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。     

共析钢的过冷奥氏体动态相变和组织超细化

通过在Gleeble-1500热模拟试验机上进行单轴热压缩实验,研究了共析钢中过冷奥氏体在A1-Ar1之间变形时的组织演变,探讨了共析钢中复相组织球化超细化的机理.结果表明:随着应变量的增加,片层珠光体在原始奥氏体晶界形成的铁素体生长前沿形核长大,并向原始奥氏体晶内推进,直至相变完成.片层珠光体生成后继续变形,发生渗碳体的溶断和球化,及铁素体的动态回复再结晶等轴化等过程.渗碳体的球化有两种机制,其一是由于Gibbs-Thomson效应,珠光体中片层状渗碳体发生溶断和球化,生成的大颗粒渗碳体主要分布在铁素体晶界;其二是纳米级渗碳体粒子伴随铁素体动态再结晶在晶内重新析出.实验证实,在合适的变形工艺条件下可以得到亚微米级铁素体与亚微米、纳米级颗粒状渗碳体的双相组织.     

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。     

B和C对铸造TiAl基合金宏观和显微组织的影响

对比研究了B和C含量的变化对铸造TiAl基合金宏观和显微组织的影响。结果表明 ，B或C含量的增加均能细化TiAl基合金的晶粒，但二者的作用特点不同。B含量对宏观组织和晶粒尺寸的影响是渐进的，而C对其影响存在一个临界含量。显微观察表明，微量的B就能使合金析出TiB2，随着合金中B含量的增加，硼化物颗粒呈不同的形貌。对于含C合金，当C含量低于临界含量时，在光学尺度上观察不到碳化物相，而当C含量高于临界含量时，合金中生成大量的Ti2AlC碳化物颗粒。讨论了B和C细化TiAl基合金的机制。