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Improving Tribological Performance of Gray Cast Iron by Laser Peening in dynamic strain aging Temperature Regime

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Chinese Journal of Mechanical Engineering 2015年第5期28卷 904-910页

作者： FENG Xu ZHOU Jianzhong MEI Yufen HUANG Shu SHENG Jie ZHU Weili School of Mechanical Engineering Jiangsu University

A high and stable brake disc friction coefficient is needed for automobile safety, while the coefficient degrades due to elevated temperature during the braking process. There is no better solution except changes in material composition and shape design optimization. In the dynamic strain aging（DSA） temperature regime of gray cast iron, micro-dimples with different dimple depth over diameter and surface area density are fabricated on the material surface by laser peening（LP） which is an LST method. Friction behavior and wear mechanism are investigated to evaluate the effects of surface texturing on the tribological performance of specimens under dry conditions. Through LP impacts assisted by DSA, the friction coefficients of the LPed specimens increase noticeably both at room temperature and elevated temperature in comparison to untreated specimens. Moreover, the coefficient of specimen with dimple depth over diameter of 0.03 and surface area density of 30% is up to 0.351 at room temperature, which dramatically rises up to 1.33 times that of untextured specimen and the value is still up to 0.3305 at 400℃ with an increasing ratio of 35% compared to that of untreated specimen. The surface of textured specimen shows better wear resistance compared to untreated specimen. Wear mechanism includes adhesive wear, abrasive wear and oxidation wear. It is demonstrated that LP assisted by DSA can substantially improve wear resistance, raise the friction coefficient as well as its stability of gray cast iron under elevated temperatures. Heat fade and premature wear can be effectively relieved by this surface modification method.

关键词： laser peening micro-dimples dynamic strain aging friction coefficient

A New Strategy for Restraining dynamic strain aging in GH4169 Alloy During Tensile Deformation at High Temperature

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Acta Metallurgica Sinica(English Letters) 2022年第11期35卷 1895-1902页

作者： Xin-Tong Lian Jin-Lan An Lei Wang Han Dong School of Materials Scienceand Engineering Shanghai UniversityShanghai 200444China Key Laboratory of Fundamental Science for National Defense of Aeronautical Digital Manufacturing Process Shenyang Aerospace UniversityShenyang 110136China Key Lab for Anisotropy and Texture of Materials Ministry of EducationNortheastern UniversityShenyang 110819China

The dynamic strain aging(DSA) behavior was investigated in GH4169 alloy during tensile deforming with electric-pulse current(EPC) at 750 ℃.The results show that DSA is restrained in the alloy when deformed with 40 *** size ofγ " phase inner grains increases obviously and δ phase is facilitated to precipitate on grain boundary in the alloy applied with EPC,due to the promotion effect of EPC on the diffusion and segregation of *** electron microscopy(TEM)results indicate that dislocations can cut through small γ" precipitate with the size of less than 10 nm,while dislocations can only bypass dislocations when γ " precipitate grow up over 20 *** growth of precipitates consumes large amounts of atoms as well as the velocity of dislocation increase,which makes dislocations difficult to be ***,when γ" precipitates grow up to a large size more than the critical size of dislocation pinning,DSA is significantly restrained in the alloy after necking deformed with EPC.

关键词： GH4169 alloy Electric-pulse current dynamic strain aging Microstructure

Effect of strain rate and temperature on the serration behavior of SA508-Ⅲ RPV steel in the dynamic strain aging process

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Journal of Iron and Steel Research International 2018年第7期25卷 767-775页

作者： Xue Bai Su-jun Wu Li-jun Wei Shuai Luo Xie Xie Peter K. Liaw School of Materials Science and Engineering Beihang University Beijing 100191 China Department of Materials Science and Engineering The University of Tennessee Knoxville TN 37996 USA Beijing Key Laboratory of Advanced Nuclear Materials and Physics Beihang University Beijing 100191 China

dynamic strain aging （DSA） effect on SA508-III reactor pressure vessel （RPV） steel was investigated. The SA508-III RPV steel was subjected to tension tests at different strain rates （1.1× 10-5 s-1 and 6.6× 10-5 s-1） and different temperatures （500 and 550 ℃） to evaluate the influence of strain rate and temperature on the serrated flow behavior, which is the repetitive and discontinuous yielding phenomenon on the stress-strain curves. The higher temperature leads to the higher density of precipitates, M23C6 carbides and needle-like Mo2C carbides. It was found that the samples under tension test of 6.6 × 10-5 s-1 and 500 ℃ possess superior mechanical properties and mainly show A-type serrations on the tension test curves. Then, the local regress method was used to filter the DSA curves, thus to show the real trend of the curves. It has been found that the less time of interaction between dislocations and precipitates under higher strain rates leads to a higher strength of the sample. The more tiny-stress drops on the 550 ℃ serration curve can be attributed to the hardening phase, M23C6 carbides and needle-like Mo2C carbides. The higher percentage of the small stress drops on the serration curves represents the higher mechanical strength.

