The Experts below are selected from a list of 492 Experts worldwide ranked by ideXlab platform
A Ueno - One of the best experts on this subject based on the ideXlab platform.
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combined effects of Low Temperature Nitriding and cold rolling on fatigue properties of commercially pure titanium
International Journal of Fatigue, 2020Co-Authors: Shoichi Kikuchi, A Ueno, Hiroyuki AkebonoAbstract:Abstract The combined effects of Low-Temperature Nitriding (LTN) and cold rolling on the microstructure of commercially pure titanium (CP titanium) were investigated. The grain size of the LTN-treated CP titanium decreased with increasing thickness reduction due to the cold rolling pre-treatment and with decreasing the Nitriding Temperature. The fatigue limit for the nitrided CP titanium depended on the grain size beneath the nitrided layer and increased with decreasing the Nitriding Temperature because of the suppression of grain-coarsening. Furthermore, the LTN at 873 K decreased the friction coefficient and reduced the wear loss of CP titanium during the ball-on-disk dry friction tests.
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improvement of fatigue properties of ti 6al 4v alloy under four point bending by Low Temperature Nitriding
International Journal of Fatigue, 2019Co-Authors: Shoichi Kikuchi, S Yoshida, A UenoAbstract:Abstract Low Temperature Nitriding (LTN) was performed for titanium alloy (Ti-6Al-4V) to improve its fatigue properties. A nitrogen compound layer was formed on the surface nitrided at Temperatures higher than 873 K, whereas nitrogen diffusion was observed on the surface nitrided at 823 K. Fatigue tests were performed by four-point bending in air under a stress ratio of 0.1. The fatigue limit for Ti-6Al-4V tended to increase with a decrease in the Nitriding Temperature. LTN at 823 K increased the fatigue limit of Ti-6Al-4V due to the formation of the surface with no nitrogen compound layer and suppression of grain-coarsening.
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Evaluation of Very High Cycle Fatigue Properties of Low Temperature Nitrided Ti-6Al-4V Alloy Using Ultrasonic Testing Technology
Key Engineering Materials, 2015Co-Authors: Shoichi Kikuchi, Y Nakamura, Stefan Heinz, Dietmar Eifler, A UenoAbstract:Fatigue tests were carried out at the stress ratio R = -1 using a 20 kHz ultrasonic testing facility to investigate the effects of Low Temperature Nitriding on the fatigue properties of Ti-6Al-4V alloy in the very high cycle fatigue (VHCF) regime in detail. The oscillation and fatigue behavior of the nitrided Ti-alloy were characterized by measuring parameters like the ultrasonic generator power, the displacement of the specimens and dissipated energy under ultrasonic cyclic load. Moreover, the surface microstructure of the nitrided Ti-alloy was characterized using a micro-Vickers hardness tester, an optical microscope, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron backscatter diffraction technique (EBSD) to clarify the fatigue fracture mechanism. The Ti-alloy nitrided at the Temperature of 873 K showed duplex S-N properties consisting of the respective fracture modes of the surface fracture and the subsurface fracture. The Low Temperature Nitriding reduced the surface fatigue life of Ti-alloy in comparison to the un-nitrided one due to the formation of a brittle titanium nitride (Ti2N), whereas the subsurface fatigue life in the VHCF regime was increased by the Low Temperature Nitriding. In addition, the fatigue fracture mechanisms of the Low Temperature nitrided Ti-alloy were discussed from viewpoints of fractography and fracture mechanics.
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evaluation of the effects of Low Temperature Nitriding on 4 points bending fatigue properties of ti 6al 4v alloy
Recent Advances in Structural Integrity Analysis - Proceedings of the International Congress (APCF SIF-2014)#R##N#APCFS SIF 2014, 2015Co-Authors: Y Nakamura, S Yoshida, S Kolicjo, A UenoAbstract:In order to improve both of the fatigue and wear resistance of titanium alloy (Ti-6Al-4 V), a Low Temperature Nitriding process was developed. This work will evaluate the effects of Low Temperature Nitriding on the microstructure and fatigue properties of titanium alloy. Low Temperature nitrided (600 °C) specimen showed higher fatigue strength compared to the conventional nitrided (850 °C) one. This was because Low Temperature Nitriding can suppress the grain-coarsening of Ti-6Al-4 V alloy during Nitriding. Then, 4-points bending fatigue fracture mechanism of Ti-6Al-4 V was discussed based on the microstructures obtained and from viewpoints of fractography.
