Atom probe field ion microscope measurements of carbon segregation at an α:α grain boundary and service failures by intergranular stress corrosion cracking

This work reports on a critical measurement to understand the intergranular stress corrosion cracking (IGSCC) of pipeline steels: the atom probe field ion microscope (APFIM) measurement of the carbon concentration at a grain boundary (GB). The APFIM measurement was related to the microstructure and to IGSCC observations. The APFIM indicated that the GB carbon concentration of X70 was ∼10 at% or less, which correlated with a high resistance to IGSCC for X70.     

磁场在材料制备中的应用

总结近几年来国内外有关磁场在材料制备中的应用现状。分别讨论和分析了稳恒磁场、旋转磁场、交变磁场、脉冲磁场和强磁场在金属凝固过程中对金属凝固组织的影响。由于稳恒磁场、旋转磁场、交变磁场、脉冲磁场和强磁场在金属凝固过程中改善凝固组织的机理各不相同,在电磁学、流体力学和金属凝固原理的理论基础上,对磁场影响金属凝固组织的主要机理分别进行了讨论。另外,根据磁场发展技术的局限性对磁场在凝固过程中的应用和进一步研究进行了展望。     

Mo粉末烧结过程的相场模拟

采用相场法模拟了表面扩散和晶界扩散机制共同作用下的四球模型和五球模型中Mo粉末压坯微粒间烧结颈长大以及孔隙的演化过程。数值模拟引入了Cahn-Hillard(CH)方程控制的相对密度场和Ginzburg-Laudau(TDGL)方程控制的长程取向场参量,并采用半隐傅立叶谱方法对上述方程进行了求解。模拟结果表明,表面扩散是Mo粉末烧结过程的主导扩散机制;压坯致密度越高,烧结完成的时间越短。     

Influence of melt treatments and turning inserts on cutting force and surface integrity in turning of Al-12Si and Al-12Si-3Cu cast alloys

The microstructures, machinability and surface characteristics of Al-12Si and Al-12Si-3Cu cast alloys were studied after various melt treatments like grain refinement and modification. Results indicate that combined grain refined and modified Al-12Si-3Cu alloys have microstructures consisting of uniformly distributed α-Al dendrites, eutectic Al-silicon and fine CuAl₂ particles in the interdendritic region. These alloys exhibited better machinability and surface characteristics in the cast condition compared with the same alloy subjected to only grain refinement or modification. Performances of the turning inserts (un-coated, PVD and Polished CVD diamond coated) were evaluated in machining Al-12Si and Al-12Si-3Cu cast alloys under dry environment using a lathe. The Polished CVD diamond coated insert outperformed the un-coated or PVD-coated cutting inserts which suffered from sizeable edge buildup leading to higher cutting force and poor surface finish. The Polished CVD diamond coated insert shows a very small steady wear without flaking of the diamond film during cutting. This paper attempts to investigate the influence of grain refinement, modification and combined action of both on the microstrutural changes in the Al-12Si and Al-12Si-3Cu cast alloys and their machinability and surface finish when different turning inserts used.     

电解生产低钛铝合金的晶粒细化及衰退行为

选用Ti质量分数为0．1％～0．3％的电解低钛铝合金，分别研究了钛对合金晶粒的细化效果和熔体保温时间对晶粒细化的衰退行为的影响，并与相应含钛量熔配低钛铝合金进行了对比。结果表明，随着Ti含量的增加，两种加钛方式的低钛铝合金样品晶粒得到明显的细化。随着保温时间的延长，所有合金的晶粒尺寸均不同程度发生了粗化，Ti对晶粒的细化效果明显发生了衰退。电解加钛铝合金晶粒细化效果的抗衰退能力优于熔配加钛铝合金，这种趋势对Ti的质量分数为0．1％～0．2％的合金特别明显。     

变形条件对SiCp/2014Al复合材料力学行为和晶粒度的影响

研究了变形温度,应变速率和变形程度等热加工参数对ＳｉＣｐ／２０１４Ａｌ复合材料力学行为和晶粒度的影响。结果表明,该材料的流动应力对变形温度和应变速率比较敏感。变形每升高４０℃,流动应力降低５￣１０ＭＰａ,应变速率每提高一个数量级,流动应力增加１．３￣１．８们。提高应变整编有利于获得细晶组织。以足够的变形程度锻造以及适当提高锻后冷却速度均有利于获得细晶组织。根据实验结果确定了该材料的流动应力与热加工     

超声波开始导入时的熔体温度对Al-Cu合金铸锭组织的影响

研究超声波开始导入时的熔体温度(即熔体过热度)对铝铜合金铸锭组织的影响,分析超声波处理条件下,熔体过热度对铝铜合金铸锭细化率的影响因素.结果表明,随着开始导入时熔体过热度的增加,铸锭的细化效果大幅度地降低.     

Microstructure and thermoelectric properties of n-type Bi2Te2.85Se0.15 prepared by mechanical alloying and plasma activated sintering

Starting from elemental bismuth, tellurium and selenium powders, n-type Bi₂Te_2.85Se_0.15 solid solution with fine microstructure was prepared by mechanical alloying (MA) and plasma activated sintering (PAS) in the present work. The effect of PAS process on microstructure and thermoelectric properties of the sintered samples was investigated. The sintering temperature of PAS process (683 K) was 80–100 K lower than that of conventional hot pressing and the whole PAS process was also greatly shortened to about 30 min. A preferentially orientated microstructure with the basal planes (0 0 l) perpendicular to pressing direction was formed in the PASed sample and the maximum figure of merit (Z) at room temperature was 1.80 × 10⁻³ K⁻¹.     

铝合金铸件凝固微观模拟研究

通过对国内外微观组织模拟方法和对微观晶粒的形核和生长的研究,开发了微观组织模拟软件。利用该软件对Al-Si合金铸件凝固过程的微观组织形态进行了数值模拟,并能预测铸件的力学性能。模拟结果与实验的结果比较接近,说明了该软件具有应用前景,但部分功能还有待在实践中进一步完善。