APPLICABILITY OF RESULTS OF LABORATORY ANALYSIS IN PRACTICE

Transcription

1 Department of Material Science and Technology APPLICABILITY OF RESULTS OF LABORATORY ANALYSIS IN PRACTICE Antonín Kříž This presentation is available at:

2 cro i M W ea rr ss e r dn a h tion c i r F ur o i v a beh barrier Thermal Co he s ive an ce Cra ck p ropa gati on Appearance Adhesion pr o pe rt es ist ies of n o i at c i f i Mod rial e mat The individual properties should combine appropriately to provide reliable performance. 2

3 Why thin films on cutting tools? Their purpose is to prevent premature failure of the cutting edge This is why thin films are required to possess specific properties. Effects of these properties must be evaluated with regard to requirements laid on the thin film-substrate system. 3

4 Correlations between laboratory analysis and the technological test of cutting edge durability in the cutting process 4

5 Film thickness measurement xy a 2R 5

6 The condition of the ball crater also provides information on the adhesive-cohesive properties of the film Ball crater - TiN film Ball crater - TiAlN (naco) film Ball crater - TiAlSiN film 6

7 Fractographic examination of thin film-substrate systems -196 C 7

8 GD-OES measurement depth concentration profiles The crater effect and redeposition of certain elements have adverse impact on the accuracy of depth concentration profile curves 8

9 Impact of the crater effect on the results of measurement Depth concentration profile TiAlSiN multi-layer 9

10 Substrate degradation revealed by GD-OES method W Ti Co C N Al 10

11 Nanoindentation measurement 11

12 ISO : 2007 (E) standard contains an algorithm covering individual situations that may occur during hardness testing. 12

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14 Suitable location for indentation 14

15 Data on additional properties obtained from nanohardness testing of the thin film-substrate system 12 F Elas tic deform ation energy [nj] Energy used for deformation Plas tic deform ation energy [nj] 10 Elastic deformation Energy [nj] 8 4,616 4,52 5,265 5,48 3,777 3,666 3,145 3,004 3,656 5,304 5,375 5,81 5,898 5,762 TiAlSiN (20 C) TiAlSiN (400 C) naco (20 C) naco (400 C) naco (800 C) Plastic deformation 0 TiN (20 C) TiN (400 C) Indentation microhardness Plastic Elastic 45 h ] a P [G Source: Ladislav PEŠEK, NOVÁ ISO NORMA NA STANOVENIE MECHANICKÝCH VLASTNOSTÍ POVLAKOV POMOCOU INŠTRUMENTOVANEJ INDENTAČNEJ SKÚŠKY TVRDOSTI, In: Proceedings of Vrstvy a Povlaky, HIT [GPa] TiN (20 C) TiN (400 C) TiAlSiN (20 C) TiAlSiN (400 C) naco (20 C) naco (400 C) naco (800 C) 15

16 Adhesive-cohesive behaviour of the thin film-substrate system Indentation method Original evaluation scale Updated evaluation scale 16

17 Quantification of adhesive-cohesive properties using image analysis F = 1492 N Indentation depth = 92.5 μm K5/A3 17

18 TiN K1/A6 TiAlSiN K5/A3 TiN II K1/A1 TiAlN K2/A5 TiAlSiN multilayer K2/A4 18

19 Adhesive-cohesive behaviour of the thin film-substrate system tested in tear-off test Strong bond between TiN film and M6C-type carbides, which are part of the microstructure of tool steel 19

20 Scratch test 20

21 Only a handful out of the many types of failure occurring during scratch testing are directly tied to the adhesion bond quality. The remaining types of failure result from the plastic deformation of substrate or from fracturing within the film. Fully exposed substrate Ls ~ 56N 21

22 Effects of pre-deposition substrate conditioning Blasting Failure at critical load LC2 ~ 36N Failure at the load of ~ 30N TiAlN + DLC film Substrate no changes Tumbling in special abrasive grit Failure at the load of ~ 28N 22

23 Tribological properties Pin-on-Disc Method: Pin-on-Disc Load: 1-10N Diameter: Rotation speed: 10 to 500 rev/min. Ball material: steel, Si3N4, ZrO2, Al2O3,WC.. f e n to ric F Tribological test plot 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 Wear track length [km] 23

24 What kind of friction coefficient is reported in literature? St ic t a Dynamic 24

25 Friction coefficient measurement Steep changes in the friction force may be due to variation in the actual contact force Fn Changes in friction force? 1,0 0,9 0,8 0,7 0,6 0,5 0,4 Which friction coefficient value is correct? 0,3 f e n to ric F 0,2 0,1 0,0 0,00 0,01 0,01 0,02 0,02 0,03 0,03 Wear track length 25

