Hard Coatings and Their Application on Cutting Tools

Coating Tool Hard Coatings and Their Application on Cutting Tools Assoc. Prof. Dr. Halil ÇALIŞKAN Bartın University Faculty of Engineering Department of Mechanical Engineering

Cutting process Rough machining Middle rough machining Cutting tools (inserts) Finishing 2

The effect of cutting parameters on tool life Extended Cutting speed-lifetime Formula T C k x y 0 Vc f a Depth of cut, a p [mm] k x y The most significant parameter on tool life is cutting speed, V c. Feed, f [mm/rev] Cutting speed, V c [m/min] 3

Cutting zone temperatures The rake angle, geometry and feed play an important role in the chip formation process Removing heat from the cutting zone through the chip (80%) is a key issue The rest of the heat is usually evenly distributed between the workpiece and the tool. 4

The effect of hard coating on chip formation 5

The development of cutting tool material The effect on end-user productivity A new insert generation New generation coatings Functional gradients Thick alumina coating Indexable inserts First coated inserts 6

Cutting material development Development of cutting tool materials Min. (log) Carbon Steel High Speed Steel Cemented Carbide Coated Carbide Inserts + Geometries New Cutting Tool Materials Cermet Ceramic cbn Diamond 7

Terminology of Hard Coatings thin film the most general term thinkness: monolayers (ultrathin) to several 100 µm (thick) coating has a protective function to the substrate hard coating main property high hardness for protection against wear thickness: several µm chemically: mainly transition metal nitrides and carbides layer a thin film may consist of more layers thickness: several nm to several 100 nm film substrate 8

Basic motivation for hard coatings We want to: prolong the lifetime of tools reduce the consumption of lubricants enhance the productivity enhance the product quality enable the machining of new materials Applications: cutting tools cold and hot forming tools plastics processing tools components (machine parts) Coating Tool example: drilling of aluminium/carbon fiber composite (uncoated/diamond coating) 9

Hard coatings WC/Co Kaplama The coatings: increase wear resistance provide a wear resistat surface with a tough substrate protect the substrate from thermal effects protect the substrate from chemical effects increase toollife increase productivity give a beautiful color, and make the wear visible Requirements: high hardness (at high temperature) low wear rate low friction coefficient chemical inertness low thermal conductivity good adhesion to the substrate ecologically acceptable suitable coating process 10

Basic ideas: (Plasma) Surface Engineering to modify the surface of the material while leaving the bulk intact to combine the high toughness of substrate material with high hardness of coating bare material covered by a coating surface modified surface modified + covered by a coating (duplex) 11

(Plasma) Surface Engineering Tribological contact A: workpiece B: coating C: substrate D: coating surface (+ lubricant) E: interface coating/substrate Quality of the tool: 15%: geometry 15%: substrate 70%: coating 12

(Plasma) Surface Engineering Surface modification Microstructural Thermal Induction hardening Flame hardening Arc hardening Laser hardening Electron beam hardening Mechanical Deep rolling Sand-blasting Laser sand blasting Chemical Difüzyon Nitriding Plasma nitriding Nitrocementation Cementation Carbonitriding Vanadizing Boronizing Aluminizing Siliconizing Chromiding Bluing Implantation (Plasma immersion) Ion implantation 13

(Plasma) Surface Engineering Deposition of a thin film From solid From liquid From gas Thermal CVD Plasma spray Electrochemical Classical Flame Electroless Low-temperature Detonation Plasma electrolytical Metal-organic Arc HVOF (High Velocity Oxy-Fuel) Cladding Plating Laser PA-CVD PVD Sputtering Evaporation 14

(Plasma) Surface Engineering (birleştirme) 15

Basic concepts of thin film design Basic idea film: functional property (hard, conductive, reflective...) substrate: structural property 16

Single layer vs multilayer single-layer coating (simplified) single-layer coating (reallistic) toplayer (native oxide) main part transition layer (interface) substrate other features: - inhomogenieties - vertical gradient - lateral gradient multilayer coating - thickness of layers, periodicity - properties of the film as a whole - properties for each layer type - conditions at the interfaces 17

The effect of multilayered design Layers prevent the propogation of crack through coating. 18

From deposition to application level 1 deposition construction of the apparatus parameters applied bias voltage too low level 2 yapısal özellikler chemical composition, microstructure, crystal structure, thickness, topography high porosity level 3 macroscopic properties level 4 application transport: electrical, thermal conductivity chemical: oxidation, corrosion resistance mechanical: hardness, adhesion, stress, friction too low adhesion too low lifetime 19

Deposition methods of hard coatings Chemical Vapor Deposition (CVD) PACVD Physical Vapor Deposition (PVD) Hibrid techniques Surface preperation 20

Chemical Vapour Deposition (CVD) basics 21

CVD Chemical Vapour Deposition Yeni kesici takım malzemeleri Kesici uçlar + Geometriler TiCl 4 N 2 Kaplamalı Karbür Sinterlenmiş karbür Al 2 O 3 CO 2 Karbon Çeliği Yüksek Hız Çeliği TiCl 4 CH 3 CN H 2 Coatin thickness: 2-12 μm The human hair: approx 75-80 μm Process temperature: approx 900ºC Process duration: 30 hours 22

advantages Chemical Vapour Deposition - excellent adhesion, higher thickness - uniform thickness on complicated geometries - possible to coat large tools disadvantages - High temperature! - additional heat treatment necessary - tolerance problems - rough surface - ecologically problematic modifications Metal-organic CVD (MO-CVD): halogenides metal-organic compunds Plasma-assisted/enhanced CVD (PA-CVD / PE-CVD): use of plasma 23

