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。     

Al/Ti液/固界面扩散溶解层形成机制及生长规律

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/固界面扩散溶解层的组织结构演变、形成机制及生长规律。实验结果表明,热处理后的扩散溶解层为TiAl3颗粒 和含少量Ti的铝基固溶体的混合组织;TiAl3相是热处理过程中最先出现也是唯一出现的新生相;扩散溶解层的生长机制和生长方向随热处理时间的延长发生了改变,在热处理开始后一段时间,扩散溶解层的生长受化学反应速度控制,与保温时间呈线性关系,之后,转变为受扩散控制,与保温时间呈抛物线关系,扩散溶解层的生长方向也由Ti基侧转变为Al基侧;扩散溶解层的厚度与热处理温度呈指数关系。     

Al/Sn二元扩散偶相界面扩散溶解层的形成机理

采用层片式扩散偶制备技术制备Al/Sn扩散偶,在不同热压温度条件下进行热处理,利用金相显微镜、扫描电镜、能谱仪、XRD衍射仪等研究Al/Sn扩散偶扩散溶解层的形貌特征与形成机理。结果表明:在0.5 MPa和230℃烧结条件下,Sn元素优先沿Al晶界扩散,然后沿其表面扩散;随着扩散时间的延长,Al与Sn元素间扩散和溶解程度增大,界面区无新物相生成,最终形成由Al和Sn的离异合金组织组成的界面过渡层且呈锯齿状形态分布;Al/Sn界面冶金结合是Al和Sn固相扩散、溶解与结晶共同作用的结果。     

Al/Cu扩散溶解层的形成机理研究

利用扫描电子显微镜和电子探针对不同退火处理的Al/Cu镶嵌式扩散偶扩散溶解层的形态和形成机理进行了研究。结果表明,当580℃保温160h退火处理后,在Al/Cu界面处形成厚度约2.5mm的扩散溶解层,其主要结构相与Al-Cu相图上相的排列位置一致。CuAl相层首先在Cu上形成,接着CuAl2在Al上形成,然后Cu4Al3、Cu5Al3、Cu3Al2、Cu9Al4和Cu3Al等五个相层依次在Cu上形成,各个扩散溶解层按照平面式长大方式长大;Al-Cu扩散溶解层的形成是Al和Cu固相扩散、溶解与二次结晶的结果,由于扩散浓度和固溶度的相互作用,导致了扩散溶解层析出的序列性。     

坡口角度及焊丝偏移量对钛/铝冷弧MIG焊接头显微组织与力学性能的影响

采用SAl 5183焊丝对TA2钛/5A05铝进行脉冲冷弧MIG焊. 研究钛侧坡口角度θ及焊丝偏移量d对接头成形及显微组织与力学性能的影响. 结果表明,坡口角度过小时,接头上部钛局部熔化而根部结合不良,Ti/Al界面组织差异大;坡口角度过大则出现焊缝下塌;坡口角度在30° ~ 45°范围内,Ti/Al界面组织差异小且结合良好. 焊丝偏向钛侧时,接头上部钛局部熔化而根部结合不良,Ti/Al界面组织差异大;焊丝向铝侧偏移过大则出现焊缝下塌;焊丝偏铝侧0 ~ 1 mm时,Ti/Al界面组织差异小且结合良好. 试验获得的优化工艺为坡口角度θ = 35°,焊丝偏铝d = 0.5 mm. 最佳工艺下,接头上部Ti/Al钎焊界面形成了Ti_3.3Al和TiAl₃两层金属间化合物;接头下部则通过形成一层TiAl₃实现钎焊结合;接头平均抗拉强度达198 MPa.     

Ti/Cu固相相界面扩散溶解层形成机制的研究

采用镶嵌式扩散偶,在不同退火处理条件下,对Ti/Cu扩散溶解层的形成机制进行了研究.利用扫描电子显微镜背散射电子像和二次电子像观察和分析扩散溶解层的形态和结构,从扩散、溶解与结晶角度研究扩散溶解层的形成机制.结果表明:在不同的扩散温度和时间下,Ti/Cu相界面扩散溶解层的形成是Ti和Cu固相扩散、溶解与结晶的结果;相界面处将几乎同时结晶出不同层数、厚度和结构的扩散溶解层;Cu或Ti原子百分含量相对较低的Cu-Ti化合物优先形成,究竟形成一个还是几个相层,这主要由Cu在Ti中和Ti在Cu中的的浓度分布决定.Ti和Cu在700℃固相扩散时,原子扩散流为Cu扩散进入Ti,Ti很少扩散进入Cu,因此,除了Cu4Ti相层在Cu丝上形成以外,其余5个相层都在Ti基体上形成;Cu2Ti和Cu3Ti2以及Cu4Ti3和CuTi化合物相层几乎同时形核并以"竹笋状"方式相向长大,互相交错重叠,表现出比较明显的浮凸;另外,Cu4Ti和CuTi2化合物相层以"平面状"方式长大.     

