报告题目：Microstructure and strengthening mechanisms in superstrong pearlitic steel and pure iron wires

报告人：张晓丹

主持人（邀请人）： 赵庆龙

报告时间：2021年11月25日19:00-20:30

报告地点：线上形式，腾讯会议会议ID：355 208 231

主办单位：材料科学与工程学院、汽车材料教育部重点实验室

摘要：In human history, the development of stronger materials through the ages is reflected with names of eras illustrating our progress. Besides phase transformations, plastic deformation is one of the major methods to produce products with reliable and predictable mechanical properties such as strength. Pearlitic steel wire, the strongest mass-produced steel, shows an excellent combination of formability and strength [1].

The deformation microstructure and tensile properties of pearlitic steel (0.8 wt % C) have been quantified in wires drawn up to a strain of 5.4 with a flow stress up to 4.5 GPa. The interlamellar spacing (ILS) decreases from 88 to 10 nm and the cementite lamellar decreases from 18 nm to about 0.7 nm with increasing strain, representing a structure, which breaks up at large strains, decomposes and releases carbon to the ferrite lamellae. The dislocation density in the ferrite lamellae increases continuously with strain and reaches about 5 × 10¹⁶ m⁻² at a strain of 5.4. The dislocations are stored as threading dislocations, as dislocation tangles and as cell boundaries with low to medium misorientation angles. An analysis of the evolution of microstructure suggests that dislocation-based plasticity is a dominating mechanism in the wire and three strengthening mechanisms are applied: boundary strengthening, dislocation strengthening and solid solution hardening with their relative contributions to the total flow stress which change as the strain is increased [2-4].

To further the understanding of the deformation mechanisms in the nanolamellar structures, microstructure and strengthening mechanisms in ultrastrong drawn iron wires have been investigated. Ultrastrong pure iron wires have been produced with a strength of 1.8 GPa at a strain of 10.35. Based on microstructural observation and quantified structural parameters, the strengthening mechanisms and strength-structure relationship have been analyzed. It is found that the <110> fiber texture intensity, boundary spacing and boundary misorientation tend to saturation due to the boundary junction motion when the drawing strain exceeds 8.89. The dislocation density in the ferrite cells/lamellae increases to ~ 3.6 × 10¹⁵ m⁻² at a drawing strain of 10.35 without saturation. Based on the systematic microstructural characterization and quantification, the d⁻¹ or (2d)^−0.5 boundary strengthening plus forest hardening are discussed [5].

[1] Xiaodan Zhang: IOP Conf. Ser.: Mater. Sci. Eng., 580, 012058 (2019).

[2] Xiaodan Zhang, Andy Godfrey, Xiaoxu Huang, Niels Hansen, Qing Liu: Acta Materialia, 59, 3422-3430 (2011).

[3] Xiaodan Zhang, Andrew Godfrey, Niels Hansen, Xiaoxu Huang: Acta Materialia, 61, 4898-4909 (2013).

[4] Xiaodan Zhang, Niels Hansen, Andrew Godfrey, Xiaoxu Huang: Acta Materialia, 114, 176-183 (2016).

[5] Hanchen Feng, Linfeng Wang, Shiyun Cui, Niels Hansen, Feng Fang, Xiaodan Zhang: Scripta Materialia, 200, 113906 (2021).

报告人简介：

Xiaodan ZHANG (ORCID 0000-0002-2874-1519)

Education

§ Doctor of Engineering, Department of Materials Science and Engineering, Tsinghua University, Beijing, China, 2009 (Supervisor: Prof. Q. Liu; Project: Fatigue related properties of steel wires for steel cords (funded by NV Bekaert SA (Belgium), in collaboration with a parallel PhD student in Katholieke Universiteit Leuven))

§ Bachelor of Engineering, Department of Materials Science and Engineering, Central South University, China, 2002

Positions

01. 2018 – present: Senior Researcher, Department of Mechanical Engineering, DTU, Denmark

05. 2016 – 12. 2017: Senior Researcher, Department of Wind Energy, DTU, Denmark

06. 2012 – 04. 2016: Researcher, Department of Wind Energy, DTU, Denmark

01. 2012 – 05. 2012: Post Doc, Department of Wind Energy, DTU, Denmark

08. 2009 – 12. 2011: Post Doc, Materials Research Division, Risø National Laboratory for Sustainable Energy, Denmark

Independent Scientific Focus Areas

Super strong steels and its microstructure, strength and property relationships;

Heterogeneous microstructure formation, strengthening mechanisms and its thermomechanical response;

Surface optimization by mechanical and chemical treatments;

Advanced in-situ/ex-situ mechanical testing in electron microscopes;

Fatigue, fracture and failure of strong metallic components (screws, bolts, gears and bearings).

Scientific Publications

In total 86 peer-reviewed publications, including 53 papers in journals, 2 invited and 32 contributed abstracts/papers in international conference proceedings, as well as 10 invited talks and 9 contributed talks at international/national conferences/symposia, 2 books and 1 book chapter.

Google Scholar: 1158 citations, h-index: 17.