Extreme nanomechanics: vacuum nanoindentation and nanotribology to 950 °C

Elevated temperature mechanical and tribological properties can be more relevant for practical wear situations than corresponding measurements at room temperature. However, high temperature nanomechanics and nanotribology is highly challenging experimentally. To overcome these challenges the NanoTest*** has been developed with active heating of the indenter and sample with resistive heaters, horizontal loading, patented thermal control method and stage design. By separately actively heating*** and controlling the temperatures of indenter and sample their temperatures can be precisely matched so that there is no heat flow and minimal/no thermal drift during the high temperature indentation,*** and measurements can be performed as reliably as at room temperature. Above 500 °C it is beneficial to use a cubic Boron Nitride indenter with gas purging to limit oxidation of samples. To achieve higher temperatures without indenter or sample oxidation an ultra-low drift high temperature vacuum nanomechanics/tribology system capable of testing to*** much higher temperatures has been recently developed (NanoTest Xtreme). The influence of time-dependent deformation on elevated temperature nanomechanical behaviour is discussed, using published results in Argon on glass-ceramic solid oxide fuel cell seal materials and previously unpublished nanoindentation measurements on single crystal silicon and polycrystalline tungsten using the NanoTest Xtreme in vacuum at temperatures up to 950 °C. Studies of the elevated temperature nano-/micro-tribological*** behaviour of wear-resistant*** nitride-based and MAX-phase coatings are also briefly reviewed.     

Scratch properties of poly(methyl methacrylate) surfaces: The time‐temperature dependence of friction and hardness

Viscoelastic‐viscoplastic behaviour is usually not taken into account in models describing the scratch properties of polymeric surfaces. In the case of a standard indentation test with stationary tip, the elastic‐plastic boundary and the boundary of the region being subjected to hydrostatic pressure beneath the tip are understood. Such well‐known models have been used in this study to understand the geometry of the groove left on the surface of a viscoelastic‐viscoplastic body by a moving diamond tip. A new apparatus was built that can control the velocity of the tip over the range 1 μm/s to 15 mm/s, at several different temperatures from −10 to +100°C. The material used was a commercial grade of cast poly(methyl methacrylate) (PMMA). The normal and tangential loads and groove size were used to evaluate the dynamic hardness, which behaved like a stress‐ and temperature‐activated process. The values for the activation energy and volumes of the dynamic hardness and of the interfacial shear stress were in good agreement with the mechanical properties usually attributed to PMMA.     

Identification of the dynamic performance of a gas foil journal bearing operating at high temperatures

This paper presents an experimental investigation of the dynamic force performance of gas foil bearings (GFBs) at high temperatures. A dynamic performance test rig with a GFB mounted on a rotating hollow shaft, heated by a cartridge heater inside the hollow shaft, and excited by two orthogonally positioned electromagnetic shakers determines the frequency dependent stiffness and damping coefficients of the test GFB for increasing shaft temperatures. The test heater temperatures are 21°C (room temperature without heating), 100°C, 200°C, 300°C, and 400°C, and the excitation frequencies are 120 Hz, 140 Hz, 160 Hz, and 180 Hz. The test rotating speed and static load are 12 krpm and 30 N, respectively. The vibration amplitude of the test GFB is adjusted to approximately 30 μm by controlling the power amplifier connected to the electromagnetic shakers throughout the series of experiments. The test results show that both the direct stiffness and damping coefficients of the test GFB increase with increasing excitation frequencies. As the shaft temperature increases, the direct stiffness coefficients decrease by ～ 8%, and the direct damping coefficients decrease by approximately 30%. A model prediction benchmarked against the test data reveals that the cross-coupled stiffness coefficients are smaller than the direct stiffness coefficients for the test GFB.     

Dynamic In Situ Measurements of Frictional Heating on an Isolated Surface Protrusion

Problems in the subject of frictional heating have been studied extensively, yet their complexity remains a barrier to further understanding. This study simplifies the frictional heating problem by examining the temperature rise due to a heat source of prescribed geometry. A single positive feature on the sliding face of the countersurface causes a local temperature rise. The cylindrical feature has a diameter of 150 µm and aspect ratio of 0.1 and slides under the larger contact area whose contact width is ~600 to ~750 µm. An infrared camera, acquiring at 870 Hz, observed the temperature rise at the contact interface between the feature and the rubber pin. The applied force for all tests was 200 mN, and the sliding velocity was varied from 10 to 200 mm/s. Maximum temperature rises of ~1–17 °C and average temperature rises of ~1–8 °C were measured. Measured values were compared to the Jaeger’s frictional heating models for sliding contacts.     

