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Laser Surface Modification of Metals and XRD Characterisation

Laser Surface Modification of Metals and XRD Characterisation. Presentation Outline. Laser surface modification. PhD Case Study. X-ray diffraction (XRD) characterisation. Residual stress calculation. Typical exam question. Material Processing Research Centre, Dublin city University.

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Laser Surface Modification of Metals and XRD Characterisation

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  1. Laser Surface Modification of Metals and XRD Characterisation

  2. Presentation Outline Laser surface modification PhD Case Study X-ray diffraction (XRD) characterisation Residual stress calculation Typical exam question Material Processing Research Centre, Dublin city University

  3. Laser Surface Modification Material Processing Research Centre, Dublin city University

  4. Laser Surface Treatment • LASER - light amplification by stimulated emission of radiation: • highly directional, coherent, and monochromatic beam of light • Laser in material processing can be used for many purposes • i.e. cutting, surface modification • Several laser surface modification methods exist: • Transformation hardening • Laser alloying/cladding • Glazing Material Processing Research Centre, Dublin city University

  5. Effects of Laser on materials Material Processing Research Centre, Dublin city University

  6. Laser System • Rofin DC-015, CO2 laser specifications: • 10.6 µm wavelength • Power capacity of 1500W • Operates in both continuous and pulsed mode • Pulse width ranges between 26µs to ~ 500ms Material Processing Research Centre, Dublin city University

  7. Laser system processing parameters Material Processing Research Centre, Dublin city University

  8. Case Study: PhD Research Material Processing Research Centre, Dublin city University

  9. Case Study: PhD Research • One in four hundred people receive hip replacement surgeries in Ireland* • Up to 250,000 annual hip replacements surgeries in USA • Approximately 20% simply being replacements of failed implants • Success rate has significantly gone up but material life is low • Typical life of an artificial hip being 15 – 20 years • Patients undergo revision surgeries throughout their lifetime • One main challenge is developing a life long artificial hip replacement • Excessive wear debris and loosening of the implant are primary causes of failure • Improving tribological properties of the implant will greatly improve its lifetime *http://www.wrongdiagnosis.com/h/hip_replacement/stats-country.htm#extrapwarning Material Processing Research Centre, Dublin city University

  10. Aims of the Study • The aim of this study is to produce surface engineered implant alloy capable of having improved tribological properties using high speed laser treatment • Using high speed laser treatment to achieve a rapid cooling rate • Rapid laser treatment can produce an amorphous structure • Advantages of laser surface engineering • Superior bonding with the substrate • Simple oxidation elimination techniques • Improved depth control and reduced distortion • Little or no sample preparation required • Less time/ energy and material required compared to convectional coating techniques Material Processing Research Centre, Dublin city University

  11. Typical Results • Topology and microstructure • LHS – Topology • RHS - cross-sectional microstructure analysis • Effects of energy fluence • 524 J/cm2 • 1048 J/cm2 • 2096 J/cm2 • Depth of processing • Overlapping • Homogeneity of treatment • Grain structure orientation Increasing Energy (a) 100 μm 50 μm (b) 50 μm 100 μm (c) 100 μm 50 μm

  12. Microstructure Analysis (a) (b) SEM cross section micrographs of samples processed using the same energy fluence (1310 J/cm2): • Titanium alloy • Stainless steel (a) (b) Material Processing Research Centre, Dublin city University

  13. Meltpool and Roughness Analysis Meltpool Analysis Roughness analysis Material Processing Research Centre, Dublin city University

  14. Laser treatment of HVOF - WC-CoCr coatings Untreated Laser treated (a) (a) & (b) Surface Topology Cross-sectional microstructure (c) (b) (c)

  15. X-ray Diffraction Material Processing Research Centre, Dublin city University

  16. X-ray Diffraction • X-rays are a form of electromagnetic radiation that have high energies and short wavelengths (on the order of atomic spacings for solids) • X-ray diffraction occurs when waves encounter a series of regularly spaced obstacle that: (1) are capable of scattering the wave (2) have spacings comparable in magnitude to the wavelength • X-rays diffraction can therefore be used for material characterisation of metal • Phase identification of metals • Determination of crystal structures • Residual stress measurements Material Processing Research Centre, Dublin city University

