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New ordered MAX phase Mo_2 TiAlC_2: Elastic and electronic properties from first-principles

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Chinese Physics B 2016年第10期25卷 323-329页

作者： M A Hadi M S Ali Department of Physics University of Rajshahi Department of Physics Pabna University of Science and Technology

First-principles computation on the basis of density functional theory(DFT) is executed with the CASTEP code to explore the structural, elastic, and electronic properties along with Debye temperature and theoretical vickers’ hardness of newly discovered ordered MAX phase carbide Mo2TiAlC2. The computed structural parameters are very reasonable compared with the experimental results. The mechanical stability is verified by using the computed elastic constants. The brittleness of the compound is indicated by both the Poisson’s and Pugh’s ratios. The new MAX phase is capable of resisting the pressure and tension and also has the clear directional bonding between atoms. The compound shows significant elastic anisotropy. The Debye temperature estimated from elastic moduli(B, G) is found to be 413.6 K. The electronic structure indicates that the bonding nature of Mo2TiAlC2is a mixture of covalent and metallic with few ionic characters. The electron charge density map shows a strong directional Mo–C–Mo covalent bonding associated with a relatively weak Ti–C *** calculated Fermi surface is due to the low-dispersive Mo 4d-like bands, which makes the compound a conductive *** hardness of the compound is also evaluated and a high value of 9.01 GPa is an indication of its strong covalent bonding.

关键词： new ordered MAX phase density functional theory calculations Debye temperature vickers hardness

Relation Between Strength and hardness of High-Entropy Alloys

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Acta Metallurgica Sinica(English Letters) 2021年第11期34卷 1461-1482页

作者： Xiaojuan Fan Ruitao Qu Zhefeng Zhang Shi-Changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Nano Science and Technology Institute University of Science and Technology of ChinaSuzhou 215132China School of Materials Science and Engineering Northwestern Polytechnical UniversityXi'an 710072China

High-entropy alloys(HEAs)are composed of multiple principal elements and exhibit not only remarkable mechanical properties,but also promising potentials for developing numerous new *** fully realize such potentials,highthroughput preparation and characterization technologies are especially useful;thereby,the fast evaluations of mechanical properties will be urgently *** the relation between strength and hardness is of significance for quickly predicting the strength of materials through simple hardness ***,up to now the strength-hardness relation for HEAs is still a *** this work,the relations between tensile or compressive strength and vickers hardness of various HEAs with hundreds of compositions at room temperature are investigated,and finally,the solution for estimating the strengths of HEAs from their hardness values is *** for hundreds of different HEAs were extracted from studies reported in the period from 2010 to *** results suggested that the well-known three-time relation(i.e.,hardness equals to three times the magnitude of strength)works for nearly all HEAs,except for a few brittle HEAs which show quite high hardness but low strength due to early ***,for HEAs with different phase structures,different strengths should be applied in using the 3-time relation,i.e.,yield strength for low ductility body-centered cubic(BCC)HEAs and ultimate strength for highly plastic and work-hardenable face-centered cubic(FCC)*** for dual-phase or multi-phase HEAs,similar 3-time relations can be also *** present approach sheds light on the mechanisms of hardness and also provides useful guidelines for quick estimation of strength from hardness for various HEAs.

关键词： High-entropy alloys vickers hardness Strength Plasticity

Development of microstructural inhomogeneity in multi-pass flow forming of TA15 alloy cylindrical parts

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Chinese Journal of Aeronautics 2020年第7期33卷 2088-2097页

作者： Xianxian WANG Pengfei GAO Mei ZHAN Ke YANG Yunda DONG Yukun LI State Key Laboratory of Solidification Processing Shaanxi Key Laboratory of High-Performance Precision Forming Technology and EquipmentSchool of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi'an 710072China

Revealing the development of microstructural inhomogeneity in the multi-pass flow forming of titanium alloy components is of great significance to the microstructure control and property *** this end,the microstructural inhomogeneity of TA15 alloy spun cylindrical parts was analyzed based on the deformation *** results indicate that the material underwent significant compressive strain in the normal direction(ND),tension strain in the rolling and circumferential directions(RD and CD),while tension strain in the CD is slightly small due to the limited material flow in this *** strain characteristics make the microstructure,especially the primary a(ap),present different morphologies in the different planes of the ***,the combined effects of inhomogeneous deformation and temperature distribution in the ND also cause the inhomogeneity of microstructure morphology and parameters in this *** analyses show that with the forming pass increasing,the aspect ratio of apincreases most in the normal-rolling plane,then in the normal-circumferential plane and least in the circumferential-rolling plane,whereas apcontent decreases in an opposite *** the ND,the aspect ratio and content of apis relatively high in the outer and inner surface areas but lowest in the central area,and these inhomogeneous characteristics can be gradually diminished with the forming pass ***,the variation of hardness inhomogeneity factor indicates that a four-pass forming with the total reduction ratio of 63%could obtain a homogenous microstructure along the ND of the TA15 alloy spun cylindrical part.

