Fundamental Mechanisms of Creep and Embrittlement in Additively Manufactured IN625 and IN718
Abstract
Additive manufacturing (AM) of metals and alloys has become popular due to cost effectiveness and, generally, retention of strength,compared to cast and wrought (conventional) alloys. Complicated metallic parts require less joining with AM leading to the cost effe,ctiveness. These AM parts are produced from a fine powder (e.g. particles 50-100 ?m in diameter) that is laser-melted and leads to a, solid, bulk, part. Often there is considerable porosity that can be substantially reduced (but not completely eliminated) by hot is,ostatic pressing (HIP). This proposal will focus on Inconel 625 and 718 alloys for jet engine and energy applications. However, ther,e are complications in these alloys systems. The PI has verified in unique creep tests for durations up to one year that the creep s,trength of Inconel 625 is retained within the temperature range of the jet engine service in which 625 components are utilized. Howe,ver, there is an unacceptable loss in creep ductility verified by the PI for AM 625 and some of the literature for wrought 718. This, proposal seeks to determine the cause of embrittlement of AM Inconel 625 and (expected) 718 Inconel to be used in jet engines. The,@##@0001,fundamental goal of this proposal is to understand the basis of the embrittlement, which will allow us to devise strategies that can,erefore, we propose a combination of microscopy, spectroscopy, atom-probe tomography and nanoSIMS in combination with high throughpu,t synthesis and characterization in order to identify critical elements for Inconel 625 and 718 alloys that can minimize embrittleme,ost to USC and Pratt and Whitney has expressed a very strong interest in mitigating the loss of ductility in AM superalloys at eleva,ted temperatures. The Pratt and Whitney collaboration ensures the possibility that the results of this work can be readily transferr,ed to the jet engine community. Letters of support for this proposal are attached. The composition at the grain boundaries would app,ear to require characterization by fairly sophisticated analytical facilities such as atom probe tomography (APT) and nanoSIMS. TEM,and SEM are necessary to characterize the precipitation of second phases and porosity. At USC, elevated-temperature fracture toughne,ss and fatigue tests would be performed in addition to creep testing to fully assess the mechanical behavior of AM 625 and 718 Inco,nel.Our experimental work has two main components. First, combinatorial materials synthesis and characterization will be used for s,electing and studying the behavior of optimal compositions of doped Inconel alloys to reduce/eliminate embrittlement. These high th,roughput techniques, are used to generate materials libraries, which are data bases that contain relevant information regarding chem,ical composition, crystal structure, and properties of the synthesized compositions. This includes automated characterization tech,niques which will be implemented to identify suitable combinations of dopants that can prevent segregation and eventual loss of duct,ility due to embrittlement (such as sulfur) in Inconel 625 and perhaps 718. Second, optimal compositions found in the combinatorial, synthesis route will be fabricated via AM, characterized and tested. In summary, the PIs will verify the embrittlement of AM 625 a,nd 718. The basis for any (expected) embrittlement will be discovered. Next, mitigation of the embrittlement will be attempted by,adding elements that tie-up the embrittlement species identified using the combinatorial techniques nanoSIMS, APT and electron micro,scopy in conjunction with creep testing.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 07, 2022
- Source ID
- N000142212712
Entities
People
- Michael Kassner
Organizations
- Office of Naval Research
- United States Navy
- University of Southern California