Microstructural control of an Al–W aluminum matrix composite during direct laser metal deposition

• Published in: Journal of alloys and compounds 2020-01, Vol.813, p.152208, Article 152208
• Main Authors: Ramakrishnan, A., Dinda, G.P.
• Format: Article
• Language: English
• Subjects: Additive manufacturing; Aluminum; Aluminum base alloys; Aluminum matrix composite; Aluminum matrix composites; Al–W intermetallics; Cellular structure; Computer simulation; Cooling rate; Densification; Intermetallic phases; Laser deposition; Metastable phases; Microhardness; Microscopy; Microstructure; Microstructure control; Nickel; Optical microscopy; Phase diagrams; Phase transitions; Rapid solidification; Solid solutions; Tungsten (W)
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2019.152208

This study focuses on the evolution of a design strategy for aluminum matrix composites (AMC) in additive manufacturing, using a mixture of 82 wt % Al and 18 wt % W (82Al–18W). Direct laser metal deposition was used to fabricate and assess the 82Al–18W AMC using three different scanning speeds (12, 6, and 1.5 mm/s). This AMC was examined by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, calculation of phase diagrams (CALPHAD), X-ray diffraction (XRD), and microhardness measurements. The hardness of the AMC increased by 50% compared to pure aluminum. The AMC showed remarkable densification during processing with uniform distribution of fine intermetallic phases and undissolved W reinforcement in the Al matrix. A notably fine microstructure was observed within the solidified melt pool, developing phases of supersaturated solid solutions of primary α-Al FCC elongated cellular/doublon microstructure in the near edge of the melt pool, and fine cellular/doublon structure in the top of the solidified melt pool. The formation mechanism of the intermetallic (Al12W, Al4W, Al5W) phases during rapid solidification from the melt, and the fine eutectic structure evolving at the outer solid-liquid boundaries of the intercellular/doublon structure that is due to the presence of Ni, and Fe impurities in W is well documented. This communication reports the influence of cooling rate on the solidification structures, stable, and metastable phases observed in the 82Al–18W AMC system activating future alloy design by LMD processing. [Display omitted] •Microstructural evolution of an 82Al–18W aluminum matrix composite system during laser metal deposition was investigated.•The formation mechanism of Al4W, Al5W, and Al12W intermetallics depending on the processing condition were identified.•The strength of the α-Al matrix is superior to pure Al as solid-solubility of W in Al increased substantially.•Laser metal deposition process can be employed for the development of new alloys via additive manufacturing.