ORIGINAL ARTICLE Heat treatment effects on Inconel 625 components fabricated by wire + arc additive manufacturing (WAAM)—part 1: microstructural characterization A. N. M. Tanvir 1 & Md. R. U. Ahsan 1 & Changwook Ji 2 & Wayne Hawkins 3 & Brian Bates 3 & Duck Bong Kim 4 Received: 10 January 2019 /Accepted: 28 April 2019 # Springer-Verlag London Ltd., part of Springer Nature 2019 Abstract Wire + arc additive manufacturing (WAAM) is a versatile, low-cost, energy-efficient technology used in metal additive manufacturing. This WAAM process uses arc welding to melt a wire and form a three-dimensional (3D) object using a layer- by-layer stacking mechanism. In the present study, a Ni-based superalloy wire, i.e., Inconel 625, is melted and deposited additively through a cold metal transfer (CMT)-based WAAM process. The deposited specimens were heat-treated at 980 °C (the recommended temperature for stress-relief annealing) for 30, 60, and 120 min and then water quenched to investigate the effect of heat treatment on microstructure and phase transformation and to identify the optimum heat treatment condition. Microstructural results show that the heat treatment, in general, eliminates the brittle Laves phases regardless of the time without changing the grain morphology. However, an increment in the amount of the delta phase is observed with the longer heat treatment periods. Additionally, the size of MC (metal carbide) of Nb is also observed to increase with heat treatment time. This study provides an in-depth understanding of the correlation between heat treatment time and microstructure in additively manufactured Inconel 625, which can facilitate determining the optimum heat treatment condition in a later study. Keywords Metal additive manufacturing . Wire + arc additive manufacturing (WAAM) . Inconel 625 . Heat treatment . Cold metal transfer (CMT) 1 Introduction Additive manufacturing (AM) is the process of making ob- jects using a layer-by-layer stacking mechanism [1]. Saving cost in machining, materials, and manufacturing time, it can provide new capabilities to industries, compared to typical manufacturing processes (e.g., casting and subtractive manufacturing) [2]. One of them is to deposit material additively in a defined and controlled pathway, which can realize the concept of “near-net-shape manufacturing” [3]. This feature helps in obtaining complex geometries more eas- ily by employing AM [4]. Other advantages of AM include mass customization, sustainable manufacturing, and energy efficient manufacturing process [5]. With these benefits, AM is growing more popular in industrial sectors through its abil- ity to provide the manufacturers with more design of freedom. Due to its significant impacts to the manufacturing industries (e.g., jet engine [6], turbine blade [7], rocket engine [8], and many other applications [9]), it is anticipated that this AM technology will change the manufacturing landscape in the near future [2]. The American Society for Testing and Materials (ASTM) categorized metal AM techniques as (a) powder bed fusion, (2) directed energy deposition, (3) binder jetting, and (4) sheet lamination [1]. Among them, powder-based AM methods (e.g., selective laser melting (SLM) and electron beam melting (EBM)) are widely used. In the powder-based systems, a laser or electron beam is used to selectively melt and sinter particles * Duck Bong Kim dkim@tntech.edu 1 Department of Mechanical Engineering, Tennessee Technological University, Cookeville, TN 38505, USA 2 Advanced Forming Process R&D Group, Korea Institute of Industrial Technology, Ulsan, Republic of Korea 44413 3 Center for Manufacturing Research, Tennessee Technological University, Cookeville, TN 38505, USA 4 Department of Manufacturing and Engineering Technology, Tennessee Technological University, Cookeville, TN 38505, USA The International Journal of Advanced Manufacturing Technology https://doi.org/10.1007/s00170-019-03828-6 Content courtesy of Springer Nature, terms of use apply. Rights reserved.