Laser Melt Injection Process Research Articles

Influence of electric-magnetic compound field on the WC particles distribution in laser melt injection

An advanced particle distribution controlling approach is proposed for laser melt injection process, which applies an electric-magnetic compound field to assist the laser melt injection process. The electric-magnetic synergistic effect on the reinforcement particle distribution in laser melt injection is investigated using numerical and experimental methods. Spherical WC particles are used as the reinforcement and their distribution in the longitudinal sections of the laser melt injection layers is examined with SEM and studied with computer graphics processing. The distributions of fluid temperature, fluid velocity and reinforcement particles in the molten pool are simulated using a 2D multi-physics model coupled with the equations of heat transfer, fluid dynamics, drag force, Lorentz force and phase transition. The results show that, the directional Lorentz force due to an electric-magnetic compound field, as a sort of volume force, can change the equivalent buoyancy acting on the particles. When the Lorentz force and gravity force are in same direction, majority of particles are trapped in the upper region of laser melt injection layer, while when the Lorentz force and gravity force are in opposite direction, most particles are concentrated in the bottom region. As a result, the distribution gradient of WC particles can be controlled by the electric-magnetic compound field, instead of the time-consuming adjustment of process parameters.

A study of laser melt injection of TiN particles to repair maraging tool steels

The tools and dies surface may suffer from severe damage in service due to sharp working conditions, such as extreme thermomechanical loading and abrasive environments. The steel and high strength alloys used for these tools are usually very expensive; hence, those in charge of surface repairing should welcome laser processes in order to increase the service life of the tool and shorten the time required to amortize the investment made. In this paper, a high power laser has been used to modify the microstructure as well as the surface properties of low nickel (14 wt.%) maraging steel by means of the laser melt injection process. The power of TiN was injected into the laser‐melted steel. The microstructure, hardness and wear resistance of the metal matrix composite ‘new surface’, followed by peak‐age hardening, have been studied. Laser parameters were optimized to obtain a defect‐free material. Laser surface processing impairs the surface properties of the maraging steel as hardness decreases in the heated regions; thus, a final age hardening treatment is necessary to obtain the required high strength typical of maraging steels. Copyright © 2014 John Wiley & Sons, Ltd.

Sliding wear resistance of metal matrix composite layers prepared by high power laser

Two laser surface engineering techniques, Laser Cladding and Laser Melt Injection (LMI), were used to prepare three different metal matrix composite layers with a thickness of about 1 mm and approximately 25–30% volume fraction of ceramic particles. SiC/Al–8Si, WC/Ti–6Al–4V and TiB 2/Ti–6Al–4V layers were prepared by a Laser Melt Injection process, whereby additional material in the form of ceramic particles is injected into the molten substrate. As a result, a microstructure characterized by hard ceramic particles distributed in a metal matrix with very strong bonding is formed in the surface layer of the treated metal. A TiB/Ti–6Al–4V metal matrix composite layer was produced on Ti–6Al–4V substrates by conventional laser cladding. A mixture of TiB 2/Ti powders has been used as a precursor to obtain two microstructurally distinct layers, namely eutectic and primary TiB particles dispersed in the Ti–6Al–4V matrix. Sliding wear properties of these metal matrix composites layers were studied at boundary lubrication conditions and compared with the wear of the substrate materials. The observed wear mechanisms are summarized and related to detailed microstructural observations. The layers have been found to show excellent interfacial bonding, coupled with dramatically improved tribological properties expressed through a relative wear resistance value ranging from 30 to 1500.

Failure of WCp/Ti-6Al-4V layer prepared by laser melt injection

Metal Matrix Composite layers consisting of WC particles (similar to 80 pin diameter) incorporated into a Ti-alloy matrix by the so-called Laser Melt Injection process were mechanically tested. Standard tensile tests as well as in-situ scanning electron microscope observations of tensile stressed surfaces were performed. Crack initiation and crack propagation processes were observed at initial and final stages of failure. Cracks initiate always in the ceramic particles. Intergranular brittle fracture of the central part of the WC particles or brittle decohesion along the WC/W2C interface form the initial failure. The crack propagates further inside the Ti matrix through brittle fracture of individual TiC dendrites and induces new cracks in the ceramic particles in the front of the main crack tip, Ductile fracture of the metal matrix, that creates the resulting fracture surface, is the final stage of the failure process. Internal tensile stresses formed during the laser processing are superimposed on the external tensile stress, which causes that local failure of the MMC layer starts at a relatively low external stress. The toughness of the Ti matrix makes the final failure process ductile.

EBSP study of reaction zone in SiC/Al metal matrix composite prepared by laser melt injection

The reaction zone in SiC/Al metal matrix composite layer prepared by Laser Melt Injection process is studied by Electron Back-Scatter Diffraction. Special attention is dedicated to the sample preparation process and also to the automatic indexing procedure when patterns of back-scattered electrons are evaluated during the surface scanning by electron beam. The orientation relationship between ceramic particles and phase formed in the reaction zone was observed by both transmission electron microscopy and by EBSD.