Nanomechanical testing Bringing it into the real world. Nanoindentation Nanoscratch/nanowear High temperature Impact/Fatigue testing

Transcription

1 An Introduction to Bringing nanomechanical measurements into the real-world Nanomechanical testing Bringing it into the real world Nanoindentation Nanoscratch/nanowear High temperature Impact/Fatigue testing Dr Krish Narain, Micro Materials Ltd., Wrexham 29 th July 2004

2 Bringing nanomechanical measurements into the real-world Outline Introduction to Micro Materials, nanomechanical testing and the NanoTest system Nanoindentation Nanoscratch testing High temperature testing Nano fatigue and impact testing Conclusions Sources of further information

3 Micro Materials Innovation track record Founded 1988, based in Wales Application labs in UK, USA, Germany, Japan Worldwide support network: LOT Oriel in Europe... Aim: to become the world leader in the development and manufacture of nanomechanical testing equipment Pioneering and progressive approach:- First commercial nano-impact tester for measuring toughness and fatigue resistance First commercial high temperature nanomechanical testing stage Bringing nanomechanical measurements into the real-world

4 Micro Materials is based in Wrexham Where is Wrexham? It is in Wales, to the west of England. What is Wales famous for? Sheep, coal-mines (now all shut), leeks and rugby - and the NanoTest

5 Micro Materials Test techniques Nanomechanical testing = nanoscale testing of the mechanical and tribological properties of materials Micro Materials Technology: Nanoindentation Nano-scratch and nano-wear testing (Nanotribology) Nano-impact testing* Contact fatigue testing* Dynamic hardness testing* High temperature nano-scale testing* * = Micro Materials techniques - patents pending

6 Road-map for development of advanced materials Lab tests at development stage Nanoindentation Nano-scratch Nano-impact High temp testing Design-in reliability Mechanical properties Hardness Stiffness Fracture toughness Load support Test under industrially relevant conditions at the nanoscale Optimised performance of thin film/coating system Tribological properties Friction Adhesion Resistance to Abrasive Wear Sliding Wear Brittle fracture Fatigue wear Dynamic Loading Corrosion Durable product = Satisfied customer!

7 The rise of nanotechnology As devices become smaller, and coatings become thinner.. mechanical and tribological properties are becoming more important hence nanoindentation has become more important Source: British Library on-line database. Keyword search on nanoindentation.

8 Nanoindentation principle unloading coating coating loading substrate substrate Indentation curve No other technique provides quantitative information about both the elastic and plastic properties of thin films and small volumes force, displacement and time are recorded throughout indentation of sample by a diamond probe Beyond nanoindentation Scanning = transverse sample movement during loading Impact = sample oscillation at constant load

9 Viscoelastic Effects during Indentation Creep displacement (nm) Epoxy 250 Polyester Aluminum 50 Steel Hold time (s) Load (mn) mn/s 0.1 mn/s mn/s Hold time = 100 sec Depth (nm) Creep at constant load Creep effects as a function of loading rate Data: Courtesy Dr Raman Singh, SUNY Stonybrook

10 No thermal drift correction necessary Loading history on polymer = load then hold for 30 s Variation in loading curve and creep with loading rate displacement (nm) loading rate (mn/s) after before creep 1. After 30s hold period at maximum load depth is the same in very slow and fast tests 2. Only an instrument with negligible thermal drift could perform these tests, with loading rates varying by x300

11 The NanoTest pendulum Bringing nanomechanical measurements into the real-world Advantages of the pendulum include large samples possible calibrated contact load high temperature stage sample oscillation (impact) options such as pin-ondisk wear testing and 2D levelling stage symmetrical indents scratching in high stiffness direction

12 NanoTest platform system a flexible nanomechanical property testing centre... 2 loading heads Nano - 10 µn mn Micro N - 20 N 3 modules Indentation Scanning Impact 10 options including High temp testing Continuous compliance Pin-on-disk wear Microscopes/AFM 3D imaging MT head Repositioning to 0.5 µm NT head Transfer stage (indenter/microscope) Microscope Stage Assembly +Z +X +Y

