Depth selective conversion electron mössbauer spectroscopy: comparison of experiment with Monte Carlo simulation of electron scattering

Recently reported experimental results in depth selective conversion electron Mössbauer spectroscopy have been compared with theory based on Monte Carlo simulation of the electron scattering in the absorber. Good agreement is found. The Monte Carlo simulation demonstrates clearly the importance of the angular interval selected by the electron spectrometer entrance aperture.     

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.     

A multichannel pulse integrator for a Mössbauer spectrometer

The multichannel pulse integrator has a 1024-channel memory with 20 bits per channel. The storage device is based on KP537PY 13A static random-access memory integrated circuits. The pulse integrator operates in Mössbauer measurement and amplitude analysis modes, in modes of data output to a computer and display on an oscilloscope screen. It is reliable and efficient, and its design is simple.     

Analysis of surface layers and wear products by Mössbauer spectral analysis

The article presents results of Mössbauer analysis conducted in order to identify structural factors which help to increase wear resistance of steel friction pairs. Wear resistance was tested in the regime of dry friction and oxidative wear using an original tribological tester. The device measured wear in conditions of a created and regulated isothermal boundary at a precisely defined distance from contact of rubbing bodies by receiving heat generated by friction. Cleaning elements were also employed to stabilise frictional resistances.Enhanced wear resistance was observed to obtain where temperature of the friction area becomes equal to the specific temperature of a given system.Mössbauer analysis was applied to surfaces of specimens made of C45, 145Cr6 counter specimens, and wear products. Application of Mössbauer analysis helped to identify composition and structures of ferrous compounds generated by friction, including oxidative secondary structures.Factors improving wear resistance in the testing included: presence of greater quantities of FeO and Fe₃O₄ combined with absence of Fe₂O₃ in the friction area of ferrous oxides, transfer of wear particles arising from ferrite, martensite and oxides between co-acting surfaces, enrichment of the specimen surface with martensite from the hard counter specimen and martensite generated in effect of diffusion impacts.     

Development of a combined tension–torsion experiment for calibration of ductile fracture models under conditions of low triaxiality

Developments in computational mechanics have given engineers tools to predict the evolution of damage in complex structures. Damage models have been developed that relate failure strain to stress triaxiality and Lode angle. Calibration of these models has traditionally relied on specimens that exhibit high triaxiality and limited Lode angle. This paper presents a specimen that can be tested in combined tension and torsion to achieve low triaxiality over a range of Lode angle. Numerical analysis of the specimen shows that it exhibits uniformity of stress–strain and stable values of triaxiality and Lode angle as plastic strain develops, both of which are desirable characteristics for calibration of ductile failure models. The design of a new displacement and rotation gage is presented that allows non-contact measurement at the gage section. Experimental results are used to develop the failure surface for 5083 aluminum.     

High resolution, low hν photoelectron spectroscopy with the use of a microwave excited rare gas lamp and ionic crystal filters

The need for not only bulk sensitive but also extremely high resolution photoelectron spectroscopy for studying detailed electronic structures of strongly correlated electron systems is growing rapidly. Moreover, easy access to such a capability in one's own laboratory is desirable. Demonstrated here is the performance of a microwave excited rare gas (Xe, Kr, and Ar) lamp combined with ionic crystal filters (sapphire, CaF(2), and LiF), which can supply three strong lines near the photon energy of hnyu hν=8.4, 10.0, and 11.6 eV, with the hν resolution of better than 600?μeV for photoelectron spectroscopy. Its performance is demonstrated on some materials by means of both angle-integrated and angle-resolved measurements.     

Development of a Methodology to Predict Cylinder Liner Scuffing in the 6V92TA Engine Lubricant Test©

The requirements placed on lubricating oils at the top ring reversal point are becoming increasingly severe due to recent changes in engine technology, most of which are driven by emissions regulations. As a result, revised engine tests to evaluate cylinder liner scuffing are being introduced to engine oil specifications. Despite the high cost and generally poor repeatability of full-scale engine data, no laboratory screener test is commercially available. In the present study, various lubricant characteristics were correlated with the level of scuffing in the Detroit Diesel 6V92TA engine test. Good initial agreement was obtained with lubricant volatility measured at 525°C, which is predicted to be the approximate contact temperature under the most extreme conditions likely to exist during normal operation.

Measurement of lubricant volatility, however, yields no indication of additive response and also appears to become less accurate when applied to unconventional basestocks. As a result, a laboratory-scale wear test was developed to predict scuffing resistance under high stress conditions. The results of the wear and volatility rests are combined using a simple equation to form the Diesel Engine Oil Scuff Test (DEOST). The resulting methodology provides an R² correlation of 70 percent with scuffing measured in the 6V92TA engine and is sensitive to both basestock characteristics and antiwear additives. In addition, the DEOST results indicated that viscosity index improvers provide little benefit under high-temperature operation, an effect commonly observed by failure of petroleum-based multigrade oils in the 6V92TA engine test.     

Forming limit prediction of anisotropic material subjected to normal and through thickness shear stresses using a modified M–K model

In some recent sheet metal forming processes such as hydroforming and incremental forming processes, normal and through thickness stresses are induced over the metal sheet, and therefore, prediction of forming limits requires considering effect of these stresses. In this investigation, a modified M–K model has been utilized to consider general stress state including normal and through thickness shear stresses on anisotropic metal sheet. This is achieved by assuming additional force equilibrium and geometrical compatibility between groove and matrix, and the numerical model has been solved by Newton–Raphson method to calculate the limiting strains. Forming limit diagrams resulting from this model have been evaluated with some published experimental data, and a good accordance between the results has been observed. It has also been concluded that exertion of normal and through thickness stresses enhances forming limits significantly.