Nathalie Renevier is a senior lecturer in tribotechnology (coatings) and course leader for undergraduate maintenance engineering courses. She has a physics, material sciences and business background with over 10 years' experience in the industry across Europe. Her expertise is in the development of plasma assisted processes and products, surface characterisations, tribological testing of thin films and thick films, nano-tribology and Lean Six-Sigma methodologies.
The purpose of this work is to present the first results obtained by Optical Emission Spectroscop... more The purpose of this work is to present the first results obtained by Optical Emission Spectroscopy (OES) in a low pressure arc discharge used for steel nitriding. In this process, workpieces are nitrided at floating potential in Ar-N 2 mixtures. OES measurements are compared to the results obtained by metallurgical analysis of nitrided steel substrates in the same conditions
Recently two new coatings based on graphite and MoS 2 have been developed. These combine very low... more Recently two new coatings based on graphite and MoS 2 have been developed. These combine very low friction with high hardness, very low wear and high load bearing capacity. Both coatings act as solid lubricants and provide protection for both the coated surface and any uncoated opposing surface. These coatings are proving successful in increasing the lifetime and productivity of cutting and forming tools and also make possible high speed unlubricated machining and several examples will be given. The graphite based coatings have exceptional wear properties under water or oil lubrication and a range of test results are presented. A number of practical applications are given including the protection of artificial hip joints and the advantages of the use of the lubricating coatings for mechanical components are demonstrated.
The ST-3001 is a multi-mode testing system which can be used for scratch adhesion tests, linear w... more The ST-3001 is a multi-mode testing system which can be used for scratch adhesion tests, linear wear tests either reciprocating or uni-directional and hardness testing. The system was based on an earlier tester ST-2000 and was further developed in a joint project supported by the European Commission.
ABSTRACT A new high current (100–300 A), low voltage (25–45 V) and low pressure (0.4–1 Pa) arc di... more ABSTRACT A new high current (100–300 A), low voltage (25–45 V) and low pressure (0.4–1 Pa) arc discharge plasma used for steel nitriding is presented and characterized by optical emission spectroscopy (OES). In this process, the nitriding rate is high even if the workpieces are nitrided at floating potential without hydrogen in Ar−N2 gas mixtures. With H2, there is no appreciable gain in nitrogen content or in growth rate of the diffusion layer. In this paper, the OES diagnostic technique has been used to characterize the different excitation processes of both neutral and ionic argon species in Ar−N2, Ar−H2 and Ar−N2−H2 gas mixtures. The reactivity of this process is evaluated by using AISI 316 L austenitic stainless steel substrates nitrided for different treatment times at 690 K.
... This supersaturated fcc structure, sometime described as expanded austenite has been observ... more ... This supersaturated fcc structure, sometime described as expanded austenite has been observed in dc plasma nitriding [8, 9, 10, 11, 12], in ECR microwave plasma treatment [5], in plasma immersion ion implantation [12, 13] or in plasma source ion implantation [14]. ...
Magnetron sputtered MoS2 coatings have been widely studied over many decades for tribological spa... more Magnetron sputtered MoS2 coatings have been widely studied over many decades for tribological space applications, their performance can be greatly improved with the intercalation of elements such as Ti. While MoS2 retains some of the crystalline characteristics found in the original MoS2 sputtering targets, as deposited MoS2/Ti composite coatings are almost completely amorphous or “quasi-amorphous”. Tribological bidirectional wear tests have been carried out on the MoS2/Ti coatings. A surface sensitive structural analysis performed before and after wear test using Reflection High Energy Electron diffraction (RHEED). Additional analytical techniques including optical microscopy, scanning electron microscopy and transmission electron microscopy have been used. The development of a preferred orientation within the coatings was observed dependent on the number of wear cycles and the applied load.
The purpose of this work is to present the first results obtained by optical emission spectroscop... more The purpose of this work is to present the first results obtained by optical emission spectroscopy (OES) in a high current, low voltage and low pressure arc discharge used for steel nitriding. The apparatus is mainly constituted of an ionisation chamber mounted on the top of the nitriding reactor itself. In this process, workpieces are nitrided at floating potential in ArN2 gas mixtures. OES measurements are done in pure argon for different arc currents and different gas pressures in the reactor. This plasma diagnostic technique has been used to characterize the different excitation processes of both neutral and ionic argon species. In the case of ArN2 gas mixtures a strong quenching effect of nitrogen on the electron energy distribution function is observed. OES measurements obtained for various nitrogen percentages in ArN2 gas mixtures are compared to the results obtained by metallurgical analysis of nitrided Armco iron substrates in the same conditions.