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development of Low Temperature Nitriding process and its effects on the 4 points bending fatigue properties of commercially pure titanium
Advanced Materials Research, 2014Co-Authors: Shoichi Kikuchi, Y Nakamura, A Ueno, Kei AmeyamaAbstract:In order to improve both of the fatigue and tribological properties of commercially pure (CP) titanium, a Low Temperature Nitriding process was developed. Cold rolling was introduced as pre-treatment of plasma Nitriding to create fine grains which could accelerate the diffusion of nitrogen into the material. Surface microstructures of the nitrided specimens pre-treated with cold rolling were characterized using a micro-Vickers hardness tester, an optical microscope, a scanning electron microscope (SEM), X-ray diffraction (XRD) and electron backscatter diffraction technique (EBSD). Titanium-nitrides (TiN and Ti2N) were formed on the surface nitrided at the Temperature greater than 600 °C. Moreover, thicker compound layer was formed in the nitrided CP titanium pre-treated with cold rolling in comparison to the only nitrided one, resulting in showing higher hardness. 4-points bending fatigue tests were performed for the specimens treated with Low Temperature Nitriding (600 °C), which could suppress the grain-coarsening, under the stress ratio R = 0.1 at room Temperature. In addition, fatigue fracture mechanism of nitrided CP titanium was discussed based on the observations of microstructure and fracture surface.
W P Tong - One of the best experts on this subject based on the ideXlab platform.
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Low Temperature Nitriding of 38crmoal steel with a nanostructured surface layer induced by surface mechanical attrition treatment
Surface & Coatings Technology, 2008Co-Authors: Jian Lu, W P Tong, Zhengsheng Han, L M Wang, K LuAbstract:A nanocrystalline surface layer was fabricated on a 38CrMoAl steel plate by means of a surface mechanical attrition treatment (SMAT). The average grain size in the top surface layer (10 pm thick) is about 10 nm, and the grain size stability can be maintained up to 450 degrees C. The effect of the surface nanocrystalline layer on the gas Nitriding process at a Lower Temperature was investigated by using structural analysis and wear property measurements. The surface nanocrystallization evidently enhances nitricling kinetics and promotes the formation of an ultrafine polycrystalline compound layer. The results of the investigation showed that this new gas Nitriding technique can effectively increase the hardness and wear resistance of the resulting surface layer in comparison with conventional Nitriding, demonstrating a significant advancement for materials processing. (c) 2008 Elsevier B.V. All rights reserved.
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Low Temperature Nitriding by means of smat
材料热处理学报, 2004Co-Authors: W P Tong, Jian Lu, H W Zhang, Z B Wang, K LuAbstract:The microstructure in the surface layer of iron and steel samples can be refined at the nanometer scale by means of a surface mechanical attrition treatment (SMAT) that generates repetitive severe plastic deformation to the surface layer.The subsequent Nitriding kinetics of the as-treated samples with the nanostructured surface layer is greatly enhanced so that the Nitriding Temperatures can be reduce to 300 ～ 400 ℃ regions. This enhanced processing method demonstrates both the technological significance of nanomaterials in advancing the traditional processing techniques, and provides a new approach for selective surface reactions in solids. This article reviews the present state of the art in this field. The microstructure and properties of SMAT samples nitrided will be summarized. Further considerations of the development and applications of this new technique will also be presented.
Peter Kogej - One of the best experts on this subject based on the ideXlab platform.