Al/Co相界面的扩散溶解层

采用镶嵌式扩散偶,在不同退火处理条件下,对Al/Co扩散溶解层进行了研究。利用扫描电子显微镜和电子探针显微分析仪观察和分析了扩散溶解层的形态和形成规律,并对其形成机理进行了探讨。结果表明,当进行600℃保温75h退火处理后,在Al/Co界面处形成了结构为Al/Co2Al9/Co4Al13/Co2Al5/CoAl/Co,并与Al-Co二元合金相图上相的位置顺序一致、厚度约170μm的扩散溶解层。CoAl相层首先在Co基体上形成,然后其余三个相层都在CoAl相层上形成;Co4Al13相层和Co2Al5相层几乎同时呈"柱状"方式分别纵向向Co块和Al丝相向生长,生长到一定的厚度,再从根部转向横向生长,最终层2和层3交错在一起;最后Co2Al9相层在Al/Co4Al13界面处形成。Al-Co扩散溶解层的形成是Al和Co固相扩散、溶解与结晶的结果,由于扩散浓度和固溶度的相互作用,导致了扩散溶解层析出的序列性。     

液-固扩散焊复合连接Ti(C,N)与40Cr的界面行为与接头强度

通过预置Ti/Cu非对称中间层对Ti(C,N)基金属陶瓷与40Cr钢进行了液-固扩散焊复合连接试验,重点研究了界面组织、接头强度及其影响因素.结果表明,通过预置Ti/Cu非对称中间层液-固扩散焊,能够分别实现Ti(C,N)基金属陶瓷与铜箔,以及铜箔与40Cr钢之间的冶金结合;Ti(C,N)基金属陶瓷界面物相呈梯度分布,形成Ti(C,N)基金属陶瓷/TiAl₂/Ti₂Cu/TiCu/铜箔结构;Ti(C,N)基金属陶瓷一侧靠近界面区域存在较大的焊接残余拉应力,以及脆弱的TiAl₂金属间化合物层,是制约焊接接头强度的关键因素;单纯以铜箔为中间层,采用常规固相扩散焊连接Ti(C,N)基金属陶瓷,即使在加热温度1223 K、压力20 MPa条件下,也难以实现Ti(C,N)基金属陶瓷与铜箔的有效连接.     

Cu-Ni扩散偶的扩散溶解层

分别在普通和真空热处理炉中对Cu/Ni镶嵌式扩散偶进行退火热处理,利用扫描电子显微镜和电子探针显微分析仪观察和分析了扩散溶解层的形态和结构,并对其形成机理进行了探讨.结果表明,Cu/Ni扩散偶在950℃、100 h退火处理时,Cu/Ni扩散溶解层主要在Ni块上形成,形状依附于原始界面,并逐渐向Ni块基体延伸,与Ni块没有界面,其结构是以Ni为溶剂、Cu为溶质的间隙固溶体;扩散溶解层的形成机理是Cu原子向Ni块扩散,Ni原子几乎不向Cu丝扩散,Cu丝溶解在Ni块里面.     

Mg1/Al1060真空扩散焊接头微观组织演变及性能分析

利用真空扩散焊接技术,实现了工业纯镁Mg1与工业纯铝Al1060的连接.采用扫描电镜、能谱仪、万能力学试验机、显微硬度测试仪、电化学工作站等对扩散反应层的微观组织、物相成分及其性能进行研究.结果表明,Mg/Al真空扩散焊会在接合处生成由镁铝系金属间化合物组成的扩散反应层,随着保温时间延长,反应层的厚度逐渐增加,微观组织形态发生明显变化.扩散初期反应层呈现为单层结构,Mg₂Al₃相会在接合界面优先析出.保温时间达到60 min时,界面会生成Mg₁₇Al₁₂新相层.当保温时间延长至90 min时,反应层演变为三层结构,由Mg₂Al₃层、Mg₁₇Al₁₂层、(Mg₁₇Al₁₂共晶+Mg基固溶体)层组成;随着保温时间延长,接头的剪切强度呈先升高后降低的趋势,在保温60 min时可承受的剪切力达到1 245.7 N,断裂发生在靠近铝侧的Mg₂Al_3...     

