Tom Pelletiers

Bio: Tom Pelletiers is an academic researcher from Research Triangle Park. The author has contributed to research in topics: Extrusion & Ultimate tensile strength. The author has an hindex of 2, co-authored 4 publications receiving 26 citations.

Effect of powder reuse on mechanical properties of Ti-6Al-4V produced through selective laser melting

Abstract: Metallic powder reuse presents attractive economic and environmental advantages for direct metal laser sintering (DMLS). However, continuous recycling of powder raises concerns of powder quality and sintered part performance, and complicates process validation. Efforts to examine the mechanical response of parts built with reused feedstocks are increasingly common in the technical literature, but none have optimized process parameters in DMLS to control for changes in material properties. In this paper, titanium powder reuse was investigated with the objective of optimizing the additive manufacturing (AM) process for reuse. Virgin Ti-6Al-4V powder was cycled a total of eight times through conditions representative of industrial DMLS machines. A full 23-factorial design of experiments (DOE) approach was employed to identify how parameter settings affect mechanical behavior, and include reuse as a process variable. The independent factors (laser power, laser speed, and hatch distance) did not significantly affect mechanical properties; however, measurements of ductility were found to be influenced by some interaction between the factors. These results were attributed to the narrow operating envelope which was required for successfully sintered specimens. Density and chemistry measurements further demonstrated no significant change with respect to reuse. The findings suggest that titanium powder can be reused up to eight times without any noticeable loss in strength or ductility.

Microstructural Assessment of a Multiple-Intermetallic-Strengthened Aluminum Alloy Produced from Gas-Atomized Powder by Hot Extrusion and Friction Extrusion.

Abstract: An aluminum (Al) matrix with various transition metal (TM) additions is an effective alloying approach for developing high-specific-strength materials for use at elevated temperatures. Conventional fabrication processes such as casting or fusion-related methods are not capable of producing Al–TM alloys in bulk form. Solid phase processing techniques, such as extrusion, have been shown to maintain the microstructure of Al–TM alloys. In this study, extrusions are fabricated from gas-atomized aluminum powders (≈100–400 µm) that contain 12.4 wt % TM additives and an Al-based matrix reinforced by various Al–Fe–Cr–Ti intermetallic compounds (IMCs). Two different extrusion techniques, conventional hot extrusion and friction extrusion, are compared using fabricating rods. During extrusion, the strengthening IMC phases were extensively refined as a result of severe plastic deformation. Furthermore, the quasicrystal approximant IMC phase (70.4 wt % Al, 20.4 wt % Fe, 8.7 wt % Cr, 0.6 wt % Ti) observed in the powder precursor is replaced by new IMC phases such as Al3.2Fe and Al45Cr7-type IMCs. The Al3Ti-type IMC phase is partially dissolved into the Al matrix during extrusion. The combination of linear and rotational shear in the friction extrusion process caused severe deformation in the powders, which allowed for a higher extrusion ratio, eliminated linear voids, and resulted in higher ductility while maintaining strength comparable to that resulting from hot extrusion. Results from equilibrium thermodynamic calculations show that the strengthening IMC phases are stable at elevated temperatures (up to ≈ 600 °C), thus enhancing the high-temperature strength of the extrudates.

Effect of powder reuse on orthopedic metals produced through selective laser sintering

Abstract: Metallic powder reuse is a simple method to significantly reduce material cost for direct metal laser sintering; however, the recycled materials must not produce defects that compromise part performance. In this study, virgin 316L and 17-4PH stainless steels, and Ti-6Al-4V powders were cycled up to eight times. Design of experiments were employed to identify how print parameters affect mechanical behavior for different reused feedstocks without compromising production quality. The study showed that recycling powder did not affect static mechanical properties and fatigue performances, with one exception – the ductility of 17-4PH. No significant variations in the part density, chemical composition, and powder properties were observed through reuses.

