In Situ Studies of TiC<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Hard Coating Tribology

TiC_1−x N _x hard coatings present time-dependent tribological behavior with an initial running-in period (500–2000 cycles) marked by an elevated friction coefficient, followed by >10000 cycles with low-friction and wear at room temperature (RT) in ambient air. The mechanisms behind this behavior are not completely understood. Tribological tests performed at RT and at different relative humidity (RH) levels revealed that a minimum value between 15 and 25% RH is needed to trigger the low-friction regime at a sliding speed of 100 mm s⁻¹. By in situ observations of transfer film growth, it could be observed that third body material is formed during this running-in period by plowing of the coating and shearing of the removed material. The appearance and thickening of the transfer film marks the beginning of the steady-state low-friction regime where the velocity is accommodated by interfacial sliding. At this stage in the tribological test, the recorded Raman spectra indicated the presence of C–H bonds in the wear track. Use of in situ analytical tools during wear tests provided insights with respect to tribological phenomena that were not available by conventional, post-mortem analysis methods.     

Dynamics of Growth of the Native Oxide of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te

The growth of the native oxide of the Cd_xHg_1?xTe (MCT) compound is studied by methods of laser and spectral ellipsometry. It is found that a non-absorbing oxide film is formed from the very beginning in the case of MCT oxidation with hydrogen peroxide vapors, whereas oxidation with atmospheric oxygen leads to the formation of absorbing layers on the surface at the first stages of the process. When the oxide film thickness reaches 1–2 nm, the oxidation rate drastically decreases. If MCT samples that were stored for a long time (for years) in air at room temperature are heated at T = 200 °C, the optical thickness of the oxide film decreases.     

Dependences of the optical characteristics of Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N films on the substrate composition and polarity

Optical properties of Ga- and N-polar triple nitrides Al _x Ga_1−x N with molar fractions of aluminum from 0 to 0.6 are studied by a nondestructive contactless method of spectroscopic ellipsometry. Correlation dependences of the shift of the fundamental absorption edge and the behavior of the real and imaginary parts of the pseudodielectric function on the composition x and polarity of the Al _x Ga_1−x N layers are revealed. It is verified that the polarity of the layers grown by molecular beam epitaxy is defined by the formation of the AlN nucleating layer.     

Using the φ-<Emphasis Type="Italic">S</Emphasis><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nomogram in calculating the dynamics of a braked wheel

The work deals with the investigation of parameters having effects on road holding and response of wheeled vehicles. A new procedure for evaluating forces in the tire contact area by means of the φ-S _x nomogram accounting for lateral effects on the wheel is put forth. The procedure may be used in assessment of the road holding ability of a vehicle during vehicle design, in selection of a functioning algorithm for the antilock braking systems of vehicles, and also in technical expertise on motor vehicle accidents.     

Effect of Grain Boundary on the Wear Behaviour of NiTi Shape Memory Alloys When <Emphasis Type="Italic">M</Emphasis><Subscript>f</Subscript> &lt; <Emphasis Type="Italic">T</Emphasis> &lt; <Emphasis Type="Italic">A</Emphasis><Subscript>f</Subscript>

Wear behaviour of NiTi SMA is closely corresponds to deformation mechanisms associated with different plastic strain accumulation process. Plastic strain accumulation is achieved by dislocation motion; however, grain boundary acts as a strong barrier. In this work, wear behaviour of single-crystalline and polycrystalline NiTi SMAs was studied to understand the effect of grain boundary on the plastic strain accumulation in the wear process. Wear tests were conducted at M_f < T < A_f, where phase boundary exists between martensitic and austenitic phases. Tests were conducted under ball-on-disc sliding wear mode, and alumina (Al₂O₃) counter-body was used. For single-crystalline NiTi SMA, transition wear occurred even when the applied load was relatively low (i.e., 100 mN). For polycrystalline NiTi SMA, with increasing applied load and wear cycles, the wear has shifted from near-zero wear stage to severe wear stage; no transition behaviour was observed. Significant differences in the wear process were discussed with respect to deformation mechanisms associated with dislocation motion in the single-crystalline and polycrystalline NiTi SMAs.     

