Grain refinement in Wire-Arc Additive Manufactured Inconel 82 alloy through controlled heat input

Abstract

In the Wire-Arc Additive Manufacturing (WAAM) process, the high heat input led to the formation of a large-sized molten metal pool, producing a coarse columnar grain structure and thus the component exhibits poor mechanical properties. So, it is important to have in-process transformation (CET: columnar to equiaxed transition) of the formed grains. This can be achieved by the proper control of the cooling rate during the solidification process. In this study, four vertical walls consisting of 10, 15, 20, and 25 layers of Inconel-82 alloy were produced using a GTAW-based AM process with varying input parameters. It has been observed that with the variation in travel speed and low frequency pulsed arc (3 Hz) the heat input varied from 705.1 J/mm (maximum) to 301.7 J/mm (minimum) which promoted the in-process grain refinement. The transformation of columnar grains into equiaxed grains having an average grain size of 19 µm was observed in the 15-layer wall. The average micro-hardness of the fabricated thin wall got enhanced from 228 HV in the 10-layer wall to 275 HV in the 15-layer wall owing to the grain refinement. Similarly, the maximum average ultimate tensile strength (UTS) and yield strength (YS) are observed in the transverse direction which is 650 MPa and 325 MPa respectively. The friction coefficient and wear rate are observed to be minimum in the 15-layer wall i.e., 0.42 and 4.7 × 10−4 mm3/Nm respectively. Furthermore, the anisotropy in the tensile properties is observed to be minimum in 15 layer wall (average UTS: 1.9 %; average YS:3.8 %).