Abstract
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-Al2O3) 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-Al2O3 at chosen locations. Optical and high resolution transmission electron microscopic (HR-TEM) observations as well as X-ray diffraction (XRD) analyses indicate that n-Al2O3 powders are partly or totally dissolved into the Ti melted pool leading to the in-situ formation of a composite consisting of fine α2 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-Al2O3 amount. A maximum of 620 HV was measured that is almost 4 times higher than the pure LMD-printed Ti structure.
Highlights
Metal matrix composites with nanoparticles (NP) as reinforcement (MMnCs–metal matrix nanocomposites) have been investigated during the last decades and significant improvements in the mechanical properties such as tensile strength, elastic modulus and wear resistance were demonstrated [1,2,3]
This paper summarizes the results of a preliminary study dealing with a new approach to fabricate metal matrix nanocomposites with the Laser Metal Deposition (LMD) process
Four millimetre Ti plates of Grade 1 supplied by Zapp AG were used as material substrate for building the investigated 3D parts
Summary
Metal matrix composites with nanoparticles (NP) as reinforcement (MMnCs–metal matrix nanocomposites) have been investigated during the last decades and significant improvements in the mechanical properties such as tensile strength, elastic modulus and wear resistance were demonstrated [1,2,3]. The higher performances were explained by the cumulative contributions of different strengthening mechanisms promoted directly or indirectly by the dispersed nanoparticles. Among these mechanisms, load transfer, Hall-Petch strengthening, Orowan strengthening, coefficient of thermal expansion and elastic modulus mismatches are often mentioned [4]. It has been shown that the processing route may contribute to some strengthening mechanisms through grain refinement and increased dislocation densities [5,6]. Traditional fabrication routes based on powder metallurgy or casting processes have been purposely optimized in order to avoid NP agglomerates within the metallic matrix
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