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Effect of hydrogen attack on acoustic emission behavior of low carbon steel

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Journal of University of Science and Technology Beijing 2002年第2期9卷 130-134页

作者： XiaogangLi ChaofangDong 等 materialsscienceandengineeringschool universityofScienceandTechnologyBeijingBeijing100083China materialsscienceandengineeringschool universityofScienceandTechnologyBeijingBeijin

In order to investigate the effect of hydrogen attack degree on acoustic emission(AE) behavior of low carbon steel during tensiling, specimens made of Low carbon steel was exposed to hydrogen gas of 18 MPa at 450 and 500℃ for 240, 480 and 720 h respectively. Experimental results show that with increase of the hydrogen attack degree, the totally AE activity decreases during tensiling. In addition, the count of AE signals with high amplitude for the specimens with hydrogen attack keeps a constant which is less than that without hydrogen attack. It is concluded that AE signals originate in the specimens with hydrogen attack from intergranular fracture induced by methane blisterings or/and microcracks on grain boundaries.

关键词： low carbon steel hydrogen attack acoustic emission

Optimization of RPC technique for refining the intermediate transformation microstructure

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Journal of University of Science and Technology Beijing 2002年第3期9卷 193-196页

作者： XueminWang ChengjiaShang 等 materialsscienceandengineeringschool UniversityofScienceandTechnologyBeijingBeijing100083China materialsscienceandengineeringschool UniversityofScienceandTechnologyBeijingBeijin

The influence of processing parameters ofrelaxation-precipitation-controlling phase transformation (RPC) technique, finish rollingtemperature, reduction ratio and relaxing time on the microstructure was studied bythermo-simulation for a low carbon Nb and Ti containing micro-alloyed steel. The microstructure wasinvestigated by optical microscope, transmission electron microscope and electron back scatterdiffraction (EBSD). The statistical results of the packet size were calculated. It shows that, afterRPC process, the steel is a composite microstructure of bainite and matensite. The bestthermo-simulation process for refinement in this experiment is deformation for 30 percent at 850 degC, and then relaxing at this temperature for 60 s to 200 s. Increasing the reduction ratio from 30percent to 60 or decreasing the deformation temperature to 800 deg C would cause the best relaxationtime to become shorter, increasing the deformation temperature to 900 deg C would cause therefinement effect to be weak.

关键词： RPC technique microstructure refinement deformation temperature reduction

Combustion synthesis of radioactive waste immobilization

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Rare Metals 2005年第2期24卷 119-124页

作者： ZHANGRuizhu GUOZhimeng LUXin JIAChengchang LINTao materialsscienceandengineeringschool UniversityofScienceandTechnologyBeijingBeijing100083China materialsscienceandengineeringschool UniversityofScienceandTechnologyBeijingBeijing100083China／／NorthChinaInstituteofWaterConservancyandHydroelectricPowerZhengzhou450011China

Using chromium oxide (CrO3) as an oxidant, the immobilization of simulating radioactive waste in perovskite (CaTiO3) structure by a combustion synthesis (CS) method was tested. The products were characterized by Archimedes liquid displacement technique, microhardness technique, X-ray diffraction, and scanning electron microscopy. The leaching rate was measured by the method of MCC-1 or MCC-2. The primary results show that the CS method can be used to solidify the immobilizate waste effectively.

关键词： combustion synthesis radioactive waste Immobilization perovskite

Influence of oxidant KMnO_4 on film-forming process of rare earth metal conversion coating on LY12 aluminum alloy

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Journal of University of Science and Technology Beijing 2002年第3期9卷 216-220页

作者： TianzhuGao JiuqingLi materialsscienceandengineeringschool UniversityofScienceandTechnologyBeijingBeijing100083China materialsscienceandengineeringschool UniversityofScienceandTechnologyBeijingBeijin

A Cu/Al galvanic couple was established to study the influence of the oxidantKMnO_4 on the film-forming process of rare earth metal (REM) conversion coating on LY12 aluminumalloy. It is found that the galvanic couple simulative experiment accords with the actual immersion,and it can be substantially used to simulate the behavior of LY12 aluminum alloy in thefilm-forming process. It is showed that the formation of the coating is quickened in CeCl_3 solutioncontaining KMnO_4 compared with that not containing KMnO_4. XPS results reveal that the coatingformed on cathode is composed of oxide or hydroxide of Ce and Mn, so the mechanism of formation ofREM conversion coating changes when KMnO4 is added.