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influence of Low Temperature Nitriding on the strain induced martensite and laser quenched austenite in a magnetic encoder made from 304l stainless steel
Scientific Reports, 2016Co-Authors: Vojteh Leskovsek, Matjaž Godec, Peter KogejAbstract:We have investigated the possibility of producing a magnetic encoder by an innovative process. Instead of turning grooves in the encoder bar for precise positioning, we incorporated the information in 304L stainless steel by transforming the austenite to martensite after bar extrusion in liquid nitrogen and marking it with a laser, which caused a local transformation of martensite back into austenite. 304L has an excellent corrosion resistance, but a Low hardness and poor wear resistance, which limits its range of applications. However, Nitriding is a very promising way to enhance the mechanical and magnetic properties. After Low-Temperature Nitriding at 400 °C it is clear that both e- and α′-martensite are present in the deformed microstructure, indicating the simultaneous stress-induced and strain-induced transformations of the austenite. The effects of a laser surface treatment and the consequent appearance of a non-magnetic phase due to the α′ → γ transformation were investigated. The EDS maps show a high concentration of nitrogen in the alternating hard surface layers of γN and α′N (expanded austenite and martensite), but no significantly higher concentration of chromium or iron was detected. The high surface hardness of this nitride layer will lead to steels and encoders with better wear and corrosion resistance.
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Influence of Low-Temperature Nitriding on the strain-induced martensite and laser-quenched austenite in a magnetic encoder made from 304L stainless steel
Scientific Reports, 2016Co-Authors: Vojteh Leskovsek, Matjaž Godec, Peter KogejAbstract:We have investigated the possibility of producing a magnetic encoder by an innovative process. Instead of turning grooves in the encoder bar for precise positioning, we incorporated the information in 304L stainless steel by transforming the austenite to martensite after bar extrusion in liquid nitrogen and marking it with a laser, which caused a local transformation of martensite back into austenite. 304L has an excellent corrosion resistance, but a Low hardness and poor wear resistance, which limits its range of applications. However, Nitriding is a very promising way to enhance the mechanical and magnetic properties. After Low-Temperature Nitriding at 400 °C it is clear that both ε- and α′-martensite are present in the deformed microstructure, indicating the simultaneous stress-induced and strain-induced transformations of the austenite. The effects of a laser surface treatment and the consequent appearance of a non-magnetic phase due to the α′ → γ transformation were investigated. The EDS maps show a high concentration of nitrogen in the alternating hard surface layers of γ_N and α′_N (expanded austenite and martensite), but no significantly higher concentration of chromium or iron was detected. The high surface hardness of this nitride layer will lead to steels and encoders with better wear and corrosion resistance.
Shoichi Kikuchi - One of the best experts on this subject based on the ideXlab platform.
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combined effects of Low Temperature Nitriding and cold rolling on fatigue properties of commercially pure titanium
International Journal of Fatigue, 2020Co-Authors: Shoichi Kikuchi, A Ueno, Hiroyuki AkebonoAbstract:Abstract The combined effects of Low-Temperature Nitriding (LTN) and cold rolling on the microstructure of commercially pure titanium (CP titanium) were investigated. The grain size of the LTN-treated CP titanium decreased with increasing thickness reduction due to the cold rolling pre-treatment and with decreasing the Nitriding Temperature. The fatigue limit for the nitrided CP titanium depended on the grain size beneath the nitrided layer and increased with decreasing the Nitriding Temperature because of the suppression of grain-coarsening. Furthermore, the LTN at 873 K decreased the friction coefficient and reduced the wear loss of CP titanium during the ball-on-disk dry friction tests.
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improvement of fatigue properties of ti 6al 4v alloy under four point bending by Low Temperature Nitriding
International Journal of Fatigue, 2019Co-Authors: Shoichi Kikuchi, S Yoshida, A UenoAbstract:Abstract Low Temperature Nitriding (LTN) was performed for titanium alloy (Ti-6Al-4V) to improve its fatigue properties. A nitrogen compound layer was formed on the surface nitrided at Temperatures higher than 873 K, whereas nitrogen diffusion was observed on the surface nitrided at 823 K. Fatigue tests were performed by four-point bending in air under a stress ratio of 0.1. The fatigue limit for Ti-6Al-4V tended to increase with a decrease in the Nitriding Temperature. LTN at 823 K increased the fatigue limit of Ti-6Al-4V due to the formation of the surface with no nitrogen compound layer and suppression of grain-coarsening.
