English
3D printing, also known as additive manufacturing (AM), with its unique ability to freely form complex metal components, greatly meets the significant demand for lightweight and high integration in the new generation of aviation equipment. It is expected to replace traditional manufacturing methods to achieve intelligent manufacturing of key components in high-end equipment. However, this enormous application prospect has long been constrained by the generally poor fatigue performance of additive manufacturing materials and components. In order to solve the international problem of fatigue resistance of 3D printing materials, in February 2024, the Material Fatigue and Fracture Team of the Institute of Metals, Chinese Academy of Sciences and the titanium alloy team jointly proposed the NAMP process of coupling regulation of microstructure and defects, successfully prepared the near microporous 3D printing Ti-6Al-4V alloy material with ultra-high tensile tensile fatigue properties (Nature, 2024), broke the world record of tensile tensile fatigue strength of all materials, and updated people's previous inherent understanding of the low fatigue performance of 3D printing materials
However, the service environment of actual engineering components is generally very complex, often accompanied by significant changes in the loading stress ratio. When the external stress ratio borne by the material or component changes, the distribution ratio of cyclic stress amplitude and maximum stress also changes, thereby inducing transitions between different fatigue cracking mechanisms. The cracking pattern of "one goes and the other goes" makes it difficult for traditional titanium alloy structures to maintain excellent fatigue performance within the full stress ratio range. A type of microstructure often only exhibits fatigue resistance advantages within a specific stress ratio range (Figure 1). Especially for additive manufacturing components with complex structures, the stress distribution during their actual service life is even more complex, inevitably subjected to fatigue loads with varying stress ratios. Therefore, how to achieve high fatigue resistance under full stress ratio conditions is the key to determining whether additive manufacturing technology can be applied on a large scale in aerospace and other fields, and it is also one of the urgent scientific challenges to be solved.
In response to new challenges, the material fatigue and fracture research team recently systematically revealed three typical "fatigue short plates" and their stress ratio sensitive ranges that are prone to fatigue cracking in titanium alloys. It was found that the net additive manufacturing (Net AM) structure without micropores can achieve synergistic optimization of the three types of fatigue short plates. Based on this, the team clearly proposes that 3D printed titanium alloys still have naturally high fatigue resistance under full stress ratio conditions. Based on the team's original NAMP process, a Net AM structured Ti-6Al-4V alloy with approximately no micropores was prepared, and its fatigue strength (Figure 1) and fatigue cracking mechanism (Figure 2) under different stress ratios were characterized. A large amount of comparative analysis of data shows that within the full stress ratio range, the fatigue strength of Net AM Ti-6Al-4V alloy is not only better than all titanium alloy materials as a whole, but also its specific fatigue strength (fatigue strength divided by density) is comprehensively better than all metal materials, as shown in Figure 3.
The research results were published in the journal Science Advances on August 22, 2025 under the title of "Naturally high fatigue performance of a 3D printing titanium alloy across all stress ratios". Dr. Qu Zhan, the special research assistant of the Institute of Metals of the Chinese Academy of Sciences, was the first author of the paper, and researcher Zhang Zhenjun, associate researcher Liu Rui, and researcher Zhang Zhefeng were the co corresponding authors of the paper. This achievement reveals the natural advantages of titanium alloy components with complex topology and load-bearing capacity prepared by additive manufacturing technology in fatigue resistance, laying the foundation for their application as dynamic load-bearing components in aerospace and other fields. Meanwhile, this study also provides new ideas for optimizing the fatigue performance of forged titanium alloys under different stress ratios.
This research was supported by the National Natural Science Innovation Research Group Project (52321001), the Outstanding Youth Fund Project (52322105), the Key Project (52130002) and the Youth Promotion Association of the Chinese Academy of Sciences Project (2021192).
Figure 1. Fatigue strength and corresponding fatigue cracking mechanism of Ti-6Al-4V alloy with different microstructure types under different stress ratios.
Figure 2. Typical fatigue fracture surfaces and corresponding fatigue crack initiation mechanisms of Ti-6Al-4V alloy with Net AM microstructure under different stress ratios. (A) Stress ratio R=-1: cracking of micro porous defects; (B) Stress ratio R=-0.5: cracking of micro porous defects; (C) Stress ratio R=0.1: coexistence of micro pore defect cracking and microstructure cracking; (D) Stress ratio R=0.5: microstructure cracking; (E) Schematic diagram of stress ratio variation, fatigue crack initiation position transformation and corresponding fatigue strength variation in Ti-6Al-4V alloy with Net AM microstructure.
Figure 3. Compared with other Ti-6Al-4V alloys and common metal structural materials, the fatigue strength distribution of Ti-6Al-4V alloy with Net AM microstructure under different stress ratios. (A) Stress amplitude vs average stress; (B) Normalized fatigue strength of material density vs normalized average stress of material density
