Microstructural Evolution of Rapidly Solidified Co-Mo and Ni-Mo Eutectic Alloys

Droplets of Co-37.6 wt pct Mo and Ni-47.7 wt pct Mo eutectic alloys were rapidly solidified during containerless processing in a 3 m drop tube. A kind of anomalous eutectic appears in these two eutectic alloys when undercooling is beyond 56 and 61 K, respectively. The two eutectic phases in anomalous eutectic were observed to grow in dendrite manner. The formation of anomalous eutectic is ascribed to the cooperative dendrite growth of the two independently nucleated eutectic phases. Current dendrite and eutectic growth theories are applied to describe the observed processes.     

Preparation and Structural Characterization of Rapidly Solidified AI-Cu Alloys

Rapidly solidified Al_(100-x)—Cu_x alloys(x = 5,10,1 5,25,35 wt%) were prepared and analyzed.High cooling rate increased the Cu solubility in 9.-AI matrix.The influence of the cooling rate on Cu solubility extension in Al was experimentally simulated.Thus the pouring was performed in metallic die and by melt spinning-low pressure(MSLP) technique.Melt processing by liquid quenching was performed using a self-designed melt spinning set-up which combined the cooling technology of a melt jet on the spinning disc with the principle of the mold feeding from low pressure casting technology.The thickness of the melt-spun ribbons was in the range of30—70 μm.The cooling rate provided by MS-LP was within 10~5—10~6 K/s after the device calibration.The obtained alloys were characterized from structural,thermal and mechanical point of view.Optical microscopy and scanning electron microscopy were employed for the microstructural characterization which was followed by X-ray analysis.The thermal properties were evaluated by dilatometric and differential scanning calorimetric measurements.Vickers microhardness measurements were performed in the study.In the case of the hypereutectic alloy with 35 wt%Cu obtained by MS-LP method,the microhardness value increased by 45%compared to the same alloy obtained by gravity casting method.This was due to the extended solubility of the alloying element in the α-AI solid solution.     

快速凝固镁合金的研究现状

简述了快速凝固镁合金的制备方法、组织结构及性能特征,介绍了国内外各合金系快速凝固镁合金的研究现状,并指出了当前研究存在的问题及发展动向.     

激冷快速凝固Al-Cu共晶合金的层片失稳研究

目的 研究热处理条件下共晶层片组织的失稳机制,通过理论建模定量阐明控制层片失稳的关键因素。方法 以Al-Cu共晶合金为研究对象,采用铜模激冷的方法使合金发生激冷快速凝固,获得2个不同冷却速率下的细化共晶层片组织,进一步对所制备的样品进行不同温度及时间的退火处理。研究了退火条件下层片组织的失稳行为,进一步建立了层片失稳的理论解析模型,并基于模型,阐明了热处理条件下共晶层片失稳的机制。结果 凝固冷速为63 K/s和28 K/s的2个样品层片组织均发生了失稳,且在相同退火温度下,冷速为63 K/s的样品(初始共晶层片更细小)更易发生失稳,当退火温度及时间相同时,冷速为63 K/s的样品层片失稳程度更高。结论 在退火条件下,受瑞利不稳定性的影响,共晶层片失稳遵循由层片组织转为棒状组织、棒状组织转变为粒状组织的演变规律;层片厚度和退火温度是层片粒化的主要影响因素。     

Microstructures and Mechanical Properties of Rapidly Solidified Mg-Al-Zn-MM Alloys

Mg-Al-Zn-M M （misch metal） alloy powders were manufactured by inert gas atomization and the characteristics of alloy powders were investigated.In spite of the low fluidity and easy oxidation of the magnesium melt,the spherical powder was made successfully with the improved three piece nozzle systems of gas atomization unit. It was found that most of the solidified powders with particles size of less than 50μm in diameter were single crystal and the solidification structure of rapidly solidified powders showed a typical dendritic morphology because of supercooling prior to nucleation.The spacing of secondary denrite arms was deceasing as the size of powders was decreasing.The rapidly solidified powders were consolidated by vacuum hot extrusion and the effects of misch metal addition to AZ91 on mechanical properties of extruded bars were also examined.During extrusion of the rapidly solidified powders,their dendritic structure was broken into fragments and remained as grains of about 3μm in size.The Mg-Al-Ce intermetallic compounds formed in the interdendritic regions of powders were finely broken,too.The tensile strength and ductility obtained in as-extruded Mg-9 wt pct Al-1 wt pct Zn-3 wt pct MM alloy wereσ-（T.S.） =383 MPa andε=10.6%,respectively.All of these improvements on mechanical properties were resulted from the refined microstructure and second-phase dispersions.     

