Laser induced surface structuring of Titanium and CFRP for structural adhesive bonding. Ante Kurtovic Airbus Group Innovations

Transcription

1 Laser induced surface structuring of Titanium and CFRP for structural adhesive bonding Ante Kurtovic Airbus Group Innovations

2 Airbus Group Innovations 2

3 Motivation 12% Composite Aluminium Steel Titanium Misc. 20% 7% 14% Composite Aluminium Steel Titanium Misc. 80% 1% 1% 6% 52% 7% 3

4 Motivation Increasing use of CFRP in aircraft! Connection between metal and CFRP 1. Challenge: galvanic corrosion between aluminium and CFRP! Use of titanium instead of aluminium How to join titanium and CFRP?! Currently connection between titanium and CFRP is realized by means of riveting 2. Challenge: high notch sensitivity of CFRP Solution: adhesive bonding! Surface preparation plays a fundamental role prior bonding Laser pre-treatment, as a new dry process, is a promising technique! 4

5 Short-pulse Laser-systems Ns-pulsed laser (25 W) Pulse width: <100 ns Wavelength: 1064 nm (IR) Pulse frequency: < 200 khz costs (total): 50 k Titanium surface pre-treatment Ns-pulsed laser (3 W) Pulse width: <20 ns Wavelength : 266 nm (UV) Pulse frequency: < 300 khz costs (total): 200 k CFRP surface pre-treatment 5

6 Laser surface pre-treatment of Titanium (Ti6Al4V) Matrixes (20mmx20mm) with 70 different laser parameters for SEM investigation. Good size for SEM Tests on metallic, ceramic and composite surfaces Investigation of the influence of different laser parameters on the structuring behavior 6

7 Laser surface pre-treatment of Titanium (Ti6Al4V) Untreated SEM magnification: x x 7

8 Laser surface pre-treatment of Titanium (Ti6Al4V) Laser treated SEM magnification: x x Nanostructured open pored surface after laser pre-treatment! 8

9 Laser surface pre-treatment of Titanium (Ti6Al4V) Increased surface area More distribution of adhesive to the surface Mechanical fixing of adhesive to the surface Oxide layer thickness of about 150 nm 9

10 Laser surface pre-treatment of Titanium (Ti6Al4V) XPS (X-Ray Photoelectron Spectroscopy): Elements Ti Al V O C N Na Cl Other Cleaned with isoprop. [at%] Laser treatment [at%] Turco 5578 treatment [at%] NaTESi treatment [at%] Chemical compound TiO 2 Al 2 O 3 V 2 O 5 Oxides/Hydroxides/ Contaminations Contaminations - Bath residues Bath residues - Contamination level reduced (C, Na, Ca, N) Wet chemical processes reveal bath residues on the surface Formation of TiO 2 on the surface 10

11 Laser surface pre-treatment of Titanium (Ti6Al4V) Wedge-Test acc. to DIN : Standardized test Exposure of samples at 95% humidity and 50 C over 1000 h Measurement of crack propagation after 0, 1.25, 24, 48, 96, 168, 336, 500 and 1000h Benchmark of laser surface pre-treatment to wet chemical pre-treatment processes Turco 5578 (alkaline etching) and NaTESi-Process (Anodising) Adhesive: FM 73 (epoxy film adhesive) 11

12 crack length [mm] Laser induced surface structuring of Titanium and CFRP for structural adhesive bonding Laser surface pre-treatment of Titanium (Ti6Al4V) Turco 5578 (etching) NaTESi (anodising) Turco 5578 / NaTESi: Higher crack growth over exposure time Partially interfacial failure Laser Laser treatment: Almost no crack propagation Cohesive failure time [h] Laser surface pre-treatment of titanium improves the long term stable durability of adhesive bonds! 12

13 Laser surface pre-treatment of Titanium (Ti6Al4V) Etching Anodising Laser TEM-Mapping-fracture Carbon (C) Nanostructure (TiO 2 ) + Carbon (C) Titanium (Ti) Oxygen(O) 25 mm Adhesive (C) penetrates into to nanostructures! 13

14 Laser surface pre-treatment of CFRP In Airbus mainly manual grinding is applied prior bonding or painting. after extreme grinding However the grinding causes several problems: operator sensitivity / reproducible quality multi curved parts thin laminates inhomogeneous resin / fiber ratio on surface after extreme grinding time consuming pollution, grinding dust in the bond shop no potential for automation Laser surface pre-treatment of CFRP is an alternative! 14

15 Laser surface pre-treatment of CFRP Surface morphology after laser pre-treatment of CFRP: Laser: UV-Laser (266 nm) Untreated UV-Laser treated Residues from the peel ply The UV-Laser removes the residues from the peel without damaging of the fibers For surface sensitive pre-treatment ns-pulsed laser systems are necessary 15

16 Laser surface pre-treatment of CFRP XPS (X-Ray Photoelectron Spectroscopy): The UV-Laser decrease the flour concentration from the peel without damaging of the fibers. P1 and P2 lead to an flour concentration below 5 at-%; the untreated surface has a concentration of about 40 at-% 16

17 Laser surface pre-treatment of CFRP G1c-Test acc. to ISO 15024:2001: Aim: Determination of fracture toughness (Mode I load) G1c: The interlaminar fracture toughness energy is the energy per unit plate wide which is necessary to produce an unit crack growth at an interlaminar crack between two plies of laminate: A ( J / m a w G C A: energy to achieve crack length the total [J] propagated crack length [J] Integration of the area of the load- Integration cross head displacement of the area of diagram the loadcross head displacement diagram 2 ) Geometry: 250 x 25 x 3 mm Adhesive: 2K System Scotch-Weld SW 9373 (3M) a: propagated crack length [mm] a: propagated w: width of crack the specimen length [mm] w: width of the specimen [mm] 17

18 Laser surface pre-treatment of CFRP G1c-Test acc. to ISO 15024:2001: Parameter: CFRP surface prior laser treatment: Fluoride based peel ply (Ref) Ageing: C / 85 %rh Adhesive: epoxy based 0 h C / 85 % rh Due to the laser treatment mainly cohesive failure in the adhesive could be observed The application of peel ply without any pretreatment leads to interfacial failure Even after ageing the laser pre-treatment leads to cohesive failure 18

19 Summary Titanium: Experiments revealed various morphologies consisting of nano-structured surfaces obtained within a particular frame of laser parameters Cleaning and activation of the surface due to laser pre-treatment Morphology after laser treatment leads to increased surface area Enhanced mechanical / chemical anchoring of adhesive Wedge test- and roller peeling test results indicated higher long stable durability of adhesive bonds with laser surface pre-treatment than Turco 5578 and NaTESi Nano-structuring of metallic surfaces (e.g. aluminium, nickel cobalt, steel, etc.) possible CFRP: Cleaning and activation of the surface due to laser pre-treatment G1c test results indicated higher long stable durability of adhesive bonds with laser surface pretreatment than untreated after peel ply removal 19

20 Thank you! This study was funded by the German Federal Ministry of Education and Research (BMBF) within the Framework Concept Research for Tomorrow s Production (funding number 02PJ ) and managed by the Project Management Agency Karlsruhe (PTKA). The authors are responsible for the contents of this publication. Ante Kurtovic Airbus Group Innovations, Metallic Technologies & Surface Engineering Munich - Germany Telephone: +49 (0) Fax: +49 (0) mailto:[email protected] 20