The effects of forced interpass cooling on the material properties of wire arc additively manufactured Ti6Al4V alloy

Abstract

To achieve improved microstructure and mechanical properties, an innovative wire arc additive manufacturing (WAAM) process with forced interpass cooling using compressed CO 2 was employed in this study to fabricate Ti6Al4V thin-walled structures. The effects of various interpass temperatures and rapid forced cooling on deposition geometry, surface oxidation, microstructural evolution, and mechanical properties of the fabricated part were investigated by laser profilometry, optical microscopy (OM), scanning electron microscopy (SEM), hardness testing and mechanical tensile testing. Results show that the microstructural evolution and mechanical properties of the deposited metal are not greatly affected by an increasing interpass temperature, however, the deposited wall tends to be widened, flattened and exhibit increased surface oxidation through visible coloration. When rapid forced cooling using CO 2 is used between deposited layers, slightly higher hardness values and increased strength can be obtained. This is mainly attributed to the combined effects of less surface oxide and high density dislocation caused by the generation of large amounts of fine-grained acicular α within the microstructure. Furthermore, forced interpass cooling not only improves deposition properties, but also promotes geometrical repeatability and also improved manufacturing efficiency through the reduction of dwell time between deposited layers. ABSTRACTTo achieve improved microstructure and mechanical properties, an innovative wire arc additive manufacturing (WAAM) process with forced interpass cooling using compressed CO 2 was employed in this study to fabricate Ti6Al4V thin-walled structures. The effects of various interpass temperatures and rapid forced cooling on deposition geometry, surface oxidation, microstructural evolution, and mechanical properties of the fabricated part were investigated by laser profilometry, optical microscopy (OM), scanning electron microscopy (SEM), hardness testing and mechanical tensile testing. Results show that the microstructural evolution and mechanical properties of the deposited metal are not greatly affected by an increasing interpass temperature, however, the deposited wall tends to be widened, flattened and exhibit increased surface oxidation through visible coloration. When rapid forced cooling using CO 2 is used between deposited layers, slightly higher hardness values and increased strength can be obtained. This is mainly attributed to the combined effects of less surface oxide and high density dislocation caused by the generation of large amounts of fine-grained acicular α within the microstructure. Furthermore, 2 forced interpass cooling not only improves deposition properties, but also promotes geometrical repeatability and also improved manufacturing efficiency through the reduction of dwell time between deposited layers.

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

“…If the aim is to increase productivity, it is not practical to let the previously deposited layer to reach room temperature. In this case, forced intercooling [205] can be used to decrease the elapsed time between two consecutive layer depositions increasing the process productivity. If post-process heat treatments are to be applied to refine the microstructure, then, forced cooling can be used with the purpose of reducing the time between deposited layers, controlling the interpass temperature, but avoiding oxidation of the part [206].…”

WAAM system with interpass temperature control and forced cooling for near-net-shape printing of small metal components

“…Derekar et al [10] have argued that a higher interpass temperature is even desired when producing aluminium alloy components, as it leads to reduced porosity. Wu et al [11] investigated the effects of the interpass temperature and forced interpass cooling using CO 2 on Ti6Al4V alloy components. They reported better surface finish and increased tensile strength at lower interpass temperatures (100°C or less).…”

Experimental Investigation of the Influence of Wire Arc Additive Manufacturing on the Machinability of Titanium Parts

“…WAAM uses a solid wire as the feedstock material and an electric arc as the heat source. Several research works have dealt with the fundamental aspects of the process such as the final material microstructure and its mechanical properties [4][5][6][7]. In this regard, the review recently presented by Rodrigues et al [8] provides an overview of the different process variants and the materials for WAAM.…”