Recent Developments in Laser Melt/Particle Injection Processing

Abstract

Investigations into crack formation in particle injected surfaces and into microstructural evolution during cladding were some of the recent developments in laser melt/particle injection processing. Both surface modification techniques involved blowing powder particles into a melt pool formed by a laser beam. When the particulate materials were metal carbides composite surface layers were formed and the thermal stresses that developed during cooling of the carbide injected layer resulted in the formation of microcracks. It was found that modest levels of preheating were sufficient to prevent cracking and that cracking was eliminated mainly by the reduction in thermal stresses and not by modifications in microstructure. With lower melting alloy powders clad overlays were formed. It was found that the limited mixing between the clad material and the substrate resulted in complex macrostructures containing fluid-flow driven segregation bands. The degree of microstructural in-homogeneity depended upon the type of substrate material and had a direct influence on the soundness of the cladding.

Laser surface modification of titanium alloys

“…Later, this average particle size was reduced to within the range 60-100 mm (Cooper and Slebodnick, 1989;Kloosterman et al, 1998;Kool et al, 1999;Pei et al, 2002). an alternative method is the preplacement of particles on the surface of the substrate alloy in the form of a slurry, where in general, the particles have a smaller average size, ~45-60 mm Pang et al, 2005).…”

Grain-Boundary Interaction between Inconel 625 and WC during Laser Metal Deposition

“…Phase δ helps refine the grain size and impeding dislocation in the structure. Introduction of tungsten carbide (WC) grains with a diameter over 10 µm into the system [27,28] shows higher wear resistance and hardness of the material. It was reported that big carbide particles could not be distributed homogenously throughout the whole volume of the sample.…”

“…This results in non uniform distribution of hardness. Metal–carbide systems are commonly deposited using two separate powder feeders with regulated feed ratios that could not provide the same carbide content in the whole volume [27,28]. Introduction of a small amount of TiC nanoparticles into Inconel [29,30,31] resulted in a modified microstructure of the material.…”

“…High-energy density of a laser beam enables fast heating followed by rapid cooling and solidification coating. As a result, the obtained microstructure is characterised by fine grains and is resistant to erosion [27,28,34]. In this study, the grain-boundary Inconel 625–WC interaction was investigated during laser metal deposition.…”

Melting of multipass surface tracks in steel incorporating titanium carbide powders

“…This necessitates the overlapping of many melted tracks, with the additional problems due to preheating of the regions of the substrate where subsequent tracks are melted, as reported for laser processing. [20][21][22][23] Hu and Baker 22 defined 'preheat' as the heat developed from melting the initial track, which then diffused by conduction throughout the work piece. Previous laser studies described overlapping investigations based on a titanium alloy, initially involved laser nitriding 22 and subsequently laser alloying which incorporated SiC powder.…”