Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 388 On Adhesion and Galling in Metal Forming MAGNUS HANSON ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6214 UPPSALA ISBN 978-91-554-7072-2 2008 urn:nbn:se:uu:diva-8417 !""# "$"" % % % & ' ( ) * ' +' !""#' , - . + ' - ' /##' ! ' ' 0123 45#646 765"5!6!' + % ) ) ' % %% ) % % ) 8 %9 ' ( % % % ) % ' ' ) % : % % ' ( % ) ' % 6 9 ' %% ) 8 9 *1;- (*+ ) ) 8 ' ( % ) ' 0 ) 8 % % % 8 % % ' 1 &<6 ) % ' ( % % ' ( % 8 % % ' 1 ) 8 8 % ' - % 8 ' = % ) 8 ) % ) ' 0 ) % % ) 8 ' % ! " # $%& !'($)*) > + !""# 0113 ? 6?!7 0123 45#646 765"5!6! $ $$$ 6#75 @ $AA '8'A B C $ $$$ 6#75D List of papers I Comparison of two test methods for evaluation of forming tool materials, M. Hanson, A. Gåård, P. Krakhmalev, S. Hogmark, J. Bergström. Accepted for publication in Tribotest. II Influence from tool roughness on the risk of work material adhesion and transfer, M. Hanson, S. Hogmark, S. Jacobson. In manuscript. III An atomistic approach to the initiation mechanism of galling, L. Vitos, K. Larsson, B. Johansson, M. Hanson, S. Hogmark. Computational Materials Science 37 (2006) 193-197. IV Influence of nitrogen content in PVD-VN coatings on galling resistance versus austenitic stainless steel, M. Hanson, U. Wiklund, S. Hogmark. In manuscript. V On adhesion of work material in metal forming, M. Hanson, S. Hogmark, E. Coronel, D.H.E. Persson. Accepted for publi- cation in International Journal of Microstructure and Materi- als Properties. VI On adhesion and metal transfer in sliding contact between TiN and austenitic stainless steel, M. Hanson, N. Stavlid, E. Coronel, S. Hogmark. Wear, in press. The author’s contribution The author has performed the major part of planning, experimental work, evaluation and writing of all included papers except Paper III, where the author has performed the experimental work and minor part of planning, evaluation and writing. Contents 1 Introduction..................................................................................................7 1.1 Aim of the thesis ..................................................................................7 1.2 The tribological problem......................................................................7 1.2.1 Tribology in general and why to study it......................................7 1.2.2 Adhesion, material transfer and galling........................................8 1.2.3 Metal forming .............................................................................11 1.2.4 Materials difficult to form ..........................................................12 1.2.5 Tool steels...................................................................................14 1.2.6 Coatings applied to forming tools...............................................15 1.2.7 Lubrication in forming operations ..............................................16 1.3 Test methods used in this work ..........................................................16 1.3.1 Tribological testing.....................................................................16 1.3.2 Analytical techniques..................................................................18 1.3.3 Theoretical calculations..............................................................21 2 Contributions .............................................................................................22 2.1 Comparison between two test methods (Paper I)...............................22 2.1.1 Aim .............................................................................................22 2.1.2 Experimental...............................................................................22 2.1.3 Results and discussion ................................................................22 2.1.4 Conclusions ................................................................................24 2.2 The contact situation in the Load-Scanner (Paper II).........................25 2.2.1 Aim .............................................................................................25 2.2.2 Experimental...............................................................................25 2.2.3 Results and discussion ................................................................25 2.2.4 Conclusions ................................................................................28 2.3 Influence of surface roughness (Paper II) ..........................................29 2.3.1 Aim .............................................................................................29 2.3.2 Experimental...............................................................................29 2.3.3 Results and discussion ................................................................29 2.3.4 Conclusions ................................................................................33 2.4 Adhesion and friction of VN and TiN against steel compared by experiments and atomistic simulations (Paper III)...................................34 2.4.1 Aim .............................................................................................34 2.4.2 Experimental...............................................................................34 2.4.3 Results and discussion ................................................................34 2.4.4 Conclusions ................................................................................36 2.5 Influence of N-content in VN (Paper IV)...........................................36 2.5.1 Aim .............................................................................................36 2.5.2 Experimental...............................................................................36 2.5.3 Results and discussion ................................................................36 2.5.4 Conclusions ................................................................................39 2.6 Influence of the oxide on stainless steel (Papers V and VI)...............39 2.6.1 Aim .............................................................................................39 2.6.2 Experimental...............................................................................39 2.6.3 Results and discussion ................................................................40 2.6.4 Conclusions ................................................................................44 3 Conclusive summary..................................................................................45 Sammanfattning på svenska..........................................................................47 Acknowledgements.......................................................................................49 References.....................................................................................................50 1 Introduction 1.1 Aim of the thesis Adhesion, galling and related problems are well known in metal forming operations such as cutting, punching, pressing, drawing, rolling, bending, stretching etc. Almost all research performed up till now has been experi- mental, and there is a fairly good understanding of when and how galling may occur. However, there is a lack in the understanding of the detailed physical and chemical mechanisms that occur in the tool/work interface at the onset of adhesion and galling. This thesis aims to elucidate these phe- nomena through dedicated sliding tests, high-resolution electron microscopy and chemical analysis, and ab initio atomic calculations. Examples of ques- tions addressed are: Which materials are prone to galling and why? How important is the surface roughness of the tool? What can be done to the tool material to prevent galling? 1.2 The tribological problem 1.2.1 Tribology in general and why to study it The word tribology derives from the Greek words tribos, meaning “to rub”, and logos, meaning “principle or logic”. Today tribology means the study of friction, wear and lubrication. Friction and wear problems cost the society a huge amount of money each year [1-3]. If, for example, the friction inside the engine and transmission in a car can be reduced then the amount of fuel needed will of course be decreased. This leads to lower costs for the car user and also less pollution to the atmosphere, which is a huge issue in these days when the environmental problems are so highlighted. Tribology can also decrease the manufacturing costs of the car itself by making better and more wear resistant materials for the tools. If the tools do not wear down and break as quickly, then the car can be manufactured at a lower cost. Lubri- cants are often important to use to achieve an acceptable level of friction. Many lubricants, though, are hazardous to the environment and therefore the trend today is to develop surfaces, which give a low level of friction without the use of lubricants. 7 One of the first to study friction was probably Leonardo da Vinci who found that two objects of the same material and the same weight but with different nominal areas