Localized swelling of Fe-Cr-Ni alloy rollers in high-temperature applications

Localized swelling has been observed in 24Cr-24Ni-Nb steel transportation rollers used in the normalizing furnace of a plate mill after prolonged service at high temperature. Due to high localized thermal and mechanical stresses, the chromia layer formed on the roller surface ruptures, exposing the roller substrate to furnace oxygen. Oxidation of second-phase carbides results in the formation of carbon monoxide at very high partial pressure. This leads to formation of voids, leading in turn to localized swelling of the roller material.     

Oxidation behavior of TiAl coated with a fine-grain Co-30Cr-4Al film

The oxidation behavior of TiAl coupons coated with a fine-grain Co-30Cr-4Al (mass %) film of about 30-m thickness has been studied at 1100–1400 K in a flow of purified oxygen at atmospheric pressure for up to 500 ks. Three oxidation stages were recognized: initial transient, parabolic, and accelerated stages. However, at 1100 K a parabolic stage continues for more than 800 ks. The activation energy for parabolic oxidation agrees with reported values for the oxidation of alumina-former alloys, although the mass gains during the parabolic stages are relatively small at 1200 and 1300 K. Micropores developed mainly at the scale/coating and coating/substrate interfaces as oxidation proceeded. This is attributable to recrystallization of the coating during oxidation and a Kirkendall effect due to preferential diffusion of Co into the substrate. The accelerated oxidation can be explained in terms of the formation of rutile mounds on the scale.     

BJ130汽车半轴摆动辗压新工艺

介绍了汽车半轴摆辗工艺原理、特点,并与传统胎模锻工艺在生产流程、生产成本、劳动强度、工件质量、生产效率以及工作环境方面进行了比较。     

混杂增强相(Al3Ti-TiB2-SiC)的形成热力学分析

对利用原位反应与高剪切液态搅拌复合专利技术制备的Al3Ti-TiB2-SiC/Al-13%Si复合材料的增强相的形成热力学进行了理论计算和分析,并采用差热分析法(DTA)进行了试验验证.研究表明:(1)Al-Ti-B体系加入到Al-13%Si熔体中可发生原位反应,形成增强相,原位反应的开始温度为905.3℃,结束温度为1 061.23℃;(2)Al-Ti-B体系加入到Al-13%Si熔体中,制备颗粒增强Al-13%Si复合材料的增强相为TiB2和Al3Ti,但TiB2形成能力最强.     

异型钢管辊挤成型过程的有限元模拟

利用非线性有限元分析软件MSC.Marc对方形异型钢管的无芯棒辊挤成型过程进行了有限元分析,得到了成型过程中应力与变形的分布与变化以及成型后异型管的结构形状。实验结果验证了有限元分析的正确性。研究结果为生产提供了有益的依据。     

高压缸液态挤压成形压力的分析及计算

采用液态挤压代替压力铸造生产铝合金高压缸，不仅克服了压铸件内部易形成气孔和氧化夹杂物的缺陷，而且提高了成品率，降低了产品成本，在分析了高压缸液态挤压成形过程的基础上，提出了成形压力计算的简化模型，并采用变形功法推导了成形压力计算公式，得到了适合实际应用的结果。     

侧吹气流方向对大功率CO2激光焊缝成形的影响

激光深熔焊过程中会在熔池上方产生等离子体云，若该等离子体云过密，将降低激光入射到工件表面能量密度。在工业应用中，常采用侧吹辅助气体来减弱等离子体云的影响。本文通过试验，研究了在不同气体流量下，侧吹气体方向不同对焊接过程稳定性和焊缝成形的影响。结果发现：使用大功率CO2激光焊接AH32时。侧吹气体方向对焊缝成形有着明显的影响。从熔池和等离子体两个方面，解释了侧吹气体方向的影响机制。     

Fe对NiAl金属间化合物光束堆焊层成形及组织结构的影响

采用X射线衍射、SEM、EDS等分析方法，研究了铁元素对光束堆焊合成NiAl金属间化合物层的成形和组织结构的影响规律。结果表明，光束堆焊镍铝混合粉制备NiAl金属间化合物层时，NiAl的高熔点导致堆焊层成形困难。在镍铝混合粉中加入适量铁粉（11at％～28at％）可以降低堆焊合金体系的熔点、改善堆焊层成形。随着铁粉加入量的增加，堆焊层的稀释率呈现先增加后降低的趋势，过多的铁粉加入量（43at％）将使熔池金属不能润湿母材。铁元素的引入使堆焊层中析出了Fe3Al相，随着堆焊层中含Fe量的增加，Fe3Al的析出量增加，堆焊层的微观组织为NiAl柱状晶和柱状晶间的Fe3Al条状相。     

2VQS发动机气缸罩冲压成形数值模拟分析

本文应用Ｌｓ－Ｄｙｎａ３ｄ非线性有限元件对桑塔纳２０００型轿车ＶＱＳ发动机气缸罩冲压成形过程进行了详尽的有限元模拟分析，通过与实测结果的比较、表明有限元预测结果可靠的。     

Application of multiscale modeling in the coating formation simulation of APS PYSZ TBCs

The process parameters of atmospheric plasma spraying (APS) influence the coating formation and properties of partially yttria stabilized zirconia (PYSZ) thermal barrier coatings (TBC). Simulations can be used to investigate this dependency and to design the coating process for a targeted production of TBCs. A whole process simulation was realized by modeling the linked subprocesses: plasma torch, plasma free jet, powder particles characteristics, and coating formation. The coating formation can be described by model approaches with different physical assumptions and geometric scales. One approach is the simulation of single powder particles hitting the substrate surface. An alternative macroscale finite element model (FEM) model approach is applied in the coating formation simulation. A group of particles is pooled in a splash that is dependent on the precalculated particle distribution in front of the substrate. A third modeling approach is applied to calculate effective mechanical and thermodynamical properties of coatings dependent on the experimentally obtained or calculated microstructure of the PYSZ TBC, which is based on different homogenization methods. The application of three simulation approaches in the whole process simulation of APS is discussed; advantages and disadvantages are elucidated. Results based on simulation and experiments are presented for a variation of process parameters. Missing links in the multiscale approach are detected to make suggestions for future modeling and simulation work. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.