活性钎焊法连接碳化硅陶瓷的连接强度和微观结构

采用三元Ag-Cu-Ti活性焊料连接常压烧结碳化硅陶瓷,研究了反应温度、保温时间等钎焊工艺对碳化硅陶瓷连接强度的影响,分析了连接界面的微观结构和反应产物. 实验结果表明,在实验范围内,钎焊温度和保温时间对碳化硅陶瓷的连接强度均有峰值,四点弯曲强度最高达到342MPa,随着钎焊温度的升高,界面反应层厚度增加,连接强度提高,但过高的钎焊温度引起焊料的挥发而使连接强度下降. 焊料中的活性元素Ti与碳化硅发生反应在连接界面形成均匀致密的反应层,反应层厚度约1μm,XRD和EDX能谱分析结果表明反应产物是TiC和Ti₅Si₃.     

SiC陶瓷与316L不锈钢真空活性钎焊北大核心CSCD

采用Ag-Cu-Ti活性钎料,通过真空钎焊方法进行了SiC陶瓷与316L不锈钢的连接,研究了接头的界面组织、特征点成分和物相,并探讨了钎焊温度(800～930℃)、保温时间(0～30 min)对接头界面组织和连接强度的影响。结果表明,SiC陶瓷与316L不锈钢钎焊抗剪断口均发生在SiC陶瓷与钎料连接界面处,由于活性元素Ti的作用,在陶瓷与钎料的界面处形成了连续的反应层,反应生成了Ti C和Ti5Si3;在316L不锈钢与钎料的界面处,生成了Fe-Ti化合物和Cu-Ti化合物。随着钎焊温度升高及保温时间延长,接头强度均呈现出一个峰值,在温度为900℃,保温20 min的工艺条件下可获得最大接头抗剪强度。     

SiC陶瓷与316L不锈钢真空活性钎焊

采用Ag-Cu-Ti活性钎料,通过真空钎焊方法进行了SiC陶瓷与316L不锈钢的连接,研究了接头的界面组织、特征点成分和物相,并探讨了钎焊温度(800～930℃)、保温时间(0～30 min)对接头界面组织和连接强度的影响。结果表明,SiC陶瓷与316L不锈钢钎焊抗剪断口均发生在SiC陶瓷与钎料连接界面处,由于活性元素Ti的作用,在陶瓷与钎料的界面处形成了连续的反应层,反应生成了Ti C和Ti5Si3;在316L不锈钢与钎料的界面处,生成了Fe-Ti化合物和Cu-Ti化合物。随着钎焊温度升高及保温时间延长,接头强度均呈现出一个峰值,在温度为900℃,保温20 min的工艺条件下可获得最大接头抗剪强度。     

Si3N4复相陶瓷半固态连接的接头组织和界面反应

根据复合材料的强化原理,用Ag-Cu-Ti钎料和TiN颗粒作为复合连接材料在半固态下连接Si3N4复相陶瓷以提高接头强度,研究了接头的组织和界面反应.结果表明,接头由母材/反应层/含微量Ti的Ag-Cu TiN/反应层/母材组成,反应层由含Ti、Si、N三种元素的一些化合物组成;TiN颗粒在Ag-Cu基体中的分布总体均匀,两者之间的界面清晰、结合致密:当TiN的加入量较小时,对连接材料与母材的界面反应没有明显影响.初步的剪切试验结果表明,采用Ag-Cu-Ti加TiN颗粒作为复合连接材料连接Si3N4陶瓷可以提高接头强度.     

Ti基复合材料界面反应扩散的微观分析

通过SiC连续纤维增强Ti基复合材料的制备及在不同条件下的热处理试验,利用TEM,SEM,EDS及XRD分析技术研究复合材料的界面反应以及产物相的形成.研究结果表明:SiC /Ti复合材料界面发生了反应扩散,反应元素C,Ti,Si在界面反应层中出现浓度波动;界面反应产物被确认为是Ti3SiC2 ,TiC和 Ti5Si3,在靠近SiC侧出现Ti3SiC2和Ti5Si3单相区,靠近Ti基体侧为Ti5Si3单相区,中间为TiC Ti5Si3双相区;SiC/Ti复合材料界面相序列为SiC┃Ti3SiC2┃Ti5Si3┃TiC Ti5Si3┃Ti5Si3┃Ti.     

