This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

A Benchmark Study on the Thermal Conductivity of Nanofluids

Cryogenic treatment (CT) of materials has shown significant improvement in their properties. Various advantages like increase in wear resistance, reduced residual stresses, increase in hardness, fa...

Cryogenic Treatment of Tool Materials: A Review

Influence of sub-zero treatments, namely: cold treatment, shallow cryogenic treatment and deep cryogenic treatment on fracture toughness of AISI D2 steel has been examined with reference to conventional heat treatment. Fracture toughness has been determined by three-point bend tests using miniature chevron-notched round bar specimens. Measurement of fracture toughness values has been supplemented by the examination of fracture surfaces, evaluation of hardness and characterization of microstructures. The obtained results infer that sub-zero treatments, in general, reduce fracture toughness of the selected steel as compared to the conventionally heat treated ones, however, the degree of reduction is lowest for deep cryogenically treated specimens and highest for shallow cryogenically treated ones. The mechanisms of initiation of fracture for all types of specimens have been identified as cracking of primary carbides and microvoid nucleation by decohesion of secondary carbides followed by cleavage, while growth of microvoids has been observed only for conventionally treated and deep cryogenically treated specimens. The variation of fracture toughness values has been explained by the microstructural characteristics of the differently treated specimens.

Influence of sub-zero treatments on fracture toughness of AISI D2 steel

http://lab.fs.uni-lj.si/lft/Documents/34--Improving%20tribological%20properties%20of%20tool%20steels%20through%20combination--objava-maj-2012.pdf

Improving tribological properties of tool steels through combination of deep-cryogenic treatment and plasma nitriding

Effects of the sub-zero treatment condition on microstructure, mechanical behavior and wear resistance of W9Mo3Cr4V high speed steel

Advantages of deep-cryogenic treatment over standard heat treatment of high speed steels for the purpose of obtaining better properties are quoted in an increasing number of scientific articles. This article deals with the most important improvements of high speed steel properties achieved by using deep-cryogenic treatment. The effect of deep-cryogenic treatment on impact and fracture toughness, on erosion wear resistance, and on the material microstructure has been tested on samples made of the PM S390 MC high speed steel. A set of test samples was heat treated by conventional methods (hardened and three times high temperature tempered), and the other set was deep cryogenic treated. From the results, it can be concluded that the application of deep-cryogenic treatment results in significantly higher wear resistance of high speed steels, but no significant improvements in toughness have been observed.

Effect of Deep-Cryogenic Treatment on High Speed Steel Properties

Computer simulation of induction hardening

The surface of the non-alloyed carbon steel was subjected to thermochemical modification by salt bath nitrocarburizing with or without postoxidation based on the Tenifer procedure in order to improve mechanical properties, corrosion and wear resistance. Nitrocarburized layers were characterized by testing their basic properties (compound layer thickness, nitrocarburizing depth, surface hardness) according to current standards. Detailed estimation of the quality of the modified metal surface was performed by additional testing of chemical compositions by EDX and X-ray diffraction, microstructure, surface roughness and topography, and corrosion resistance. The corrosion resistance was investigated in a water solution of 5% NaCl using electrochemical polarization methods and electrochemical impedance spectroscopy. The corrosion properties of the treated and nontreated samples are compared among themselves and with the properties of austenitic stainless steel. The surface layer obtained after nitrocarburization treatment consists mainly of e-Fe2–3N and γ′-Fe4N. The surface layer of the samples after post-oxidation consists also of e-Fe2–3N and γ′-Fe4N, but contains additionally Fe3O4. The results obtained show that nitrocarburizing and post-oxidation treatments, based on the Tenifer procedure, result in better mechanical and corrosion properties of non-alloyed carbon steel. The corrosion properties of the thermochemically modified non-alloyed carbon steel were improved and approach the corrosion properties of austenitic stainless steel, known for its very good corrosion resistance.

