An analysis of the bonding mechanisms active in a high power diode laser generated two-stage ceramic tile grout

Changes in the wettability characteristics of an alumina bioceramic occasioned by high power diode laser (HPDL) surface treatment were apparent from the observed reduction in the contact angle. Such changes were due to the HPDL bringing about reductions the surface roughness, increases in the surface O2 content and increases in the polar component of the surface energy. Additionally, HPDL treatment of the alumina bioceramic surface was found to effect an improvement in the bonding characteristics by increasing the work of adhesion. An electronic approach was used to elucidate the bonding characteristics of the alumina bioceramic before and after HPDL treatment. It is postulated that HPDL induced changes to the alumina bioceramic produced a surface with a reduced bandgap energy which consequently increased the work of adhesion by increasing the electron transfer at the metal/oxide interface and thus the metal-oxide interactions. Furthermore, it is suggested that the increase in the work of adhesion of the alumina bioceramic after HPDL treatment was due to a correlation existing between the wettability and ionicity of the alumina bioceramic; for it is believed that the HPDL treated surface is less ionic in nature than the untreated surface and therefore exhibits better wettability characteristics.

To improve the strengths of the adhesive joints of high density polyethylene (HDPE) and polypropylene (PP) to steel, the surfaces of HDPE and PP sheets have been treated by DC glow discharge to increase the polar component of surface energy significantly. Present study investigates the effect of mechanical polishing prior to surface modification of substrates of HDPE and PP sheets by exposure to DC glow discharge, on the surface energy and their adhesive joint strength to steel. The mechanical polishing has been carried out by abrading with 120, 220, 400, 600, 800, and 1000 grade emery paper of grit sizes 8.33, 4.54, 2.5, 1.67, 1.2, and 1 micron, respectively. The surface energy of a given surface has been evaluated by measuring contact angles of sessile drops of two test liquids of known surface tension components, such as deionized water and formamide. It is observed that 800‐grade emery paper of grit size 1.2 micron has been found most effective in terms of their reduction in contact angles and enhancement of their surface energies. The change in surface energy due to surface modification has also been evaluated by measuring the surface energies of unpolished sheets exposed to DC glow discharge. The surface modification of the polymers by glow discharge for 120 s at a power level of 13 W decreases the contact angle more on mechanically polished specimens than that observed on unpolished sheets. Due to glow discharge treatment, the polar component of surface energy increases significantly in HDPE and PP, especially when they are mechanically polished (800 grade) prior to glow discharge. However, in case of the HDPE sheets, the effect of glow discharge on the polar component of surface energy is significantly higher compared to that for dispersion component of surface energy, whereas the polar component of surface energy of the PP sheet is lower than the dispersion component of surface energy. But in both the cases, mechanical polishing prior to glow discharge appears to affect the polar component of surface energy. Mechanical polishing of the HDPE and PP sheets by abrading with 800‐grade emery paper prior to glow discharge treatment, increases the adhesive joint strengths over those observed in case of unpolished polymers exposed to glow discharge. However, the use of prior mechanical polishing increases the joint strength only by a little more than 10% compared to a five to seven times increase in strength observed as a consequence of exposure to glow discharge of as received samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1140–1149, 2001

Identification of the principal elements governing the wettability characteristics of ordinary Portland cement following high power diode laser surface treatment

The influence of a high power diode laser (HPDL) generated glaze on the wetting characteristics and the subsequent HPDL enamelling of ordinary Portland cement

Significant changes to the wettability characteristics of a common engineering carbon steel (EN8) were effected after high power diode laser (HPDL) surface treatment. These modifications have been investigated in terms of the changes in the surface roughness of the steel, the presence of any surface melting, the polar component of the steel surface energy and the relative surface O2 content of the steel. The morphological and wetting characteristics of the mild steel and the enamel were determined using optical microscopy, scanning electron microscopy, X-ray photoemission spectroscopy, energy-dispersive X-ray analysis and wetting experiments by the sessile drop technique. This work has shown that HPDL radiation can be used to alter the wetting characteristics of carbon steel so as to facilitate improved enamelling. Furthermore, standard mechanical, physical and chemical testing of the HPDL-fired enamel glaze revealed the glaze to possess similar properties to those of a conventionally fired enamel glaze in terms of bond strength, rupture/impact strength, wear and corrosion resistance. Such similar performance can be attributed to the two glazes possessing the same mechanical properties and similar amorphous structure, despite their very different firing techniques.