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Evaluation of Very High Cycle Fatigue Properties of Low Temperature Nitrided Ti-6Al-4V Alloy Using Ultrasonic Testing Technology
Key Engineering Materials, 2015Co-Authors: Shoichi Kikuchi, Y Nakamura, Stefan Heinz, Dietmar Eifler, A UenoAbstract:Fatigue tests were carried out at the stress ratio R = -1 using a 20 kHz ultrasonic testing facility to investigate the effects of Low Temperature Nitriding on the fatigue properties of Ti-6Al-4V alloy in the very high cycle fatigue (VHCF) regime in detail. The oscillation and fatigue behavior of the nitrided Ti-alloy were characterized by measuring parameters like the ultrasonic generator power, the displacement of the specimens and dissipated energy under ultrasonic cyclic load. Moreover, the surface microstructure of the nitrided Ti-alloy was characterized using a micro-Vickers hardness tester, an optical microscope, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron backscatter diffraction technique (EBSD) to clarify the fatigue fracture mechanism. The Ti-alloy nitrided at the Temperature of 873 K showed duplex S-N properties consisting of the respective fracture modes of the surface fracture and the subsurface fracture. The Low Temperature Nitriding reduced the surface fatigue life of Ti-alloy in comparison to the un-nitrided one due to the formation of a brittle titanium nitride (Ti2N), whereas the subsurface fatigue life in the VHCF regime was increased by the Low Temperature Nitriding. In addition, the fatigue fracture mechanisms of the Low Temperature nitrided Ti-alloy were discussed from viewpoints of fractography and fracture mechanics.
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development of Low Temperature Nitriding process and its effects on the 4 points bending fatigue properties of commercially pure titanium
Advanced Materials Research, 2014Co-Authors: Shoichi Kikuchi, Y Nakamura, A Ueno, Kei AmeyamaAbstract:In order to improve both of the fatigue and tribological properties of commercially pure (CP) titanium, a Low Temperature Nitriding process was developed. Cold rolling was introduced as pre-treatment of plasma Nitriding to create fine grains which could accelerate the diffusion of nitrogen into the material. Surface microstructures of the nitrided specimens pre-treated with cold rolling were characterized using a micro-Vickers hardness tester, an optical microscope, a scanning electron microscope (SEM), X-ray diffraction (XRD) and electron backscatter diffraction technique (EBSD). Titanium-nitrides (TiN and Ti2N) were formed on the surface nitrided at the Temperature greater than 600 °C. Moreover, thicker compound layer was formed in the nitrided CP titanium pre-treated with cold rolling in comparison to the only nitrided one, resulting in showing higher hardness. 4-points bending fatigue tests were performed for the specimens treated with Low Temperature Nitriding (600 °C), which could suppress the grain-coarsening, under the stress ratio R = 0.1 at room Temperature. In addition, fatigue fracture mechanism of nitrided CP titanium was discussed based on the observations of microstructure and fracture surface.
Marcel A. J. Somers - One of the best experts on this subject based on the ideXlab platform.
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A simple model for nitrogen-induced lattice expansion of γ'N and γ N phases in Fe–Cr–Ni alloys with different chromium contents
Philosophical Magazine Letters, 2020Co-Authors: Marcel A. J. SomersAbstract:A recent publication on Low-Temperature Nitriding of Fe–Cr–Ni alloys with various combinations of Cr and Ni contents showed experimentally the co-existence of γN and γ'N phases. An important result...
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thermo chemical mechanical simulation of Low Temperature Nitriding of austenitic stainless steel inverse modelling of surface reaction rates
Surface & Coatings Technology, 2020Co-Authors: Omer C Kucukyildiz, Marcel A. J. Somers, Mads Rostgaard Sonne, Jesper Thorborg, Jesper Henri HattelAbstract:Abstract A multi-physics thermo-chemical-mechanical 1-dimensional implicit finite difference model is presented to simulate the evolution of composition and residual stress profiles over the expanded austenite case developing during Low Temperature Nitriding of austenitic stainless steels. The model combines 1-dimensional diffusion of nitrogen in the depth direction with a concentration-dependent diffusivity, elasto-plastic accommodation of the lattice expansion, stress gradient-induced diffusion of nitrogen, solid solution-strengthening by nitrogen and trapping of nitrogen by chromium atoms. The rate of the surface reaction governing the transfer of nitrogen from the gas to the solid is unknown and was evaluated by inverse modelling. The modelling was applied adopting the surface reaction rate as the only fitting parameter and taking mass-uptake curves (thermogravimetry) as the constraint, while all other data were taken from established literature values. Very good agreement is achieved between the predicted and experimental composition-depth profiles. Further, the applicability of the present model to plasma Nitriding was verified by simulating (not fitting) the evolution of composition-depth profiles obtained after plasma Nitriding of stainless steel. The good to very good agreement of the present model's predictions with experimental data for gaseous and plasma Nitriding, indicates that the essential multi-physics influences and parameters are taken into account, with a minimum of adjustable parameters.
