1. Advanced Coatings and Surface Engineering Laboratory Surface Engineering Task Repot 2009/2/10

2. Advanced Coatings and Surface Engineering Laboratory Content Summary of the mechanical and tribological properties of CrN/AlN superlattice coatings High temperature oxidation study of CrN/AlN superlattice coatings Updates for the work of AlN ‘smart’ coatings Ready to use the Modulated pulse power (MPP) to produce the optimized coating system for the die casting dies

3. Advanced Coatings and Surface Engineering Laboratory Example of the Multilayered Superlattice Cr/Cr x N y /CrN/AlN Coatings 75-500 single layers with bilayer period from 2.5 to 20 nm 2-3 um thickness substrate CrN AlN Cr/Cr(N) graded Schematic drawing Typical multilayered structure Interface between the superlattic layers and the graded adhesion layer CrN/AlN Graded CrN Cr Bilayer period=22 nm

4. Advanced Coatings and Surface Engineering Laboratory Deposition system: – Pulsed closed field unbalanced magnetron sputtering (P-CFUBMS); – The Cr and Al targets were installed facing opposite to each other; – The targets were powered by Advanced Energy Pinnacle Plus Dual Channel Power Supply; – The substrate holder was rotated back and forth between Cr and Al targets to deposit CrN and AlN nanolayers; – The thickness of individual layer thickness were controlled by the target power density and the settle periods of the substrates facing each target. – 400-1000 W Target power; 2 mTorr working pressure, 50% N 2 flow, -50 V substrate bias Cryo Pump Stepping motor Cr Al Ar+N 2 Substrate

5. Advanced Coatings and Surface Engineering Laboratory Exaples of the TEM Micrographs Bilayer period=3 nm Bilayer period=5 nm CrN AlN

6. Advanced Coatings and Surface Engineering Laboratory Mechanical and tribological properties of CrN/AlN coatings as a function of CrN layer thickness CrN/AlN superlattice coatings exhibit greatly improved mechanical and tribological properties compared to single layer CrAlN coatings

7. Advanced Coatings and Surface Engineering Laboratory Comparison of the wear track and wear depth of single layer CrAlN coating and CrN/AlN coating Single layer CrAlN CrN/AlN superlattice Test parameters: 3N normal load, WC-Co ball, 5000 testing cycles

8. Advanced Coatings and Surface Engineering Laboratory Oxidation behavior of CrN/AlN superlattice coatings

9. Advanced Coatings and Surface Engineering Laboratory LAXRD pattern of CrN/AlN coatings with two different bilayer periods 3.0 nm 12 nm

10. Advanced Coatings and Surface Engineering Laboratory SEM micrographs of CrN/AlN coatings of different bilayer periods after annealed at different temperatures 800 o C 900 o C 1000 o C

11. Advanced Coatings and Surface Engineering Laboratory XRD patterns of CrN/AlN coating with 3.0 nm bilayer period annealed at different temperatures

12. Advanced Coatings and Surface Engineering Laboratory Isothermal oxidation test at 800 o C for different periods 60hr150hr300hr

13. Advanced Coatings and Surface Engineering Laboratory Isothermal oxidation test at 800 oC for different periods 60hr150hr300hr

14. Advanced Coatings and Surface Engineering Laboratory Hardness of CrN/AlN coatings measured after thermal annealing tests

15. Advanced Coatings and Surface Engineering Laboratory Sumarry CrN/AlN superlattice coatings exhibit further improved mechanical and wear resistance to the single layer CrAlN coatings CrN/AlN superlattice coatings also show excellent oxidation resistance both for high temperatures and long periods oxidation attack. Challenge: for complex shape dies (using MPP is a promising approach)

16. Advanced Coatings and Surface Engineering Laboratory Progresses in the work for AlN ‘smart’ coatings Dr. Fengli Wang has left ACSEL Ph.D. student Masood took over the research work on the development of AlN based ‘smart’ coatings. New Ph.D. student Ningyi Zhang will work on the other piezoelectric coating material LiNbO 3 which is also a potential ‘smart’ coating candidate.

