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NUMERIcAL SIMULATION OF MAcRO-SEGREGATION IN STEEL INGOT DURING SOLIDIFIcATION

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Acta Metallurgica Sinica(English Letters) 2004年第3期17卷 288-294页

作者： c.W.Ma H.F.Shen T.y.Huang B.c.liu Department of Mechanical Engineering Tsinghua University Beijing 100084 ChinaDepartment of Mechanical Engineering Tsinghua University Beijing 100084 ChinaDepartment of Mechanical Engineering Tsinghua University Beijing 100084 ChinaDepartment of Mechanical Engineering Tsinghua University Beijing 100084 China

A mathematical model coupling the momentum, energy and species conservation equa-tions was proposed to calculate the macro--segregation of Fe--c alloy ingot during solid-ification. The corresponding simulation software which concurrently solves the macro-scopic mass, momentum, energy and species conservation equations has been developedby applying the SIMPLE algorithm.The thermo--solutal convection in a NH_4 cl--H_2O ingot is verified and the result showsgood agreement with that reported. Then macro--segregation in a steel ingot is simu-lated by using the developed program. The steel ingot is in a rectangular mold with ariser. The fluid flow is mainly induced by the temperature field and the solid fraction.The macro--segregation pattern is mainly affected by the thermo--induced convectionin the mushy zone. The negative segregation forms along the walls of the casting.The positive segregation forms at the top center of the casting into the riser. Thespecies concentration reaches the peak in the center of the ingot where solidificationends lastly.

关键词： macro-segregation thermo-solutal convection steel ingot numerical simulation

Enhanced pitting corrosion resistance of a Zr-based metallic glass by ultraviolet light irradiation

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Journal of Iron and Steel Research International 2023年第8期30卷 1642-1649页

作者： Z.chen D.P.Wang S.Wang y.X.Geng y.X.Guo y.c.Wu Z.G.liu y.y.Zhang y.X.Wang School of Materials Science and Engineering Jiangsu University of Science and Technology.Zhenjiang 212003JiangsuChina School of Mechanical Engineering Jiangsu University of Science and TechnologyZhenjiang 212003JiangsuChina

The influence of ultraviolet light irradiation on the pitting corrosion performance of a Zr_(2)Ni metallic glass was examined using electrochemical methods and immersion test in 0.05 mol/L Nacl *** the results of potentiostatic polarization,the pitting potential of the ultraviolet light-irradiated sample shifted positively with a value of~300 mV,revealing the enhanced pitting corrosion resistance of the *** corrosion morphology after the immersion test also demonstrated lower degree of corrosion damage and improved pitting resistance of the sample with ultraviolet light irradiation.X-ray photoelectron spectroscopy analysis revealed more zirconium enrichment in the passive film and no chloride ions adsorption for the samples with ultraviolet irradiation,accounting for the suppression of the pit generation and *** findings indicate that ultraviolet light irradiation improves the pitting corrosion resistance of the Zr-based metallic glasses,which are promising structural materials to be used in corrosion environments with high ultraviolet irradiation.

关键词： Metallic glass Pitting-corrosion Ultraviolet light irradiation Passive film

Designing hetero-structured ultra-strong and ductile Zr-2.5Nb alloys:Utilizing the grain size-dependent martensite transformation during quenching

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维普期刊数据库

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Journal of Materials Science & Technology 2022年第30期125卷 198-211页

作者： S.y.liu J.y.Zhang J.Kuang X.y.Bao D.D.Zhang c.L.Zhang J.K.yang G.liu J.Sun State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China

