Journal of Materials Processing Technology 178 (2006) 135–142 Thermal process maps for predicting solidification microstructure in laser fabrication of thin-wall structures Srikanth Bontha a , Nathan W. Klingbeil a, ∗ , Pamela A. Kobryn b , Hamish L. Fraser c a Department of Mechanical and Materials Engineering, Wright State University, Dayton, OH 45435, USA b Materials and Manufacturing Directorate (AFRL/MLSC), Air Force Research Laboratory, WPAFB, OH 45433, USA c Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210, USA Received 21 July 2005; received in revised form 19 October 2005; accepted 9 March 2006 Abstract The ability to predict and control microstructure in laser-deposited materials requires an understanding of the thermal conditions at the onset of solidification. To this end, the focus of this work is the development of thermal process maps relating solidification cooling rate and thermal gradient (the key parameters controlling microstructure) to laser deposition process variables (laser power and velocity). Attention is restricted to thin-wall deposits, which are commonly manufactured using Laser Engineered Net Shaping (LENS™) and other small-scale laser deposition techniques. The approach employs the 2D Rosenthal solution for a moving point heat source traversing a semi-infinite substrate, which has been previously used in the literature to guide the development of process maps for controlling melt pool size and residual stress. In the current study, cooling rates and thermal gradients at the onset of solidification are numerically extracted from the 2D Rosenthal solution throughout the depth of the melt pool, and results are plotted on dimensionless process maps for predicting solidification microstructure. Results suggest that changes in laser power and velocity can have a substantial effect on solidification cooling rate and thermal gradient, which depending on the material system could have a significant effect on the resulting microstructure. Results are further plotted on solidification maps for predicting grain morphology specifically in Ti–6Al–4V, and the effects of laser power and velocity on trends in grain morphology are discussed. Although the Rosenthal predictions neglect the nonlinear effects of temperature-dependent properties and latent heat of transformation, a comparison with 2D nonlinear thermal finite element (FEM) results suggests that they can provide reasonable estimates of trends in grain morphology. In particular, both the Rosenthal and FEM results indicate a trend from columnar toward mixed/equiaxed microstructure with increasing laser incident energy, which is in keeping with recent experimental observations of thin-wall Ti–6Al–4V deposits. © 2006 Elsevier B.V. All rights reserved. Keywords: Laser deposition; Solidification microstructure; Titanium; Rosenthal solution; Finite elements 1. Introduction Laser deposition of titanium alloys and other metallic ma- terials is a promising technology for aerospace applications, because it can substantially reduce both the buy-to-fly ratio and production lead time compared with conventional manu- facturing methods [1–4]. Moreover, laser-based material de- position will potentially enable the direct manufacture of ad- vanced aerospace components made of multiple or function- ally graded materials [5,6], or smart structures containing em- ∗ Corresponding author. Department of Mechanical and Materials Engineer- ing, Wright State University, 209 Russ Engineering, 3640 Colonel Glenn Hwy., Dayton, OH 45435, USA. Tel.: +1 937 775 5088; fax: +1 937 775 5009. E-mail address: nathan.klingbeil@wright.edu (N.W. Klingbeil). bedded sensors or electronic components. Finally, the flexi- bility of laser deposition allows virtually unlimited creation of advanced alloys through the use of elemental blends [7], which may ultimately span the next generation of aerospace materials. Despite their strong potential, the success of laser-based ma- terial deposition processes as viable manufacturing alternatives for aerospace components may ultimately hinge on the ability to consistently control the microstructure and resulting mechan- ical properties of the deposit. To date, only limited experimen- tal data exists to link deposition process variables (e.g., laser power and velocity) to resulting microstructure (e.g., grain size and morphology) in laser-deposited titanium alloys [1–3,8–12], and suitable microstructures have typically been obtained only by trial and error. As a result, simulation-based methods are needed to predict the effects of process variables on resulting 0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.03.155