铝液原位反应生成TiAl_3晶须的条件和机制分析

分析了液相原位反应生成 Ti B2 颗粒过程中 ,Ti Al3晶须的生成条件和生长机理。结果表明 ,预制块中 Ti与B的摩尔比显著影响 Ti Al3晶须的生成 ,Ti Al3晶须的生长机理为 VL S机制 ,由于晶须生长过程中触媒液滴中的 Ti参加反应 ,使它与一般晶须生长的 VL S机制有所不同     

Formation of Yb α-SiAlON whiskers by heat treatment of hot-pressed bulk samples

Novel α-SiAlON whiskers with various morphologies were produced at the surface of hot-pressed bulk samples by heat treatment at an elevated temperature of 1800 °C. Other than straight whiskers with or without nodules on their heads, curved bow-like and kinked whiskers were also observed. The growth mechanisms of different whiskers were discussed in detail, and it was proposed that the VLS (vapour–liquid–solid) mechanism was the predominant growth mode responsible for the formation of a majority of whiskers. With continuous vaporization and consumption by reactions, the liquid droplet necessary for VLS would be exhausted in some cases, and at this time VS mechanism could also become active.     

91W-6Ni-3Fe难熔合金、TiAl合金和铁基合金在熔铝中的耐腐蚀行为(英文)

采用静态浸没腐蚀试验研究91W-6Ni-3Fe难熔合金(91W)、TiAl金属间化合物和两种常用铁基合金(QT700和H13 钢)在750℃铝液当中的腐蚀性能。通过3D光学显微镜、SEM、EDS 和XRD研究样品的表面形貌,腐蚀界面和相组成。结果表明:91W具有最好的耐铝液腐蚀性能,QT700次之,H13再次之,TiAl合金的耐铝液腐蚀性能最差。四种金属材料的腐蚀失重均符合抛物线规律,材料在经过一开始的加速腐蚀阶段后,腐蚀速率趋于稳定。材料在铝液当中溶解遵循扩散-反应机制,91W材料在铝液当中的腐蚀主要由扩散这一速控步骤所决定,而TiAl合金的腐蚀性能差主要是由于TiAl-(TiAl3)-Al扩散偶反应具有较低的激活能。     

熔盐法合成莫来石晶须

以Al_2(SO_4)_3·18H_2O和SiO_2为反应原料,在Na_2SO_4熔盐中于不同的温度下(700, 800, 900, 1000, 1100和1200 ℃)合成了莫来石晶须,利用XRD、SEM、FESEM和TEM等手段对合成粉体的相组成和形貌进行了表征.结果表明:合成的莫来石粉体由纳米尺度的束状莫来石晶须组成;晶须直径为50～200 nm,长度为5～10 μm;熔盐法合成莫来石晶须的最佳温度为1000 ℃.还对莫来石晶须的形成机理进行了探讨.     

Al-Ti 液固界面的组织结构演变

采用镶嵌式扩散偶技术制备 Al-Ti 扩散偶,在 Al 熔点以上,Ti 熔点以下进行扩散热处理,研究 Al-Ti液-固界面扩散反应层的组织结构演变及生长机制。实验结果表明,热处理后的扩散反应层为TiAl3颗粒和铝的混合组织,以TiAl3和液相铝的平衡化学位共存区逐层生长,生长界面朝铝基一侧移动;TiAl3相是热处理过程中最先出现也是唯一出现的新生相;钛相变前后,扩散反应层的生长机制发生了改变。相变前,由钛向液相铝中的溶解速度控制;相变后,转变为Al、Ti原子的化学反应速度控制,生长速度大幅度加快。     

Preparation and characterization of mullite whiskers from silica fume by using a low temperature molten salt method

Mullite whiskers were prepared from silica fume in molten Al₂(SO₄)₃-Na₂SO₄ mixture salts at low temperatures. The resulting mullite whiskers, as well as the nucleation and growth mechanism in the molten environment, have been investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TG-DTA) techniques. XRD studies showed that the materials obtained were orthorhombic mullite. SEM, TEM and HRTEM results revealed that the mullite whiskers were single crystal fibers with diameters ranging from 30 to 150 nm and lengths of over several microns. According to thermodynamic analysis, mullite phase might be spontaneously formed in molten salts as the temperature reached the decomposition temperature of aluminum sulfate (1023 K). Moreover, the mullite crystals grew along [1 1 1] crystal plane firstly and developed into fibrous microstructure finally.     