To further improve the service performance of Zr-2.5Nb alloy worked as pressure tubes in pressurized heavy water reactors,more investigation about the microstructure and thermomechanical processing route of Zr-2.5Nb alloy need to be *** this work,a hetero-structured Zr-2.5Nb alloy was prepared by applying a novel *** analysis reveals that the alloy exhibits a grain sizedependent martensite substructure transition during post-rolling *** hetero-structure consists of equiaxed primaryαgrains and the lamellae groups containing both parallelα’dislocation martensite andα’twin *** with the previously reported Zr-Nb alloys,the present Zr-2.5Nb alloys manifest the highest yield strength(∼710 MPa),together with a high ultimate tensile strength(∼844 MPa)and good ductility(∼17.1%).The enhanced mechanical properties are found to arise from the properly.c.ntrolled fraction/size of the two types of martensite,which not only significantly strengthens the alloy but also contributes to a stronger strain hardening.A model based on the grain-size-dependent critical resolved shear stress for dislocation slip and twinning has been proposed to explain theα’martensite substructures transition at a critical grain size dc=3.3μ*** this size,the critical resolved shear stress(cRSS)for twinning is higher than that for thec+a>***,theα’dislocation martensite is more favorable to ***,theα’twin martensite would exhibit a high *** present work indicates that making use of the grain size-dependent martensite transformation to tailor the heterostructure in Zr alloys is an effective strategy to overcome the strength–ductility trade-off in the material.

关键词： Zr-Nb alloys Heterogeneous structure Martensitic transformation Grain size Strength

Effect of Nitrogen content on Microstructures and Mechanical Properties of WB_2(N) Films Deposited by Reactive Magnetron Sputtering

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Journal of Materials Science & Technology 2015年第12期31卷 1217-1225页

作者： y.M.liu D.y.Deng H.Lei Z.L.Pei c.L.Jiang c.Sun J.Gong Institute of Metal Research Chinese Academy of Sciences

In the present study,WB 2（N） films are fabricated on silicon and yG8 substrates at different N 2 pressures by reactive magnetron *** influence of N 2 partial pressure（P （N2）） on the film microstructure and characteristics is studied systematically,including the chemical composition,crystalline structure,residual stress,surface roughness as well as the surface and the cross-section ***,nano-indentation and ball-on-disk tribometer are performed to analyze the mechanical and tribological properties of the *** results show that the addition of nitrogen apparently leads to the change of the structure from（1 0 1） to（0 0 1） orientation then to the amorphous structure with the formation of BN *** the addition of nitrogen can greatly refine the grain size and microstructure of the ***,the residual stress of the film is also found to change from tensile to compressive stress as a function of P （N2）,and the compressive stress increases with P （N2）,The WB 2（N） films with small nitrogen content,which are deposited at P （N2） of 0.004 and 0.006 Pa,exhibit better mechanical,tribological and corrosion properties than those of other *** increase of nitrogen content accelerates the formation of BN phase and fast decreases the film *** addition,the large N 2 partial pressure gives rise to the target poisoning accompanied by the increase of the target voltage and the decrease of the deposition rate.

关键词： Reactive magnetron sputtering Nanocomposites WB 2(N) films Residual stress Mechanical properties

A review of friction stir welding of steels： Tool, material flow, microstructure, and properties

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Journal of Materials Science & Technology 2018年第1期34卷 39-57页

作者： F.c. liu y. Hovanski M.P. Miles c.D. Sorensen T.W. Nelson Department of Mechanical Engineering Brigham Young University Provo UT 84602. USA Manufacturing Engineering Technology Brigham Young University Provo UT 84602 USA

considerable progress has been achieved in friction stir welding （FSW） of steels in every aspect of tool fab- rication, microstructure control and properties evaluation in the past two decades. With the development of reliable welding tools and precise control systems, FSW of steels has reached a new level of technical maturity. High-quality, long welds can be produced in many engineering steels. compared to traditional fusion welding, FSW exhibits unique advantages producing joints with better properties. As a result of active control of the welding temperature and/or cooling rate, FSW has the capability of fabricating steel joints with excellent toughness and strength. For example, unfavorable phase transformations that usu- ally occur during traditional welding can be avoided and favorable phase fractions in advanced steels can be maintained in the weld zone thus avoiding the typical property degradations associated with fusion welding. If phase transformations do occur during FSW of thick steels, optimization of microstructure and properties can be attained by.c.ntrolling the heat input and post-weld cooling rate.

