A research team led by Profs. ZHANG Zhefeng and ZHANG Zhenjun from the Institute of Metal Research (IMR) of the Chinese Academy of Sciences has proposed an innovative strategy to fabricate an anti-fatigue 3D-printed titanium alloy by separately regulating their microstructure and defects, called net-additive manufacturing preparation (NAMP).
The study was published in
Nature on Feb. 28.
Additive manufacturing (AM), also known as three-dimensional (3D) printing, is a disruptive technology in the manufacturing field. However, the poor fatigue performance of 3D-printed materials under cyclic loading—compared with traditional manufacturing—seriously limits the application of such materials as structural components in important fields such as space exploration and aviation.
In this study, in terms of their previous fatigue prediction theories, the researchers proposed a groundbreaking concept: 3D-printed microstructures (i.e., Net-AM microstructures) have naturally high fatigue resistance. However, their low-fatigue performance of 3D materials may be overshadowed by the negative effects of microvoids induced by the current printing process.
To verify this concept, they invented the Net-Additive Manufacturing Process (NAMP), including a hot-isostatic pressing (HIP) to eliminate the microvoids and a subsequent high-temperature-short-time (HTSt) heat treatment to restore the AM microstructure with fine martensite lath, which can successfully restore a nearly void-free Net-AM microstructure to the titanium alloy. Interestingly, the Net-AM microstructure has remarkably high fatigue resistance, which exceeds the resistance of all other additively manufactured and even forged titanium alloys. The Net-AM microstructure also shows the highest specific fatigue strength (i.e., fatigue strength/density) of all reported materials in the world.
The fatigue cracks of the microstructures prepared using the NAMP process normally nucleated at clean primary β grain boundaries and fine martensite lath, successfully avoiding many traditional fatigue weaknesses and preventing localized damage accumulation, thus exhibiting extremely high fatigue resistance.
This study reveals the naturally high fatigue resistance of the 3D-printed microstructure and the potential advantages of 3D printing technology in the production of structural components, and also points out clear directions for 3D printing anti-fatigue manufacturing.
Microvoid distribution and microstructure of as-printed state and other three states. (Image by IMR)
Evaluation on the fatigue strength and specific fatigue strength of the Net-AM microstructure in comparison with other microstructures as well as other materials. (Image by IMR)
The fatigue cracking modes and corresponding microstructural information. (Image by IMR)
