Pratik Shukla

Laser shock peening and mechanical shot peening processes applicable for the surface treatment of technical grade ceramics: A review

Laser shock peening and conventional mechanical shot peening are both comparable processes generally applicable to surface treat various metals and alloys. Commercial advantages offered by the laser systems such as flexibility, deep penetration of laser-induced shocks with precise control of the thermal pulses, shorter process times, high speeds, accuracy and aesthetics are attractive in comparison with the mechanical shot peening technique. Laser shock peening in the recent years has proved to be successful with steels, aluminium and titanium surfaces and metallic alloys in general. Nevertheless, minimal research has been conducted on laser shock peening and mechanical shot peening of technical grade ceramics. This article presents an update of the theory and to-date relevant literature within the two subject areas, as well as a comparison and a contrast between the mechanical and laser shock peening techniques. In addition, various gaps in knowledge are identified to propose further research for the development of both the techniques applicable to the surface treatment of technical grade ceramics.

Fracture toughness of a zirconia engineering ceramic and the effects thereon of surface processing with fibre laser radiation

Vickers hardness indentation tests were employed to investigate the near-surface changes in the hardness of a fibre laser-treated and an as-received ZrO2 engineering ceramic. Indents were created using 5, 20, and 30 kg loads to obtain the hardness. Optical microscopy, white-light interferometry, and a coordinate measuring machine were then used to observe the crack lengths and crack geometry. Palmqvist and half-penny median crack profiles were found, which dictated the selection of the group of equations used herein. Computational and analytical approaches were then adapted to determine the K1c of ZrO2. It was found that the best applicable equation was: K1c = 0.016 (E/H)1/2 (P/c3/2), which was confirmed to be 42 per cent accurate in producing K1c values within the range of 8 to 12 MPa m1/2 for ZrO2. Fibre laser surface treatment reduced the surface hardness and produced smaller crack lengths in comparison with the as-received surface. The surface crack lengths, hardness, and indentation loads were found to be important, particularly the crack length, which significantly influenced the end K1c value when K1c = 0.016 (E/H)1/2 (P/c3/2) was used. This is because, the longer the crack lengths, the lower the ceramics resistance to indentation. This, in turn, increased the end K1c value. Also, the hardness influences the K1c, and a softer surface was produced by the fibre laser treatment; this resulted in higher resistance to crack propagation and enhanced the ceramics K1c. Increasing the indentation load also varied the end K1c value, as higher indentation loads resulted in a bigger diamond footprint, and the ceramic exhibited longer crack lengths.

Laser surface structuring of ceramics, metals and polymers for biomedical applications: A review

Abstract This chapter provides a review of the literature in relation to laser-induced periodic surface structures (LIPSSs) found on metals, ceramics and polymers applicable within the biomedical and biotechnology sectors. The fundamental theory behind LIPSSs in general is addressed first followed by the state of the art in generating LIPSSs on metallic, polymeric and ceramics materials as an overview. Thereafter, an outline of the laser processing parameters required to create such surface structures for the aforementioned materials is given, followed by applications of such structures on various biomedical grade materials. Moreover, current and future trends in relation to LIPSSs are presented herein. A discussion of new prospectives and the current gap in knowledge is also addressed for future research in this area.

Modulating the wettability characteristics and bioactivity of polymeric materials using laser surface treatment

It has been thoroughly demonstrated previously that lasers hold the ability to modulate surface properties of materials with the result being utilization of such lasers in both research and industry. What is more, these laser surface treatments have been shown to affect the adhesion characteristics and biofunctionality of those materials. This paper details the use of a Synrad CO2 laser marking system to surface treat nylon 6,6 and polytetrafluoroethylene (PTFE). The laser-modified surfaces were analyzed using three-dimensional surface profilometry to ascertain an increase in surface roughness when compared to the as-received samples. The wettability characteristics were determined using the sessile drop method and showed variations in contact angle for both the nylon 6,6 and PTFE. For the PTFE, it was shown that the laser surface treatment gave rise to a more hydrophobic surface with contact angles of up to 150° being achieved. For the nylon 6,6, it was observed that the contact angle was modulated appro...

