粉末冶金Ti-14Mo-2.1Ta-0.9Nb-7Zr合金热变形行为

在Gleeble-1500D热模拟机上对粉末冶金制备的新型医用Ti-14Mo-2.1Ta-0.9Nb-7Zr合金进行等温热压缩实验,研究该合金在温度为780~960℃,应变速率为0.001~1s-1,变形为60%的条件下的高温变形及动态再结晶行为。采用包含变形激活能Q和温度T的双曲正弦形式修正的Arrhenius关系来描述该合金高温压缩变形时的最大变形抗力方程;并引入参数α(ε),n(ε),Q(ε)和A(ε)得到包含σ,ε·,T,ε的本构方程。结果表明:由本构方程计算得到的应力值和实验值有较好相关性(R=0.99430),平均相对误差为5.327%;最后采用加工硬化率法通过对θ-σ和lnθ-ε曲线进行三次多项式拟求解拐点的方法,得到了不同变形条件下发生动态再结晶的临界应力和临界应变值,建立了临界应力和Z参数的关系,获得动态再结晶的临界应力方程,而临界应变εc主要集中在0.01~0.04,不同变形条件下该合金发生动态再结晶的临界应变变化极小。     

反应堆压力容器用SA508Gr.4N钢的热变形行为

利用Gleeble-1500D热模拟试验机,在温度为1050~1250℃、应变速率为0.001~0.1s-1、真应变量0.16的条件下,研究和分析SA508Gr.4N钢高温塑性变形及动态再结晶行为。结果表明:SA508Gr.4N钢的高温真应力-应变曲线主要以动态再结晶为特征,峰值应力随变形温度的降低或应变速率的升高而增加,属于温度和应变速率敏感材料;在真应力-应变曲线的基础上,建立材料热变形本构方程,较好地表征了材料高温流变特征,其热激活能为383.862kJ/mol;其硬化率-应力(θ-σ)曲线均呈现拐点且-dθ/dσ-σ曲线出现极小值;临界应变随应变速率的增大与变形温度的降低而增加,且临界应变(εc)与峰值应变(εp)之间具有一定相关性,即εc/εp=0.517;临界应变与Z参数之间的函数关系为εc=8.57×10-4 Z0.148。     

钒氮微合金钢动态再结晶动力学及影响因素

为研究钒氮微合金钢的动态再结晶动力学及影响因素,选取3种对比成分的钒氮微合金钢发生动态再结晶的流变应力曲线,利用硬化速率一应力(θ-σ)曲线获得了饱和流变应力σsat、峰值应力σp、动态再结晶临界应力σc及稳态应力σss的准确值及上述特征应力值与σp的依赖关系,回归得到应变速率敏感的中碳钒氮微合金钢动态再结晶临界应变ε...     

B4CP/2009Al复合材料动态再结晶临界条件

目的 研究B4CP/2009Al复合材料的热变形流变行为,确定B4CP/2009Al复合材料发生动态再结晶的临界条件。方法 采用Gleeble-1500热模拟机对体积分数为25%的B4CP/2009Al复合材料进行热压缩试验,热压缩温度为300~500 ℃,应变速率为0.001~1 s?1,并建立热变形本构方程。基于加工硬化率曲线(θ-σ),获得动态再结晶临界条件。结果 B4CP/2009Al复合材料的流变应力随温度的升高和应变速率的降低而降低。临界应力(σc)与峰值应力(σp)存在线性关系：σc=0.2992σp+22.4698,引入Zener-Hollomon参数描述变形条件对临界条件的影响,得到临界应变与Z参数的关系：εc=1.35×10?3Z0.047 39。结论 B4CP/2009Al复合材料的流变应力曲线以动态再结晶软化机制为主要特征,B4C增强颗粒的加入促进了复合材料的动态再结晶。     

23CrNi3Mo钢动态再结晶行为和组织演变研究

利用Gleeble-1500热模拟试验机进行单道次热压缩变形,通过控制变形温度(900,950,1 000,1 050℃)和应变速率(0.01,0.1和1 s-1)研究了23CrNi3Mo钢的动态再结晶行为,分析了变形温度、应变速率对动态再结晶行为和组织演变的影响.结果表明:23CrNi3Mo钢动态再结晶的再结晶激活能为293.23 kJ/mol;采用θ-σ模型较精确地获得了发生动态再结晶的临界应变与峰值应变,并确定了其平均比值εc/εp=0.63;确定了材料常数和热变形本构方程.通过对热模拟实验数据的分析和显微组织观察,建立了不同变形条件下动态再结晶模型和晶粒尺寸模型.     