Dynamic analysis of indentation rolling resistance of steel cord rubber conveyor belt

To study the variation trend of the indentation rolling resistance of a rubber conveyor belt under different environmental temperatures, the sinusoidal compression displacement test was first carried out on the rubber matrix at six temperatures between -20 °C and 40 °C by a high and low temperature universal testing machine. Elastic modulus E₁, E₂ and loss factor tan θ of the rubber matrix were identified using the Fourier series. Then, the dynamic contact characteristics between the idling roller and conveyor belt were analyzed by the viscoelastic mechanics theory. Hence, the calculation equation of the indentation rolling resistance in the full thickness direction of the conveyor belt was deduced. Finally, a practical calculation and experimental verification of the indentation rolling resistance of the steel cord rubber conveyor belt at different temperatures were conducted. The results showed that the drop of the indentation rolling resistance of the conveyor belt was significant when the temperature was increased in the range of -20–10 °C. In the range of 10–40 °C, the influence of the increase of the ambient temperature on the indentation rolling resistance was relatively weak. Additionally, it is found that the contact force in the vertical direction and the idling roller diameter are important factors that affect the indentation rolling resistance of the conveyor belt. The influence of belt speed on the indentation rolling resistance is weak.     

Effect of high hydrostatic pressure on the external friction coefficient

Experiments are carried out to determine the molecular and mechanical components of the specific friction force under the effect of hydrostatic pressure of up to 140 MPa. The molecular component of the friction coefficient declines by up to two times under the effect of the hydrostatic pressure in various fluids. It is found that the combined influence of the temperature and hydrostatic pressure on the mechanical properties and the contact pressure leads to considerable variations in the deformation component of the static friction coefficient in plastic contact at temperatures of up to 200°C and under pressures of up to 140 MPa. The dependence of the hardness of structural materials on the hydrostatic pressure is analyzed to predict the effect of the latter on the deformation component of friction. It is shown that with increasing pressure within the above range the hardness grows in proportion to the square of the pressure and is inversely proportional to the initial hardness. The formula for calculating the dependence of the indentation depth of a spherical indenter in elastic contact on the hydrostatic pressure is derived.     

Experimental approach on stress–strain analysis of weldment in Ti-TWBs at elevated temperatures

This paper aims at presenting an experimental investigation of the mechanical properties of the weldment in titanium tailor-welded blanks (Ti-TWBs) at different elevated temperatures. High-contrast image patterns were laser-marked on the surface of Ti-TWB weldment. During the transverse tensile test of Ti-TWB, the images of weldment deformations and their corresponding applied loads were captured simultaneously by a dual-image vision system. After the image processing, the true stress–strain data of the weldment were evaluated successfully. Also, the stress–strain behaviors of the weldment for Ti-TWBs at different elevated temperatures were measured by heating up the specimens to specified temperatures (300°C, 500°C, and 600°C) using an induction coil specially connected to the induction furnace. Finally, the results show that, similar to the "as received" titanium sheets, increase in temperature enhances the ductility of the weldment favorably, thus reducing the required load for the related metal working.     

Effect of different temperatures on the metallographic structure and tensile property of 2024‐T4 alloy in integral heating single point incremental forming

To study the tensile property and metallographic structure evolution of 2024‐T4 high‐strength aluminum alloy in integral heating single point incremental forming (IHSPIF), the warm tensile tests were carried out at 120–240°C with the strain rates of 0.1–0.001 s^?1. Its results could provide a certain theoretical reference to the IHSPIF. The integral heating was different from the local heating, which was to heat the overall sheet to be deformed. It was found in the tensile tests that at the strain rate of 0.01 s^?1, the optimum forming temperature was determined to be 210°C at which the ductility was the best. The material dynamically recovered at 240°C. The following IHSPIF tests were conducted at different temperatures. By observing the organization of the sidewall of the square tapered parts, the alloy dynamically recovered appeared at 210°C and its grains coarsened at 240°C. Considering the temperature interval of 30 and below the recrystallizing temperature of aluminum alloy, it was concluded that the optimal temperature for the integral heating IHSPIF was about 150°C.     

