施加复合电磁搅拌对A357合金微观组织的影响

在半固态加工技术中，电磁搅拌是最早应用于制备非枝晶浆料的方法之一，同时也是半固态触变压铸技术最早获得工业应用的重要技术基础之一。采用自行开发的电磁搅拌器，研究了多种不同电磁搅拌方式在不同工艺条件下，单独施加或复合施加对A357合金微观组织的影响。试验结果表明：单一施加旋转感应电磁搅拌时，浆料径向组织很不均匀；单一施加无芯感应电磁搅拌。当搅拌电流较小时，径向组织也不均匀，增大电流，浆料质量有明显改善；采用（旋转感应＋无芯感应）复合电磁场进行复合电磁搅拌时，可在电流较小时获得满意的浆料质量。     

Development of ultra light magnesium-lithium alloys

Magnesium-lithium alloys are among the lowest density metallic materials. Addition of lithium, with a relative density of 0·53, in magnesium reduces the density of the alloy significantly. Furthermore, addition of nearly 11 wt.% lithium converts hexagonal close packed structure of pure magnesium to a body centered cubic lattice, markedly improving formability of the alloy. The development of these alloys, however, had been hampered due to the high reactivity of lithium and magnesium in the molten state and also, due to poor creep resistance and instability of mechanical properties at room temperature. In an attempt to indigenize these ultra light alloys for possible applications in Indian satellite programme, detailed research work was initiated in DMRL. The difficulties associated with producing sound cast ingots have been overcome by controlling melting and casting parameters of these alloys. Extensive work has been done on structure-property correlation of alloys with varying lithium content and minor alloying additions. Based on these work, advanced magnesium-lithium alloys have been developed with improved tensile properties, room temperature stability and creep resistance. Wrought products (plates/sheets) of magnesium-lithium alloy have been supplied to ISAC, Bangalore and are being used in their INSAT-2 programme. This paper describes the systematic studies carried out in the laboratory to indigenize these ultra light alloys.     

Non-contact methods of measuring moisture concentration in external layers of building partitions II—Monitoring of the water vapour condensation on porous surfaces

This paper present the results of the investigation into a potential application of laser radiation for the detection of phase transition processes occurring on the surface layers of porous materials. An attempt was made to discuss in the approximation equations, the relationships between coefficients of the reflected light, the temperature and humidity of the surrounding environment. Laser light reflected from the porous surface carries information about the roughness of the structure. The presence of water microdrop on the surface of the porous material, as a result of condensation and thus a phase transition, leads to the phase displacement of individual rays, which is represented by different images. Therefore, a comprehensive analysis of the reflected light parameters allows a dynamic study of the phase transition phenomena without mechanical intervention.     

平面Z-型软磁铁氧体频率特性的研究

研究分析了Co2Z材料显微结构与磁性能的关系,在普通铁氧体工艺中引入预磁化处理方法,并适当控制二次再结晶现象,成功地研制出高性能的Co2Z型宽频材料,Z-型铁氧体材料的共振频率可达1.8GHz以上,截止频率在1GHz附近,起始磁导率在8-13之间,介电常数相对较低(ε'<30)。     

微合金钢模拟焊接热影响区组织和韧性研究

采用焊接模拟试验方法，研究了不同峰值温度（Tmax）和不同冷却时间（t8/5），对合Ti-N、TI-NB-N两种微合金钢热影响（HAZ）显微组织、奥氏体晶粒度、冲击韧性影响。试验结果表明：Ti-N钢焊接热影响区比Ti-Nb-n钢具有更高的冲击韧性、更适用于大线能量的焊接条件。     

Pb（Sc1／2Ta1／2）O3铁电体的有序结构和介电性质）

通过铌铁矿预合成法制备Ｐｂ（Ｓｃ１／２Ｔａ１／２）Ｏ３（ＰＳＴ）陶瓷，经适当的热处理获得了钙钛矿化合物Ｂ位离子的高有序和高无序试样，ＰＳＴ陶瓷的介电性质研究结果表明，高有序试样（Ｓ＝０．７７）的居里温度为２９℃，并具有较低的介电常数表现出普通铁电体性质特征，而高元序试样（Ｓ＝０）具有很高的介电常数，并表现出明显的弥散性相转变和Ｔｍ的频率色散行为，即高介电常数的驰豫铁电体性质。文中还利用ＸＲＤ，ＳＥ     

Effect of pretreatments and freezing rate on the firmness of potato tissue after a freeze–thaw cycle

The texture of potato tissue after a freeze–thaw process using different freezing rates and different pretreatments was analysed, in order to select the best strategy for optimum preservation of the textural characteristics of pre‐frozen potato. Ten blanching conditions were tested and a two‐step blanching process with calcium chloride (0.07 g mL^?1) proved the most effective in protecting the tissue after a freeze–thaw process (maximum load force around 10–55% of the raw tissue, depending on potato batch, for air‐blast freezing and 20–60% for immersion freezing). Vacuum impregnation at 100 and 400 mbar, even when followed by different pre‐drying treatments to remove excess water, was very detrimental to resistance to a freeze–thaw process (maximum load force below 10% of the raw tissue for air‐blast freezing and below 20% for immersion freezing). Microstructure analysis confirmed better tissue integrity retention with ethyleneglycol immersion freezing instead of air‐freezing. Differences were found between batches with a 6‐month difference in storage time, indicating that the fresher batch was more suitable for freezing.     

复合微粒高性能混凝土的二级界面显微结构及耐久性研究

将天然纳米纤维材料及活性球形掺合料复合应用于高性能混凝土中,用以改善高性能混凝土的二级界面,探讨胶凝材料的颗粒紧密堆积及显微结构。对混凝土力学性能的研究表明:改善混凝土的二级界面,可以大幅度提高其抗弯强度和弹性模量;对耐久性的研究表明,由于加入了纳米纤维材料,改善了体系颗粒级配及二级界面显微结构,增加了体系密实度,是提高混凝土抗冻性、抗渗性的有效途径。因而,研究高性能混凝土的二级界面显微结构,对于提高高性能混凝土的宏观物理力学性能及耐久性存在巨大潜能。     

低碳钢热变形过程中铁素体的织构形成规律

利用背散射电子衍射取向成像技术定量分析了热模拟单向压缩条件下Q235碳素钢热变形时铁素体的织构形成规律。结果表明,在710℃纯铁素体热压缩过程中,形成〈100〉和〈111〉方向的线织构。〈111〉方向织构增强的速度较快,到应变为1.0时达最大值,然后随应变的加大而减弱;〈100〉方向织构在形变量较小时增强的速度较慢,在大应变时增强的速度很快。大应变时虽导致一定程度的动态再结晶,使铁素体晶粒细化,但组织不均匀,织构过强,造成强烈的各向异性。在奥氏体与铁素体两相区变形时,先共析铁素体因形变同样产生强烈的织构。随着形变温度的提高和先共析铁素体的减少,织构减弱。     

添加CaF2-YF3的AlN陶瓷的热导率

用CaF2和YF3做添加剂，在1750℃制备了热导率高于170W/m.K的的AlN陶瓷，并用XRD和SEM研究了AlN陶瓷在烧结过程中的相组成，微结构以及晶格参数的变化，并讨论了其对热导率的影响，研究发现，当使用CaF2-YF3做添加剂时，微结构差异对AlN陶瓷热导率的影响很小，AlN陶瓷的热导率主要由AlN晶格氧缺陷浓度决定，由于CaF2-YF3能有效降低AlN颗粒表面的氧含量，从而有利于获得高的热导率。