Fabrication of Metal Matrix Composite by Laser Metal Deposition-A New Process Approach by Direct Dry Injection of Nanopowders.

Laser Metal Deposition (LMD) offers new perspectives for the fabrication of metal matrix nanocomposites (MMnCs). Current methods to produce MMnCs by LMD systematically involve the premixing of the nanopowders and the micropowders or require in-situ strategies, thereby restricting the possibilities to adjust the nature, content and location of the nano-reinforcement during printing. The objective of this study is to overcome such restrictions and propose a new process approach by direct injection of nanoparticles into a metallic matrix. Alumina (n-AlO) nanoparticles were introduced into a titanium matrix by using two different direct dry injection modes in order to locally increase the hardness. Energy dispersive X-ray spectroscopy (EDS) analyses validate the successful incorporation of the n-AlO at chosen locations. Optical and high resolution transmission electron microscopic (HR-TEM) observations as well as X-ray diffraction (XRD) analyses indicate that n-AlO powders are partly or totally dissolved into the Ti melted pool leading to the in-situ formation of a composite consisting of fine α lamellar microstructure within a Ti matrix and a solid solution with oxygen. Mechanical tests show a significant increase in hardness with the increase of injected n-AlO amount. A maximum of 620 HV was measured that is almost 4 times higher than the pure LMD-printed Ti structure.