  17. Two parallel x-rays of wavelength λ impinging on a crystal surface at angle θ. • Parallel to the surface is a row of crystal planes, separated by distance dhkl • Assumptions: the same thing happen at the deeper planes reached by other penetrating X rays. • From simple geometry, SQ=QT= dhkl sinθ which emerges as Bragg’s Law • Interplanar spacing, dhkl Diffraction of x-rays by planes of atoms (A-A’) and (B-B’). Material Processing Research Centre, Dublin city University

  18. X-ray diffractometer T= x-ray source, S = Specimen, C = detector, and O = axis. Material Processing Research Centre, Dublin city University

  19. Diffraction pattern polycrystalline -iron Material Processing Research Centre, Dublin city University

  20. Stress Measurements Material Processing Research Centre, Dublin city University

  21. Stress Measurements • X-ray diffraction can be used as a form of uniform stress measurement • When stress is applied lattice spacings change from stress free values • measuring the change in lattice position gives strain • Consider conventional stress measurement technique – electric resistance • Strain is measured by resistance caused by extension of the gauge • In x-ray method, the strain gauge is spacing of lattice planes • Applied stress is force per unit area – if the external force is removed the stress disappears • Residual stress is the stress that persists in the absence of an external force • Residual stress causes fatigue crack resulting in failure of components Material Processing Research Centre, Dublin city University

  22. Stress Measurements • X-ray stress measurement assumes uniaxial stress • Uniaxial stress considers stress in a single direction • Consider a rod of cross sectional area A stressed elastically in tension by force F • Stress σ = F/A in y direction but none in x or z direction • The stress σy produces a strain • If the bar is isotropic the strain is related by: x-rays Material Processing Research Centre, Dublin city University

  23. XRD Stress Measurements • Back reflection x-ray measurement is used to measure strain using x-rays: • Residual stress measurements are given by: Where, • E – Young modulus • dn – spacing of planes parallel to the axis under stress • d0 - the spacing of same planes in absence of stress • ν – Poisson's ratio Material Processing Research Centre, Dublin city University

  24. Ti-6Al-4V XRD pattern Material Processing Research Centre, Dublin city University

  25. Questions Material Processing Research Centre, Dublin city University

  26. Q1. Figure 1 below shows the as-received XRD pattern for Ti-6Al-4V alloy: Calculate the peak positions (2θ) for peak 1, 2, 3 and 4 given the following: • Cu Kα(λ = 1.5405 Å) radiation system used • Order of reflection, n = 1 Material Processing Research Centre, Dublin city University

  27. Q2. Subsequent to laser treatment, shift in peak positions were observed : (b) Determine the dhkl (interplanar spacing) of the peaks given the following: (c) Calculate the residual stress σy given that: • Young modulus of Ti-6Al-4V alloy, E = 113.8 GPa • Possion’s ratio, ν = 0.342 Material Processing Research Centre, Dublin city University

  28. Additional Reading Material Determination of Crystal Structures W.D. Callister, Materials science and engineering an introduction, 5th Edition,Chp 3 Stress measurement using XRD B.D. Cullity and S.R. Stock, Elements of X-ray Diffraction, 3rd Edition, Chapter 15 Case Study: PhD research Online: Applied Physics A - Process mapping of laser surface modification of AISI 316L stainless steel for biomedical applications Online: Int. Journal of Material Forming - Surface modification of HVOF thermal sprayed WC-CoCr coatings by laser treatment

  29. Publications • Applied Physics A: DOI 10.1007/s00339-010-5843-5 • Process mapping of laser surface modification of AISI 316L stainless steel for biomedical applications • Accepted 10 June 2010 • Int. Journal of Material Forming: DOI 10.107/s12289-010-0891-0 • Surface modification of HVOF thermal sprayed WC-CoCr coatings by laser treatment • Accepted 17 June 2010 • Analysis of Microstructural changes during Pulsed CO2 Laser Surface Processing of AISI 316L Stainless Steel • Accepted for publication – Advanced Materials Research (AMR) Material Processing Research Centre, Dublin city University

  30. Formulas Question 1 Question 2 (b) (c) Material Processing Research Centre, Dublin city University

  31. Solutions Question 1 Question 2 Material Processing Research Centre, Dublin city University

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