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martensitic nucleation mechanism

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Science China(Technological Sciences) 1997年第4期40卷 387-395页

作者：陈奇志桑灿吴杏芳柯俊 Department of Material Physics University of Science and Technology Beijing Beijing 100083 China

A sort of special dislocation configuration was deformation-induced in an Fe-Ni-V-C alloy by in-situ elongation tests of TEM. The cooling in-situ observations, as well as the SADPs from the region of the special dislocation configurations, proved that they are martensitic nuclei. In martensitic transformation, a nucleus changed into a small martensitic sub-plate, and a group of parallel sub-plates that formed from a group of parallel nuclei made up a big martensitic plate martensitic transformation involved opposite shear between adjacent martensitic nuclei. By using the reduced-cell method, the crystallographic structure of observed martensitic nuclei was indexed as a face-centered orthogonal (FCO) lattice, which was explained by the nucleation mechanism proposed by the present authors. The crystallographic analysis confirmed that the defect faulting involved in martensitic nucleation took place among three close pakked planes, instead of between two adjacent planes as an ordinary stacking fault.

关键词： iron-nickel alloy TEM martensitic transformation nucleation crystallographic structure.

Effect of partial replacement of carbon by nitrogen on intergranular corrosion behavior of high nitrogen martensitic stainless steels

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Journal of Materials Science & Technology 2019年第10期35卷 2357-2364页

作者： Wei-Chao Jiao Hua-Bing Li Jing Dai Hao Feng Zhou-Hua Jiang Tao Zhang Da-Ke Xu Hong-Chun Zhu Shu-Cai Zhang School of Metallurgy Northeastern UniversityShenyang 110819China Corrosion and Protection Division Shenyang National Laboratory for Materials ScienceNortheastern UniversityShenyang110819China

The microstructure evolution and intergranular corrosion(IGC) behavior of high nitrogen martensitic stainless steels(MSSs) by partial replacing C by N were investigated by using microscopy, X-ray diffraction, nitric acid tests and double-loop electrochemical potentiokinetic reactivation(DL-EPR) tests. The results show that the partial replacement of C by N first reduces and then increases the size and content of precipitates in high nitrogen MSSs, and converts the dominant precipitates from M23C6 to M2N,furthermore first improves and then deteriorates the IGC resistance. The high nitrogen MSS containing medium C and N contents provides good combination of mechanical properties and IGC resistance.

关键词： High nitrogen martensitic stainless steels Precipitation Intergranular corrosion DL-EPR

Behavior of Nb influence on structure and properties of 30Cr13 cast martensitic stainless steel

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Journal of Iron and Steel Research(International) 2019年第5期26卷 462-471页

作者： Yang-fan Jin Tuo Zhang Qi-yu Zang Yi-tao Yang School of Materials Science and Engineering Shanghai University Shanghai 200444 China

The microstructure, mechanical properties and corrosion resistance of 30Cr13 martensitic stainless steel (MSS) with different Nb contents were investigated by using the optical microscope, scanning electron microscope, X-ray diffractometer, HRC hardness measurement apparatus and tensile testing machine. Nb was found to retard the formation of austenite and promote the precipitation of carbides by calculating. The results showed that the addition of 0.2 wt.% Nb elements could improve the strength and corrosion resistance of 30Cr13 martensitic stainless steels while the reduction in toughness was less because of the inhibited effect on Cr-rich carbides precipitation by Nb addition. Specially, M23C6-type carbides almost disappeared in 0.6Nb-MSS. Moreover, the main existent form of Nb element was NbC and the strong carbide-forming ability of Nb element increased the quantity of carbides with the morphology changing from sphericaltype to chain-type. 0.2Nb-MSS shows excellent strength, adequate toughness and sufficient corrosion resistance for the application.

关键词： Niobium addition martensitic stainless steel Microstructure Mechanical property Corrosion resistance

Effect of low-energy proton on the microstructure, martensitic transformation and mechanical properties of irradiated Ni-rich TiNi alloy thin films

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International Journal of Minerals,Metallurgy and Materials 2020年第4期27卷 538-543页

作者： Hai-zhen Wang Yun-dong Zhao Yue-hui Ma Zhi-yong Gao Science and Technology on Materials Performance Evaluation in Space Environment Laboratory School of Materials Science and EngineeringHarbin Institute of TechnologyHarbin 150001China Lanzhou Seemine SMA Co.Ltd. Lanzhou 730010China

Ni–48.5at%Ti thin films were irradiated in the austenite phase by different energy-level protons at a dose rate of 1.85×1012 p/(cm2·s),and the total dose was 2.0×1016 p/cm2.The microstructures of the thin films before and after irradiation were evaluated by transmission electron microscopy(TEM)and grazing-incidence X-ray diffraction(GIXRD),which showed that the volume fraction of Ti3Ni4 phase elevated with proton energy level.The influence of proton irradiation on the transformation behavior of the TiNi thin films was investigated by differential scanning calorimetry(DSC).Compared with the unirradiation film,the reverse transformation start temperatures(As)decreased by about 3°C after 120 keV proton-irradiation.The proton irradiation also had a significant effect on the mechanical properties of the TiNi thin films.After 120 keV energy proton-irradiation,the fracture strength increased by 8.44%,and the critical stress increased by 21.1%.In addition,the nanoindenter measurement image showed that the hardness of the thin films increased with the increase of proton-irradiation energy.This may be due to the defects caused by irradiation,which strengthen the matrix.

