Effect of temperature on tribological performance of a silicon nitride ball material with a linear perfluoropolyalkylether

The effect of temperature in rolling contact performance of a hot isostatically pressed (HIP) silicon nitride ball material with a linear perfluoropolyalkylether (PFPAE) was studied using a ball-on-rod type rolling contact fatigue tester. The test temperature ranged from ambient to 343°C for a period of 24 h at a stress of 5.5 GPa using thin dense chrome (TDC)-coated T-15 bearing races. The lubricant and its decomposition products, specifically acid fluoride and acids, attacked Si₃N₄ balls at all test temperatures resulting in corrosion pitting. The presence of metal fluoride on all the Si₃N₄, transferred from the races, was detected by X-ray photon spectroscopy (XPS). The thickness of the oxide layer formed on the balls, as determined by Auger electron spectroscopy (AES) increased with temperature. The changes in physical properties of post-test lubricant showed that the lubricant was stable at temperatures up to 288°C. The change in viscosity was constant up to 288°C and with a significant change above 288°C. The FTIR analysis of 316 and 343°C post-test lubricant showed the presence of carboxylic acid. The total acid number (TAN) increased linearly up to 288°C and accelerated at 316 and 343°C. The study indicates that the use of Si₃N₄ balls with a linear PFPAE results in an incompetent tribo system.     

Low-Stress Abrasive Wear Behaviour of a 0.2% C Steel: Influence of Microstructure and Test Parameters

A low (0.2%) carbon steel has been subjected to heat treatment to form varying quantities of ferrite plus martensite in its microstructure. This was achieved by holding the samples in the two-phase (ferrite plus austenite) region at three different temperatures (750, 780, and 810°C) for a specific duration followed by quenching in ice water. In another exercise, the steel was also subjected to annealing treatment by austenitizing at 890°C followed by furnace cooling for comparison purposes. The samples were subjected to low-stress (three-body) abrasion tests using an ASTM rubber wheel abrasion test apparatus at different wheel speeds (150, 273 and 400rpm corresponding to linear speeds of 1.79, 3.26 and 4.78m/s respectively) for different sliding distances at a fixed load of 49N. Crushed silica sand particles of size ranging from 212 to 300 m were used as the abrasive medium. The wear rate of samples decreased progressively with sliding distance until a (nearly) steady-state condition was attained. This was considered to be due to abrasion-induced work hardening of subsurface regions as well as the greater tendency of protrusion of the harder martensite/pearlite phase at longer sliding distances, thereby providing greater resistance to wear. Decreasing wear rate with increasing treatment temperature 750–810°C could be attributed to the greater volume fraction of the hard martensite phase in the samples containing ferrite plus martensite. The lower wear rate observed in the case of the samples containing ferrite plus martensite over the annealed ones comprising ferrite and pearlite was attributed to the higher bulk hardness of the former. Increasing linear speed from 1.79 to 3.26m/s led to an increase in wear rate. This could be attributed to greater tendency of the abrasive particles to create deeper scratches and scouping (digging). A reduction in wear rate with a further increase in the linear speed from 3.26 to 4.78m/s could be due to a change in the mechanism of wear from predominantly sliding to rolling of the abrasive particles in view of the increased plastic deformability characteristics of the specimens due to higher frictional heating. The present investigation clearly suggests that it is possible to attain a desired combination of bulk hardness and microstructure (consisting of ferrite plus martensite) leading to optimum abrasion resistance in low-carbon steels. The quantity of the two phases in turn could be varied by suitably controlling the heat-treatment temperature.     

A 14-Bit Code-to-Current Converter

A high-precision code-to-current converter ensuring a conversion error corresponding to 14 bits is described. The output current of the converter is ±250 mA, and the conversion nonlinearity is 0.015%. The converter circuit has insignificant time (0.001%/h) and temperature (0.001%/10°) drifts. The suppression of supply voltage variations is 70 dB.     