ABSTRACT Carbon/chromium (C/Cr) coatings were co-deposited using unbalanced magnetron sputtering ... more ABSTRACT Carbon/chromium (C/Cr) coatings were co-deposited using unbalanced magnetron sputtering deposition technique. The tribological properties including wear mechanism and microstructures of the coatings were investigated using pin-on-disc tribometer, X-ray diffraction (XRD) and transmission electron microscope (TEM). The coatings were characterised by a high hardness (∼2200 HV), a low coefficient of friction (<0.1) and a very low wear rate under very high loads. The pin-on-disc tests of C/Cr coated tool steel against WC ball (5 mm of diameter) revealed low friction coefficient 0.06–0.1 depending on load and low wear rate ∼10−17 m3/Nm with little dependence on load and sliding speed for the test using load up to 80 N and siding speed up to 400 mm/s for 1 h. Critical sliding speed was found above which, the wear rate was higher. The pin-on-disc tests of C/Cr coated austenitic 316 stainless steel against WC ball under a load of 10 N at siding speed of 400 mm/s for 1 h revealed a low friction coefficient ∼0.1 and a very low wear beyond the limitation of the as used wear measurement technique could detect. Microstructure of the coated stainless steel was investigated. XRD profiles of the coating exhibited typical patterns for amorphous-like material, with no crystal-like peaks identified. Cross-sectional TEM analysis of the rubbed tracks of the coated stainless steel revealed some deformation in the substrate near the interface. However, no sign of interfacial spallation was observed, indicative of excellent adhesion of the coating to the substrate. The selected area electron diffraction patterns taken from the rubbed and unrubbed regions of the coating were interpreted and discussed. The tribological performance of this novel C/Cr coating is believed to be closely related to its graphite nature. The high resolution TEM (HRTEM) cross-section analysis of the coating on stainless steel substrate revealed that the outer-most surface of the rubbed track was reoriented due to the rubbing in a 1-h pin-on-disc test under a load of 10 N. Finally, the relationship between deposition parameters and tribological performance of the coating is also discussed in this paper.
ABSTRACT Plasma-assisted nitriding is an attractive surface treatment for metallurgical surface m... more ABSTRACT Plasma-assisted nitriding is an attractive surface treatment for metallurgical surface modification to improve wear, hardness and fatigue resistance of ferrous and non-ferrous materials. For this purpose, ion nitriding by a d.c. glow discharge is generally efficient for numerous materials. However, for some metals and alloys, the processing temperature, dominated by the discharge parameters, is too high and cannot be controlled independently from the plasma reactivity. This paper reviews the following solutions for low-temperature plasma-assisted nitriding: pulsed d.c. discharge, thermionically assisted d.c. triode arrangements, plasma implantation, electron cyclotron resonance systems and thermionic arc discharges. We focus on metallurgical results obtained by these techniques on austenitic stainless steel and aluminium.
In the industry, High Speed Machining (HSM) is recognised as one of the key manufacturing technol... more In the industry, High Speed Machining (HSM) is recognised as one of the key manufacturing technologies for higher productivity and lower production costs. Existing cutting tools are coated to improve the tool life and the performance. These coatings are all based on the principle that the coating is much harder than the work piece material. The objective of this paper
Self-lubricating low friction MoS2/Ti composite coatings were deposited onto hard coated carbide ... more Self-lubricating low friction MoS2/Ti composite coatings were deposited onto hard coated carbide inserts using a hybrid process and were tested for dry high-speed milling and turning of steel. Dry machining is an important objective in industry to reduce environmental and production costs. It was shown that dry machining using MoS2/Ti composite coatings is possible in some cases. Following an already
Miniaturisation of devices and a paradigm shift toward using compliant material require small sca... more Miniaturisation of devices and a paradigm shift toward using compliant material require small scale characterisation techniques such as nanoindentation [1]. Initial non-conformity of contact and delayed elasticity on the unloading curve are not currently taking into account in nanoindentation methods [2, 3], where the unloading curve is seen fully elastic. A different approach has been taken which considers actual localised deformation during nanoindentation, thus the proposed method [4] is able to acquire untainted elastic or viscoelastic response data. The method, validated for both viscous and non-viscous materials, takes into account the correction of the stiffness associated with the delayed elasticity at initial unloading and determines modulus with less variability even if testing conditions are non-quasi-static. The key step in the methodology is to account for initial conformity of the contact, the nose-out phenomena and delayed elasticity. Thus a full elastic point (FEP) i...
UInternal combustion engine components have been a main research interest over many decades. The ... more UInternal combustion engine components have been a main research interest over many decades. The structural mechanics and dynamics of the piston rings has been a large focus of work in order to gain a greater understanding of the how the piston ring dynamics affect the piston ring. Piston rings are often coated to reduce the level of wear on the ring as they will suffer substantial levels of material loss during operation. To further the understanding of the ring allows for a more accurate estimate of its behaviour.
