Phase Change Mechanisms in Pulsed Laser-Matter Interaction

2004 ◽  
Vol 850 ◽  
Author(s):  
Xianfan Xu
Keyword(s):  
Phase Change ◽  
Critical Point ◽  
Spinodal Decomposition ◽  
Nanosecond Laser ◽  
Micro Machining ◽  
Laser Micro Machining ◽  
Thermodynamic Critical Point ◽  
Matter Interaction ◽  
Explosive Phase ◽  
Change Mechanisms

ABSTRACTLaser micro-machining is finding many applications in materials processing and manufacturing. Various laser techniques are being used to fabricate micro-electronics, optics, and medical components. This paper will mainly deal with the fundamental issues involved in laser-matter interaction. Our studies are focused on laser induced thermal and thermomechanical phenomena and phase change mechanisms that determine the materials removal process during laser micro-machining. It is shown that during nanosecond laser machining, explosive phase change could occur, during which the liquid is superheated to close to the thermodynamic critical point, followed by an explosive, homogeneous phase transformation. On the other hand, it is observed in the experiment that the time needed for nucleation during laser induced phase explosion is on the order of one nanosecond. Thus, when a laser with a pulsewidth of the order of picosecond or less is used, it is likely that the material can be heated above the critical point, and another type of phase change, spinodal decomposition is possible. Molecular dynamics studies showed that with the use of a femtosecond laser pulse, it is possible to superheat the material to above the critical point, and spinodal decomposition is the dominant mechanism for materials removal.

Generation of Surfaces with Isotropic and Anisotropic Wetting Properties by Curved Water Jet Guided Laser Micro-Machining

2020 ◽  
Author(s):  
Yi Shi ◽  
Jian Cao ◽  
Kornel Ehmann
Keyword(s):  
Water Jet ◽  
Nanosecond Laser ◽  
Micro Machining ◽  
Metallic Surfaces ◽  
Wetting Properties ◽  
Laser Micro Machining ◽  
Jet Trajectory ◽  
Wide Range ◽  
Secondary Motion ◽  
Motion Speed

Abstract This experimental work utilizes a newly developed method, curved water jet guided laser micro-machining, to generate micro features on metallic surfaces. During the process, material is removed by a high-power nanosecond laser beam which is transmitted through a high-pressure micro water jet via total internal reflection. To achieve intricate texturing patterns, a secondary motion component is superimposed on the XY motion of the workpiece provided by the motion stage. The secondary motion is generated by deflecting the water jet trajectory by a controllable dielectrophoretic force. The induced secondary motion of the water jet cuts the processing time to one half when generating texture patterns for isotropic wetting as compared to processes with only XY motion. The ability to alter the water jet's trajectory by tens of microns at high frequencies, which is beyond the capability of conventional CNC machines, allows a wide range of different micro patterns to be generated, profoundly increasing the flexibility and efficiency of the process as compared to conventional approaches. As a demonstration, surface textures for isotropic and anisotropic behaviors are generated on stainless steel surfaces. The influence of feature spacing, motion speed (frequency) and texturing patterns on surface wettability are studied.

Nanosecond laser micro machining using an external beam attenuator

2003 ◽  
Author(s):  
Johan Bosman ◽  
Henk Kettelarij ◽  
Corne J.G.M. de Kok
Keyword(s):  
Nanosecond Laser ◽  
External Beam ◽  
Micro Machining ◽  
Laser Micro Machining

Generation of Surfaces With Isotropic and Anisotropic Wetting Properties by Curved Water Jet Guided Laser Micro-Machining

2020 ◽  
Author(s):  
Yi Shi ◽  
Jian Cao ◽  
Kornel F. Ehmann
Keyword(s):  
Water Jet ◽  
Nanosecond Laser ◽  
Micro Machining ◽  
Metallic Surfaces ◽  
Wetting Properties ◽  
Laser Micro Machining ◽  
Jet Trajectory ◽  
Wide Range ◽  
Secondary Motion ◽  
Motion Speed

