Effect of heat treatment on the microstructure and mechanical properties of Monel K500 alloy fabricated via L-PBF and LP-DED

This study examines and compares the effect of different heat treatments (HT) on the microstructure and mechanical properties of Monel K500 fabricated using laser powder bed fusion (L-PBF) and laser powder directed energy deposition (LP-DED) technologies. The as-fabricated Monel K500 specimens exhibited dendritic microstructure and elemental micro-segregation due to high cooling rates induced during the fabrication process. The applicability of HT proposed in the literature for wrought Monel K500 was investigated for L-PBF and LP-DED using four different HT procedures involving hot isostatic pressing (HIP), solution annealing (SA), and aging. The mechanical properties of test specimens were evaluated using uniaxial tensile testing at room temperature. The microstructural evolution of test specimens during HT was analyzed using a scanning electron microscope. For all HT conditions investigated, L-PBF Monel K500 specimens consistently displayed higher strength and lower ductility compared to the LP-DED counterparts. The HT procedure involving HIP at 1160°C for 3hr at 100 MPa, SA at 1100°C for 15 min, and three step aging at 610°C for 16 hr, 540°C for 6 hr, and 480°C for 8 hr resulted in highest strength for both L-PBF and LP-DED fabricated Monel K500.Mechanical Engineerin

Hyaluronan turnover and hypoxic brown adipocytic differentiation are co-localized with ossification in calcified human aortic valves

The calcification process in aortic stenosis has garnered considerable interest but only limited investigation into selected signaling pathways. This study investigated mechanisms related to hypoxia, hyaluronan homeostasis, brown adipocytic differentiation, and ossification within calcified valves. Surgically explanted calcified aortic valves (nﾠ=ﾠ14) were immunostained for markers relevant to these mechanisms and evaluated in the center (NodCtr) and edge (NodEdge) of the calcified nodule (NodCtr), tissue directly surrounding nodule (NodSurr); center and tissue surrounding small ﾓprenodulesﾔ (PreNod, PreNodSurr); and normal fibrosa layer (CollFibr). Pearson correlations were determined between staining intensities of markers within regions. Ossification markers primarily localized to NodCtr and NodEdge, along with markers related to hyaluronan turnover and hypoxia. Markers of brown adipocytic differentiation were frequently co-localized with markers of hypoxia. In NodCtr and NodSurr, brown fat and ossification markers correlated with hyaluronidase-1, whereas these markers, as well as hypoxia, correlated with hyaluronan synthases in NodEdge. The protein product of tumor necrosis factor-? stimulated gene-6 strongly correlated with ossification markers and hyaluronidase in the regions surrounding the nodules (NodSurr, PreNodSurr). In conclusion, this study suggests roles for hyaluronan homeostasis and the promotion of hypoxia by cells demonstrating brown fat markers in calcific aortic valve disease

Investigating the effect of defects on the crack initiation of additively manufactured IN718 using crystal plasticity simulations

This study aims to analyze the effect of defects location on the fatigue behavior of additively manufactured IN718. A competing mechanism exists between persistent slip bands (PSBs) and volumetric defects on the initiation of fatigue cracks in AM IN718 under cyclic loading. Crystal plasticity simulations were performed to reveal the relative importance in crack initiation due to defects and PSBs. Cyclic loading was applied on a defect laden polycrystalline aggregate and the defect locations were systematically varied. The crack nucleation cycles and locations were captured using a strain contrast-based crack initiation criterion. The findings suggest that the presence of large defects affects the cyclic strain localization and crack initiation behavior of the AM IN718 material.Mechanical Engineerin

Revealing Texture Induced Abnormal Tensile Deformation Behavior in Additively Manufactured Haynes 282 Using Crystal Plasticity Simulations

A ductile fracture typically features a dimpled surface appearance because of micro-void coalescence and a circular cup-and-cone morphology. Tensile fracture surfaces of additively manufactured Haynes 282, a nickel-base superalloy, in this work exhibit an elliptical shape – an aberration to classic fracture surface. Both microstructural characterization and fractography were performed using scanning electron microscopy (SEM) on the tensile deformed surfaces to assess the fracture behavior. To gain better mechanistic insights into the governing factors of this elliptical shape fracture, crystal plasticity finite element (CPFE) simulations were performed using the experimentally calibrated material parameters. Uniaxial tensile loading simulations were carried out on a polycrystalline aggregate where the initial texture was varied to the CPFE simulation to emulate the experimental microstructure. The mechanical response and shape of the fracture surface obtained from the simulations were compared with the experimental tensile deformed surface to illustrate the texture dependent deformation inhomogeneity.Mechanical Engineerin

Selection of turbulence models via multiscaling analysis of an axisymmetric pipe flow and heat transfer

To fully evaluate a turbulent flow, Direct Numerical Simulation (DNS) is the most accurate method by far and requires considerable computational power and time; not optimum for industry standards. Developing an alternative model, providing results with reasonable accuracy would resolve this issue. Reynolds Averaged Navier Stokes (RANS) modeling has proven its worth in addressing this phenomenon. In this study, we investigated the RANS turbulence models from COMSOL for fully developed single-phase flow in a two-dimensional axisymmetric pipe domain with constant heating at the wall and periodic boundary conditions at the inlet and outlet. Heat transfer in the fluid module has been added to address the heat transfer phenomenon. We evaluated the computed results with existing DNS data to match the accuracy of the RANS models. RANS simulations are conducted for friction Reynolds number, i.e., Re_{\tau}= 180, 314, and 395 with varying Prandtl numbers, i.e., Pr = 0.71, 2, 5, and 7. Multiscaling analyses in the flow's inner, outer, and meso scaling regions are performed for fluid and heat transfer profiles, i.e., mean streamwise velocity, Reynolds shear stress, mean streamwise temperature, and turbulent heat flux, to compare with the DNS data. The investigation reports the scaling analysis's effectiveness and shows that RANS turbulence models can be used to describe such flow with reasonable accuracy.Comment: We have a major revision of this paper. I will share the updated one once I have i

Fatigue strength prediction through defects-based analysis of L-PBF 17-4 PH stainless steel

Murakami’s approach has been used in the high cycle fatigue regime to relate the fatigue limit to the critical defect size and location in additively manufactured (AM) metallic materials. However, the applicability of this model has not yet been thoroughly examined for AM materials in the very high cycle fatigue (VHCF) regime. Therefore, this study investigates the possibility of relating the volumetric defect features to the fatigue strength of 17-4 precipitation hardened (PH) stainless steel (SS) manufactured via laser-powder bed fusion (L-PBF) additive manufacturing technology. The 17-4 PH SS specimens are manufactured using an EOS M290 L-PBF system, heat-treated, machined, polished, and tested in the VHCF regime using an ultrasonic fatigue testing system. Careful fractography has also been performed on all fractured specimens to determine the volumetric defects responsible for the crack initiation.Mechanical Engineerin