Ni3Al+Ni7Hf2定向共晶合金的凝固行为

研究了Ni3Al/ Ni7Hf2定向共晶复合材料的组织和凝固行为。结果表明, Ni- 5.8Al-32Hf 和 Ni-4Al-26Hf-8Cr-4W 合金是这类Ni3Al/ Ni7Hf2定向共晶复合材料的合适成分。这两种合金在铸态下存在Ni3Al和Ni7Hf2相。缓慢凝固时会出现少量β-NiAl相。三元合金和五元合金的凝固范围分别为41℃和57℃,临界G/R值分别为5×105和7×106℃*s*cm－2 。对三元合金在温度梯度G=250℃*cm－1 和生长速率R=5μm*s－1,对五元合金在G=350℃ cm－1和R=1μm*s－1 条件下制备了平行于生长方向定向排列Ni3Al/Ni7Hf2片状共晶材料。     

快速凝固铝硅合金材料及其在汽车中的应用

本文介绍了快速凝固技术的特点及在高硅铝合金中的应用潜力,综述了快速凝固高硅铝合金的制取方法及研究现状,扼要总结了快速凝固高硅铝合金在汽车工业中的应用,最后提出这一研究领域中存在的问题及发展前景。     

快速凝固7000系超高强铝合金的研究现状

在对传统7000系高强铝合金分析的基础上,着重阐述了快速凝固超高强铝合金的发展过程、存在问题和研究现状.快速凝固技术可有效细化组织、提高合金元素的极限固溶度、抑制宏观和微观偏析,并提高超高强铝合金的综合性能,最后提出了快凝超高强铝合金的应用和发展前景.     

快速凝固粉末铝合金的制备和应用

本文综述了快速凝固粉末冶金现状，首先指出了快速凝固粉末冶金的特点，然后重点介绍快速凝固合金粉末的制备和成形固化技术，最后简要介绍了快速凝固粉末冶金技术在开发新型铝合金上的应用。     

快速凝固高强高导铜合金的研究现状及展望

本文综述了快速凝固高强度高导电率铜合金的研究现状 ,并对将来的发展趋势作了展望。指出 ,快速凝固铜合金的凝固过程对合金的最终显微组织结构起重要作用 ,因而 ,对其进行深入细致的研究具有重要意义。     

快速凝固Bi-Mn合金的结构及磁性研究

用自制真空熔体喷溅快速凝固冷却设备制作了６种成分的Ｂｉ－Ｍｎ合金薄带,用Ｘ射线衍射仪及振动样品磁强计测量了淬火态及退火态粉末试样的物相及磁性,得到了饱和磁化强度与乘磁随含Ｍｎ量的线性变化关系,及矫顽力随含Ｍｎ量的变化具有峰值存在,从磁性测量数据导出了淬火态试样中Ｍｎ在Ｂｉ中的固溶度扩展至２．４ｗｔ％。在含１６％Ｍｎ淬火态试样中获得较多的ＢｉＭｎ淬火高温相。     

原位生成TiC粒子在快凝Al-Fe合金中变化行为的研究

通过OM,SEM和TEM等手段研究了在常规铸态以及快速凝固Al-8wt?合金中原位生成TiC粒子时相组成及显微组织的变化.同时结合利用外加法制备的常规铸态和快速凝固Al-8wt?/TiC合金的显微组织变化,得出了原位反应TiC粒子的生成及其在合金熔体中的变化行为:在常规铸态下生成的尺寸较大的八面体TiC颗粒在快速凝固过程中将发生全部或部分溶解,在随后的快冷过程中将重新析出并形成细小的TiC粒子,原位生成的TiC粒子在快速凝固过程中同样可以对α-Al起到促发形核的作用.     