13 Indenter characteristics Low compliance True depth sensing Low thermal drift (without need to use rings) High stability High sensitivity to indent<10nm reguarly No interferometer for calibrations Scheduling ability - for AUTOrun Ease of Use Good vibration isolation Capture raw data Scratch in stiff direction of indenter Expandable and upgradeable Uniform loading on all sides of indenter don t want to balance springs or be subject to piezo errors Frame, load, depth and diamond area calibrations. Uniform frame compliance vs load Load resolution <50nN Max depth 200 micron (with high load option Option to auto load cal between indents Full analysis software Break-out points as standard

14 Indentation: mapping (1) How homogeneous is my coating? An example of nanoindentation as a QA tool rapid, automatic scheduling of arrays of indentations - 10,000 points per single run - or 100 scratches

15 NanoTest software - Mapping Mechanical Properties Stainless steel plasma-carburized at 450 deg C Hardness Elastic modulus Elastic recovery Good correlation between H and E Large areas with slightly different properties Original microstructure of steel responsible

16 Indentation: Case study Quantitative measurement of the mechanical properties of thin films Comparison of load ranges Technique SPM NanoTest MicroTest Hardness Applied Force nn-µn 10 µn-500 mn 100 mn - 20 N N-kN Si wafer nickel plating passivation layer Al pad Aim: determine the hardness and modulus of top layer in IC bond pad without substrate influence In collaboration with Wolfson School of Mechanical and Manufacturing Engineering, Loughborough Uni, UK

17 Depth-profiling with the load-partial unload technique 1 quick-and-easy experiment at a single point: 20-cycle load-partial-unload Depth controlled nm Comes as standard with basic Indentation module coating Hardness coating + substrate constant hardness decreasing hardness Elastic modulus 1/10 film thickness Modulus: extrapolation to zero-depth produces rapid and quantified variation in hardness and modulus with depth

18 Plasma-polymerised Coatings The mechanical properties of thin, soft coatings can only be tested by nano-scale materials testing (nanoindentation, Nanotribology, nano-impact) Aim: to determine the mechanical properties of thin plasma polymers on aluminium Plasma polymerisation forms polymer networks where the cross-link density depends on deposition conditions Can we use nanoindentation to optimise the deposition parameters? Low power Higher power Collaborative research between MML and Corrosion and Protection Centre, University of Manchester Institute of Science and Technology (UMIST), UK.

19 Depth profiling with the load-partial-unload technique Plasma-polymers deposited at 100 W and 25 W power 100 W 25 W 25 W 100 W 20 cycle load-partial-unload experiment takes 30 mins

20 Plasma-polymerised Coatings Nanoindentation revealed clear differences in mechanical properties with coating deposition conditions Deposited at 100 W Hardness = 0.7 GPa Modulus = 10 GPa Deposited at 25 W Hardness = 0.4 GPa Modulus = 15 GPa (compare - polyester with 50 % crystallinity has H ~ 0.28 GPa, Modulus ~ 3.5 GPa so plasma-polymers are harder and stiffer than highly crystalline thermoplastics) nanoindentation provides quantitative hardness and elastic modulus values and shows how coating properties can be optimised Nanoindentation testing of plasma-polymerised hexane films B.D. Beake (MML), S. Zheng (MML), Morgan Alexander (UMIST) Journal of Materials Science vol. 37 (2002) in press.

21 Mapping hardness and modulus Nanomechanical properties of burnt polyurethane foams in resin z z y y Modulus (GPa) Hardness (MPa) optical image Nano-mechanical properties of heterogeneous, multi-phase soft samples can be quantitatively mapped

22 MicroTest pendulum Coil Ceramic Capacitor plates Indenter

23 MT 10 micron indentations into Al

24 MicroTest 20 micron indentations into Al Note consistent values of reduced modulus at 10 and 20 µιχρο

25 MicroTest 6.4N indentations into W Reduced modulus lit value = 320 GPa Is equivalent to lit value of Young s modulus of 410 Despite poor sample quality (see loading curves) still v. accurate

26 Nano-and Micro-scratch test principle Sample motion during loading makes nano-scratch tests possible transverse sample motion with XYZ stage loading coating substrate 1. Force, displacement, friction, acoustic emission and time are recorded throughout the scratching of a test sample by a diamond probe 2. Can test much thinner coatings and more local scratch behaviour than conventional scratch test

27 Scanning module: Nanoscratch testing Two main types of scanning experiment providing different information. Single ramped load scratches at a critical load (Lc) failure occurs this can be a measure of adhesion strength Constant load multi-pass scratches - resistance to sliding/abrasive wear

