Functional Gradient Hardmetals: From Research To Application

Transcription

1 New Materials - B2B/B2R&B, 21.Nov.2011, Bratislava/SK Functional Gradient Hardmetals: From Research To Application Walter Lengauer Vienna University of Technology PHYSICAL METALLURGY GROUP Prof. W. Lengauer web: walter.lengauer@tuwien.ac.at 1

2 Content Introduction: Physical Metallurgy Research Group / TU Vienna Introduction to the field Hardmetals, cermets: types and application examples Graded materials, functional gradient hardmetals Preparation & Production of FGHMs Sintering, gas-phase interaction, Microstructure Industrial processes Application & Testing Cutting tests Diamond-coated hardmetals, PVD-coated hardmetals Summary & Outlook 2

3 Introduction: Organisation Physical Metallurgy Research Group in the frame of TU Vienna Vienna University of Technology (founded 1815) - 1/15 Faculty of Technical Chemistry - 1/8 Institute of Chemical Technologies and Analytics - 1/4 Branch Chemical Technologies - 1/5 Research Group of Physical Metallurgy - 1/6 TU Vienna, historic building at Karlsplatz 3

4 Physical Metallurgy Research Group Research Fundamentals Borides, carbides, nitrides: Refractory compounds Diffusivity, phase equlibria, solid-state properties Research Hardmetals/Cermets/Powders Sintering technology, nitrogen sintering, gas-phase analysis Functional Gradient Hardmetals, Cermets TiC/Ti(C,N) and WC powder synthesis Alternative binder phases in hardmetals Binder-phase analysis and alloying Ultra-fine hardmetals and doping Publications 130 scientific papers (cit./paper: 12x, ISI -Thomson-Reuters) 60 technical and proceeding papers 4

5 Physical Metallurgy Research Group Students Since 1995: 23 Doctoral theses, 24 diplomas, 3 Post Doc s 28 Guest students from D, F, I, CZ, SK, ARG Cooperations Industry Producers of hardmetals, powders, ball bearings, paper rolls (A, D, CH, L, USA, IL, S, FIN) Academic TU Bergakademie Freiberg, Inst. of Materials Science, Prof. Rafaja CNRS-UMR 6538, IFREMER and Univ. Brest, Mr. Bohn INSA and Univ. Rennes I, Dr. Guillou, Dr. Tessier 5

6 Introduction to the field: Hardmetals and Cermets Microstructure of hardmetals and cermets Schematic structure hardmetal cermet hard phase hard phase binder phase binder phase Hardmetals and cermets are composite materials with a hard phase embedded in a ductile binder phase preparation: liquid-phase sintering of pressed powders at C 6

7 Hardmetals and Cermets Microstructure of hardmetals and cermets Real structure hardmetal cermet WC (Ti,Ta,Nb)C core-rim structure 5µm Trend towards fine-grained hardmetals and cermets 7

8 Hardmetals Grain size depends on application Classification of hardmetals along the WC grain size >6.0 µm 6.0 µm 2.5 µm 1.3 µm 0.8 µm 0.2 µm <0.2 µm extra coarse grained coarse grained medium grained fine grained submicron grained ultra fine grained nano grained mining structural milling drilling turning drilling (electronics) surface engineering 8

9 Hardmetals Heavy thermo-mechanical/chemical load upon use 9

10 Hardmetals Onsets for hardmetal design (surface, near surface) Various fields of R&D Substrate near surface Chipbreaker Geometry Cutting Edge Coating 10

11 Coating of Hardmetals and Cermets Coating Coated inserts, microstructural cross section multilayer coating interface hardmetal substrate Problems: (1) abrupt change of properties at the interface (2) restricted thickness of coating, emergency properties need for tailoring the hardmetal substrate 11

12 Graded Materials Stresses in materials Macroscopic interface vs. graded structure upon loading layers: stress pile-up at interfaces gradient: smooth stress distribution preparation of graded near-surface structures in the hardmetal substrate, compatible with coating but also of use in uncoated grades 12

13 Preparation and Production of FGHMs Functional gradient hardmetals (FGHMs) Sintering in reactive atmosphere: nitrogen, carbon monoxide Boundary conditions: use of existing methods and equipment N 2, CO powder formulation sintering process sintering furnaces coating processes graded structure 5-150µm compatible with entire process route of hardmetal manufacturing 13

