Sasan Dadbakhsh

Effect of selective laser melting layout on the quality of stainless steel parts

Purpose – Selective laser melting (SLM) is increasingly used for the manufacture of end‐use metal tools and parts, requiring the careful identification of a range of appropriate process parameters and conditions to achieve desirable properties and quality. Process conditions such as the relation between layout of parts and internal gas flow within the SLM platform can influence the consolidation of metal powers and therefore the quality and properties of the final parts. The purpose of this paper is to investigate the effect of part layout on quality and mechanical properties of cylindrical 316L stainless steel parts manufactured by SLM.Design/methodology/approach – The cylindrical 316L stainless steel parts were manufactured in two directions, one perpendicular to the gas flow direction and one parallel to it. The investigation first focuses on visual inspection and porosity measurements to compare the quality factors such as delamination and porosity of the parts. A mechanical test procedure including t...

Effect of layer thickness in selective laser melting on microstructure of Al/5 wt.%Fe2O3 powder consolidated parts.

In situ reaction was activated in the powder mixture of Al/5 wt.%Fe2O3 by using selective laser melting (SLM) to directly fabricate aluminium metal matrix composite parts. The microstructural characteristics of these in situ consolidated parts through SLM were investigated under the influence of thick powder bed, 75 μm layer thickness, and 50 μm layer thickness in various laser powers and scanning speeds. It was found that the layer thickness has a strong influence on microstructural outcome, mainly attributed to its impact on oxygen content of the matrix. Various microstructural features (such as granular, coralline-like, and particulate appearance) were observed depending on the layer thickness, laser power, and scanning speed. This was associated with various material combinations such as pure Al, Al-Fe intermetallics, and Al(-Fe) oxide phases formed after in situ reaction and laser rapid solidification. Uniformly distributed very fine particles could be consolidated in net-shape Al composite parts by using lower layer thickness, higher laser power, and lower scanning speed. The findings contribute to the new development of advanced net-shape manufacture of Al composites by combining SLM and in situ reaction process.

Surface finish improvement of LMD samples using laser polishing

Laser metal deposition (LMD) is an additive manufacturing (AM) process used for repairing and fabricating metallic parts. One of the major drawbacks of this process is the relatively rough surface of the manufactured parts. In this work, surface polishing using laser for LMD parts was studied. Using the LMD process, a series of block samples of Inconel 718 were produced. The top surface of the samples was then laser scanned using combinations of parameters. The surface roughness of the samples was evaluated and subsequently, optimum process parameters set for laser polishing were predicted using analytical experimental design (DoE) software. The results showed the capability of a laser to improve the finishing surface of the LMD parts to about 2 µm Ra, which can be acceptable for many industrial applications. The relation of laser energy to final surface roughness was also studied, showing the strong dependency of surface finish on laser energy.

Additively Manufactured and Surface Biofunctionalized Porous Nitinol

Enhanced bone tissue regeneration and improved osseointegration are among the most important goals in design of multifunctional orthopedic biomaterials. In this study, we used additive manufacturing (selective laser melting) to develop multifunctional porous nitinol that combines superelasticity with a rationally designed microarchitecture and biofunctionalized surface. The rational design based on triply periodic minimal surfaces aimed to properly adjust the pore size, increase the surface area (thereby amplifying the effects of surface biofunctionalization), and resemble the curvature characteristics of trabecular bone. The surface of additively manufactured (AM) porous nitinol was biofunctionalized using polydopamine-immobilized rhBMP2 for better control of the release kinetics. The actual morphological properties of porous nitinol measured by microcomputed tomography (e.g., open/close porosity, and surface area) closely matched the design values. The superelasticity originated from the austenite phase formed in the nitinol porous structure at room temperature. Polydopamine and rhBMP2 signature peaks were confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy tests. The release of rhBMP2 continued until 28 days. The early time and long-term release profiles were found to be adjustable independent of each other. In vitro cell culture showed improved cell attachment, cell proliferation, cell morphology (spreading, spindle-like shape), and cell coverage as well as elevated levels of ALP activity and increased calcium content for biofunctionalized surfaces as compared to as-manufactured specimens. The demonstrated functionalities of porous nitinol could be used as a basis for deployable orthopedic implants with rationally designed microarchitectures that maximize bone tissue regeneration performance by release of biomolecules with adjustable and well-controlled release profiles.

