] [ P. Eh. Hovsepian, A.P. Ehiasarian. Nanotechnology Centre for PVD Research, Sheffield Hallam University, UK

Transcription

1 [ Nanoscale Multilayer PVD Coatings Deposited by the Combined HIPIMS/UBM Technology for Applications in Aerospace, Automotive and Biomedical Industries. P. Eh. Hovsepian, A.P. Ehiasarian Nanotechnology Centre for PVD Research, Sheffield Hallam University, UK

2 [ The paper discusses advanced nanoscale multilayer PVD coatings dedicated to serve applications in aerospace automotive and medical industries. In all these sectors the demand for coatings for protection of special grades of automotive or aerospace alloys against environmental attack as well as the demand for dry high speed machining of both very hard or very soft often called "sticky" materials is ever growing. CrAlYN/CrN coatings utilising a nanoscale multilayer structure with a typical bi-layer thickness of 4.2nm have been developed to protect light- weight Ti-45Al-8Nb alloys known as γ-tial against wear and aggressive environmental attack at high temperatures. Thermo gravimetric quasi isothermal oxidation tests carried out in air at 8500C revealed that after 1000 hours exposure CrAlYN/CrN coated γ-tial alloys showed four times smaller weight gain compared to the uncoated material. In sulphidation tests after 1000 hours exposure to aggressive H2/H2S/H2O atmosphere the CrAlYN/CrN protected γ-tial alloys showed reduced weigh gain by factor of four as compared to the uncoated substrate. High temperature pin-on-disc tests revealed that the friction coefficient is temperature dependent. However, unlike most of the nitride PVD coatings, which tend to increase their friction coefficient with temperature, CrAlYN/CrN reduces its friction coefficient from 0.56 at room temperature to 0.4 at 6500C, which demonstrates the excellent high temperature tribological behaviour of the coating.

3 PVD Coatings, Design Strategy Application Tailored Smart Material Selection Coating Structure Selection Coating Deposition Technology Selection

4 [ Monolithic Columnar Nanoscale Multilayer Structure, BF TEM image Structure, BF TEM image 3.2 nm The concept of "superhardening" introduced by James Koehler, University of Illinois in TiAlN, University of Linköping CrN/NbN, Sheffield Hallam University Q=G A -G B / G A +G B Q- critical stress to move a dislocation across the interface G A, G B, shear modulus of material A and B

5 Superlattice hardening effect U. Helmersson et al, J. App. Phys. 62, (1987) M.Shinn,et al, J. Mater.Res.7 (4) (1992)

6 Influence of the "superlattice" period on the hardness of the TiAlN/CrN coating. I.Wadsworth et al, Surf. and Coat. Technol , (1997).

7 Mechanical failure in monolithically (a) and superlattice (b) grown coatings Q. Luo, et al. Wear, (1999), 74.

8 Industrial Scale Hauzer HTC 1000/4 PVD Coater at SHU a) XSEM of CrN/NbN Coated knife blade b) BF XTEM showing the nanoscale multilayer structure on the tip of the blade, P.Eh. Hovsepian et al, Surf. and Coat. Technol. 133, (2000).

9 Δ SHU Nanoscale Multilayer Coating Family CrAlYN/CrN TiAlN / VN CrN / NbN C / Cr CrAlN interface TiAlN interface CrN interface CrN interface SUBSTRATE SUBSTRATE SUBSTRATE SUBSTRATE Δ = 4.0 nm High temperature oxidation resistant Dry machining, automotive and aero engines. Δ = 3.2 nm High hardness low friction Al and Ti cutting Δ = 3.4 nm Corrosion and Wear resistant Δ = 2 nm Low friction - tribological

10 [ TiAlCN/VCN * Nanoscale Multilayer Coatings Dedicated to Machining of "Sticky" Alloys Used in Aerospace, Automotive and Biomedical Industries * A. P. Ehiasarian, P. Eh. Hovsepian, UK Patent: GB B,

11 Alticut EC Project Demonstrator selection Automotive component [ Engine head Fiat 1.9 JTD Material: AlSi9Cu1 Machining operations to be considered for the component are: Face milling Drilling Tapping Thread milling and/or roll tapping CENTRO RICERCHE FIAT Hauzer Techno Coating P V D / P A C V D T E C H N O L O G Y

