MICROSTRUCTURES OF IN SITU TiN-Ti5Si3 COMPOSITES PREPARED BY SELECTIVE LASER MELTING

The selective laser melting (SLM) was used to process the high-energy ball milled Si3N4-Ti (mole ratio of 1 : 9) nanocomposite powder in which the average grain sizes of Si3N4 and Ti were both less than 20 nm. The TiN reinforced Ti5Si3 matrix in situ composites were prepared by means of the synthesis reaction 9Ti+Si3N4=4TiN+Ti5Si3. As the milling time increased, the average particle size of the milled Si3N4-Ti composite powder decreased and the resultant specific surface area increased. The densification level of laser processed TiN-Ti5Si3 composites increased accordingly to 97.2%. The morphologies of TiN reinforcing phase in the corresponding SLM processed structures experienced a successive change from a poly-angular shape to a near-spherical shape and finally to a dendritic shape.