影响定向空心片陶瓷型芯性能的一个重要因素—方石英含量的控制

本文对某型号发动机定向空心锅轮叶片生产中陶瓷型芯的性能进行分析，力图弄清方石英含量对陶瓷型芯综合性能及其对定向凝固无余量空心叶片生产的影响。     

影响定向空心叶片陶瓷型芯性能的一个重要因素──方石英含量的控制

本文对某型号发动机定向空心涡轮叶片生产中陶瓷型芯的性能进行统计分析，力图弄清方石英含量对陶瓷型芯综合性能及其对定向凝固无余量空心叶片生产的影响。     

硅基陶瓷型芯方石英含量与叶片浇注不露芯率的关系EI

本文从硅基型芯的强度与方石英含量、方石英含量与叶片浇注不露芯率之间的关系进行了分析，重点讨论了对方石英含量的控制，为提高叶片不露芯率提出可信依据。     

Al2O3纤维对SiO2基陶瓷型芯的烧缩阻滞

向SiO₂基体粉料中添加Al₂O₃纤维,采用热压注法制备Al₂O₃/SiO₂陶瓷型芯。分析Al₂O₃纤维含量对陶瓷型芯性能的影响。研究结果表明：Al₂O₃纤维含量对Al₂O₃/SiO₂陶瓷型芯的线收缩率、体积密度和抗弯强度均有较大的影响。当Al₂O₃纤维含量大于1wt%时,Al₂O₃/SiO₂陶瓷型芯的线收缩率大幅度降低,稳定在0.335%左右,体积密度随之降低,稳定在1.790 g · cm^-3左右;当Al₂O₃纤维含量为1wt%时,陶瓷型芯抗弯强度达最大值20.48 MPa。分析了Al₂O₃纤维对Al₂O₃/SiO₂陶瓷型芯烧结收缩的阻滞作用机制。     

莫来石对氧化铝基陶瓷型芯的高温抗变形能力的影响

研究了在不同状态下,氧化铝基陶瓷型芯中莫来石的含量及其微观结构对氧化铝基陶瓷型芯高温抗变形性能的影响.结果表明,氧化铝基陶瓷型芯具有优良的热强性能归因于高温下莫来石柱状晶群的存在.     

造孔剂含量对多孔BiScO3-PbTiO3高温压电陶瓷性能的影响

为研究造孔剂含量对多孔BiScO_3-PbTiO_3(记作BS-PT)高温压电陶瓷性能的影响,采用炭黑作为造孔剂,通过传统固相烧结法对不同初始固相体积分数的准同型相界附近的BS-PT/炭黑混合物制备出多孔高温压电陶瓷.利用X射线衍射仪对多孔陶瓷进行物相分析,通过扫描电子显微镜观察样品的新鲜断面和抛光热腐蚀后的表面显微结构,并对其压电、介电和水声性能进行研究.结果表明:制备的不同初始BS-PT体积分数多孔压电陶瓷均为立方钙钛矿相结构,孔隙通道密实化清晰可见,没有显著的缺陷,气孔的形状是长条形的,长度从几微米到几十甚至上百微米不一,气孔之间是孤立的;随着造孔剂炭黑的体积分数从20%增加至50%,气孔率线性地从8.3%增加至22.1%,εr、d33及d31逐渐下降,静水压优值(HFOM)逐渐增大.多孔压电陶瓷的性能强烈依赖于孔隙空间结构,如气孔率、孔径、孔隙形态及连接方式.     

电熔MgAl2O4对Al2O3-MgAl2O4复合耐火材料高温蠕变性能的影响

以烧结板状刚玉和电熔镁铝尖晶石为原料、磷酸为结合剂,在1680℃下制备了刚玉-镁铝尖晶石复合耐火材料样品。在1500℃、0.2 MPa的条件下保温50 h测试试样高温蠕变性能,采用XRD、SEM和EDS分析蠕变前后试样的物相组成及显微结构,分析镁铝尖晶石添加量对刚玉-镁铝尖晶石复合耐火材料高温蠕变性能的影响。结果表明:刚玉-镁铝尖晶石复相材料较纯刚玉材料有着更好的抗蠕变性。镁铝尖晶石骨料在蠕变过程中会与氧化铝基质之间发生固溶反应而在尖晶石颗粒周围形成二次尖晶石层,有效连接了基质与骨料,提高了试样的抗蠕变性。在二次尖晶石层形成的过程中由于Mg;有着更高的迁移速率和在反应界面两侧较高的厚度比,会诱发柯肯达尔效应,导致界面处空位大量积累和孔隙的产生。     