26 Friction coefficient measurement Actual relation between contact and friction forces Contact force Friction force (correlates with contact force) Friction coefficient as the ratio between friction force and actual load μ = instant friction force/instant load μ = instant friction force/nominal load Friction coefficient as the ratio between friction force and nominal load Difference between instant and nominal loading force in μ calculation 26

27 Impact of roughness on the friction coefficient tick ý k. třefor ní př i r ůzné drs nos ti Kinetic friction Kine coefficient different roughness values 0,62 0,62 0,61 Koef. tření 0,61 0,60 0,60 0,59 0,59 0,58 0,58 Ra = 6,23 Ra = 4,53 Impact of surface roughness on the kinetic friction coefficient. Equal parameter values and identical materials were used for both cases. The only difference between specimens was their roughness. 27

28 Wear measurement Calculating certain characteristics describing the film s wear resistance, such as the wear coefficient, requires that the depth and actual profile of the wear track are known. The wear track depth is typically measured using a contact profilometer. The profile is measured in several locations of the track. The results are susceptible to distortion 0.81µm The profilometer record does not reflect the actual wear Substrate visibly exposed, thin film thickness of 4µm For these reasons, a method other than conventional contact profilometer measurement had to be used 28

29 Wear measurement Measurement tool Advantages Scales Simple and inexpensive Disadvantages Readings are affected by the presence of foreign material Contact profilometer Simple, relatively fast Provides data on separate lines on the surface, low accuracy Laser scanning profilometry Very accurate and relatively fast Costly Optical profilometer Simple, rapid Not usable for intricate shapes On-line measurement of distance between the arm and the specimen Continuously recording changes The change may not always be in agreement with the change in wear We use Olympus LEXT3000 laser confocal microscope for measuring the wear track in collaboration with the research centre FORTECH. 29

30 Wear measurement methodology We use Olympus LEXT3000 laser confocal microscope for measuring the wear track in collaboration with the research centre FORTECH. Correct setting of the measuring length is of importance. The shorter the measuring length, the better the match between the recorded and the actual profile. 30

31 Another application of the PIN-on-DISC tester For the simulation of a cutting process to be as faithful as possible, a method was derived from pin-on-disc testing, where the disc represents the machined material and the abrading pin acts as a tool, sliding on the material. In this configuration, conditions similar to those on a cutting tool flank can be achieved. Tested system Sliding edge Tracks on the machined surface 31

32 Fretting test Friction properties can be evaluated using fretting test. It consists in test ball or tip polishing through the film while oscillating at low frequency. The direct outcome of measurement is a friction coefficient curve (fretting coefficient) depending on the number of cycles. 32

33 Fretting tester 33

34 TiN Real-world example 500 cycles, 1 N load, PIN AISI ,000 cycles, 2 N load, PIN Si3N4 Run PIN material Load No. of cycles 1 AISI steel 1N Si3N4 2N 1,000 3 Si3N4 10 N 1,000 4 Si3N4 10 N 2,500 Fretting test parameters 1,000 cycles, 10 N load, PIN Si3N4 2,500 cycles, 10 N load, PIN Si3N4 34

35 Fretting test 5,000 cycles; 11.4 N load; pin material: tungsten carbide 0,7 0,6 0,5 TiAlSiN 0,4 TiAlN+DLC 0,3 TiALN f e n to ric F 0,2 0, Number of cycles 35

36 TiAlSiN film PIN: tungsten carbide TiAlN + DLC film TiAlN film 36

37 Comparison between fretting test and PIN-on-DISC test 5,000 cycles, PIN tungsten carbide Fretting test Film Load [N] - F Friction coefficien t F PIN-on-DISC Load [N] - T Friction coefficient T Substrate exposure F Substrate exposure T TiAlSiN local local TiAlN complete did not occur TiAlN +DLC did not occur did not occur 37

38 Cyclic impact test arrangement Formation of the impact crater: the loss of the material's ability to undergo plastic deformation results in various forms of degradation (cracks, work-hardened areas) Monitored parameters of the impact crater include its depth, width and state of surface Formation of the impact crater occurs in approximately three stages : Initially, massive plastic deformation occurs, The growth of the crater ceased mainly due to greater contact area of the crater and the ball. Areas in the vicinity of the crater walls exhibit loss of plasticity, Crack initiation and chipping of work-hardened regions occur. This mechanism leads to further growth of the crater 38