The purpose of this work is to present the first results obtained by Optical Emission Spectroscop... more The purpose of this work is to present the first results obtained by Optical Emission Spectroscopy (OES) in a low pressure arc discharge used for steel nitriding. In this process, workpieces are nitrided at floating potential in Ar-N 2 mixtures. OES measurements are compared to the results obtained by metallurgical analysis of nitrided steel substrates in the same conditions
Recently two new coatings based on graphite and MoS 2 have been developed. These combine very low... more Recently two new coatings based on graphite and MoS 2 have been developed. These combine very low friction with high hardness, very low wear and high load bearing capacity. Both coatings act as solid lubricants and provide protection for both the coated surface and any uncoated opposing surface. These coatings are proving successful in increasing the lifetime and productivity of cutting and forming tools and also make possible high speed unlubricated machining and several examples will be given. The graphite based coatings have exceptional wear properties under water or oil lubrication and a range of test results are presented. A number of practical applications are given including the protection of artificial hip joints and the advantages of the use of the lubricating coatings for mechanical components are demonstrated.
The ST-3001 is a multi-mode testing system which can be used for scratch adhesion tests, linear w... more The ST-3001 is a multi-mode testing system which can be used for scratch adhesion tests, linear wear tests either reciprocating or uni-directional and hardness testing. The system was based on an earlier tester ST-2000 and was further developed in a joint project supported by the European Commission.
ABSTRACT A new high current (100–300 A), low voltage (25–45 V) and low pressure (0.4–1 Pa) arc di... more ABSTRACT A new high current (100–300 A), low voltage (25–45 V) and low pressure (0.4–1 Pa) arc discharge plasma used for steel nitriding is presented and characterized by optical emission spectroscopy (OES). In this process, the nitriding rate is high even if the workpieces are nitrided at floating potential without hydrogen in Ar−N2 gas mixtures. With H2, there is no appreciable gain in nitrogen content or in growth rate of the diffusion layer. In this paper, the OES diagnostic technique has been used to characterize the different excitation processes of both neutral and ionic argon species in Ar−N2, Ar−H2 and Ar−N2−H2 gas mixtures. The reactivity of this process is evaluated by using AISI 316 L austenitic stainless steel substrates nitrided for different treatment times at 690 K.
... This supersaturated fcc structure, sometime described as expanded austenite has been observ... more ... This supersaturated fcc structure, sometime described as expanded austenite has been observed in dc plasma nitriding [8, 9, 10, 11, 12], in ECR microwave plasma treatment [5], in plasma immersion ion implantation [12, 13] or in plasma source ion implantation [14]. ...
Magnetron sputtered MoS2 coatings have been widely studied over many decades for tribological spa... more Magnetron sputtered MoS2 coatings have been widely studied over many decades for tribological space applications, their performance can be greatly improved with the intercalation of elements such as Ti. While MoS2 retains some of the crystalline characteristics found in the original MoS2 sputtering targets, as deposited MoS2/Ti composite coatings are almost completely amorphous or “quasi-amorphous”. Tribological bidirectional wear tests have been carried out on the MoS2/Ti coatings. A surface sensitive structural analysis performed before and after wear test using Reflection High Energy Electron diffraction (RHEED). Additional analytical techniques including optical microscopy, scanning electron microscopy and transmission electron microscopy have been used. The development of a preferred orientation within the coatings was observed dependent on the number of wear cycles and the applied load.
The purpose of this work is to present the first results obtained by optical emission spectroscop... more The purpose of this work is to present the first results obtained by optical emission spectroscopy (OES) in a high current, low voltage and low pressure arc discharge used for steel nitriding. The apparatus is mainly constituted of an ionisation chamber mounted on the top of the nitriding reactor itself. In this process, workpieces are nitrided at floating potential in ArN2 gas mixtures. OES measurements are done in pure argon for different arc currents and different gas pressures in the reactor. This plasma diagnostic technique has been used to characterize the different excitation processes of both neutral and ionic argon species. In the case of ArN2 gas mixtures a strong quenching effect of nitrogen on the electron energy distribution function is observed. OES measurements obtained for various nitrogen percentages in ArN2 gas mixtures are compared to the results obtained by metallurgical analysis of nitrided Armco iron substrates in the same conditions.