/pdf/modification-of-carbon-steel-surface-by-the-tenifer-process-3k04og5fmr.pdf

Modification of carbon steel surface by the Tenifer® process of nitrocarburizing and post-oxidation

The rule of Ameen whereby steel made cylinders with no phase transformations during quenching approach the spherical shape is contrary to the finding of Berger, who observes an elongation of thin and long work pieces. If the prediction of Ameen is correct, cylinders should decrease in length during heat treatment. This paper describes a first step of broader investigation of strain hardening and distotion of cylinders during gas quenching in gas nozzle field. To make more general predictions about the distortion of cylinders which show no phase transformations during heat treatment, different dimensions of cylinders where investigated by means of numerical and experimental methods. The prediction of dimension and shape changes during gas quenching of steel cylinders has been performed by numerical simulation using the commercial Finite Element Program SYSWELD. The austenitic steel SAE30300 was selected as investigated material ; it shows no phase transformations during perfomed heating and cooling. The investigations show a good agreement between the kinematic strain hardening model and the experimental data, whereas the isotropic model is not in line with the experimental data. If the ratio of length and diameter is greater then 3, the relative changes in length displayed against the Biot number give uniform curves for all investigated geometies and heat transfer coefficients.

Prediction of Distortion of Cylinders without Phase Transformations

The rule of Ameen whereby steel made cylinders with no phase transformations during quenching approach the spherical shape is contrary to the finding of Berger, who observes an elongation of thin and long work pieces. If the prediction of Ameen is correct, cylinders should decrease in length during heat treatment. 



This paper describes a first step of broader investigation of strain hardening and distortion of cylinders during gas quenching in a gas nozzle field. To make more general predictions about the distortion of cylinders which show no phase transformations during heat treatment, different dimensions of cylinders (lengths 50 mm, 100 mm and 200 mm, diameters 10 mm up to 100 mm) were investigated by means of numerical and experimental methods. 



The prediction of dimension and shape changes during gas quenching of steel cylinders has been performed by numerical simulation using the commercial Finite Element Program SYSWELD. The austenitic steel SAE30300 (German grade X8CrNiS18.9) was selected as investigated material; it shows no phase transformations during performed heating and cooling. 



The investigations show a good agreement between the kinematic strain hardening model and the experimental data, whereas the isotropic model is not in line with the experimental data. If the ratio of length and diameter is greater than 3, the relative changes in length displayed against the Biot number give uniform curves for all investigated geometries and heat transfer coefficients.



Mas- und Formanderungen bei Wellen ohne Phasenumwandlungen



Die Regel von Ameen besagt, dass sich Bauteile nach einer Abschreckung der Kugelform annahern, falls sie wahrend der gesamten Warmebehandlung keine Phasenumwandlung durchlaufen. Diese Regel ist nicht konsistent zu experimentellen Ergebnissen von Berger, der bei langen und dunnen Wellen Verlangerungen festgestellt hat. Wenn die Regel von Ameen korrekt ware , hatten sich die Zylinder dagegen verkurzen mussen.



In diesem Paper werden erste Ergebnisse einer breiter angelegten Untersuchung bezuglich der Verfestigung und des Verzuges von Wellen vorgestellt, die in einem Gasdusenfeld abgeschreckt wurden. Um das Verzugsverhalten von Bauteilen, die wahrend der gesamten Warmebehandlung keine Phasenumwandlungen zeigen, allgemeiner beschreiben zu konnen, sind zunachst Wellen mit unterschiedlichen Durchmessern (10 mm bis 100 mm) und Langen (50 mm, 100 mm und 200 mm) untersucht worden. In diesem Zusammenhang wurden sowohl numerische Studien als auch begleitend experimentelle Untersuchungen durchgefuhrt. Die numerischen Studien wurden mit dem kommerziellen FE-Programm SYSWELD durchgefuhrt. Als Material kam der nicht umwandelnde Stahl X8CrNiS18.9 zum Einsatz.



Die numerischen Studien zeigten eine gute Ubereinstimmung mit den experimentellen Daten, wenn mit einer kinematischen Verfestigung gerechnet wurde. Das isotrope Modell zeigte dagegen fur bestimmte Geometrien signifikante Abweichungen von den experimentellen Ergebnissen. Daruber hinaus wurde festgestellt, dass die relativen Langen- und Durchmesseranderungen mit der BIOT-Zahl beschrieben werden konnen, falls das Langen-Durchmesser-Verhaltnis groser als 3 ist.

Darko Landek

Papers

Effect of Deep-Cryogenic Treatment on High Speed Steel Properties

Computer simulation of induction hardening

Modification of carbon steel surface by the Tenifer® process of nitrocarburizing and post-oxidation

Prediction of Distortion of Cylinders without Phase Transformations

Prediction of Distortion of Cylinders without Phase Transformations