Laser interaction of Haynes 282 (H282), a nickel-based superalloy renowned for its application in the turbine exhaust sections of aero engines and in advanced ultra-supercritical boilers, is explored to increase productivity through laser powder bed fusion (PBF-LB) process. Currently, PBF-LB processes typically employ 20-40 mu m layer thickness for this alloy. This study aims to determine the suitable process parameter variations, to reduce the build time to half, through focus offset and higher (60 mu m and 90 mu m) layer thickness.

Single and multi-track laser experiments were performed over a wide range of power and speed permissible in PBF-LB process machine, to determine optimized parameters. Laser focus offset effect on melting and melt pool dimensions were analysed. Effect of power, speed and hatch distance on melt pool behaviour and dimensions are characterized, with high power resulting in deeper melt pool and slower speed resulting in wider melt pool. Effect of change in melting mode due to offset of laser focal plane with respect to build plate is discussed.

The feasibility of building 110 mm tall build with 60 mu m and 90 mu m layer thickness with similar to 40-60 % reduction in build time compared to standard process parameters, is presented with microstructural and mechanical characterization.

Beam shaping is considered a technology capable of dramatically improving quality and robustness of Laser Metal Fusion (LMF) processes. However, systematic investigations of its effects on melt-pool dynamics, temperature field and microstructure are still required. In this work, we propose an integrated approach combining a Computational Fluid Dynamics (CFD) model, in-situ temperature measurements and metallographic analysis to explore programmable ring beam profiles, ranging from Gaussian-dominant to ring-dominant configurations. This method, initially proposed on Ti-6Al-4V bead-on-plate tracks, validates melt-pool temperatures measured in-process by a dual-wavelength pyrometer against CFD predictions, which are in turn validated with metallographic cross-sections. Ring modes lowered peak temperature by up to 35 %, transforming deep-narrow pools (aspect ratio approximate to 0.9) into shallow-wide ones (approximate to 0.4). This suppressed humping at line energies >= 0.28 J mm-1, whereas lower energies produced only superficial melting. Simulations matched pyrometer data within 5 % whenever pool width equalled the pyrometers’ sensing spot; all tracks solidified into ultrafine alpha with retained beta, independent of beam mode. Therefore, the combination of in-situ, ex-situ and CFD tools offers a practical workflow for assisting data-driven process optimization and can be easily extended to other LMF processes, with its potential implementation in industrial Laser Powder Bed Fusion.

Laser powder bed fusion (PBF-LB) processing of Haynes 282 using a layer thickness of 90-μm is studied for process capability and feasibility for increased productivity. To optimize the build rate while producing metallurgically sound parts, the effect of laser parameters on the resulting melt pool dimensions and porosity are analyzed. In a previous study, individual parameters such as laser power, scan speed and hatch distance and combination have been studied. In this study, three levels of hatch distance have been investigated while varying power and speed to same extent at all three (3) hatch distance. Similarly, the highest power level has been studied for the effect of speed and hatch distance. The melt pool dimensions, and porosity were measured in the plane parallel to the build direction. Comparison of measured responses with individual parameters provides partial trends of melt pool dimensions and porosity. It was observed that high power and/or low speed and low hatch distance increase the melt pool dimensions and reduce porosity until keyhole mode is reached. Variation of two parameters while keeping the third parameter constant was found to affect porosity due to the transition from lack of fusion type defects to keyhole porosities. The presence of dominant type of defect is identified using average feret ratio, which is the ratio of maximum length to minimum length across parallel surfaces inside a defect. It is found successful to use the combination study of process parameters and resultant type of defects to map the process to achieve minimal defects is identified for 90-μm layer thickness, through the combination study of process parameters and the resultant type of defects. 

Nickel-based superalloy Haynes 282 specimens were manufactured using the Laser Powder Bed Fusion process with a powder layer thickness of 60 and 90 microns to study the effect of laser power, laser scan speed, and hatch distance on the melt pool dimensions and porosity. The melt pool dimensions and porosity were measured at the center of the cubes parallel to the build direction. Variation of melt pool depth and overlap exist within the same sample signifying the scatter present in the process. Laser scan speed was found to be the most significant parameter for porosity and hatch distance was found to be the most significant parameter affecting the average melt pool overlap depth in the cubes built with 60 microns layer thickness. Interaction of speed and hatch distance was found to be the most significant parameter for porosity and Laser scan speed was the most significant parameter for average melt pool overlap depth in cubes built with 90 microns layer thickness. Comparison of measured responses with individual parameters provides partial trends of melt pool dimensions and porosity. As the heat input is captured better in line energy and area energy density, a better trend of the melt pool dimensions data and marginal trend of porosity in comparison with energy densities is discussed. The ratio of maximum length to minimum length of defects such as porosity and lack of fusion is measured to determine the shape of the defects and averaged to provide insight into the dominant shape of defect for a given set of parameters.