The use of post‐mortem Raman spectroscopy in explaining friction and wear behaviour of sintered polyimide at high temperature

Due to their thermal stability and high strength, polyimides are an aromatic type of polymer that is used in sliding equipment functioning under high loads and elevated temperature. However, its tribological behaviour under high temperature and atmospheric conditions is not fully understood. It has been reported that a transition from high towards lower friction occurs ‘somewhere’ in the temperature region between 100°C and 200°C; however, a correlation with changes in the polyimide molecular structure remains difficult to illustrate and it is not certain whether or not this transition is correlated to lower wear. In the present work sliding experiments under controlled bulk temperatures between 100°C and 260°C are performed. A transition is observed in both friction and wear at 180°C which is further explained by microscopic analysis of the transfer film on the steel counterface and Raman spectroscopy of the worn polymer surfaces. A close examination of the spectra reveals transitions in relative intensity of certain absorption bands, pointing to different orientation effects of the molecular conformation at the polymer sliding surface at 180°C. Copyright © 2006 John Wiley & Sons, Ltd.     

Evaluation of a hot oil immersion drying method for the upgrading of crushed low-rank coal

Coal is the most abundant fuel on earth, and low-rank coal (LRC) such as sub-bituminous coal and lignite makes up about half of all coal deposits. LRC is inconvenient to use due to its low caloric value and high content of moisture together with the strong tendency of spontaneous combustion due to these oxygen rich coals, etc. Solving these problems would substantially improve the efficiency of LRC usage. In this study, we describe a drying technique utilizing hot oil immersion. This upgrading process may be executed easily under relatively low temperature condition due to the difference of heat capacity and thereby pressure gradient between coal and heating oil. This results in greatly reducing its energy cost. Drying tests of Indonesian lignite were performed with refined waste oil and B-C heavy oil, which were heated to 120°C, 130°C or 140°C. Following 10 min of treatment, the moisture content of the upgraded coal was improved from 32% to 2.0–3.2%, and its high heating value from 3,000 kcal/kg to 6,000 kcal/kg.     

Design and Implementation of a Three-Dimensional Temperature Measurement System for Indoor Object Monitoring

Abstract

In this paper, we report the design of a system equipped with a multielement thermopile for monitoring the temperature of indoor objects. We evaluate the performance of our measurement system, which comprises two microcontrollers, an analog-to-digital converter, two stepping motors, and four microswitches. We use an RS-232 or a wireless RS-232 interface that transmits temperature values and uses colors to indicate the temperature range on a PC screen. The system is inexpensive and can be used for three-dimensional temperature measurements. The effective detection range of this system is from ?20°C to 120°C or 180°C; the measurement error is within ±1°C. Experimental results demonstrate the effectiveness of the system for monitoring temperatures of remote indoor objects. Hence, it is possible to identify a hot spot in electrical heating equipment, a smoldering source hidden in upholstery, or the activities of a person in a room.     

Tribological Evaluation of an Al2O3-SiO2 Ceramic Fiber Candidate for High Temperature Sliding Seals

A test program to determine the relative slitting durability of an alumina-silica candidate ceramic fiber for high temperature sliding seal applications is described. Pin-on-disk tests were used to evaluate the potential seal material by sliding a tow or bundle of the candidate ceramic fiber against a superalloy test disk. Friction was measured during the tests and fiber wear, indicated h the extent of fibers broken in the tow or bundle, was measured at the end of each test. Test variables studied included ambient temperature from 25° to 900°C, loads from 1.3 to 21.2 N, and sliding velocities from 0.025 to 0.25 m/sec. In addition, the effects of fiber diameter and elastic modulus on friction and wear were measured. Thin gold films deposited on the superalloy disk surface were evaluated in an effort to reduce friction and wear of the fibers.

In most cases, wear increased with test temperature. Friction ranged from 0.36 at 500°C and low velocity (0.025 miser) to over 1.1 at 900°C and high velocity (0.25 m/sec). The gold films resulted in satisfactory lubrication of the fibers at 25°C. At elevated temperatures diffusion of substrate elements degraded the films. These results indicate that the alumina-silica (Al₂O₃SiO₂) fiber is a good candidate material system for high temperature sliding seal applications. More work is needed to reduce friction.     