SiC陶瓷真空钎焊接头显微组织和性能

在高真空条件下采用Ti-35Zr-35Ni-15Cu(质量分数/%)钎料对SiC陶瓷进行了钎焊连接,研究了接头界面组织的形成过程以及工艺参数对接头性能的影响。结果表明:钎料与SiC陶瓷发生了复杂的界面反应,生成了多种界面产物。当钎焊温度为960℃,保温时间为10min时,SiC陶瓷侧形成了连续的TiC和Ti5Si3+Zr2Si层,同时Ti5Si3+Zr2Si向钎缝中心生长呈长条状。SiC陶瓷到接头钎缝中心的显微组织依次为:SiC/TiC/Ti5Si3+Zr2Si/Zr(s,s)/Ti(s,s)+Ti2(Cu,Ni)/(Ti,Zr)(Ni,Cu)。钎焊温度为960℃,保温时间为30min时,长条状的Ti5Si3+Zr2Si贯穿了整个接头。钎焊接头强度随着钎焊温度的升高和钎焊时间的延长都呈现先增大后减小的趋势。当钎焊温度为960℃,保温时间为10min时,接头的剪切强度最高,达到了110MPa。     

Zr对(Ag-Cu-Ti)-SiCp钎焊SiC陶瓷/钛合金连接层组织结构的影响

使用Ag-Cu-Ti合金粉,SiC粉和Zr粉组成的混合粉末钎料,真空无压钎焊再结晶SiC陶瓷与Ti合金,观察Zr加入前后接头连接层组织结构的变化,研究了Zr的作用．结果表明,Zr加入前,连接层主要由Ag、SiC、Cu—Ti、Ti3SiC2、和Ti-Si相组成．Zr加入后,连接层主要由SiC、Ti1-xC、Ti-Si、AgTi和AgCu4Zr相组成．Zr的加入提高了连接层中Ti的活度,使SiC颗粒表面反应层Ti3SiC2转变,生成了Ti1-zC和TiSi相;提高了Ti与SiC颗粒的反应速度,使SiC颗粒减少;促进Ti与Ag的反应,生成了AgTi．Zr的加入导致连接层流动性的改善、连接层与SiC陶瓷界面结合强度的提高和接头热应力的降低,适量Zr的加入使接头剪切强度明显提高（达23．6MPa）．     

碳化硅质焊料连接氮化硅/碳化硅陶瓷的性能研究

采用以碳化硅为主相的焊料,在无压的条件下,连接氮化硅结合碳化硅陶瓷.结果表明:焊料在室温到1323K的干燥和烧结过程中,体积稳定,稍有膨胀.在1173K保温3h的条件下,连接的样品拉伸强度达到1.76MPa,热震残余强度保持率为82%.接头致密,并且焊料层与母材显微结构非常相似,界面处有明显的元素扩散,这对于提高结合强度和热震性能有重要作用.     

用Fe粉坯连接SiC陶瓷的工艺研究

以Fe金属粉压坯作为连接材料,采用高温钎焊连接工艺连接反应烧结SiC陶瓷.通过正交实验得到了最佳连接工艺为：保温时间3 min,连接温度1250℃,降温速率为5℃/min,压坯厚度0.6mm（0.375g）.弯曲实验结果表明,采用该工艺得到的接头最大弯曲强度为13.6MPa.界面SEM分析表明,不同工艺下得到的接头界面微观结构相似,连接界面形成了2个反应层,相应的界面微观结构为SiC/反应层1,反应层2,反应层1/SiC.反应层1与SiC形成了紧密的连接,反应层1,反应层2界面处各相相互咬合在一起.     

铬含量和烧结工艺对Fe_3Si基合金涂层组织结构的影响

目前,关于以碳化硅粉、铬粉为原料原位生成Fe_3Si基合金涂层的研究鲜见报道。以碳化硅、铬粉为主要原料,以聚氧硅烷为胶粘剂,采用无压烧结技术在Q235钢基体表面制备Fe_3Si基合金涂层,采用扫描电镜、能谱仪和X射线衍射仪分析涂层的形貌和结构,并测试涂层的硬度,研究了Cr含量和烧结工艺对Fe_3Si基合金涂层性能的影响。结果表明:Cr元素对SiC的分解有助催化作用,有利于Fe_3Si基合金涂层的生成;Cr含量低时,涂层组织由Fe_3Si相和石墨相组成;随着Cr含量增加,涂层中的石墨相转变为硬质的(Fe,Cr)_7C_3相,形成Fe_3Si相+(Fe,Cr)_7C_3相的组织结构,涂层与基体连接更加紧密,涂层硬度提高,Cr/SiC质量比为0.6~0.8时,所得膜层质量较好;制备Fe_3Si基合金涂层较合适的烧结工艺为真空,烧结温度1 120℃,保温时间60 min。     

Joint strength and interfacial microstructure in silicon nitride/nickel-based Inconel 718 alloy bonding

Joining of Inconel 718 alloys to silicon nitrides using Ag–27Cu–3Ti alloys was performed to investigate the microstructural features of interfacial phases and their effect on joint strength. The Si3N4/Inconel 718 alloy joints had a low shear strength in the range 70.4–46.1 MPa on average, depending on joining temperature and time. When the joining time was held for 1.26 ks at 1063 K, shear, tension, and four-point bending strength were 70.4, 129.7, and 326.5 MPa on average. The microstructures of the joints typically consisted of six types of phases. They were TiN and Ti5Si4 between silicon nitride and filler metal, a copper- and silver-rich phase, island-shaped Ti–Cu phase, a Ti–Cu–Ni alloy layer between filler and base metal, and diffusion of titanium into the Inconel 718 alloys. With increasing joining temperature, the thickness increase of the Ti–Cu–Ni alloy layer was much greater than that of the reaction layer. Thus the diffusion rate of titanium into the base metal was much greater than the reaction rate with silicon nitride. This behaviour of titanium results in the formation of a Ti–Cu–Ni alloy layer in all the joints. The formation of these layers was the cause of the strength degradation of the Si3N4/Inconel 718 alloy joints. This fact was supported by the analyses of fracture path after four-point bending strength tests.     