快速凝固高强高导铜合金的研究现状及展望

本文综述了快速凝固高强度高导电率铜合金的研究现状 ,并对将来的发展趋势作了展望。指出 ,快速凝固铜合金的凝固过程对合金的最终显微组织结构起重要作用 ,因而 ,对其进行深入细致的研究具有重要意义。     

Mg-Cu-Zn-Y快速凝固组织的演化及压缩性能研究

采用快速凝固法制备了Mg65+χ(Cu0.66 Y0.34)30-χ Zn5(χ=0、5、10、15)合金样品,并通过X射线衍射(XRD)、扫描电子显微镜(SEM)对制得样品的结构和组织进行了表征.结果表明,χ=0的S-1样品主要由基体相、尺寸较小的块状Mg2Cu相和少量的MgZnY相组成,随着Mg含量的增加,样品中还会出现片状的Mg相及颗粒状的MgZnY相,同时Mg相会有所增加,且其尺寸也增大.通过测试合金的压缩应力应变曲线,发现χ=10的S-3样品具有高的强度和良好的塑性,其最大压缩强度达到1098MPa,断裂时的应变值高达14%.     

Microstructure of Al-Si Alloys Rapidly Solidified from the Different Temperature Melts

1.IotroductionCoolingratehasasignificanteffectonsolidifyingmicrostructureofAl-Sialloys,ithaJsbeenshownthatthemorphologyofeutecticsiliconchangesfromplatestofiberswhenthecoolingrateisincreased[1'2].Rapidsolidificationprocessingprovidesawaytogreatlyre-finemicrostructure.Inmelt-spinningprocess,alargecircumferentialvelocityoftherotatingwheelisac-companiedbyalargecoolingandsolidificationrate.SoasmallsizeofAl-richandSi-richphaseswasgainedinthespunribbonsofAlSialloysl3].Obviously,themicrostructure…     

Microstructure Evolution of Cu-Pb Monotectic Alloys Processed in Drop Tube

Rapid solidification of Cu-Pb monotectic alloys has been accomplished during free fall in a 3m drop tube.Both macrosegregated and uniformly dispersed structures are observed in Cu-40wt pct Pb alloy droplets,whereas droplets of composition Cu-64wt pct Pb exhibit only macrosegregation morphologies.The microstructures are strongly dependent on droplet size.The higher undercooling tends to facilitate liquid phase separation and results in more extensive macrosegregation in smaller droplets.There exists a pronounced tendency for the Pb-rich liquid to occupy the surface of the droplets of both compositions,resulting from the quite lower surface tension of the Pb-rich phase and cauing a Pb-rich layer at the surface of the solidified droplet.The nucleation of monotectic cells in the Cu-40 wt pct Pb droplets with dispersed structures preferentially occurs at the droplet surface.A single nucleation event takes place more frequently as droplet size is reduced.     

Zr对快速凝固铝锂合金微观组织和力学性能的影响EI

采用多级快速冷凝装置研制了四种成分的快速凝固铝理合金，研究了Ｚｒ在合金中的存在形式及其对合金微观组织和力学性能的影响。     

Effects of Additional Elements on Microstructure and Precipitation Behaviour in Rapidly Solidified Al-Ti Base Alloys

Rapidly solidified Al-Ti base alloys were prepared by melt spinning at the cooling rate about 107 K/s. The melt-spun ribbons were used to observe the dricrostructures after heat treatment.In the supersaturated Al-Tl-Si alloy, age hardening occurred after 1 h anneal in the temperature range of 4000~500℃, which seems to be attributed to the precipitation of metastable Ll2- (Al,Si)3Ti phase. However. the microhardness was relatively low because of the low v/o and the insufflcient stability of precipitates. Thus. Cr was added to Al-Ti-Si alloys in order to stabilize the microstructures and to increase the v/o of precipitate5. As a result. the alIoys containing Cr were evaluated to possess the improved properties at the service temperature.