Mechanical assessment and microstructural characterization of parts processed by additive manufacturing, with direct energy deposition, of the Inconel 625 and 718 alloys with aerospace application

Abstract

The additive manufacturing (AM), in a general way, is useful to fabricate parts layer by layer according to a geometry processed in CAD software. Until current days, several AM methods have been developed with success to fabricated complex geometries and processing different materials. Regarding metallic alloys with the aerospace application, two methods are highlighted, Direct energy deposition (DED) and powder bed fusion (PBF). Among these, DED delivers a higher deposition rate than PBF, yet PBF provides better quality surfaces. Despite the rising number of scientific publications and projects related to AM and DED, there is a considerable lack of information about the processing parameters at DED, microstructural evolution and mechanical properties of several metallic alloys. In the literature revision performed between 2015 and June of 2020 focused on the IN625 and IN718 alloys processed by AM, approximately twice the publications are using PBF than DED. Amongst the DED papers, a lack of information about proper processing parameters of different equipment and materials was observed. Also, the use of conventional heat treatment application was found controversial, once the microstructural evolution of alloys processed by AM is not the same than wrought alloys. Another remark is the lack of information about mechanical properties at high temperatures, with few tensile results, and only one study dedicated to thermomechanical fatigue. Therefore, in this proposal, the selected material is the Inconel superalloys IN625 and IN718, processed by laser-based L-DED. This proposal seeks to fulfill the primary objectives. The first objective is the assessment of mechanical properties of the mentioned alloys processed by L-DED, focused on the tensile tests, thermomechanical fatigue (350-650°C), and isothermal fatigue at 650°C. To fulfill this goal is necessary to conduct the parameters process developing in L-DED equipment with laser capacity of 1 kW, reference BeAM modulo, focused on producing parts with the minimum number of defects and the best surface quality. Also, it will be conducted a study of the influence of the post-heat treatments in the microstructural features and phases tracking. The second objective will be to contribute in two of the work packets (WP) stated in the ongoing thematic project FAPESP 2016/11309-0, "WP2: study and development of DED (direct energy deposition) process" and "WP3: processing and characterization of materials obtained by additive manufacturing (AM)". This project will supply information about the processing window for the IN625 and IN718, post-heat treatments, and mechanical behavior of these alloys, assessed at room temperature and high temperature. The contribution of this project is meant for future projects seeking to build large parts in the aerospace industry. (AU)