The Effect of Heat Treatment on Sliding Wear Behaviour of a Zinc-Based Alloy Containing Nickel and Silicon

This investigation deals with the observations made pertaining to the sliding wear behaviour of a zinc-based alloy containing nickel and silicon in partially lubricated condition. Wear tests were conducted over a range of applied pressures and sliding speeds. The effect of microstructural changes brought about through T6 heat treatment involving solutionizing followed by artificial ageing on wear behaviour was also investigated. The wear rate increased with pressure. The slope of the wear rate versus pressure plots was low initially up to a specific pressure. This was followed by a higher slope beyond the (specific) pressure. In some cases, the rate of change in wear rate, i.e. the slope, decreased at still higher pressures. Moreover, the (specific) pressure decreased with sliding speed in general. Increasing sliding speed caused the wear rate of the as-cast zinc-based alloy to increase up to a sliding speed of 2.68m/s. The trend reversed at a still higher speed of 4.60m/s. However, increasing wear rate with speed was noted for the heat-treated alloy over the entire speed range. Heat treatment led to reduced wear rate up to a sliding speed of 2.68m/s. An opposite trend was observed at a higher speed of 4.60m/s in this case. Specimen seizure was noted at speeds above 2.68m/s in the case of the as-cast alloy whereas seizure took place only at 4.60m/s for the heat-treated alloy samples. Frictional heating increased with pressure and speed. The specific response and changing mode of distribution of various phases were thought to be responsible for the typical wear behaviour of the alloy in specific material and test conditions. The predominance of parameters like thermal stability and cracking tendency over each other is suggested to lead to the varying wear behaviour of the alloy in different (material and sliding) conditions. The wear response of the samples has been substantiated through characteristics of their wear surfaces, subsurface regions and debris.     

Measurement of Sub-Nanometer Lubricant Films Using Ultra-Thin Film Interferometry

The ultra-thin film interferometric method of measuring the thickness of very thin films in lubricated contacts has been refined so as to be able to measure films down to 0.3nm with a standard deviation of 0.15nm. The main remaining source of measurement variation for films below 3nm thick is the surface roughness of the contacting solids. This modified technique has been applied to study the film-forming properties of three fluids, hexadecane, a dilute solution of surfactant in hexadecane, and cyclohexane. Purified hexadecane shows a very slightly enhanced oil-film thickness below 1nm. The long-chain surfactant forms a boundary film 2nm thick. Cyclohexane behaves as though it forms a surface layer about 1nm thick with viscosity three times the bulk fluid viscosity.     

An Infrared Pyrometer for Monitoring the Temperature of Materials in Vacuum Systems

A pyrometer of IR radiation for monitoring the melting and strengthening temperatures of metals in vacuum systems is described. A diaphragmed optical system is used, which ensures the required spatial resolution and protects the pyrometer from the vaporizing metal. The measured temperature range is 20–1200°C, and the measurement accuracy is 2% at a time constant of 1 s.     

A Solar Spectromagnetograph

A new solar spectromagnetograph for measuring the full magnetic-field vector and line-of-sight velocities is described. A new version of a polarization analyzer ensuring parallel measurements of six polarization components of spectral lines is considered. The spectromagnetograph allows the use of any algorithms for obtaining the magnetic fields vector, in particular, the Babcock algorithm and the Fourier transform technique. The sensitivity of the instrument for the longitudinal and transverse magnetic field is 3–5 and 20–30 G, respectively, and 10 m/s for the line-of-sight velocities.     

Multichannel Strain-Gauging System Equipped with Microprocessor for Strength Measurements of Structures

The structure of a 64-channel microprocessor strain-measuring system designed for operation with strain gauges and thermal transducers is discussed. The system measures strain and temperature during strength and thermal-strength tests of structures of machines and buildings. The computer codes have been designed in the Borland C++ Builder medium for operations with isolated transducers (1/4-bridge mode), and in the modes 1/2-bridge, bridge, and thermal transducer. The system has been certified. The paper describes examples of its practical utilization in strength tests of struts of the Tupolev-154B airliner and of the undercarriage foreleg of an aerobatic airplane.     

The FOZAN-II Fast-Response Chemiluminescent Airborne Ozone Analyzer

The design of the FOZAN-II dual-channel automatic fast-response (1 s) chemiluminescent ozone analyzer for a M55 Geophysicahigh-altitude aircraft is described. Its measured concentrations range is 10–500 g/m³; relative error, 10%; operating temperature range, –95+40°C; and its operating pressure range, 1100–30 mbar (0–22 km). The device has a built-in reference ozone generator (relative error of <6%) allowing one to autocalibrate the device in flight. Solid-state chemiluminescent sensors manufactured with the use of a coumarin 307 dye and a cellulose-acetate-based substrate have an operation lifetime exceeding 25 h, are highly sensitive, and are rugged. Results obtained during one of the flights near the South Pole in September 1999 are presented.     