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high Temperature solution Nitriding and Low Temperature Nitriding of aisi 316 effect on pitting potential and crevice corrosion performance
Applied Surface Science, 2018Co-Authors: Federico Bottoli, Morten Stendahl Jellesen, Thomas Lundin Christiansen, Grethe Winther, Marcel A. J. SomersAbstract:Abstract Stainless steels grade AISI 316 was subjected to high Temperature solution Nitriding and Low-Temperature Nitriding in order to dissolve various amounts of nitrogen in the bulk (up to approx. 0.45 wt%) and in a surface layer (up to approx. 13 wt%), respectively. Potentiodynamic polarization tests in a 0.1 M NaCl solution and crevice corrosion immersion tests in 3 wt% FeCl3 solution were studied before and after the bulk and surface treatments. Nitrogen addition in the bulk proved to have a beneficial effect on the pitting resistance of the alloy. The formation of a zone of expanded austenite at the material surface through Low-Temperature Nitriding resulted in a considerable improvement of the pitting potential and the crevice corrosion performance of the steels.
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Low-Temperature Nitriding of Deformed Austenitic Stainless Steels with Various Nitrogen Contents Obtained by Prior High-Temperature Solution Nitriding
Metallurgical and Materials Transactions A, 2016Co-Authors: Federico Bottoli, Grethe Winther, Thomas L. Christiansen, Kristian Vinter Dahl, Marcel A. J. SomersAbstract:In the past decades, high nitrogen steels (HNS) have been regarded as substitutes for conventional austenitic stainless steels because of their superior mechanical and corrosion properties. However, the main limitation to their wider application is their expensive production process. As an alternative, high-Temperature solution Nitriding has been applied to produce HNS from three commercially available stainless steel grades (AISI 304L, AISI 316, and EN 1.4369). The nitrogen content in each steel alloy is varied and its influence on the mechanical properties and the stability of the austenite investigated. Both hardness and yield stress increase and the alloys remain ductile. In addition, strain-induced transformation of austenite to martensite is suppressed, which is beneficial for subsequent Low-Temperature Nitriding of the surface of deformed alloys. The combination of high- and Low-Temperature Nitriding results in improved properties of both bulk and surface.
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composition dependent variation of magnetic properties and interstitial ordering in homogeneous expanded austenite
Acta Materialia, 2016Co-Authors: Bastian Brink, Kenny Stahl, Thomas Lundin Christiansen, Mikkel Fougt Hansen, Cathrine Frandsen, Marcel A. J. SomersAbstract:Abstract The crystal structure and magnetic properties of austenitic stainless steel with a colossal interstitial content, so-called expanded austenite, are currently not completely understood. In the present work, the magnetic properties of homogeneous samples of expanded austenite, as prepared by Low-Temperature Nitriding of thin foils, were investigated with magnetometry and Mossbauer spectroscopy. At room Temperature, expanded austenite is paramagnetic for relatively Low and for relatively high nitrogen contents (yN = 0.13 and 0.55, respectively, where yN is the interstitial nitrogen occupancy), while ferromagnetism is observed for intermediate nitrogen loads. Spontaneous volume magnetostriction was observed in the ferromagnetic state and the Curie Temperature was found to depend strongly on the nitrogen content. For the first time, X-ray diffraction evidence for the occurrence of long-range interstitial order of nitrogen atoms in expanded austenite was observed for high nitrogen contents.
