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Tribological testing of commercial CrN, (Ti,Al)N and CrC/C PVD coatings: Evaluation of galling and wear characteristics against different high strength steels.
Högskolan Dalarna, Materialvetenskap.
2011 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, no 16, 4045-4051 p.Article in journal (Refereed) Published
Abstract [en]

The increasing use of high strength steels in a variety of mechanical engineering applications has illuminatedproblems associated with galling in sheet metal forming operations. Galling is a tribological phenomenonassociated with transfer of material from the steel sheet to the tool surface during forming resulting in seizureof the tool/steel sheet contact and extensive scratching of the steel sheet surface. As a result, a number ofconcepts have been developed in order to reduce the tendency of galling in sheet metal forming, including thedevelopment of new dry lubricants, new forming tool steel grades and improved surface engineeringtreatments such as the deposition of low friction CVD- and PVD-coatings. In the present study the potentialperformance of three commercial PVD coatings, including CrN, (Ti,Al)N and a CrC/C DLC-based coating, in theforming of hot and cold rolled high strength steel as well as electro and hot-dip galvanized high strength steelhas been evaluated using pin-on-disc testing under lubricated contact conditions. Post-test examination ofthe tribosurfaces using FEG-SEM and EDS analyses was performed in order to evaluate the mechanismscontrolling the tendency to material transfer and wear. The results show that in contact with the hot and coldrolled steel the material pick-up tendency of the PVD coatings tend to increase in the order CrC/C–CrN–(Ti,Al)N while in contact with the two galvanized steel sheets, the CrC/C and the (Ti,Al)N coating show a significantlylower material pick-up tendency as compared with the CrN coating. Further, the substrate hardness has astrong influence on the wear of the PVD coatings and consequently on the friction characteristics and gallingtendency of the coating/substrate composite. Low substrate hardness, resulting in a low load bearing capacity,increases the tendency to cracking and subsequently chipping of the brittle coating.

Place, publisher, year, edition, pages
2011. Vol. 205, no 16, 4045-4051 p.
Keyword [en]
PVD coatings, tool steel, high strength steel sheet, galling, friction, wear.
National Category
Metallurgy and Metallic Materials
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
URN: urn:nbn:se:uu:diva-159386DOI: 10.1016/j.surfcoat.2011.02.053OAI: oai:DiVA.org:uu-159386DiVA: diva2:444685
Available from: 2011-09-29 Created: 2011-09-29 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Galling of high strength steels and stainless steels in sheet metal forming as evaluated using pin-on-disc testing
Open this publication in new window or tab >>Galling of high strength steels and stainless steels in sheet metal forming as evaluated using pin-on-disc testing
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The thesis focuses on the problem galling in sheet metal forming operations. Galling occurs when sheet metal transfers from the sheet surface onto the tool surface and causes surface damages to following sheets in the forming operation. When this happens the tool must be replaced causing production stops and additional expenses.

The increasing use of high strength steel grades combined with the desire to use more environmentally friendly or no lubricants exposes the tools used for sheet metal forming for tougher forming conditions with higher contact pressures and thus an increasing risk for material pick-up and galling. To prevent this new tool steels, lubricants and coatings have been developed. In this thesis a number of tool steels, high strength steels, stainless steels, coatings and lubricants have been investigated with the test method pin-on-disc testing in order to explain how different premises, such as chemical composition, mechanical properties and surface topography influence on the galling tendency in sheet metal forming.

The results show that there is a big difference in performance between a conventional cast tool steel and a powder metallurgy tool steel with respect to the galling tendency. The results also show that the surface topography of both the tool steels and the sheet materials influence on the performance of the lubricants and the galling tendency.   

When coating a tool steel, the substrate hardness is of greatest importance for the performance and wear of the coating. For the different coatings investigated, the performance of the coatings depends on whether the sheet material is zinc coated or not. However, the CrC/C coating investigated show a good performance with respect to the galling tendency in contact with all of the investigated high strength steel grades.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2012. viii+30 p.
Keyword
Galling, sheet metal forming, high strength steels, stainless steels
National Category
Metallurgy and Metallic Materials Manufacturing, Surface and Joining Technology
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-164717 (URN)978-91-506-2266-9 (ISBN)
Supervisors
Available from: 2012-07-18 Created: 2011-12-23 Last updated: 2012-07-18Bibliographically approved

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