12 Alticut EC Project Demonstrator selection Aeronautic component 1 [ A wingbox rib of a typical Airbus wing Material: Aluminum 7010-T7651 CENTRO RICERCHE FIAT Hauzer Techno Coating P V D / P A C V D T E C H N O L O G Y

13 Introduction 2: Problem Material reactions at the cutting interface, BUE High cutting forces High surface roughness Tool life time Solution Inert tool surface Low coefficient of friction Low coefficient of friction, Long lasting tool geometry High wear resistant surfaces Good coating is: Inert, low friction and highly wear resistant

14 Introduction 2 : State-of-the-art, ( DB-AG report): M. Lahres et al., Surf. and Coat. Technol 91 (1997) Diamond and DLC coatings are classified as suitable coatings due to the ability of Carbon to inhibit reactions with the work piece material: no BUE formation. Me-N and uncoated CC are classified as unsuitable coatings : great BUE formation. SHU Experience: TiAlN/VN combines superhardeness with exceptionally low coefficient of friction due to formation of V 2 O 5. In cutting Al - alloys, similar or better performance when compared to DLC coatings.

15 THE STRATEGY BEHIND MeVCN/VCN To exploit the synergy of V+C by combining them in a nanoscale multilayer structured PVD coating to achieve a Low Friction and Highly Wear Resistant tool surface.

16 TiAlCN/VCN Coating Structure Δ= 2.2 nm 200 nm Low angle XRD Pattern of TiAlCN/VCN Superlattice Coating Low mag. BF XTEM Image, Overall Structure

17 Δ= 2.2 nm BF XTEM Image of TiAlCN/VCN and TiAlN/VN Nanoscale Multilayer Structured Coatings Base Layer TiAlCN/VCN TiAlN/VN

18 Novel High Power Impulse Magnetron Sputtering (HIPIMS) Technology The HIPIMS discharge in action. A powerful source for highly ionised metal plasmas used for surface pre treatment and deposition of high quality coatings. Patented for surface pre treatment by SHU in USA and Europe: A.P. Ehiasarian, P. Eh. Hovsepian, W.-D. Münz, US Pat. US , (2005), EP (2001).

19 Interface structure and chemistry after HIPIMS etching with V + substrate Concentration, at% Atomic% Al K Atomic% Ti K Atomic% V K Atomic% Cr K Atomic% Fe K Atomic% Ni K Atomic% Cu K 10 coating Distance from interface, nm

20 TiAlCN/VCN Coated Cutting Tools for Machining of Al and Ti Alloys

21 MILLING TEST Evaluation criteria: Flank wear 0.23mm, or Radial (tip) wear 0.50mm 24,000 rpm, 1,886 m/min 0.33 mm/rev, 2-flute Depth 4 mm, width 2 mm

22 0.3 Flank Wear / No. of Passes in Al 7010-T 7651 Alloy 25 mm dia, HSS, 2- Flute End Mill, Vc:1884 m/min, Ap: 4 mm, Ae: 2 mm, Vf: 0.33 mm/rev. Flank Wear (mm) No. of Passes Uncoated TiAlCrYN DLC TiAlN/VN TiAlCN/VCN 1 pass: m

23 SEM images of the tool surface after dry machining Al 7010-T 7651 alloy TiAlN/VN after 1000 m cutting length TiAlCN/VCN after 8000 m cutting length

24 Life time of TiAlVCN/VCN coated turning inserts in machining of forged Ti acetabular cups (orthopaedic implants) at SYMMETRY Medical inc., UK [ Number of Components turned per turning tip. Constant surface speed of 60 m/min, Feed of 0.15 mm/rev, water based coolant. Coated tip Uncoated tip

25 Carbon accumulation at the columnar boundaries as well as vertical segregation to form a lateral phase at the interfaces of the nanolayers STEM Bright-Field image Z-contrast image Growth direction

