Investigations on Similar, Dissimilar and Functionally Graded Materials Depositions using Double Wire Arc Additive Manufacturing
Creators: name: ASHISH KUMAR
Publisher: name: Zenodo
Year: 2022

description: In this thesis, investigations on depositions of similar, dissimilar and functionally graded<br> materials using gas metal arc welding (GMAW)-based wire arc additive manufacturing<br> (WAAM) employing single and double wire feed techniques were carried out. Initially<br> single bead geometry model was developed utilizing response surface methodology and<br> experiments conducted utilizing Box-Behenken design of experiments for deposition of<br> austenitic stainless steel (ASS) 304L by WAAM. Bead geometry parameters i.e., bead width,<br> bead height and bead cross-sectional area etc. were expressed in terms of the process<br> parameters like voltage, wire feed rate, torch speed and gas flow rate. A multi-bead<br> deposition model was proposed to determine optimal process parameters for near-net shape<br> deposition in WAAM utilizing a genetic algorithm (GA) and single bead geometry model.<br> The proposed approach was validated through deposition of three shapes, i.e., slice, wall and<br> block. It was revealed that optimal bead sizes and degree of overlapping were different for<br> fabricating different shaped parts. Mechanical testing and metallurgical characterization<br> were carried out to compare the deposited ASS304L through single wire feed (SWF) and<br> double wire arc additive manufacturing (DWAAM) techniques. DWAAM deposition was<br> seen to deliver higher deposition rate and superior mechanical properties compared to that of<br> the single wire feed deposition for ASS 304L. The effects of process parameters on bead<br> geometry and microstructures in deposition of dissimilar austenitic-ferritic stainless steels<br> (ASS304L/FSS430L) by DWAAM were also investigated. Bead size and deposition rate<br> was increased in dissimilar ASS304L/FSS430L depositions by DWAAM with voltage, wire<br> feed rate and gas flow rate. The microstructure of dissimilar ASS304L/FSS430L contained<br> with a large number of dendrites having growth direction along the temperature gradient.<br> Moreover, contents of major allowing elements in the deposited ASS304L/FSS430L were<br> seen to vary with the wire feed rate, and mass fraction of element Ni got enhanced with<br> increase of ASS 304L wire feed rate. Bimetallic structures (BMS) comprising of Inconel 625<br> and ASS 304L with and without a functionally gradient intermediate layer (IL) were<br> deposited through DWAAM. The functionally gradient IL was made by gradually changing<br> the compositions from pure Inconel 625 to pure 304L stainless steel (SS) by varying the feed<br> rates of two wires. Scanning electron microscopy and energy dispersive spectroscopy tests<br> were conducted to investigate microstructures and chemical composition variations at the<br> interface of the BMS. It was found that the chemical composition altered gradually through<br> the addition of IL compared to the sudden change in case of BMS without IL. Microstructure<br> of pure ASS304L, ASS304L/IN625 (50%/50%) BMS, and pure IN 625 were found as<br> columnar dendritic structure with some amount of secondary dendrite, columnar dendrites<br> with secondary dendrite, and columnar dendrites, respectively. Tensile tests, microhardness<br> study and fracture morphology of the BMS revealed better mechanical properties of the<br> BMS with IL (BMS-IL) compared to that without IL. The DWAAM method exhibited<br> capability of fabrication of high-quality similar, dissimilar, bimetallic and functionally<br> gradient materials structures.