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关键词： 模数   有限补缩   膨胀量   压边冒口   直浇道  

摘要： 介绍了均衡凝固理论在薄饼类铸铁件生产中的应用,从原理入手,对加工薄饼类铸铁件工艺特点进行分析,确定具体的工艺参数并计算压边冒口尺寸,从而解决了传统工艺铸造的不足。

关键词： Ti2AlNb钛合金   化学成分   铸锭组织  

摘要： 采用真空自耗电弧炉进行3次熔炼,获得了准160 mm的Ti2AlNb钛合金铸锭。对铸锭横截面不同位置、纵向不同位置进行金相组织观察和化学成分检测。结果表明:铸锭显微组织从边部到心部依次为细小等轴晶、类柱状晶、粗大等轴晶。Al元素含量在铸锭中含量为7.46%~8.38%,Nb元素含量分布为40.82%~42.03%。合金元素成分波动都较小,同时杂质元素C、N、H、O的含量都较低,符合GB/T3620.2标准对钛合金主元素波动范围和杂质含量的规定。

关键词： 3104铝合金铸锭   均匀化工艺   弥散相   硬度  

摘要： 深人研究不同均匀化工艺对3104铝合金铸锭组织、性能的影响,利用金相显微镜、扫描电镜、透射电镜及硬度仪进行检测和分析。结果表明:均匀化时间和温度对非平衡结晶相熔断程度有影响;在540℃以上保温时间越长,非平衡结晶相熔断越彻底;慢的冷却速率和500℃长时间保温会使弥散相长大;在605℃保温时会促使更多的弥散相析出,弥散相尺寸和数量与硬度值有一定的关系;合理提高均匀化温度有助于弥散相的均匀析出。

关键词： mushy layer   magnetohydrodynamics   stability  

摘要： During directional solidification of binary alloy mixtures, instability in the solid/liquid interface appears due to constitutional undercooling. As a result of this instability, a reactive porous medium, namely mushy layer, is formed, and it separates the liquid phase from the solid phase completely. The intrinsic structure of the mushy layer is of fine-scale dendritic crystal that shelters solute in the interstitial fluid. In a gravitational field, the rejection of lighter solute components from an advancing solidification front brings about unstable density gradient. Ensuing convective motions in the mush are driven by a density difference. The convection can change the solid matrix of the mushy layer. Hence, the dynamic response of the mushy layer is driven by interaction among heat transfer, solute transport and convection. As a contactless control tool, external magnetic field can change the heat and solute transport, which has a significant effect on the phase change process. Therefore, when magnetic field, thermal diffusion, solute transport and buoyancy convection are considered simultaneously in the phase transformation process, the mechanism of mushy region will become more complex and interesting. In this paper, the effect of external magnetic field on the stability of mushy layer during binary alloy solidification is studied. The coupling effects of magnetic field, temperature field, concentration field and convection are considered in the model. Including the direct mode and the oscillation mode, the resulting dispersion relation reveals the influence of magnetic field on the stability of mushy layer through linear stability analysis. It is found that the Lorentz force can reduce the instability effect which is caused by buoyancy convection. In the oscillation mode, an external magnetic field brings about a stabilizing effect on the mushy layer, but in the direct mode, the effect of external magnetic field on stability of the mushy layer is uncertain.

关键词： 等离子弧堆焊   显微硬度   组织   Fe-Cr-Mo-C系  

摘要： 采用等离子弧堆焊技术对不同Mo含量的Fe-Cr-Mo-C系合金进行堆焊,研究不同Mo含量对Fe-Cr-Mo-C堆焊层组织和性能的影响。采用扫描电子显微镜(SEM)和X射线衍射仪(XRD)对堆焊层组织和物相进行分析,采用显微硬度计对堆焊层显微硬度进行测试。结果表明:Fe-Cr-Mo-C合金组织由γ,M_(23)C_(6),M_(2)C以及M_(6)C组成,随着合金中Mo含量的增加,M_(23)C_(6)数量逐渐减少,蜂窝状的共晶碳化物M_(2)C数量逐渐增多,且M_(2)C逐渐转变为菊花状的共晶碳化物M_(6)C,大量高硬度M_(2)C均匀分布在堆焊层中,使得w(Mo)8.2%和w(Mo)10.1%合金堆焊层顶端显微硬度平均值较高,达到HV_(0.2)795,有利于促进堆焊层耐磨性的提高。

关键词： 糊状层   磁流体动力学   稳定性  

摘要： 利用线性稳定性方法研究了外加磁场对二元合金凝固过程中糊状层稳定性的影响,且模型同时考虑了温度场、浓度场和流动的耦合作用.利用计算得出的色散关系式分析了磁场对糊状层稳定性的影响,其中包括直接模式和振荡模式.给出了不同情况下外加磁场对糊状层稳定性的影响,发现磁洛伦兹力可以减小由浮力引起的失稳效应.振荡模式下外加磁场对糊状层产生稳定作用,但直接模式下外加磁场对糊状层的稳定作用具有不确定性.本文所给出结果为工业中利用外加磁场改善产品的质量提供了重要的理论参考.

