Spectroscopic diagnostics of plasma during laser processing of aluminium

The role of the plasma in laser–metal interaction is of considerable interest due to its influence in the energy transfer mechanism in industrial laser materials processing. A 10 kW CO2 laser was used to study its interaction with aluminium under an argon environment. The objective was to determine the absorption and refraction of the laser beam through the plasma during the processing of aluminium. Laser processing of aluminium is becoming an important topic for many industries, including the automobile industry. The spectroscopic relative line to continuum method was used to determine the electron temperature distribution within the plasma by investigating the 4158 ° Ar I line emission and the continuum adjacent to it. The plasmas are induced in 1.0 atm pure Ar environment over a translating Al target, using f/7 and 10 kW CO2 laser. Spectroscopic data indicated that the plasma composition and behaviour were Ar-dominated. Experimental results indicated the plasma core temperature to be 14 000–15 300 K over the incident range of laser powers investigated from 5 to 7 kW. It was found that 7.5–29% of the incident laser power was absorbed by the plasma. Cross-section analysis of the melt pools from the Al samples revealed the absence of any key-hole formation and confirmed that the energy transfer mechanism in the targets was conduction dominated for the reported range of experimental data.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58114/2/d7_19_021.pd

Femtosecond laser machining of multi-depth microchannel networks onto silicon

Direct writing of multi-depth microchannel branching networks into a silicon wafer with femtosecond pulses at 200 kHz is reported. The silicon wafer with the microchannels is used as the mold for rapid prototyping of microchannels on polydimethylsiloxane. The branching network is designed to serve as a gas exchanger for use in artificial lungs and bifurcates according to Murray's law. In the development of such micro-fluidic structures, processing speed, machining range with quality surface, and precision are significant considerations. The scan speed is found to be a key parameter to reduce the processing time, to expand the machining range, and to improve the surface quality. By fabricating a multi-depth branching network as an example, the utilization of femtosecond pulses in the development of microfluidic devices is demonstrated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90801/1/0960-1317_21_4_045027.pd

Diagnostics of nanosecond dynamics of the plasma produced during KrF excimer laser ablation of zirconia in vacuum

A 248 nm KrF excimer laser was used to ablate the yttria stabilized ZrO2ZrO2 target in vacuum while an intensified charge coupled device camera was used to get the time-resolved side view images of the induced plume/plasma. Two components, plume and plasma, can be clearly distinguished from the images with delay time less than 300 ns. The center of the plasma is found moving along the direction tilted ∼55°, instead of 90°, from the surface of the target while the processing laser came along ∼40°. The movement velocities and the explosion rates of the plasma during the first 2 μs after the laser strike were calculated. Time- and spatial-resolved emission spectra from excited Zr atoms in the plasma have been measured to determine the corresponding excitation temperature. The dynamic evolution of the plasma is outlined based on the experimental results. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69773/2/JAPIAU-92-2-666-1.pd

Spatially and temporally resolved temperature measurements of plasma generated in percussion drilling with a diode-pumped Nd:YAG laser

Results of spectroscopic temperature measurements of the laser-induced plasma generated during percussion drilling with a high power diode-pumped, pulsed Nd:YAG laser are presented. SAE 52100 steel was drilled with varying average powers. Helium and oxygen were each used as the shield gas. Emission spectra were collected with a monochrometer and an intensified charge coupled detector connected to the optical multichannel analyzer. The plasma electron temperatures were calculated from the relative intensities of the spectral lines. The spatial and temporal temperature distributions are presented. Both drilling times and spatial distributions indicate energy absorption by the plasma. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71333/2/JAPIAU-84-8-4122-1.pd

Numerical and experimental analysis for solidification and residual stress in the GMAW process for AISI 304 stainless steel