关键词： Reactor pressure vessel steel SA508-Ⅲ steel dynamic strain aging Serration behavior

Verification of Interpretation of dynamic strain aging for Intermediate Temperature Embrittlement in Ni-Bi Alloy

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Journal of Iron and Steel Research International 2015年第7期22卷 602-606页

作者： Wu-qiang YANG Min XU Ye MENG Lei ZHENG Xiao-dong MENG School of Materials Science and Engineering University of Science and Technology Beijing Henei Cisri Dekai Technology Company Limited

Intermediate temperature embritttement （ITE） is a general phenomenon in Ni alloys and recently was interpreted by dynamic strain aging （DSA）. The relationship between ITE and DSA was studied by a binary Ni-Bi alloy. The experimental alloy of well-controlled purity was produced by vacuum induction inching and then heat-treated properly. Tensile tests were performed at various tensile temperatures, and the elongation at fracture was used to indicate the ductility. In order to identify the mechanisms of fracture and ITE, fracture morphologies of the samples of low ductility were observed by scanning electron microscopy. According to the tensile ductility, Ni-Bi alloy shows an obvious embrittlement behavior in the intermediate temperature range （700--750℃ ）. However, the stress strain curves of Ni-Bi alloy and the fracture morphologies indicate that DSA does not exist over the whole temperature range. Based on the experimental results and literatures, the interpretation of DSA was then discussed and proved to be invalid for elucidating the general feature of ITE in Ni-Bi alloy and Ni-based superalloys.

关键词： intermediate temperature embrittlement Ni-Bi alloy dynamic strain aging stress-strain curve fracture morpbology

A DISLOCATION-MECHANICS-BASED CONSTITUTIVE MODEL FOR dynamic strain aging

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Acta Mechanica Solida Sinica 2002年第2期15卷 119-126页

作者： Guo Yangbo Tang Zhiping Cheng Jingyi Univ Sci & Technol China Dept Modern Mech Hefei 230027 Peoples R China

dynamic strain aging (DSA) is an important phenomenon in solutehardened metals and seri- ously affects the mechanical properties ofmetals. DSA is generally induced by the interaction between themoving dislocations and the mobile solute atoms. In this paper, onlythe interaction between moving disloca- tions and mobile solute atomsin a dislocation core area (core atmosphere) will be taken intoaccount. To es- tablish the constitutive model which can describe theDSA phenomenon, we improved the Zerilli-Armstrongdislocation-mechanics-based thermal viscoplastic constitutiverelation, and added the effect of the interaction between the movingdislocations and core atmosphere.

关键词： dynamic strain aging solute atoms core atmosphere tantalum

EFFECT OF dynamic strain aging ON LOW CYCLE FATIGUE BEHAVIOUR OF 18-8 AUSTENITIC STAINLESS STEEL

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Acta Metallurgica Sinica(English Letters) 1993年第6期6卷 420-425页

作者： PENG Kaiping CHEN Wenzhe OIAN Kuangwu Fuzhou University,Fuzhou,China teaching assistant,Department of Mechanical Engineering,Fuzhou University,Fuzhou 350002,China

Studies were made of the symmetric tensile-compressive low cycle fatigue behaviour and the influence of dynamic strain aging(DSA)pre-treatment of 18-8 austenitic stainless steel. Within the testing amplitude range of strain.±0.5 % to±1.5 %,the three processes of cyclic hardening,cyclic saturation and cyclic softening were *** the same amplitude of strain,the peak stress of the samples pre-treated by DSA is higher than that of solid-solu- tion and cold working pre-treatment,but no remarkable differences of the fatigue lives of them were *** observation shows that the uniform and stable dislocation networks with high density form after DSA pre-treatment,which increases the cyclic peak *** cyclic softening results from the low dislocation density and elongated cell structure with low energy.