关键词： 喷雾结冰   凝固潜热   气泡雾化喷嘴   空气源热泵   能效比  

摘要： 通过实验诊断和能耗分析研究了喷雾结冰喷嘴的性能和喷雾结冰凝固潜热的回收。研究结果发现,气泡雾化喷嘴在低能耗下能提供颗粒平均直径较小且尺寸分布相对集中的液雾;喷雾结冰过程中水滴释放的凝固潜热,以对流方式将周围的空气加热,环境温度越低冷空气温升幅度越大,喷雾结冰效率越高,提高喷雾量将有助于凝固潜热的回收;研究结果表明将喷雾结冰凝固潜热回收过程与空气源热泵系统耦合,能明显提高空气源热泵低温运行的能效比,拓展了空气源热泵的温度适应范围和凝固热的利用。

关键词： 铌微合金化   HRB400钢   加热温度   珠光体   贝氏体  

摘要： 利用Gleeble热模拟仪、高温激光共聚焦显微镜、透射电子显微镜研究了铌含量(0.011%~0.055%)及加热温度(1 100~1 250℃)对HRB400钢20 mm板组织和性能的影响。结果表明,1 180℃加热1 h时20 mm钢板中随铌含量增加,铁素体比例减少,贝氏体比例增加,屈服强度升高;铌含量0.024%时,组织中铁素体比例50.8%、珠光体比例39.0%,贝氏体比例10.2%,屈服强度426 MPa,抗拉强度685 MPa,伸长率24.0%,断面收缩率61.3%。铌析出物尺寸随加热温度升高逐渐细化,数量逐渐增多;1 180℃加热时铌含量析出物尺寸7~88 nm,呈弥散分布。

关键词： Zr-Nb-Ti alloy   structural stability   cluster formula approach   elastic modulus   mechanical property  

摘要： Metastable bcc beta-Zr alloys generally have low elastic modulus, magnetic susceptibility, good mechanical properties, corrosion resistance, and biocompatibility, which are ascribed to co-alloying of multiple elements to enhance the structural stability of the bcc-beta phase. This work systematically investigated the effects of Nb and Ti elements on the structural stability of the bcc-beta phase and mechanical properties of Zr-Nb-Ti alloys. Various binary [Zr-Zr-14] (Zr, Nb)(3) alloy compositions were designed by the cluster formula approach, based on which Ti was substituted for the base Zr to form ternary alloys. Alloy rods were prepared by the copper-mold suction-cast method with vacuum protection. The microstructure and mechanical properties of the alloys were characterized using XRD, OM, and TEM etc. The results show that the crystal structures of the Zr-Nb binary alloys could change from hcp-alpha to bcc-beta with increasing Nb content, whereas, the.-phase always coexists with the beta-phase. An appropriate amount of Ti addition can significantly inhibit the precipitation of., resulting in the further improvement of the stability of the beta-phase. The single beta-[Ti-Zr-14]Nb-3 (Zr-17.37Nb-2.98Ti, mass fraction, %) ternary alloy exhibited not only a low elastic modulus of E=57 GPa but also a good tensile property with a high yield strength of sigma(YS)=557 MPa and an elongation of delta=15.5%.

关键词： 住宅   外墙   装饰材料   分类  

摘要： 随着经济的高速发展,投入各行各业的资金的迅速提升,极大的推动了我国各行业的发展,建筑行业作为一个关系国计民生的基础行业,在我国大量资金流涌入的推动下,我国建筑行业生产规模和数量都取得很大的成就,一个个高耸的楼盘拔地而起,其中楼盘销售程度的好坏不仅与房地产公司的良好信誉度有着莫大的关系,而且与楼盘的外观有着千丝万缕的联系,本文以住宅外墙装饰材料为研究对象,首先对我国住宅外墙装饰材料的种类以及其的一些特性进行了分析,紧接着对我国住宅外墙选取不同装饰材料的要点进行分析,为我国建筑行业外观修饰贡献自己的力量。