Fabrication of FGM structure with gradation of stainless steel and low carbon steel using twin wire arc additive manufacturing

Abstract

Twin wire arc additive manufacturing (T-WAAM) offers the capability to fabricate functionally graded material (FGM) tailoring in a variation of compositional elements and the related properties. In this context, two feedstocks, SS 316L (SS) and ER-70S6 (LCS), were used to fabricate a FGM structure using a T-WAAM setup integrated with gas-tungsten-arc-welding (GTAW) power source. The variation of elemental compositions of the fabricated structure was obtained by controlling the feed rate of the two different feedstock materials. The two extreme ends of the fabricated wall were made of pure SS and LCS, whereas the intermediate zones were fabricated by mixing 75% SS+25% LCS, 50% SS+50% LCS, and 25% SS+75% LCS. The intermixed zones exhibited complex microstructural, mechanical, and tribological phenomena. It showed duplex phase formation, i.e., austenite (FCC) and ferrite (BCC), where the microstructure varied from austenite+martensite to bainite+pearlite to polygonal ferrite. The average hardness and wear behaviour of these zones is better than that of pure SS and LCS. Maximum hardness value of 398 HV is observed at 50–50 SS and LCS mixing zone. This SS-LCS combination shows a remarkable surface durability and excellent wear resistance. The coefficient of friction, specific wear rate, and wear depth in this zone are 0.128, 0.01 × 10³ mm³/Nm and 2.687 µm, respectively. This research offers a feasible and flexible approach to fabricating FGM, tailored design, and renovation of components, where hardness and wear interaction are more prominent.