关键词： Deformation history Microstructural inhomogeneity Multi-pass flow forming TA15 alloy cylindrical parts vickers hardness

Effect of hot deformation on α→β phase transformation in 47Zr-45Ti-5Al-3V alloy

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Transactions of Nonferrous Metals Society of China 2018年第10期28卷 1947-1957页

作者： Yuan-biao TAN Li-yuan Ji Wen-chang LIU Song XIANG Fei ZHAO Yi-long LIANG Guizhou Key Laboratory of Materials Structure and Strength College of Materials and MetallurgyGuizhou UniversityGuiyang 550025China State Key Laboratory of Metastable Materials Science and Technology College of Materials Science and EngineeringYanshan UniversityQinhuangdao 066004China

The effect of strain rate and deformation temperature on theα→βphase transformation in 47Zr-45Ti-5Al-3V alloy with an initial widmanstattenαstructure was *** the deformation temperature of 550°C,the volume fraction ofαphase decreased with increasing strain *** 600 and 650°C,the volume fraction ofαphase firstly increased to a maximum value with increasing strain rate from 1×10-3 to 1×10-2 s-1,and then *** 700°C,the microstructure consisted of singleβ*** a given strain rate,the volume fraction ofαphase decreased with increasing deformation *** decreasing strain rate and increasing deformation temperature,the volume fraction and size of globularαphase *** 650°C and 1×10-3 s-1,the lamellarαphase was fully *** variation in the volume fraction and morphology ofαphase with strain rate and deformation temperature significantly affected the hardness of 47Zr-45Ti-5Al-3V alloy.

关键词： 47Zr-45Ti-5Al-3V alloy hot deformation phase transformation vickers hardness microstructure

Effects of La_(2)O_(3) addition on microstructure development and physical properties of harder ZTA-CeO_(2) composites with sustainable high fracture toughness

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Journal of Rare Earths 2021年第7期39卷 844-849,I0003页

作者： Zhwan Dilshad Ibrahim Sktani Nik Akmar Rejab Abdul Fatah Zulkarnain Rosli Ali Arab Zainal Arifin Ahmad Department of Mechanical and Energy Engineering Erbil Technical Engineering CollegeErbil Polytechnic UniversityErbil44001Iraq Structural Materials Niche Area School of Materials and Mineral Resources EngineeringEngineering CampusUniversiti Sains Malaysia14300Nibong TebalPenangMalaysia State Key Laboratory of Explosion Science and Technology Beijing Institute of TechnologyBeijing 100081China

The influence of La_(2)O_(3) inclusion(0-3 wt%) on the micro structure,phase formation and mechanical properties of zirconia toughed alumina(ZTA) added with 5.0 wt% CeO_(2) was *** CeO_(2) composites were sintered at 1600℃ for 4 *** microstructure,phase formation,density,fracture toughness and hardness properties were characterised through FESEM,Microscopy Image Analysis Software and XRD diffractometer,Archimedes principle and vickers indentation technique,*** XRD,image processing and FESEM reveal the existence of LaAl_(11)O_(18).The addition of La_(2)O_(3) incites the sintering,microstructure refinement,densification of ZTA-CeO_(2) matrix and phase ***,the hardness of ZTA-CeO_(2) ceramics is increased rapidly based on refinement of Al_(2)O_(3) grains,densification of ZTA-CeO_(2) composites and porosity *** is observed that the fracture toughness is enhanced through in situ formation of elongated LaAl_(11)O_(18) *** addition of 0.7 wt% La_(2)O_(3) culminated in the achievement of the optimum findings for density(4.41 g/cm^(3)),porosity(0.46%),hardness(1792 HV) and fracture toughness(8.8 MPa·m^(1/2)).Nevertheless,excess La_(2)O_(3) is proven to be detrimental as it displays poor mechanical properties due to the poor compactness of numerous LaAl_(11)O_(18) grains,coarsening of Al_(2)O_(3) grains and decline in density.

关键词： ZTA-CeO_(2) Ceramic composite Microstructural design Fracture toughness vickers hardness Rare earths

Theoretical investigation on the electronic structure,elastic properties, and intrinsic hardness of Si2N20

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Chinese Physics B 2012年第6期21卷 421-430页

作者：丁迎春陈敏高秀英蒋孟衡 College of Optoelectronics Technology Chengdu University of Information TechnologyChengdu 610225China

According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli （bulk modulus, Young’s mod-ulus, and shear modulus） are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the vickers hardnesses of the Si2N2O structures. We further estimate the vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.

