Selective laser melting (SLM) is a transformative additive manufacturing technique that enables the production of complex metallic components with high precision. Understanding the microstructural evolution during the SLM process is crucial for optimising the mechanical properties and performance of the fabricated parts. This study focuses on developing a predictive model for the microstructure evolution of Ti6Al4V alloy during SLM. The model integrates thermal simulations with phase transformation kinetics using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory to predict the formation and dissolution of alpha and martensite phases. The thermal history of the SLM process was simulated using Finite Element Analysis (FEA) in Abaqus, which provided the temperature distribution and cooling rates experienced by the material. These thermal profiles were then used to drive the microstructure evolution model, which predicts the phase fractions and grain structures resulting from the SLM process. The model was validated against experimental data, showing good agreement in predicting phase fractions and microstructural features. Our results highlight the significant impact of processing parameters, such as laser power and scanning speed, on the microstructure of Ti6Al4V. Higher laser powers and slower scanning speeds were found to promote the formation of coarser microstructures, while faster cooling rates led to finer grains and higher martensite fractions. This comprehensive modelling approach provides valuable insights into optimising SLM process parameters to achieve desired microstructural characteristics and improve the mechanical performance of Ti6Al4V parts. The developed model is a robust tool for guiding the design and optimisation of SLM processes, reducing the reliance on trial-and-error methods, and enhancing the efficiency and quality of additive manufacturing for critical applications in aerospace, biomedical, and automotive industries.

Inconel 718 is used in a wide range of industries such as oil and gas, nuclear, aviation, and etc. due to its excellent mechanical properties. The use of additive manufacturing (AM) to manufacture parts is increasing rapidly Due to the dimensional limitations in the manufacturing of parts using the additive manufacturing methods, these parts must be connected to other parts in different applications with the help of conventional methods such as welding. In this research, the thermal analysis of plasma welding of an Inconel 718 sheet made by SLM method using ABAQUS software is discussed. Input heat with Gaussian distribution was entered into the model by DFLUX subprogram with FORTRAN program language. In order to validate the thermal model, the temperature was measured during the welding process using a thermocouple. A relatively good match is observed between the numerical and experimental thermal analysis results. The microstructure of the welded samples was examined with an optical microscope and the microstructure of base metal, fusion zone, and heat affected zone were investigated. The dendritic structure in the welding area and the occurrence of recrystallization in the heat-affected area was evident. The tensile test results showed that the sample without welding has a higher yield and ductility.

One of the major challenges in the Selective laser melting process is the generation of residual stresses in the processed parts. The residual stress can have detrimental effects on the dimensional accuracy, mechanical properties and performance of the part. In most industrial components, such as turbine blades, the cross section of the part changes along its length which can affect the amount of residual stress. The most important parameters of Selective laser melting process include laser power, scanning speed, layer thickness and hatch spacing. These parameters are effective on the thermal profile created during the manufacturing process. Therefore, they can play an essential role in the formation of residual stresses in parts. In this paper, the effect of hatch spacing parameter on the residual stress magnitude of Inconel 625 samples with different cross sections has been investigated experimentally, so that the energy density does not exceed the appropriate range for the density of the samples. Using the non-destructive X-ray diffraction method, the residual stresses measured in the center of the sample surface and the intersection of the two variable sections of the samples. The results showed that the use of a larger hatch space significantly reduces the amount of residual stress. Also, the comparison of the amount of residual stress in the center of the surface of the lower and upper parts of the samples shows that the amount of residual stress in the interface between the two cross sections is reduced by almost half.

In the present work, the Selective laser melting (SLM) has been chosen as a controlled thermomechanical processing route in which the required temperature and strain for the occurrence of dynamic recrystallization is provided. The 316L stainless steel as representative material was constructed by SLM under specified parameters (laser power, layer thickness, hatch spacing, scan strategy, and scan speed). The printed material’, s microstructure was carefully analyzed through electron back scattered diffraction. The presence of considerable fine grains (< 20 μ, m) through the printed microstructure was considered as evidence for the occurrence of dynamic recrystallization during the manufacturing process. The high fraction of sub-boundaries (~79. 7%) and sub-grains indicated the capability of the material for substructure development in the course of additive manufacturing process, and the fact that the new fine grains were formed through continuous dynamic recrystallization mechanism. The creation of plastic strains through the parts structure during SLM, which was required for dynamic recrystallization, was discussed relying on the expansion and contraction of the layers during repeated heating and cooling cycles. The amount of plastic microstrain was estimated to be around ~0. 56 considering the layer thickness and depth of the melt pool. The hot compression tests were conducted at 1000℃,and various strain rates of 0. 001, 0. 01 and 0. 1 s-1 and the corresponding critical strains of dynamic recrystallization (~0. 2) were calculated, which was well lower than those created during additive manufacturing process.

