TiN coatings. The optimum TiN/SiNx coating thickness appears to be approximately 0.75 μm. This remarkable fatigue performance appears to be due to a combination of improved microstructure, adhesion, hardness and surface topography.

Hard TiN/SiN x multilayer coatings with an equiaxed microstructure were prepared using a dual-cathode unbalanced reactive-magnetron sputtering system. These multilayer coatings were then annealed at 1000 °C for 1 h in vacuum. These TiN/SiN x multilayer coatings before and after annealing were characterized at room temperature and compared in terms of microstructure and mechanical properties. X-Ray diffraction and cross-sectional transmission electron microscopy studies showed that the layer structure of these coatings is preserved after annealing at 1000 °C when the SiN x layer thickness is 0.8 nm or greater. The high hardness of these multilayer coatings is either maintained or improved after annealing. Therefore, with proper control of the SiN x thickness, TiN/SiN x multilayer coatings demonstrate excellent thermal stability and are potential candidates for high-temperature tribological applications.

Amorphous and crystalline alumina thin films were grown by reactive magnetron sputtering. A pulsed d.c. bias was applied to both the aluminum target and the substrate to maintain a stable deposition process and high deposition rate. An external solenoid coil was placed underneath the substrate to form a magnetic trap between the substrate and the target, thus enhancing ion bombardment of the growing film. Effects of substrate bias and magnetic trap on film properties were investigated. Under optimum conditions, crystalline alumina films were obtained at substrate temperatures of ∼340°C, with hardness ∼25 GPa and refractive index 1.65–1.85 in the visible region. Friction and wear properties of crystalline and amorphous alumina thin films were compared.

TiN coatings have been widely used in various tribological applications. However, TiN coatings predominantly grow with a columnar grain structure, and these columnar grain boundaries become the sites for crack initiation, resulting in premature failure of TiN coatings. In this paper, we report the use of amorphous SiN x to periodically interrupt the growth of TiN in order to suppress the columnar structure. The growth was performed in a dual-cathode unbalanced reactive magnetron sputtering system. The resulting TiN/SiN x multilayer coatings, when deposited under optimum conditions (TiN layer thickness=2.0 nm, SiN x layer thickness=0.5 nm and substrate bias=−80 to –90 V) are smooth and exhibit an equiaxed grain structure with no evidence of columnar growth. The highest hardness is in excess of 45 GPa.

The interaction between water vapor (D2O) and boron-modified Ni3(Al,Ti)(110) was investigated using temperature-programmed desorption and X-ray photoelectron spectroscopy. Boron dosing was performed using a solid-state boron ion source. Results showed that boron reacts with water to form hydroxyls at temperatures as low as 130 K. D2 desorption occurs at ∼950 K from boron-modified Ni3(Al,Ti)(110), indicating strong B–D bonding. Surface diffusion coefficients of atomic D, obtained from dissociation of water, on clean and boron-modified Ni3(Al,Ti)(110) surfaces were measured at 270 K with electron-stimulated desorption. The surface diffusion coefficient of atomic D on 0.05 monolayer boron-modified surface is about 10 times smaller than that on the boron-free surface. This slower diffusion of atomic hydrogen may explain why boron improves the ductility of polycrystalline Ni3Al in moist environments.

Ultrathin films of carbon nitride were grown using d.c. magnetron sputtering in a single cathode deposition system. A high frequency pulsed bias was applied to both the target and the substrate during deposition to help sustain a stable plasma and enhance ion bombardment of the growing film. These films exhibit excellent corrosion resistance at film thickness down to 1 nm. Atomic force microscopy measurements reveal an atomically smooth surface. The role of pulsed bias and bombardment by ionized species in obtaining low defect-density coatings is discussed.

Possible reasons for the high ductility of Ni3Fe and its insensitivity toward the testing environment have been investigated. Thermal desorption experiments have shown that water dissociates on clean Ni3Fe surfaces to produce atomic hydrogen. Ductility measurements of cast and cold-rolled polycrystalline Ni3Fe demonstrated that the reduced ductility was obtained only when the testing was performed with oxygen carefully removed. X-ray photoemission studies indicate that oxygen interacts with water to form hydroxyls, thereby suppressing the production of atomic hydrogen. Hydrogen desorption from the Ni3Fe surface requires a lower activation energy, resulting in a smaller surface hydrogen concentration at a given temperature. Hence it is possible that there is insufficient hydrogen to cause the nucleation and growth of brittle cracks for severe embrittlement.

A single-cathode magnetron sputtering system was used to deposit CN x and CN x /TiN coatings onto Si (100) and polished M2 substrates. It was shown that optimum choice of substrate bias and pressure is required to obtain smooth films with maximum hardness and wear performance for carbon nitride. This work that it is possible to obtain CN x /TiN composite films using the same single-cathode approach, although the C/Ti ratio required to achieve the best hardness and wear properties has yet to be optimized.