Gas Metal Arc Welding (GMAW) process was analyzed by combining a finite element thermomechanical model for temperature and stress with solidification model. Model prediction was compared with experimental data in order to validate the model. The effects of welding process parameters on these welding fields were analyzed and reported. The effort to correlate the residual stress and solidification was initiated, yielding some valuable results. The solidification process was simulated using the formulation based on the Hunt-Trivedi model. Based on the temperature history, solidification speed and primary dendrite arm spacing were predicted at given nodes of interest. Results show that the variation during solidification is usually within an order of magnitude. The temperature gradient was generally in the range of 10 4 –10 5 K/m for the given welding conditions (welding power = 6 kW and welding speed = 3.39 to 7.62 mm/sec), while solidification speed appeared to slow down from an order of 10 −2 to 10 −3 m/sec during solidification. SEM images revealed that the Primary Dendrite Arm Spacing (PDAS) fell in the range of 10 1 −10 2 μm. The range of predicted sizes was in agreement with the experimental values. It was observed that the average size of the PDAS was dependent upon the welding speed. The PDAS fell between 7.5 to 20 μm for columnar and 10 to 30 μm for equiaxed dendrites, for welding speeds between 3.39 to 7.62 mm/sec. When the welding speed increased, it was observed that the average size of the PDAS decreased, as the model had predicted. For grain growth at the Heat Affected Zone (HAZ), Ashby's model was employed, and the prediction was in agreement with experimental results. For the residual stress calculation, the same mesh generation used in the heat transfer analysis was applied to make the simulation consistent. The analysis consisted of a transient heat analysis followed by a thermal stress analysis. An experimentally measured strain history was compared with the simulated result. The relationship between microstructure and the stress/strain field of welding was also obtained.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44769/1/10853_2004_Article_5089117.pd

Room temperature growth of biaxially aligned yttria-stabilized zirconia films on glass substrates by pulsed-laser deposition

Room temperature deposition of biaxially textured yttria-stabilized zirconia (YSZ) films on amorphous glass substrates was successfully achieved by conventional pulsed-laser deposition. The influence of the surrounding gases, their pressure and the deposition time on the structure of the films was studied. A columnar growth process was revealed based on the experimental results. The grown biaxial texture appears as a kind of substrate independence, which makes it possible to fabricate in-plane aligned YSZ films on various substrates.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48915/2/d31327.pd

Modelling of high-density laser-material interaction using fast level set method

A high-energy-density laser beam-material interaction process has been simulated considering a self-evolving liquid-vapour interface profile. A mathematical scheme called the level-set technique has been adopted to capture the transient liquid-vapour interface. Inherent to this technique are: the ability to simulate merger and splitting of the liquid-vapour interface and the simultaneous updating of the surface normal and the curvature. Unsteady heat transfer and fluid flow phenomena are modelled, considering the thermo-capillary effect and the recoil pressure. A kinetic Knudsen layer has been considered to simulate evaporation phenomena at the liquid-vapour interface. Also, the homogeneous boiling phenomenon near the critical point is implemented. Energy distribution inside the vapour cavity is computed considering multiple reflection phenomena. The effect of laser power on the material removal mode, liquid layer thickness, surface temperature and the evaporation speed are presented and discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48909/2/d10320.pd

Mass removal modes in the laser ablation of silicon by a Q-switched diode-pumped solid-state laser (DPSSL)

A fundamental study on the Q-switched diode-pumped solid-state laser interaction with silicon was performed both experimentally and numerically. Single pulse drilling experiments were conducted on N-type silicon wafers by varying the laser intensity from 108–109 W cm−2 to investigate how the mass removal mechanism changes depending on the laser intensity. Hole width and depth were measured and surface morphology was studied using scanning electron microscopy. For the numerical model study, Ki et al's self-consistent continuous-wave laser drilling model (2001 J. Phys. D: Appl. Phys. 34 364–72) was modified to treat the solidification phenomenon between successive laser pulses. The model has the capabilities of simulating major interaction physics, such as melt flow, heat transfer, evaporation, homogeneous boiling, multiple reflections and surface evolution. This study presents some interesting results on how the mass removal mode changes as the laser intensity increases.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48912/2/d6_12_023.pd

Role of preheating and specific energy input on the evolution of microstructure and wear properties of laser clad Fe-Cr-C-W alloys

Synthesis of Fe-Cr-C-W alloy (10 : 4 : 1 : 1, wt(%)) was carried out on AISI 1016 steel substrate using laser cladding technique which lead to the development of a suitable alternate for cobalt bearing wear resistant alloys. This study involved understanding of process variables like preheating temperature and specific energy input on the evolution of microstructures and their effect on wear resistance properties. The microstructure was examined with a scanning electron microscope and various types of complex carbides were identified using both energy dispersive x-ray and auger spectroscopy facilities. A combination of MC, M 7 C 3 and M 6 C types of carbides of certain proportions (formed at a preheating temperature of 484°C with specific energy input of 9.447 KJ/cm 2 ) has been found to be most attractive for achieving an optimum combination of microhardness and steady state friction coefficient values. A similar advantage may be derived at a lower level of specific energy input of 8.995 KJ/cm 2 but with a higher preheating temperature of 694°C. However, increasing the specific energy input to 12.376 KJ/cm 2 can significantly soften the matrix.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44761/1/10853_2004_Article_268390.pd