Mathematical modelling of the fibre laser surface processing of a zirconia engineering ceramic by means of three-dimensional finite-element analysis

The thermal effects of fibre laser surface treatment on a ZrO2 engineering ceramic were studied using a computational finite-element model (FEM). Temperature increases on the surface and the bulk of the ZrO2 during the fibre laser processing were measured using an infra-red thermometer and specifically located thermocouples. The results showed an error of 5 per cent with the surface and 18 per cent within the bulk of the ZrO2 when comparing the experimental readings with those of the FEM. The FEM revealed a relationship between the traverse speed, power density, time, depth, and the temperature during various stages of the fibre laser surface treatment of the ZrO2. By utilizing data obtained from a thermogravimetry-differential scanning calorimetry (TG-DSC), the FEM predictions of the temperature distribution were used to map phase transformations and significant events occurring during the fibre laser surface treatment of the ZrO2. The mapping revealed that the fibre laser surface treatment generally resulted in a phase transformation of the ZrO2 at various temperatures changes as further shown in the article.

Modification of fracture toughness parameter K1c following CO2 laser surface treatment of Si3N4 engineering ceramic

Abstract Surface treatment of a Si3N4 engineering ceramic assisted by a CO2 laser was conducted to identify changes in the fracture toughness parameter K1c. The K1c was determined by using a Vickers macrohardness indentation method before and after the CO2 laser surface treatment. Optical microscopy and infinite focus variation techniques were then adopted to measure the crack length and to investigate the surface morphology as well as the crack geometry within the engineering ceramic. Thereafter, computational and analytical methods were employed to calculate the K1c. Chemical analysis was further conducted to elucidate the change in composition as a result of the CO2 laser surface irradiation. The results showed that a decrease in the near surface hardness of 7 and 44% in the resulting crack lengths was found with the Si3N4 engineering ceramic following the CO2 laser surface treatment. This inherently led to an increase in the K1c. A rise in the K1c of 64% for the Si3N4 engineering ceramics was found (under the applied conditions) in comparison to the as received surface. This occurred due to the Si3N4 engineering ceramic being oxidised and further forming a new surface layer, which was somewhat softer than that of the as received or laser unaffected surface. Compositional analysis showed that the formation of the new surface layer as a result of the CO2 laser surface treatment was found to be SiO2.

Distribution of temperature during fibre laser radiation and effects thereon phase transformation of ZrO2 engineering ceramic

Abstract Distribution of surface and the bulk temperature was recorded during fibre laser surface treatment of ZrO2 engineering ceramic. The experimental readings were then compared with a finite element model which showed the flow and distribution of the laser induced heat as a result of the fibre laser surface treatment. Moreover, thermogravimetry–differential scanning calorimetry was used to collect data with respect to physical changes during heating and cooling of the ZrO2 engineering ceramic. The thermogravimetry–differential scanning calorimetry data and the finite element model predictions were then used to map the phase transitions within the ZrO2 engineering ceramic resulting from fibre laser surface treatment. The mapping revealed that the fibre laser surface treatment had generally resulted in a phase transformation of the ZrO2 engineering ceramic from the monoclinic (M) state to a mixture of tetragonal and cubic (T+C) followed by partially formed liquid (L) phase during fibre laser surface treatment and from L to T+C then T, followed by the M state during solidification.

