Chapter 4 fundamentals of lasermaterial interaction and. There is no sense in modern thermodynamics of the notion of the he at contained in a body, but in the present context the energy deposited within a material by laser irradiation manifests itself as. A semiclassical twostep heating model to investigate thermal transport in metals caused by ultrashort laser heating is also presented. Pulsed laser heating and melting 49 the form of work that changes the total internal energy of the body. Modification of surfaces by laser heating has become a very important aspect of modern materials science. Laser processing of metals is based on the flow of heat that is generated by the absorbed. Carbon dioxide lasers are the traditional laser heat treatment method which has now become the standard laser method for treating metals. Lasers can be used as effective tool to heat metal surfaces. Pdf multilayer metal films such as metallic coatings on metal substrate are important elements in modern engineering applications. The question of reflectivity laser processing covers a broad range of laser induced sample modifications that are all ultimately based on the coupling of. No material is used up other than the material cut, unless you include the wear and tear of time on the laser device.
Theoretical model for heat conduction in metals during. Transient thermal and nonthermal electron and phonon relaxation after shortpulsed laser heating of metals ashutosh giri and patrick e. Heating and melting model induced by laser beam in solid. This control is exercised throughthe properselection of laser processing parameters to achieve the desired material modi. The results of the theoretical model indicate that heat conduction would not be uniform from focal spot or crater at the surface of target metal, when an ultra short laser will interact with the metal. When a plasma appears on the target surface, the laser heating of a target may occur in several ways. The portuguese society of materials spm, and the spanish materials society sociemat are affiliated with metals and their members receive a discount on the article processing charges. This work studies heat transfer mechanisms during ultrafast laser heating of metals from a microscopic point of view.
Ultrafastlaser heating induces thermal nonequilibrium between electrons and phonons in metal, which can be described by the ttm 10. Pdf femtosecond laser heating of multilayer metalsi. Finally, laserproduced plasmas in metals have been used in the recombination phase as laser media and as strong xray and vacuum ultraviolet sources elton 1990. Transient thermal and nonthermal electron and phonon.
This book discusses the heating of metals by laser beams at intensity levels too low, or radiation times too short, to cause target material ablation and plasma formation near the metal surface. Sparks studied the laser heating of several metallic solids. Qiu and tien 5 calculated application regimes for the onestep and twostep heating processes and also regimes for hyperbolic and parabolic heating. Never cut these materials cleveland public library. All these elements play a role in the choice of the best laser processing solution. The specificity of this approach to the topic rests with the factors governing heating kinetics under the above mentioned conditions. Laser annealing is possible on steel and stainless steel when heating the metal slowly and for relatively long period of time, a superficial change of color occurs. Recent developments of optical devices make it possible to obtain almost any arbitrary pulse shapes. Heating without melting, commonly know as heattreating. Improved twotemperature model and its application in. Pdf on the short pulse laser heating of metals a new. Laser ablation is the process of removing material with very intensive, pulsed laser radiation. Open access free for readers, with article processing charges apc paid by. First principles most laser cutting is carried out using co 2 or nd.
Simulation of laser heating of aluminum and model validation via. When annealing metals, no material is removed unlike when laser engraving. Applications range from aesthetic branding to unique. Modeling of ultrashort laser pulsetrain processing of. This work studies microscopic energy deposition and transport processes durmg shortpulse laser heating of multilayer metals. By finetuning the laser parameters it is easy to create legible markings. You probably want a solid state laser over a co2 laser, but that all depends on what you plan to do, and how much you want to pay. The same set of input data presented in table 1 was used for the calculations in both models. The heating process is composed of three processes. For more information on laser annealing, read our laser annealing application page.
Aug 28, 2008 calculations of the transient and steady. Pdf lasers are widely used in modifying metallic surfaces. Department of mechanical engineering advanced energy. Various twotemperature models that can be used to describe the nonequilibrium heat transfer are presented. Just saying a co2 laser is like a lightbulb, a solid state laser is like a diode, which one do you think will last. But it does have some drawbacks, and this is why new types of laser heat treatments are starting to take the fore. Modeling of ultrashort laser pulsetrain processing of metal. A coulomb explosion is a cold alternative to the dominant laser etching technique of thermal ablation, which depends on local heating, melting, and vaporization of molecules and atoms using lessintense beams. High average laser powers can have a serious adverse impact on the ablation quality in ultrashort pulsed laser material processing of metals.