39 Inclined cyclic impact test Inclined cyclic impact testing at a specific angle can be used for simulating the shear stress component and for assessing the adhesive properties of thin films. This testing method also simulates stress conditions induced by milling. Variation in the tool contact angle during milling J.C.A. Batista et. al.:impact testing of duplex and non-duplex (Ti,Al)N and Cr.N PVD coatings. Surface and Coatings Technology (2003) K.-D. Bouzakisa,et. al.: The inclined impact test, an efficient method to characterize coatings cohesion and adhesion properties. Thin Solid Films (2004)

40 Low-frequency impact tester - low frequency of impact - about 0.8 Hz - the impact energy of the indenter can be changed by changing the drop height - the indenter on the specimen can be set accurately to be perpendicular to the surface, depending on the height of the specimen < 10 N max. 65 Weight Pin holder Pin Coating 4 6 mm - a weight of up to 1,000 g - indenters 4 6 mm ball - easy to determine the impact energy (as it is proportional to the potential energy of the indenter) Substrate 40

41 High-frequency impact tester - the indenter is attracted by an electromagnetic coil - up to 50 Hz - accelerometric and acoustic emission measurements - the holder with the indenter are returned to their initial position by a spring force - the test piece is mounted on a rotating and extending stage 41

42 The use of acoustic emission for evaluation of cyclic impact testing response Piezoelectric acoustic emission sensor mounted by the specimen Instrument for procesing acoustic emission data Acoustic event evaluation software 42

43 Impact crater shape in Cr-DLC film changing with number of blows d5000 = 1.6 µm, d10000 = 1.8 µm, d13000 = 3.2 µm, d14000 = 10.2µm [Ing. Šimeček] 43

44 Impact crater examples TiN film at 20 C, F = 10 N upon: a) 1,000, b) 2,500, c) 5,000 blows TiAlN film, F = 10 N upon: a) 1,000, b) 2,500, c) 5,000 blows 44

45 Planned design modifications for field applications Multi-axis loading Loading with the presence of liquid Opening a crack Testing under special climatic conditions 45

46 Application-specific tests Rotation tribological test The rotation speed of the polypropylene pin was 3,000 rev/min. The test was split into several time intervals ending in 5th,15th, 30th, 60th and 90th minute. Detailed view of the wear track with no film, where individual types of wear are marked, upon 30-minute test 46

47 Wear track on specimen with no film upon 90-minute test. Confocal micrograph. Wear track on specimen with TiAlN+DLC film upon 90-minute test. Confocal micrograph. The rotation tribological tests brought a very important finding: glass fibres distributed randomly throughout polypropylene matrix have no substantial effect on the surface damage mechanism. No traces of considerably degrading abrasive wear have been detected in any test run. 47

48 Monitoring the damage of the film, whose integrity was compromised by a specific network of purposefully made scratches. The damage consisted in the polypropylene film tearing off. F Coated sample Network of scratches (made by a scratch tester) 48

49 Condition of thin film deposited on cutting tools Documenting the state of tool by means of Alicona profilometer Discontinuous thin film on the cutting edge of a tool 49

50 Thermal load on tool placed in furnace with oxidizing atmosphere at 800 C 50

51 Documenting the state of the cutting edge by means of confocal microscope SEM Confocal microscope

52 Special test based on technological testing techniques Evaluation of cutting forces, vibration, acoustic signals and temperature in the turning process Thermal imaging system ThermaCAM SC2000 Spectral sound-level meter CNC lathe Kistler dynamometer Vibration monitoring system 52

53 Correlating cutting process data yields additional findings on the behaviour and properties of the thin film-substrate system ] [B lv s re p d n u o S M easu remen t 0 4 3, f [H z] Multi spectral noise analysis Cutting force curves Film No. 4 0,3 0,25 0,2 [V U iy s te In ] 0,15 0,1 0, T ime Vibration intensity Cutting edge and chip temperature curves 53

54 Conclusion The choice of analytical techniques must be governed by the type of application of the system. The amount of time available and purpose of the analysis must be taken into account. The approach to inspection of a proven type of film will be different from seeking new applications for an existing film or from developing a new system. Available equipment and staff play their role as well. Despite that, even laboratories lacking special or expensive instruments may offer a number of tests and analyses which, upon appropriate and sensitive evaluation, yield valuable information. The key is the comprehensive approach, effort to seek correlations and consulting experts from other sites. Too often have we specialist teams and expensive equipment at hand, yet we do not know what our colleagues in the laboratory, company or university next door are working on. 54