Investigation of interface reaction between TiAl alloys and mold materials

This paper describes the investment casting of TiAl alloys. The effects of mold mateiral and mold preheating temperature for the investment casting of TiAl on metal-mold interfacial reaction were investigated by means of optical micrography, hardness profiles and an electron probe microanalyzer. The mold materials examined were colloidal silica bonded ZrO₂, ZrSiO₄, Al₂O₃ and CaO stabilized ZrO₂. When compared with conventional titanium alloy, the high aluminum concentration of TiAl alloys helps to lower their reactivity in the molten state. The Al₂O₃ mold is a promising mold material for the investment casting of TiAl in terms of the thermal stability, formability and cost. Special attention need to be paid to thermal stability and mold preheating when developing the investment casting of TiAl alloys.     

Reaction procedure of a graphite fiber reinforced Ti-Al composite produced by squeeze casting-in situ reaction

The in situ reaction procedure and microstructure evolution of a graphite fiber reinforced Ti-Al composite (Grf/Ti-Al) was investigated, and the stability of TiAl3 at high temperature was discussed. As-cast material was prepared by pressing molten pure aluminum into a preform, which was composed of titanium particles and graphite fibers. The in situ reaction procedure of the as-cast material was investigated by differential scanning calorimetry (DSC), and phases in the products were detected by X-ray diffraction (XRD). Experimental results showed that TiAl3 was formed first. With an increase in temperature, TiC and Al4C3 were observed, but TiAl3 decreased. In the final product, Al2O3 and TiO2 were observed. It was considered that the previous forming TiAl3 decomposed, then TiC precipitated, and subsequently, oxidation resulted in the formation of Al2O3 and TiO2.     

稀土铝钛硼中间合金的细化能力与长效性

采用铝热反应法制备Al5Ti1B和Al5Ti4RE1B中间合金,并对其进行物相、微观组织和细化效果分析;对比中间合金中第二相的晶体结构以及形核能力,并从第二相分解和沉淀的角度分析Al5Ti1B1RE的细化长效性。结果表明：Al5Ti4RE1B比Al5Ti1B具有更强的细化能力和细化长效性;XRD和EDS分析显示,RE和TiAl3结合生成Ti2Al20RE相,该相为面心立方结构,晶格常数为1.469 nm;相比TiAl3而言,Ti2Al20RE具有更多的晶面和Al晶体匹配,使得Al5Ti4RE1B比Al5Ti1B具有更强的细化能力;Ti2Al20RE比TiAl3的溶解温度高,溶解过程中稀土对铝液粘度的影响是造成Al5Ti4RE1B细化长效性好的主要原因。     

金属熔滴碰撞、铺张数值分析

基于金属熔滴沉积成形的3D打印技术,其成形质量与金属熔滴及基板参数有很大关系。本文对金属铝熔滴在不同参数下,比如：熔滴直径、滴落速度、比热、导热系数、潜热以及基板温度等,其凝固过程中的最大铺展因子关系进行了研究。采用VOF对自由表面进行追踪的方法,建立包括对流和相变的计算方程和能量方程的仿真模型,耦合水平集函数,跟踪熔融粒子与周围空气之间的接口,获得的最大传播因子之间的关系,与在文献中出现的实验数据吻合。     

