The Effect of Powder Characteristics on Build Quality of High-Purity Tungsten Produced via Laser Powder Bed Fusion (LPBF)

Two high-purity tungsten powders, produced via different manufacturing techniques, were characterized to determine size distribution, morphology, thermal properties, and flow characteristics and, thus, the likely suitability for Laser Powder Bed Fusion (LPBF) production. Specimens from duplicate builds were produced with the two powders and characterized for density, defect mechanisms, and thermal penetration into the substrate plate to compare apparent power densities. The first powder was a chemically reduced powder with irregular morphology and the second, a plasma spheroidized powder with highly spherical morphology. The latter was found to have tighter morphological control and size distribution, having a third of particles at the modal particle size in comparison to a fifth of the chemically reduced powder. This led to better flow characteristics, and an increase of 1.5 g cm−3 (1500 kg m−3) in the packing densities seen in the powder bed which corresponds to 57 pct theoretical density vs 50 pct theoretical density in the chemically reduced powder. As a result, the specimens produced from the plasma spheroidized powder had higher densities (97.3 vs 88.5 pct) and the dominant defect mechanism moved from lack of fusion dominated in the chemically reduced powder to cracking dominated in the plasma spheroidized. The plasma spheroidized powder also showed higher apparent power densities (effective absorptivities) as evidenced by an 80 pct deeper penetration of the laser into the substrate plate.

Crystallization of Spherical Dielectric Oxide Particles in a Melting-Spheroidization Process Using Chemical Flame

BaNd2Ti4O12 dielectric oxide particles were spheroidized by melting them with a LPG-O2 flame to improve packing and fluidity of the powder. Changes in the particle morphology, structure and crystallinity during the process were investigated. It is revealed that most of the as-melted particles are dense, spherical and amorphous with smooth surfaces, which crystallize in the annealing process to form polycrystalline spherical particles with uneven surfaces. Annealing at above 1100°C is necessary for the spheroidized powder to recover its crystallinity and dielectric properties.

Plasma Spheroidized Alumina/Zircon Mixtures

The plasma-spray process is specified by the associated processing parameters, where these influence the properties of the resultant deposits. This article describes the preparation and processing of composite powders for use in thermal spraying by mixing high purity zircon and alumina powders. The spheroidized powder were obtained by high energy ball milling and rapid solidification from the molten state during plasma spraying. The article discusses the processes involved in spray drying and plasma spheroidization, describing thermal analysis and mullitization kinetics in the spheroidized alumina/zircon mixtures.