The Experts below are selected from a list of 22812 Experts worldwide ranked by ideXlab platform
Glenn Cassar - One of the best experts on this subject based on the ideXlab platform.
-
evaluating the effects of pirac Nitrogen Diffusion treatments on the mechanical performance of ti 6al 4v alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: T. Bonello, J. Housden, Elazar Y. Gutmanas, I. Gotman, J Avelarbatista C Wilson, A Matthews, A Leyland, Glenn CassarAbstract:Abstract Powder Immersion Reaction Assisted Coating (PIRAC) is a relatively simple Nitrogen Diffusion based process which has been proposed as a technique capable of considerable improvements in the tribological performance of ceramics and metals alike; however, the necessary exposure of the substrate material to high temperatures for several hours may have an adverse effect on the bulk properties of materials such as titanium alloys. The effect of PIRAC treatments on the bulk metallography and mechanical properties of Ti–6Al–4V has been studied. Following PIRAC Nitrogen-Diffusion treatment, studies using X-ray diffraction and cross-sectional microscopy have shown evidence of the formation of a thin (~1.4 µm) TiN/Ti 2 N layer, together with the presence of some Ti 3 Al intermetallic phase. Semi-logarithmic S–N plots show a deleterious effect after PIRAC treatment in terms of material cyclic fatigue strength, particularly at higher treatment temperatures. Samples processed at 800 °C for 4 h however exhibit better fatigue performance than others treated at lower temperatures for longer nitriding times. Fractographic inspection has shown that fatigue cracks originate at (or near) the surface for the untreated Ti-alloy and from the subsurface regions following Diffusion treatment, owing to the build-up of compressive stresses in the latter, which hinder crack propagation.
-
Evaluating the effects of PIRAC Nitrogen-Diffusion treatments on the mechanical performance of Ti–6Al–4V alloy
Materials Science and Engineering: A, 2014Co-Authors: T. Bonello, Allan Matthews, Adrian Leyland, J. C. Avelar-batista Wilson, J. Housden, Elazar Y. Gutmanas, I. Gotman, Glenn CassarAbstract:Abstract Powder Immersion Reaction Assisted Coating (PIRAC) is a relatively simple Nitrogen Diffusion based process which has been proposed as a technique capable of considerable improvements in the tribological performance of ceramics and metals alike; however, the necessary exposure of the substrate material to high temperatures for several hours may have an adverse effect on the bulk properties of materials such as titanium alloys. The effect of PIRAC treatments on the bulk metallography and mechanical properties of Ti–6Al–4V has been studied. Following PIRAC Nitrogen-Diffusion treatment, studies using X-ray diffraction and cross-sectional microscopy have shown evidence of the formation of a thin (~1.4 µm) TiN/Ti 2 N layer, together with the presence of some Ti 3 Al intermetallic phase. Semi-logarithmic S–N plots show a deleterious effect after PIRAC treatment in terms of material cyclic fatigue strength, particularly at higher treatment temperatures. Samples processed at 800 °C for 4 h however exhibit better fatigue performance than others treated at lower temperatures for longer nitriding times. Fractographic inspection has shown that fatigue cracks originate at (or near) the surface for the untreated Ti-alloy and from the subsurface regions following Diffusion treatment, owing to the build-up of compressive stresses in the latter, which hinder crack propagation.
M. Meinert - One of the best experts on this subject based on the ideXlab platform.
-
Role of the Ta buffer layer in Ta/MnN/CoFeB stacks for maximizing exchange bias
Journal of Applied Physics, 2020Co-Authors: Mareike Dunz, M. MeinertAbstract:Ta/MnN/CoFeB systems show high exchange bias of about 1800 Oe at room temperature; however, their thermal stability is limited by Nitrogen Diffusion that occurs during annealing processes [Quarterman et al., Phys. Rev. Mater. 3, 064413 (2019) and Dunz et al., AIP Adv. 8, 056304 (2018)]. In this study, we investigate the consequences of Nitrogen Diffusion in Ta/MnN/CoFeB exchange bias stacks in dependence on the Ta buffer layer thickness. Furthermore, we test the effects of introducing a TaN x layer between MnN and Ta as a Diffusion barrier. Our findings show that the Ta buffer layer plays a decisive role in determining the exchange bias in the Ta/MnN/CoFeB system. It acts as a crystallographic seed layer for better growth of MnN and as a Nitrogen sink during the annealing process. We show that both of these functions are crucial for the outcome of high exchange bias. Additionally, our results reveal that the measures decreasing Nitrogen Diffusion, even though being beneficial in terms of thermal stability, mostly lead to decreased crystallinity and thus weaker exchange bias.
