Laser shock peening of titanium for enhanced fatigue performance
Shot peening is the most widely applied surface enhancement technology for protection against fatigue. This technology induces a plastically deformed surface layer, residual stress field and strengthened microstructure by impacting the metal surface with high speed spherical shot made from ceramic, steel or glass. Greatly improved fatigue properties are achieved. Shot peening has already been used on rotor parts in aero-engines, such as compressor blades, turbine disks and turbine blades.
Laser shock peening is a new generation surface enhancement technology, which also is a kind of mechanical enhancement of surface properties. The laser pulse creates rapid local heating creating a mechanical shock wave transmitted into the metal surface creating a similar surface enhancement effect to shot peening. The anti-fatigue property is improved by the residual stress and strengthened microstructure.
Damage to surface caused by foreign objects impacting on compressor parts is still a serious problem. The greater depth of the laser shock peening surface enhancement compared to traditional shot peening has highlighted it as a very promising technique to further improved fatigue life of these parts especially following surface damage of the components. Reports have already suggested that laser shock peening can be used effectively on compressor blades and compressor disks, and also to the application of turbine parts.
This project will focus on understanding the microstructural changes induced by laser shock peening to understand the fatigue resistance that is imparted. This will be investigated as function of the laser shock peening parameters before ultimately testing the fatigue performance of differently treated test components.
Surface and cross sectional analysis will be conducted metallographically initially but then complemented using FIB-SEM for site-specific analysis. The depth of the surface layer means that Plasma FIB will be used to create these cross sections. This analysis will be conducted for a range of processing conditions to more clearly understand the maximum depth that can be achieved without other deleterious effects, such as roughening or cracking of the surface occurring. When a set of conditions has been determined the laser shock peening with these conditions will be applied to test samples which can be tested in fatigue. This test will use ex situ X-ray computed tomography to regular monitor the samples for initiation and propagation of damage and will help determine what is the maximum size of defect that can be tolerated in these samples after the laser shock peening treatment.
Funding covers tuition fees and annual maintenance payments of at least the Research Council minimum (currently £14,296) 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.
Applicants should have or expect to achieve at least a 2.1 honours degree in Materials Science, Physics, Chemistry or a related subject.