Mechanical Properties of 316 Stainless Steel Structure produced by Pulsed Micro-plasma Additive Manufacturing

Abstract

An innovative pulsed micro-plasma additive manufacturing (AM) system is proposed for the fabrication of thin-walled 316 stainless steel parts. During the deposition process, the heat accumulation from the micro-plasma can be controlled effectively by adjusting the following parameters: the AM current, pulse length of the plasma arc, and scanning speed. The width of the pool can reach 3.0 mm. The microstructural analysis, micro-hardness tests, and tensile strength tests were performed. The results of the structural characterisation showed that columnar dendrites predominated in the microstructure of thin-walled elements and exhibited epitaxial growth from the bottom to the top and from the middle to both sides, while the top grains had more variations in growth orientation. The grains had a core-shell structure with a growth orientation along the < 100 > direction of the austenite structure, and the boundary was composed of migrated C and Cr. The micro-hardness of the thin-walled structure (240–320 Hv0.3) decreased with increasing the deposition thickness. The tensile strength and yield strength of the thin-walled parts were 669 and 475 MPa, respectively. The fracture mechanism was that cracks formed along the pores along the pores of the grain boundary and then propagated along them, ultimately leading to the fracture.