Introduction to Instrumented Indentation Testing (IIT)

Transcription

1 Introduction to Instrumented Indentation Testing (IIT) Innovation Center Oak Ridge, Tennessee Pierre Morel

2 OUTLINE 1. Instrumented indentation testing Theory 2. MTS Instruments technology 3. Test knowledge

3 IIT Procedure Apply a specific, quasi-static or dynamic, load-time history on a diamond indenter Measure the displacement-time response of the sample Use these data to extract certain mechanical properties based on analytical models Hardness, Young s modulus, stress-exponent for creep, storage modulus, loss modulus, etc.

4 IIT Procedure Apply a specific, quasi-static or dynamic, load-time history on a diamond indenter Measure the displacement-time response of the sample Use these data to extract certain mechanical properties based on analytical models Hardness, Young s modulus, stress-exponent for creep, storage modulus, loss modulus, etc.

5 Load history Approach detect the point of contact zero load (P), displacement (h) and time (t) Load Detect limit (P, h, or t) Hold (15-20 seconds) Unload (80-90%) Hold for thermal stability check Unload (100%) Load (mn) 0 Time (s)

6 IIT Procedure Apply a specific, quasi-static or dynamic, load-time history on a diamond indenter Measure the displacement-time response of the sample Use these data to extract certain mechanical properties based on analytical models Hardness, Young s modulus, stress-exponent for creep, storage modulus, loss modulus, etc.

7 Result outputs Output from various control signals and sensors from the beginning of the approach until the indenter leaves the surface of the sample. P (V) h (V) t (s) Data at this point is representative of both the instrument and the specimen response.

8 Indentation test Load Displacement

9 Load- displacement curve S = dp dh P max Load (mn) Slope = S Displacement (nm)

10 Load-displacement behavior Aluminum, typical of soft metallic behavior, shows very little displacement recovery upon unloading Fused silica, typical of ceramic behavior, shows large elastic recovery upon unloading Load (mn) Load (mn) 30 Aluminum Fused silica Displacement (nm)

11 IIT Procedure Apply a specific, quasi-static or dynamic, load-time history on a diamond indenter Measure the displacement-time response of the sample Use these data to extract certain mechanical properties based on analytical models Hardness, Young s modulus, stress-exponent for creep, storage modulus, loss modulus, etc.

12 Separating Sample / Instrument response Determine the actual point of contact Absolute zero point for P, h and t Apply calibrations (P and h) Correct for instrument compliances Load and displacement Correct for thermal instabilities Now you have a load-displacement curve that is representative of the materials response to the indenter!

13 IIT, what we re after! 300 H and E at the maximum Load or Displacement S = dp dh P max Load (mn) Slope = S Displacement (nm)

14 Important relationships The unloading curve follows a power law P = αh t m Contact stiffness is the slope of the unloading curve S = dp dh t P max

15 Accommodating deformation For an ideally plastic indentation, h c h t h t = h c INDENTER SAMPLE e.g. Cu INDENTER For an elastic/plastic indentation, h c < h t h t h c SAMPLE e.g. Al 2 O 3 Contact depth is determined from the displacement, load, and contact stiffness h c = h t ε P max S

16 IIT Procedure Apply a specific, quasi-static or dynamic, load-time history on a diamond indenter Measure the displacement-time response of the sample Use these data to extract certain mechanical properties based on analytical models Hardness, Young s modulus, stress-exponent for creep, storage modulus, loss modulus, etc.

17 Hardness & Young s modulus Hardness is the mean pressure the material will support H = P A Young s modulus is calculated from the composite response modulus, E r 1 π E r = β 2 S A Though not shown explicitly here, both H and E require load, depth and stiffness for calculations E r 1 ν = Ei 2 i 1 ν + E s 2 s 1

18 Berkovich geometry (diamond tip) Three-sided geometry gives a sharp tip Residual indentation shape is material dependent Fused Silica Nickel Aluminum alloy

19 Contact area and the area function The tip function for the ideal Berkovich tip A = 24.56h c 2 Experimental tip function Arbitrary form Coefficients determined experimentally A = 24.56h c i=0 C i h c 1 2 i

20 Indentation Obstacles to overcome Properties as a continuous function of depth Viscoelastic behavior We need another way to determine the elastic contact stiffness, S Constant strain rate experiment The Continuous Stiffness Measurement technique (CSM)

21 Strain-Rate Effects Constant loading rate Hardness varies greatly with depth due to changing strain rate Constant strain rate Hardness is constant with depth when the strain rate is held constant Hardness (GPa) Indium Maximum load of 10 mn 1 sec loading 10 sec loading 30 sec loading Constant strain rate 0.1 (sec -1 ) Displacement (nm)

