Rapidly solidified Al-alloy powders produced by the plasma melt and rapid solidification (PMRS) method

Plasma spraying is a line-of-sight process involving the injection of a powder feedstock into a high-temperature plasma jet. Rapidly solidified powder in the size range < 1-50 μm can be produced through the fragmentation of the molten or semi-molten particles upon impact on a solid substrate. This paper reports the production of rapidly solidified powders in the systems AlSi, AlTi and AlNi using the plasma melt and rapid solidification (PMRS) technique. The experiments show the process/microstructure relationship in the production of these powders. Examination of the powders was carried out using metallographic techniques involving optical microscopy, scanning electron microscopy (SEM) with EDAX and X-ray diffractometry (XRD). The particle-size distribution of the powders was obtained by a X-ray sedimentation method. The results show that the particle-size distribution and microstructure of the powder are dependent on a number of factors which include the substrate rotating speed, the distance between the plasma torch and the rotating substrate, the plasma gas composition and the initial size of the powders. For low melting-point alloys such as AlSi, the determining factor is the rotating substrate speed; however, for high melting-point alloys such as AlTi, the auxiliary gas flow is an important factor.