Delphine Retraint - One of the best experts on this subject based on the ideXlab platform.
-
the effect of surface mechanical attrition treatment on low temperature plasma nitriding of an austenitic stainless steel
Surface & Coatings Technology, 2013Co-Authors: M Chemkhi, Delphine Retraint, A Roos, C Garnier, Laurent Waltz, Clemence Demangel, Gwenaelle ProustAbstract:Abstract The combined effect of superficial nanocrystallisation by SMAT (Surface Mechanical Attrition Treatment) followed by plasma nitriding on the mechanical properties of a medical grade austenitic stainless steel was studied. SMAT conditions were optimised to enhance Nitrogen Diffusion. Experimental observations (energy dispersive X-ray spectroscopy profiles, cross-sectional optical micrographs, phase analysis by X-ray diffraction and micro-hardness profiles) show that polishing away a very thin layer after SMAT and before nitriding significantly improves Nitrogen Diffusion into the substrate, yielding a 50% thicker nitrided layer. Possible causes for this improvement are discussed.
-
Duplex surface treatments combining surface mechanical attrition treatment (SMAT) and low temperature plasma nitriding
2013Co-Authors: M Chemkhi, Delphine Retraint, A Roos, Laurent Waltz, Guillaume Montay, Clemence DemangelAbstract:SMAT and plasma nitriding are two surface treatments that enhance the mechanical properties of surface layers by inducing superficial nanostructures and the formation of hard phases, respectively [1-2]. The idea of this work is to combine SMAT with nitriding: SMAT provides a superficial nanostructure with nanosized grains and a high dislocation density and thus creates a large volume fraction of grain boundaries and defects; during subsequent nitriding these "fast" Diffusion pathways enhance atomic Nitrogen Diffusion. However, contradictory views can be found in the literature: in some cases mechanical attrition pretreatment creates oxide barriers hindering Nitrogen incorporation [3]. Therefore, the aim of this investigation is to characterise and to discuss the microstructure evolution of an austenitic stainless steel AISI 316 - ASTM F138 subjected to surface mechanical attrition treatment followed by low temperature plasma nitriding. In addition, a polishing step (after SMAT and before nitriding) was introduced to examine the effect and the interaction of the contamination induced by SMAT in the surface [4] on the Nitrogen Diffusion. The treated samples were characterized using several observations (Scanning electron microscopy (SEM), cross-sectional optical micrographs, micro-hardness profiles and X-ray diffraction). They show that polishing away a very thin layer after SMAT and before nitriding significantly improves Nitrogen Diffusion into the substrate, yielding a 50% thicker nitrided layer with respect to nitrided only. The thermal stability of the nanostructure induced by SMAT was analysed by Transmission Electron Microscopy (TEM). Furthermore, additional chemical analyses by Energy Dispersive X-ray spectrometry (EDS) were performed to try to understand the effect of SMAT on the Nitrogen Diffusion. Finally, the residual stress profiles of each treated sample were measured. A combined system of blind-hole drilling and digital speckle pattern interferometry [5] was used to measure the in-depth residual stresses.
