Contents lists available at ScienceDirect Materials Characterization journal homepage: www.elsevier.com/locate/matchar Microstructural characterization of laser metal powder deposited Alloy 718 Andreas Segerstark a, ⁎ , Joel Andersson a , Lars-Erik Svensson a , Olanrewaju Ojo b a Department of Engineering Science, University West, Trollhättan SE-461 86, Sweden b Department of Mechanical Engineering, University of Manitoba, Winnipeg R3T 5V6, Canada ARTICLE INFO Keywords: Laser metal deposition Additive manufacturing Powder Superalloy Microstructure ABSTRACT A microstructural study of Laser Metal Powder Deposition (LMPD) of Alloy 718, using a low (40 J/mm) and high (100 J/mm) heat inputs (HIs) was performed. The microstructure was characterized in as-deposited condition as well as after a standard heat-treatment, using optical microscope (OM), scanning electron microscope (SEM) and Transmission Electron Microscope (TEM). Laves, MC-carbides, γ′ and γ″ are observed in the interdendritic areas of both conditions. However, the dendritic core only consists of γ-matrix. The high HI condition shows a slightly larger Primary Dendrite Arm Spacing (PDAS) as compared to the low HI condition. Additionally, the particle size of the Nb-rich constituents in the interdendritic regions (Laves-phase and Niobium carbide) is larger in the high HI sample. After heat-treatment, the Laves phase dissolves and is replaced by δ-phase in the interdendritic regions, while γ′, γ″ and MC-carbide remain in the interdendritic regions. However, the γ″ precipitates seems to be less developed in the dendritic core as compared to the interdendritic regions, especially in the high HI sample. This can be attributed to a heterogeneous distribution of Nb in the microstructure, with a lower Nb content in the dendritic core as compared to close to the interdendritic regions. 1. Introduction Laser Metal Powder Deposition (LMPD) is an Additive manu- facturing (AM) method that deposits material by blowing powder into a melt pool, created by a laser, on a metallic substrate. The method has shown potential as a repair method for components with columnar or single crystal structures, as these structures are attainable with this method, as shown by [1, 2]. Other applications for the method is to add features to simpler castings, refurbish end of life components, and de- posit corrosion resistant or wear resistant coatings on components [3]. Pinkerton et al. [4] investigated the effect of the melt pool shape and thermal history in laser metal deposition of Waspaloy powder. The thermal history of various deposition conditions was correlated to the microstructure and grain structure of the material. They found that the grain structure of the deposits changed significantly with varying laser power and powder feeding rate in the range of 350–560 W, for the laser power and 0.21 g/s–0.63 g/s, for the powder feeding rate. Columnar grains generally formed at lower powder feeding rates and formed in the (001) orientations. Zhang et al. [5] deposited thin walled Alloy 718 sample, 12 layers high, using a heat input of approximately 190 J/mm. It was found that Laves phase formed in the interdendritic regions of the deposit. The Laves phase area fraction was found to increase with an increased distance away from the substrate. This was attributed to the increased number of thermal cycles in the bottom of the sample, which resulted in diffusion of Nb into the γ-matrix and a successive reduction of Laves phase. Additionally, γ″ precipitates are formed at the bottom of the sample. Tian et al. [6] have reported γ″ precipitation in LMPD of Alloy 718 powder when depositing on a thin wall substrate with the dimension 50.8 mm, 2.26 mm and 50.8 mm (length, width and height, respec- tively). The layers were built by first depositing a border which then was filled using a cross hatched scanning pattern. Temperature mea- surements showed that the temperature was in a temperature range of 600–700 °C in the bottom of the deposit, throughout the whole build (~20 min). In the bottom part of the deposit, γ″ precipitates are found in the dendritic core as well as in the interdendritic regions. However, in the top the γ″ was only found in the interdendritic regions, close to the Nb-rich constituents. In this study, an investigation of how the formation of phases in Alloy 718 can be controlled by changing the heat input (HI) has been carried out. To do this a lower (40 J/mm) and higher HI (100 J/mm), henceforth referred to low HI and high HI respectively, was used to prepare thin walled samples. The parameter settings, although referred to low and high HI, both have a quite low energy input with the main focus of being used for repair of aerospace components. The built ma- terial was evaluated both in the as-deposited condition and after a heat treatment cycle originally developed for repair welding [7]. The built https://doi.org/10.1016/j.matchar.2018.06.020 Received 19 September 2017; Received in revised form 6 June 2018; Accepted 13 June 2018 ⁎ Corresponding author. E-mail address: andreas.segerstark@hv.se (A. Segerstark). Materials Characterization 142 (2018) 550–559 Available online 18 June 2018 1044-5803/ © 2018 Elsevier Inc. All rights reserved. T