Rheological behavior of β-Ti and NiTi powders produced by atomization for SLM production of open porous orthopedic implants

Abstract

The growing interest for Selective Laser Melting (SLM) in orthopedic implant manufacturing is accompanied by the introduction of novel Ti alloys, in particular β-Ti for their excellent corrosion resistance as well as favorable combination of high mechanical strength, fatigue resistance and relatively low elastic modulus. As part of the SLM process for producing quality β-Ti parts powder flowability is essential to achieve uniform thickness of powder layers. In this work the flowability of different gas atomized β-Ti, including NiTi, powders has been studied. Their rheological properties were compared to those of commercially available plasma-atomized Ti-6Al-4V powder using a newly developed semi-automatic experimental set-up. Not only the particle size, shape and size distribution of the powders display a large influence on the powder flowability but also particle surface properties such as roughness, chemical composition and the presence of liquid on the surface of the particles. It was found that plasma or gas atomization production techniques for SLM powder have a considerable effect on the particle topography. Among the powders studied regarding SLM applicability only rheological properties of the fine size fraction (25-45 μm) of Ti-45Nb didn't conform to SLM processing requirements. To improve flowability of the Ti-45Nb powder it was annealed both in air and argon atmosphere at 600°C during 1 h, resulting in an improved rheological behavior suitable for SLM processing.

Modeling of solidification microstructure evolution in laser powder bed fusion fabricated 316L stainless steel using combined computational fluid dynamics and cellular automata

“…By doing this, the recoating rack and powder bed interaction are mimicked, and the desired layer thickness is obtained. The final packing density in the DEM result is ~51%, which is in a reasonable range observed in experimental measurements in the literature (50% -61%) [42,43]. The particle trajectories during the DEM powder deposition simulation and the resulting powder layer configuration are shown in Figure 1 been proven [6,18,[45][46][47][48].…”

Influence of Gas Flow Speed on Laser Plume Attenuation and Powder Bed Particle Pickup in Laser Powder Bed Fusion

“…Moreover, poor flowability can make it challenging to achieve homogenous layers during powder recoating. 38 In Zone III, due to the dominant cohesive forces, the powder has very high pickup speed but no flowability and tends to agglomerate. Pleass and Jothi 39 showed that it is impossible to spread powder layers with a very fine Ni-alloy powder (5-9 lm IN625) in the commercial LPBF system they used, due to severe particle agglomeration.…”

Understanding powder bed fusion additive manufacturing phenomena via numerical simulation

“…The DEM output is the location and radius of each particle that is transferred to the CFD model as initial conditions. Using DEM and input parameters taken from literature [37,38], O Zhang and Zhang [34] found a packing density of 51% against experimental values in between 50% and 61% [39,40] (Fig. 5).…”