关键词： Joining Stainless steels carbon steels High strength low alloy (HSLA) steels Advanced high strength steels (AHSS) Oxide dispersion strengthened (ODS) steels

Simultaneous enhancement of mechanical and shape memory properties by heat-treatment homogenization of Ti_(2)Ni precipitates in TiNi shape memory alloy fabricated by selective laser melting

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Journal of Materials Science & Technology 2022年第6期101卷 205-216页

作者： H.Z.Lu L.H.liu c.yang X.Luo c.H.Song Z.Wang J.Wang y.D.Su y.F.Ding L.c.Zhang y.y.Li National Engineering Research center of Near-net-shape Forming for Metallic Materials South China University of TechnologyGuangzhou 510640China Musculoskeletal Oncology Department Sun Yat-Sen University Cancer CenterGuangzhouGuangdong ProvinceChina Shenyang Aircraft Design and Research Institute Shenyang 110035China Guangdong Huayi Plumbing Fittings Industry.c.. Ltd.Kaiping 529321China School of Engineering Edith Cowan University270 Joondalup DriveJoondalupPerthWA 6027Australia

The excellent shape memory and mechanical properties of Ti Ni shape memory alloys(SMAs) fabricated using selective laser melting(SLM) are highly desirable for a wide range of critical applications. In this study, we examined the simultaneous enhancement of mechanical and shape memory properties using heat-treatment homogenization of Ti_(2)Ni precipitates in a Ti_(50.6)Ni_(49.4)SMA fabricated using SLM. Specifically, because of the complete solution treatment, nanoscale spherical Ti_(2)Ni precipitates were homogeneously dispersed throughout the grain interior. Interestingly, the resultant SMA exhibited an ultrahigh tensile strength of 880 ± 13 MPa, a large elongation of 22.4 ± 0.4%, and an excellent shape memory effect, with a recovery rate of > 98% and ultrahigh recoverable strain of 5.32% after ten loading–unloading cycles. These simultaneously enhanced properties are considerably superior than those of most previously reported Ti Ni SMAs fabricated using additive manufacturing. Fundamentally, the enhancement in tensile strength is ascribed to precipitation strengthening and work hardening, and the large plasticity is mainly attributed to the homogeneous nanoscale globular Ti_(2)Ni precipitates, which effectively impeded the rapid propagation of microcracks. Furthermore, the enhanced shape memory properties are derived from the suppression of dislocation movement and formation of retained stabilized martensite by the presence of high-density dislocations, nanoscale Ti_(2)Ni precipitates, and abundant interfaces. The obtained results provide insight into the enhancement of the two types of properties in Ti Ni SMAs and will accelerate the wider application of SMAs.

关键词： Shape memory alloy Selective laser melting Heat treatment Mechanical properties Shape memory properties

Sy.c.ronous optimization of strengths, ductility and corrosion resistances of bulk nanocrystalline 304 stainless steel

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Journal of Materials Science & Technology 2020年第2期37卷 161-172页

作者： S.G.Wang M.Sun S.y.liu X.liu y.H.Xu c.B.Gong K.Long Z.D.Zhang Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang110016China