Materials and process aspects of selective laser melting of metals and metal matrix composites: A review

Materials and process aspects of selective laser melting of metals and metal matrix composites : A review

Study on static strain aging of 6082 aluminium alloy

Abstract In this study both the quench aging and static strain aging kinetics of a 6082 Al alloy were investigated at a temperature range of 130–200°C using the Vickers hardness and tensile test. The activation energy and dislocation density were determined at different stages of the aging phenomenon. The former was used to analyse the kinetics of aging and the latter to interpret the competition of strengthening and recovery mechanisms during aging. It is shown that different activation energies are achieved depending on the aging time and temperature relating to formation of appropriate precipitates at different stages of aging. Moreover, it is revealed that prestrain reduces the activation energy. A linear equation is proposed between the dislocation density and the plastic strain after static strain aging. The competition of recovery with strengthening mechanisms during strain aging is discussed with regard to dislocation density after aging.

Consolidation behaviour and microstructure characteristics of pure aluminium and alloy powders following Selective Laser Melting processing

Selective Laser Melting (SLM) is an additive manufacturing process that directly consolidates metal powders to form near net shape or net shape components. A few commercial SLM systems have started to process a select choice of aluminium alloys. These alloys are generally based on conventional casting alloys that do not represent the highest performance aluminium alloys for aerospace application. This paper studies the consolidation behaviour and resulting microstructure of pure aluminium, 6061 alloy powder and a mixture of 6061 alloy powder with copper powder under different SLM processing parameters. It has found that the addition of copper powder to 6061 Al powder considerably changes the consolidation behaviour and the microstructure evolution, resulting in a denser and much finer microstructure. This work therefore demonstrates the premise to develop specific aluminium alloy powders for the SLM process and enabling the fabrication of high performance aluminium based products.

Selective laser sintering of polystyrene: a single-layer approach

ABSTRACT Selective laser sintering (SLS) is a powder bed-based additive manufacturing technique to produce complex three-dimensional parts. Although every thermoplastic polymer theoretically can be processed via this technique, variable material behaviour complicates the optimisation of the processing parameters. This study investigates the processability of polystyrene by SLS by evaluating bed temperatures and laser parameters. The morphology of single-layer parts is examined through scanning electron microscopy and roughness measurements to find an indication for the optimal processing parameters. Additionally, the effect of carbon black (CB) (as a colouring additive) on the processability of polystyrene is studied. It is found that polystyrene without CB is processable at a bed temperature just below the glass transition temperature. The addition of CB reduces the consolidation of single layers. The single-layer investigation is extended to, and shown to correlate with, a preliminary investigation of the relative density of multilayer parts.

Additively manufactured metals for medical applications

Abstract Additive Manufacturing (AM) allows to produce improved, custom made, patient specific and complex shaped medical implants. Both mechanical and biological aspects as well as type of implant and patient specific requirements determine the shape of the implant and the material it will be made of. The current chapter reviews the metals and metallic alloys that can be successfully processed by powder bed fusion AM technologies, focusing on the interrelationship between their chemistry and microstructure, on one hand, and their biological and mechanical behavior, respectively, on the other hand.

Microstructural Analysis and Mechanical Evaluation of Ti‐45Nb Produced by Selective Laser Melting towards Biomedical Applications

Selective laser melting (SLM) is an additive manufacturing (AM) technique to produce complex parts. However, Ti-45Nb (with a low stiffness as well as an excellent biocompatibility and corrosion resistance) is not yet developed by this process towards biomedical applications. Therefore, this work is to analyze SLM Ti-45Nb with an engineered content of porosity. It is shown that the combination of porosity and the material property can lead to an elastic modulus within the range observed for a bone. The matrix contains only a β-phase after laser rapid solidification. The β-phase is composed of larger laser solidified grains embedding numerous submicron/ultrafine subgrains. The ultrafine subgrains enable a high ductility in conjunction with a satisfactory compressive strength (despite the presence of porosity). The SLM full melting, assessed by the shear strength evaluations, also contributes to the satisfactory mechanical strength. The findings are very promising to benefit biomedical implants for load-bearing applications.