焊后热处理对钛/铝FSB接头组织及性能的影响

研究了6082铝合金和TC4钛合金分别添加钎料锌和镍下的搅拌摩擦钎焊(FSB)搭接接头微观组织及焊后热处理后接头界面金属间化合物(IMC)的生成种类和先后顺序以及生长动力学模型。研究表明:添加钎料锌时,界面金属间化合物主要由AlZn、TiAl、TiAl2、TiAl3组成,先后顺序为TiAl2→TiAl3→TiAl→AlZn,并获得了界面IMC层的生长动力学模型为;添加钎料镍时,界面金属间化合物层主要由TiNi、Al3Ni2、Ti3Al和TiAl组成,先后顺序为776 K以下,Ti-Ni-Al焊接界面金属间化合物形成的顺序是Al3Ni2→TiNi→TiAl→Ti3Al,776 K以上时生成顺序为Al3Ni2→TiNi→Ti3Al→TiAl,并获得了界面IMC层的生长动力学模型。界面IMC层的厚度均随着温度的提高或保温时间的延长而增加。添加锌的接头的剪切强度由未热处理时的154 MPa提高到194 MPa,而添加钎料镍的接头由142 MPa提高至166 MPa。     

Al—Ti—C中间合金的相组成及其细化特性

用专利方法制备出各种成分的Al-Ti-C中间合金作为铝及铝合金的晶粒细化剂。对该系列中间合金的组织和物相分析表明：在制备中间合金过程中,C与Ti反应充分,生成TiC和TiAl3两种管二相,且TiAl3析出量取决于中间合金的Ti含量和Ti/C含量比。用于纯铝的晶粒细化试验表明：与Al-Ti-C中间合金相比,Al-Ti-C中间合金的晶粒细化效率更高;Al-Ti-C中间合金只有在组织中TiC与TiAl3保持适当比例时,才能对纯铝产生良好的晶粒细化效果,不含TiAl3的Al-Ti-C中间合金的晶粒细化作用很微弱;用Al-Ti-C中间合金细化纯铝晶粒时,响应时间短,但衰退较快,且不能通过熔体搅拌法予以消除。分析和探讨了Al-Ti-C中间合金的晶粒细化机理,认为“碳化物理论” 不能充分解释Al-Ti-C的晶粒细化机理,提出“Ti在TiC或TiAl3颗粒表面富集引发包晶反应”的晶粒细化机制。     

In-flight oxidation of aluminum in the twin-wire electric arc process

This paper examines the in-flight oxidation of aluminum sprayed in air using the twin-wire electric arc (TWEA) thermal spray process. Aerodynamic shear at the droplet surface increases the amount of in-flight oxidation by promoting entrainment of the surface oxides within the molten droplet and continually exposing fresh fluid available for oxidation. Mathematical predictions herein confirm experimental measurements that reveal an elevated, nearly constant surface temperature (∼2273 K) of the droplets during flight. The calculated oxide volume fraction of a “typical” droplet with internal circulation compares favorably to the experimentally determined oxide content (3.3–12.7%) for a typical TWEA-sprayed aluminum coating sprayed onto a room temperature substrate. It is concluded that internal circulation within the molten aluminum droplet is a significant source of oxidation. This effect produces an oxide content nearly two orders of magnitude larger than that of a droplet without continual oxidation.     

铝合金P-MIG焊接过程熔滴过渡行为的结构负载声发射表征

通过在线检测铝合金PMIG焊接过程的结构负载声发射信号,研究熔滴过渡行为的表征,以及熔滴过渡形式变化对声发射信号特征参数的影响. 结果表明,焊接过程中检测到的结构负载声发射信号时域波形包含了较多的PMIG焊接过程熔滴过渡特征信息,利用时域波形及其平均振铃计数、平均正峰值等特征参数可以对PMIG焊接过程中的熔滴过渡现象进行表征. 当熔滴过渡频率相同时,随着熔滴过渡对液态熔池的冲击作用增大,声发射信号特征参数相应增大;当熔滴过渡频率不同时,熔滴过渡频率越大,熔滴体积越小,对液态熔池的冲击作用越小,声发射信号特征参数相应减小.     