Surface chemistry of fluorine containing ionic liquids on steel substrates at elevated temperature using Mössbauer spectroscopy

Ionic liquids have properties that make them attractive as solvents for many chemical synthesis and catalysis reactions. Consequently, research has focused on their application as advanced solvents. Recently, ionic liquids were shown to have promise as a lubricant due to many of the same properties that make them useful as solvents. The focus of this paper is to study the surface chemistry of ionic liquid lubricated steel in sliding contact to temperatures from room to 300 °C. Tribological properties were evaluated using a pin on disk tribometer with high temperature capability (up to 800 °C). Chemistry was studied using Mössbauer spectroscopy and X-ray photoelectron spectroscopy. Samples used for tribological evaluation were 1 inch diameter polished M50 disks. Samples used for studying the surface chemistry were enriched ⁵⁷Fe grown via thermal evaporation. Some ⁵⁷Fe samples were oxidized to Fe₂O₃ and Fe₃O₄ prior to treatment with ionic liquids. The metallic and oxidized ⁵⁷Fe samples were then reacted with ionic liquids at elevated temperatures. Three ionic liquids were used in this study; 1-n-ethyl-3-methylimidazolium tetrafluoroborate (BF₄), 1,2-di-methyl-3-butylimidazolium bis(trifluoromethylsulfonyl)imide (TFMS), and 1,2-di-methyl-3-butylimidazolium hexafluorophosphate (PF₆). This study was focused on understanding the high temperature stability of the liquids in contact with metal and under tribological stress. Therefore, the friction data was collected in the boundary (or mixed boundary/EHL) lubrication region to enhance surface contact. BF₄ provided a friction coefficient of 0.04 for both the room and 100 °C tests and varied between 0.07 and 0.2 for the 300 °C test. The results from TFMS lubrication showed a friction coefficient of 0.025 at room temperature and 0.1 at 100 °C. The 300 °C test friction coefficient ranged between 0.1 and 0.3. Chemical analysis of the surface revealed corrosion of the surface due to reaction between the ionic liquids and steel/iron substrates.     

Effect of Operating Temperature on Tribological Behavior of As-Plated Ni-B Coating Deposited by Electroless Method

The present work investigates the tribological behavior of electroless Ni-B coating in its as-plated condition at elevated operating temperatures. Ni-B coating is deposited using an electroless method on AISI 1040 steel specimens. Coating characterization is done using scanning electron microscopy, energy-dispersive X-ray analysis, and X-ray diffraction techniques. Vicker's microhardness and surface roughness are measured. Friction and wear tests are carried out on a pin-on-disc tribological test setup at room and elevated temperatures of 100, 300, and 500°C. The tribological behavior deteriorates at 100°C compared to room temperature. Electroless Ni-B coating shows excellent wear resistance at 300°C, which again degrades at 500°C due to severe oxidation and softening of the deposits. The worn surface of the coatings is analyzed using optical microscopy and scanning electron microscopy. Within the temperature range considered, the wear mechanism changes from adhesion to a combination of adhesion and abrasion as the temperature rises from ambient condition to 100°C, following which the wear mechanism is predominantly abrasive. The formation of a tribochemical oxide film also affects the tribological behavior of the coatings at high temperature.     

Quantification of extreme thermal gradients during in situ transmission electron microscope heating experiments

Studies on materials affected by large thermal gradients and rapid thermal cycling are an area of increasing interest, driving the need for real time observations of microstructural evoultion under transient thermal conditions. However, current in situ transmission electron microscope (TEM) heating stages introduce uniform temperature distributions across the material during heating experiments. Here, a methodology is described to generate thermal gradients across a TEM specimen by modifying a commercially available MEMS-based heating stage. It was found that a specimen placed next to the metallic heater, over a window, cut by FIB milling, does not disrupt the overall thermal stability of the device. Infrared thermal imaging (IRTI) experiments were performed on unmodified and modified heating devices, to measure thermal gradients across the device. The mean temperature measured within the central viewing area of the unmodified device was 3–5% lower than the setpoint temperature. Using IRTI data, at setpoint temperatures ranging from 900 to 1,300°C, thermal gradients at the edge of the modified window were calculated to be in the range of 0.6 × 10⁶ to 7.0 × 10⁶°C/m. Additionally, the Ag nanocube sublimation approach was used, to measure the local temperature across a FIB-cut Si lamella at high spatial resolution inside the TEM, and demonstrate “proof of concept” of the modified MEMS device. The thermal gradient across the Si lamella, measured using the latter approach was found to be 6.3 × 10⁶°C/m, at a setpoint temperature of 1,000°C. Finally, the applicability of this approach and choice of experimental parameters are critically discussed.     