关键词： copper containing aluminum alloy rare earth metal conversion coating galvanic couple simulative experiment

Lubrication in strip cold rolling process

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Journal of University of Science and Technology Beijing 2004年第4期11卷 368-372页

作者： JianlinSun YonglinKang TianguoXiao JianzeWang materialsscienceandengineeringschool UniversityofScienceandTechnologyBeijingBeijing100083China

A lubrication model was developed for explaining how to form an oil film inthe deformation zone, predicting the film thickness and determining the characteristics oflubrication in the strip rolling process, combined with the knowledge of hydrodynamic lubricationand rolling theories. Various mineral oils with viscosities from 0.032 to 1.6 Pa-s were used toobtain different film thicknesses in the strip cold rolling. Results from the experiment andcalculation show that the oil film forming in hydrodynamic lubrication is up to the bit angle and ahigher rolling speed or a higher rolling oil viscosity. The mechanism of mechanical entrainmentalways affects the film thickness that increases with the rolling oil viscosity increasing or thereduction rate decreasing in rolling.

关键词： rolling strip lubrication film

Tantalum oxide barrier in magnetic tunnel junctions

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Journal of University of Science and Technology Beijing 2004年第4期11卷 324-328页

作者： GuanghuaYu TingtingRen WeiJi JiaoTeng FengwuZhu materialsscienceandengineeringschool UniversityofScienceandTechnologyBeijingBeijing100083China

Tantalum as an insulating barrier can take the place of Al in magnetic tunneljunctions (MTJs). Ta barriers in MTJs were fabricated by natural oxidation. X-ray photoelectronspectroscopy (XPS) was used to characterize the oxidation states of Ta barrier. The experimentalresults show that the chemical state of tantalum is pure Ta^(5+) and the thickness of the oxide is1.3 nm. The unoxidized Ta in the barrier may chemically reacted with NiFe layer which is usuallyused in MTJs to form an intermetallic compound, NiTa_2. A magnetic 'dead layer' could be produced inthe NiFe/Ta interface. The 'dead layer' is likely to influence the spinning electron transport andthe magnetoresistance effect.

关键词： magnetic tunnel junctions (MTJs) insulating barrier TaO_x X-rayphotoelectron spectroscopy (XPS)

Effect of junction potential on the EMF of bielectrolyte solid-state sensors

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Journal of University of Science and Technology Beijing 2005年第1期12卷 81-84页

作者： FushenLi HuiXia LingWang YanhongZhang LifenLi materialsscienceandengineeringschool UniversityofScienceandTechnologyBeijingBeijing100083China

The EMF (electromotive force) expressions of bielectrolyte solid-state sensors derived from classical thermodynamics are not rigorous. They are only applicable in some special situations. In order to expand their applicable scope, they should be derived from irreversible thermodynamics theory. There is a junction potential term in the EMF equations of double solid electrolyte sensors derived from irreversible thermodynamics. The junction potential involves the ion transference numbers and the electron transference numbers of two kinds of solid electrolytes. When the transference numbers of reaction ions in the two solid electrolytes equal 1 only, the junction potential term is zero and two types of EMF equations become the same.

关键词： solid electrolyte sensor electromotive force junction potential transference number

Verification of topological relationship in 2-D grain growth process by simulation

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Journal of University of Science and Technology Beijing 2004年第2期11卷 138-140页

作者： ChaoWang GuoquanLiu YaSun XianggeQin materialsscienceandengineeringschool UniversityofScienceandTechnologyBeijingBeijing100083China

Behaviors of the quasi-steady state grain size distribution and thecorresponding topological relationship were investigated using the Potts Monte Carlo method tosimulate the normal grain growth process. The observed quasi-steady state grain size distributioncan be well fit by the Weibull function rather than the Hillert distribution. It is also found thatthe grain size and average number of grain sides are not linearly related. The reason that thequasi-steady state grain size distribution deviates from the Hillert distribution may contribute tothe nonlinearity of the relation of the average number of grain sides with the grain size. Theresults also exhibit the reasonability of the relationship deduced by Mullins between the grain sizedistribution and the average number of grain sides.

关键词： grain growth grain size distribution topology Monte Carlo simulation Hillert distribution

Thermo-stability of ultra-fine non-equilibrium microstructures

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Journal of University of Science and Technology Beijing 2004年第4期11卷 338-342页

作者： HuibinWu ShanwuYang AiminGuo ShaoqiangYuant ChengjiaShangt XinlaiHe materialsscienceandengineeringschool UniversityofScienceandTechnologyBeijingBeijing100083China

The evolution of the microstructures and hardness of a bainitic plate steelduring tempering at 650 deg C has been investigated. The steel was manufactured by RFC(relaxation-precipitation controlling phase transformation) technique. A part of the plate wasreheated to 930 deg C and held for 1 h before quenched into water (RQ). No obvious change wasdetected by means of optical microscopy in the RFC steel tempering for 0.5 h, while dislocationcells were formed inside the bainite laths, accompanied by an obvious drop of hardness. The bainitelaths started to coalesce in some regions, but the sample hardness kept nearly constant duringtempering from 1 to 7 h. With further tempering, polygonal ferrite was formed in local regions whilethe hardness decreased dramatically. The RQ samples softened faster during tempering and finallytransformed into the polygonal ferrite completely. These results indicate that the thermo-stabilityof fine non-equilibrium microstructures is tightly related to their history.

关键词： microalloyed steel bainite and martensite tempering RFC technique