Hf-doped amorphous filler breaks barrier to achieve ultrahigh-strength vacuum brazing of TC4 titanium alloy and 316L stainless steel
image: The structural design, fabrication, brazing and interfacial elemental characterization of Hf-doped Ti-Zr-Cu-Ni amorphous filler for TC4/316L joints.
Credit: Aqsa Bano, Fushuai Jin, Jilong Wang, Peng Li, Zhiwei Qin, Zhenyang Zhang, Wenqian Han, Xin Jiang, Honggang Dong
Titanium alloys like Ti-6Al-4V (TC4) feature lightweight, high strength and outstanding corrosion resistance, are widely used in aerospace, shipbuilding and nuclear industries. Combining TC4 with SS316L stainless steel can reduce structural weight and lower costs. Nonetheless, the joining process faces a metallurgical challenge: the formation of brittle intermetallic compounds that compromise joint reliability between titanium alloys and stainless steels. The formation of TiFe and TiFe₂ intermetallic creates potential crack initiation sites, subsequently degrading the overall mechanical strength of the bonded interface.
In a study published in KeAi’s journal China Welding, a research team from Dalian University of Technology developed a novel Hf-containing Ti-Zr-Cu-Ni amorphous ribbon filler to regulate the interfacial microstructure and produce ultrahigh-strength TC4/SS316L vacuum-brazed joints. The team’s Hf-modified Ti-Zr-Cu-Ni amorphous filler provides a feasible low-temperature vacuum brazing approach for TC4/316L composite structural components, offering process parameters and interfacial control theory for lightweight, corrosion-resistant equipment in aviation, shipbuilding and nuclear industries.
“Hf and Zr remain concentrated within the brazing seam helping stabilize the amorphous matrix and inhibit grain coarsening, while balanced Ti, Cu, Fe diffusion forms graded transition layers that relieve thermal residual stresses between the dissimilar metals,” says corresponding author Honggang Dong. “This layered microstructure solves two major bottlenecks: excessive formation of brittle phase generation and severe residual stress mismatch in titanium-stainless steel dissimilar joints.”
The team started by investigating brazing temperatures ranging from 910 to 950 ℃ and holding times from 5 to 40 min. “The results showed that the joint reached an optimal shear strength of 360 MPa ± 12 MPa at 910 ℃ for 40 min, and 353 MPa ± 9 MPa under 910 ℃/10 min,” shares Dong. “When the brazing temperature exceeded 930 ℃, coarse intermetallic layers grew rapidly and reducing the joint strength by nearly half.”
Microstructure characterization revealed three zones in the optimized joints: a (α+β)-Ti diffusion layer with fine α-Ti lamellae near TC4, a central eutectic/intermetallic brazing seam, and an Fe-Cr-rich reaction layer adjacent to SS316L. Kinetic calculation showed layer growth follows parabolic time dependence and Arrhenius temperature rules; the diffusion activation energy on the TC4 side reaches 261 kJ/mol, substantially higher than 149.6 kJ/mol on the stainless steel side, indicating that the Ti substrate dominated interdiffusion behavior.
Contact the author: Honggang Dong, School of Materials Science and Engineering, Dalian University of Technology, China; Email: donghg@dlut.edu.cn
The publisher KeAi was established by Elsevier and China Science Publishing & Media Ltd to unfold quality research globally. In 2013, our focus shifted to open access publishing. We now proudly publish more than 300 world-class, open access, English language journals, spanning all scientific disciplines. Many of these are titles we publish in partnership with prestigious societies and academic institutions, such as the National Natural Science Foundation of China (NSFC).