Microstructural evolution in silicon alloyed γ-Ti–Al alloys after thermomechanical processing

Abstract

The microstructures of silicon alloyed γ-Ti–Al alloys containing silicide particles have been studied after thermomechanical treatments to investigate microstructural evolution. Important parameters including temperature, forging strain, and sequence of thermomechanical treatments were systematically studied. Isothermal forging below the eutectoid temperature resulted in inhomogeneous dynamic recrystallisation with fine equiaxed grains in recrystallised areas and residual α₂ + γ lamellae elsewhere. Eutectic silicides play an important role in destruction of the as cast structure by promoting dynamic recrystallisation during deformation and static recrystallisation on subsequent annealing. There is evidence that silicon, in solution, also enhances recrystallisation. The presence of fine silicides produced by precipitation in the solid state restricts the size of grains produced by both dynamic and static recrystallisation. Silicon also alters significantly the phase equilibrium between the α and γ phases.     

相变温度附近等温热处理对Mg97Zn1Y2合金组织演化的影响

研究了相变温度附近等温热处理温度和保温时间对含长周期结构Mg97Zn1Y2合金的组织的影响，并对演变机理进行了探讨。主要研究结论如下：500℃固溶处理时，随着时间的增加，长周期结构有增长的趋势。采用等温热处理可以将Mg97Zn1Y2合金中的枝晶组织转变为球状晶，当合金保温温度范围从540℃~600℃时，组织尺寸由大-小-大的顺序变化，即经过了粗化、分离及球化至最后粗化三个过程。在等温热处理温度为575℃的组织大致演变趋势为：枝晶态-不规则球形+块状-球形状，当保温时间15min，其组织为均匀、圆整的球状晶。     

Performance analysis of a k‐nearest neighbor searching technique

Abstract

A transfer admittance is treated as a two‐terminal network driven by cascaded dependent sources. By complex‐curve fitting, each of the four admittances of a conventional two‐port model can be approximated over a wideband with a rational function of frequency. A SPICE2‐acceptable R‐L‐C two‐port model can then be derived by applying continued fractions to the rational functions. Examples are included to demonstrate the applications of this method.     

Effects of Zn and Y on hot-tearing susceptibility of Mg–xZn–2xY alloys

The effect of Zn and Y on hot-tearing susceptibility (HTS) of Mg–xZn–2xY (x?=?1, 1.67, 2.67) alloys is investigated. It is found that the microstructure of the alloys is mainly composed of α-Mg, long-period stacking-ordered (LPSO) phase and W-phase. Both theoretical and experimental results illustrated that HTS of the investigated alloys is in the following order: Mg–1Zn–2Y > Mg–1.67Zn–3.34Y > Mg–2.67Zn–5.34Y. For Mg–2.67Zn–5.34Y alloy, LPSO phase content reaches at the maximum and its grain size reaches at minimum of 16.4 µm, and the pinning effect of the LPSO phase on grain boundaries is considered to be an important reason for reducing HTS of the alloy.     

常压水热法制备BTZ粉体及其在Y5V瓷粉中的应用

采用常压水热法制备锆钛酸钡粉体,研究了工艺参数对锆钛酸钡粉体颗粒大小的影响,以及粉体颗粒、Ba/(Ti+Zr)摩尔比对制成的Y5V瓷粉介电性能的影响。结果表明:选择改进的加料方式,再通过洗涤控制,可以得到粒度(D50)在0.4~0.5μm、Ba/(Ti+Zr)摩尔比为1.0的粉体;其能与抗还原剂、助熔剂很好匹配,获得性能优良(εr≥15000,tanδ<30×10–4,–80%≤?C/C20≤+30%)的镍内电极MLCC用Y5V瓷料。     

基于单片机空气质量检测系统

由粉尘传感器测量空气粉尘浓度,转换成数字量送单片机,单片机分析处理转换成浓度值再与设定浓度值比较;显示器显示空气中粉尘测量浓度和设定浓度;当粉尘浓度超限时,声光报警;     