17. Advanced Coatings and Surface Engineering Laboratory MPP™ - An Alternative HPPMS/HiPIMS Technology Modulated Pulse Power - MPP™ – High power pulse magnetron sputtering technique – Heart of technology is the Zpulser™ plasma generator  Produces a multi-step DC pulse First step – ignition of low power discharge Second step – low power discharge Third step – transient stage from low power discharge to high power discharge Forth step- high power discharge  Zpulser™ now at ACSEL

18. Advanced Coatings and Surface Engineering Laboratory MPP™ Technology Modulated Pulse Power (MPP) Provides: High ionization degree of metal species (see the plasma density) high deposition rates (for both metal and insulating films) Deposition of dense and uniform films Easy scaling up (has moderate peak power, reduced cost) Influencing film properties and structure by modulated pulse parameters (various controls) dc MPP Dc Cr MPP Cr The same power density on the target

19. Advanced Coatings and Surface Engineering Laboratory MPP System in ACSEL Hiden electrostatic quadrupole plasma mass spectrometer (EQP) Unbalanced magnetrons (100 mm x 280 mm) MPP system and EQP plasma analyzer Closed magnetic configuration Zpulser MPP generator

20. Advanced Coatings and Surface Engineering Laboratory Plasma Characterization Hiden EQP mass-energy analysis –Compared conventional DC and MPP power with closed-field unbalanced magnetrons Only used one active magnetron –Measured Mass peak intensities – 52 Cr +1 (plus isotopes), 40 Ar +1, and 26 Cr +2 Ion energy distributions – 52 Cr +1, 40 Ar +1, and 26 Cr +2

21. Advanced Coatings and Surface Engineering Laboratory Comparison of DC and MPP Positive Ion Mass Scans 52 Cr +1 40 Ar +1 52 Cr +1 40 Ar +1 26 Cr +2 Significant increase in the number of both target metal and gas ions for MPP than dc discharge Number of ions much greater for MPP than DC In MPP, number of ions increased when average-peak power increased DC sputtering P ave =3.5 kW MPP TM sputtering P ave =3.5 kW

22. Advanced Coatings and Surface Engineering Laboratory Microstructure Comparison (DcMS, PMS, MPP) f N2 =20-30% (h-Cr 2 N) DcMSPMSMPP f N2 =50-60% ( c-CrN) Zone-T columnar grainsHigh density and fine grains

23. Advanced Coatings and Surface Engineering Laboratory Wear Resistance Pin-on-disc test (3 N, 40 rpm, 5000 cycles, 1mm WC-Co ball) The COF is lower in the MPP CrN coatings than in dc and PMS CrN coatings.

24. Advanced Coatings and Surface Engineering Laboratory Using Two Pulse Shapes Working pressure: 5 mTorr Nitrogen flow rate percentage: 40% Two pulse shapes alternating (see the figures below) Substrate bias: floating 700  s (6/6), 100 Hz rep rate Duration: 1S and 3S 1500  s (6/10), 30 Hz rep rate Duration: 1S and 2S A A

25. Advanced Coatings and Surface Engineering Laboratory Video showing Modulated Pulse Power Pulse

26. Advanced Coatings and Surface Engineering Laboratory Two pulse shapes with 1s Duration 700  s (6/6), 100 Hz rep rate 1500  s (6/10), 30 Hz rep rate Denser structure with finer grains Properties:  Hardness: 28.713  1.615GPa  Young’s Modulus: 314.966  11.87GPa  H/E ratio: 0.091  COF: 0.25 P ave =0.8 kW Duration: 1S P ave =3.5 kW Duration: 1S

27. Advanced Coatings and Surface Engineering Laboratory MPP Summary Excellent ionization of sputtered species (denser coating and excellent adhesion) High rate process (Cr coating depositions) Conducted EQP analysis of MPP and DC plasmas for closed-field UBMs –Number of ions increased when average-peak power increased Many more 52 Cr +1 ions for MPP than DC Significant number of Ar ions –Average energy for 52 Cr +1 ions ~ 2eV Very small high energy tail Almost mono-energetic source of ions MPP CrN coatings prepared at a floating substrate bias exhibited denser microstructure, comparable hardness and improved wear resistance to dc sputtered CrN coatings synthesized using -50 V dc substrate bias. MPP CrN coatings deposited using multiple pulse shapes exhibit further improved H/E ratio and wear resistance, where a low COF of 0.25 has been identified.