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Influence of CVD and PVD coating micro topography on the initial material transfer of 316L stainless steel in sliding contacts: A laboratory study
Dalarna University, School of Technology and Business Studies, Materials Technology. Ångström Tribomaterials group, Uppsala University. (Tribologi)ORCID iD: 0000-0001-5536-3077
Dalarna University, School of Technology and Business Studies, Materials Technology. Ångström Tribomaterials group, Uppsala University. (Tribologi)
2017 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 388-389, p. 29-38Article in journal (Refereed) Published
Abstract [en]

Austenitic stainless steels generally display poor tribological properties in sliding contacts partly due to their strong adhesion and transfer tendency to the counter surface. As a result machining of austenitic stainless steels is frequently associated with significant problems such as high stresses and high temperatures resulting in rapid tool wear. In the present study, the influence of coating micro topography on the initial material transfer of 316L stainless steel in sliding contacts has been evaluated using a scratch testing equipment. Coating materials include modern CVD Ti(C,N)-Al2O3-TiN and PVD (Ti,Al)N-(Al,Cr2)O3 coatings deposited on cemented carbide and pre- and post-coating grinding and polishing treatments were used to obtain different micro topographies of the coating surface. Pre- and post-test characterization of the surfaces was performed using high resolution scanning electron microscopy, energy dispersive X-ray spectroscopy and optical surface profilometry.

The results show that the intrinsic topography of the as-deposited CVD and PVD coatings promotes material transfer. For the as-deposited CVD coating the nanoscale topography of the crystals controls the transfer while for the PVD coating the µm-scale droplets and craters control the transfer. Post-polishing of the coating, especially in combination with pre-polishing of the substrate, significantly improves the tribological performance of the surface reducing the friction coefficient and the material transfer tendency. However, the presence of µm sized droplets and craters in the PVD coating limit the possibility to obtain a smooth post-polished surface and its resistance to material pick-up. In contrast, post-polishing of the CVD coating does not suffer from intrinsic coating defects which results in low friction and a very high resistance to material pick-up.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 388-389, p. 29-38
Keywords [en]
Material transfer; CVD and PVD coatings; Surface topography; Stainless steel; Metal cutting
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
URN: urn:nbn:se:du-23915DOI: 10.1016/j.wear.2016.12.003OAI: oai:DiVA.org:du-23915DiVA, id: diva2:1063471
Available from: 2017-01-10 Created: 2017-01-10 Last updated: 2019-03-26Bibliographically approved
In thesis
1. Investigation of topography, adhesion and diffusion in sliding contacts during steel and titanium alloy machining
Open this publication in new window or tab >>Investigation of topography, adhesion and diffusion in sliding contacts during steel and titanium alloy machining
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of the present thesis work is to increase the fundamental knowledge of the tribological contact between the cutting tool and the work material in three different cutting operations, i.e. hard milling of cold work tool steels, turning in 316L stainless steel and turning in Ti6Al4V alloy, respectively. The influence of cutting parameters and tool surface topography on the initial material transfer tendency and resulting wear and wear mechanisms were investigated under well controlled cutting conditions. High resolution scanning electron microscopy (SEM) and surface analysis, including energy dispersive X-ray spectroscopy (EDS), Auger electron spectroscopy (AES) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), were used in order to characterize the worn cutting tools on a sub-µm scale and deepen the understanding of the wear mechanisms prevailing at the tool / work material interface. The characterization work includes the analysis of worn tool surfaces as well as cross-sections of these. Also, the back side of collected chips were analysed to further understand the contact mechanisms between the tool rake face and chip.

The results show that the transfer tendency of work material is strongly affected by the surface topography of the rake face and that an appropriate pre- and post-coating treatment can be used in order to reduce the transfer tendency and the mechanical interaction between the mating surfaces. The continuous wear mechanisms of the cutting tools were found to be dependent on the work materials and the cutting parameters used. In hard milling of cold work tool steels, polycrystalline cubic boron nitride shows a combination of tribochemical wear, adhesive wear and mild abrasive wear. In the turning of 316L stainless steel and Ti6Al4V alloy, using medium to high cutting speeds/feeds, the wear of cemented carbide is mainly controlled by diffusion wear of the WC phase. Interestingly, the diffusion wear processes differ between the two work materials. In contact with 316L stainless steel crater wear is controlled by atomic diffusion of W and C into the passing chip. In contact with Ti6Al4V crater wear is controlled by the diffusion of C into a transfer work material layer generating a W-rich and TiC interfacial layer which repeatedly is removed by the passing chip. The experimental work and results obtained illustrates the importance of in-depth characterization of the worn surfaces in order to increase the understanding of the degradation and wear of tool materials and coatings in metal cutting operations.

Place, publisher, year, edition, pages
Uppsala University, 2019
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-29700 (URN)
Public defence
(English)
Supervisors
Available from: 2019-03-27 Created: 2019-03-19 Last updated: 2019-04-08Bibliographically approved
2.
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Saketi, SaraOlsson, Mikael

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