The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform

Sriram Sundararajan - One of the best experts on this subject based on the ideXlab platform.

  • correlation between evolution of surface roughness parameters and micropitting of Carburized Steel under boundary lubrication condition
    Surface & Coatings Technology, 2018
    Co-Authors: Derek White, Sriram Sundararajan
    Abstract:

    Abstract This paper investigates the evolution of amplitude and spatial roughness parameters during rolling contact fatigue experiments on Carburized samples with around 0%, 15% and 70% retained austenite (RA) under boundary lubrication condition. The 0% RA samples failed due to early crack initiation and rapid crack propagation. The 15% and 70% RA samples showed initiation and propagation of micropitting. Four amplitude surface parameters (Ra, RRMS, Rsk and Rku) and one spatial parameter (2D auto-correlation length) were analyzed for correlations between micropitting initiation and propagation during RCF cycles. It was observed that during run-in, a significant decrease in Ra and RRMS were observed, while the correlation length increased and stabilized for all samples. The evolution of the 2D autocorrelation length correlated well with the evolution of crack propagation. It was observed that, while Ra and RRMS values follow the same trend as propagation of micropitting, skewness and kurtosis can be used to better predict initiation and propagation of micropitting on the surface. Significant propagation of micropitting was accompanied by a decreasing trend of skewness and increasing trend of kurtosis. Transverse directional correlation length also showed good correlation with propagation of micropitting, with the correlation length decreasing during increase of micropitting on sample surfaces.

  • investigating the effect of retained austenite and residual stress on rolling contact fatigue of Carburized Steel with xfem and experimental approaches
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018
    Co-Authors: Sriram Sundararajan
    Abstract:

    Abstract In this study, the effects of retained austenite (RA) and residual stress on rolling contact fatigue (RCF) of Carburized AISI 8620 Steel were investigated through modeling and experiments. In modeling, a two-dimensional finite element RCF model was developed to examine the crack propagation and fatigue life of Carburized AISI 8620 Steel. An extended finite element method (XFEM) was used to initiate and propagate the cracks in the model. A Voronoi Tessellation was randomly generated to simulate the randomness of the microstructures in Steel. The cracks were initiated on the grain boundaries of a Voronoi cell prior to the simulations at different locations in the RCF model. The RCF life of the samples was determined by rolling contact fatigue tests. The results in both simulations and experiments showed that the higher level of RA and compressive residual stress achieved improved RCF life through mitigation of crack propagation. The effect of increased RA led to significant improvement on RCF life as compared to increased in compressive residual stress.

  • the evolution of hardness and tribofilm growth during running in of case Carburized Steel under boundary lubrication
    Tribology International, 2018
    Co-Authors: Alexander D Jenson, Sriram Sundararajan
    Abstract:

    Abstract Many newly manufactured components are subject to a run-in procedure. The objective of this study was to understand how the surface hardness of 16MnCr5 bearing Steel evolved during running-in and how varying contact pressure and initial composite roughness affected this evolution. The evolution of the tribofilm formed by zinc dialkyl dithiophosphate (ZDDP) and how it contributed to the measured hardness was also analyzed. The results indicated a higher initial composite roughness led to greater gains in hardness as compared to higher contact pressure during the running-in process. Tribofilm growth appeared to have little to no significant effect on the measured surface hardness increase during running-in and the primary contributor to the observed hardness increase was work hardening.

  • the effect of contact pressure and surface texture on running in behavior of case Carburized Steel under boundary lubrication
    Wear, 2017
    Co-Authors: Jeremy J Wagner, Alexander D Jenson, Sriram Sundararajan
    Abstract:

    Abstract Many engineering tests start with a run-in procedure, as it is commonly accepted that running-in at some fraction of the target load is beneficial due to a reduction in surface roughness. However, the choice of load and duration is often based on historical context or the experience and philosophies of the testing personnel. The objectives of this study were to (1) evaluate the effects of contact pressure and initial composite roughness on the surface evolution during the initial stage of testing, and (2) use this information to determine if there is an optimal load and time for the run-in portion of a test. These tests were conducted with a disc-type machine using Carburized Steel specimens with a circumferential lay direction and oil with anti-wear additives under specific conditions of slide-to-roll ratio, entraining velocity, oil spin-off temperature, and oil/additive package. The specimen surface was inspected using non-contact profilometery every minute for the first 10 minutes of testing, with a subsequently increasing inspection interval for a total of 150 minutes. The data demonstrate that the surface roughness reduces within the first few minutes of testing and remains stable for a period of time, which is dependent on the pressure and initial composite roughness. Additionally, hardness measurements indicate that hardness gains are occurring during the test, but over a longer timeframe.

Ulrich Prahl - One of the best experts on this subject based on the ideXlab platform.