关键词： TiNi thin film proton irradiation microstructure martensitic transformation mechanical properties

Strain-induced martensitic transformation in biomedical Co-Cr-W-Ni alloys

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Rare Metals 2020年第3期39卷 241-249页

作者： Zi-Yi Zhu Li Meng Leng Chen School of Materials Science and Engineering University of Science and Technology BeijingBeijing100083China Metallurgical Technology Institute Central Iron and Steel Research InstituteBeijing100081China

The nucleation,variant selection,and orientation dependence of the strain-induced martensitic transformation(SIMT)process in biomedical Co-Cr-W-Ni alloys were investigated.The experimental results show that theε-hexagonal-close-packed phase was preferentially formed at theΣ3 twin boundaries and high-angle grain boundaries during the tensile process.The theoretical analysis shows that the variant selection of SIMT is governed by Schmid’s law.However,the SIMTedε-phase did not form equally on the two sides of the annealing twins,even though they had the same Schmid factor.This phenomenon is related to the mechanical work developed by the formation of theε-phase.Only the side which has both high Schmid factor and high mechanical work can initiate the SIMT process.A strongfiber texture was formed,and theε-variants tended to appear in grains with orientations close to theanddirections during the tensile process.These results can provide theoretical guidance for controlling the SIMT process of Co-Cr-W-Ni alloys to fabricate more reliable stents.

关键词： Biomedical Co-Cr-W-Ni alloys Straininduced martensitic transformation Nucleation Variant selection Orientation dependence

Hydrogen trapping in high strength 0Cr16Ni5Mo martensitic stainless steel

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Journal of Central South University 2015年第11期22卷 4128-4136页

作者：孙永伟陈继志刘军 College of Materials Science and Chemical Engineering Harbin Engineering University Luoyang Ship Material Research Institute

Hydrogen trapping behavior has been investigated by means of thermal desorption spectroscopy(TDS) for a high strength steel after it was tempered at the temperatures of 430 °C, 500 °C and 520 °C, respectively. The loss of ductility was characterized by slow strain rate test(SSRT) and microscopic observation. It shows that with hydrogen charging the fracture feature transfers from ductile to brittle, resulting in the loss of ductility. Undeformed microstructure immediately beneath the fracture surface in charged specimen corresponds to badly ductility compared to the obviously streamline plastic deformation in uncharged specimen. The activation energies for the peaks present in the TDS analysis are calculated for all tested steel and the activation energies for all temperature peaks are similar, corresponding to the similar types of hydrogen traps.

关键词： martensitic stainless steel hydrogen trapping ther

IMPROVEMENT　OF　THE　O－P　THERMODYNAMIC　MODEL　OF　THERMOELASTIC　martensitic　TRANSFORMATION

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中国有色金属学会会刊：英文版 1995年第2期5卷 55-60页

作者： Yang, Guanjun Hao, Shiming Northwest Inst for Nonferrous Metal Research Baoji China

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关键词： thermoelastic martensitic transformation thermodynamic model calorimetric experiment

Microstructure effect on nanohardness distribution for medium-carbon martensitic steel

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Science China(Technological Sciences) 2006年第1期49卷 10-19页

作者： OHMURA Takahito TSUZAKI Kaneaki Steel Research Center National Institute for Materials Science Tsukuba 305-0047 Japan

Nanoindentation measurement was performed to evaluate the local hardness distribution for quenched and tempered martensitic steel with ferrite-cementite constituent. The ratio of standard deviation to the average nanohardness was 15.4% when nanoin-dentation tests were carried out at the peak load of 1000 μN, while that of the Vickers hardness was only 1.5% at 9.8 N. Electron backscatter diffraction analysis and SEM ob-servation all showed that the large scattering of nanohardness did not depend on the crystallographic orientation of each grain but from the inhomogeneous microstructure in the sub-micron scale such as cementite distribution. Compared with the results on tung-sten single crystals with different surface orientations as well as another martensite proc-essed by modified-ausforming with the same chemical composition but more homogene-ous cementite distribution, the nanohardness showed smaller scattering, supporting the conclusion.

关键词： martensitic steel, cementite, hardness distribution, nanoindentation.

Nucleation barrier of fcc(γ)→hcp(ε) martensitic transformation in Fe-based alloys

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Science China(Technological Sciences) 2004年第1期47卷 121-128页

作者： HUANG Xing CHEN Shipu School of Materials Science and Engineering Shanghai Jiao Tong University Shanghai 200030 China School of Materials Science and Engineering Shanghai Jiao Tong University Shanghai 200030 China

Based on the dislocation theory and Olson's stacking fault model, a model describing the nucleation of an hcp(ε) martensite embryo at low-angle grain boundary is proposed with the influence of external stress field taken into account. The dependences of temperature (T), shear stress (τ) and dislocation density at grain boundary on the martensite nucleation in FeMnSi based alloy, as an example, are numerically simulated. It has been shown that there exist the subcritical and critical embryos during the course of ε-phase nucleation. The free energy difference between them is just the energy barrier of embryo growth. Depending on T and τ, the characteristic embryo sizes may vary in wide ranges and decrease with increasing σ and decreasing T. The energy condition of martensitic transformation at Ms and critical shear stress (τc) is discussed from the viewpoint of kinetics and thus the TEM observed result that stacking fault energy is not zero at Ms temperature is reasonably explained. Besides, it is predicted that the high dislocation density at grain boundary can promote the nucleation of fcc→hcp transformation in Fe-based alloys.

关键词： martensitic transformation, stacking fault mechanism, nucleation, energy barrier, temperature, stress, dislocation density.