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Wear and wear mechanisms of cemented carbide in the turning of Ti6Al4V
Dalarna University, School of Technology and Business Studies, Materials Technology. (Tribology)ORCID iD: 0000-0001-5536-3077
Dalarna University, School of Technology and Business Studies, Materials Technology. (Tribology)
2019 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944Article in journal (Refereed) Submitted
Abstract [en]

Titanium and titanium alloys such as Ti-6Al-4V are generally considered as difficult-to-machine materials. This is mainly due to their high chemical reactivity, poor thermal conductivity and high strength, which is maintained at elevated temperatures. As a result, the cutting tool is exposed to rather extreme contact conditions resulting in plastic deformation and wear. In the present work, the mechanisms behind the crater and flank wear of uncoated cemented carbide inserts in the turning of Ti6Al4V are characterized using high resolution scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and high resolution Auger electron spectroscopy (AES).

The results show that for combinations of low cutting speeds and feeds crater and flank wear were found to be controlled by an attrition wear mechanism while for combinations of medium to high cutting speeds and feeds a diffusion wear mechanism was found to control the wear. For the latter combinations, high resolution SEM and AES analysis reveal the formation of an approximately 100 nm thick carbon depleted WC-layer at the cemented carbide/Ti6Al4V interface due to the diffusion of carbon into the adhered build-up layers of work material on the rake and flank surfaces.

Place, publisher, year, edition, pages
2019.
Keywords [en]
Turning, Cemented carbide, Ti6Al4V, Attrition wear, Diffusion wear, SEM, EDS
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
URN: urn:nbn:se:du-29658OAI: oai:DiVA.org:du-29658DiVA, id: diva2:1296437
Available from: 2019-03-15 Created: 2019-03-15 Last updated: 2019-07-24Bibliographically 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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