Thesis
A mechanical and microstructural study of corrosion resistant alloys produced using wire arc additive manufacturing
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2025
- Thesis identifier
- T17501
- Person Identifier (Local)
- 202088239
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- This thesis investigates the production of corrosion resistant alloys (CRA) through wire arc additive manufacturing (WAAM). This work has analysed the properties of three (3) alloys when this method is used for manufacture. Furthermore, the environmental impact of adopting WAAM has been considered. The development of these alloys was quantified through microstructural analysis and mechanical testing. Methods for the analysis of mechanical properties included hardness, impact, fatigue and tensile testing. Changes in process parameters employed for the production of precipitation-hardening stainless steel 15-5PH were investigated. This investigation observed that the heat input during deposition had a significant impact on the mechanical properties of this alloy. In addition, post weld heat treatment can be used to control the resulting properties. Of those investigated in this study, the most effective process relied on a heat input of 0.565kJ/mm followed by the standard H1150 aging heat treatment. This combination of process parameters achieved partial compliance with the requirements of ASTM standard A693. It was identified that this high heat input during deposition led to in-situ heating causing the matrix to be solutionised. This improved its response to the following aging treatment, resulting in superior properties as strengthening phases had been able to develop. Furthermore, the nickel-based superalloys; Inconel 625 and 718 were also studied. The mechanical properties of these alloys were compared against the results from previous literature. In addition, the results of fatigue testing were compared against alloys produced by other manufacturing processes. It was identified that Inconel 625 produced through this process achieved the performance required by standard ASTM B443 with fatigue performance exceeding that of conventional processing for this alloy. WAAM produced Inconel 718 did not achieve the required mechanical properties as defined by standard ASTM B637. This difference was due to the formation of the weakening δ phase caused by precipitating elements not being returned to solution following segregation during solidification. However, the fatigue performance was found to be comparable with existing literature. The columnar grains and δ made the material more sensitive to crack growth at lower stress ranges, leading to reduced fatigue performance compared with the literature. It was found that the strengthening mechanism of the alloy plays a major role in the sensitivity of its mechanical properties to process parameters and post weld heat treatment when produced using WAAM. This is most significant for precipitation hardening alloys such as 15-5PH stainless steel and Inconel 718. 15-5PH stainless steel showed up to a 5x increase in Charpy impact energy following heat treatment and up to a 25% reduction in yield strength depending on the process parameters. Hardness was shown to vary up to 20% between all cases of process parameters and heat treatment. Inconel 718 was shown to exhibit a 72% increase in hardness with proper heat treatment. Solid solution strengthening alloys such as Inconel 625 were less sensitive as they are not dependent on the development of precipitates within the matrix, for strengthening. Hardness was shown to reduce by 16% following heat treatment. These differences account for improvements in the fatigue strength of WAAM Inconel 625 when compared to the wrought alloy, while the results for Inconel 718 showed a slight reduction in fatigue strength. A methodology for the comparison of the environmental impact of manufacturing methods was applied to the production of CRA components through WAAM. It was identified through a case study of an Inconel 625 impeller that significant reductions in the primary energy consumption and carbon dioxide emissions can be achieved. In addition, the calculated carbon dioxide emissions were found to be sensitive to the carbon emission signature of the energy supply used during manufacture due to the significant contribution of electrical energy in deposition and heat treatment.
- Advisor / supervisor
- Toumpis, Athanasios
- Galloway, Alex
- Resource Type
- DOI
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