טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentKonstantino Eitan
SubjectEffects of Laser Surface Treatment on Mechnical Properties
of Ti-6Al-4V Alloy
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Emeritus Eli Altus


Abstract

LST was used as a tool to improve fatigue life of Ti-6Al-4V alloy as well as repairing accumulated fatigue damage. Results show a significant improvement in the fatigue life of treated specimens (50% improvement) and up to full healing of the fatigue damage. In order to characterize the effects of the LST on the material, several characterization methods were used. SEM was used to study the microstructural changes. Micro hardness measurements were preformed. XRD and Hole drilling method were used to determine the near surface residual stresses, and AES was used to find the oxygen penetration profiles. An IR camera detected the surface temperature field during laser treatment cycle.

A predictive model was developed relying on the theories of thermal and diffusion induced stresses. The model is based on the formation of local, non-uniform residual stresses from both oxygen diffusion and thermal plastic deformation. The model predicts the fatigue life of laser treated specimens up to the phase transformation temperature (1000°C for Ti-6Al-4V). The model also predicts the crack initiation location in the treated area. The healing phenomenon was modeled based on theories of defect movements due to stress induced diffusion.