-
theoretical modelling of iron nitriding coupled with a nanocrystallisation treatment application to numerical predictions for ferritic stainless steels
Applied Surface Science, 2012Co-Authors: Benoit Panicaud, M Chemkhi, A Roos, Delphine RetraintAbstract:Abstract This paper analyses a recently developed duplex process combining nitriding with nanocrystallisation. A model is proposed to show how Nitrogen Diffusion mechanisms are modified within ferritic steels due to the nanostructure near the top surface. This model is based on micro-mechanical and micro-physical approaches, and also on the thermodynamics of irreversible processes. It takes into account size effects influencing the Nitrogen Diffusion, including mechanical stresses at the different length scales. Several models are investigated and numerical applications are performed. The results are compared to literature in order to demonstrate the generality of the present methodology.
-
Microstructural evolution of a 316L alloy subjected to surface nanocrystallisation and low-temperature plasma nitriding
2012Co-Authors: M Chemkhi, Delphine Retraint, A Roos, Clemence Demangel, Gwenaelle Proust, Laurent WaltzAbstract:SMAT (Surface Mechanical Attrition Treatment) and plasma nitriding are surface treatments that enhance the mechanical properties of surface layers by inducing superficial nanostructures and formation of hard phases, respectively. By combining the two, the nanocrystalline layer generated by SMAT is thought to enhance the atomic Diffusion of Nitrogen into the material during the nitriding step. In this paper, a series of SMAT and nitriding experiments has been carried out at temperatures of 425°C for 20 h. Several observations (Transmission Electron Microscopy (TEM), scanning electron microscopy (SEM), crosssectional optical micrographs, micro-hardness profiles) show that polishing away a very thin layer after SMAT and before nitriding significantly improves Nitrogen Diffusion into the substrate, yielding a 50% thicker nitrided layer with respect to nitrided only. Furthermore, it improves the friction behaviour of the 316L steel. Additional chemical analyses by Energy Dispersive X-ray spectrometry (EDS) were performed to try to understand the effect of SMAT on the Nitrogen Diffusion.
M Chemkhi - One of the best experts on this subject based on the ideXlab platform.
-
the effect of surface mechanical attrition treatment on low temperature plasma nitriding of an austenitic stainless steel
Surface & Coatings Technology, 2013Co-Authors: M Chemkhi, Delphine Retraint, A Roos, C Garnier, Laurent Waltz, Clemence Demangel, Gwenaelle ProustAbstract:Abstract The combined effect of superficial nanocrystallisation by SMAT (Surface Mechanical Attrition Treatment) followed by plasma nitriding on the mechanical properties of a medical grade austenitic stainless steel was studied. SMAT conditions were optimised to enhance Nitrogen Diffusion. Experimental observations (energy dispersive X-ray spectroscopy profiles, cross-sectional optical micrographs, phase analysis by X-ray diffraction and micro-hardness profiles) show that polishing away a very thin layer after SMAT and before nitriding significantly improves Nitrogen Diffusion into the substrate, yielding a 50% thicker nitrided layer. Possible causes for this improvement are discussed.
-
Duplex surface treatments combining surface mechanical attrition treatment (SMAT) and low temperature plasma nitriding
2013Co-Authors: M Chemkhi, Delphine Retraint, A Roos, Laurent Waltz, Guillaume Montay, Clemence DemangelAbstract:SMAT and plasma nitriding are two surface treatments that enhance the mechanical properties of surface layers by inducing superficial nanostructures and the formation of hard phases, respectively [1-2]. The idea of this work is to combine SMAT with nitriding: SMAT provides a superficial nanostructure with nanosized grains and a high dislocation density and thus creates a large volume fraction of grain boundaries and defects; during subsequent nitriding these "fast" Diffusion pathways enhance atomic Nitrogen Diffusion. However, contradictory views can be found in the literature: in some cases mechanical attrition pretreatment creates oxide barriers hindering Nitrogen incorporation [3]. Therefore, the aim of this investigation is to characterise and to discuss the microstructure evolution of an austenitic stainless steel AISI 316 - ASTM F138 subjected to surface mechanical attrition treatment followed by low temperature plasma nitriding. In addition, a polishing step (after SMAT and before nitriding) was introduced to examine the effect and the interaction of the contamination induced by SMAT in the surface [4] on the Nitrogen Diffusion. The treated samples were characterized using several observations (Scanning electron microscopy (SEM), cross-sectional optical micrographs, micro-hardness profiles and X-ray diffraction). They show that polishing away a very thin layer after SMAT and before nitriding significantly improves Nitrogen Diffusion into the substrate, yielding a 50% thicker nitrided layer with respect to nitrided only. The thermal stability of the nanostructure induced by SMAT was analysed by Transmission Electron Microscopy (TEM). Furthermore, additional chemical analyses by Energy Dispersive X-ray spectrometry (EDS) were performed to try to understand the effect of SMAT on the Nitrogen Diffusion. Finally, the residual stress profiles of each treated sample were measured. A combined system of blind-hole drilling and digital speckle pattern interferometry [5] was used to measure the in-depth residual stresses.
