Environmentally assisted cracking of aerospace and marine aluminium alloys: new insights from multiscale correlative imaging
Aluminium alloys show properties 10-30 times better than pure aluminium. They find widespread application where high strength and light weight are critically important. In ambient and atmospheric conditions an oxide layer forms on the aluminium that provides significant protection from the environment.
Environmentally assisted cracking (EAC) can lead to catastrophic failure under stresses and environmental conditions that are not serious in themselves. This makes EAC a particularly dangerous failure mechanism.
There are many standard tests available to measure the performance of different aluminium alloys and determine their resistance to EAC and these are useful for this purpose. These tests are conducted on samples many mm or cm in size and multiple important measurements can be made. There is a problem which is that the cracks that initiate and propagate due to EAC are very complex and whilst they may be many mm or cm in length the crack front is nanometre-sized in width. There is a lack of connectivity in our understanding at the macroscale (of the large tests specimens) and the nanoscale (the dimensions of the crack tip/front). It is important to effectively link these two scales so that we can understand the stress state and environment at the nanoscale and in turn interrogate the possible mechanisms enabling the propagation of the crack.
This PhD will investigate EAC in 5XXX and 7XXX series aluminium alloys pertinent to marine and aerospace applications. A combination of world leading time-lapse X-ray 3D (computed tomography) imaging, electron microscopy and some of the first large area serial section electron tomography will be used to provide a time-resolved and multiscale picture of how these cracks nucleate and propagate. Manchester is one of the few places world-wide able to capture this time dependent 3D information. This will be used to quantify the hierarchical morphology and local stress intensity and will provide a new level of insight into these complex cracks to the benefit of our industrial collaborators.
Applicants should have or expect to achieve at least a 2.1 honours degree in Materials Science, Physics or Physical Chemistry.
Funding covers tuition fees and annual maintenance payments of at least the Research Council minimum (currently £14,057) for eligible UK and EU applicants. EU nationals must have lived in the UK for 3 years prior to the start of the programme to be eligible for a full award (fees and stipend). Other EU nationals may be eligible for a fees-only award.