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Jalal Al-Lami - Microstructure and mechanical performance of nickel-based superalloys additively manufactured by powder-bed fusion.

Investigator: Jalal Al-Lami

Supervisor: Dr. Minh-Son Pham

Co-supervisor: Dr. Christopher Gourlay

Collaborators: Cross Manufacturing Company, Dr. Connor Myant (Imperial – Dyson school)

Title: Microstructure and mechanical performance of nickel-based superalloys additively manufactured by powder-bed fusion.

Description:

Additive Manufacturing (AM) has become widely accepted as a new paradigm for the design and production of high-performance components used in a range of demanding applications. Compared with traditional manufacturing, AM has different characteristics arising from the rapid cooling and thermal cycles that occur because of the repeated deposition of material. It is generally found that metallic alloys made by AM have higher strength, but they have lower ductility, shorter fatigue lives and lower creep resistance levels compared with metallic alloys made by other manufacturing processes. To manufacture components with the desired mechanical properties, it is important to obtain in-depth understandings of the solidification microstructure and its evolution during subsequent thermal cycles. In this PhD research, fundamental studies on the microstructure of Inconel 718 alloy will be carried out. Laser powder-bed fusion will be used to fabricate the alloy. Subsequently, advanced electron microscopy will be used to examine crystal phase, texture, chemical distribution and grain microstructure from the atomic scale up to mm. The consolidation of prints will also be investigated. Finally, the mechanical performance of the AM alloys will be studied in relation to the observed microstructure and consolidation.

Jalal Al-Lami
Figure – (a) Microstructure of Inconel 718 superalloy fabricated by laser powder-bed fusion, and (b) High-resolution image of precipitates in the microstructure shown in (a).

Bogdan Dovgyy - Use of Machine Learning to design alloys for additive manufacturing

Title: Use of Machine Learning to design alloys for additive manufacturing

Investigator: Bogdan Dovgyy

Supervisor: Dr. Minh-Son Pham

Co-supervisor: Prof. David Dye

Abstract: Additive manufacturing (AM) has unique characteristics (e.g., rapid solidification and thermal cycles) that are very different to other processes. Most of existing alloys were initially designed for slow solidification processes, not for AM. This is partly responsible for unsolved metallurgical and mechanical performance challenges in metal additive manufacturing, increasing the barrier for the full realisation of AM. To search for alloys suitable for AM, we have developed key criteria that successfully assisted the selection of a highly printable high entropy alloy. This PhD study project aims at developing an algorithm that integrates the criteria into a platform of machine learning (ML) and thermodynamics phase diagram to assist the search for new alloys for AM process. The printability (in particular, the microstructure and mechanical properties) of a selected alloy manufactured by selective laser melting to verify the effectiveness of the developed ML platform. Subsequently, the relationships between the alloy microstructures and process parameters will be studied to improve the ML platform and enable the effective tailoring of microstructures.

Figure 1. (a) Alloy development cycle for additive manufacturing, (b) scanning strategy-microstructure relationship of a selected multi-component alloy.
Figure 1. (a) Alloy development cycle for additive manufacturing, (b) scanning strategy-microstructure relationship of a selected multi-component alloy.

Minsoo Jin - Rapid solidification microstructure formation in cubic and non-cubic alloys fabricated by selective laser melting

Title: Rapid solidification microstructure formation in cubic and non-cubic alloys fabricated by selective laser melting

Investigator: Minsoo Jin

Supervisor: Dr. Minh-Son Pham

Co-supervisor: Dr. Chris Gourlay

Rapid solidification in additive manufacturing (AM) process results in unique microstructures such as fine cells, epitaxial crystal growth and meta-stable phases. Such microstructures often lead to undesired mechanical properties of AM alloys (e.g., anisotropy, strong but less ductile and shorter fatigue/creep lives), making alloys fabricated by AM process less favourable in load-bearing application compared to other manufacturing processes. Understanding how crystals grow in rapid cooling and how they follow up with sudden changes in solidification direction will enable an effective control of microstructure to obtain desirable mechanical properties for high load-bearing application. The aim of the PhD project is to study the crystal formation in rapid cooling with sudden changes in solidification direction and subsequent microstructure evolution of both cubic and non-cubic alloys. Cubic crystals (namely, a Nickel superalloy and CoCrFeMnNi high entropy alloy) and a non-cubic alloy will be printed with different scanning paths by selective laser melting and examined by high resolution scanning/transmission electron microscopy to gain in-depth understandings of microstructure formation in AM.

