Laser treatment of dual matrix cast iron with presence of WC particles at the surface: Influence of self-annealing on stress fields B.S. Yilbas a,n , S.S. Akhtar a , C. Karatas b , K. Boran c a Mechanical Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia b Engineering Faculty, Hacettepe Universitesi, Ankara, Turkey c Faculty of Technology, Gazi Universitesi, Ankara, Turkey article info Article history: Received 8 April 2015 Received in revised form 28 June 2015 Accepted 3 July 2015 Keywords: Laser surface treatment WC particles Residual stress abstract Laser control melting of dual matrix cast iron surface is carried out. A carbon film containing 15% WC particles is formed at the surface prior to the laser treatment and the spiral tracks are adopted for laser scanning at the workpiece surface. Morphological, metallurgical, microhardness, and scratch resistance of the laser treated surface are examined using analytical tools. Temperature and stress fields in the laser irradiated region are predicted incorporating ABAQUS finite element code. Predictions of temperature and residual stress at the laser treated surface are validated with the thermocouple and the X-ray dif- fraction data. It is found that surface temperature and residual stress predictions agree well with their counterparts corresponding to thermocouple data and findings of X-ray diffraction technique. Laser treated surface is free from asperities including voids and micro-cracks despite the mismatch of thermal expansion coefficients of WC and dual matrix cast iron. This behavior is attributed to the self-annealing effects of recently formed spiral tracks on the previously formed tracks during the laser treatment process; in which case, the self-annealing effect modifies the cooling rates and lowers thermal stress levels in the laser treated layer. Laser treated layer consists of a dense region composing of fine grains and WC particles, dendritic and featherlike structures below the dense layer, and the heat affected zone. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction Laser treatment of metallic surfaces improves tribological and mechanical characteristics of the surfaces [1] and extends the fa- tigue life [2]. In addition, laser processing has several advantages over the conventional methods because of the local treatment, precision of operation, and the low cost. In laser surface proces- sing, many factors affect the end product quality assessed by sur- face texture, microhardness, scratch resistance, microstructure, morphology, and etc. The selection of the process parameters plays a major role in achieving the desired end product quality of the laser treated surface. Since laser treatment involves with high temperature processing, rapid solidification under high cooling rates results in high thermal stress levels in the laser treated re- gion. This, in turn, causes asperities such as voids and micro-crack networks in the treated region and limits the practical applications of the laser treated surfaces. Laser control melting improves the surface quality; however, the residual stress formed at the surface region lowers the fracture toughness and the performance of the surface response to the tribological tests [3]. The self-annealing affect created during laser treatment is one of the solutions to minimize the high stress field formed in the laser treated layer. In this case, heat conduction across the path of laser scanning and laser repetition rate during the surface processing may create a self-annealing affect in the treated layer. Moreover, the laser treatment of metallic surfaces with presence of hard particles, such as WC, require proper control and appropriate selection of the laser treatment parameters due to the mismatch of thermo- mechanical properties of the constituting elements in the treated layer. On the other hand, the model studies provide useful in- formation about the physical processes, in terms of thermal and stress fields, taking place during the laser treatment process. Consequently, investigation of the laser treatment of metallic surfaces with presence of hard particles and thermal stress field developed in the treated layer becomes essential. Considerable research studies were carried out to examine la- ser treatment of steel and iron based composites. Laser treatment of dual matrix structured cast iron surface was investigated by Sun et al. [4]. They showed that the wear resistance of the treated layer was almost 1.6 times of that of the nodular cast iron substrate. The improvement in wear resistance was due to combined results of Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/optlastec Optics & Laser Technology http://dx.doi.org/10.1016/j.optlastec.2015.07.003 0030-3992/& 2015 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail address: bsyilbas@kfupm.edu.sa (B.S. Yilbas). Optics & Laser Technology 76 (2016) 6–18