Numerical Simulation of Dilution in Laser Metal Deposition by Powder Injection

Laser deposition is a method of depositing material by which a powdered material is melted and consolidated by use of a laser in order to coat part of a substrate or fabricate a near-net shape part. The development of an accurate predictive model for laser deposition is extremely complicated due to the multitude of process parameters and materials properties involved. In this work, the metal powder used in the laser cladding/deposition process is injected into the system by using a coaxial nozzle. The interaction of the metallic powder stream and the laser causes melting to occur, which is known as the melt pool. The metal is deposited onto a substrate; moving the substrate allows the melt pool to solidify and thus produces a track of solid metal. In cladding/deposition operations, dilution is often defined as the amount of intermixing of the deposit and substrate. In this process, it is desirable to have minimum dilution but at the same time to have a metallurgical bonding between the substrate and deposit. Therefore, it is very critical to understand and predict the degree of dilution in the process. In this study, a heat transfer and fluid flow model for laser deposition is developed to predict dilution under varying process parameters. The material for both substrates and the powder is Ti-6Al-4V, but 5% of steel powder was added to observe the actual degree of dilution. The laser used is a direct diode laser. Experimental validation of the predicted dilution is also presented.