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In the present study, the influence of laser energy density (LED) on geometrical characteristics, mechanical properties and microstructure of Inconel 718 parts fabricated by laser engineered net shaping (LENS) were investigated. Thin walls and block specimens were designed and fabricated under a total of 25 different energy density combinations. The material properties, including part dimensional shrinkage, surface roughness, surface hardness, and microstructures, including, porosity, geometrical dilution, average grain size and dendrite arm spacing (DAS), were evaluated. The results of this investigations indicate that with the increase of LED, the part shrinkage and surface roughness present a down and up trend, whereas the porosity, geometrical dilution, grain size and DAS increase with increasing of LED and there is no statistically significant effect of LED on the surface micro hardness. Taking account of the material characterization results, the energy density window for LENS process of Inconel 718 is suggested between 98.21 J/mm2 to 107.14 J/mm2. The outputs of this study could provide an insightful view of the effects of energy input on mechanical and microstructural properties of as-deposited Inconel 718 alloy by LENS process.

The molten pool temperature during laser engineered net shaping (LENS) could directly affect the microstructure and phase compositions of materials in the molten pool, thereby affecting the mechanical properties of the fabricated parts. To achieve a well-built solid structure, the research on fundamentals and methods of molten pool thermal behavior monitoring is of great significance. Using a high-resolution infrared camera, this paper realized real-time temperature tracking of Inconel 718 deposition in the LENS process. The effects of deposition variables, such as laser power and scanning speed, on the molten pool temperature and cooling rate have been investigated. In addition, the effects of the molten pool temperature on the molten pool depth and dendrite arm spacing (DAS) have been analyzed. The results suggest that the molten pool temperature increases with increasing of the laser power while it drops first and then rises with increasing of the scanning speed. The molten pool temperature increases nonlinearly with increasing of the number of layers during the material deposition process.

The amount of heat input, expressed as energy density, is one of the key parameters for laser additive manufacturing process. It will affect the melt pool dynamics, such as melt pool/powder interaction and temperature distribution, during the material solidification process, thus exerting an important influence on the forming accuracy and properties of the fabricated part. This paper investigates the effect of energy density on the forming accuracy and physical/mechanical properties of Inconel 718 part fabricated by LENS technique. Specifically, geometrical accuracy and relative density are measured with thin wall specimens. Surface roughness test is performed with block specimens. Based on the experimental results of the forming accuracy, relative density, and surface roughness, the suggested energy density ranges from 83.33 J/mm2 to 137.5 J/mm2.

In order to improve the accuracy and efficiency of damage assessment, a novel method to evaluate the damage state for remanufacturing blanks based on the magnetic and surface texture feature fusion was developed. Through modeling of the magnetic and surface texture features, sample entropy parameters from the magnetic intensity and its gradients were extracted, and energy, entropy, contrast, and correlation parameters from surface texture were obtained. The two-layered feature fusion model comprised of the data layer and the index layer was established. In the data layer, parameters of the magnetic and surface texture features and their nonlinear mapping relationships with damage were obtained. In the index layer, the information fusion between the magnetic and surface texture features was carried out by Dempster-Shafer (D-S) evidence theory. Finally, fatigue test samples were selected to verify the feasibility of the proposed method. Results show that the method can be used to determine the damage states of the remanufacturing blanks, which provides theoretical and technical decision support for remanufacturability of the components.

Due to high strength and ductility, AISI 4141 alloy steel is widely used in many industrial applications, such as gears and blades. When it is composed to harsh working environment, severe mechanical failures may happen. In order to save the high added value of the components, necessary repairing techniques are required to recover their functionality. Laser Engineered Net Shaping (LENS) is an innovative technology for metal parts repairing and rebuilding due to its metallurgical bonding and exhibit heat affected zone (HAZ). Compared to other repairing processes, LENS cannot only reduce the manufacturing time and cost, increase material utilization, but also provide an outstanding as-fabricated mechanical properties. Considering the compatibility and availability of powder materials, the selection of to-be-fabricated materials are important and decisive to the mechanical properties and the quality of the deposits. In this investigation, nickel-based and cobalt based superalloys are deposited onto AISI 4140 steel substrate using laser engineered net shaping (LENS) process to verify the feasibility of these superalloys for repairing of AISI 4140 workpieces. The micro-hardness, tensile strength, fracture and wear resistance are analyzed to testify the resistance of deformation, tension and anti-friction performance of deposited materials.

As an important factor during direct energy deposition (DED) additive manufacturing process, powder stream distribution will not only affect the deposition rate, but also the powder-gas and power-powder interactions, and thus the consequent quality and property of the fabricated part. This paper created an analytical model to illustrate the powder stream distribution under the four-jet nozzles in the DED. To validate the proposed model, weight measurement method was used to track the powder stream distributions at different positions under the nozzle. Additionally, the effects of the input variables, including powder flow rate, gas flow rate and particle size, on the powder stream distribution were also analyzed. The results suggest a relatively good agreement between the modelling and experimental measurements. At the end, the powder deposition efficiency (PDE) was estimated based on the simulation results.