The Magnetometric System of the СПРУТ-VI Instrument Package

The magnetometric system of the -VI instrument package installed on board the Mir orbital station in 1999 is described. The system was a fluxgate magnetometer that enabled high-precwasion vector measurements (with a resolution of 0.1 nT for each component) of the magnetic field over a range of ±65000 nT. The operating temperature range of the sensing device was –170 to +80°C and the temperature range of the system electronics was –55 to +60°C. The system was used for studying fluctuations of the Earth's magnetic field and characteristics of various particle formations in near-equatorial and low latitudes as well as calculating the pitch-angle distribution of fluxes of charged particles and determining the exact spatial coordinates of isolated malfunctions in microcircuits.     

Temperature Modeling in a Total Knee Joint Replacement Using Patient-Specific Kinematics

This paper reports the implementation of a computer modeling approach that uses fluoroscopically measured motions of total knee replacements as inputs and predicts patient-specific implant temperature rises using computationally efficient dynamic contact and thermal analyses. The multibody dynamic simulations of two activities (gait and stair) were generated from the fluoroscopic data to predict contact pressure and slip velocity time histories for individual elements on the tibial insert surface. These time histories were used in a computational thermal analysis to predict average steady-state temperature rise due to frictional heating on each element. For the standard condition, which assumes an ultra-high molecular weight polyethylene (UHMWPE) tibial component and cobalt-chrome femoral component, 1Hz activity frequency, friction coefficient of = 0.06, and convective heat transfer coefficient of h = 30 (W/(m²·K)), the predicted maximum temperature rise on the medial compartment was 9.1 and 14°C for continuous activities of gait and stair respectively. The sensitivity of the temperature rise to activity rate, heat partitioning to the femoral component, and convective heat transfer coefficient was explored. The model is extremely sensitive to the thermal properties of the femoral component and predicts order of magnitude changes in contact temperature with order of magnitude changes in thermal conductivity. A survey of thermal conductivity for current and proposed scratch resistant femoral component implant materials shows variations greater than an order of magnitude.     

A Wide Range Measuring System for Thin Lubricating Film: From Nano to Micro Thickness

This paper introduces a newly developed lubricating-film-thickness measuring system, which implements the multi-beam intensity-based (MBI) scheme proposed recently by the authors. Some details about the software of the testing system and instrumentation of the MBI approach are discussed. For efficient determination of the fringe order range of measured points, a simple counting strategy was suggested. It is shown that this measuring system can provide a measurement range from nano to micrometers and a high resolution on the nanometer level. Besides being able to detect ultra-thin lubricating film thickness, the system can also measure tiny local variations in film thickness on a nano-scale in the conventional EHL regime. The capability of the system is demonstrated by the determination of film thickness in the range of 1nm to 2.542m with a standard deviation of 0.89nm. In addition, some analyses are given for further understanding the optical EHL and the testing system in this paper.     

Minithermostat for Medical and Biological Studies

A desktop liquid thermostat designed for keeping unchanged the temperatures of test tubes with samples under study in the range from –20 to +70°C is described. The device consists of two units—a temperature-controlled container and heating–cooling unit connected to the container with a flexible hose in which a liquid heat carrier circulates. To maintain high temperatures (>40°C), the heat carrier is heated by an electrical heater. To cool it below room temperature, the unit uses thermoelectric converters based on the Peltier effect. The accuracy in maintaining a given temperature is up to ±0.2°C, and the time of cooling from room temperature down to –20°C does not exceed 10 min.     

Time-of-Flight Trigger Based on a Time-to-Amplitude Converter

A time-of-flight trigger based on a time-to-amplitude converter and differential discriminator is described. The trigger has a short decision time (60 ns) and high (100%) efficiency of useful event selection.     

