Microstructural Evolution Of 316l Stainless Steel Prepared By Ultrasonic Vibration Assisted Laser Melting Deposition Technique

Ultrasonic vibration with different ultrasonic powers of 0, 600, 1000 and 1400 W was applied during laser melting deposition of 316L stainless steel. The effects of ultrasonic power on the grain morphologies and sizes, the microstructure formation mechanism and grain growth characteristics of 316L stainless steel were studied. The results show that the application of ultrasonic vibration can break large sized columnar grains of the directional epitaxial growth, resulting in a refinement of microstructure, and increase the accumulative misorientations and dislocation densities along the long axis of grains. By promoting the convections in the melt pool, and reducing the temperature gradient along the deposition direction, the application of ultrasonic vibration accelerates the transitions of growth directions for columnar grains. The application of ultrasonic vibration also helps to increase the cooling rate during solidification, resulting in refinements of both columnar grains and the interior columnar dendrites.