Phase transformations during laser processing of aerospace metallic materials Milton Sergio Fernandes de Lima 1,2,3 a * 1 Programa de Pós-Graduação em Engenharia Aeronáutica e Mecânica, Instituto Tecnológico de Aeronáutica, Praça Marechal Eduardo Gomes, 50, 12228-900 São José dos Campos, SP, Brazil 2 Rede Tematica de Materiais, Universidade Federal de Ouro Preto, Praça Tiradentes, 20, 35400- 000 Ouro Preto, MG, Brazil 3 Instituto de Estudos Avançados, Trevo AAA Amarante, 1, 12228-970 São José dos Campos, SP, Brazil a msflima@gmail.com * corresponding author Keywords: Laser processing; aerospace materials, phase transformations. Abstract. Phase transformations in laser processed metallic materials usually occur under very high temperature gradients and during a short time. Therefore, laser materials processing has been usually associated to high heating and cooling rates. However, before understanding the temperature evolution of the target, the absorptivity and the optical penetration must be considered. This paper presents some conjectures about the how the metal absorbs the laser radiation and how rapid phase transformations take place. It would be proposed that the interface response functions could be a possible way to understand phase transformations from liquid or high temperature solid solution conditions. Finally, it will be presented some results about laser processed materials of aerospace interest: steels, titanium and aluminium, which will illustrate the practical applications of the theories. Introduction From the earliest ages the human being lives have been governed by sunlight. In a short time scale, day and night dictate life and death for tenths thousand years and, on a larger scale, the amount of sunlight establishes hot or cold seasons. All this power soon attracted attention from illuminated scientists and philosophers. One of more legendary applications of the sunlight power is the Archimedes Light Ray [1]. Archimedes (circa 287 BC–212 BC) was a Greek philosopher and scientist who dedicates his life to some of most prominent discoveries, such as hydrodynamic forces acting on a lever and the “Archimedes Screw”. During the siege of Syracuse (circa 214–212 BC), it seems that he managed to focus sun power from a number parabolic mirrors to burn roman warships. Although it is unlikely that the mirrors had done the job, this ancestor of the modern solar furnaces enlightens the possible use of focused light power. Although the solar radiance upon Earth is approximately 1.3 kW/m² [2], the beam quality is very poor, mainly because of the wide wavelength distribution and atmospheric influences. The “death ray” appears again in The War of the Worlds (1898), a science fiction novel by H. G. Wells [3]. The book is written as a chronicle of facts following the Martian invasion in the United Kingdom. The Martians incinerate anybody disagreeing with the new status quo with a heat-ray weapon, either using manual guns or tripod robots. Of course, this weapon filled the dreams of the military for decades, even in the present days. Not surprising that the massive development of high power lasers has been mainly funded by military agencies, particularly the U.S. and Soviet. Fortunately, all this focused power has been proven much more useful in the factories than on the battlefield and we could enjoy laser welded cars, laser cut coronary stents, laser surgeries and many other things. The present contribution deals with two major subjects: how the laser interacts with a given material and the phase changes the material undergoes during and after laser exposition. The final properties of the targeted material will drastically change with the laser processing conditions so the Advanced Materials Research Vol. 1135 (2016) pp 179-201 Submitted: 2015-07-05 © (2016) Trans Tech Publications, Switzerland Revised: 2015-10-28 doi:10.4028/www.scientific.net/AMR.1135.179 Accepted: 2015-10-29 Online: 2016-03-15 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 73.243.211.194-24/12/15,16:48:49)