表面处理对球墨铸铁接触疲劳性能的影响

本文研究了激光微熔处理和高频感应加热淬火对球墨铸铁表面组织、接触疲劳强度和接触疲劳破坏过程的影响。结果表明,激光处理和高频淬火均可提高球铁的接触疲劳强度,但其接触疲劳破坏过程和形式却不同,前者是由于硬化层与基体间裂纹扩展造成大块深层剥落,后者则是表层裂纹在油楔作用下造成小块浅层脱落。     

深冲汽车簿钢板织构的表述方法

利用晶体学性质,将深冲汽车薄板的两种主要特征织构表述于反极图之中,再利用织构定量技术便能简捷地分析深冲钢板的织构与深冲性能的关系。经验证,此法与ODF定量分析所得的结果一致。     

MICROSTRUCTURE AND MECHANICAL BEHAVIOUR OF Al-Li-Zr AND Al-Li-Cu-Mg-Zr ALLOYS

The aging response,tensile and impact properties of two kinds of Al-Li based alloys havebeen studied.The microstructure,deformation as well as fracture behaviour in the alloys wereobserved with SEM and TEM.It was found that the mechanisms of deformation and fracturefor different heat-treated alloys with the same chemical composition are quite different.Thecauses leading to the drop of ductility,toughness as well as anisotropy in peak-aged alloyshave been analysed.Finally,possible methods to improve the ductility and toughness of the al-loys have been discussed.     

ELECTRON MICROANALYSIS FOR LASER MELTED ZONE IN 45 STEEL WITH Fe-Ni-Cr COATING

The Fe-Ni-Cr coating laver has been alloyed with 45 steel base metal by transverse.flow typeCO_2 gas laser of maximum output 5kW.The characteristics of the melted zone and the es-sence of the“bright band”has been investigated using the electron microscopy.The resultsshow that the“bright band”belongs to the melted zone and is a vertical section of the planecrystal,The width of the“bright band”equals the height of the plane crystal,which decreaseswith the increase of laser beam scanning rate and the decrease of laser power.This has beenexplained in terms of constitutional supercooling G/R.     

TEMPERED BAINITE EMBRITTLEMENT IN SOME STRUCTURAL STEELS

The variations of microstructures and mechanical properties of steels 15CrMnMoV,18Mn2CrMoB,18Cr2Ni4W,30CrMnSi,30CrMnSiNi2 and 40CrMnSiMoV,which weretempered at different temperatures after austempering and continuous cooling at given rates,have been investigated.Based on the experimental results,the behaviour and mechanism oftempered bainite embrittlement(TBE)have been discussed.Finally,the theoretical and prac-tical basis for selecting the optimum tempering temperature of steels with bainite structure af-ter heat treatment are proposed.     

EFFECT OF DYNAMIC STRAIN AGING ON PURE BENDING FATIGUE STRENGTH OF AUSTENITIC STAINLESS STEEL

The effect of various dynamic strain aging(DSA)pre-treatment processes on pure bendingfatigue strength of an 18-8 austenitic stainless steel was investigated.The results show thatDSA pre-treatment processes increase remarkably the fatigue strength and the strengtheningeffects increase with increasing pre-strain temperature and pre-strain.The fatigue limit ofspecimens pre-treated by DSA is 87% higher than that by solution treatment,and 20% high-er than that by cold-working.TEM observations show that the uniform and stable dislocationnetworks with high density formed after DSA pre-treatment,which suppress effectively theinitiation and propugation of fatigue cracks and increase the fatigue strength of materials.     

PHASE INTERFACE SEGREGATION OF Mg IN A Ni-BASE SUPERALLOY IN100

The segregation of Mg to phase interfaces in a nickel base superalloy IN 100 has been investi-gated using EPT(Electron Microprobe Technique).AES(Auger Electron Spectroscopy)and EDS analyses on thin TEM film.The results show that Mg segregates to the phase inter-faces of MC/γ and γ′/γ.The segregation concentration and layer thickness of Mg onMC/γ phase interface are larger than that on γ′/γ phase interface.Mg is not only a grainboundary segregation element,but also a phase interface segregation one.     

THERMAL DEMAGNETIZATION AND RANDOMNESS OF DOMAIN NUCLEATION OF SINGLE PHASE Nd_2 Fe_(14) B

Based on the observation of temperature variation of both domain structure and magnetic con-trast.the thermal demagnetization and randomness of domain nucleation was discussed.     

GRAIN SHAPE EFFECT IN SUPERPLASTIC DEFORMATION

The method controlling grain shape in TMT processing and the effect of grain shape on char-acteristic parameters in superplastic deformation were discussed.The accommodation velocityof grahl boundary sliding,which is the dominant mechanism in superplastic deformation,andthe contribution of each mechanism to the total strain,as influenced by grain shape,were ana-lyzed.Grain shape has been shown to be an essential structural factor for superplasticity.Thenan analysis was made about the effect of grain shape on the region transition strain rate sothat a new concept,critical aspect for superplasticity,was worked out.These predictions werecompared with the measured results in an Al-Zn-Mg alloy.     

DETERMINATION OF SPACE GROUP OF PrCo_(12)B_6 COMPOUND BY CONVERGENT BEAM ELECTRON DIFFRACTION

The space group of PrCo_(12)B_6,compound has been determined using the convergent beam elec-tron diffraction method.The space group is found to be R3m.