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The Wear and Corrosive-Wear Response of Tungsten Carbide-Cobalt Hardmetals Under Woodcutting and Three Body Abrasion Conditions

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The Wear and Corrosive-Wear Response of Tungsten Carbide-Cobalt Hardmetals Under Woodcutting and Three Body Abrasion Conditions The wear and corrosive-wear response of tungsten carbide-cobalt hardmetals under woodcutting and three body abrasion conditions Submitted to the Faculty of Engineering of the University of Erlangen-Nürnberg in fulfillment of the requirements for the degree of DOKTOR-INGENIEUR by Natasha Sacks Erlangen 2002 Das Verschleiß- und Korrosions-Verschleißverhalten von Wolframkarbid-Kobalt-Hartmetallen bei der Holzzerspanung und unter Drei-Körper-Abrasivverschleiß Der Technischen Fakultät der Universität Erlangen-Nürnberg zur Erlangung des Grades DOKTOR-INGENIEUR vorgelegt von Natasha Sacks Erlangen 2002 Als Dissertation genehmigt von der Technischen Fakultät der Universität Erlangen-Nürnberg Tag der Einreichung: 19. Dezember 2002 Tag der Promotion: 31. März 2003 Dekan: Prof. Dr. Winnacker Berichterstatter: Prof. Dr. H.-G. Sockel Prof. Dr. P. Schmuki Table of Contents i Table of Contents 1 Introduction (English) ........................................................................................... 1 2 Introduction (German)........................................................................................... 3 3 Objectives .............................................................................................................. 6 4 Literature Review................................................................................................... 7 4.1 Woodcutting tool wear.................................................................................................7 4.1.1 Wood...................................................................................................................................... 7 4.1.2 Tool wear ............................................................................................................................... 8 4.1.3 Methods used to assess the blunting of the cutting edges.................................................... 8 4.1.4 Influence of force, temperature and speed.......................................................................... 10 4.1.5 Tool wear relating to the cutting of natural wood................................................................. 13 4.1.6 Tool wear relating to the cutting of synthetic wood products............................................... 15 4.2. Woodcutting tools.....................................................................................................17 4.3 Tungsten carbide hardmetals ...................................................................................18 4.3.1 Hardmetal manufacture ....................................................................................................... 18 4.3.2 Hardmetal constituents ........................................................................................................ 20 4.3.3 Porosity ................................................................................................................................ 26 4.3.4 Hardness.............................................................................................................................. 26 4.4 Corrosion ....................................................................................................................28 4.4.1 Galvanic corrosion and Stern’s rule..................................................................................... 28 4.4.2 Corrosion of cobalt............................................................................................................... 29 4.4.3 Corrosion of WC .................................................................................................................. 30 4.4.4 Corrosion of WC-Co ............................................................................................................ 31 4.5 Wear.............................................................................................................................32 4.5.1 Abrasive wear ...................................................................................................................... 33 4.5.2 Lubrication ........................................................................................................................... 36 4.5.3 Abrasive wear of WC-Co alloys........................................................................................... 37 4.5.4 Corrosive-wear..................................................................................................................... 41 4.5.5 Corrosive-wear of WC-Co alloys ......................................................................................... 43 5 Experimental Methods ........................................................................................ 45 5.1 Material Characterization...........................................................................................45 5.1.1 Investigated hardmetals....................................................................................................... 45 5.1.2 Hardmetal quality evaluation ............................................................................................... 46 5.1.3 Density ................................................................................................................................. 47 5.1.4. Magnetic saturation ............................................................................................................ 48 5.1.5 Coercivity ............................................................................................................................. 48 5.1.6 Hardness and fracture toughness ....................................................................................... 48 5.1.7 Surface roughness............................................................................................................... 49 5.1.8 Quantitative microstructure analysis.................................................................................... 50 5.2 Woodcutting tests ......................................................................................................50 5.3 Corrosion tests...........................................................................................................53 5.4 Three body abrasive wear tests................................................................................57 Table of Contents ii 6 Results.................................................................................................................. 63 6.1 Material characterization ...........................................................................................63 6.2 Woodcutting tests ......................................................................................................64 6.2.1 Cutting edge widths and wear rates in the incipient wear stage ......................................... 64 6.2.2 Cutting edge widths and wear rates in the steady wear stage ............................................ 70 6.2.3 Microstructural examination................................................................................................. 73 6.2.4 Summary of the main findings ............................................................................................. 82 6.3 Corrosion tests...........................................................................................................83 6.3.1 Microstructural examination................................................................................................. 92 6.3.2 Summary of the main findings ............................................................................................. 96 6.4 Abrasive wear and corrosive abrasive-wear tests ..................................................96 6.4.1 Comparison of the wear rates under dry, water and tannic acid conditions........................ 97 6.4.2 Comparison of the wear rates under varied tannic acid concentration ............................... 99 6.4.3 Comparison of the wear rates under varied applied normal force..................................... 101 6.4.4 Comparison of the wear rates under varying abrading wheel speed ................................ 106 6.4.5 Microstructural examination............................................................................................... 109 6.4.6 Summary of the main findings ........................................................................................... 116 7 Discussion ..........................................................................................................118 7.1 Evaluation of the wear response during the woodcutting tests ..........................118 7.1.1 Influence of the wood-tool set-up on the wear process..................................................... 118 7.1.2 Influence of the wood type on the wear process ............................................................... 119 7.1.3 Comparison between the wear response of the two hardmetal woodcutting knives......... 121 7.1.4 Comparison of the initial and the steady state wear stages .............................................. 123 7.2 Corrosion response of the hardmetals ..................................................................123 7.3 Evaluation of the wear response during the three body abrasion tests .............125 7.3.1 Evaluation of the general wear process for the investigated system ................................ 125 7.3.2 Influence of fluids on the wear process ............................................................................. 128 7.3.3 Influence of corrosion on abrasive wear...........................................................................
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