The transient reflectivity changes predicted from the twostep model agree with subpicosecond laser heating experiments. Mathematical modeling of melting during laser heating of metal plate. Generally, as the material temperature increases, so does the absorption of laser light. Subsequent heating of the ionic product also results in a. The temperature dependences of the electron heat capacity for the gold, specific heat, and thermal.
The damage thresholds of some metals were predicted for 0. Laser heating of metals provides a systematic and comprehensive presentation of the fundamental principles underlying the physical and chemical mechanisms governing the interaction of laser radiation with solid targets, and in particular metals in gaseous environments, for a wide range of beam parameters. Adding carbon to the surface of ironbased alloys by heating the metal to below its melting point usually 1,560 and 1,740f and putting it in contact with carbonrich solids, liquids, or gasses. For intensity values up to about 1x10 4 wcm 2, the absorbed power depends on the wavelength. Photoconductivity is an important property of semiconductors, and is also a complex phenomenon. Osa heat accumulation in ultrashort pulsed scanning laser. The materials that the laser can cut materials like wood, paper, cork, and some kinds of plastics. The cwmode continuous wave, as opposed to pulsed mode laser in a mixed ndylf or ndyag lasers can be used for heating most metals and dark samples. We note that the heterogeneous interface considered here involves three primary temperature variables two in the metal and one in the dielectric. You probably want a solid state laser over a co2 laser, but that all depends. Pdf pulsed laser heating and melting semantic scholar. Pulse brevity down only to the nanosecond regime is sufficient to localize thermal ablation before the heat is conducted far, the. Innovating clean energy technologies in advanced manufacturing. Applications of laser processing are diverse and include, in addition to the selective.
By employing ultrafastlaser heating that creates strong thermal nonequilibrium between electrons and phonons in metal, it is possible to isolate the effect of the direct electronphonon coupling across the interface and thus facilitate its study. Laserheating of n 2 oiii at lower pressures, 1020 gpa, to about 2000 k fig. Laser radiation begins to act on the bounded region of the surface of the metal plate at the initial moment of time. Using lasers and infrared heating in heat treatment processes. The process of laser beam in solid material offers a great potential for the new product design, for example, welding, cutting of metals, drilling of holes, laser shock hardening and laser glazing. Key parameters, pulse dur ation to relaxation, relaxation to diffusion, and laser shortpulse laser heating on metals 725 heating intensity, are introduced to characterize short pulse laser heating processes. The heating of metals silver and aluminium by ultrashort laser pulses is analysed proceeding from a spatially nonuniform kinetic equation for the electron distribution function. Aspects of heat flow in laser processing of metals diva portal. The colorless ceramic powders would require mixing with a small powder of a nonreacting metal powder such as pt or a co 2 laser. The laser process efficiency can be defined by the balance between the quality of the mark, the marking time and the cost of the laser system.
Fast analytic simulation for multilaser heating of sheet. The question of reflectivity laser processing covers a broad range of laserinduced sample modifications that are all ultimately based on the coupling of. The steadystate value of t for metals cooled with a surfaceheattransfer coefficient h is not reduced substantially by increasing the cooling efficiency past a. The authors own interests in laser processing have been involved in the main with laser processing of semiconductors, especially iivi materials such as cdte, but also amorphous silicon. Effects of shortterm laser beam heating on the absorptivity.
With respect to the scanning speed, a sharp transition between a smooth, reflective and an uneven, dark ablated surface is observed. Computational study of heat transfer and gas dynamics in. Threedimensional laser heating model and entropy generation. Interactive multibeam laser machining simulation is crucial in the context of tool path planning and optimization of laser machining parameters. Pulsed lasers provide a better heating rate and a reduced heataffected zone. Heating up metal takes time, therefore, slow marking speeds should be used. Process heating is one of fourteen manufacturingfocused technology assessments prepared in support of chapter 6. Heating and melting model induced by laser beam in solid material. They concluded that for fast heating at higher temperature, the laser pulse duration is much longer than the electron.