Tribological and electrical properties of nanocrystalline Cu films deposited by DC magnetron sputtering with varying temperature

Cu films were deposited on Si substrates by direct current (DC) magnetron sputtering at three different substrate temperatures such as room temperature (RT), 100 °C and 200 °C. Possible mechanisms for substrate temperature dependent microstructure evolution in Cu films are discussed in this paper. Enhanced mechanical properties such as high hardness, high elastic modulus, low friction coefficient and high wear resistance of the films were obtained at deposition temperature of 100 °C. However, high friction coefficient as well as high wear rate was measured in films deposited at room temperature and 200 °C.     

EBSD coupled to SEM in situ annealing for assessing recrystallization and grain growth mechanisms in pure tantalum

An in situ annealing stage has been developed in‐house and integrated in the chamber of a Scanning Electron Microscope equipped with an Electron BackScattered Diffraction system. Based on the Joule effect, this device can reach the temperature of 1200°C at heating rates up to 100°C/s, avoiding microstructural evolutions during heating. A high‐purity tantalum deformed sample has been annealed at variable temperature in the range 750°C–1030°C, and classical mechanisms of microstructural evolutions such as recrystallization and grain coarsening phenomena have been observed. Quantitative measurements of grain growth rates provide an estimate of the mean grain boundary mobility, which is consistent with the value estimated from physical parameters reported for that material. In situ annealing therefore appears to be suited for complementing bulk measurements at relatively high temperatures, in the context of recrystallization and grain growth in such a single‐phase material.     

Tribological behavior of NiAl matrix composites with addition of oxides at high temperatures

NiAl, NiAl–Cr–Mo alloy and NiAl matrix composites with addition of oxides (ZnO/CuO) were fabricated by powder metallurgy route. It was found that some new phases (such as NiZn₃, Cu_0.81Ni_0.19 and Al₂O₃) are formed during the fabrication process due to a high-temperature solid state reaction. Tribological behavior was studied from room temperature to 1000 °C on an HT-1000 ball-on-disk high temperature tribometer. The results indicated that NiAl had high friction coefficient and wear rate at elevated temperatures, while incorporation of Cr(Mo) not only enhanced mechanical properties evidently but also improved high temperature tribological properties. Among the sintered materials, NiAl matrix composite with addition of ZnO showed the lowest wear rate at 1000 °C, while CuO addition into NiAl matrix composite exhibited the self-lubricating performance and the best tribological properties at 800 °C.     

In situ thermal measurements of sliding contacts

This study examines frictional heating and the associated temperature rise for a sliding circular contact using an in situ thermal micro-tribometer. Observation of the contact temperature used a radiometric approach to measure local temperature at the sliding interface with an emphasis on full field imaging and thermal accuracy. Filled natural rubber samples were slid against optically smooth CaF₂ counter-samples. Temperature rise was measured for externally applied normal forces ranging from∼100 to 1000 mN and sliding velocities ranging from∼250 to 1000 mm/s, producing temperature rises between ∼3 and 26 °C. Measured temperature rise was compared to the analytical models of Jaeger, Archard, and Tian and Kennedy for the average temperature rise in sliding contacts.     

Effect of platinum on sintering morphology of porous YSZ ceramics

Platinum/yttria‐stabilized zirconia (Pt/YSZ) porous ceramics were prepared by sintering of the Pt/PMMA/YSZ stripe‐like membrane with a porogen of spherical polymethyl methacrylate (PMMA) and a precursor of platinum (Pt) of chloroplatinic acid. The microstructure of raw and processed material and Pt/ZrO₂ calcination process at different sintering temperatures were investigated. The results showed that the spherically porous structure of Pt/YSZ was observed at a sintering temperature below 400 °C due to the thermal decomposition of PMMA. However, the pores were shrunk about 35% in diameter when YSZ compacts were sintered at the temperature of 1,450 °C. In addition, the spherical pores can be retained in the compacts when the content of Pt <5% and then gradually merged into changing when the content of Pt increased to 50%. The relative density was increased from 42% to 90% and the open porosity was decreased from 60% to 10% when Pt was added with content from 5% to 80%. The change of microstructure for Pt/YSZ is due to the migration of Pt and YSZ in the composites. The preferential migration and coalescence proceeded for Pt in Pt/YSZ is about 500 °C and YSZ clusters can keep stable until up to 900 °C. However, the growth of YSZ particle in the sintering process was hindered by the scattering of Pt phase.