14 FGHMs - Thermodynamics Nitrogen equilibrium pressure p>p EQ : indiffusion, p<p EQ : outdiffusion ln p(n 2 ) p>p EQ in-diffusion 2a. p EQ 2b. 1. sintering at p=p EQ 2. p and T adjustment for 2a. in-diffusion or 2b. out-diffusion 1. p<p EQ out-diffusion T L temperature A D: different composition 1,2: different pressure 14

15 FGHMs Regular Gradient Outer nitride enrichment regular gradient Hardness vs. microstructure HV0.025 / GPa graded structure ~30µm regular gradient Depth / µm hardness at surface similar to coating smooth decrease towards interior 15

16 FGHMs Inverse Gradient Hardmetal with inverse gradient 1. TiCN depletion in surface zone upon sintering 2. internal nitridation 1. high T, low p: N outdiffusion 2. low T, high p: N indiffusion N 2 N 2 soft & hard & tough brittle Ti(C,N) enrichment below surface 16

17 FGHMs Regular/Inverse Gradient, Kinetics Regular and inverse gradient Tailored cutting edge and faces Layer growth Cutting edge Ti(C,N), free hardness 60 d² / µm² free WC+Co Ti(C,N) regular 10 interior Annealing time / h inverse WC+Co toughness Ti(C,N), interior 17

18 FGHMs Industrial Manufacture Industrial manufacturing of graded hardmetals Sintering furnace (high pressure) and sintering tray 18

19 FGHMs Industrial Manufacture Industrially manufactured cutting inserts Grades for turning and milling 19

20 FGHMs Application Examples & Testing Hardmetal with regular gradient - turning Cutting test as a function of zone thickness Depth of Crater KT / mm TTM Cutting Time / min VB max insert geometry: SNUN v c = 200 m/min, a p = 2.0 mm, f = 0.2 m/rev KT continuous turning, steel CK45N; Rm = 627 N/mm 2 20

21 FGHMs Application Examples & Testing Hardmetal with inverse gradient - milling Inverse gradients show excellent VB max behaviour wear land VB max / mm Width of Wear Land / mm 0,4 0,3 0,2 0,1 0,0 Ck45 v c = 315m/min a p = 2.5mm f = 0.2mm/Ur Tool path / m coated P25-HM 7N inverse 7N inverse + 1h 7N inverse + 5h KT VB max 21

22 FGHMs Application Examples & Testing Diamond-coated FGHMs Cutting inserts FGHM and microstructure before coating diamond diamond coating on cutting edge, cleaved smaples graded ungraded 22

23 FGHMs Application Examples & Testing Diamond-coated FGHMs Tests with abrasives (SiC, air jet 5 bar) nozzle abrasives coating substrate time: 120s graded substrate, only traces of jet time: 100s ungraded substrate, layer removal 23

24 FGHMs Application Examples & Testing Systematic tests on various coated FGHMs - turning Continuous turning tool insert microstructure test set-up 24

25 FGHMs Application Examples & Testing Systematic tests on various coated FGHMs - turning Close inspection of the cutting edge crater depth KT 25

26 FGHMs Application Examples & Testing Systematic tests on various coated FGHMs - turning Cutting time upon VB max = 0.3mm clear outperformance of FGHMs with regular gradient (nitrogen-enriched) 26

27 FGHMs Application Examples & Testing Manufacturing performance of FGHMs - turning Stamping punches almost 100% performance increase 27

28 Summary on FGHMs Functional Gradient Hardmetals Result of a close cooperation industry research (University) From laboratory scale (thermodynamics, kinetics) to manufacture (reproducible production and application) About 10 years to enter safe and reliable industrial processes Several world-wide patents About 14 academics involved (industry + University) 28

29 Outlook Trends in substrate technology Various areas of research Fine-grained hardmetals and cermets FG cermets Replacement of WC and TaC W price: US$/kg in 1.5 years, Ta price: mobile phones Alternative binder phases Nano precipitates Unconventional routes reactive sintering, application of microwaves (debinding) FG cermet, low W content 29