This work elucidates and analyses the factors responsible for modifications of the wettability characteristics of metallic materials after high power diode laser (HPDL) treatment. It was found that interaction of EN3 and EN8 mild steel with HPDL radiation resulted in the wettability characteristics of the mild steels altering to various degrees depending upon the laser processing parameters. Such changes in the wettability characteristics of the mild steels were found to be due essentially to: (i) modifications to the surface roughness; (ii) changes in the surface O2 content and (iii) the increase in the polar component of the surface energy. Work was conducted to isolate each of these influential factors, thereby allowing the magnitude of their influence to be determined. This analysis revealed that surface roughness was the primary influential factor governing changes in contact angle, θ, and hence the wettability characteristics of the mild steels. Surface energy, by way of microstructural changes, was also shown to influence, to a lesser extent, changes in the wettability characteristics, whilst surface O2 content, by way of process gas, was found to play a minor role in inducing changes in the wettability characteristics of the mild steels.

Carbon steel wettability characteristics enhancement for improved enamelling using a 1.2kW high power diode laser

High power diode laser (HPDL) surface melting and laser peening (LP) experiments have been carried out with application to modify the pitting corrosion resistance of 316L austenitic stainless steel in Na+Cl− environment, by thermal (HPDL), mechanical (LP with coating) or thermo-mechanical effects (LP without coating).Surface modifications have been analyzed with Optical microscopy, SIMS, EΡMΑ, and XRD measurements, in order to ensure a global understanding of surface states after both laser treatments. Electrochemical testings perfonned in NaCl 0.05 M have consisted of free potential recordings and anodic polarizations at 2 mV/s.The results show that HPDL surface meltings carried out with a 1 kW diode at 25 kW/cm2, drive to a 400 µm affected depth with a surface refinement (5 µm dendrite arm spacings), a dissolution of inclusions (Si, Fe, Ca, Al aggregates) and the generation of 5-6 % δ ferrite, together with a small compressive stress field (-100 MPa). The resulting effect is a +220 mV anodic shift of pitting potentials, attributed to the dissolution of inclusions, despite the occurrence of a small Cr segregation.LP experiments with Nd:YAG pulsed lasers between 5 and 25 GW/cm2 (3 ns and 10 ns durations) drive to enhanced compressive stresses (-500 MPa), deformation bands systems, without modification of the chemical content. The resulting effect is an increase of pitting potentials (up to +100 mV) due to a modification of inclusion-matrix interfaces. Additionnaly, XPS investigations of the passive film reveal thicker passive film layers on LP surfaces, less prone to damage by Cl- ions. This reveals a mechanochemical effect of LP, not demonstrated without coating, due to ablation effects on the metal surface.High power diode laser (HPDL) surface melting and laser peening (LP) experiments have been carried out with application to modify the pitting corrosion resistance of 316L austenitic stainless steel in Na+Cl− environment, by thermal (HPDL), mechanical (LP with coating) or thermo-mechanical effects (LP without coating).Surface modifications have been analyzed with Optical microscopy, SIMS, EΡMΑ, and XRD measurements, in order to ensure a global understanding of surface states after both laser treatments. Electrochemical testings perfonned in NaCl 0.05 M have consisted of free potential recordings and anodic polarizations at 2 mV/s.The results show that HPDL surface meltings carried out with a 1 kW diode at 25 kW/cm2, drive to a 400 µm affected depth with a surface refinement (5 µm dendrite arm spacings), a dissolution of inclusions (Si, Fe, Ca, Al aggregates) and the generation of 5-6 % δ ferrite, together with a small compressive stress field (-100 MPa). The resulting effect is a +220 mV anodic shift of pi...