关键词： 18-8 austenitic stainless steel dynamic strain aging low cycle fatigue

dynamic strain aging of Austenitic Stainless Steel for Ultra-supercritical Unit

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Dynamic Strain Aging of Austenitic Stainless Steel for Ultra...

Internal friction studies on dynamic strain aging in P91 ferritic steel

第十五届中国体视学与图像分析学术会议

作者：周红伟何宜柱 School of Materials Science and Engineering Anhui Key Lab of Materials Science and ProcessingAnhui University of Technology

dynamic strain aging(DSA) behavior of niobium(Nb)-stabilized austenitic stainless steel(TP347 H) was studied from 298 to 973 K via tensile testing,transmission electron microscopy(TEM)and internal friction(IF).The effect of DSA was negligible from 573-673 K,but it became significant at 773-873 K and strain rates of 3 × 10 s,8 × 10 s,and 8 × 10 *** results indicate that a dislocation planar slip is dominant in the strong DSA *** Snoek-like peak located at 625 K is highly sensitive to the diffusion of free carbon(C) atoms in the solid *** C-Nb octahedrons are caused by C chemical affinity to substitutional Nb solute *** are very stable and capture most free C atoms;they inhibit DSA at a low pre-strained temperature of 573-673 *** the high pre-strained temperature from 773 to 873 K,C-Nb octahedrons break to form free C and Nb atoms,indicating that the Snoek-like peak is *** interaction between C atoms and dislocation is responsible for the DSA at low temperatures of 573-673 *** Cr and Nb atoms lock in the dislocation—this contributes to the DSA from 773 to 873 K.

关键词： Austenitic stainless steel Nb additional element dynamic strain aging Internal friction

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Internal friction studies on dynamic strain aging in P91 fer...

Effect of dynamic strain aging on Hardness in the Heat-Affected Zone of SUS316 Steel Welds

第十五届全国金相与显微分析学术年会

作者：周宏伟何宜柱 School of Materials Science and Engineering Anhui Key Lab of Materials Science and ProcessingAnhui University of Technology

The temperature of dynamic strain aging(DSA) regime in P91 steel is between 250 ℃ and 500 ℃.The activation energy(Q) for onset of DSA is 73 kJ/mol,while that for finale of DSA is 202 kJ/*** are two main Internal friction(IF) speaks,Snoek and SKK with activation energy are 67.9 kJ/mol and 121 kJ/mol respectively,were *** that activation energy of 73 kJ/mol is equal to that of C atom body diSusion in α-Fe,and 202 kj/mol is equal to binding energy between C atoms and moving *** results confirm the mechanism of DSA which is explained by the diffusion of C atoms and pinning between C and moving *** these investigation,it could be concluded that DSA in P91 steel are resulted from C atom diffusion and pinning dislocation,instead of Cr or Mo atoms.

关键词： P91 steel Tensile serrated yielding Internal friction dynamic strain aging Activation energy

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材料科学与工程（中英文A版） 2023年第1期13卷 13-25页

作者： Lina Yu Kazutoshi Nishimoto Kazuyoshi Saida Graduate School of Engineering Osaka UniversityOsaka 565-0871Japan

DSA(dynamic strain aging)phenomenon in SUS316 steel was investigated using isothermal and non-isothermal tensile tests of simulated HAZ(heat-affected zone)thermal *** tensile tests were performed on SUS316 in the peak temperature range of 20-700°C,with strain rates varying from 4.2×10^(-3)to 4.2×10^(-5)s^(-1).Based on the appearance of discontinuous plastic flows,expressed as serrations,and the hardening phenomenon of the tensile samples,the conditions for the occurrence of DSA in the SUS316 steel were ***,the extent of hardening due to DSA was evaluated by comparing the hardness values of the SUS316 and SUS316EHP steels after the tensile *** confirm the effect of DSA on hardness in the HAZ of the welded SUS316 steel,non-isothermal tensile tests of the simulated HAZ thermal cycles were performed using a Thermec *** relationship between the increase in Vickers hardness due to DSA and the strain in the HAZ was determined;the effect of DSA on hardness in the HAZ could be *** DSA in SUS316 steel was found to be mainly attributed to the dynamic interaction of dislocations with C and N interstitial atoms during high-temperature deformation.

关键词： dynamic strain aging hardness serration heat-affected zone SUS316