ABSTRACT Carbon/chromium (C/Cr) coatings were co-deposited using unbalanced magnetron sputtering ... more ABSTRACT Carbon/chromium (C/Cr) coatings were co-deposited using unbalanced magnetron sputtering deposition technique. The tribological properties including wear mechanism and microstructures of the coatings were investigated using pin-on-disc tribometer, X-ray diffraction (XRD) and transmission electron microscope (TEM). The coatings were characterised by a high hardness (∼2200 HV), a low coefficient of friction (<0.1) and a very low wear rate under very high loads. The pin-on-disc tests of C/Cr coated tool steel against WC ball (5 mm of diameter) revealed low friction coefficient 0.06–0.1 depending on load and low wear rate ∼10−17 m3/Nm with little dependence on load and sliding speed for the test using load up to 80 N and siding speed up to 400 mm/s for 1 h. Critical sliding speed was found above which, the wear rate was higher. The pin-on-disc tests of C/Cr coated austenitic 316 stainless steel against WC ball under a load of 10 N at siding speed of 400 mm/s for 1 h revealed a low friction coefficient ∼0.1 and a very low wear beyond the limitation of the as used wear measurement technique could detect. Microstructure of the coated stainless steel was investigated. XRD profiles of the coating exhibited typical patterns for amorphous-like material, with no crystal-like peaks identified. Cross-sectional TEM analysis of the rubbed tracks of the coated stainless steel revealed some deformation in the substrate near the interface. However, no sign of interfacial spallation was observed, indicative of excellent adhesion of the coating to the substrate. The selected area electron diffraction patterns taken from the rubbed and unrubbed regions of the coating were interpreted and discussed. The tribological performance of this novel C/Cr coating is believed to be closely related to its graphite nature. The high resolution TEM (HRTEM) cross-section analysis of the coating on stainless steel substrate revealed that the outer-most surface of the rubbed track was reoriented due to the rubbing in a 1-h pin-on-disc test under a load of 10 N. Finally, the relationship between deposition parameters and tribological performance of the coating is also discussed in this paper.
ABSTRACT Plasma-assisted nitriding is an attractive surface treatment for metallurgical surface m... more ABSTRACT Plasma-assisted nitriding is an attractive surface treatment for metallurgical surface modification to improve wear, hardness and fatigue resistance of ferrous and non-ferrous materials. For this purpose, ion nitriding by a d.c. glow discharge is generally efficient for numerous materials. However, for some metals and alloys, the processing temperature, dominated by the discharge parameters, is too high and cannot be controlled independently from the plasma reactivity. This paper reviews the following solutions for low-temperature plasma-assisted nitriding: pulsed d.c. discharge, thermionically assisted d.c. triode arrangements, plasma implantation, electron cyclotron resonance systems and thermionic arc discharges. We focus on metallurgical results obtained by these techniques on austenitic stainless steel and aluminium.
In the industry, High Speed Machining (HSM) is recognised as one of the key manufacturing technol... more In the industry, High Speed Machining (HSM) is recognised as one of the key manufacturing technologies for higher productivity and lower production costs. Existing cutting tools are coated to improve the tool life and the performance. These coatings are all based on the principle that the coating is much harder than the work piece material. The objective of this paper
Self-lubricating low friction MoS2/Ti composite coatings were deposited onto hard coated carbide ... more Self-lubricating low friction MoS2/Ti composite coatings were deposited onto hard coated carbide inserts using a hybrid process and were tested for dry high-speed milling and turning of steel. Dry machining is an important objective in industry to reduce environmental and production costs. It was shown that dry machining using MoS2/Ti composite coatings is possible in some cases. Following an already
Miniaturisation of devices and a paradigm shift toward using compliant material require small sca... more Miniaturisation of devices and a paradigm shift toward using compliant material require small scale characterisation techniques such as nanoindentation [1]. Initial non-conformity of contact and delayed elasticity on the unloading curve are not currently taking into account in nanoindentation methods [2, 3], where the unloading curve is seen fully elastic. A different approach has been taken which considers actual localised deformation during nanoindentation, thus the proposed method [4] is able to acquire untainted elastic or viscoelastic response data. The method, validated for both viscous and non-viscous materials, takes into account the correction of the stiffness associated with the delayed elasticity at initial unloading and determines modulus with less variability even if testing conditions are non-quasi-static. The key step in the methodology is to account for initial conformity of the contact, the nose-out phenomena and delayed elasticity. Thus a full elastic point (FEP) i...
UInternal combustion engine components have been a main research interest over many decades. The ... more UInternal combustion engine components have been a main research interest over many decades. The structural mechanics and dynamics of the piston rings has been a large focus of work in order to gain a greater understanding of the how the piston ring dynamics affect the piston ring. Piston rings are often coated to reduce the level of wear on the ring as they will suffer substantial levels of material loss during operation. To further the understanding of the ring allows for a more accurate estimate of its behaviour.
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Papers by Nathalie M Renevier