Ti-6Al-2Zr-1Mo-1V合金热变形激活动态再结晶的临界条件识别及表征

热压缩实验获得Ti-6Al-2Zr-1Mo-1V合金在温度1073～1323K,应变速率0.01～10s-1条件下的真应力-应变曲线,以此作为识别及表征动态再结晶临界条件的底层数据。对比分析流变应力曲线发现高温、低应变速率下动态回复型软化态势显著;低温、高应变速率下动态再结晶型软化态势显著。引入材料加工硬化率θ,结合θ-σ曲线拐点判据识别了流变应力曲线隐含表征激活动态再结晶的特征参量:临界应变、临界应力。采用含动态再结晶激活能Q的Arrhenius方程求得α、β、n1、n2等材料常数并获得该合金动态再结晶激活能对应变速率及温度的响应图。进一步引入表征动态再结晶临界条件的临界应变模型,获得了临界应变与各热力参数之间的数学关系,验证表明该临界模型预测精度最大为12.9%。     

Nb-Ti微合金高强钢动态再结晶动力学及临界条件

在Gleeble-3500 热模拟试验机上对Nb-Ti微合金高强钢进行了热模拟压缩试验,研究了其在变形温度为900~1 100 ℃、应变速率为0. 01~5 s-1 、最大变形量为70%条件下的动态再结晶行为。对流变曲线的分析及微观组织观察结果表明,低温高应变速率下流变曲线未显现出典型动态再结晶特征,但此条件下已发生动态再结晶。使用双曲正弦形Arrhenius关系计算的Nb-Ti微合金钢变形激活能为404 kJ/mol。利用加工硬化原理和Cingara-McQueen模型确定了动态再结晶初始临界应力和应变,分析了由Cingara-McQueen模型计算临界应力值偏高的原因,建立了临界应力、应变和Z参数之间的定量关系,得到了动态再结晶临界应力和应变方程:σ_c=0.335Z0.144,εc=0.005 9Z0.079。通过对θ-ε曲线进行分析,建立了最大软化速率处应变(εm)和变形条件的关系。在此基础上使用Avrami型动态再结晶动力学模型计算了不同变形条件下的再结晶体积分数,结果表明此模型可准确预测Nb-Ti微合金高强钢动力学。     

30%Cr-Cu复合材料热变形及动态再结晶临界条件

采用放电等离子烧结法(SPS)制备出30%Cr-Cu复合材料,对其致密度、硬度和导电率等相关性能进行测试,并观察分析该复合材料的显微组织。利用Gleeble-1500D型热模拟试验机在变形温度650~950℃、应变速率0.001~10s-1、变形量60%的条件下对30%Cr-Cu复合材料进行热模拟压缩试验。对热压缩试验得到的真应力-应变数据进行拟合、计算和分析,构建该复合材料的本构方程,同时得到材料的加工硬化率θ,利用材料的lnθ-ε曲线出现有拐点和-(lnθ)/ε-ε曲线对应有最小值这一判据,分析该复合材料的动态再结晶临界条件。结果表明:30%Cr-Cu复合材料的真应力-应变曲线主要以动态再结晶软化机制为特征,峰值应力随应变速率的增加和温度的降低而升高;该复合材料的lnθ-ε曲线出现拐点,-(lnθ)/ε-ε曲线对应有最小值,该最小值所对应的应变为临界应变εc,且εc随变形温度的升高和应变速率降低而减小,εc与Zener-Hollomon参数Z的函数关系为εc=2.38×10-3 Z0.1396。     

新型奥氏体耐热钢CHDG-A的动态再结晶行为及其动力学模型

进行新型奥氏体耐热钢(CHDG-A)的热压缩实验,研究了在900~1100℃、应变速率为0.01-10 s^-1条件下这种钢的热变形特征。结果表明:随着变形温度的提高或应变速率的降低这种钢的流变应力显著降低。基于Arrhenius模型构建了这种材料的本构方程,得到CHDG-A热变形激活能Q为515.618 kJ/mol。微观组织分析结果表明,动态再结晶(DRX)是该材料在实验热变形条件下最主要的软化方式,DRX形核主要通过晶界弓出,变形温度的升高和应变速率降低均有利于再结晶形核。基于真应力-应变曲线求得动态再结晶用Z参数表示的峰值和临界值(σ_p、ε_p、σ_c和ε_c),并确定了ε_c/ε_p,σ_c/σ_p的比值分别为0.52和0.98。同时,还基于Avrami方程建立了CHDG-A的DRX动力学模型。     

20 A 钢热塑性变形的应力-应变本构模型研究

目的研究20A低碳钢在高温条件下的热变形行为及本构模型。方法采用Gleeble-1500型热模拟压缩试验,研究在不同变形温度及变形速率条件下,材料的真实应力-应变之间的关系。结果 20A钢属于对温度和应变速率都敏感的材料,其流变曲线呈现出周期性动态再结晶特征。结论通过对实验数据运用最小二乘法、多元线性回归方法及Arrhenius方程处理,得到了20A材料热变形本构模型为σ=8.8650ε0.1445ε·0.1283exp(3475.23/T),为20A钢塑性加工过程的控制及模拟提供了理论基础。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.