A rapid, effective and repeatable technique for repairing the damaged skins of various military aircraft, both fixed and rotary winged, using a high power diode laser (HPDL) is described herein. The HPDL was traversed across the surface of an APC-2 repair patch, thereby melting a thermoplastic adhesive placed in between the repair patch and an Alclad substrate, consequently bonding the repair patch to the Alclad substrate. When subjected to single lap shear tests, the shear strength of the HPDL bond was 47.8 ± 4.7 MPa, compared to 32.4 ± 3.7 MPa for the induction welded samples. When subjected to the Boeing wedge test, the HPDL samples had a 1 h crack growth rate that was rated as very good (1.9 ± 0.5 mm/h); for the induction welded samples the 1 h crack growth rate that was rated as good (2.7 ± 1.2 mm/h). Of great significance was processing time achieved with the HPDL, which was reduced from 11.75 mins when employing induction welding to 2.75 mins with the HPDL. Moreover, the HPDL has been shown in this work to be a tool for bonding that is superior to its contemporary counterparts. It is, therefore, distinctly possible that even stronger bonds could be achieved with the HPDL if different adhesives were used.A rapid, effective and repeatable technique for repairing the damaged skins of various military aircraft, both fixed and rotary winged, using a high power diode laser (HPDL) is described herein. The HPDL was traversed across the surface of an APC-2 repair patch, thereby melting a thermoplastic adhesive placed in between the repair patch and an Alclad substrate, consequently bonding the repair patch to the Alclad substrate. When subjected to single lap shear tests, the shear strength of the HPDL bond was 47.8 ± 4.7 MPa, compared to 32.4 ± 3.7 MPa for the induction welded samples. When subjected to the Boeing wedge test, the HPDL samples had a 1 h crack growth rate that was rated as very good (1.9 ± 0.5 mm/h); for the induction welded samples the 1 h crack growth rate that was rated as good (2.7 ± 1.2 mm/h). Of great significance was processing time achieved with the HPDL, which was reduced from 11.75 mins when employing induction welding to 2.75 mins with the HPDL. Moreover, the HPDL has been shown in this...

Laser surface treatment to enhance the adhesive bonding between steel and CFRP: Effect of laser spot overlapping and pulse fluence

During the last years a new laser beam scanning system for heat treatment of metals with high power diode lasers was developed. The new external scanning optics is an optional tool, that can be used with common standard high power diode lasers (focal distance ≥ 300 mm). It works with high power diode lasers in the multi-kilowatt range up to 5 kilowatt laser power. The new system opens the door to a wide field of applications, that were not possible before. Heat treatment of metal surfaces with a track width of more than 50 mm at once is one of the capabilities.Furthermore different approaches were gone to make the handling of the system more easier for the user. Real-time temperature control with cycle times in the range of microseconds ensures a reproducible hardening result even for complex 3D-shaped parts with difficult heat flow conditions. The latest status of the developments and examples are presented.During the last years a new laser beam scanning system for heat treatment of metals with high power diode lasers was developed. The new external scanning optics is an optional tool, that can be used with common standard high power diode lasers (focal distance ≥ 300 mm). It works with high power diode lasers in the multi-kilowatt range up to 5 kilowatt laser power. The new system opens the door to a wide field of applications, that were not possible before. Heat treatment of metal surfaces with a track width of more than 50 mm at once is one of the capabilities.Furthermore different approaches were gone to make the handling of the system more easier for the user. Real-time temperature control with cycle times in the range of microseconds ensures a reproducible hardening result even for complex 3D-shaped parts with difficult heat flow conditions. The latest status of the developments and examples are presented.

This article deals with the high power diode laser (HPDL) surface treatment to overcome water droplet erosion of Low Pressure Steam Turbine (LPST) moving blades used in high rating conventional, critical and super critical thermal power plants. The materials generally used in these steam turbines are titanium alloy (Ti6Al4V), precipitate hardened stainless steel (17Cr-4Ni PH), X20Cr13 and X10CrNiMoV1222 steels. During incubation period as well as under prolonged testing, the HPDL surface treatment of these materials except for 17Cr-4Ni PH steel has enhanced the droplet erosion resistance significantly. This is due to increased hardness and formation of fine-grained martensitic phase due to rapid heating and cooling rates associated with laser treatment. The droplet erosion results of HPDL laser surface treatment of all these materials and their analysis form the main part of the article.

Welding thin sheet metal with high power diode lasers closes the feed rate gap between conventional techniques like TIG- or plasma-welding and CO2- or Nd:YAG-laser welding. Because of its size a high power diode laser can be integrated in common mobile linear welding devices. The weld seams are narrower comparing to TIG-welding, even with filler wire. Deep penetration welding with filler wire is performed with a lower heat input if a high power diode laser is used. That minimizes distortion and refinishing. Some applications for mobile use of high power diode lasers are presented. Heat treatment of conventional or laser beam welded carbon steel or TRIP-steel sheets is used to avoid cracking. High power diode lasers are well suited for that task. Surface temperature controlled post heat treatment of crack sensitive welds is presented in the paper.Welding thin sheet metal with high power diode lasers closes the feed rate gap between conventional techniques like TIG- or plasma-welding and CO2- or Nd:YAG-laser welding. Because of its size a high power diode laser can be integrated in common mobile linear welding devices. The weld seams are narrower comparing to TIG-welding, even with filler wire. Deep penetration welding with filler wire is performed with a lower heat input if a high power diode laser is used. That minimizes distortion and refinishing. Some applications for mobile use of high power diode lasers are presented. Heat treatment of conventional or laser beam welded carbon steel or TRIP-steel sheets is used to avoid cracking. High power diode lasers are well suited for that task. Surface temperature controlled post heat treatment of crack sensitive welds is presented in the paper.