轴向压缩下不加劲T型/Y型管节点性能的研究

使用有限元分析软件ABAQUS对轴向压缩载荷下T型和Y型管节点的失效模式﹑极限强度和具体性能进行研究。不加劲管节点的性能可从用于试验的管节点的数据库中提取。在数值分析中,使用修正弧长法可准确地模拟节点的性能,并有助于研究其真正的失效模式。通过数值分析发现,失效模式包括弦构件的局部弯曲、椭圆化变形、弦的塑性破坏。通过数值模拟得出的结果显示:节点表面的临界面积与椭圆化变形﹑变形量和应力有关。此外,对数值分析所预测出的极限强度与已有的试验结果进行了比较和验证。尽管已对管节点进行了大量的研究,但多集中于对极限强度和应力集中系数的估算上而不是对节点性能的具体研究,而此研究是一个全面解释轴向压缩下节点性能的具体研究。在已有的文献资料中很难看到这样深入又详细的节点研究。     

改性Y型分子筛上苯与多乙基苯的液相烷基转移

为获得高性能的液相烷基转移反应催化剂,采用不同的方法对Y型分子筛进行改性处理。采用N_2吸附-脱附、程序升温脱附(NH_3-TPD)和吡啶吸附红外(Py-IR)等手段对样品进行了表征,并在连续微型固定床反应器中考察了改性Y型分子筛上苯和多乙基苯烷基转移反应的催化性能。结果表明,催化剂的烷基转移反应性能与Y型分子筛的孔道和B酸量有密切的关系。通过铵离子交换和酸处理改性均可以提高催化剂的B酸量、比表面积、孔容和孔径;水蒸汽处理会降低酸量;铵离子交换和酸处理复合改性的Y型分子筛催化性能最好。适宜的反应条件为:反应温度180~240℃,反应压力2.5~4.0 MPa,总物料重量空速3~5 h~(-1),苯与二乙苯的质量比2~4,在该条件下二乙苯转化率大于65%,乙基选择性大于98%。该催化剂性能稳定,1 000h运行后活性仍没有下降。     

挤压温度对Mg-6Zn-1Mn-4Sn-0.5Y镁合金组织和性能的影响

通过光学显微镜（OM）,X 射线衍射（XRD）,扫描电子显微镜（SEM）,电子背散射衍射（EBSD）以及拉伸试验对360和420℃挤压的Mg-6Zn-1Mn-4Sn-0.5Y变形镁合金的组织和性能进行了研究。研究结果表明,合金铸态和时效态的相组成为α-Mg, Mn, Mg7Zn3, Mg2Sn, 和 MgSnY相。挤压温度从360℃增加到420℃,动态再结晶完成,晶粒长大,合金的屈服强度,抗拉强度以及延伸率分别由259MPa, 350MPa 和 18.3% 降低至 239MPa, 332MPa和12.5%。理论计算和拉伸试验结果表明,细晶强化和固溶强化对合金屈服强度的增加产生决定性影响。     

低压等离子喷涂纳米YSZ涂层的结构及力学性能

采用低压等离子喷涂技术制备具有新型结构的纳米YSZ涂层,研究电弧电流和粉末松装密度对涂层微观结构以及力学性能的影响。结果表明,松装密度为0.95g/cm3的粉末在喷涂过程中因电流升高而引起的晶粒生长的程度远低于松装密度为1.4g/cm~3的粉体。当电流超过350A后,两种粉末所对应的涂层的Weibull模量分布均发生从二元结构向单一值的转变,但转变后涂层的结构均呈现出有别于传统涂层结构的细等轴晶结构。硬度与弹性模量的分析结果表明具有细等轴晶结构的涂层较在350A电流下形成的二元结构纳米涂层具有更高的平均硬度与弹性模量。当采用密度为1.4g/cm~3的粉末时,所对应涂层的断裂韧性Weibull曲线随电流波动较大。