On May 8, a paper entitled "Making ultrastrong steel tough by grain-boundary delamination" (DOI: 10.1126/science.aba9413) was published online at Science by the team of Professor Huang Mingxin, Department of Mechanical Engineering, University of Hong Kong, a user of China Scattered Neutron Source (CSNS).
The paper demonstrates the important progress made by Huang Mingxin's team in the development of high-strength, high-tenacity deformation distribution steels (D&P steels), the first user experimental results of CSNS to be published in Science.
Low-cost alloys with excellent performance have long been the basis for the development of industries such as automotive, aerospace and defense.
However, it is often difficult to balance the strength (load-bearing capacity) and fracture toughness (fracture resistance) of a material.
In recent years, Huang Mingxin's team has worked with the CSNS General Powder Diffractometer (GPPD) team to systematically characterize and study the series of samples.
They used neutron diffraction as a means of studying the role of sub-stable austenite and dislocation in the fracture behavior of low-cost D&P steels.
Neutron diffraction has the advantages of high penetration, high resolution, non-destructive and can be used to analyze the tissue structure characteristics of complex materials such as woven structures.
With the support of the GPPD team, Huang Mingxin's team efficiently obtained important microscopic parameter information such as phase volume fraction and dislocation density of low-cost D&P steel by neutron diffraction spectroscopy (Figure 1).
Supported by the GPPD data, Huang Mingxin's team has pioneered a new mechanism for high yield strength induced stratified cracking and toughening of grain boundaries, breaking the traditional understanding that increasing strength reduces material fracture toughness.
The new mechanism has resulted in a low-cost D&P steel with very high yield strength (~2 GPa), excellent toughness (102 MPa-m1/2) and good ductility (19% uniform elongation) (Figure 2).
The crystalline phase in D&P steel has large distortions, defects, meritocracy, etc., which require high neutron diffraction data, and the high resolution and good diffraction peak pattern of GPPD ensure the data quality required in this study.
At the same time, the GPPD designed a rotating sample rod specifically for this type of experiment to eliminate the influence of meritocracy on data analysis.
GPPD is one of the three spectrometers built in the first phase of China's fractured neutron source, and since its operation opened in 2018, it has successfully completed nearly 90 user project studies, and many user experimental results have been published in Science, Nature Communication, Advanced Materials and other journals.
Figure 1 Neutron diffraction profile of super-steel, obtained at the GPPD of CSNS
Figure 2 (A) A three-dimensional diagrammatic model depicting the relationship between sample loading direction and D&P steel organization. (B) Engineering stress-strain curves. (C) J-integral resistance curve.
It will provide an advanced and powerful research platform for China's materials science and technology, physics, chemical engineering, life sciences, resource environment and new energy.
The foundation stone of the China Fractional Neutron Source Project was laid in October 2011, the first targeting success was achieved in August 2017, and the neutron beam flow was successfully obtained, which passed the national acceptance in late August 2018 and was officially opened to Chinese and foreign users in late September.
