## 1 Introduction  
Laser directed energy deposition (Laser-DED) is an additive manufacturing (AM) technique in which feedstock materials can be fed in powdered form and deposited on metallic substrates using focused laser energy [1; 2; 3]. DED machines are capable of high deposition rates, can add and subtract material (hybrid) in the same operation, and develop multi-functional, multi-materials structures [4; 5] in a near single step operation [6; 7; 8]. Laser-based AM processes such as DED have cooling rates in the range of \(10^{3}\) to \(10^{5}\) K/s, and are known to produce metastable phases and microstructural features such as fine dendrites, nano-scaled precipitates, acicular grains, etc. [9; 10]. Furthermore, the laser-processed microstructure depends a great deal on the material system. For example, in DED fabricated Inconel 718 (IN718) alloy, Laves phases rich in Nb and Mo form a unique striated and segregated network in a \(\gamma\)-phase-rich matrix [9]. Grain boundary segregation of precipitates give rise to features spread over multiple length scales; cellular meso-grains, and nano-scale carbide precipitates. Further, a previously solidified track of metallic material is also subjected to a secondary heating and cooling during layer-wise fabrication of a bulk component during the laser DED process [11; 12]. Due to the finite width of the laser scanning track (a hatch scan) and the laser scanning depth (a layer), the laser DED process essentially leads to rapid micro-casting of the metallic material. Currently, material characterization and quality control is performed mostly using destructive techniques [13], which are not always feasible for rapid, in-field testing. Nondestructive evaluation (NDE) allows us to perform material characterization without the need for any destructive testing. Several NDE methods [14; 15] includingultrasonic testing (UT) [16; 17; 18; 19; 20; 21] and X-ray micro computed tomography (CT) [22; 23; 24; 25] have been explored. The field implementable nature of UT makes it highly attractive and gives it an edge over radiography. Recent advances in additive technology including process parameter optimization have helped in establishing processing parameters that give a good starting point for quality control. This would typically eliminate any large defects, such as macro-cracking in the as-fabricated state. Considering these factors, microstructural changes and small-scale defects that do not affect the fabrication are typically found to be challenging to inspect. Applying NDE techniques to inspect these structures would produce a baseline NDE response, i.e., the \"as-manufactured\" state or the \"initial state\". Based on in-service activities such as fatigue loading, this initial state can evolve from microstructural changes including phase evolution, etc., to macroscale changes including crack growth, which is typically defined as a \"damage state\". This is a relative term and a clear definition is dependent on application and structure. Fundamentally, the ability to discern between initial state and damage state from an inspection or NDE perspective depends on the damage-feature size and the ability of the technique to resolve this feature. Therefore, it is very important to understand the baseline UT response for quality control of the structures fabricated using any advanced manufacturing techniques. If the baseline response is misunderstood as a damage state, then it could lead to several false positives. Furthermore, there is lot of interest in going towards in situ characterization, while the structures are being fabricated. But it is important to first understand the initial state in an ex situ manner. Therefore, it is important to first address and understand the baseline response from these complex microstructures before addressing the inspectibility of these structures.