Pdf laser heating of sheet metal and thermal stress development. Abstract an analytical method and a twodimensional finite element model for treating the problem of laser heating and. Heat transfer mechanisms during shortpulse laser heating. In the present study, threedimensional laser heating model is introduced using an electron kinetic theory approach, the energy analysis is carried out to predict the first and second law efficiencies, and the entropy generation number is computed during the process. However, estimations of some important thermal and optical properties in the existing twotemperature. During the laser heating process, thermal stresses develop in the region heated by. During ultrafast laser interaction with metal, the electrons and lattices are not in equilibrium. Heating and melting model induced by laser beam in. A quick look at heat treating processes for metals. Lasermaterials interactions, different laser types, the technical and commercial growth of laser cutting and the state of the art. Any subsurface heating is accomplished by conduction. Annealing possibilities using the conventional method of annealing, the laser is used out of focus to get a large laser spot for heating the material and the marking speed is set very low becauseheating takes some time. Using a double temperature model with nonlocal heat flow and a laser pulse length of 1 ps, the calculated surface temperatures of the electron and phonon subsystems are presented for cu, nb, and pb.
Micro and nanoscale heat transfer in femtosecond laser. Heat accumulation in ultrashort pulsed scanning laser. Current simulation approaches for heat transfer analysis 1 rely on numerical finite element methods or any of its variants, nonsuitable for interactive applications. It is a technology which gains increasingly greater importance for drilling, eroding, welding, structuring and marking of all kinds of materials. Etching can be done on almost anything, wood, cardboard, aluminum, stainless steel, plastic, marble, stone, tile, and glass.
In metals, local surface heating is very rapid and produces a thin hot layer on a relatively cool bulk material. Defect structures on metal surfaces induced by pulsed laser irradiation. A quick look at heat treating processes for metals machine. Heat transfer mechanisms during shortpulse laser heating of. This paper presents an overview of the subject of laser cutting. Laser heat treatment transformation hardening annealing. Transitions to electron temperature decay in noble metals after shortpulsed laser heating this work examines the effects of photonically induced interband excitations from the dband to states at the fermi energy on the electron temperature decay in noble metals. Investigating the influence of the sample temperature, it is experimentally shown that this effect stems from heat.
The change in the electron population in the dband and the conduction band causes a. The most relevant processing parameters are the laser power and the beammaterial interaction time. Comparative simulations using the models described above have been performed for the laser heating of a gold nanoparticle with radius nm in a surrounding medium of water. For context within the 2015 qtr, key connections between this technology assessment, other qtr technology chapters, and other chapter 6 technology. Chapter 4 fundamentals of lasermaterial interaction and application to multiscale surface modi. Laser heating has several advantages over con ventional heating methods including plasma arc and. Heat transfer across metaldielectric interfaces liang guo. Laser materials interactions, different laser types, the technical and commercial growth of laser cutting and the state of the art. Laser heating of n 2 oiii at lower pressures, 1020 gpa, to about 2000 k fig. Hopkinsa department of mechanical and aerospace engineering, university of virginia, charlottesville. Chapter 4 fundamentals of laser material interaction and application to multiscale surface modi.
When a plasma appears on the target surface, the laser heating of a target may occur in. Heat generated by a laser beam above a metal surface is dissipated by. The specificity of this approach to the topic rests with the factors governing heating. Analysis article pdf available in international journal of heat and mass transfer 3717. Improved twotemperature model and its application in ultrashort laser heating of metal films the twotemperature model has been widely used to predict the electron and phonon temperature distributions in ultrashort laser processing of metals.
Laser heating of metals provides a systematic and comprehensive presentation of the fundamental principles underlying the physical and chemical mechanisms governing the interaction of laser radiation with solid targets, and in particular metals in gaseous environments, for a. Particularly, special attention has been paid to the femtosecond laser heating of thin. In this process the laser is used to heat the surface of materials. Theoretical studies have been performed on the interaction of short laser pulse with metals.