Ti-Al-C系复合材料的微观组织演变

以Ti粉、纯Al和碳纤维为原料,采用浸渗-反应合成法制备出Ti-Al-C系复合材料。首先将Ti粉和碳纤维制成预制件,再将熔融的纯Al压入预制件,制备出铸态的复合材料。随后将铸态的复合材料分别在600至1260 ℃间进行原位反应,保温时间为1 h。通过SEM和EDX 分析了复合材料的显微组织和产物的元素成分,同时,采用XRD分析复合材料的相组成。结果表明,在较低温下,TiAl3和Al4C3首先生成;随着温度的进一步升高,TiAl3 分解,TiC析出;在高温下,氧化现象发生,有Al2O3生成。Ti-Al-C系复合材料在原位反应过程中遵循生成-分解-析出-氧化机制。     

温度对硫酸钠熔盐中合成莫来石晶须的影响

以硫酸铝和二氧化硅为原料,硫酸钠熔盐作为介质,进行了在不同温度下合成莫来石晶须的试验.利用XRD、DSC、SEM等手段对合成晶须的相组成、结构和形貌进行了研究.结果表明:在800 ℃时莫来石开始成核,900 ℃时大量形成莫来石,1000 ℃合成反应基本完成,1100 ℃以上合成的莫来石开始分解,在1200 ℃时莫来石晶须大部分被分解.莫来石晶须的形貌与尺寸强烈地取决于合成温度.在本实验体系中,当合成反应温度在1000 ℃左右时,可获得直径在50～100 nm,长度约3～8 μm的莫来石晶须.     

钛-铝双丝超音速电弧喷涂过程中熔滴粒子几何特性研究

为了研究工艺参数对钛-铝双丝超音速电弧喷涂熔滴粒子尺寸的影响规律,通过对喷枪出口处气流速度、气体质量流率和金属熔滴质量流率的分析测定,以Nukiyama-Tanasawa模型为基础,建立了喷涂粒子的平均直径与喷涂电压和电流间的解析关系,并对喷涂电压和电流对熔滴粒子平均直径的影响进行了计算机模拟仿真.结果表明:在喷枪结构和雾化气体压力一定时,雾化粒子的平均直径随喷涂电流的增大而增大,随喷涂电压的升高而减小,但总的变化幅度却较小.利用激光粒度分析仪对一定喷涂工艺条件下所得的粒子平均直径进行实验分析,结果与计算值之间的相对误差为9.52%,扫描电镜观察表明粒子形态以球形颗粒为主.     

基于金属液滴水平重叠沉积工艺对表面形貌和内部质量优化研究

在铝熔滴在铝基板上沉积、凝固过程中,研究了不同工艺参数下的对成形表面形貌和内部质量的影响规律。通过对单一金属液滴沉积行为研究,建立了横向搭接沉积数值模型,并对两个,三个,四个熔融液滴重叠形态的进化和温度变化过程进行分析和实验验证。实验表明：数值模拟与实验结果有良好的一致性,从而得到了最优参数。该研究对实现金属微液滴重叠沉积生产的有效过程控制至关重要,为液滴水平重叠沉积复杂金属提供了技术支持和参考。     

金属熔滴连续沉积、凝固重叠工艺及实验验证

金属熔滴均匀连续沉积是一种新型的3D打印技术和快速原型(RP)技术。本文系统研究了铝熔滴连续沉积到基板表面的瞬态传热传质现象,沉积机理主要包括金属熔体的毛细现象及固液界面的传热、凝固、搭接和重熔。采用VOF方法对连续沉积的金属熔滴在水平固定铝基板表面沉积进行3D建模。针对凝固传热过程中不同参数下熔滴在铝基板表面沉积、凝固进行了研究,通过数值计算与实验验证,各种工艺参数的影响,如喷射速度、基板温度、熔滴直径与碰撞最大铺展因子的影响,显示了很好的一致性。基于上述研究,成形形貌和内部微观结构之间的定量关系进一步验证了金属熔滴连续沉积、凝固重叠工艺的可行性。此工艺为金属微沉积制造实施有效的过程控制提供指导。     

金属液滴垂直搭接成形工艺研究

通过研究铝合金熔滴的垂直搭接过程中不同工艺参数下的对成形表面形貌和内部质量的影响规律。通过对单一金属液滴沉积行为研究,建立了垂直搭接沉积数值模型,并对多个熔融液滴垂直重叠形态的进化和温度变化过程进行分析和实验验证。实验表明：数值模拟与实验结果有良好的一致性,从而得到了最优参数。该研究对实现金属微液滴垂直搭接生产的有效过程控制至关重要,为制造复杂金属提供了技术支持和参考。