26 Layer Composition, EELS [ STEM Image and Line Scan C C TiAlVN C N V Ti

27 XTEM image of TiAlN/VN coating after wear test showing formation of highly lubricious V2O5 tribo-film

28 [ Nanoscale Multilayer Coatings for High Temperature Protection Against Environmental Attack

29 HIPIMS-ABS Days, Sheffield Hallam University, July, 2005 A project strongly driven by industrial needs [ hot corrosion resistance lifetime wear resistance titanium aluminides (γ-tial) mechanical properties cost savings oxidation resistance 3

30 Nanoscale Multilayer CrAlYN/CrN Deposited by HIPIMS/UBM, (Pat. pending, H10245PGB, ) Ti- free formula, Y- stabilised interface by Y + and Cr + ion etching using HIPIMS CrAlN interface SUBSTRATE CrAlYN/CrN nanoscale multilayer, (Δ = 4.7 nm) deposited by HIPIMS or UBM or combined HIPIMS/UBM technique.

31 Coating-Substrate Interface Microstructure STEM Bright Field STEM Z-Contrast CrAlYN/CrN CrAlN γ-tial High density Y and Cr implanted zone 5nm

32 Local Epitaxial Growth in HIPIMS Lattice Imaging Atomic Resolution TEM image of the interface SAD Patterns CrAlN Coating CrAlN Coating Interface γ-tial Substrate γ-tial Substrate

33 Local epitaxial growth on large areas due to HIPIMS pre treatment of the substrate Growth defects originating from droplets during arc etching, ABS technology Homogeneous contrast along interface signifies local epitaxial growth on substrate (steel) grain Critical Load L c [N CrAlYN/CrN arc etch 65 CrAlYN/CrN HIPIMS etch

34 XTEM images of the structure of CrAlYN/CrN deposited by various techniques: a) HIPIMS/HIPIMS and b) HIPIMS UBM. CrAlYN/CrN nanoscale multilayer CrAlN base layer substrate a) HIPIMS/HIPIMS b) HIPIMS/UBM

35 High Temperature Phase and Hardness Stability of CrAlYN/CrN [

36 High Tempearture Tribological Behaviour of CrAlYN/CrN

37 High Temperature Oxidation and Corrosion Resistance of CrAlYN/CrN 3 Weight Gain, mg/cm CrAlYN/CrN γ-tial uncoated Al2Au TiAlCr Weight gain after 1000 hours exposure to air at 850C Weight gain after 1000 hours exposure to H 2 /H 2 S/H 2 O at 750C

38 Thermogravimetric data for various coatings from quasi-isothermal tests carried out 850C in air

39 Dry High Speed Milling of Hardened, (58 HRC) High Speed Steel

40 As-deposited and coated end mill after heat treatment: 850 C, 1 hour

41 Tool Life Time in A2, (58 HRC) Steel, 8 mm CC Ball Nose End Mill, Speed 385 m/min TiAlCrYN TiAlN (50:50) Extreme TiAlN/CrN TiAlSiN CrAlYN/CrN, Arc Etching CrAlYN/CrN, HIPIMS Etching Life time, mins

42 NP gas turbine buckets and OSVAT engine valves coated with CrAlYN/CrN nanoscale multilayer coating at SHU

43 Rolling dies and pushing rods for diesel engines coated with CrAlYN/CrN nanoscale multilayer coating.

44 Conclusions: The utilisation of the nanoscale multilayer concept and employment of advanced deposition methods such as HIPIMS provide a powerful tool for production of new generation application tailored PVD coatings. CrAlYN/CrN and TiAlCN/VCN have shown promising results as protective coatings used in aerospace and automotive engine applications. Both coatings are close to industrialisation.

45 Acknowledgements The hard work and dedication of all the researchers at the Nanotechnology Centre for PVD Research at Sheffield Hallam University in UK is highly acknowledged. The long years of cooperation with the Centre for Microanalysis of Materials, University of Illinois and Lawrence Berkeley National Research Labs, Berkeley CA is gratefully acknowledged. The research on CrAlYN/CrN nanoscale multilayer coatings utilising HIPIMS pre treatment have been carried out within FP6 Integrated Project INNOVATIAL, n NMP3 - CT The financial support of the EC and the intellectual support of all partners are deeply acknowledged.