By Chunlei Shen
A team led by Zhang Zhefeng, a researcher at the Institute of Metals, Chinese Academy of Sciences, has successfully developed 3D printed titanium alloy materials with high fatigue resistance, breaking the world record for fatigue strength of 3D printed titanium alloys. The relevant research findings were published in Nature on February 29th.
3D printing technology, a rapid prototyping technique, involves the layer-by-layer deposition of powdered metals or plastics using lasers or electron beams to construct objects or products. Previous studies have revealed that 3D printed materials generally exhibit poor performance under cyclic loading conditions, significantly limiting their widespread application as structural load-bearing components.
Zhang Zhefeng told Chinese Science News that his team believed that under ideal conditions, the titanium alloy structure directly fabricated by 3D printing technology, known as the Net-AM structure, should inherently possess extremely high fatigue performance. However, defects such as pores generated during the printing process mask the inherent advantages of the structure, becoming a bottleneck for its practical engineering applications.
Traditionally, improving the fatigue performance of materials involves eliminating defects such as pores, a measure adopted by most researchers. Since 2019, Zhang Zhefeng's team has been studying the fatigue performance of 3D printed titanium alloys. They found that using hot isostatic pressing (HIP) to eliminate printing pores would simultaneously destroy the original structure of the 3D printed material, resulting in no significant improvement in material fatigue performance. Therefore, they proposed an innovative approach - reprocessing the structure that had undergone HIP to adjust it back to its original 3D printed state, thereby restoring its natural high fatigue performance. However, the challenge they faced was how to adjust the structure back to its original 3D printed state.
After attempting numerous different processing techniques, Zhang Zhefeng's team discovered that grain boundary diffusion, defect disappearance, and phase transformation processes of 3D printed Ti-6Al-4V alloy could be achieved within different processing windows. Based on this, they invented the NAMP (defect and structure stepwise control) new technology, ultimately producing nearly pore-free near-Net-AM structure titanium alloy. The fatigue strength of the Ti-6Al-4V alloy increased from the original printed state of 475 megapascals to 978 megapascals, doubling the fatigue strength. This near-Net-AM structure Ti-6Al-4V alloy not only has the highest tensile-tensile fatigue strength among all titanium alloys but also has the highest specific fatigue strength (fatigue strength divided by density) among the reported materials fatigue data.
"This achievement revises the previous understanding of the inherently low fatigue performance of 3D printed materials, demonstrating broad prospects for the application of 3D printed materials as structural load-bearing components in critical fields such as aerospace," Zhang Zhefeng said.
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