The interaction of water vapor and oxygen with polycrystalline Ni3Fe has been studied by Auger electron spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermal desorption. Water adsorbs molecularly on the surface at or below 150 K. Between 150 and 200 K, some adsorbed water molecules desorb in vacuum, while others dissociate into hydroxyls, atomic oxygen, and hydrogen. XPS studies suggest iron to be the active species in controlling the dissociation of water on polycrystalline Ni3Fe surface. Water dissociation into atomic hydrogen is greatly suppressed by the presence of small concentrations of oxygen in water vapor.

The interaction of water vapor with single crystal Ni 3 (Al, Ti) has been studied with Auger electron spectroscopy, photoemission spectroscopy and thermal desorption. Water adsorbs molecularly onto the (111) and (100) surfaces at 140 K. When warmed up to room temperature, water remains as an intact molecule on (111), but dissociates to surface hydroxyl and atomic oxygen on (100). The latter process is accompanied by the evolution of hydrogen and oxidation of Al. It appears that the dissociation of water is structure-sensitive and that Al is the active species in controlling the dissociation of water on Ni 3 Al surfaces.

Carbon nitride thin films were synthesized using d.c. unbalanced magnetron sputtering of a high-purity graphite target in a nitrogen-containing plasma onto various substrates held at ambient temperatures. The N/C ratio was found to vary from zero to 0.8 depending on deposition conditions. There was evidence of multiple bonding states for carbon and nitrogen (sp, sp2 and sp3), and the bulk of the film was found to be amorphous. Nanoindentation studies showed that under appropriate substrate bias conditions the carbon nitride coating hardness can be enhanced to levels well above that of conventional amorphous hard carbon coatings. CNx coatings replicate the substrate topography, giving rise to surface roughness equal to or better than the original substrates. Lubricated tribotesting showed the relationship between wear performance and deposition conditions. Under pure sliding in air, the CNx coating provided a 30-fold reduction in wear rate for M2 steels (compared with uncoated M2) under our testing conditions.

Low cycle fatigue behaviors in Nb-bearing high strength, low alloy (HSLA) steel have been studied at plastic strain amplitudes Δϵ p /2 ranging from 1 × 10 −5 to 1 × 10 −2 in air and in ultrahigh vacuum (UHV). Microcracks are initiated along slip lines both in air and in UHV, and grain boundaries act as effective barriers to the propagation of microcracks. Coffin-Manson relations are reasonably satisfied for the microcrack initiation life N i and the fatigue life N f both in air and in UHV. The accumulated total cyclic plastic strain energy W i required for fatigue crack initiation and the accumulated total cyclic plastic strain energy W f required for fatigue failure are expressed mathematically in the form of K ( Δϵ p /2) N . The computed values of W i and W f are in good agreement with the values determined experimentally. The vacuum environment enhances N i , N f , W i and W f . The environmental effect becomes greater as the plastic strain amplitude decreases.

STM lithography by pulsing the tip-sample bias was used to deposit nanometer-sized clusters on a copper surface using gold tips. Prior to writing each cluster, we extracted the local tip radius of curvature from STM images of slip band steps previously formed on the copper surface. This novel technique permitted in-situ observation of changes in both cluster size and local tip structure while using a single tip. It was found that the cluster diameter increases with the square root of tip radius. Using a model in which we assume that deposition occurs only from that region of the tip within a certain distance from the sample surface, we were able to derive an expression consistent with the experimental data.

Silver single crystals oriented in the single glide orientation were fatigued in air and vacuum. The surface morphology was observed using a scanning tunneling microscope. A gold film deposited on the silver surface was used as a reference marker so that the same region can be observed upon repeated fatigue cycling. Pit-shaped features were observed to form within a narrow range of cycles and to eventually develop into micro-sized cracks, lending support to the notion that cracks are formed by a nucleation process. In addition, by measuring the slip band height and spacing as a function of cycling, we were able to determine the slip irreversibility and the Coffin-Manson exponents in both environments. With these two sets of data, we were able to verify a new scaling relationship for fatigue life based on our earlier theoretical work.

The role of surface chemistry in the initiation of fatigue cracks was studied for silver single crystals. Fatigue tests up to crack initiation were carried out on pure silver specimens and specimens surface-alloyed with gold. The ambient used was oxygen. Concurrent investigations of the effect of gold on oxygen adsorption on Ag(111) surfaces were carried out using X-ray photoelectron spectroscopy. A strong correlation was observed between the number of cycles to crack initiation and the reactivity of slip steps exposed by the fatigue process as well as the rate of oxygen adsorptio on the exposed slip steps. It was also found that oxygen adsorbed on the slip steps was transported into subsurface regions during fatigue. When the same test was performed in bromine, subsurface transport of bromine was not observed; yet the fatigue life up to crack initiation was found to be the same as that in oxygen. The absence of bromine transport is likely due to its larger atomic size. Based on these studies, we conclude that the dominant mechanism for accelerating fatigue crack initiation in an active environment is the reduction of dislocation reversibility by strong adsorption of ambient species on exposed slip steps.