-
theoretical modelling of iron nitriding coupled with a nanocrystallisation treatment application to numerical predictions for ferritic stainless steels
Applied Surface Science, 2012Co-Authors: Benoit Panicaud, M Chemkhi, A Roos, Delphine RetraintAbstract:Abstract This paper analyses a recently developed duplex process combining nitriding with nanocrystallisation. A model is proposed to show how Nitrogen Diffusion mechanisms are modified within ferritic steels due to the nanostructure near the top surface. This model is based on micro-mechanical and micro-physical approaches, and also on the thermodynamics of irreversible processes. It takes into account size effects influencing the Nitrogen Diffusion, including mechanical stresses at the different length scales. Several models are investigated and numerical applications are performed. The results are compared to literature in order to demonstrate the generality of the present methodology.
-
Microstructural evolution of a 316L alloy subjected to surface nanocrystallisation and low-temperature plasma nitriding
2012Co-Authors: M Chemkhi, Delphine Retraint, A Roos, Clemence Demangel, Gwenaelle Proust, Laurent WaltzAbstract:SMAT (Surface Mechanical Attrition Treatment) and plasma nitriding are surface treatments that enhance the mechanical properties of surface layers by inducing superficial nanostructures and formation of hard phases, respectively. By combining the two, the nanocrystalline layer generated by SMAT is thought to enhance the atomic Diffusion of Nitrogen into the material during the nitriding step. In this paper, a series of SMAT and nitriding experiments has been carried out at temperatures of 425°C for 20 h. Several observations (Transmission Electron Microscopy (TEM), scanning electron microscopy (SEM), crosssectional optical micrographs, micro-hardness profiles) show that polishing away a very thin layer after SMAT and before nitriding significantly improves Nitrogen Diffusion into the substrate, yielding a 50% thicker nitrided layer with respect to nitrided only. Furthermore, it improves the friction behaviour of the 316L steel. Additional chemical analyses by Energy Dispersive X-ray spectrometry (EDS) were performed to try to understand the effect of SMAT on the Nitrogen Diffusion.
Isabelle Jauberteau - One of the best experts on this subject based on the ideXlab platform.
-
expanding microwave plasma process for thin molybdenum films nitriding Nitrogen Diffusion and structure investigations
Surface & Coatings Technology, 2011Co-Authors: Isabelle Jauberteau, Said Touimi, Armand Passelergue, Jean-louis Jauberteau, Therese Merlemejea, S Webe, Annie Essaudou, J AubretoAbstract:Transition metal nitrides exhibit very interesting properties for mechanical and catalytic applications. Thin nitride layers are expected to prevent metal films from oxidizing under working conditions. Molybdenum thin films of about 200 nm thick and deposited on Si (100) wafers are processed in pure N2, (Ar-35%N2) and (Ar-25%N2-30%H2) expanding microwave plasma at 673 K. Secondary neutral mass spectrometry (SNMS) and Raman spectroscopy are both used to make correlations between the composition and the structure of the as-formed compounds. The low Nitrogen Diffusion up to a depth of about 40 nm is correlated to the formation of well crystallized MoO2 of monoclinic structure acting as a barrier of Diffusion for Nitrogen, in molybdenum films exposed to pure N2 and (Ar-35%N2) plasma. The large Nitrogen Diffusion into the film exposed to ternary (Ar-25%N2-30%H2) plasma is correlated to the reduction of MoO2 oxides by hydrogen species such as atomic hydrogen, NHxb3...contained in ternary plasma. The formation of Mo-N phases with defects could take place in molybdenum films processed at 673 K compared to the results obtained at 873 K.
