Corrosion performance of additively manufactured (AM) components
Lead Research Organisation:
Swansea University
Department Name: College of Engineering
Abstract
Additive manufacturing (AM) is a rapidly developing technology which offers increased design freedom and flexibility, as well as shorter lead times and reduced wastage. The viability of AM is consequently of significant interest to a range of industries including automotive, aerospace and nuclear.
Whilst AM presents many opportunities, its flexibility gives rise to a wide array of process variables which impact the properties of parts. The lack of knowledge regarding the reliability and reproducibility of parts limits the integration of AM into several industries, particularly those in which safety critical components are used. Whilst there exists a large amount of literature focused on the tensile properties of AM parts, there appears to be a gap in knowledge surrounding the associated corrosion properties. The effect of microstructural variations on corrosion resistance, particularly corrosion fatigue remains widely unknown to industry.
In light of both this gap in understanding, and the opportunities offered by AM, the research programme aims to investigate the corrosion performance of components produced using laser powder bed fusion (LPBF). LPBF make use of high local heat densities from a laser to create high rates of heating and cooling which in turn allows powder fusion and solidification. Residual stress and strain, anisotropic, heterogeneous microstructure, precipitate formation, inhomogeneous segregation of elements and non-equilibrium structures have all been observed in AM parts. Furthermore, lack of sufficient powder fusion can result in porosity.
This project aims to investigate the effect of both build, and post build heat treatment, parameters, on the corrosion performance of AM components. The results will be compared with those obtained in the case of components manufactured using traditional processing methods.
The primary material on which research will be focused is stainless steel 316L, due to its relatively low cost, stability during processing and desirable properties of the as-built material. As yet, the corrosion resistance of stainless steel AM components remains largely unexplored and it is therefore of interest to clarify whether the AM process changes the corrosion resistance of manufactured parts.
Initial research will focus on the effect of laser scanning build parameters, for example laser power and speed, on the metallurgy, and corrosion properties of material produced. The properties will be compared to those obtained in the case of wrought samples.
-Microscopy will be used to ascertain the effect of varying parameters on the metallurgy of components produced.
-Time lapse microscopy and the Scanning vibrating electrode technique (SVET) will be used to study the mechanism of corrosion in situ. The mechanism will be linked to the microstructural features observed.
-Scanning Kelvin probe microscopy (SKPFM) will be utilized to study the corrosion potential values associated with varying parts of the microstructure.
-Conventional advanced electrochemical techniques such as open circuit potential and potentiodynamic polarisation will be used to study the bulk properties of material.
-Hardness, tensile and fatigue testing will be used to investigate the mechanical properties of components. The density and porosity of built parts will also be measured.
-Post heat treatment;
Whilst as-built 316L can have exceptionally high tensile properties, there can be a trade-off with other properties such as ductility. Post build steps such as annealing and hot isostatic pressing (HIP) can therefore be used to improve mechanical properties and reduce porosity but can also lead to sensitization and chromium carbide formation during heat treatment. The presence of chromium depleted regions results in intergranular corrosion, stress corrosion cracking and pitting formation.
Whilst AM presents many opportunities, its flexibility gives rise to a wide array of process variables which impact the properties of parts. The lack of knowledge regarding the reliability and reproducibility of parts limits the integration of AM into several industries, particularly those in which safety critical components are used. Whilst there exists a large amount of literature focused on the tensile properties of AM parts, there appears to be a gap in knowledge surrounding the associated corrosion properties. The effect of microstructural variations on corrosion resistance, particularly corrosion fatigue remains widely unknown to industry.
In light of both this gap in understanding, and the opportunities offered by AM, the research programme aims to investigate the corrosion performance of components produced using laser powder bed fusion (LPBF). LPBF make use of high local heat densities from a laser to create high rates of heating and cooling which in turn allows powder fusion and solidification. Residual stress and strain, anisotropic, heterogeneous microstructure, precipitate formation, inhomogeneous segregation of elements and non-equilibrium structures have all been observed in AM parts. Furthermore, lack of sufficient powder fusion can result in porosity.
This project aims to investigate the effect of both build, and post build heat treatment, parameters, on the corrosion performance of AM components. The results will be compared with those obtained in the case of components manufactured using traditional processing methods.
The primary material on which research will be focused is stainless steel 316L, due to its relatively low cost, stability during processing and desirable properties of the as-built material. As yet, the corrosion resistance of stainless steel AM components remains largely unexplored and it is therefore of interest to clarify whether the AM process changes the corrosion resistance of manufactured parts.
Initial research will focus on the effect of laser scanning build parameters, for example laser power and speed, on the metallurgy, and corrosion properties of material produced. The properties will be compared to those obtained in the case of wrought samples.
-Microscopy will be used to ascertain the effect of varying parameters on the metallurgy of components produced.
-Time lapse microscopy and the Scanning vibrating electrode technique (SVET) will be used to study the mechanism of corrosion in situ. The mechanism will be linked to the microstructural features observed.
-Scanning Kelvin probe microscopy (SKPFM) will be utilized to study the corrosion potential values associated with varying parts of the microstructure.
-Conventional advanced electrochemical techniques such as open circuit potential and potentiodynamic polarisation will be used to study the bulk properties of material.
-Hardness, tensile and fatigue testing will be used to investigate the mechanical properties of components. The density and porosity of built parts will also be measured.
-Post heat treatment;
Whilst as-built 316L can have exceptionally high tensile properties, there can be a trade-off with other properties such as ductility. Post build steps such as annealing and hot isostatic pressing (HIP) can therefore be used to improve mechanical properties and reduce porosity but can also lead to sensitization and chromium carbide formation during heat treatment. The presence of chromium depleted regions results in intergranular corrosion, stress corrosion cracking and pitting formation.
Organisations
People |
ORCID iD |
| Matthew Ritchie (Student) |