稀土镁合金热变形行为和组织演变研究

目的 通过热模拟试验研究Mg-3.94Gd-2.0Y-0.78Zn-0.56Mn(质量分数)合金的高温变形特性,建立合金的本构方程,并分析变形条件对显微组织的影响。方法 在Gleeble3500热模拟机上进行单向压缩试验,变形温度为350~500 ℃,变形速率为0.0005~0.5 s^?1,变形量为60%。结果 流变应力受到应变速率与变形温度的共同影响,计算得到了合金的本构方程。当变形速率一定时,随着变形温度的升高,动态再结晶比例逐渐提高,而再结晶晶粒尺寸也逐渐增大,在变形速率为0.0005 s^?1时,当变形温度从350 ℃增大到500 ℃时,动态再结晶晶粒尺寸从1.2 µm增大到51.3 µm;当变形温度一定时,随着变形速率的升高,再结晶比例逐渐降低,而再结晶晶粒尺寸也逐渐减小,在变形温度为500 ℃时,当变形速率从0.0005 s^?1增大到0.5 s^?1时,动态再结晶晶粒尺寸从51.3 µm减少到11.0 µm。结论 得到了合金的本构方程,再结晶晶粒尺寸随温度的升高而逐渐增大,随变形速率的升高而逐渐减小。     

700℃超超临界锅炉材料GH4700镍基合金组织演变研究

通过热压缩实验、组织分析同时结合热力学和动力学计算方法,对700℃超超临界锅炉材料GH4700镍基合金组织演变进行研究,结果表明:GH4700镍基合金具有较高的变形温度和应变速率敏感性,随着变形温度的下降和应变速率的增大,合金的流变应力迅速升高,其动态再结晶形核方式为典型的应变诱导晶界迁移形核;其热变形激活能及晶粒长大激活能分别为345.0948kJ/mol和252.05kJ/mol。     

考虑摩擦效应的工业纯钛TA2热压缩变形本构方程及热加工图

目的 研究工业纯钛TA2在变形温度为800~950 ℃、应变速率为0.001~1 s^?1、压下量为50%条件下的热压缩变形行为,构建材料高温本构方程及热加工图。方法 利用Gleeble–3500热模拟试验机进行热压缩试验,对实测流变曲线进行摩擦修正,通过线性回归拟合等方法建立本构方程,基于动态材料模型构建工业纯钛TA2热加工图,确定材料最佳热变形区域。结果 工业纯钛TA2热变形激活能Q为473.491 kJ/mol,应力指数n为3.876 6;最佳热变形参数为变形温度850~950 ℃、应变速率0.02~0.35 s^?1。结论 工业纯钛TA2摩擦修正后的流变应力值均低于实测值,流动应力随变形温度的升高和应变速率的减小而降低。所建立的Arrhenius本构模型可较为准确地描述工业纯钛高温流变行为。工业纯钛TA2在中高温中等应变速率条件下加工性能良好,该区域材料发生了动态再结晶组织转变。     

热变形参数对Ti-6554合金流动软化行为的影响

目的 研究不同热变形参数下Ti-6554合金对应变速率敏感指数m、应变硬化指数n的影响。方法 采用Gleeble-3500热模拟实验机,在变形温度为810~930 ℃、应变速率为0.001~10 s⁻¹条件下,对Ti-6554合金进行等温恒应变速率热压缩实验。结果 应变速率敏感指数m随应变速率的升高和变形温度的降低而减小,当真应变为0.9时,m在变形温度为930 ℃、应变速率为0.001 s⁻¹的条件下达到峰值,为0.43。应变硬化指数n随应变速率的升高呈先升高后降低的趋势,在高温区间(870~930 ℃)的软化程度较大。结论 Ti-6554合金对变形温度、应变速率等热变形参数十分敏感,该合金的流动应力随着应变速率的升高和变形温度的降低而增大。分析微观组织可知,从应变速率敏感指数m角度考虑,该合金发生软化行为的最佳区域是变形温度为870~930 ℃、应变速率为0.001 s⁻¹。从应变硬化指数n的角度考虑,在变形温度为870~930 ℃条件下,Ti-6554合金在低应变速率区间(0.001~0.01 s⁻¹)的软化行为以动态再结晶(DRX)为主,在高应变速率区间(0.1~10 s⁻¹)的软化行为以动态回复(DRV)为主。     

Ti-6Cr-5Mo-5V-4Al合金热加工性能研究

目的 基于应变速率敏感系数、温度敏感系数,研究Ti-6Cr-5Mo-5V-4Al(Ti-6554)合金的热加工性能。方法 通过Gleeble-3500热模拟实验机,在温度为953~1 043 K、应变速率为0.001~10 s^?1时,对Ti-6Cr-5Mo-5V-4Al合金进行高温压缩实验。建立不同应变下的应变速率敏感系数图、温度敏感系数图,分析不同变形条件下的微观组织。结果 随着应变速率的增加,应变速率敏感系数逐渐下降,而低温度敏感系数区域主要集中在低应变速率区域。基于微观组织表征,发现变形过程中存在明显的动态相变和动态再结晶过程。结论 确定Ti-6554合金的合理加工条件为953~964 K、0.001 s^?1和1 037~1 043 K、0.001 s^?1。     