28 Nanoscratch/Nanotribology Key advantages of the NanoTest for nano-scratch testing Scratching occurs in high stiffness direction for pivot Direct calibration of tangential (frictional) forces possible Ramped load scratch test 1. Low load scan 2. Ramped scratch 3. Final low load scan On-load deformation Off-load deformation Critical load Friction forces Acoustic Emission Optical Microscopy

29 Carbon films on Si as protective overcoats for hard disk, MEMS Precise determination of Critical load (Lc) for film failure Friction force data Displacement data Microscopy Nanoscratching of thin hard ta-c films on Si for MEMS Friction Track end 50 µm Depth 100 µm

30 Micro-scratch testing Critical load is a function of 1) deposition conditions 2) coating thickness Substrate temperature effects on the microhardness and adhesion of diamond-like thin films, E Martinez, MC Polo, E Pascual and J Esteve, Diamond and Related Materials 8 (1999)

31 Nanowear testing Nanowear testing of ceramic composites Load ramp used in multi-pass scratch test 5 x 400 mn scratches then final topography scan at 0.2 mn Scans 1-5 Scan 6

32 Nanowear testing Nanowear testing of ceramic composites Zirconia/Mullite Alumina/Zirconia Zirconia/Alumina ~1 µm wear depth ~2 µm wear depth ~3 µm wear depth Clear differences in nano-/micro- scale wear resistance between different ceramic composites Correlates to nanoindentation hardness

33 2 different PET samples - clear differences in nano-scratching wear with processing history... Nanotribology dplast dtotal extent of ploughing differences in elastic recovery (dp/dt) Evaluate sliding wear resistance of different coating formulations Biaxially drawn PET film - 50% crystalline dplast dtotal Uniaxially drawn PET film ~ 30% crystalline BD Beake (MML) and GJ Leggett (UMIST), Polymer 2002, 43,

34 Conventional nanoscale testing techniques provide part of the solution Nanoindentation mechanical properties (hardness, modulus, creep) Nanoscratch tribological properties (resistance to abrasive/sliding wear) But All material properties are temperature-dependent Materials often fail by fatigue not overload

35 Nanomechanical testing at high temperatures Horizontal loading configuration has key advantages for drift-free high temperature testing heat flows upwards away from electronics Nanoindentation and nano-scratch testing to 750 o C Thermal drift minimal

36 Nanoindentation of solgel coating on Si 4.2 µm solgel coating - spin coated onto Si and cured at 350 deg. C 20 µm spheroconical indenter Modulus drops with temperature Reduced modulus solgel coating on Si as function of temperature Er [GPa] depth [nm] 100C RT Data courtesy of Philips Research, Netherlands

37 Nanoindentation of Si(111) At room temperature Si(111) undergoes phase changes Nanoindentation Parameters:- Loading rate = 1.67 mn/s Hold period at maximum load = 5s Unloading rate = 0.56 mn/s Pop-out during unloading Phase changes Si-I diamond-type to Si-II β-tin on loading to Si-XII and Si-III on slow unloading What happens at higher temperatures?

38 High temperature nanoindentation of Si(111): slow unloading 29 deg. C 200 deg. C 100 deg. C 300 deg. C

39 Thermal barrier coatings Nanoindentation of EB-PVD TBC (Zirconia/8wt% yttria) 25, 500 and 750 degrees C Heterogeneous columnar coating complex indentation response even at RT Probability distribution functions can be used to determine results affected by porosity and natural scatter Sapphire indenter mounted in Mo stub was used for 750 degree indentations 3 curves at 750 deg. C Fracturing during loading Clear fracturing during loading Minimal drift at 90% unloading J.R. Nicholls, S.A. Impey, R.G. Wellman, A.G. Dyer (all Cranfield University) and J.F. Smith (Micro Materials), ICMCTF 2003 Aerospace critical that the high temperature mechanical properties of TBCs are well understood at the nanoscale

