The Influence of Porosity on Fatigue Crack Initiation in Additively Manufactured Titanium Components

Area of Science:

• Materials Science
• Mechanical Engineering
• Additive Manufacturing

Background:

• Fatigue life of additively manufactured parts is limited by porosity.
• Electron beam melting (EBM) of Ti-6Al-4V parts exhibits significant scatter in fatigue performance due to defects.

Purpose of the Study:

• To investigate the critical role of pore size and location in determining fatigue life.
• To identify the most harmful defects influencing fatigue crack initiation in EBM Ti-6Al-4V.

Main Methods:

• Utilized X-ray computed tomography to characterize all pores in fatigue samples before testing.
• Monitored fatigue crack initiation and growth using in-situ X-ray computed tomography.
• Employed various ranking strategies, including defect size, aspect ratio, and proximity to the surface.

Main Results:

• Fatigue crack initiation constitutes over 70% of the total fatigue life.
• The initiating defect was often not the largest, but within the top 35% of large defects.
• Incorporating proximity to the surface and pore aspect ratio identified the initiating defect within the top 3% of most harmful defects.

Conclusions:

• Pore characteristics, specifically proximity to the surface and aspect ratio, are crucial for predicting fatigue life.
• Optimizing EBM deposition parameters to control pore distribution relative to applied stresses can maximize fatigue life.