Chinese Scientists Develop High Fatigue-resistant 3D Printed Titanium Alloy

From the Chinese Academy of Sciences was informed that recently, the Chinese Academy of Sciences Institute of Metals Zhang Zhefeng team prepared a 3D printed titanium alloy material with high fatigue resistance, the research results were published on 29 February in the journal "Nature" (Nature).
3D printing, also known as additive manufacturing, because of its unique free-form ability to greatly meet the needs of high-end equipment and components for highly integrated, multi-functional, lightweight, integrated, is considered a disruptive technology in the field of manufacturing, in the aerospace and other fields to get great attention and initial application. However, compared with traditional manufacturing technologies, the fatigue performance of 3D printed materials under cyclic loading is generally poor, which seriously restricts their wide application as structural load-bearing parts.
For the first time, researchers have explicitly proposed that ideally the titanium alloy tissue itself (called Net-AM tissue) directly prepared by 3D printing technology should have naturally ultra-high fatigue properties, while defects such as porosity generated during the printing process mask the fatigue-resistant advantages of its own tissue, leading to a significant reduction in the fatigue properties of the actual measured 3D printed materials. However, the current process of eliminating porosity is often accompanied by tissue coarsening, while the treatment of refined tissues can bring about the recurrence of porosity and even trigger new unfavourable factors such as the enrichment of α-phase at grain boundaries, which can be described as a dilemma.
For the first time in Ti-6Al-4V alloys, researchers have found that grain boundary migration and porosity growth of 3D printed state tissues at high temperatures exhibit asynchronous properties with the phase transition process. This implies that there exists a valuable heat treatment process window for both slat tissue refinement and effective suppression of grain boundary α-phase enrichment and porosity recurrence. To this end, the researchers cleverly exploited this process window and invented a new process of stepwise defect and organisation modulation, and finally prepared a nearly porosity-free near-Net-AM organised Ti-6Al-4V alloy. Its tensile-tensile fatigue strength was enhanced from 475 MPa in the pristine state to 978 MPa, an increase of 106%.
By comparison, it is found that this near-Net-AM organised Ti-6Al-4V alloy not only has the highest tensile-tensile fatigue strength among all titanium alloy materials, but also has the highest specific fatigue strength (fatigue strength divided by density) among the fatigue data of the materials reported so far.
This achievement updates people's previous inherent understanding of the low fatigue performance of 3D printed materials, reveals the unique advantages of 3D printing technology in fatigue-resistant manufacturing, and demonstrates the broad application prospects of 3D printed materials as structural load-bearing parts in aerospace and other important fields.