X-ray analysis of pore formation in direct metal deposition and its causes

Laser direct metal deposition has wide applications in the areas of rapid manufacturing, surface coating and component repair. Defects of interlayer and intralayer porosity are often observed in laser deposited structures and repaired components. Interlayer porosity can be controlled to some extent by adjusting processing parameters, but there is still disagreement as to the source of intralayer porosity and whether processing conditions, parameters or initial powder materials are the dominant causal factors. In this work, two samples of Ti-6Al-4V powder, prepared using gas-atomization and plasma-atomization, were analyzed using laser diffraction and micro computed tomography with the Xradia Micro XCT machine for any initial porosity content. A 1.5 kW diode laser with a coaxial deposition head was then used to deposit a number of thin-wall structures with the different powders at different processing parameters. The deposited structures were characterized using scanning electron microscopy (SEM) and optical microscopy. The results show the effects of the processing conditions and initial powder characteristics on intralayer porosity and final deposit properties