Processing and Microstructure of Laser Melt Injected WCp in a Ti-6Al-4V Matrix 2002-01-1414
In this study the Laser Melt Injection (LMI) process is explored to create a Metal Matrix Composite (MMC) consisting of 80 μm sized WC particles embedded in the top layer of a Ti-6Al-4V alloy. In particular the influences of the principal process parameters, e.g. power density, scanning speed and power flow rate, on the dimensions of the laser track and microstructural features are examined. Typical dimensions of a single laser track are, depending on the laser parameters, a width of 1.8 mm and a depth of 0.7 mm. The volume fraction of the WC particles is about 0.25- 0.30. An important finding is that the particle distribution is homogeneous and that the particles are injected over the whole depth and whole width of the melt pool. Further, an advantageous point is that this particular material system allows a certain variation of the processing parameters and that larger surface areas can be treated by an overlap of laser tracks. The microstructure was investigated by advanced transmission electron microscopy including energy filtering techniques and scanning electron microscopy with an integrated Electron Back-Scatter Diffraction/Orientation Imaging Microscopy (OIM). In the resolidified Ti-alloy melt pool TiC dendrites and W grains are found. Around the WC particles a W2C layer was detected, followed by a TiC layer. Occasionally a crystal orientation relation between WC, W2C and TiC is observed, depending on the WC interface. When the surface of the WC particle is close to (0001) the preferred growing direction can be retained while the misfit at the WC/W2C interface is minimized.