Lubrication of Silicon Nitride and Silicon Carbide by Water: Running in,Wear and Operation of Sliding Bearings

The purpose of this work was to establish the conditions for the operation and break-in of water-lubricated ceramic bearings. The experiments consisted of sliding 1/4 silicon nitride or—carbide balls against pre-polished disks of the same material in water until tribochemical wear generates smooth conformal surfaces that allow hydrodynamic lubrication (<0.002) by very thin water films. This running in was performed at various sliding speeds (0.01-4m/s) and loads (0.5-20N). The minimum sliding speed for low friction were 0.04m/s for silicon nitride and 0.5m/s for silicon carbide, much lower than for conventional bearings. The load carrying pressures were 60-80MPa, which is higher than the usually pressures of thrust bearings. The hydrodynamic fluid film thickness was estimated with a standard integration of Reynolds' equations modified for circular geometry, it was to be 5-15nm for silicon nitride, 25nm for silicon carbide. Operation over long distances (80km) allowed us to measure the wear rate during hydrodynamic lubrication; this was found to be <2×10^–11mm³/nm, a rate acceptable for industrial application. A novel method completed during this work allows the determination of the wear rate during run-in. It varies with sliding velocity for silicon nitride, from 1 to 6×10^–5mm³/nm; it is constant at 4×10^–6mm³/nm for silicon carbide.     

On reconstruction of cracks with interacting edges

A method for the reconstruction of the configuration of cracks is suggested based on finding heat sources that model the interaction between cracks edges (such as friction and collapse) in solids exposed to external ultrasound. The input information for reconstruction is a stationary temperature field on a solid boundary. The functional of nonreciprocity was constructed; the study of this functional made it possible to convert the problem of determining a cracks parameters into a few transcendental equations; explicit formulas were obtained for small cracks. The results of computational experiments on reconstruction of the parameters of a straight crack are considered.Translated from Defektoskopiya, Vol. 40, No. 10, 2004, pp. 62–69.Original Russian Text Copyright © 2004 by Vatulyan, Solovev.     

Single-Electron Characteristics of a ФЭУ-184U Photomultiplier Tube

Single-electron and time characteristics of a -184U photomultiplier tube with a uviol window are presented. The -184U single-electron resolution can reach a value of 63–64%, and, in case of single-electron light-striking of the photocathode, the photoelectron transit time distribution (full width at half maximum) is 6 ns.     

Error Corrections in a Sampling Sliding Along a Pulse Envelope Based on Decoding Tables

Code combinations of 2 ⁿ symbols +1 and –1 suggested for identification of characteristic features leading edge, trailing edge, maximum, minimum, horizontal portion, start of leading edge, end of leading edge, start of trailing edge, and end of trailing edge in a binary-code envelope of a pulse measured by an eddy-current transducer (ECT) scanning a tested surface generate a group code. This group code ensures for four levels of noise immunity the maximal likelihood in identification of reference sequences distorted by noise. The structure of a product code, which is also generated by the reference fragments, results in a higher capability of correcting for errors in moving samplings of signal envelopes, in particular, it reduces the degree of uncertainty in identification of the most important features of ECT pulses. The paper suggests simple decoding algorithms and regular logical structures that provide a high efficiency of the procedure eliminating errors in binary sequences of coded envelopes.     

A Stable Temperature Sensor Based on GaAs Structures with Schottky Barriers

The current–voltage and temperature–voltage characteristics of a GaAs structure with a Schottky barrier were measured, and their dependence on technological factors and temperature were determined. The main technological parameters of the device (the concentration of free carriers n ₀ in the base of diodes, the area S of the contact of the barrier-forming metal, and the value of the direct current I through the structure) were optimized. As a result, an element with a highly linear temperature–voltage characteristic was obtained. For Pd–GaAs structures with S 0.32 mm² (d 640 m), I 10 A, and n ₀ = (1–3) × 10¹⁶ cm^–3, the thermal sensitivity coefficient is 2 mV/°C, and the nonlinearity coefficient is < 0.5% within a range of 100 K, which is much lower than obtained theoretically. A highly stable temperature sensor is manufactured on the sensitive element offered.     

A Two-Section Gas-Filled Ionization Chamber for Neutron Flux Measurements

A promising design of a -type two-section gas-filled ionization chamber is described for the first time. A relationship between the design parameters, gas pressure, and characteristics of the material is determined, under which full compensation of the background currents from the -radiation and the measurement of thermal neutron fluxes in a range of 400 to 7 ×10⁹cm^–2s^–1at a load characteristic with a 5% nonlinearity are provided. Test results of the chamber are presented.