  • core microstructure dependent bending fatigue behavior and crack growth of a case hardened Steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2019
    Co-Authors: H Farivar, D Novokshanov, Silvia Richter, D Lenz, Wolfgang Bleck, Ulrich Prahl
    Abstract:

    Abstract Carburizing is a thermo-chemical surface treatment through which a very hard martensitic layer develops in the external surface (case) of Steel components resulting in substantial improvement in the fatigue life. Nevertheless, the overall fatigue properties of Carburized Steel components are yet severely dependent on the microstructure which develops in the interior region (core). This paper deals with the effects of core microstructure on bending fatigue behavior and fatigue crack growth of Carburized Steel parts. V-notched Steel specimens were fabricated and subjected to two case hardening cycles where, respectively, bainitic-martensitic and ferritic-bainitic-martensitic microstructures developed in the core regions supported by similar fully martensitic microstructures in the case. 4-point plane bending fatigue tests were conducted to study the fatigue behavior of the heat-treated specimens. Furthermore, the effects of the core microstructures on fatigue crack growth resistance were also investigated. Hardness measurements revealed that both batches of specimens have similar hardness properties on the exterior surfaces, in the case-hardened layers and also in the cores. Moreover, the results showed that the specimens with the bainitic-martensitic core microstructure provide a marginally better fatigue performance in the finite life regime as compared to the ferrite-containing counterparts. More noticeable difference was, however, observed in the corresponding endurance limits where the former demonstrated a higher magnitude than the latter. Besides, the bainitic-martensitic core microstructure resisted the fatigue crack propagation more effectively than the ferrite-containing specimens.

  • microstructural adjustment of Carburized Steel components towards reducing the quenching induced distortion
    Journal of Materials Processing Technology, 2019
    Co-Authors: H Farivar, Ulrich Prahl, Marcus Hans, Wolfgang Bleck
    Abstract:

    Abstract It is crucial to control and minimize the geometrical distortions resulted from the application of carburizing and quenching processes. This is particularly of the utmost importance for high quality Steel products such as power transmission components which require high performance and dimensional precision in the range of micrometers. Carburized Steel components are quenched from hardening temperature to room temperature to acquire a very hard martensitic layer (case). During the quenching process, due to the phase transformation-induced volumetric expansion in case and the interior region (core), unwanted dimensional changes may occur. In the present work, the effects of a modified hardening temperature and different soaking times on the core microstructure, the final dimensional stability and the mechanical properties are systematically investigated. Navy C-ring specimens are employed to quantify and correlate the effect of the developed microstructural constituents, magnitude of distortion, distribution of residual stresses and hardness values (macro, micro and nanohardness). Mini-tensile specimens are additionally fabricated out of the Navy C-rings’ core to evaluate the overall tensile behavior of the developed microstructures. The results show that by application of the modified hardening temperature the quenching-induced distortion can be reduced up to 27% while retaining the hardness properties of the case and core similar to that in the reference specimens which are quenched from a typical hardening temperature. The overall tensile properties of the core microstructures developed by the reference and modified heat treatments also show a nearly similar behavior.

  • icme based process and alloy design for vacuum Carburized Steel components with high potential of reduced distortion
    4th World Congress on Integrated Computational Materials Engineering, 2017
    Co-Authors: H Farivar, Ulrich Prahl, G Rothenbucher, R Bernhardt
    Abstract:

    Carburized Steel components are usually quenched from a hardening temperature, which lies in a complete austenitic phase, to room temperature. This leads to a microstructure comprised of mostly martensite plus bainite giving rise to unwanted heat-treatment-induced distortion. However, having a soft phase of ferrite dispersed throughout the microstructure can be quite effective in this regard. This is attributed to the capability of ferrite in accommodating the plasticity resulted from austenite-to-martensite transformation expansion. In the context of this work, it is demonstrated that how a proper selection of chemical compositions and a hardening temperature can greatly suppress the associated distortion. Hence, in order to systematically design a new Steel alloy which fits to the above mentioned conditions, an ICME-based methodology has been employed. Thus, a series of calculations have been carried out by means of the well-known thermodynamic-based software Thermo-Calc® and the scripting language of Python. The austenite to ferrite phase transformation kinetics is also captured by the software DICTRA® generating a virtual TTT (Time-Temperature-Transformation) diagram which is subsequently utilized for further finite element simulations in the software Simufact.forming®. The carburizing process, the following phase transformations and the effect of the developed microstructure on the final distortion are simulated in macro-scale through Simufact.forming. The finite-element-based results of the Simufact.forming have in turn been enhanced by the results of the above-mentioned thermodynamic-based computational tools. At a later stage the simulation outcomes are experimentally validated by employing Navy C-Ring specimens.

Toshifumi Mawatari - One of the best experts on this subject based on the ideXlab platform.

