Diode-pumped nanosecond Nd:YAG laser micromachining of Ti-3Al-2.5V tubes for fatigue life study

Due to its superior properties such as high strength to weight ratio, great creep and corrosion resistance, amenable to cold working, etc., Ti-3Al-2.5V is widely used in making seamless tubing in hydraulic systems in aerospace applications. Defects can develop on the surface of the tube during service. Under periodic loading of hydraulic impulse pressure, micro-crack can develop from the defects and propagate changing to macro-crack and finally fracture of the tube can happen, causing leakage or system failure. Assessment of residual life of the titanium tubes with defects is thus imperative to avoid hydraulic leak failure within required service hours. In this paper, we present results using a diode-pumped nanosecond pulsed Nd: Yttrium-Aluminum-Garnet (Nd:YAG) laser for micromachining the Ti-3Al-2.5V tube for fatigue life study. Laser notches of length of 12.7 mm were produced on outer surface of the titanium tubes. Notch depths were generated through repetitive scanning of the laser beam. Scanning electron microscope (SEM) images of the laser generated notch, the crack propagation profile and the fatigue lives of the titanium tubes are presented and discussed in this paper. It is demonstrated that the nanosecond pulsed Nd:YAG laser can produce consistent pre-cracks on the Ti-3Al-2.5V tubes with designated dimensions for fatigue crack growth life study.