关键词： elastic property vickers hardness electronic structure

Introduction of porous structure:A feasible and promising method for improving thermoelectric performance of Bi_2Te_3 based bulks

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Journal of Materials Science & Technology 2018年第12期34卷 2458-2463页

作者： Jie Hu Xi’An Fan Chengpeng Jiang Bo Feng Qiusheng Xiang Guangqiang Li Zhu He Yawei Li The State Key Laboratory of Refractories and Metallurgy Wuhan University of Science and Technology Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education Wuhan University of Science and Technology National-provincial Joint Engineering Research Center of High Temperature Materials and Lining Technology Wuhan University of Science and Technology

The porous p-type BiSbTebulks containing irregularly and randomly oriented pores were obtained by artificially controlling the relative density of sintered samples during resistance pressing sintering process. It is demonstrated that the thermoelectric performances are significantly affected by the porous structure, especially for the electrical and thermal conductivity due to the enhanced carrier scattering and phonon scattering. The increasing porosity resulted in the obvious decrease in electrical and thermal conductivity, and little change in Seebeck coefficients. It is encouraging that the reduction of thermal conductivity can compensate for the deterioration of electrical performance, leading to the enhancement in thermoelectric figure of merit(ZT). The maximum ZT value of 1.0 was obtained for the sample with a relative density of 90% at 333 K. Unfortunately, the increase in porosity also brought in obvious degradations in vickers hardness from 51.71 to 27.74 HV. It is worth mentioning that although the vickers hardness of the sample with a relative density of 90% decreased to 40.12 HV, it was still about twice as high as that of the zone melting sample(21.25 HV). To summarize, introducing pores structure into bulks properly not only enhances the ZT value of BiTebased alloys, but also reduces the use of raw materials and saves production cost.

关键词： Thermoelectric materials Porous structure Bi_2Te_3 Thermal conductivity vickers hardness

hardness of resin cement cured under different thickness of lithium disilicate-based ceramic

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Chinese Medical Journal 2011年第22期124卷 3762-3767页

作者： ZHANG Xuan WANG Fu Medical Office Chinese People＇s Liberation Army General Hospital Beijing 100853 China

Background The lithium disilicate-based ceramic is a newly developed all-ceramic material, which is lithium disilicate-based and could be used for fabricating almost all kinds of restorations. The extent of light attenuation by ceramic material was material-dependent. Ceramic materials with different crystal composition or crystalline content would exhibit distinct light-absorbing characteristics. The aim of this study was to analyze the influence of ceramic thickness and light-curing time on the polymerization of a dual-curing resin luting material with a lithium disilicate-based ceramic. Methods A lithium disilicate-based ceramic was used in this study. The light attenuation caused by ceramic with different thickness was determined using a spectral radiometer. The commercial dual-cured resin cement was light-cured directly or through ceramic discs with different thickness （1, 2 and 3 mm, respectively） for different times （10, 20, 30, 40, 50 and 60 seconds, respectively）. The polymerization efficiency of resin cement was expressed in terms as vickers hardness （VHN） measured after 24 hours storage. Two-way analysis of variance （ANOVA） and Tukey＇s HSD tests were used to determine differences. Results Intensity of polymerizing light transmitted through ceramic discs was reduced from 584 mW/cm2 to about 216 mW/cm2, 80 mW/cm2 and 52 mW/cm2 at thicknesses of 1 mm, 2 mm and 3 mm, respectively. Resin cement specimens self-cured alone showed significantly lower hardness values. When resin cement was light-cured through ceramic discs with a thickness of 1 mm, 2 mm and 3 mm, no further increasing in hardness values was observed when light-curing time was more than 30 seconds, 40 seconds and 60 seconds, respectively. Conclusions Within the limitation of the present study, ceramic thickness and light-curing time had remarkable influence on the polymerization of dual-cured resin cement. When resin cement is light-cured beneath a lithium disilicate ceramic with different thicknes

关键词： lithium disilicate ceramic polymerization vickers hardness thickness dual-cured resin cement light-curing time

Relationship between hardness and Deformation during Cold Rolling Process of Complex Profles

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Chinese Journal of Mechanical Engineering 2023年第5期36卷 315-329页

作者： Dawei Zhang Linghao Hu Bingkun Liu Shengdun Zhao Xi’an Key Laboratory of Intelligent Equipment and Control School of Mechanical EngineeringXi’an Jiaotong UniversityXi’an 710049China

The hardening on surface of complex profles such as thread and spline manufactured by cold rolling can efectively improve the mechanical properties and surface quality of rolled parts. The distribution of hardness in superfcial layer is closely related to the deformation by rolling. To establish the suitable correlation model for describing the relationship between strain and hardness during cold rolling forming process of complex profles is helpful to the optimization of rolling parameters and improvement of rolling process. In this study, a physical analog experiment refecting the uneven deformation during complex-profle rolling process has been extracted and designed, and then the large date set (more than 400 data points) of training samples refecting the local deformation characteristics of complexprofle rolling have been obtained. Several types of polynomials and power functions were adopted in regression analysis, and the regression correlation models of 45# steel were evaluated by the single-pass and multi-pass physical analog experiments and the complex-profle rolling experiment. The results indicated that the predicting accuracy of polynomial regression model is better in the strain range (i.e., ε hardness out strain range (i.e., ε > 1.2) of training samples can be well described by power regression model;so the correlation relationship between strain and hardness during complex-profle rolling process of 45# steel can be characterized by a segmented function such as third-order polynomial in the range ε 1.2;and the predicting error of the regression model by segmented function is less than 10%.

关键词： Complex profle Cold rolling Multi passes Equivalent strain vickers hardness