Precipitation of grain boundary a in a laser deposited compositionally graded Ti–8Al–xV alloy – an orientation microscopy study R. Banerjee * , D. Bhattacharyya, P.C. Collins, G.B. Viswanathan, H.L. Fraser Department of Materials Science and Engineering, The Ohio State University, 477 Watts Hall, 2041 College Road, Columbus, OH 43210, USA Received 13 August 2003; received in revised form 12 September 2003; accepted 18 September 2003 Abstract A graded ternary Ti–8Al–xV alloy (all compositions in wt%) has been deposited using the laser engineered net-shaping (LENS TM ) process. A compositional gradient in the alloy, from binary Ti–8Al to Ti–8Al–20V, has been achieved within a length of 25 mm. The feedstock used for depositing the graded alloy consisted of elemental Ti, Al, and V powders. Due to the columnar growth morphology of the b grains in these LENS TM deposited Ti alloys, the same prior b grain boundary often extends across lengths 10 mm. Using orientation microscopy techniques in a scanning electron microscope, the crystallography of precipitation of grain boundary a across the same boundary with changing composition has been investigated in detail. It was observed that while most grain boundary a precipitates maintain a Burgers or near-Burgers orientation relationship with only one of the b grains, a few of these precipitates develop a Burgers orientation relationship with the other b grain. In some rare instances, the grain boundary a did not develop a Burgers or near-Burgers orientation relationship with either b grains. Interestingly, in many cases while the grain boundary a maintained Burgers relationship with one of the b grains, precipitates of two different variants decorated the boundary, in a near-alternate fashion. Ó 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Laser deposition; Titanium alloys; Aluminium; Scanning electron microscopy; Transmission electron microscopy 1. Introduction Two of the upcoming technologies for direct laser deposition of metallic components using the solid freeform fabrication (SFF) route are the LENS TM [1] and Directed Light Fabrication (DLF) [2] processes. The LENS TM process was developed at the Sandia National Laboratories and subsequently commercial- ized by the Optomec Design Company of Albuquer- que, New Mexico while the DLF process was developed at the Los Alamos National Laboratories in the early 1990s. Both processes are similar in that they used a focused laser beam as a heat source to melt metallic powder and create a solid, three-dimensional object. A variety of metals and alloys have been de- posited using LENS TM [1,3]. The alloys deposited using this process have primarily been from pre-alloyed powders of the desired composition. However, the use of a powder feedstock in the LENS TM process allows for the flexibility to deposit a blend of elemental powders and create an alloy in situ. This is a very at- tractive proposition since if successful, it could poten- tially reduce the costs of processing to a large extent. In addition, using elemental powder blends in a system with multiple hoppers also allows the possibility of depositing graded compositions within the same sam- ple. There have been a few studies on the deposition of alloys from elemental powder blends using laser-de- position processes similar to LENS TM (for e.g., [4,5]). Takeda et al. [4] and Steen et al. [5] have used this approach to study laser deposited Fe–Cr–Ni and Fe– Co–Al alloys, respectively. Since the LENS TM process is expected to have a significant impact on the fabri- cation of components of intricate design complexity in Acta Materialia 52 (2004) 377–385 www.actamat-journals.com * Corresponding author. Tel.: +1-614-292-6263; fax: +1-614-292- 7523. E-mail address: banerjee.8@osu.edu (R. Banerjee). 1359-6454/$30.00 Ó 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2003.09.038