Materials Science and Engineering A 528 (2011) 914–919 Contents lists available at ScienceDirect Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea Effect of laser shock processing on fatigue crack growth of duplex stainless steel C. Rubio-González a,∗ , C. Felix-Martinez a , G. Gomez-Rosas b , J.L. Oca ˜ na c , M. Morales c , J.A. Porro c a Centro de Ingeniería y Desarrollo Industrial, Pie de la Cuesta, 702, Desarrollo San Pablo, Querétaro, Qro., 76130, Mexico b Universidad de Guadalajara, Guadalajara, Jal, Mexico c Departamento de Física Aplicada a la Ingeniería Industrial, E.T.S.I.I., Universidad Politécnica de Madrid, Spain article info Article history: Received 31 May 2010 Received in revised form 30 August 2010 Accepted 8 October 2010 Keywords: Fatigue test Laser shock processing Residual stress abstract Duplex stainless steels have wide application in different fields like the ship, petrochemical and chemical industries that is due to their high strength and excellent toughness properties as well as their high corrosion resistance. In this work an investigation is performed to evaluate the effect of laser shock processing on some mechanical properties of 2205 duplex stainless steel. Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life and reduces fatigue crack growth rate. A convergent lens is used to deliver 2.5 J, 8 ns laser pulses by a Q-switched Nd:YAG laser, operating at 10 Hz with infrared (1064 nm) radiation. The pulses are focused to a diameter of 1.5 mm. Effect of pulse density in the residual stress field is evaluated. Residual stress distribution as a function of depth is determined by the contour method. It is observed that the higher the pulse density the greater the compressive residual stress. Pulse densities of 900, 1600 and 2500 pul/cm 2 are used. Pre-cracked compact tension specimens were subjected to LSP process and then tested under cyclic loading with R = 0.1. Fatigue crack growth rate is determined and the effect of LSP process parameters is evaluated. In addition fracture toughness is determined in specimens with and without LSP treatment. It is observed that LSP reduces fatigue crack growth and increases fracture toughness if this steel. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Laser shock processing (LSP) is a relatively new surface treat- ment technique and has been shown to be effective in improving the fatigue properties of a number of metals and alloys. Potential applications are directed to aerospace and automotive industries. The beneficial effects of LSP on static, cyclic, fretting fatigue and stress corrosion performance of aluminum alloys, steels and nickel- based alloys have been demonstrated [1–9]. Since laser beams can be easily directed to fatigue-critical areas without masking, LSP technology is expected to be widely applicable for improving the fatigue properties of metals and alloys, particularly those that show a positive response to shot peening. Duplex stainless steels have wide applications in different fields like the ship, petrochemical and chemical in industries. The main applications of these steels are related to their high strength and excellent toughness properties as well as their high corrosion resistance. The outstanding mechanical properties of these steels are due to its duplex microstructure with approximately equal amounts of austenite  and ferrite ı. However, when the steel is subjected to high temperature its susceptibility for sigma () phase ∗ Corresponding author. Fax: +52 442 2119839. E-mail address: crubio@cidesi.mx (C. Rubio-González). formation raises due to extended exposure to temperatures ranging from 600 ◦ C to 900 ◦ C [10]. Sigma phase is a very hard and brittle intermetallic compound that affects impact properties of duplex stainless steel. There has been interest to evaluate the effect of shot peening on the fatigue behavior of 2205 duplex stainless steel [11]; and the effect of burnishing on stress corrosion cracking susceptibility of that steel [12]. However, few works are available that investi- gate the effect of laser peening on the fatigue behavior of duplex stainless steel. The changes in surface hardness, wear resistance, and corrosion resistance with and without laser peening has been reported in [13]. The objective of this work is to examine the effect of laser shock processing on the fatigue behavior and of 2205 duplex stain- less steel specimens. Process parameters such as pulse density are varied. The effect of LSP on fatigue crack growth rate, fracture toughness, micro-hardness, and residual stresses are investigated. A microscopic evaluation of fracture surfaces and microstructure is presented as well. In the laser shock processing of metals, the sample is either com- pletely immersed in water or in air. A water jet may be used also to produce a water wall with constant thickness on the sample. The laser pulse is then focused onto the sample. The schematic of how the process works in water is shown in Fig. 1. When the laser beam is directed onto the surface to be treated, it passes through the trans- 0921-5093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2010.10.020