Selective laser melting (SLM) is an additive manufacturing technique in which a laser beam with a high energy density is used to melt a metal powder substrate. Although this technique has several advantages, including the possibility of fabricating complex metal components quickly, there are concerns about the mechanical properties of the parts produced by the SLM method. This is study aims to ensure the achievement of acceptable mechanical properties including yield stress, tensile strength, and elongation percentage compared to conventional manufacturing methods. For this purpose, samples of 316L stainless steel were printed using the SLM machine. These samples and samples of annealed 316L bar were tested under same conditions and by the same equipment. Despite the large differences in microscopic structure, no significant differences were observed in mechanical properties. Also, the obtained results were compared with the results related to the sample made by the DLD additive manufacturing method, which is similar to SLM in terms of energy source and raw materials. The result represents that the mechanical strength and microhardness of the sample produced by the SLM technique are higher than the other samples, and the elongation percentage is within the desirable range. The yield stress, tensile strength, and elongation are respectively 595Mpa, 696Mpa, and 34. 5%, all of which are within the acceptable range required by the standards for such samples. The investigation of the microstructure shows a complete austenitic cellular structure without considerable solidification defects. Overall, the SLM additive manufacturing is a reliable process to produce 316L stainless steel parts in terms of mechanical properties.

Additive manufacturing methods and/or 3D printing have become increasingly popular with particular emphasis on methods used for metallic materials. Selective laser melting (SLM) process is one of the additive manufacturing methods for production of metallic parts. The method was developed specifically to process metal parts that need to be more than 99 percent dense. In this method, according to a predefined pattern, the top surface of the powder layer is scanned by the laser and a local (Selective) melt pool is produced in the place of the laser spot which results in a fully dense layer after solidification. In this study, a semi-coupled thermo-mechanical simulation of SLM process is carried out in ABAQUS finite element software. In order to simulate the moving heat flux and update material properties from the powder to the dense solid, the ability of the software for employing user -defined subroutines is used. Investigation of the residual stress distribution and distortion of a part built using SLM process are the main objectives of this simulation. Results presented for two different mechanical boundary conditions show that when the bottom face of the layer is clamped, the top face of the built layer deforms in a concave shape, while the lateral faces of the layer have simply-supported boundary conditions and the bottom face of the layer is free, the part is warped.

Abstract Introduction: Considering the nature of the additive manufacturing process and the produced layered structure, the possible gradient in microstructure can be predictable. For this purpose, the morphology and microstructure of the cross-section from top to bottom was evaluated. The morphology of the last and first printed layers, were also investigated. Methods: Ti-10Mo was printed using mixed powder in 120 layers, each thickness of 25µm, by Selective laser melting (SLM) with a laser power of 95 W, a scanning speed of 600 mm.s-1, and a hatching distance of 88 µm under argon atmosphere. Density was measured, and the constituent phases were identified by XRD. The microstructural feature was studied by optical and scanning electron microscopies. Findings: The printed samples were dense, and the relative density was about 98.53%. Details in microstructural evaluation show spectacular Mo-enriched rims, which reveal the circumstance of Mo dissolution in molten Ti and homogenization, consequently. Also, a gradient in Mo dissolution is seen along the cross-section. So that, at the top, the sides of molten pools that are mostly Mo enriched are seen as thick white and bright rims in electron microscopy and as white to light purple in optical microscopy. However, at the bottom, the rims seem to be really thinner and smoother, which can be in consequence of enhanced diffusion of the Mo to Ti matrix. Here, the promoted diffusion could be in the result of heat transfer from the newly printed layer to the previous printed ones.

The use of metallic 3D printers in medical manufacturing has enabled the creation of complex medical products customized to each patient's specific anatomical information through CAD/CAM. This technology has allowed the examination of three-dimensional (3D) bone scaffolds as models for human bone geometry. Gradually, 3D printing has become a promising tool for creating grafts and scaffolds for bone tissue engineering, particularly in orthopedic fractures. The present study explores the use of a medical-grade titanium alloy coated with chitosan containing wollastonite nanoparticles (WS-NPs) at varying concentrations (0, 5, 10, and 15 wt%) to fabricate a 3D porous metallic scaffold using Selective laser melting (SLM). Materials characterization was performed using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) analysis, while mechanical tests were conducted to determine the compressive strength, fracture toughness, elastic modulus, and Poisson ratio of the samples. The study involved fabricating a 3D porous metallic scaffold using SLM and a medical-grade titanium alloy coated with chitosan containing wollastonite nanoparticles (WS-NPs) at varying concentrations (0, 5, 10, and 15 wt%). The samples were characterized using SEM and XRD analysis, and mechanical tests were conducted to determine their properties. The samples were also subjected to a Simulated Body Fluid (SBF) and phosphate-buffered saline (PBS) test to evaluate their bioactivity and biodegradation rate, as well as an MTT toxicity test. The feasibility of the prostheses was tested for 1, 3, 7, and 14 days, and the results were analyzed. The SEM images and XRD analysis showed the surfaces of scaffold parts produced in nanometer dimensions, confirming the corresponding coating as well as the phases in the scaffold. The sample containing 10 wt% WS-NPs had the highest elastic modulus of about 420 MPa and compressive strength with a coating containing 10 wt% WS-NPs in a chitosan matrix. The results showed that the percentage of porosity changed from 52% to 48% in sample 2 and sample 3, respectively, as the compressive strength increased. The third sample exhibited promising biological behavior for orthopedic applications. The objective of this work is to fabricate and characterize a 3D porous metallic scaffold coated with chitosan containing wollastonite nanoparticles for bone tissue engineering applications. The study successfully fabricated a 3D porous metallic scaffold using SLM and a medical-grade titanium alloy-coated with chitosan containing wollastonite nanoparticles (WS-NPs) at varying concentrations. The results demonstrated that the sample containing 10 wt% WS-NPs had the highest elastic modulus and compressive strength. The third sample exhibited potential for orthopedic applications due to its promising biological behavior.