铸造工艺参数和细化剂对K4169高温合金铸态组织的影响Ⅰ.晶粒组织及晶粒细化机理

研究了K4169高温合金在各种工艺条件下及向熔体中加入复合细化剂时的晶粒组织。结果表明，降低浇注温度和加入复合细化剂可以明显细化冷凝后基体的晶粒和提高铸件断面等轴晶的比例。在通常的浇注温度1400℃下加入复合细化剂。对合金熔体进行或不进行过热处理时，可使圆柱锭的晶粒分别细化至ASTM1.7级和ASTM3.2级；断面等轴晶的比例分别达96％和99％以上。当浇注温度为1420℃、加入复合细化剂并对合金熔体进行过热处理时。可使圆柱锭晶粒细化至ASTM M10.5级，断面等轴晶的比例达90％以上。提出了晶粒细化的机理并对晶粒细化后断面等轴晶比例增大的现象进行了分析。     

微量Si、Mg元素对细化剂作用效果的影响

研究了6063合金中的微量Si、Mg元素对Al-Ti-C中间合金细化效果的影响,并探讨了其影响机理。结果表明：微量的Si、Mg元素均能促进Al-Ti-C中间合金对6063铝合金的细化作用,一般Si的含量在0.5％时,Al-Ti-C的细化效果最佳。在细化温度相同的情况下,Mg的促进作用更明显一些并且不存在“温度效应”。试验表明,当6063铝合金中同时存在微量的Si、Mg元素时,Al-Ti-C的细化效果会更加显著。     

氩弧重熔对管线钢接头表层组织的影响

采用氩弧重熔单道和多道处理管线钢接头，不公使焊缝表层的柱状晶组织细化，而且使接头焊趾部位出现圆滑过渡，同时也细化了焊趾部位热影响区的粗大晶粒。接头表层组织的细化和焊趾部位的圆滑过渡都有利于提高管线钢接头的疲劳和腐蚀性能。     

基于模型特征的新型有限元网格划分方法研究

开孔构件的开孔形式各异,增加了其网格划分难度.另外,全六面体网格划分一直是有限元网格划分中的难点之一,实现开孔构件的全六面体网格划分具有重要的现实意义.文章基于开孔实体的参数化特征模型思想,提出了一种非自由边界分割有限元网格划分方法,可以针对开孔实体的几何特征和力学特征,对多种类型的开孔构件进行全六面体网格划分,生成的网格质量均匀、局部加密方便且疏密过渡合理.经实例应用表明,此种网格划分方法具有通用性强、简单、实用、高效等特点.     

MgCO3与La2(CO3)3对镁合金晶粒细化效果对比的研究

在镁铝系合金晶粒细化工艺过程中，传统的变质剂采用的是MgCO3或C2Cl6等，在本文分别用MgCO3和La2(CO3)3处理AZ91D镁合金。实验结果表明，La2(CO3)3的细化效果要优于MgCO3对镁合金的晶粒细化效果。     

Mechanical alloying of Mo—Si—Fe powders

Mechanical milling behavior of Mo-Si-Fe powders was investigated u sing XRD, SEM and TEM techniques. The mixtures of elemental molybdenum (>99%), s ilicon (>99%) and iron (>98%) powders with a stoichiometry of Mo5-xFe xSi3 (x=0.5, 1, 2) were milled in a planetary mill for up to 195 h. For all three powder mixt ures, high-energy milling of 60h led to formation of the Mo(Fe, Si) supers aturated solid solution (Moss); and to a remarkable expansion of the solub ility of Fe, Si in molybdenum. The transformation of Moss to an amorphous phase was identified after longer time milling. In the milling process, the grain size of Mo (Fe, Si) decreased gradually and the internal stress increased linearly. After 40 h milling, the grain size was reduced to about 11 nm. SEM analysis of milled powders showed that the particle size increased initially with milling time. After 195 h milling, particles exhibited a spherical morphology and the particle size were reduced to about 100 nm.     

低压脉冲电场下纯铝的晶粒细化

研究了低压脉冲电场作用下纯铝凝固组织的变化，考察了放电电压和处理时间对纯铝晶粒尺寸的影响。结果表明：低压脉冲电场可以显著地细化纯铝的凝固组织。随着放电电压的提高，纯铝的晶粒尺寸逐渐减小；当放电电压达到400V时，晶粒尺寸略有回弹。随着处理时间的增加，纯铝的晶粒尺寸逐渐减小；当处理时间大于15min时，纯铝的晶粒尺寸随着处理时间的增加而略有增大。     

Fe、Si对工业纯铝晶粒细化的影响

通过AlTiB晶粒细化剂对高纯铝、工业纯铝的细化及Al-10Ti中间合金、Fe、Si对工业纯铝的细化，研究了Fe、Si在工业纯铝晶粒细化过程中的作用。试验结果表明，0.3％的AlTiB晶粒细化剂对工业纯铝有良好的细化效果，但不能细化高纯铝；Fe、Si作为晶粒细化剂单独加入时，有不同程度的细化作用。分析认为，Fe、Si在工业纯铝晶粒细化过程中有双重作用，即促进型壁晶核的游离和增加α-Al在型壁形核的质点数目。     

Synthesis mechanism of titanium carbide nano-fiber during self-propagating high temperature synthesis

Titanium carbide nano-fiber was synthesized by self-propagating high temperature synthesis (SHS) method. The final products after the SHS reaction were titanium carbide containing excess carbon and metallic titanium, which were removed by additional leaching process. TEM observation revealed that the average diameter is about 20 nm. Neutron diffraction analysis was carried out to study non-stoichiometric number of the titanium carbide. The non-stoichiometric numbers of the titanium carbide were 0.89–0.94. The Rietveld refinement of each patterns converged to good agreement (÷2=0.49–1.34). The formation mechanism of the carbide is related to a liquid-solid reaction including the preferential diffusion process of carbon atom into liquid titanium. This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials,” organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei University, Seoul, Korea on October 25–26, 2002.     

制备多物相AlTiC合金的Ti与C熔体反应法

将Ti与C同时加入Al熔体可制备出Ti与C摩尔比分别大于、等于、小于4的3种含不同物相的Al—TiC合金：Al—TiAl3-TiC、Al—TiC、Al-Al4C3-TiC。对纯铝的细化实验表明：不含过量Ti的后两种合金的细化效果相近，Al4C3在Al—TiC合金中的大量出现不会进一步降低合金的细化能力；含TiAl3的第一种合金的细化效率远高于后两者的；TiC物相在基体中以离散颗粒或聚集团形式在Al基体中分布；Al4C3相极脆，易与空气中的水蒸汽反应而分解。分析表明Ti与C在Al熔体中反应生成TiC是通过两条途径同时进行的：熔体中的固体C颗粒与溶解态的Ti直接反应；固体C颗粒和Al反应生成的A4C3与溶解态的Ti发生反应。