40 Thermal barrier coatings Hardness and modulus of TBCs decrease with temperature Hardness [ GPa ] Youngs Modulus [ GPa ] Hardness [ GPa ] R.T. (polished) 500 C (calculated) 750 C (polished) Youngs Modulus [ GPa ] R.T. (polished) 500 C (calculated) 750 C (polished) Linear (R.T. (polished)) Linear (500 C (calculated)) Linear (750 C (polished)) Standard Normal Distribution Standard Normal Distribution Hardness Room Temp ± 1.04 GPa 500 C 4.15 ± 0.74 GPa 750 C 2.89 ± 0.49 GPa Reduced Modulus Room Temp ± GPa 500 C ± GPa 750 C ± GPa

41 Nano-impact testing The need for dynamic testing Materials can fail by fatigue not overload so optimisation based on nanoindentation/scratch may be insufficient for applications where materials are exposed in service and/or in processing to fatigue wear or erosive wear (impact wear) Dynamic nanomechanical tests (nano-impact and contact fatigue) have been developed by Micro Materials to address this problem

42 Impact Nano-impact testing - simulating fatigue wear and failure 2 different methods Sample oscillation Pendulum impulse impact High frequency oscillation High cycle fatigue Accurately controlled impacts Known energy to failure Wear mechanisms

43 1N load repetitive contact testing reveals clear differences. Collaboration with Ito Tecnologia Cerámica, Castellon, Spain Impact at high load = Contact fatigue testing A and C fracture easily but B and D do not fracture within 500s Can we correlate with fracture toughness data? Can we correlate with microstructure?

44 Effect of microstructure on impact performance Coating B Does not fail in impact test Coating C Fails quickly in impact test small needle-like crystals aid impact resistance larger rounded crystals do not help impact resistance Collaboration with Ito Tecnologia Cerámica, Castellon

45 Hardness and Young s Modulus did not vary Scratch testing frustrated by high surface roughness Impact testing of ceramic coatings: comparison fracture toughness from SEM Collaboration with Ito Tecnologia Cerámica, Castellon Correlation with fracture toughness data from SEM Low depth change = high fracture toughness Impact resistant samples had high fracture toughness Time-to-failure Change in Probe Depth measures of resistance to brittle fracture Micro-impact testing: a new technique for investigating fracture toughness BD Beake (MML), Maria Jesus Ibanez Garcia (ITC Spain) and JF Smith (MML), Thin Solid Films (2001)

46 Time-to-failure Impact results on thin hard multilayer coatings on glass Short time-to-failure Long time-to-failure Repetitive impacts at the same position Sharp probe to induce fracture quickly Monitor depth vs. time failures are very clear Long time to failure = more tough, durable

47 MEMS: nanostructured Si and SiO 2 Fracture and fatigue wear by Nano-impact testing Unimplanted SiO 2 1 x N cm -2 implanted SiO 2 Damage regimes in the impact test: 1 = before impact 2 = plastic deformation 3 = slow crack growth (fatigue) 4 = abrupt failure and material removal 5 = further slow crack growth 1 impact every 4 s in these tests Fatigue resistance from time-to-failure Ion-implantation improves toughness BD Beake (MML), J Lu, Q Xue, and T Xu, (all Lanzhou Institute of Chemical Physics) Proc FMC8 2003

48 Fatigue and Fracture Wear of ta-c films 80 nm on Si 80 nm on Si 60 nm on Si 5 nm on Si Damage mechanism in the impact test: before impact - plastic deformation - slow crack growth (fatigue) - abrupt failure and material removal - further slow crack growth time-to-first-failure to rank impact resistance some plastic deformation of the substrate does occur (depth at failure)

49 DLC: is it tough enough for your application? Diamond-like-carbon (DLC) has high hardness and low friction so it is being considered for many applications But its fatigue properties have not been fully tested this is particularly important as It is prone to poor adhesion It has been considered as an inert coating for biomedical devices The NanoTest is being used to investigate the toughness and durability of DLC coatings to fatigue wear with the nano-impact facility

50 Impact failure of 550 nm DLC film on Silicon Coating debonding - adhesion failure Abrupt depth change at failure > film thickness CVD Coating Deposition RF Power Coating fracture cohesive failure Depth change at failure less than film thickness Nano-impact shows how deposition conditions influence coating performance Time-to-failure Failure mechanism BD Beake et al, Diamond and Related Materials, 11, 1606, 2002

51 Carbon coating much tougher than DLC MICRO Impact cube corner indenter Nano-impact testing reveals fatigue differences on coatings of the same hardness DLC coating on tool steel Carbon coating on tool steel Coating failure Multiple coating failures depth vs. time impact plot for multilayered DLC coating at 1mN short time-to-failure depth vs. time impact plot for multilayered carbon coating at 1mN long time to failure

