Assessment of TI-6AL-4V Laser Clad Repair
Abstract
Damaged components and a lack of spare components are issues which are currently affecting military aircraft capability. Laser Cladding is an additive manufacturing technique which shows promise in repairing damaged aviation components. However, there are considerable certification requirements for critical components which stand to gain the most benefits from laser clad repair methodologies. These requirements involve establishing crack growth rate data for the laser clad material to gain confidence in the reliability of the repair’s performance on in-service aircraft. This research seeks to understand the fatigue behavior of Ti-6Al-4V that has undergone a simulated laser clad repair, with unrepaired specimens also tested to allow for comparison. Half of the clad repaired specimens were subjected to a heat treatment process with the intention of relaxing the residual stress within the clad repair and underlying substrate. Firstly, the residual stress was measured utilising the non-destructive High Energy X-ray Diffraction (HEXD) and destructive slitting techniques. Whilst the HEXD method was able to successfully identify lattice strain within the material, a significant amount of scatter was present in the results. The slitting method was able to quantify the residual stress within each clad repair category, however this method is unable to identify the entire residual stress field within the material. Fatigue testing was conducted on the samples with significant challenges experienced in initiating crack growth within the area of interest, which required specimen redesigns. Quantitative fractography was next conducted on the failed fracture surfaces, with the marker band technique utilized to determine fatigue crack growth rate. Marker band detection was challenging, with only a small number of specimens exhibiting observable marker bands due to the tortuous nature of the Ti-6Al-4V fracture surfaces. The baseline material correlated well to reference Ti-6Al4V material data from the Metallic Materials Properties Development and Standardization database. Both of the laser clad repairs experienced faster fatigue crack growth rate in comparison to the baseline case, which was attributed to the microstructural changes due to the clad process. The application of heat treatment improved the repair performance; however heat treatment may not be available for all aircraft repair applications. Whilst this research presents material data that would assist in establishing a damage tolerance methodology for laser clad repaired materials, a significant amount of data is required to enable any successful certification for application to in-service aircraft.
Degree
M.Sc.
Advisors
Sangid, Purdue University.
Subject Area
Industrial engineering|Military studies|Optics
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