Characterization, preparation, and reuse of metallic powders for laser powder bed fusion: a review

Laser powder bed fusion(L-PBF) has attracted significant attention in both the industry and academic fields since its inception, providing unprecedented advantages to fabricate complex-shaped metallic components. The printing quality and performance of L-PBF alloys are infuenced by numerous variables consisting of feedstock powders, manufacturing process,and post-treatment. As the starting materials, metallic powders play a critical role in infuencing the fabrication cost, printing consistency, and properties. Given their deterministic roles, the present review aims to retrospect the recent progress on metallic powders for L-PBF including characterization, preparation, and reuse. The powder characterization mainly serves for printing consistency while powder preparation and reuse are introduced to reduce the fabrication costs.Various powder characterization and preparation methods are presented in the beginning by analyzing the measurement principles, advantages, and limitations. Subsequently, the effect of powder reuse on the powder characteristics and mechanical performance of L-PBF parts is analyzed, focusing on steels, nickel-based superalloys, titanium and titanium alloys, and aluminum alloys. The evolution trends of powders and L-PBF parts vary depending on specific alloy systems, which makes the proposal of a unified reuse protocol infeasible. Finally,perspectives are presented to cater to the increased applications of L-PBF technologies for future investigations. The present state-of-the-art work can pave the way for the broad industrial applications of L-PBF by enhancing printing consistency and reducing the total costs from the perspective of powders.

Characterization of nanoparticle mixed 316L powder for additive manufacturing

Nanoparticles reinforced steels have many advantaged mechanical properties.Additive manufacturing offers a new method for fabricating nanoparticles reinforced high performance metal components.In this work,we report the application of low energy ball milling in mixing nanoparticles and micron 316 L powder.With this method,0.3 and 1.0 wt% Y2 O3 nanoparticles can be uniformly distributed on the surface of 316 L powder with the parameters of ball-to-powder ratio at 1:1,speed at 90 rpm and 7 h of mixing.The matrix 316 L powders remain spherical in shape after the mixing process.In the meantime,the effect of low energy ball milling and the addition of Y2 O3 nanoparticles on the powder characteristics(flowability,apparent density and tap density) are also studied.Results show that the process of low energy ball milling itself can slightly decrease the flowability and apparent density of the 316 L powder.The addition of 0.3 and 1.0 wt% Y2 O3 nanoparticles can also decrease the flowability,the tap density and the apparent density compared with the original 316 L powder.All of these changes result from the rough surface of the mixed powder produced by ball milling and the addition of Y2 O3 nanoparticles.The powder’s rough surface can increase the coefficient of friction of powders.The mixture of 316 L powder and Y2 O3 nanoparticles can be successfully used for selective laser melting(SLM).The relative density of SLM 316 L-Y2 O3 is measured at 99.5%.However,Y2 O3 agglomerations were observed which is due to the poor wettability between 316 L and Y2 O3.

Flow properties of fine powders in powder coating

Three types of nanoparticles and their combinations were blended into a fine powder, which has been used in the powder coating industry. To study their effects on flow properties, the modified powder samples were characterized using a variety of techniques that tested the powder under different powder states ranging from dynamic to static. It was found that all three nanoparticles improved the flow properties of the powder to some degree, though the amounts of the nanoparticles needed were different depending on their physical properties. Secondly, inconsistency among these powder characterization techniques was also found. This is attributed to the different states of the powder samples during a measurement including dynamic, dynamic-static and static states. It was confirmed that characterization techniques which test the flow properties of a powder under all three states are needed to fully describe the flow properties of the powder. Finally, the effects of combinations of nanoparticles were explored, and it was found that combinations of nanoparticles can intensify, weaken or combine the effects of their component nanoparticles. The effects of nanoparticle combinations are not a simple summation of the effects of their comnonent nanoparticles.