Cyclic Deformation and Damage Mechanisms in additive manufactured Ti-6Al-4V with Graded Microstructures

Lead Research Organisation: Coventry University
Department Name: Ins for Future Transport & Cities

Abstract

Additive manufacturing (AM), also called 3D printing, has been widely recognised to be capable of offering a range of logistical, economic and technical advantages when compared with conventional manufacturing processes. For example, AM has opened up new business opportunities for the aerospace sector because of its reduced time-to-market and higher buy-to-fly ratio, in particular for titanium alloys. However, the widespread adoption of AM by industries for the production of metallic engineering parts/components remains a challenge. Lack of knowledge about the reliability of AM-built materials and associated concerns about engineering structural integrity has been identified as one of the hurdles to successfully commercialise this promising manufacturing process.

Ti-6Al-4V is the most prevalent titanium alloy and is widely used in aerospace applications. Rolls-Royce PLC at Derby has applied AM technologies to repair aero-engine BLISKS (Bladed-Disks) and GE Aviation in the USA has developed AM-built fuel nozzles for the LEAP aero-engines. With AM moving into the production of more heavily loaded end-use components, particularly within the aerospace sector, improved understanding of the mechanical behaviour of AM parts/components under cyclic (fatigue) loading is essential. This requires the development of a mechanistic based lifetime assessment procedure for safety-critical engineering systems that contain AM-built parts/components.

By engaging actively with both the UK's world-renowned AM manufacturing technology centre (MTC) and an end-user (Rolls-Royce PLC), this project will develop an experimentally-validated microstructure-based model that can be adopted when undertaking a lifetime prediction against fatigue crack initiation in AM-built Ti-6Al-4V.

Planned Impact

The aim of this project is to enhance the confidence of both AM manufacturers and end-users that AM-built materials (in particular Ti-6Al-4V for the aerospace sector) are at least as safe and reliable as those produced by the traditional machine from solid processes. This will be achieved by developing a microstructure-based self-consistent model, validated by multi-scale experiments, to predict mechanical behaviour of the AM-built Ti-6Al-4V under cyclic loads at high temperature. Since the presence of graded microstructures for AM-built metallic materials, including AM steels, nickel and titanium alloys, is directly related to the essence of AM processes, i.e. the layer-by-layer building philosophy, this project will have broad benefits to both current and potential AM end-users ranging from aerospace, nuclear, automotive as well as biomedical industries. For example, the nuclear industry will use AM to make safety-critical lugs on steam generators (current forging capacity in the world isn't big enough to make these lugs).

This project is of strong relevance and interest to industry, with significant potential future benefits for the UK economy. Rolls-Royce PLC, a global leader in aerospace manufacturing, have applied AM processes to repair damaged aero-engine BLISKS for more than 5 years and produced a prototype front bearing aero-engine by AM in 2015. They will be one of the project beneficiaries by gaining a mechanistic understanding of fatigue behaviour of AM-built Ti-6Al-4V with graded microstructures. The project will provide Rolls-Royce PLC and other AM end-users with much needed assurance to the use of AM-built components. The widespread adoption of AM technologies by industry will improve manufacturing energy efficiency (an economic impact) by increasing material utilisation and minimising scrap material associated with component fabrication. In this sense, this project will help reduce the CO2 footprint and thus generate an environmental benefit.

One of the goals for the UK's stakeholders in aerospace, and other industries who are considering the utilisation of AM technologies, is to keep fully informed of advances in manufacturing technologies. This also aligns with UK's strategic decision of keeping and developing the core technology in advanced manufacturing. The proposed work will represent an outstanding example of world-leading AM research carried out in the UK. By interacting with the UK's High Value Manufacturing Catapult (the MTC), I will be able to meet and discuss the research outcomes with policy-makers, legislators and a wide range of professionals including business people. This will improve information flow and accelerate innovation and development in the AM sector.

The postdoctoral researcher as well as myself (an early career academic at Coventry University) will gain skills in both in situ neutron and synchrotron X-ray diffraction and tomography and developing self-consistent models for materials with graded microstructures. This project will expose me to wider networks of academic and industrial partners both nationally and internationally.
 
Description It is generally recognised that electron beam melted (EBM) Ti-6Al-4V alloys exhibit a microstructural gradient along the build direction, but there have been some inconsistent experimental observations and debate as to the origin and magnitude of this effect. Through our research, it was found that The graded microstructure resulted in a decrease in micro-hardness which correlated very well with the mean a lath width by following a Hall-Petch relation. These observations can be attributed to the thermal gradient in the EBM powder bed that produced a cooling rate gradient along the build height.
Exploitation Route We have published our research outcomes, ongoing research is to further developing materials models to understand this field. In addition, I have organised and will be chairing a research impact symposia at Norway via the ESIAM19 international conference.
Sectors Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology

URL https://www.sciencedirect.com/science/article/pii/S0921509318316952?via%3Dihub
 
Description enabling Sixty Years creep-fatigue life of the NExt generation nuclear Reactors 'SYNERgy'
Amount £1,247,261 (GBP)
Funding ID EP/R043973/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 01/2019 
End 12/2023
 
Description Beihang University 
Organisation Beihang University
Department School of Materials Science and Engineering
Country China 
Sector Academic/University 
PI Contribution We applied and performed synchrotron X-ray diffraction and tomography to study the cracking mechanism on the high-performance material provided by the partner.
Collaborator Contribution The partner provided in-kind material to support the synchrotron X-ray experiment.
Impact Peng H, Shi Y, Gong S, Guo H, Chen B, "Microstructure, mechanical properties and cracking behaviour in a ?'-precipitation strengthened nickel-base superalloy fabricated by electron beam melting" (2018) Materials & Design, vol. 159, pp. 155-169
Start Year 2017
 
Description USTB 
Organisation University of Science and Technology Beijing
PI Contribution We performed microstructure characterisation and numerical modelling simulation to analyse the material performance for electron beam melted high Nb-TiAl alloys
Collaborator Contribution Fabrication of electron beam melted high Nb-TiAl alloys and supply the materials to support the research.
Impact Kan W, Chen B, Jin C, Peng H, Lin J, "Microstructure and mechanical properties of a high Nb-TiAl alloy fabricated by electron beam melting" (2018) Materials & Design, vol. 160, pp. 611-623 Kan W, Liang Y, Peng H, Chen B, Guo H, Lin J "Microstructural degradation of Ti-45Al-8Nb alloy during the fabrication process by electron beam melting" (2017) JOM, vol. 69, pp. 2596-2601
Start Year 2017