Interaction of CO2, Nd:YAG, excimer and high power diode laser (HPDL) radiation with the surface of an Al2O3/SiO2 based ceramic was found to affect significant changes in the wettability characteristics of the material. It was observed that interaction with CO2, Nd:YAG and HPDL radiation reduced the enamel contact angle from 118° to 31°, 34° and 33° respectively. In contrast, interaction with excimer laser radiation resulted an increase in the contact angle to 121°. Such changes were identified as being due to: (i) the melting and partial vitrification of the Al2O3/SiO2 based ceramic surface as a result of interaction with CO2, Nd:YAG HPDL radiation, (ii) the surface roughness of the Al2O3/SiO2 based ceramic increasing after interaction with excimer laser radiation, (iii) the relative surface oxygen content of the Al2O3/SiO2 based ceramic increasing after interaction with CO2, Nd:YAG and HPDL radiation. The work has shown that the wettability characteristics of the Al2O3/SiO2 based ceramic could be controlled and/or modified with laser surface treatment. Moreover, it was found that changes in the wettability characteristics of the Al2O3/SiO2 based ceramic are related to the effects of laser wavelength, that is whether the wavelength of the laser radiation has the propensity to cause surface melting.Interaction of CO2, Nd:YAG, excimer and high power diode laser (HPDL) radiation with the surface of an Al2O3/SiO2 based ceramic was found to affect significant changes in the wettability characteristics of the material. It was observed that interaction with CO2, Nd:YAG and HPDL radiation reduced the enamel contact angle from 118° to 31°, 34° and 33° respectively. In contrast, interaction with excimer laser radiation resulted an increase in the contact angle to 121°. Such changes were identified as being due to: (i) the melting and partial vitrification of the Al2O3/SiO2 based ceramic surface as a result of interaction with CO2, Nd:YAG HPDL radiation, (ii) the surface roughness of the Al2O3/SiO2 based ceramic increasing after interaction with excimer laser radiation, (iii) the relative surface oxygen content of the Al2O3/SiO2 based ceramic increasing after interaction with CO2, Nd:YAG and HPDL radiation. The work has shown that the wettability characteristics of the Al2O3/SiO2 based ceramic could be contro...

Due to its inherent versatility and advantageous operating characteristics, the high power diode laser (HPDL) is being recognised as an appropriate tool for many engineering tasks. This work details the characteristics and feasibility of a technique to remove industrial epoxy grout using a 120W HPDL. The highest removal rate was achieved with an O2 process gas owing to the high reactive nature of the gas. A threshold power density of approximately 300 W/cm2 was found to exist below which removal did not occur. Furthermore, the minimum interaction time, below which there was no removal of epoxy tile grout, was found to be approximately 0.5 s. The maximum theoretical removal rate that may be achievable using the HPDL was calculated as being 66 mm2/s. A microstructural analysis revealed significant differences in the epoxy grout surface structure before and after the HPDL radiation. The surface of the HPDL-treated samples exhibited a collection of grouped particles with pores and gaps, whereas the untreated samples displayed a continuous monostructured plane surface. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analyses revealed changes in the chemical composition of the epoxy grout after the HPDL radiation. In particular, CaO and CO2 were found in the HPDL treated samples resulting from decomposition of CaCO3 (limestone). In addition, SiO2 that existed in the un-treated epoxy grout material was not detected after HPDL processing due to the compound verification. A thermogravimetric and differential thermal analysis (TG-DTA) identified a sequence of thermal history for the epoxy grout which therefore allowed the prediction of the reactions that occur in the epoxy grout due to HPDL interaction.Due to its inherent versatility and advantageous operating characteristics, the high power diode laser (HPDL) is being recognised as an appropriate tool for many engineering tasks. This work details the characteristics and feasibility of a technique to remove industrial epoxy grout using a 120W HPDL. The highest removal rate was achieved with an O2 process gas owing to the high reactive nature of the gas. A threshold power density of approximately 300 W/cm2 was found to exist below which removal did not occur. Furthermore, the minimum interaction time, below which there was no removal of epoxy tile grout, was found to be approximately 0.5 s. The maximum theoretical removal rate that may be achievable using the HPDL was calculated as being 66 mm2/s. A microstructural analysis revealed significant differences in the epoxy grout surface structure before and after the HPDL radiation. The surface of the HPDL-treated samples exhibited a collection of grouped particles with pores and gaps, whereas the untreated ...