52 Mapping variations in high-strain rate deformation Grids of impacts to determine differences in toughness/ductility Toughness map for ABS 25wt% rubber 21 Mapping of fatigue properties across crab shell 18 nm position (microns) Impact depth (nm) position (microns) position (microns) position (microns) At this highly localised scale the ductility varies with distribution of micron/sub-micron sized rubber particles in the ABS matrix Applications in Milling Prediction Nano-scale ductility of crab shell varies across the shell Finer mesh sizes can be used to investigate this behaviour at much smaller scale Collaboration in progress with University of Maryland

53 Indentation: viscoelastic materials Testing the viscoelastic properties of thin films and small volumes requires the ability to access a wide range of strain rates The NanoTest system has far greater strain rate choice than other systems because 1. Ultra-slow loading, long creep tests etc, are possible due to excellent thermal stability (~ nm/s) 2. Very high strain rates accessible use nanoimpact

54 Impact behaviour: brittle and ductile materials Repetitive impact tests on brittle and ductile materials More ductile Less ductile Little plastic deformation before failure Clear fracture event(s) Time-to-failure characterises impact resistance Focus on ability to absorb energy More plastic deformation = more ductile Less plastic deformation = less ductile

55 Nano-impact ductile materials Nano-impact of Rubber-modified ABS Polymer 1 impact every 7 s; 5 mn impact force; spherical test probe Incorporation of 25 % rubber leads to greater depth change on repetitive impact at the same position

56 Fatigue and Fracture Wear of ta-c films Procedure developed for analysing fracture behaviour Sort initial time to failure in individual tests into ascending order Plot time to failure vs. probability of the sample failing in that time Use time for failure probability of 0.5 to rank impact resistance Fracture resistance of 80 nm ta-c films 1 Probability of fracture = 0.5 at 75 s Probability of fracture Impact time (s) Probability of fracture within 300 s = 0.9 A key advantage of nano-scale impact is the possibility of repeat testing at different locations

57 Impact behaviour of coatings on M42 tool steel 1 mn impact load 5 mn impact load Failure probability at time t failure probability at time t time to failure (s) time to failure (s) Failure probability at time t mn impact load time to failure (s) Red = 1 Blue = 2 Green = 3 coating1 poor coating 2 good Coating 3 good at low load

58 Bringing nanomechanical measurements into the real-world Conclusions 1. Nanoindentation is fast becoming an essential tool in the optimisation of the mechanical and tribological properties of thin coated systems and advanced materials, for applications where hardness and stiffness are important. 2. The pendulum arrangement has key advantages for reliable scratch testing. Scratching occurs in high stiffness direction for pivot and direct calibration of tangential (frictional) forces are possible. 3. Nano-scratch and nano-wear tests can accurately reveal differences in coating adhesion and wear resistance of coatings and bulk materials. This information can be used to aid materials processing and coating design.

59 Conclusions New materials testing techniques impact/fatigue testing and high temperature nanoindentation testing - have been developed to extend the capability of nanoindentation instruments Important since coatings are subjected to fatigue and extremes of temperature in service Development of these techniques is a notable advance enabling testing under contact conditions that more closely simulate those in service for the first time Test results can therefore be used with greater confidence to optimise the mechanical properties of coatings and surface treatments for specific applications Bringing nanomechanical measurements into the real-world

60 Acknowledgements Dr Jim Smith (Micro Materials) Dr Stephen Goodes (Micro Materials) Rob Parkinson (NEWI, UK) Prof John Nicholls and co-workers (Cranfield Uni, UK) Dr Jinjun Lu and co-workers (LSL, Lanzhou, China) Dr Nathalie Renevier (Teer (now at UCLAN), UK) Dr Rego and co-workers (MMU, UK) Dr Daniel Lau (NTU, Singapore) Philips Research (Eindhoven, Netherlands) Further information High temperature testing TCS Associate Rob Parkinson NEWI/Micro Materials Nano-impact testing Dr Nigel Jennett Project Leader on NPL Project MPP2.2 Nano-impact

61 THANK YOU FOR LISTENING HOW TO FIND FURTHER INFORMATION: micromaterials.co..co.uk references customer profiles application notes