冷轧Ti/Al层状复合材料固-液反应过程中的界面微观组织演变

将冷轧Ti/Al层状复合材料在675~750 ℃下进行不同时间的退火处理,退火过程中钛和铝都保持过剩,研究了Ti/Al层状复合材料的界面微观组织演变。结果表明：Ti和Al的界面层由2个亚层组成,其中一个为紧密的TiAl₃亚层,其微观结构为紧密的TiAl₃层,其中分布着随机取向的充满Al的裂纹,另一个为颗粒状的TiAl₃亚层,其微观组织结构是颗粒状的TiAl₃分布在Al基体中。在不同的退火温度和时间条件下,紧密TiAl₃亚层的厚度几乎没有变化,但是颗粒状亚层的厚度随着退火温度及时间的增加而增加;另外,界面层中的TiAl₃颗粒的体积分数在不同的温度下均随着退火时间的延长而下降。因此提出了反应扩散模型来描述界面层的形成机理,在此模型中,TiAl₃相是化学反应和扩散的结果,并且也考虑了TiAl₃相的溶解。计算结果表明TiAl₃相的形成与生长由化学反应控制,其等效厚度与退火时间之间遵循线性规律,这主要是因为Ti和Al原子能够快速地通过紧密的薄TiAl₃亚层。     

Effect of HEA/Al composite interlayer on microstructure and mechanical property of Ti/Mg bimetal composite by solid-liquid compound casting

In this study,HEA/AI composite interlayer was used to fabricate Ti/Mg bimetal composites by solidliquid compound casting process.The Al layer was prepared on the surface of TC4 alloy by hot dipping,and the FeCoNiCr HEA layer was prepared by magnetron sputtering onto the Al layer.The influence of the HEA layer thickness and pouring temperature on interface evolution was investigated based on SEM observation and thermodynamic analysis.Results indicate that the sluggish diffusion effect of HEA can ...     

Effect of Ternary Elements on the Oxidation Behavior of Aluminized TiAl Alloys

The effects of ternary elements added to TiAl on the coating layer formed by the pack-aluminizing process was studied with respect to oxidation resistance and mechanical properties. All the TiAl specimens, with various amounts of Nb, Cr, Fe, and V, were pack aluminized under identical conditions using a high-activity process. Among the ternary alloying elements tested, Nb showed the best property of the TiAl₃ coating layer formed on the surface and, consequently, the best oxidation resistance. The TiAl₃ coating layer becomes thicker and has a finer grain size as the content of Nb or Cr is increased. Microhardness tests revealed that the addition of Nb or Cr improved the toughness of the coating layer and thus improved the cracking resistance. Cyclic oxidation tests showed that the TiAl₃ coating layer formed on the TiAl alloy has better oxidation resistance with increasing Nb content. The ductility and oxidation resistance of the TiAl₃ coating layers improved with Nb addition, which contributes to the grain refinement of TiAl₃. The Nb present in the TiAl₃ coating layer inhibits grain growth by the solute-drag effect and retards inward diffusion of Al to the TiAl matrix by forming (Nb, Ti)Al₃ precipitates during high-temperature oxidation.     

冷轧Ti/Al层状复合材料中TiAl3相在退火过程中的形成机理及生长动力学

将冷轧Ti/Al层状复合材料在525～625℃温度范围内退火0～128 h,并对复合材料的界面显微组织演变进行研究.结果表明,仅金属间化合物TiAl3相在Ti/Al界面形成,大多数TiAl3晶粒为细小的等轴晶,其平均尺寸从数百纳米到数微米,且随温度和/或退火时间的增加而增加,其中退火温度对晶粒尺寸的影响远大于退火时间的...     

The improvement of high temperature oxidation of Ti–50Al by sputtering Al film and subsequent interdiffusion treatment

The high temperature oxidation resistance of Ti–50Al can be improved by sputtering an Al film and subsequent interdiffusion treatment at 600 °C for 24 h in high vacuum. In these conditions, a TiAl₃ layer is formed on the surface, which exhibits good adhesion with Ti–50Al substrate and provides high oxidation resistance. Cyclic and isothermal oxidation tests show that the Ti–50Al with 3–5 μm Al film can dramatically reduce the oxidation at 900 °C in air, at which the parabolic oxidation rate constant K_p of specimen with 5 μm Al film is only about 1/15,000 of that of bare Ti–50Al. XRD and SEM results indicate that the TiAl₃ layer can promote the formation of a protective Al₂O₃ scale on the surface as well as react with γ-TiAl to form TiAl₂ during the oxidation. Simultaneously, layers of Al₂O₃/TiAl₂/Al-enriched γ-TiAl/Ti–50Al are also formed on specimens. The TiAl₂ layer thickness will decrease gradually with increasing the oxidation time. After oxidation at 900 °C for 300 h, there is a clearly discontinuous thin layer of Ti₃₇Al₅₃O₁₀ compound observed in between Al₂O₃ and TiAl₂.     