纳米SiO2含量对尼龙6/SiO2纳米复合材料蠕变性能的影响

通过原位聚合法制备了尼龙6/SiO2纳米复合材料。利用扫描电镜观测了复合材料的表面形貌,结果表明,纳米SiO2颗粒均匀地分布在尼龙6基体中。利用电子万能试验机对不同纳米SiO2含量的复合材料进行了短期(24 h)蠕变性能的测试,结果表明,随着纳米SiO2含量的增加,复合材料的抗蠕变性能也随着增大;在30 MPa、40 MPa和50 MPa的应力水平下,纳米SiO2含量为5%的纳米复合材料的蠕变应变分别比纯尼龙6降低了38.4%、61.0%和71.9%。     

Ti-Al-Sn-Zr-W-Si高温钛合金的蠕变性能

为大幅度拓展Ti-Al-Sn-Zr-W-Si高温钛合金的工程应用,优化了Ti-Al-Sn-Zr-W-Si高温钛合金的热处理工艺,研究了该钛合金的蠕变性能,并采用扫描电子显微镜观察了蠕变实验前后合金的微观组织特征及断口形貌。研究表明,经合理热处理工艺后,该合金在550和600℃均体现出优异的蠕变性能。蠕变实验后,合金的微观组织发生了明显的变化:在颈缩区呈明显的纤维状,而在均匀塑性变形区,由于回复再结晶,合金的显微组织呈现细小的晶粒。     

析出相对Ti60钛合金蠕变和持久性能的影响

研究了固溶态的Si、硅化物以及α2相对Ti60高温钛合金蠕变和持久性能的影响.结果表明,α片层之间析出的硅化物能提高Ti60钛合金的600℃蠕变抗力,且当α片层内部有α2相析出时蠕变抗力提高更明显,但是硅化物的大量析出和大颗粒硅化物的存在却降低了Ti60钛合金的600℃持久性能;α2相的析出同时提高材料的蠕变抗力和持久性能;减少硅化物的析出以提高固溶态的Si对低应力下蠕变抗力的作用不显著,但是能改善高应力下的持久性能.在蠕变和持久实验条件下固溶态的硅和硅化物的不同作用,可通过不同外加应力水平下材料变形机制的差异加以解释.     

HPMC添加量及烧结温度对粉煤灰支撑体性能的影响

以燃煤电厂燃烧后的废弃物粉煤灰为原料,二氧化锰(MnO₂)为烧结助剂,羟丙基甲基纤维素(HPMC)为粘结剂,通过滚压成型法和固态粒子烧结法制备单管式陶瓷膜支撑体,通过对原料的热稳定性、成品的纯水通量、抗折强度、微观形貌、晶相组成以及耐酸碱度进行表征,探究HPMC的添加量对于支撑体性能的影响。结果表明,HPMC的引入可以增强粉煤灰基支撑体泥料的粘性和塑性,在烧结温度为1 150℃,HPMC的添加量为2wt.%时,抗折强度为24.65 MPa、纯水通量为6 794.71 L/(m²·h·MPa)、耐酸碱腐蚀性能优异且稳定。HPMC作为粘结剂在苛刻条件下仍然可以制备出低成本、效果优的粉煤灰基陶瓷膜支撑体,达到资源化利用的目的。     

烧结温度对单管式黄土陶瓷支撑体性能的影响

以中值粒径为38.78μm的洛川黄土为骨料,采用滚压成型法和固态粒子烧结法制备单管式黄土基陶瓷膜支撑体。探究烧结温度对黄土陶瓷支撑体性能的影响。通过热重分析、三点弯曲法、压汞法、自制装置、质量损失法、X-射线衍射、扫描电镜对单管式黄土基陶瓷膜支撑体的热稳定性、抗折强度、孔隙率、纯水通量、耐酸碱度、晶相组成的分析及表面形貌的观察对支撑体进行了表征。研究表明,烧结温度确实能影响黄土陶瓷支撑体的性能;当烧结温度为1100℃时,支撑体的表面光滑,孔隙率达到了20.08%、抗折强度为32.46 MPa、纯水渗透率为893 L/(m^2·h·MPa)、酸碱腐蚀重量损失率为0.42%与0.24%,平均孔径和中值孔径分别为4.68、2.68μm。在此烧结温度下可生产出成本合理、效果优良的陶瓷膜支撑体。     