Abstract This experimental work utilizes a newly developed method, curved water jet guided laser micro-machining, to generate micro features on metallic surfaces. During the process, material is removed by a high-power nanosecond laser beam which is transmitted through a high-pressure micro water jet via total internal reflection. To achieve intricate texturing patterns, a secondary motion component is superimposed on the XY motion of the workpiece provided by the motion stage. The secondary motion is generated by deflecting the water jet trajectory by a controllable dielectrophoretic force. The induced secondary motion of the water jet cuts the processing time to one half when generating texture patterns for isotropic wetting as compared to processes with only XY motion. The ability to alter the water jet’s trajectory by tens of microns at high frequencies, which is beyond the capability of conventional CNC machines, allows a wide range of different micro patterns to be generated, profoundly increasing the flexibility and efficiency of the process as compared to conventional approaches. As a demonstration, surface textures for isotropic and anisotropic behaviors are generated on stainless steel surfaces. The influence of feature spacing, motion speed (frequency) and texturing patterns on surface wettability are studied.

scholarly journals Femtosecond versus nanosecond laser micro-machining of InP: a nondestructive three-dimensional analysis of strain

2007 ◽  
Vol 22 (8) ◽  
pp. 970-979 ◽  
Author(s):  
Lu Xu ◽  
Donnacha Lowney ◽  
Patrick J McNally ◽  
A Borowiec ◽  
A Lankinen ◽  
...  
Keyword(s):  
Dimensional Analysis ◽  
Three Dimensional ◽  
Nanosecond Laser ◽  
Micro Machining ◽  
Laser Micro Machining

Laser micro machining of 3C–SiC single crystals

2006 ◽  
Vol 83 (4-9) ◽  
pp. 1400-1402 ◽  
Author(s):  
Sandra Zoppel ◽  
Maria Farsari ◽  
Robert Merz ◽  
Johann Zehetner ◽  
Günther Stangl ◽  
...  
Keyword(s):  
Single Crystals ◽  
Micro Machining ◽  
Laser Micro Machining

Implications of Phase Change on the Aerodynamics of Centrifugal Compressors for Supercritical Carbon Dioxide Applications

2020 ◽  
Author(s):  
Giacomo Persico ◽  
Lorenzo Toni ◽  
Paolo Gaetani ◽  
Ernani Fulvio Bellobuono ◽  
Alessandro Romei ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Power Systems ◽  
Phase Change ◽  
Critical Point ◽  
Fluid Dynamic ◽  
Flow Analysis ◽  
Design Strategy ◽  
Ideal Gas ◽  
New Challenges ◽  
Line Design

Abstract Closed Joule-Bryton cycles operating with carbon dioxide in supercritical conditions (sCO2) are nowadays collecting a significant scientific interest, due to their high potential efficiency, the compactness of their components, and the flexibility that makes them suitable to exploit diverse energy sources. However, the technical implementation of sCO2 power systems introduces new challenges related to the design and operation of the components. The compressor, in particular, operates in a thermodynamic condition close to the critical point, whereby the fluid exhibits significant non-ideal gas effects and is prone to phase change in the intake region of the machine. These new challenges require novel design concepts and strategies, as well as proper tools to achieve reliable predictions. In the present study, we consider an exemplary sCO2 power cycle with main compressor operating in proximity to the critical point, with an intake entropy level of the fluid lower than the critical value. In this condition, the phase change occurs as evaporation/flashing, thus resembling cavitation phenomena observed in liquid pumps, even though with specific issues associated to compressibility effects occurring in both the phases. The flow configuration is therefore highly nonconventional and demands the development of proper tools for fluid and flow modeling, which are instrumental for the compressor design. The paper discusses the modeling issues from the thermodynamic perspective and then highlighting the implications on the compressor aerodynamics. We propose tailored models to account for the effect of the phase change in 0D mean-line design tools as well as in fully 3D computational fluid-dynamic (CFD) simulations. In this way, a design strategy is build-up as a combination of mean-line tools, industrial design experience, and CFD for detailed flow analysis. The application of the design strategy reveals that the potential onset of the phase change might alter significantly the performance and operation of the compressor, both in design and in off-design conditions.

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