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See T.L.,University of Manchester | Liu Z.,University of Manchester | Cheetham S.,BAe System Operations Ltd | Dilworth S.,BAe System Operations Ltd | Li L.,University of Manchester
Applied Physics A: Materials Science and Processing | Year: 2014

Surface contaminations (originating from manufacturing processes), smooth surface, and poor wettability of carbon fiber reinforced polymer (CFRP) composite impair its successful paint adhesion. Surface pre-treatment of composite materials is often required. Previous approaches of using manual sand-papering result in non-uniform surface conditions and occasional damages to the fibres. Furthermore, the process is labour intensive, slow and can be hazardous to the workers if protections are not appropriate. This paper reports an investigation into a new surface treatment method based on laser multi-tasking surface abrading and surface cleaning/texturing for the improvement of paint adhesion. A KrF Excimer laser with a wavelength of 248 nm is used as the laser source. Significant improvement in paint adhesion has been demonstrated compared with as-received and sand-papered samples. This improvement is achieved by eliminating surface contaminants, minimizing chain scission and increasing in surface active functional groups as well as increasing in surface roughness. The former two play dominant roles. © 2014, Springer-Verlag Berlin Heidelberg.

See T.L.,University of Manchester | Liu Z.,University of Manchester | Liu H.,University of Manchester | Li L.,University of Manchester | And 3 more authors.
Optics and Lasers in Engineering | Year: 2015

This paper presents an investigation on ablation characteristics of HR4 nickel cast alloy with a Ti:Sapphire femtosecond laser (100 fs pulse width, 800 nm wavelength and 1 kHz repetition rate). The ablation characteristics including laser material interaction parameters, i.e. ablation threshold, optical penetration depth and incubation factor are estimated based on ablated geometries from two ablation methods, i.e. spot ablation and line ablation. The work shows that the single pulse ablation threshold is dependent on the laser fluence and the number of pulses (NOP). The ablation threshold decreases with the NOP, where it reaches an asymptotical value due to incubation effect. By varying the laser fluence, two ablation regimes are identified which are the low fluence ablation regime and the high fluence ablation regime. The former is governed by optical penetration depth; and the latter is governed by the energy penetration depth. It is also observed that the laser material interaction parameters obtained based on ablation diameters through the line ablation agree with the values obtained through the spot ablation but not with those obtained based on ablated depth through the line ablation. It is found that the evaluation of the laser material interaction parameters based on ablated diameters is more reliable compared to those based on ablated depth. The ablation threshold (low fluence ablation region) for the HR4 nickel alloy is estimated to be Fth1=0.39J/cm2 with the incubation factor, ξ=0.8 and optical penetration depth of 47.3 nm. © 2014 Elsevier Ltd.

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