22 Constant Indentation Strain Rate Five strain rates Hardness is constant with displacement Hardness varies with strain rate Hardness (GPa) Indium Constant indentation strain rates 0.1 (sec -1 ) 0.05 (sec -1 ) 0.01 (sec -1 ) (sec -1 ) (sec -1 ) Displacement (nm)

23 Continuous Stiffness Measurement technique - force oscillation Nominal Force, P/P = Constant 8 Load (mn) Nominal Force Excitation Force Time (seconds) Load (mn) Time (seconds)

24 CSM - Elastic & Viscoelastic Elastic Viscoelastic Response displacement (nm) φ = 0 φ = Excitation force (µn) Response displacement (nm) Excitation force (µn) Time (milliseconds) Time (milliseconds)

25 Dynamic model C D E F S K f C K s C i B A Mass = m A. Sample B. Indenter Column; mass=m C. Load Application Coil D. Indenter Support Springs; Stiffness=K s E. Capacitive Displacement Gauge; Damping Coefficient=C i F. Load Frame; Stiffness=K f =1/C f

26 CSM - experiments The excitation force (F) is continuously adjusted such that the corresponding displacement amplitude (h) remains constant at 1 nm We control F, measure h, and monitor the phase angle between the two ( φ ) using a frequency specific lock-in-amplifier S = 1 1 ( ) F h cosφ K s mω 2 K f 1 Cω = F h sin φ C Iω

27 Dynamic stiffness on fused silica 0.25 Stiffness (mn/nm) Stiffness from unloading slope Stiffness from CSM Load (mn)

28 Elastic modulus on fused silica 100 Elastic modulus (GPa) Using CSM stiffness Using stiffness from unloading slope Surface Penetration (nm)

29 Paints (example: finger nail polish) 0.2 Hardness (GPa) Nail Polish 1 Nail Polish 2 Nail Polish Penetration into test surface (nm )

30 Low-K materials for ICs Continuous measure of modulus with indentation depth Each curve is an average of ten indentations Thin overcoat makes itself obvious Elastic modulus (GPa) from surface: 100 nm SiON/ 1.2 μm polymer/ Si from surface: 1.2 μm polymer/ Si Surface penetration (nm)

31 Problems with time-dependence Conventional stiffness determination unreasonable 150 Polymer thin film Negative stiffness??? Large amounts of timedependent deformation Large time-dependent recovery Load (mn) Time-dependent deformation Time-dependent recovery Displacement (nm)

32 CSM calculations - polymers Storage modulus, G, and loss modulus, G, are determined from the contact stiffness and the material damping, respectively. G = E 3 = π 6 S A Where: S: Contact stiffness A: area of contact Cω: Contact Damping G = E 3 = π Cω 6 A

33 Storage and Loss Modulus on Polyurethane Storage Modulus, E' (MPa) Indentation Berkovich Indentation Flat Punch DMA Tension Loss Tangent, tan δ Indentation Berkovich Indentation Flat Punch DMA Tension Frequency, f (Hz) Indentation Berkovich Frequency, f (Hz) Loss Modulus, E" (MPa) Frequency, f (Hz) Indentation Flat Punch DMA Tension Indentation with flat punch and Berkovich Comparison with DMA testing

34 IIT and CSM In conclusion, Apply a load measure the corresponding displacement, stiffness, and damping Isolate the materials response Correct for instrument compliances and thermal instabilities Use analytical models to extract the mechanical properties of interest as a continuous function of the indenter s displacement into the sample: H, E, E, and E MTS patented CSM technique is absolutely critical for accurate and meaningful characterization of time dependent materials and near-surface properties.

35 Technology

36 Nano Instruments Products Indentation Tensile

37 Nano Mechanical Actuating Transducer Coil/magnet assembly Leaf spring Capacitance gauge Lateral force probe Indenter Sample

38 NMAT Technology Separation of Displacement and Load measurement Zero force on the center plate of capacitive gage Linear behavior in Load application Less error on load application No risk of lateral motion during indentation

39 Testing Knowledge 1. Surface Find 2. Surface Approach 3. Scratch testing

40 Surface Find Test Segment Target location for Indent Delta X for surface Find Delta Y for surface Find

41 Approach Test Segment Load vs. Displacement slope Displacement

42 Scratch test Penetration Displacement Along scratch path Pre-Scratch Profile Scratch Post-Scratch Profile

43 Scratch test results

44 Thank you Let s get working on the instrument!