This study presents a unique melting strategy in electron beam-powder bed fusion of Alloy 718 to tailor the grain morphology from the typical columnar to equiaxed morphology. For this transition, a specific combination of certain process parameters, including low scanning speeds (400-800 mm/s), wide line offsets (300-500 mu m) and a high number of line order (#10) was selected to control local solidification conditions in each melt pool during the process. In addition, secondary melting of each layer with a 90. rotation with respect to primary melting induced more vigorous motions within the melt pools and extensive changes in thermal gradient direction, facilitating grain morphology tailoring. Four different types of microstructures were classified according to the produced grain morphology depending on the overlap zone between two adjacent melt pools, i.e., fully-columnar (overlap above 40 %), fully-equiaxed (overlap below 15 %), mixed columnar-equiaxed grains, and hemispherical melt pools containing mixed columnar-equiaxed grains (overlap similar to 20-25 %). The typical texture was <001>; however, the texture was reduced significantly through the transition from the columnar to equiaxed grain morphology. Along with all four different microstructures, shrinkage defects and cracks were also identified which amount of them reduced by a reduction in areal energy input. The hardness was increased through the transition, which was linked to the growth of the.” precipitates and high grain boundary density in the fully-equiaxed grain morphology.

Electron beam melting (EBM) is gaining rapid popularity for production of complex customized parts. For strategic applications involving materials like superalloys (e.g., Alloy 718), post-treatments including hot isostatic pressing (HIPing) to eliminate defects, and solutionizing and aging to achieve the desired phase constitution are often practiced. The present study specifically explores the ability of the combination of the above post-treatments to render the as-built defect content in EBM Alloy 718 irrelevant. Results show that HIPing can reduce defect content from as high as 17% in as-built samples (intentionally generated employing increased processing speeds in this illustrative proof-of-concept study) to &lt;0.3%, with the small amount of remnant defects being mainly associated with oxide inclusions. The subsequent solution and aging treatments are also found to yield virtually identical phase distribution and hardness values in samples with vastly varying as-built defect contents. This can have considerable implications in contributing to minimizing elaborate process optimization efforts as well as slightly enhancing production speeds to promote industrialization of EBM for applications that demand the above post-treatments.

Electron Beam Powder Bed Fusion process for Alloy 718 was investigated, in the sense of microstructural evolution with varying process conditions. The existence of a geometric relationship between the melt front and the processing parameters was observed. By understanding and capitalizing on this relationship, it was possible to obtain columnar, equiaxed or bimodal microstructure.

New approaches for efficient NDT inspection of modern additively manufactured metallic components are required urgently to qualify and validate the next generation of metallic parts across a range of industries. Ultrasonic testing is a fundamental component of NDT for such additive manufacturing processes. This work studies the ultrasonic propagation characteristics of EBM manufactured sample coupons in Inconel 718material. Fundamental longitudinal and shear wave velocity measurements are experimentally measured in 3 orthogonal build directions of the sample coupons. Results show a dependency of the ultrasonic velocities and the build direction. The measured velocities are further verified in a phased array measurement showing successful results that highlights the potential of continued studies with synthetic apertures techniques.

Electron beam melting (EBM) is a powder-bed fusion process within the group of additive manufacturing (AM) technology that is used to fabricate high performance metallic parts. Nickel-Iron base superalloys, such as Alloy 718, are subjected to successive heating and cooling at temperatures in excess of 800 °C during the EBM process. Characterization of the dendritic structure, carbides, Laves and δ-phase were of particular interest in this study. These successive thermal cycles influence the microstructure of the material resulting in a heterogeneous structure, especially in the building direction. Hence, the aim of this study was to gain increased fundamental understanding of the relationship between the processing history and the microstructure formed within a single layer. Different numbers of tracks with equal heights were for this purpose produced, varying from one to ten tracks. All tracks used the same process parameters regardless of number and/or position. Microstructure characteristics (sub-grain structure, grain structure and phases) were analyzed by optical microscopy, scanning electron microscopy equipped with energy disperse spectroscopy and electron backscatter diffraction. The direction of dendrites changed in the overlap zones within the tracks due to re-melting of material in the overlap zone. The primary dendrite arm spacings slightly increased along multi-tracks owing to a slight decrease in cooling rate by addition of the next tracks. Epitaxial growth of grains were observed in all samples due to partial re-melting of grains in previous layers and surface nucleation was also found to occur in all tracks.

Additive manufacturing (AM) of Ni-based superalloys such as Alloy 718 may obviate the need for difficult machining and welding operations associated with geometrically intricate parts, thus potentially expanding design possibilities and facilitating cost-effective manufacture of complex components. However, processing AM builds completely free from defects, which may impair mechanical properties such as fatigue and ductility, is challenging. Anisotropic properties, microstructural heterogeneities and local formation of undesired phases are additional concerns that have motivated post-treatment of AM builds. This work investigates the microstructural changes associated with post-treatment of Alloy 718 specimens produced by Electron Beam Melting (EBM) for as-built microstructures at 3 build heights: near base plate, in the middle of build and near the top of the build. Two different post-treatment conditions, hot isostatic pressing (HIP) alone and a combined HIP with solutionising and two-step aging were examined and compared to the results for the as-built condition. The influence of various post-treatments on minor phase distributions (δ, γ″, carbides), overall porosity, longitudinal grain widths and Vickers microhardness was considered. The HIP treatment led to significant reduction in overall porosity and dissolution of δ phase, which led to appreciable grain growth for both post-treatment conditions. The variation in hardness noted as a function of build height for the as-built specimens was eliminated after post-treatment. Overall, the hardness was found to decrease after HIP and increase after the full HIP, solutionising and aging treatment, which was attributed to dissolution of γ″ during HIP and its re-precipitation in subsequent heat treatment steps.