Abrasive and Adhesive Wear Behavior of Arc-Evaporated Al<Subscript>1−<Emphasis Type=Italic>x</Emphasis></Subscript>Cr<Subscript><Emphasis Type=Italic>x</Emphasis></Subscript>N Hard Coatings

During the last decade, the usage of difficult-to-machine materials such as austenitic stainless steels has increased continuously in various industrial applications. Tools such as blind hole taps, punches, or deep drawing molds are often exposed to severe wear while machining/forming these materials, mainly due to excessive adhesion and material transfer. On combination with abrasive wear due to work-hardened wear debris, tool lifetime in these applications is often limited. In this study, ball-on-disc experiments were carried out with arc-evaporated AlCrN coatings with different Al/(Al + Cr) ratios against Al₂O₃ and austenitic stainless steel balls in ambient atmosphere. Test temperatures of 25, 500, and 700°C were chosen for the hard Al₂O₃ balls simulating severe abrasive loads, whereas 25, 150, and 250°C were used for the softer stainless steel material to evaluate the adhesive wear behavior. Characterization of the wear tracks was done by scanning electron microscopy in combination with energy-dispersive X-ray analysis and optical profilometry. The best abrasive wear resistance during testing against Al₂O₃ was observed for the coating with the highest Al content. In the case of the austenitic stainless steel balls, sticking of the ball material to the coating surface was the dominating wear mechanism. The influence of test temperature, chemical composition, and surface roughness was studied in detail.     

Tribological Properties of Organic Functionalized ZrB<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Epoxy Composites

The tribological behaviors of epoxy composites filled with organic functionalized ZrB₂–Al₂O₃ were environmentally investigated and compared with those with as-received fillers under both dry and oil sliding conditions in this work. The worn surfaces and the transfer films on the counterparts were characterized by scanning electronic microscope (SEM), and the frictional temperature rising was investigated by infrared thermometer. The results demonstrated that the coefficient of friction (CoF), the wear rate, as well as the frictional temperature rise of the epoxy composites were all decreased due to the introduction of ZrB₂–Al₂O₃ fillers. And with the increase in filler content, similar variation tendencies of CoF and wear rate of epoxy composites were observed under the different sliding conditions. Besides, the organic functionalization of ZrB₂–Al₂O₃ fillers, which made the epoxy composites exhibit lower CoF and wear rate than those with as-received fillers, lowered the frictional temperature as well. In comparison, the epoxy composites filled with 5 vol% modified fillers presented better tribological properties, suggesting a stronger interfacial bonding between modified fillers and epoxy matrix. The dominant wear mechanisms of filled composites under dry and oil sliding conditions could be inferred as the combination of adhesive wear and abrasive wear and the fatigue wear, respectively, on the basis of SEM images of worn surfaces.     

Environmental Effects on the Tribology and Microstructure of MoS<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–C Films

The tribology of molybdenum disulfide (MoS₂)–Sb₂O₃–C films was tested under a variety of environmental conditions (ambient 50% RH, 10⁻⁷ Torr vacuum, 150 Torr oxygen, and 8 Torr water) and correlated with the composition of the surface composition expressed while sliding. High friction and low friction modes of behavior were detected. The lowest coefficient of friction, 0.06, was achieved under vacuum, while sliding in 8 Torr water and ambient conditions both yielded the highest value of 0.15. Water vapor was determined to be the environmental species responsible for high friction performance. XPS evaluations revealed a preferential expression of MoS₂ at the surface of wear tracks produced under vacuum and an increase in Sb₂O₃ concentration in wear tracks produced in ambient air (50% RH). In addition, wear tracks produced by sliding in vacuum exhibited the lowest surface roughness as compared to those produced in other environments, consistent with the picture of low friction originating from well-ordered MoS₂ layers produced through sliding in vacuum.     

