Search Results

Multilayers of tungsten carbide/carbon (WC/C) with an amorphous structure and multilayers of titanium nitride/titanium-aluminum nitride (TiN/(Ti,Al)N) with a polycrystalline structure, prepared by physical vapor deposition have been subjected to nanoindentation testing. The investigation has been aimed at establishing whether the load-displacement responses provides accurate information on the fracture mechanisms and whether such mechanisms can be characterized using a new technique for cross-sectional electron microscopy of the nanoindentations. Analysis of the load-displacement curves showed that it can be used to identify the cracking mechanisms occurring in the multilayers and that cross sectioning of the nanoindentations is necessary if a more complete understanding of the multilayer coatings behavior is required.

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.

With a well-controlled laser melt injection (LMI) process, for the first time the feasibility is demonstrated to produce SiC particles (SiCp) reinforced Ti6Al4V functionally graded materials (FGMs). SiCp are injected just behind the laser beam into the extended part of the laser melt pool that is formed at relatively high beam scanning velocities. The process allows for the minimization of the decomposition reaction between SiCp and Ti6Al4V melt, and also leads to FGMs of SiCp/Ti6Al4V instead of a homogeneous composite layer on Ti6Al4V substrates. An injection model is designed based on the temperature/viscosity field of the laser pool for a deeper understanding the mechanism of formation of the FGMs with LMI. The model is based on finite element calculations of the temperature field in the melt pool, physical considerations of the LMI process and it is supported by experimental observations.