Browsing by Subject "Vickers hardness"

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Impact of Porosity Type on Microstructure and Mechanical Properties in Selectively Laser Melted IN718 Lattice Structures
(University of Texas at Austin, 2021) Ramachandra, S.; Ravichander, B.B.; Farhang, B.; Ganesh-Ram, A.; Hanumantha, M.; Marquez, J.; Humphrey, G.; Swails, N.; Amerinatanzi, A.
Laser Powder Bed Fusion (LPBF), one of the most employed additive manufacturing techniques for metals, has opened new dimensions in realizing strong and weight reducing structures. In this study, Inconel 718 (IN718) unit cell designs, were fabricated through the LPBF technique and analyzed. Among the plethora of lattice structures in existence, BCC, BCC-Z, FCC, FCC-Z, Gyroid, Diamond and Schwarz structures have been selected to focus on. A relationship between the mechanical properties including yield strength, failure stress and strain, and hardness with each type of unit cell was established. Also, the effect of the possible defects on the hardness value was examined using microstructural analysis on samples. Scanning Electron Microscopy (SEM) analysis was also performed to examine the possible defects and its effect on the hardness of the as-built part. The SEM images of the grain structures indicated higher levels of isotropy in Gyroid, and Diamond samples compared to the rest of the samples which relates to the load bearing capacities of each unit cell structure. A similar trend was observed in terms of the uniformity of meltpool which can be linked with the consistency in yield characteristics. Further, Diamond and BCC-Z structures displayed high values of hardness in comparison with rest of the samples.
Investigating the Effect of Heat Transfer on the Homogenity in Microstructure and Properties of Inconel 718 Alloy Fabricated by Laser Powder Bed Fusion Technique
(University of Texas at Austin, 2021) Farhang, B.; Ravichander, B.B.; Ganesh-Ram, A.; Ramachandra, S.; Hanumantha, M.; Hall, W.; Dinh, A.; Amerinatanzi, A.; Shayesteh Moghaddam, N.
Laser Powder Bed Fusion (LPBF) of metallic components is associated with microstructure and inhomogeneity of properties in the fabricated components. In a recent work by the authors, a novel technique of considering a border surrounding the main part during the LPBF fabrication is proposed to address the issue of inconsistency in microstructure across the cross section of LPBF-fabricated parts. This study, on the other hand, aims to investigate the effect of such border on the microstructure homogeneity along the build direction of LPBF-fabricated parts. For this purpose, a cubic sample surrounded by a cubic border was fabricated to control the rate of heat transfer and then improve the microstructure across the cross section. Also, a sample with identical dimensions and the same process parameters was printed without border as a reference to be compared. To investigate the variation of the properties along the build direction, microstructure and hardness results were compared between areas near and away the substrate for both samples. For the area away from the substrate, in both samples, a deeper pool, less surface porosity, and higher Vickers hardness was observed compared to the area near the substrate. It was found out that, regardless of the focused area, the sample fabricated with border possesses deeper pools, higher level of density as well as higher hardness value. However, in term of homogeneity along the build direction, no significant improvement was observed for the sample fabricated with the cubic border.
Investigation of the Properties of Reinforced IN718 Structures Fabricated using Laser Powder Bed Fusion
(University of Texas at Austin, 2021) Ravichander, B.B.; Farhang, B.; Ganesh-Ram, A.; Hanumantha, M.; Ramachandra, S.; Shinglot, Y.; Amerinatanzi, A.; Shayesteh Moghaddam, N.
Inconel 718 (IN718) superalloy, known for its high strength and corrosion resistant behavior, is widely used in the aerospace and automotive industries. Laser power bed fusion (LPBF), one of the commonly used techniques of additive manufacturing, enables the fabrication of structures with a variety of local properties. Using the same material, components with spatially varying properties can be fabricated through applying different processing parameters. In this study, IN718 composite structures were fabricated using four types of rod reinforcements with different geometry. A different set of process parameters was used to fabricated reinforcing rods compared to that of the main part. The bonding quality at the interface between the main part and reinforcements was determined by defect analysis on the microstructure results. Also, Vickers hardness test was performed at the interface in order to examine the mechanical properties of the samples. It was found out that a similar level of densification and hardness value, slightly less than the plain sample, can be achieved using helical and arc reinforcing rods. By contrast, significantly lower density and hardness were observed for the sample reinforced by square rods compared to the plain sample.
Microstructural and Mechanical Characterization of Laser Powder Bed Fusion of IN718 Overhangs
(University of Texas at Austin, 2021) Hanumantha, M.; Farhang, B.; Ravichander, B.B.; Ganesh-Ram, A.; Ramachandra, S.; Finley, B.E.; Swails, N.; Amerinatanzi, A.
Inconel 178 (IN718), a nickel-chromium-based superalloy known for its superior properties is used in aerospace, oil, and gas industries. Due to its high hardness, IN718 is difficult to be machined. Therefore, fabrication of IN718 components with complex geometries is a big challenge when conventional manufacturing techniques are used. Laser powder bed fusion (LPBF) technique can be used to fabricate IN718 parts with high precision. During fabrication of overhang structures, supports are typically employed, which significantly increases the use of resources such as material consumption and postprocessing. The focus of this study is to determine the angle at which an overhang structure can be fabricated without employing supports. To this aim, the angled-overhang samples with varied angles (30°-90°) were manufactured with no support. The effect of overhang state on the microstructural and mechanical properties of the LPBF-processed IN718 samples was analyzed. According to the microstructural analysis, the deepest melt pools in the overhang sample seemed to be at a hanging angle of 45°. Moreover, the overhang sample fabricated at 45° had the greatest Vickers hardness value of 382.90 HV. This study urges a reconsideration of the common approach of selecting supports for overhang samples in the LPBF process when a higher quality of the as-fabricated parts is desired.
A Microstructure and Hardness Study of Functionally Graded Materials Ti6Al4V/TiC by Laser Metal Deposition
(University of Texas at Austin, 2015) Zhang, Jingwei; Zhang, Yunlu; Liou, Frank; Newkirk, Joseph W.; Brown-Taminger, Karen M.; Seufzer, Walliam J.
Crack free functionally graded material (FGM) Ti6Al4V-TiC has been fabricated by laser metal deposition (LMD) using TiC and Ti6Al4V powder which were premixed for different ratios. This study focuses on the influence of laser processing parameters and TiC compositional distribution on microstructure, Vickers hardness and phase. The microstructure is analyzed by scanning electron microscopy (SEM), x-ray diffraction (XRD) and hardness tests. Primary carbide, eutectic carbide and unmelted carbide are found in the deposit area. When laser power increased, the primary and secondary dendrite arm spacing increased. The laser power and scanning speed did not influence the Vickers hardness distribution significantly.