Development in laser peening of advanced ceramics

Laser peening is a well-known process applicable to surface treat metals and alloys in various industrial sectors. Research in the area of laser peening of ceramics is still scarce and a complete laser-ceramic interaction is still unreported. This paper focuses on laser peening of SiC ceramics employed for cutting tools, armor plating, dental and biomedical implants, with a view to elucidate the unreported work. A detailed investigation was conducted with 1064nm Nd:YAG ns pulse laser to first understand the surface effects, namely: the topography, hardness, KIc and the microstructure of SiC advanced ceramics. The results showed changes in surface roughness and microstructural modification after laser peening. An increase in surface hardness was found by almost 2 folds, as the diamond footprints and its flaws sizes were considerably reduced, thus, enhancing the resistance of SiC to better withstand mechanical impact. This inherently led to an enhancement in the KIc by about 42%. This is attributed to an induction of compressive residual stress and phase transformation. This work is a first-step towards the development of a 3-dimensional laser peening technique to surface treat many advanced ceramic components. This work has shown that upon tailoring the laser peening parameters may directly control ceramic topography, microstructure, hardness and the KIc. This is useful for increasing the performance of ceramics used for demanding applications particularly where it matters such as in military. Upon successful peening of bullet proof vests could result to higher ballistic strength and resistance against higher sonic velocity, which would not only prevent serious injuries, but could also help to save lives of soldiers on the battle fields.

Laser surface treatment of engineering ceramics and the effects thereof on fracture toughness

Surface treatment of Si3N4 and ZrO2 engineering ceramics with a CO2 laser and a fibre laser was conducted to identify changes in the fracture toughness (K1c). Vickers macro hardness indentation tests were employed prior to and after the laser treatment to investigate the near surface changes in the hardness of the engineering ceramics. Optical microscopy was then used to observe the near surface integrity, crack lengths and crack geometry within the engineering ceramics. A co-ordinate measuring machine was used to observe the diamond indentations and to measure the lengths of the cracks in the ceramics. Thereafter, computational and analytical methods were employed to determine the K1c. A decrease in the near surface hardness and the resulting crack lengths was found with both materials after the laser treatment. This in turn led to increase in the K1c for both engineering ceramics. A rise in K1c of 64 % for Si3N4 and 40 % was obtained for ZrO2 ceramics using the CO2 laser treatment. Fibre laser treatment induced 50 % increase with ZrO2 and 51 % with Si3N4 ceramics. The likely cause of this increase is the softening of the near (top) surface layer through some degree of melting and redistribution of the melt zone, along with surface oxidation that changed the engineering ceramics composition.Surface treatment of Si3N4 and ZrO2 engineering ceramics with a CO2 laser and a fibre laser was conducted to identify changes in the fracture toughness (K1c). Vickers macro hardness indentation tests were employed prior to and after the laser treatment to investigate the near surface changes in the hardness of the engineering ceramics. Optical microscopy was then used to observe the near surface integrity, crack lengths and crack geometry within the engineering ceramics. A co-ordinate measuring machine was used to observe the diamond indentations and to measure the lengths of the cracks in the ceramics. Thereafter, computational and analytical methods were employed to determine the K1c. A decrease in the near surface hardness and the resulting crack lengths was found with both materials after the laser treatment. This in turn led to increase in the K1c for both engineering ceramics. A rise in K1c of 64 % for Si3N4 and 40 % was obtained for ZrO2 ceramics using the CO2 laser treatment. Fibre laser treatment...

Laser sealing of dissimilar polymers for manufacturing packaging products

Laser sealing of thin/dissimilar polymers has the potential to become a superior technique that could be applied to a range of general packaging products. Upon successfully applying laser sealing to such products could result to faster throughputs, shorter lead-times, lower energy consumption, and in turn, a competitive advantage for packaging product manufacturers. The work herein is focused on the physical laser-material interaction resulting from laser sealing a 42 μm high density linear polyethylene (HDLPE) film to a 1 mm polypropylene (PP) substrate. The paper also details a comparison of laser sealing with the conventional pressure/heat sealing process. The results showed that a 10.6 μm wavelength laser, the required parameters to produce an acceptable seal were: 60 W of laser power, 1.67 mm spot diameter, and a traverse speed of 300 mm/min using a double pass. Microstructural study showed sufficient bonding of the laser sealed region with an amorphous zone. Defects were also present in various areas when comparing the results of laser sealing to the conventional sealing process. Nonetheless, the peel strength tests showed laser sealing required up to 30% higher force than the conventionally sealed HDLPE film to PP substrate. A steady-state finite element model of the laser sealing process showed distribution of heat at the film/seal activation temperature. This confirmed the sealing temperature at the laser-polymer interaction zone to gain further understanding of the new process as a whole.