Microstructure of Compositionally Graded Ti+Ti15Mo Alloys Prepared by Direct Laser Deposition

In this study the microstructure of compositionally graded Ti+Ti15Mo alloys prepared by direct laser deposition using different laser powers of 400 W, 600 W and 800 W is characterized. The composition in the gradient material varied from Ti(75%)-Ti15Mo(25%) to Ti(25%)-Ti15Mo(75%) by 5% in the adjacent layers. Microstructure investigations in the vertical cut were performed by precise microhardness mapping and complemented by microstructural observations by SEM, electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS). The microstructure of the 3D printed samples consists mostly of columnar grains orientated perpendicular to the plotted layers. The increasing laser power slightly increases the width of these grains, but effectively reduces the amount of unsolved Ti15Mo particles and increases the homogeneity of the structure. The microhardness of gradient Ti+Ti15Mo alloys varied in the range of 270-570 HV and is affected by both the composition and the laser power. The influence of the phase composition on the HV values is discussed in detail.