The following list of publications by our team reflect our research at the Institute
Laser-assisted fabrication of deterministic lateral displacement structures on P20 die steel masters for microfluidic particle separation
Pavan Pandit & G. L. Samuel
Micro features play a vital role in microfluidic devices as they induce laminar or patterned flow. Laser micromachining is an evolving technique in the fabrication of such micro features with various complicated shapes and sizes on metallic and polymeric surfaces. A variety of shapes and sizes are utilized in biomedical applications, such as bio-implants, bioreactors and particle separation modules. In this research work, the authors have attempted to fabricate a passive device for particle separation that works on the principle of Deterministic Lateral Displacement (DLD). Displacement of the particles in the microfluidic regime separates the particles in a size range of 5–17 µm. This separation is accomplished using appropriately placed microposts which act as diversions for the flow lines, bifurcating them into primary and secondary branches. The authors have fabricated these features using a two-step process: fabrication of P20 die steel masters using 1030 nm Ultrashort Pulsed Laser (Yb) and transferring the features to poly dimethyl siloxane (PDMS)-based polymeric devices using soft fabrication. The circular posts of diameter 40 ± 2 µm and triangular features inscribed in a circle of diameter 40 ± 2 µm are arranged in three configurations with varying row shift fractions (ɛ), namely 0.45, 0.57 and 0.70, resulting in a tilt angle (α) of 25 ± 1°, 30 ± 1° and 35 ± 1°. The effect of the tilt angles on the pressure and velocity gradients on the fluid flow and the particle deformation is studied. The microscopy of the fabricated steel masters and PDMS devices is carried out to characterize the micro-features for their shape, size and the heat-affected zones. 3D profilometry is carried out to determine the quality of the micro-holes. Polymeric devices are further fabricated using die steel masters by soft fabrication.
A review on the fatigue behaviour of AlSi10Mg alloy fabricated using laser powder bed fusion technique
A.Raja, Srinivasa Rakesh Cheethirala, Pallavi Gupta, Nilesh J.Vasa, R.Jayaganthan
Laser powder bed fusion (LPBF) of AlSi10Mg alloy is widely studied for the aerospace and automotive applications. Considering safety over cost, fatigue life of the material is very critical for these applications. This article reviews the interrelationship between the LPBF process parameters-microstructure-crack initiation and crack growth mechanisms under fatigue loading conditions. It addresses current problems and potential opportunities in the fabrication of fatigue-resistant AlSi10Mg alloy for light weight structural applications. The methodology for mechanical testing techniques, specimen design guidelines, post-manufacturing treatments, and other aspects of AM parts ought to be standardised. It is possible to standardise the LPBF process thorough understanding of the interrelationships among process parameters, structural aspects such as microstructure of solidified material, and mechanical properties of the fabricated part. The deformation and fracture mechanism during the cyclic loading of influences the fatigue resistance of AlSi10Mg alloy. Influence of these microstructural features, grain morphology, texture, pore size, shape distribution, and surface roughness on the fatigue properties are vital for any applications that prioritize safety over cost. The hierarchical microstructure in the LPBF processed material showed an interesting crack growth mechanism, this mechanism of crack growth is an important novelty of this work. The influence of process of sample removal and post processing on the fatigue properties are significantly control the fatigue properties. Heating the substrate of the built sample and certain post processing conditions were observed to relieve the stress in the as-built material. Post-heat treatment observed to improve the fatigue property of the selective laser melted AlSi10Mg alloy owing to the homogeneous redistribution of Si particle from the cellular boundaries and stress relief. Hence, in this review, the inter-relationship between the LPBF process parameters-microstructure-crack initiation and crack growth mechanisms under cyclic loads were studied in detail. The major aspects reviewed in this article include influence of process parameters on fatigue life and their interaction with the formation of defects. Further, specific factors dictating the fatigue characteristics in as-built and post processed AlSi10Mg alloy are elaborately discussed, concluded by fatigue models detailing the fatigue failure mechanisms.