CVD coating of inserts Chemical Vapour Deposition TiN Al 2 O 3 The most common CVD layers today are TiN, Ti(C, N) and Al 2 O 3 TiCN provides flank wear resistance TiCN Al 2 O 3 provides temperature protection (plastic deformation resistance) TiN provides easy wear detection and nice cosmetics 24

The advantages with CVD coatings The ability of making thick coatings Ability to make uniform coating thickness Very good adherence to the carbide substrate The very good wear resistance Possibility to make oxide coatings 25

Plasma-assisted chemical vapor deposition 26

Plasma-assisted chemical vapor deposition

Vacuum basics 28

Plasma basics Plasma is partially ionized gas. It contains atoms, ions and electrons. Widespread industrial applications: - deposition of thin films - activation and cleaning of surfaces - sterilization in medicine... plasma in a sputtering apparatus: filament It enables chemical reactions at low temperature, synthesis in non-equilibrium conditions. In most cases it needs vacuum. Target 29

Physical Vapour Deposition (PVD) basics

Physical Vapour Deposition (PVD) basics 31

Physical Vapour Deposition (PVD) basics 32

Physical Vapour Deposition (PVD) types

PVD coating process Electron beam evaporation flament target 34

Physical Vapour Deposition (PVD) types 35

PVD coating of inserts Physical Vapour Deposition Proses temperature: approx. 500ºC Coating thickness: 2-6 μm 37

Sputtering techniques

Sputtering techniques 41

PVD coating of inserts Physical Vapour Deposition PVD provide good edgeline toughness and it is tougher than CVD coatings PVD coatings can maintain a sharp cutting edge PVD can be used on brased tips PVD can be used on solid carbide tools The most common PVD layers today are TiN, Ti(C, N), TiAlN,TiAlCrN and now also aluminium oxides 42

PVD vs. CVD coating process - Thinner coating - Sharper edges - Tougher - Thicker coating - More wear resistant - Thermal resistant 43

The coating of a modern turning grade Structure and build-up of the coating layers and substrate Al 2 O 3 Coating for chemical and thermal wear resistance TiCN MTCVD coating for mechanical wear resistance Functional gradient For optimized hardness and toughness Cemented carbide Plastic deformation resistance 44

The effect of hard coatings on cutting tool performance! 45

Periodicity of multilayers 2-fold rotation 3-fold rotation 48

Periodicity of multilayers 1-fold rotation 2-fold rotation 3-fold rotation 49

Hybrid techniques

Readily coatable materials - Heat treatable steels - Tool steels - Austenitic steels - Precipitation hardened steels - Structural steels - Nitrided steels (after pre-treatment) - Cemented carbides - Nickel and titanium alloys Conditionally coatable materials - Cast iron (lamellar graphite is better) - Chromium- and nickel-plated metals Tool materials (only for light duty as adhesion between the galvanic plating and the base material is limited) - Copper alloys (cleaning is complex) - Aluminium alloys (low coating temperature required; limited stress resistance) - Ceramics (must be electrically conductive or metallised) Not coatable materials - Sintered metal with open pores (not vacuum-compatible) - Plastics (not high-temperature resistant and not electrically conductive) Choice of the substrate material Tool steel / cemented carbide / ceramic materials Tool steel tempering temperature is critical! For most PVD above 500 C: 51

Surface preparation Chemical cleaning - ultrasound bath - proper choice of detergents - rinsing with water, drying with hot air Lab hygiene - low concentration of dust - proper choice of materials in the lab - handling of clean tools Quality control - inspection before deposition - inspection after deposition - documentation - use of test samples - tolerance limits 52

Surface preparation Ion etching - done in-situ - DC, RF or pulsed plasma (argon) - 0.1 µm of material removed - cleaning of hydrocarbons, oxide layer 53

The effects of hard coatings on cutting performance 54

Cutting forces Lower cutting forces with the coated tools! (Lu et al., 2014) 55

Surface roughness Better surface quality with the coated tools! (Fukui et al., 2004) 56

Residual stress Lower tensile residual stress with the coated tools! (Davim, 2010) 57

Tool life Higher tool life with the coated tools! (Çalışkan et al., 2013) 58

Some properties of hard coatings 59

References 1. Lu, L.; Wang, Q.-m.; Chen, B.-z.; Ao, Y.-c.; Yu, D.-h.; Wang, C.-y.; Wu, S.-h.; Kim, K. H. Microstructure and cutting performance of CrTiAlN coating for high-speed dry milling. Transactions of Nonferrous Metals Society of China 2014, 24 (6), 1800-1806. 2. Fukui, H.; Okida, J.; Omori, N.; Moriguchi, H.; Tsuda, K. Cutting performance of DLC coated tools in dry machining aluminum alloys. Surface and Coatings Technology 2004, 187 (1), 70-76. 3. Davim, J. P. Surface integrity in machining. Springer: 2010; Vol. 1848828742. 4. Çalışkan, H.; Kurbanoğlu, C.; Panjan, P.; Čekada, M.; Kramar, D. Wear behavior and cutting performance of nanostructured hard coatings on cemented carbide cutting tools in hard milling. Tribology International 2013, 62 (0), 215-222. 75

In preperation of this presentation, it was benefited from the presentations of Dr. Miha Cekada from Jozef Stefan Institute and Sadvick Company. 76