TWI Technical Literature Review 25286
By A Wilson
Extensive studies have been published on surface treatment methods (Ebnesajjad and Ebnesajjad, 2006). Typically, surface treatments are used to prepare surfaces for adhesive bonding, coating or joining, or conversely to create a hydrophobic or oliophobic surface structure. Lasers offer several advantages, complementing the range of surface modification techniques, which include plasma, corona discharge, mechanical abrasion and chemical methods.
The attributes of lasers include:
- Limited thermal damage to components (negligible heat-affected zone)(HAZ).
- Extremely precise (~10µm repeatability).
- Contactless machining at the micro/nano level.
- Applicable across a wide range of material types.
- Negligible consumables requirement.
Excimer laser and Nd:YAG laser treatments have been very successful in improving the adhesion properties of poly(etheretherketone) (PEEK) and polypropylene (PP,) amongst other polymers. There is a wide range of gases (for example xenon mono-chloride (XeCl) and krypton fluoride (KrF) which can be used to produce various wavelengths of light (usually in the ultraviolet (UV)), tailored to each polymer. While excimer laser treatment is very successful and has been studied extensively, there is a desire to move towards fibre lasers, to negate the need for consumable toxic gases. There are fewer investigations of PP and PEEK treated with such laser sources, especially fibre lasers, and ultrashort pulsed-lasers.
Additionally, laser micro-machining is an increasingly active field, particularly in the pulsed-lasers industry. Laser micro-machining is a topic that covers several areas of laser microprocessing, including laser engraving/scribing, drilling, cutting, polishing, marking and even laser welding in some cases. In this document, laser micro-machining will largely refer to laser engraving/scribing.
This review focuses on the laser surface modification of polymers and stainless steels (SSs) and the laser micro-machining of SSs and titanium (Ti) alloys. Specifically, AISI 316L stainless steel (SS) and Ti-6Al-4V alloys are used extensively in applications where tribological properties and corrosion resistance are important.
This literature review is arranged as:
- Fundamentals of pulsed-lasers and pulsed-laser-material interaction.
- Laser surface modification.
- Laser micro-machining.