Intense laser matter interaction in atoms, finite systems and condensed media: recent experiments and theoretical advances
Krishnan, S., Mudrich, M.
This special issue of the European Journal of Physics: Special Topics entitled “Intense Laser Matter Interaction in Atoms, Finite Systems and Condensed Media” published a set of 21 articles aiming to put in perspective this burgeoning area of science, application and technology. The invention of chirped pulse amplification by Strickland and Mourou, which led to their Nobel prizes in 2018, has ushered in a new era in photon–matter interaction where coherent intense light pulses in the optical and infrared domains play a central role. This development has not only called in creative experimental methods, but has demanded new theoretical approaches working in the non-perturbative and highly nonlinear regimes of light–matter interaction. Both for fundamental physics as well as key applications these have played an essential role. Key pillars of this subject, captured in this collection, are laser-induced nanometer-scale plasmas ignited in unsupported nanoparticles, laser-based particle acceleration taking advantage of unprecedented field gradients, the generation of high-order harmonics opening up attosecond science and ultrafast X-ray spectroscopy, and the generation of terahertz pulses for time-domain spectroscopy of new materials.
Heat Treatment Design for IN718 by Laser Metal Deposition with High Deposition Rates: Modeling, Simulation, and Experiments
Chongliang Zhong, Venkatesh Pandian Narayana Samy, Norbert Pirch, Andres Gasser, Gandham Phanikumar, Johannes Henrich Schleifenbaum
Laser metal deposited processed Ni-based superalloy IN718 is characterized by elemental micro-segregation, anisotropy, and Laves phases due to the rapid solidification and therefore needs homogenization heat treatment to achieve comparable properties of wrought alloys. In this article, we report a simulation-based methodology to design heat treatment IN718 in a laser metal deposition (LMD) process by using Thermo-calc. Initially, the finite element modeling simulates the laser melt pool to compute the solidification rate (G) and temperature gradient (R). Then, the primary dendrite arm spacing (PDAS) is computed through Kurz-Fisher and Trivedi modeling integrated with finite element method (FEM) solver. Later, a DICTRA homogenization model based on the PDAS input values computes the homogenization heat treatment time and temperature. The simulated time scales are verified for two different experiments with contrast laser parameters and are found to be in good agreement confirmed with the results from scanning electron microscopy. Finally, a methodology for integrating the process parameter with the heat treatment design is developed, and a heat treatment map for IN718 is generated that can be integrated with an FEM solver for the first time in the LMD process.
Nanosecond and sub-nanosecond laser-assisted microscribing of Cu thin films in a salt solution
Sooraj Shiby, Nilesh J Vasa, Matsuo Shigeki
Pulsed laser-based material removal is a preferred technique for microscribing of copper (Cu) film coated on polymers, as the pulse width limits the heat diffusion. However, experimental studies have shown that microscribing of Cu in air results in recast/redeposit formation and oxidation. Although the water medium can reduce these effects to a certain extent, the material removal rate is lesser for Cu. This article reports the influence of laser pulse duration on a hybrid method to enhance the pulsed laser-assisted microscribing of a copper thin film in the presence of an environmentally friendly sodium chloride salt solution (NaCl). The focused laser beam irradiation of Cu film results in ablation with a temperature of the zone well above the boiling point of Cu, which in turn, can assist in accelerating the chemical reaction. In this hybrid scribing technique, along with laser-based material removal, laser-activated chemical etching also helps in removing the material selectively. A sub-nanosecond laser with a pulse width of 500 ps (picosecond [ps] laser) and a nanosecond laser with a pulse width of 6 ns (nanosecond [ns] laser), with a wavelength of 532 nm, are used to understand the influence of laser pulse duration on this hybrid material removal mechanism. Hybrid microscribing with the ps- and ns lasers in salt solution resulted in an increase in the channel depth by ≈5 µm and ≈9 µm, respectively, compared to the channel depth obtained in deionized water. The theoretical model shows that during the ns laser ablation, the cooling rate is slower, resulting in a high temperature in the ablation zone for a longer duration and improved material removal.