Laser powder bed fusion for metal additive manufacturing: perspectives on recent developments

Abstract: While significant progress has been made in laser powder bed fusion (L-PBF) for metal additive manufacturing (AM), there is still limited large scale adoption of this advanced manufacturing techniq

Research status of laser additive manufacturing for metal: a review

Abstract: Additive manufacturing (AM) especially laser additive manufacturing (LAM), a novel manufacturing technique of layer-by-layer forming according to geometric model, provides a decent option for materials processing. It owns advantages of rapid prototyping, customization, high material utilization, and the ability to form complicated structures. This paper reviews popular LAM techniques of selective laser sintering/melting, laser metal deposition and laser direct writing. The development status of metallic materials including pure metal, steel, superalloy, titanium and aluminum alloy is presented. The challenges and application limitations of LAM are involved and the development trend in the future is forecasted. In summary, this paper gives an overview of metal LAM expecting to made helpful suggestions on future research and development.

Review of laser powder bed fusion (LPBF) fabricated Ti-6Al-4V: process, post-process treatment, microstructure, and property

Abstract: Laser powder bed fusion (LPBF) is a timely important additive manufacturing technique that offers many opportunities for fabricating three-dimensional complex shaped components at a high resolution with short lead times. This technique has been extensively employed in manufacturing Ti-6Al-4V parts for aerospace and biomedical applications. However, many challenges, including poor surface quality, porosity, anisotropy in microstructure and property, and difficulty in tailoring microstructure, still exist. In this paper, we review the recent progress in post-process treatment and its influence on the microstructure evolution and material performance, including tensile, fatigue, fracture toughness, creep, and corrosion properties. The contradictions in simultaneously achieving high strength/ductility and strength/fracture toughness/creep resistance have been identified. Furthermore, research gaps in understanding the effects of the emerging bi-modal microstructure on fatigue properties and fracture toughness require further investigation.

Extreme shear-deformation-induced modification of defect structures and hierarchical microstructure in an Al–Si alloy

Abstract: Extreme shear deformation is used for several material processing methods and is unavoidable in many engineering applications in which two surfaces are in relative motion against each other while in physical contact. The mechanistic understanding of the microstructural evolution of multi-phase metallic alloys under extreme shear deformation is still in its infancy. Here, we highlight the influence of shear deformation on the microstructural hierarchy and mechanical properties of a binary as-cast Al-4 at.% Si alloy. Shear-deformation-induced grain refinement, multiscale fragmentation of the eutectic Si-lamellae, and metastable solute saturated phases with distinctive defect structures led to a two-fold increase in the flow stresses determined by micropillar compression testing. These results highlight that shear deformation can achieve non-equilibrium microstructures with enhanced mechanical properties in Al–Si alloys. The experimental and computational insights obtained here are especially crucial for developing predictive models for microstructural evolution of metals under extreme shear deformation. Extreme deformation of alloys is important for processing and applications. Here, extreme shear deformation of an Al–Si alloy induces grain refinement, multi-scale fragmentation of lamellae and generation of various defects, enhancing the mechanical properties of micropillars.

Shear assisted processing and extrusion of enhanced strength aluminum alloy tubing

Abstract: Shear Assisted Processing and Extrusion (ShAPE) enables the extrusion of many alloys with enhanced properties. In this study, ShAPE was used to extrude tubes of aluminum alloy 6063 measuring 12 mm in diameter at extrusion speeds up to 3.8 m/min, an increase of 10 times over what has previously been reported for ShAPE. Increasing the extrusion speed from 0.7 to 3.8 m/min resulted in using 68% less process energy at steady state without any loss in mechanical properties. As-extruded tubes had ultimate tensile strengths on par with conventional T5 extrusions and double the elongation at break. ShAPE extruded tubes that underwent a T5 heat treatment had yield and ultimate strengths of 198 and 234 MPa, respectively, which is ~30% higher than standard T5 material and comparable to T6 properties. Microstructural analyses were performed on as-extruded and T5 treated tubes. Grain refinement below 20 μm was identified, with no detectable growth of macroscale Mg2Si strengthening precipitates. Nanoscale β″ was not observed in the as-extruded materials but was prominent after T5 heat treatment suggesting that β″ strengthening precipitates were solutionized in situ during the ShAPE process. The ability to perform solution heat treating in situ, rather than post-extrusion, eliminates an energy intensive process step and is applicable to a wide variety of alloys.