Dislocation activities at the martensite phase transformation interface in metastable austenitic stainless steel: An in-situ TEM study

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:703

Article

Liu, Jiabin²  Chen, Chenxu²  Feng, Qiong³  Fang, Xiaoyang²  Wang, Hongtao¹  Liu, Feng⁴  Lu, Jian⁵  Raabe, Dierk⁶ 

[1] Zhejiang Univ, Inst Appl Mech, Hangzhou 310027, Zhejiang, Peoples R China

[2] Zhejiang Univ, Coll Mat Sci & Engn, Hangzhou 310027, Zhejiang, Peoples R China

[3] China Railway Electrificat Survey Design & Res In, Tianjin 300250, Peoples R China

[4] Northwestern Polytech Univ, Xian 710072, Shaanxi, Peoples R China

[5] City Univ Hong Kong, Dept Mech & Biomed Engn, Hong Kong, Hong Kong, Peoples R China

[6] Max Planck Inst Eisenforsch GmbH, Max Planck Str 1, D-40237 Dusseldorf, Germany

关键词: Martensitic transformation;    In-situ transmission electron microscopy;    Deformation;    Dislocations;   

DOI  :  10.1016/j.msea.2017.06.107

来源: Elsevier

【 摘 要 】

Understanding the mechanism of martensitic transformation is of great importance in developing advanced high strength steels, especially TRansformation-Induced Plasticity (TRIP) steels. The TRIP effect leads to enhanced work-hardening rate, postponed onset of necking and excellent formability. In-situ transmission electron microscopy has been performed to systematically investigate the dynamic interactions between dislocations and alpha ' martensite at microscale. Local stress concentrations, e.g. from notches or dislocation pile-ups, render free edges and grain boundaries favorable nucleation sites for alpha ' martensite. Its growth leads to partial dislocation emission on two independent slip planes from the hetero-interface when the austenite matrix is initially free of dislocations. The kinematic analysis reveals that activating slip systems on two independent {111} planes of austenite are necessary in accommodating the interfacial mismatch strain. Full dislocation emission is generally observed inside of austenite regions that contain high density of dislocations. In both situations, phase boundary propagation generates large amounts of dislocations entering into the matrix, which renders the total deformation compatible and provide substantial strain hardening of the host phase. These moving dislocation sources enable plastic relaxation and prevent local damage accumulation by intense slipping on the softer side of the interfacial region. Thus, finely dispersed martensite distribution renders plastic deformation more uniform throughout the austenitic matrix, which explains the exceptional combination of strength and ductility of TRIP steels.

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