Background of a “<Emphasis Type="Italic">dE + E</Emphasis>” phoswich detector

A method for estimating the γ-ray background of a phoswich detector of the “dE + E” type is discussed. The phoswich detector is composed of an outer thin detector and an inner total-absorption detector and is used for β-ray spectrometry. The calculated background of the phoswich detector with an area 40 cm² inside 5-cm-thick lead shielding is shown to be 0.095 ± 0.019 counts/s. The contribution of the high-energy background to the total level is 77%.     

<Emphasis Type="Italic">CAD-Based Virtual Assembly Prototyping – A Case Study</Emphasis>

This paper presents the methodology for quantifying the blade assembly process with the future objective of fully automated assembly planning. The proposed method is aimed at eliminating the expensive and time-consuming physical prototyping needs by analysing and evaluating the feasibility of the blade assembly process using a CAD-based virtual prototype. The virtual prototype of the entire assembly operation is created for the blade assembly from a torque converter of an automobile transmission system. This model development is implemented using ProEngineer. Owing to the modelling requirements, the design intents, pertinent parameters, and their relationships in the entire blade assembly process must be captured and integrated into the model. The virtual assembly prototyping package developed is capable of computing and offering computer animated simulations of the interference of the blade tabs with the turbine and the pump shell during the assembly process. The work focuses on quantifying the blade assembly process by expertly defining some benchmarks and indices based on the kinematic behaviour of the assemblages. The benchmarks can also be used for documenting, evaluating, and comparing the blade assembly designs in various assemblages of torque converters to improve and transfer the experiences of the designers embedded in the model, for the torque converter industry. The model developed in this work has been tested and verified to be effective with a real torque converter model built at a local company. The results of the experiments are discussed. ID="A1"Correspondance and offprint requests to: Dr Y.-J. Lin, Department of Mechanical Engineering, The University of Akron, Akron, OH 44325–3903, USA. E-mail: yl@uakron.edu     

Microstructural and Tribological Properties of A356 Al–Si Alloy Reinforced with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Particles

In the present study, the effect of the Al₂O₃ particles (average size of 12 μm, 3 and 10 wt.%) reinforcement on the microstructure and tribological properties of Al–Si alloy (A356) was investigated. Composites were produced by applying compocasting process. Tribological properties of unreinforced alloy and composites were studied, using pin-on-disc tribometer, under dry sliding conditions at different specific loads and sliding speed of 1 m/s. Microhardness measurements, optical microscope and scanning electron microscope were used for microstructural characterization and investigation of worn surfaces and wear debris. During compocasting of A356 alloy, a transformation from a typical dendritic primary α phase to a non-dendritic rosette-like structure occurred. Composites exhibited better wear resistance compared with unreinforced alloy. Presence of 3 wt.% Al₂O₃ particles in the composite material affected the wear resistance only at specific loads up to 1 MPa. The wear rate of composite with 10 wt.% Al₂O₃ particles was nearly two order of the magnitude lower than the wear rate of the matrix alloy. Dominant wear mechanism for all materials was adhesion, with others mechanisms: oxidation, abrasion and delamination as minor ones.     

Formation of silicon nanocrystals in Si—SiO<Subscript>2</Subscript>—<Emphasis Type="Italic">α</Emphasis>-Si—SiO<Subscript>2</Subscript> heterostructures during high-temperature annealing: Experiment and simulation

Experiments and simulations are performed to study the formation of silicon nanocrystals (Si-NCs) in multilayer structures with alternating ultrathin layers of SiO₂ and amorphous hydrogenized silicon (α-Si:H) during high-temperature annealing. The effect of annealing on the transformation of the structure of the α-Si:H layers is studied by methods of high-resolution transmission electron microscopy, Raman spectroscopy, and photoluminescence spectroscopy. The conditions and kinetics of Si-NC formation are analyzed by the Monte Carlo technique. The type of the resultant crystalline silicon clusters is found to depend on the thickness and porosity of the original amorphous silicon layer located between SiO₂ layers. It is shown that an increase in the thickness of the α-Si layer in the case of low porosity leads to the formation of a percolation silicon cluster instead of individual Si nanocrystals.     