Si-modified aluminide coatings deposited on Ti46Al7Nb alloy by slurry method

Ti46Al7Nb alloy has been used as the research substrate material for the deposition of water-based slurries containing Al and Si powders. The diffusion treatment has been carried out at 950 °C for 4 h in Ar atmosphere. The structure of the silicon-modified aluminide coatings 40 μm thick is as follows: (a) an outer zone consisting of TiAl₃ phase and titanium silicides formed on the matrix grain boundaries composed of TiAl₃–type Ti₅Si₃; (b) a middle zone containing the same phase components with the matrix TiAl₃ and the silicides Ti₅Si₃, which formed columnar grains; (c) an inner zone, 2 μm thick, consisting of TiAl₂ phase. Cyclic oxidation tests were conducted in 30 cycles (690 h at high temperature) and showed a remarkably higher oxidation resistance of the Ti46Al7Nb alloy with the protective coating in comparison with the uncoated sample.     

冷轧热处理钛-铝箔制备微叠层Ti-Al系金属间化合物板材

通过钛箔、铝箔叠加烧结制备出微叠层Ti-Al系金属间化合物合金板材。对不同烧结条件下获得的板材组织和相组成进行分析。结果表明,当烧结温度到达到Al的熔点以上时,高温自蔓延反应（SHS）在Ti箔和Al箔之间发生,生成α-Ti、Ti3Al、TiAl、TiAl2和TiAl3等相;随着烧结时间的延长,α-Ti、TiAl2和TiAl3逐渐消失,最终获得包含Ti3Al和TiAl的叠层结构板材。由于铝的熔化,柯肯达尔效应和反应前、后摩尔体积的变化在烧结过程中产生大量的孔洞,随后的热压处理将孔洞消除并获得致密的合金板材。     

Microstructure and synthesis mechanism of Al-Ti-C-Sr master alloy

Al-5Ti-0.5C-8Sr (mass fraction,%) master alloy was prepared using a melt reaction method.The microstructure and synthetic process of the master alloy were investigated by optical microscopy,X-ray diffraction,scanning electron microscopy and X-ray energy-dispersive spectrum.The results show that the master alloy is composed of α(Al),TiAl3,TiC,Al4Sr and Al-Ti-Sr phases.The synthesis mechanisms of the master alloy are as follows:TiAl3 is formed through the reaction between K2TiF6 and Al melt at 850 ℃;when the melt was heated up to 1 200?1 300 ℃,TiC was formed through the reaction:Ti+C(s)=TiC(s);Al4Sr was formed through the binary uniform reaction when Sr was added into the melt;after the following solidification process in the peritectic reaction:L(Al,Sr)+α(TiAl3)→β(Al-Ti-Sr),the enwrapped structure was formed with the outer layer of Al-Ti-Sr phase and the internal layer of TiAl3 phase.     

The kinetics of two-stage formation of TiAl3 in multilayered Ti/Al foils prepared by accumulative roll bonding

The solid-state reactions of Ti/Al multilayered samples produced by Accumulative Roll Bonding (ARB) have been investigated using differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. The kinetics of the formation of the intermetallic compound TiAl₃ was highlighted. Experimental evidence and analysis of the data shows that, there was a two-stage process in the formation of TiAl₃ in the ARB Ti/Al reactive multilayered samples. Calorimetric and microstructural analyses also suggest that the interdiffusion of Al and Ti which led to solid solutions preceded the formation of intermetallic compounds. Despite the apparent chaos in the thickness of the ARB multilayered samples, the distribution of layer spacing did not become broad enough to lose the main features of the double exothermal behaviour. Isothermal DSC shows a larger Avarami constant in ARB Ti/Al multilayered structures than was found in Ti/Al thin films. A modified model based on thin films was set up to describe the kinetic characteristics of the formation of the intermetallic compound TiAl₃ in ARB samples.     

Formation of Brittle Phases During Pulsed Current Gas Tungsten Arc Welding of Titanium to Aluminum Alloys

Welding of titanium alloy TA15 to aluminum alloy Al 2024 was conducted by pulsed current gas tungsten arc welding using AlSi12 filler metal. Formation process of phases near the Ti/Al interface was discussed. Titanium and aluminum were partially fusion welded in the upper part while brazed together in the middle and bottom parts of the joint. In the upper part of the joint, intermetallics Ti₃Al + Ti₅Si₃, TiAl + Ti₅Si_3, and TiAl₃ were formed as three layers orderly from the titanium side to the weld metal. In the middle and bottom parts of the joint, intermetallics Ti₅Si₃ and TiAl₃ were formed as two layers near the Ti/Al interface.