Effect of high temperature creep on the fire response of restrained steel beams

At room temperature, and at service load levels, creep has little effect on the performance of steel structures. However, under fire conditions, creep becomes a dominant factor and influences fire resistance of steel members. Under fire conditions, significant forces develop in restrained steel beams and these forces induce high stresses in the steel section. The extent of creep deformations is affected by magnitude and rate of development of stress and temperature in steel. In this paper, the effect of high temperature creep on fire response of restrained beams is investigated. Current high temperature creep models are compared. Finite element model created in ANSYS was validated by comparing the predictions with fire test data. The validated model was applied to investigate the effect of load level, heating rate, fire scenario and fire induced axial restraint on the extent of creep deformations. Results from the parametric study indicate that the influence of high temperature creep increases with the increase in axial restraint, heating rate, and load level. Generally, neglecting high-temperature creep effect stiffens the structural response and leads to reduced deflections but larger restraint forces. Therefore, neglecting high temperature creep in fire resistance analysis of steel structures can lead to unconservative predictions.     

Nd对AM50力学性能及高温性能的影响

对加Nd的AM50镁合金铸态试样进行固溶处理(420℃/12 h),研究了Nd对其显微组织、力学性能和抗高温蠕变性能的影响.结果表明:Nd的加入细化了晶粒,导致AM50合金室温力学性能的提高.Nd在AM50合金中形成了Al11Nd3高温稳定相,Al11Nd3的存在使加Nd的AM50合金在200℃的稳态蠕变率及高温(150℃)力学性能大幅度提高.     

Si对AM50力学性能和高温蠕变性能的影响

在基体合金AM50中分别加入Si和Ca,研究了Si和Ca对AM50-xSi合金的微观组织、力学性能及蠕变性能的影响.结果表明:加入Si后,合金高温蠕变性能随Si量的增加而增加并超过了AS41的水平;在AM50-xSi中加入微量Ca以后,合金中的Mg2Si相得到细化,从汉字状转变成颗粒状,室温及150℃拉伸性能明显提高.     

Plasma-sprayed self-sealing ceramic coatings: Materials chemistry and high temperature protective properties

The principal theoretical and experimental data relating to the structure and the protective action of self-sealing ceramic coatings (SSCCs) used to prevent non-aqueous corrosion phenomena (T ? 900 K) on metallic surfaces in chemically aggressive environments (oxidation, carburization, nitridation, sulphidation, attack by molten metals etc.) are reviewed. The plasma spray process used to deposit SSCCs is described and some of their properties are summarized. The results obtained in an investigation of the protective efficiency of SSCCs on Incoloy 825 and titanium substrates, which are particularly susceptible to metal dusting and oxidation-nitridation corrosion phenomena, are reported. It is hoped that the work described in this paper will stimulate new approaches to the development and characterization of these novel protective coatings as it is necessary to optimize the prevention of non-aqueous corrosion in many applications.     

Effect of porosity and alumina content on the high temperature mechanical properties of compocast aluminium alloy-alumina particulate composite

The effects of volume fraction of alumina and porosity on the tensile strength of Al-4 wt% Mg-alumina compocast particulate composite tested at various temperatures up to 623 K have0 been investigated with the help of a phenomenological model. The contribution of porosity on reduction of strength of composites at various levels of alumina content has been expressed as a linear function of porosity and the resulting equation contains two experimentally determined parameters, ₀, the ultimate tensile strength at zero porosity level and , a weakening factor. It is observed that decreases with an increase in volume fraction of alumine in the composite and it becomes more sensitive to alumina content of the composite with a rise in temperature. Ate given alumina contenta increases with a rise in test temperature but this effect is gradually countered by increasing alumine content of the composite. Finally, in a composite having 10.3 vol % alumina decreases with an increase in temperature. This may have occurred because the extent of particle-matrix debonding is determined by the plastic soak in the matrix and the fracture strain of a composite increases or decreases with temperature when the alumina content lies below or above 9.0 vol % of alumina respectively. At any test temperature ₀ of the composite decreases rapidly with an increase in volume fraction of alumina, but the rate of decrease of ₀ reduces at higher alumina levels. However at the elevated temperatures of 473K and 573K a sharp fall in ₀ is observed at alumina contents beyond 9.0 vol %. At a lower level of alumina content below about 8.98 vol % the fracture strain of the composites increases with an increase in temperature. However, in the case of higher alumina content beyond the level mentioned above the fracture strain of the composites decreases with the rise in temperature. At a given porosity level the fracture strain of a composite having about 9.4 vol % alumina decreases with an increase in temperature. Scanning electron microscopic observations show that the extent of the growth and linkage of voids before fracture become extensive at higher temperature. At ambient temperature the composites fail by a mixed mode of ductile and clevage fracture. At 573K a number of considerably small dimples along with the larger ones are observed in the fractured surface. At this temperature a large number of newly formed fine grains are observed in the matrix.