The skipping strategy to reduce the effect of the autocorrelation on the <Emphasis Type="Italic">T</Emphasis><Superscript>2</Superscript> chart’s performance

In this article, we consider the T ² control chart for bivariate samples of size n with observations that are not only cross-correlated but also autocorrelated. The cross-covariance matrix of the sample mean vectors were derived with the assumption that the observations are described by a first-order vector autoregressive model—VAR (1). To counteract the undesired effect of autocorrelation, we build up the samples taking one item from the production line and skipping one, two, or more before selecting the next one. The skipping strategy always improves the chart’s performance, except when only one variable is affected by the assignable cause, and the observations of this variable are not autocorrelated. If only one item is skipped, the average run length (ARL) reduces in more than 30 %, on average. If two items are skipped, this number increases to 40 %.     

A small Raman laser based on a KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> : Nd<Superscript>3+</Superscript> Crystal (λ=1.538 µm) with passive resonator <Emphasis Type="Italic">Q</Emphasis> switching

Generation properties of a Raman laser based on a KGd(WO₄)₂ : Nd³⁺ crystal and operating in a mode of passive resonator Q switching by a YAG : V³⁺ crystal at a wavelength safe for human eyes is studied. A small laser with a mass of 35 g, operating over a wide temperature range at a wavelength of 1.54 µm and an output energy of >6 mJ, has been created on the basis of these studies.__________Translated from Pribory i Tekhnika Eksperimenta, No. 2, 2005, pp. 112–113.Original Russian Text Copyright © 2005 by Ustimenko, Zabotin.     

<Emphasis Type="Bold">Laser Sintering of Silica Sand – Mechanism and Application to Sand Casting Mould</Emphasis>

Silica sand is commonly used in the foundry industry. With a high melting point of 160°C, the silica sand is normally sintered in a high-temperature furnace. However, silica with contents of calcium, aluminium, magnesium, and chlorine, etc. can form low-melting point eutectics. Therefore, a relatively low-power laser can be used to sinter the silica sand directly. The investigation of the mechanism and process for direct laser sintering of the silica sand, without any binder, is presented in this paper. Combined with rapid prototyping (RP) technology, the laser sintering of the silica sand can be used to directly fabricate a sand casting mould, called a rapid sand casting mould. By avoiding the time-consuming process of fabricating a pattern, the rapid sand casting mould process has the potential of further reducing the lead time for producing a casting product. Some important issues, such as the lead time of producing a sand mould, its accuracy, and surface finish, etc., are discussed.     

Gas-discharge He–Ne laser with a wavelength of 1.52 <Emphasis Type="Italic">µ</Emphasis>m for telecommunications systems

Results of a detailed study of a gas-discharge He–Ne laser with a wavelength of 1.52 µm for telecommunications systems are reported. Some important parameters of the laser are measured, such as the laser beam divergence (M ²), the laser power as a function of temperature, laser power stability, noise characteristics of laser radiation, etc. A possibility of laser microminiaturization is mentioned, which is of interest for its application under conditions of intense electromagnetic interference.     

Experimental study of effects of water-cement ratio on the acoustic emission rate “<Emphasis Type="Italic">a</Emphasis>” values in concrete

The critical microcracks make durability of the concrete seriously weakened, and the water-cement (w/c) ratio plays a key role in the durability of concrete, acoustic emission (AE) rate “a” value is an effective parameter to evaluate the amount of critical microcracks quantitatively, so the study on the influence factors and the distribution of w/c ratio on the value “a” can provide a promising reference value for the practical engineering. A total of 90 specimens in different w/c ratio are tested under axial compression in the experiment. The whole damage evolution processes are monitored by fulldigital AE acquisition system. The differences of the amount of critical microcracks in different w/c ratio are explored based on the AE rate process theory, and the rule of the effects of w/c ratio on the rate “a” value is revealed through the analysis of fracture energy and cumulative AE energy in the failure process. The results show that a linear relationship was observed between cumulative AE energy and rate “a” value, the amount of critical microcracks and the rate “a” value increase with the increase of w/c ratio, while the cumulative AE energy and cumulative AE hits are on the contrary.