  • Effects of Substrate Surface Treatment on Durability of Thermally Sprayed WC Cermet Coating in Rolling/Sliding Contact
    The Proceedings of the Machine Design and Tribology Division meeting in JSME, 2002
    Co-Authors: Akira Nakajima, Toshifumi Mawatari
    Abstract:

    Using a two-roller testing machine, the authors have examined the surface durability of thermally sprayed WC-Cr-Ni cermet coating in lubricated rolling or rolling with sliding contact conditions. In the present investigation, the coating of 20 to 200μm in thickness was formed onto the blasted or ground roller specimens made of a thermally refined carbon Steel, an induction hardened carbon Steel and a Carburized alloy Steel by means of the high energy type flame spraying (Hi-HVOF) as well as the conventional high velocity oxygen-fuel flame spraying (HVOF). The WC cermet coated roller finished to a mirror-like condition was mated with the Carburized Steel roller without coating and a maximum Hertzian stress of PH=1.2 or 1.4GPa was applied in line contact. As a result, it was found that the coating on the blasted substrate roller generally shows a higher durability compared with that on the ground substrate roller and this difference appears more distinctly as the coating thickness decreases. In addition, it was also confirmed that the life to flaking of coated roller is prolonged as the hardness of substrate is raised and the coating thickness increases.

  • effects of substrate surface treatment on durability of thermally sprayed wc cermet coating in rolling sliding contact
    The Proceedings of the Machine Design and Tribology Division meeting in JSME, 2002
    Co-Authors: Akira Nakajima, Toshifumi Mawatari
    Abstract:

    Using a two-roller testing machine, the authors have examined the surface durability of thermally sprayed WC-Cr-Ni cermet coating in lubricated rolling or rolling with sliding contact conditions. In the present investigation, the coating of 20 to 200μm in thickness was formed onto the blasted or ground roller specimens made of a thermally refined carbon Steel, an induction hardened carbon Steel and a Carburized alloy Steel by means of the high energy type flame spraying (Hi-HVOF) as well as the conventional high velocity oxygen-fuel flame spraying (HVOF). The WC cermet coated roller finished to a mirror-like condition was mated with the Carburized Steel roller without coating and a maximum Hertzian stress of PH=1.2 or 1.4GPa was applied in line contact. As a result, it was found that the coating on the blasted substrate roller generally shows a higher durability compared with that on the ground substrate roller and this difference appears more distinctly as the coating thickness decreases. In addition, it was also confirmed that the life to flaking of coated roller is prolonged as the hardness of substrate is raised and the coating thickness increases.

Karsten Stahl - One of the best experts on this subject based on the ideXlab platform.

  • A study on highly-loaded contacts under dry lubrication for gear applications
    Tribology International, 2018
    Co-Authors: M Yilmaz, D. Kratzer, Thomas Lohner, Klaus Michaelis, Karsten Stahl
    Abstract:

    Highly-loaded contacts in gearboxes are usually lubricated by oil or grease in order to reduce friction and wear and to dissipate heat. Eliminating the fluid lubricant would reduce the no-load losses of gearboxes significantly and omit the use of expensive seals. Surface coatings have strong potential to improve the wear resistance in tribological contacts under dry lubrication, combined with low friction properties. The aim of this study is to investigate highly-loaded uncoated and coated contacts under dry lubrication for gear applications. Case-Carburized Steel 16MnCr5 was considered as substrate material. Uncoated, tetrahedral amorphous carbon (ta-C) coated and molybdenum disulphide (MoS2) coated surfaces were investigated experimentally at a twin-disk test rig and theoretically by means of tribosimulations. All experimental investigations were accompanied by friction and temperature measurements as well as by surface photos and roughness measurements. The experimental results show that under dry lubrication coated contacts can have significant improved tribological performance compared to uncoated contacts. However, the tribological performance is not comparable with highly-loaded lubricated contacts. The theoretical results based on a parametric study show that the thermal conductivity and the modulus of elasticity of the coating have the strongest effect on the contact temperature and the von Mises stress distribution, respectively.

Zhengle Wang - One of the best experts on this subject based on the ideXlab platform.

  • the effect of shot peening on rolling contact fatigue behaviour and its crack initiation and propagation in Carburized Steel
    Wear, 1991
    Co-Authors: Hongbin Xiao, Eryu Shao, Qing Chen, Dengzhen Wu, Zhaohong Chen, Zhengle Wang
    Abstract:

    Abstract A series of rolling contact fatigue tests has been done using a Carburized Steel with and without shot peening. Continuous observations were carried out on the initiation and propagation of cracks. The distribution of and change in residual stress in the course of rolling were measured. Changes in microstructure were observed by transmission electron microscopy. Distributions of retained austenite before and after shot peening were determined by X-ray diffraction. The contact fatigue lifetime is lengthened and the crack propagation rate decreased by shot peening. In the course of rolling, the high residual stress induced by shot peening was not relaxed after repeated rolling contact. On the basis of the experimental results, the effect of shot peening on rolling contact fatigue behaviour in Carburized Steel has been analysed, which will be valuable in practice.