-
a nitriding process of very thin molybdenum films in an expanding microwave plasma at low temperature
Microelectronics Systems Education, 2010Co-Authors: Said Touimi, Isabelle Jauberteau, S Weber, Armand Passelergue, R Mayet, Jean-louis Jauberteau, Annie Bessaudou, Jacques AubretonAbstract:A transfer of Nitrogen of about 20 at % is detected in very thin molybdenum films of about 200 nm thick coated on Si (100) wafers heated at 673 K and exposed to ternary (Ar-N2- H2) plasma. The Nitrogen Diffusion goes with a noticeable decrease of the remaining oxide layers in the whole film thickness. On the contrary, pure N2 gas exposure leads to a slight Diffusion of Nitrogen into the first molybdenum layers up to a depth of about 40 nm, only and an enhancement of oxygen amount also. Hydrogen species contained in the plasma reduce the oxide layers which act as Nitrogen Diffusion barrier. The Nitrogen Diffusion decrease with increasing distance of the workpiece surface from the centre of the discharge as well as the occurrence of Nitrogen Diffusion in molybdenum layers at room temperature highlight the role of NHx<3 active species of the plasma on the reactivity of the surface. The morphology of the nitrided surface consists of slightly smaller grains compared with those corresponding to untreated molybdenum films ranging in size from 30 to 50 nm wide. In contrast to substrates heated at 873 K, the tetragonal Mo2N structure has not been detected in molybdenum films heated at 673 K.
-
A nitriding process of very thin molybdenum films in an expanding microwave plasma at low temperature
IOP Conference Series: Materials Science and Engineering, 2010Co-Authors: Said Touimi, Isabelle Jauberteau, S Weber, Armand Passelergue, R Mayet, Jean-louis Jauberteau, Annie Bessaudou, Jacques AubretonAbstract:A transfer of Nitrogen of about 20 at % is detected in very thin molybdenum films of about 200 nm thick coated on Si (100) wafers heated at 673 K and exposed to ternary (Ar-N2- H2) plasma. The Nitrogen Diffusion goes with a noticeable decrease of the remaining oxide layers in the whole film thickness. On the contrary, pure N2 gas exposure leads to a slight Diffusion of Nitrogen into the first molybdenum layers up to a depth of about 40 nm, only and an enhancement of oxygen amount also. Hydrogen species contained in the plasma reduce the oxide layers which act as Nitrogen Diffusion barrier. The Nitrogen Diffusion decrease with increasing distance of the workpiece surface from the centre of the discharge as well as the occurrence of Nitrogen Diffusion in molybdenum layers at room temperature highlight the role of NHx
-
plasma nitriding of thin molybdenum layers at low temperature
Surface & Coatings Technology, 1999Co-Authors: Isabelle Jauberteau, Jean-louis Jauberteau, M N Semeria, A Larre, J Piaguet, Jacques AubretonAbstract:Abstract An expanding plasma of pure N 2 gas, (Ar–N 2 ) and (Ar–N 2 –H 2 ) gas mixtures activated by microwave is used for thermochemical processing of Mo film by nitriding at 400°C. Auger electron spectroscopy (AES) indicates that (Ar–35% N 2 ) and (Ar–25% N 2 –30% H 2 ) exposures result in a Nitrogen Diffusion greater than after pure N 2 and (Ar–10% N 2 ) exposures. The (Ar–N 2 ) plasma removes 50 at.% of oxygen from the surface Mo layers. The addition of H 2 in (Ar–N 2 ) gas mixture at 400°C and 600°C leads to a large increase of Nitrogen Diffusion since the Nitrogen amount remains constant up to a depth of about 50 nm and 200 nm, respectively. This is strongly correlated to the large decrease of passive oxides and carbides layers of Mo film. The nitrided layers could act as a barrier to Diffusion, preventing Mo film from oxidizing further.