Structural materials usually suffer from several attacks during their service,such as tension,fatigue and *** is necessary to sy.c.ronously improve these properties for their lightweight and longlifetime,but corrosion resistance and ductility are generally inverse correlation with strength,it is very difficult to simultaneously optimize all three ***,bulk nanocrystalline 304 stainless steel(BN-304SS)produced by severe rolling technology possessed the larger yield and ultimate tensile strengths with sufficient elongation(>40%)during tensile test,the larger saturation stress and longer lifetime during low-cycle fatigue,the enhanced uniform and pitting corrosion resistances during fiveday immersion test in 6 mol/L Hcl,the lowered stress corrosion cracking(Scc)susceptibility with larger yield(~2.40 GPa)and ultimate tensile(~2.66 GPa)strengths,and enough elongation(>30%)during stress corrosion in comparison with conventional polycrystalline 304 stainless steel(cP-304 SS)*** uniform and pitting corrosion resistances of fractured BN-304SS were enhanced in comprsion with those of fractured cP-304 SS during seven-day immersion test in 1 mol/L *** results demonstrated the strengths,ductility and corrosion resistances of BN-304SS can be simultaneously optimized by severe rolling *** improved results of BN-304SS in different disciplines were understood by its valence electron configurations rather than traditional microstructural parameters.

关键词： Stainless steel Pitting corrosion Stress corrosion Tensile properties Low-cycle fatigue Severe rolling technology

A dissolution-diffusion sliding model for soft rock grains with hydro-mechanical effect

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第3期10卷 457-467页

作者： Z.liu c.y.Zhou B.T.Li y.Q.Lu X.yang Guangdong Engineering Research center for Major Infrastructure Safety School of Civil Engineering Sun Yat-sen University

The deformation and failure of soft rock affected by hydro-mechanical（HM） effect are one of the most concerns in geotechnical engineering, which are basically attributed to the grain sliding of soft rock. This study tried to develop a dissolution-diffusion sliding model for the typical red bed soft rock in South china. Based on hydration film, mineral dissolution and diffusion theory, and geochemical thermodynamics, a dissolution-diffusion sliding model with the HM effect was established to account for the sliding rate. combined with the digital image processing technology, the relationship between the grain size of soft rock and the amplitude of sliding surface was presented. An equation for the strain rate of soft rocks under steady state was also derived. The reliability of the dissolution-diffusion sliding model was verified by triaxial creep tests on the soft rock with the HM coupling effect and by the relationship between the inversion average disjoining pressure and the average thickness of the hydration film. The results showed that the sliding rate of the soft rock grains was affected significantly by the waviness of sliding surface, the shear stress, and the average thickness of hydration film. The average grain size is essential for controlling the steady-state creep rate of soft rock. This study provides a new idea for investigating the deformation and failure of soft rock with the HM effect.

关键词： Soft rock Hydro-mechanical (HM) effect Mineral dissolution-diffusion Grain sliding model

construction of Non-Equilibrium Gas Distribution Functions through Expansions in Peculiar Velocity Space

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Advances in Applied Mathematics and Mechanics 2023年第6期15卷 1456-1472页

作者： Z.y.yuan Z.chen c.Shu y.y.liu Z.L.Zhang School of Energy and Power Engineering Nanjing University of Science and TechnologyNanjingJiangsu 210094China School of Naval Architecture Ocean and Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China Department of Mechanical Engineering National University of Singapore10 Kent Ridge Crescent119260Singapore

Gas distribution function plays a crucial role in the description of gas flows at the mesoscopic *** the presence of non-equilibrium flow,the distribution function loses its rotational symmetricity,making the mathematical derivation *** both the chapman-Enskog expansion and the Hermite polynomial expansion(Grad’s method),we observe that the non-equilibrium effect is closely related to the peculiar velocity space(c).Based on this recognition,we propose a new methodology to construct the non-equilibrium distribution function from the perspective of polynomial expansion in the peculiar velocity space of *** coefficients involved in the non-equilibrium distribution function can be exactly determined by the compatibility.c.nditions and the moment *** new framework allows constructing non-equilibrium distribution functions at any order of truncation,and the ones at the third and the fourth order have been presented in this paper for illustration *** validations demonstrate that the new method is more accurate than the Grad’s method at the same truncation error for describing non-equilibrium ***-dimensional benchmark tests are performed to shed light on the applicability of the new method to practical engineering problems.

关键词： Non-equilibrium gas distribution function peculiar velocity space complete poly-nomial expansion