Uppsala, Sweden
Uppsala, Sweden

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Heinrichs J.,Uppsala University | Gerth J.,Uppsala University | Thersleff T.,Uppsala University | Bexell U.,Dalarna University | And 2 more authors.
Tribology International | Year: 2013

An intermittent sliding test was used in order to study the formation and build-up of tribofilms during intermittent sliding of PVD coated HSS against case hardening steel (20NiCrMo2). Two cutting tool coatings were tested, TiN and AlCrN, and the influence of sliding speed was evaluated. With moderate speed, two tribofilms were formed separately, one consisting of Mn, Si, Al and O on an intermediate layer of Fe and one consisting of Fe, Mn, Cr and O on an intermediate layer of Cr and Mn. At low sliding speeds an uneven transfer of steel occured while high sliding speeds resulted in thermal softening of the substrate leading to coating failure. AlCrN provided better substrate protection at high speeds than TiN did. © 2012 Elsevier Ltd.


Heinrichs J.,Uppsala University | Gerth J.,Uppsala University | Bexell U.,Dalarna University | Larsson M.,Primateria AB | Wiklund U.,Uppsala University
Tribology International | Year: 2012

A sliding test is used in order to evaluate the influence of tool surface roughness on the material transfer in intermittent and continuous sliding of PVD coated HSS against case hardening steel (20NiCrMo2). Two cutting tool coatings, TiN and AlCrN, and three different surface roughnesses are tested. For polished surfaces the same types of material transfer are obtained irrespective of sliding mode and coating type. If the surfaces are too rough, the tribofilms do not grow thick enough to separate the surfaces and the work material is abrasively worn in both sliding modes. With increased sliding distance, cracking of the TiN coating occurs while the AlCrN coating remains intact. © 2012 Elsevier Ltd. All rights reserved.


Gerth J.,Uppsala University | Larsson M.,Primateria AB | Wiklund U.,Uppsala University
Tribologia | Year: 2011

Gear hobbing is widely used for production of cylindrical gears in the Swedish transmission industry. The hob, usually consisting of a homogenous HSS (High Speed Steel) body coated with a ceramic PVD (Physical Vapour Deposition) coating, is designed for regrinding and recoating several times without affecting its cutting geometries. Efficient usage of the tool, considering production costs and gear quality, requires reconditioning before wear starts to affect the gear quality negatively and certainly before tool wear renders reconditioning impossible. Hobs of today generally lack in reliability, making it difficult to judge when they have to be taken out for reconditioning. This work presents a survey of wear as observed on today's state of the art hobs used by Swedish gear manufactures. It aims to identify damage mechanisms and the common problems in order to enable future production of more reliable hobs. The tools were temporarily borrowed from the production and the analyses were made non-destructively using optical microscopes. This was complemented by destructive crosssectional analysis on two of the hobs. Wear was most commonly located on the rake faces and the cutting edges of the cutting teeth. It mainly propagates by discrete fractures which appear to originate at local defects in the coating or at the interface. High intrinsic stress in the coating likely promotes coating spallation and accelerates the wear of the cutting edge.


Gerth J.,Uppsala University | Heinrichs J.,Uppsala University | Nyberg H.,Uppsala University | Larsson M.,Primateria AB | Wiklund U.,Uppsala University
Tribology International | Year: 2012

TiN coated HSS test cylinders from an intermittent sliding test were compared with TiN coated HSS milling inserts from a single insert milling test. A 20NiCrMo2 case hardening steel was used as counter material and work material in the two tests. HSS test cylinders, coated with AlCrN, TiAlN and Al 2O 3, were also tested in the intermittent sliding test and evaluated with regard to material adhesion. Two distinctly different tribofilms were formed on test cylinders as well as on cutting inserts. One consisting of Mn, Si, Al and O and one consisting of Fe, Mn, Cr, Si and O. The transferred material was similar in appearance and composition, both when comparing the two test methods and when comparing the different tool coatings. © 2012 Elsevier Ltd.

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