• Laser surface engineering of polymeric materials and the effects on wettability characteristics

      Waugh, David G.; Avdic, Dalila; Woodham, K. J.; Lawrence, Jonathan; University of Lincoln (Scrivener/John Wiley & Sons., 2014-12-23)
      Wettability characteristics are believed by many to be the driving force in applications relating to adhesion. So, gaining an in-depth understanding of the wettability characteristics of materials before and after surface treatments is crucial in developing materials with enhanced adhesion properties. This chapter details some of the main competing techniques to laser surface engineering followed by a review of current cutting edge laser surface engineering techniques which are used for wettability and adhesion modulation. A study is provided in detail for laser surface treatment (using IR and UV lasers) of polymeric materials. Sessile drop analysis was used to determine the wettability characteristics of each laser surface treated sample and as-received sample, revealing the presence of a mixed-state wetting regime on some samples. Although this outcome does not follow current and accepted wetting theory, through numerical analysis, generic equations to predict this mixed state wetting regime and the corresponding contact angle are discussed.
    • Modifications of surface properties of beta Ti by laser gas diffusion nitriding

      Ng, Chi-Ho; Chan, Chi-Wai; Man, Hau-Chung; Waugh, David G.; Lawrence, Jonathan; University of Chester; Queen's University; The Hong Kong Polytechnic University (AIP Publishing, 2016-03-31)
      b-type Ti-alloy is a promising biomedical implant material as it has a low Young’s modulus and is also known to have inferior surface hardness. Various surface treatments can be applied to enhance the surface hardness. Physical vapor deposition and chemical vapor deposition are two examples of this but these techniques have limitations such as poor interfacial adhesion and high distortion. Laser surface treatment is a relatively new surface modification method to enhance the surface hardness but its application is still not accepted by the industry. The major problem of this process involves surface melting which results in higher surface roughness after the laser surface treatment.This paper will report the results achieved by a 100W CW fiber laser for laser surface treatment without the surface being melted. Laser processing parameters were carefully selected so that the surface could be treated without surface melting and thus the surface finish of the component could be maintained. The surface and microstructural characteristics of the treated samples were examined using x-ray diffractometry, optical microscopy, three-dimensional surface profile and contact angle measurements, and nanoindentation test.