2209双相不锈钢本构模型及热加工参数优化

目的 优化2209双相不锈钢热加工区间,提升其高温变形稳定性。方法 在Gleeble–3800热模拟机上开展压缩实验,分析不同温度(950~1 150 ℃)和应变速率(0.01~10 s^?1)下的应力–应变曲线特征,构建基于Arrhenius的双曲正弦本构模型,综合分析热加工图和变形微观组织演变特征。结果 流变应力随变形温度的降低和应变速率的增大而增大;在失稳条件下(950 ℃/0.01 s^?1),奥氏体相所受应变能较小,只有一部分奥氏体晶粒发生了变形;温度升高(1 100 ℃/0.01 s^?1)后,奥氏体相仍为等轴状晶粒,铁素体相承担塑性变形,此时表现为明显的应变分布不均匀现象;随着应变速率升高到稳定条件(1 100 ℃/1 s^?1),奥氏体相承受了更大的塑性变形,且在压缩方向应力的作用下呈现条带状分布,同时发生了γ→δ的转变,这有利于提高钢的热塑性。结论 获得了2209双相不锈钢最佳加工区域(1 070~1 130 ℃、1~7 s^?1),该区域功率耗散系数较大且变化梯度较小,材料热加工性能稳定。     

铸态30CrMnSiNi2A钢的热变形行为与热加工图

目的 研究铸态30CrMnSiNi2A钢的热变形行为,并建立热加工图评估出合适的热变形参数。方法 在变形温度900~1 200 ℃和应变速率0.01~10 s⁻¹条件下开展热压缩实验,分别构建应变0.2、0.4、0.6、0.8下的热加工图,结合扫描电镜对变形后的微观组织进行分析。结果 30CrMnSiNi2A钢在压缩过程中真应力的变化是加工硬化和动态软化协同作用的结果;在低应变速率时(0.01、0.1 s⁻¹),流动曲线在应力值达到峰值应力(σp)后都表现出流动软化现象,而在高应变速率下流动曲线则表现出连续的加工硬化现象。结论 根据变形试样的微观组织和塑性流动是否稳定,可将热加工图分为3个区:流动失稳区、不完全动态再结晶区、完全动态再结晶区,在完全动态再结晶区内的晶粒细小均匀,所以将变形温度1 100~1 180 ℃、应变速率0.01~0.5 s⁻¹确定为适合于30CrMnSiNi2A钢的加工窗口。     

铸态Mg−2Sc−2Y−0.5Zr合金热压缩行为及热加工图

目的 研究铸态合金Mg?2Sc?2Y?0.5Zr合金热压缩行为及热加工图,根据合金的用途和再结晶程度,确定最佳热加工艺参数,为合金后续变形提供参考。方法 通过实验设计合金成分,称取一定质量的纯镁锭和二元中间合金,在真空熔炼炉中加热至760 ℃,保温至熔化,搅拌,静止,然后在钢磨具中空冷,得到合金锭。实际成分通过电感耦合等离子体原子发射光谱法测定;切取合适大小的铸锭进行X射线衍射实验。用于热压缩的铸态样品为圆柱形试样(?10 mm×15 mm) ,在进行热压缩实验前,对所有样品表面进行抛光。使用Gleeble?3800热压缩模拟试验机对铸态Mg?2Sc?2Y?0.5Zr合金进行热压缩试验,变形温度为573~723 K,应变速率为0.001~1 s^?1。经热压缩后将各试样立即进行水淬,以保持压缩变形组织。将压缩样品沿着纵轴切割压缩样品,然后抛光、蚀刻,并使用扫描显微镜进行检查,以观察微观结构的演变,计算该合金的变形激活能,并构建合金高温变形的本构方程,建立真应变为0.5时的热加工图。结果 得到了铸态Mg?2Sc?2Y?0.5Zr合金热变形本构方程及真应变为0.5时的热加工图,合金热变形发生了动态回复和动态再结晶,合金的热变形激活能Q为198.58 kJ/mol。结论 根据用途和再结晶程度,铸态Mg?2Sc?2Y?0.5Zr合金的最佳加工参数为变形温度623~673 K、应变速率0.001~0.01 s^?1,以及变形温度723 K、应变速率0.001~1 s^?1。     

Aermet100钢高温变形动态再结晶晶粒演变行为

目的研究高温变形对合金动态再结晶晶粒尺寸的影响。方法利用Gleeble 3500热模拟试验机对Aermet100超高强度钢进行了热模拟压缩,分析了动态再结晶晶粒在变形温度为800~1040℃、应变速率为0.01~10 s-1条件下的演变行为。结果研究发现,Aermet100钢动态再结晶晶粒随变形温度的升高而增大,随应变速率的增大而减小,高温、低应变速率变形后获得的动态再结晶晶粒尺寸较大,再结晶充分;低温、高应变速率获得的动态再结晶晶粒尺寸细小,但再结晶不完全。结论根据实验数据,建立了动态再结晶晶粒尺寸随Zener-Hollomon参数变化的理论模型,为Aermet100钢锻造工艺优化提供了理论依据。     

GH4049合金的热变形行为及组织演变

在Gleeble-1500热模拟机上进行GH4049合金的热压缩实验,获得合金在温度为1090~1180℃、应变速率为0.1~50s-1条件下的应力-应变曲线。对峰值应力进行线性回归获得合金在不同变形条件下的材料常数,通过非线性回归建立合金的热变形本构方程。结果表明:随着变形温度升高,动态再结晶更加充分,晶粒尺寸变大;随着应变速率增加,晶粒组织趋于均匀,晶粒尺寸先减小后增大。     

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.