Minsoo Jin
Side-branching of cells due to the 90° change in the heat flux in a cubic crystal fabricated by selective laser melting

Jedsada Lertthanasarn - Multiscale hierarchical lattices: Crystal plasticity-based FEM modelling

Project Title                       Multiscale hierarchical lattices: Crystal plasticity-based FEM modelling

Investigator                       Jedsada Lertthanasarn

Supervisor                          Dr. Minh-Son Pham

Co-Supervisor                   Prof. Fionn Dunne

Duration                              36 months

Abstract                              

The advent of additive manufacturing technology enables the fabrication of intricate lattices of a wide range of materials from polymers, metals to ceramics. Tailoring lattice structures can lead to the generation of lightweight materials with improved functionality. Previously reported studies on lattice materials had only focused on lattices with single orientations (analogous to single crystals). Such single-oriented lattices suffer substantial drops in load-bearing capacity. Inspired by the hardening mechanisms by tailoring crystal microstructures (such as grains, precipitates and phases) in metallurgy, we design macro lattices (i.e. meta-crystals) that mimic crystal microstructures to bring the rich knowledge in metallurgy to lattice design. The application of this approach to metals leads to the generation of multi-scale hierarchical lattices over wide length scales: from Å up to mm and beyond. This PhD study project focuses on using crystal plasticity-based finite element methods (CP-FEM) to simulate the deformation behaviour of hierarchical lattices. Together with experimental study, this CP-FEM approach will offer an integrated platform to develop hierarchical lattice materials with designed properties specifically tailored for desired energy absorption and load transfer.

Jedsada
Experiment versus FEM simulation of the deformation behaviour of an FCC lattice

Chen Liu - Architected materials inspired from hardening mechanisms in metallurgy

Title: Architected materials inspired from hardening mechanisms in metallurgy

Investigator: Chen Liu

Supervisor: Dr Minh-Son Pham

Co-supervisor: Prof David Dye

Description:

Architected materials whose constituents are constructed in a controlled manner are lightweight and used for a widely range of applications, such as aerospace, automobile and medical implants. We propose a novel approach that mimics the microstructure found in crystals to bring the hardening mechanisms such as boundary hardening, precipitation hardening and multiphase hardening found in high performance metals to develop a new class of architected materials that are tough and lightweight. This PhD study uses sophisticated CAD software and 3D printing to realise the mimicry, and studies the properties of architected materials.  Strength and toughness of crystal-inspired architected materials are investigated using mechanical tests followed by digital image correlation analysis. Metallic alloys are also used to fabricate crystal-inspired materials, leading to meta-crystals that contain multiscale hierarchical lattices across different lengthscales: from atomic up to centimetres. This PhD project will examine the microstructure and mechanical properties of meta-crystals to study the behaviour of meta-crystals that are currently not understood.

Chen Liu
Figure 1. a) Crystal-like model of a lattice material containing 64 meta-grains separated by twin boundaries which are highlighted, b) Symmetrical shear bands in the lattice material. Colour represents the degree of shear strain.

Alessandro Piglione - Microstructures and fatigue behaviour of Ni single crystals made by casting and additive manufacturing

Title: Microstructures and fatigue behaviour of Ni single crystals made by casting and additive manufacturing

Investigator: Alessandro Piglione

Supervisor: Dr. Minh-Son Pham

Co-supervisor: Prof. Fionn Dunne

Industrial partner: Beijing Institute for Aeronautical Materials (BIAM)

 

Abstract: Nickel single-crystal components play a key role in the operation of modern jet engines. Understanding their fatigue behaviour at elevated temperatures leads to significant improvements in their reliability, thereby enabling the full exploitation of their potential for an improved efficiency. Whilst most of the previous studies focus on uniaxial fatigue testing, fundamental studies will be carried out in this project in order to understand the fatigue behaviour of nickel single-crystals in complex multi-axial loading conditions. In particular, the main efforts will be directed towards (1) understanding cyclic deformation mechanisms in high-temperature rotating-bending fatigue conditions, and (2) assessing the influence of surface notches on the components’ fatigue life. In addition, this project will explore Ni single-crystal fabrication via additive manufacturing. Solidification microstructures and deformation behaviours of additive manufactured parts will be investigated and compared with those of the components fabricated by casting.

Fatigue striations in a nickel single-crystal after a rotating-bending fatigue test.
Fatigue striations in a nickel single-crystal after a rotating-bending fatigue test.