Issues in Metal Matrix Composites Fabricated by Laser Powder Bed Fusion Technique: A Review

Abstract

Technologies for the additive manufacturing (AM) of metals have progressed throughout the years, with significant improvements in both quality of AM components and wider scale application. In just about every current application for powder bed fusion (PBF) processes, the powders used are alloys of base metals like aluminum, iron, nickel, cobalt, and titanium, with a chemistry sometimes adapted to enable their processing by a laser-based system. While the current state of development enables the production of parts for demanding industries such as aerospace, a new class of materials such as metal matrix composites (MMCs) could enhance further applications of AM-fabricated metallic parts. MMCs combine a metallic powder with a reinforcing agent, a ceramic powder being the most commonly used. These powders can be mixed, blended, or mechanically alloyed together into a composite powder, before being consolidated layer-by-layer into the designed part. [1] This part will exhibit reinforcement particles dispersed within the bulk metal matrix. The MMCs development thus needs to achieve enhanced properties through a compromise between tenacity of the matrix and the rigidity of reinforcing particles. Figure 1 shows a schematic of processed MMC and its processing steps.The PBF process uses a high energy laser to fuse powder particles into a near net shape component. Combining different parameters (preprocessing, processing, etc.) to produce a fully dense part in AM is, however, a complex process. The consolidation process involves multiple phenomena such as heating (thermal expansion), melt pool formation, solidification, and cooling (thermal contraction), all of which occur simultaneously and in a repeated manner. [2,3] This process complexity is increased significantly when trying to attain fully dense MMC from metal and ceramic. Multiple reasons are involved, ranging from the raw materials used to interactions between laser and powder. A segregation of dissimilar materials found in the composite powder (mixed powder system) can arise on the build platform during feeding. [4] This would create issues of particles clustering and uneven dispersion, encouraging further defects formation.The capability of fabricating fully dense components with desired properties (mechanical, electrical, etc.) and less defects in AM has been the focus of researchers and industries. [5] However, inherent defects like porosities and surface roughness in AM parts remain a challenge. Various factors related to AM machines, material properties, and processing parameters are responsible for these defects.Processing parameters influence the overall quality of AM parts by influencing temperature gradients, consolidation and solidification, thermal-induced stresses as well as the susceptibility of PBF-processed part to defects. Changes in powder chemical composition can influence consolidation and defect generation. [6,7] Proper considerations must, thus, be given in understanding, predicting, and preventing defects in PBF-processed

Processability of A6061 Aluminum Alloy Using Laser Powder Bed Fusion by In Situ Synthesis of Grain Refiners

“…The debonding can be explained by the poor wettability of B 4 C particles from melted Al [46,58]. In addition, the thermal mismatch between Al and B 4 C [59], combined with the rapid cooling involved in the LPBF process, can induce interfacial debonding, crack initiation, and propagation [60,61]. A consequence of this debonding is the pull-out of B 4 C particles and the formation of pores that can originate after the polishing procedure, as shown in Figure 5b,c.…”

“…As a matter of fact, Sullivan et al [30] characterized crack-free A6061 RAM2 samples processed on an EOS M290 LPBF machine by Elementum 3D (the company owner of the material and the RAM patent, Erie, CO, USA, using a preheating of 200 • C of the building platform. The use of preheating has an important role in avoiding thermal cracks in metal matrix composite, mitigating thermal gradient in the material [61]. Additionally, the preheating might have a beneficial impact on the adhesion between ceramic particles and metal matrix, avoiding particles debonding: in fact, the temperature increment can enhance the wettability of B 4 C particles by molten aluminum and promote a stronger interfacial bond [58,62].…”

Effect of Heat Treatment on Fracture Behavior of AISI 630 Alloy Manufactured by Directed Energy Deposition

“…It can obtain high surface quality, but its molding size is limited by the powder bed. [11][12][13][14][15] Directed energy deposition (DED) utilizes a high-energy laser beam to melt synchronously conveyed powders to manufacture parts. It has the advantages of high flexibility, no space limit, and high forming efficiency.…”

Special Issue: Surface Modification of Engineering and Functional Materials

“…Thus, another promising direction of investigation is metallic coating formation around reinforcing particles, especially nanoparticles, obtaining near-spherical powder suitable for selective laser melting [11]. Such particles coated by the same metal or alloy with matrix should provide excellent matrix-reinforcement wettability and improved bonding, leading to low porosity and improved properties.…”