A New Laser Scan Method for Microstructural Control in Selective Laser Melting Process
2019
Background/Objectives: In selective laser melting (SLM) process, laser scan pattern is one of most important parameters to understand the evolution of microstructures in a part. Mechanical properties of a fabricated part are highly dependent on the evolution of microstructure. Recently, some researchers have tried to controlthe microstructures by using diverse methods. This paper proposes a method based on overlap laser scanning technique to control the microstructure in a part.
Methods/Statistical analysis: This paper uses an overlap laser scanning technique. To implement the laser scan pattern, two different sets of laser power and scan speed are used. Default set has laser power(95W) and scan speed (125 mm/s), respectively. For overlap scan, 4 different sets are used. The representative Vickers hardness (Hv) for 5 different sets are determined by averaging 10 times measurement. The representative values are compared for the effectiveness of proposed overlap scan method. To understand the change of Vickers hardness with the different sets, the size and shape of acicular α´ martensite and the concentration of O and N elements are observed.
Findings: From the measurements, Vickers hardness increases with the energy density for the overlap laser scan by about 18%, comparing to one without overlap laser scan. With the increase of the energy density for overlap laser scan, the refinement of the acicular α´ martensite increases. The change of the hardness shows the similar tendency with the change of the concentration of O and N elements.
Improvements/Applications: The results of this paper show the possibility of the microstructure design. It can also improve the design freedom by freely assigning the mechanical properties.
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