Joining of Si-Ti-C-O fibre-assembled ceramic composites with 72Ag-26Cu-2Ti filler metal

Si-Ti-C-O fibre-assembled ceramic composites were joined with 72Ag-26Cu-2Ti filler metal at 1123 K and 1223 K in vacuum. The composites consisted of Si-Ti-C-O fibres, which were assembled unidirectionally, and oxide material filling the spaces between the fibres. During the joining process, frothing occurred at the joining interfaces. Joining interfaces were observed by SEM and analysed by electron probe microanalysis and X-ray diffraction. The strength of the joints was evaluated by four-point bending tests. Most of Si-Ti-C-O fibre/filler metal interfaces and the oxide material/filler metal interfaces were firm without cracking and separation. At the fibre/metal interfaces, a high concentration of titanium was confirmed. Among the specimens joined at 1123 K, the average strength, measured by the bending test, was 96 MPa. It was inferred that the defects at the joining interfaces formed by frothing had decreased the strength of the joints. Metallizing of the surfaces to be joined with the same filler metal as a pretreatment before joining, was effective in preventing frothing during joining and improving the joining strength. The average strength of the joints with pretreatment was 211 MPa.     

树脂基多孔碳孔结构对Cf/SiC复合材料连接性能的影响

连接技术是实现大尺寸以及复杂构型C_f/SiC复合材料制备及工程化应用的关键技术。本工作使用酚醛树脂作为碳源, 通过反应连接法实现了C_f/SiC复合材料的稳定连接, 研究了多孔碳坯的体积密度和孔径对接头连接性能和微观结构的影响, 讨论了惰性填料含量对接头连接性能和显微组织的影响。研究表明: 树脂基多孔碳素坯的体积密度和孔径分别选定在0.71~0.90 g·cm^-3和200~600 nm比较合适, 随着多孔碳素坯孔径增加, 游离硅尺寸逐渐增大; 当孔径为190 nm时, 连接件强度最大为(125±12) MPa。添加SiC惰性填料可以明显减小多孔碳素坯的体积收缩, 当SiC惰性填料质量分数为50%时, 连接件强度最高达到(216±44) MPa, 基本与基体材料强度相当。总体而言, 本研究为实现C_f/SiC复合材料稳定连接提供了理论指导, 对实现复杂形状或大型C_f/SiC复合材料的制备和工程应用具有重要意义。     

Joining of Silicon Carbide Using MgO-Al2O3-SiO2 Filler

Pressureless sintered SiC specimens were joined using MgO-Al2O3-SiO2 (MAS) filler. MAS filler showed excellent behaviour of wetting on SiC substrate above 1480 °C, and the wettability was much influenced by the joining atmosphere. The joining was carried out at 1500 and 1600 °C for 30 min in Ar atmosphere. The flexural strength of the joined specimen showed 342–380 MPa up to 800 °C. However, the flexural strength of the joined specimen decreased to about 80 MPa at 900 °C due to softening of the joint interlayer. The results of the XRD and WDS showed that the reaction between SiC and the MAS filler produced the oxycarbide glass.     

高体积比SiCp/6063Al复合材料的铝基钎料制备及钎焊工艺研究

采用快速甩带技术制备了(Al-10Si-20Cu-0.05Ce)-1Ti(质量分数/％)急冷箔状钎料,并对60％体积分数的SiCp/6063Al复合材料进行真空钎焊实验,然后对钎料及接头的显微组织与性能进行测定和分析.结果表明,急冷钎料的微观组织细小、成分均匀,厚80～90μm,主要包含Al、CuAl2、Si和Al2Ti等相.当升高钎焊温度(T/℃)或延长保温时间(t/min),SiCp/钎料界面的润湿性改善,6063Al基体/钎料间互扩散和溶解作用增强,接头连接质量逐渐提高.当T=590℃、t=30 min时,接头抗剪强度达到112.6MPa;当T=590℃、t=50 min时,少量小尺寸SiCp因液态钎料排挤而分散于钎缝,因加工硬化而使接头强度递增7.3％.然而,当T≥595℃、t≥60 min时,SiCp偏聚于钎缝,导致接头组织恶化,且剪切断裂以脆性断裂为主.综合考虑钎焊成本与接头强度使用要求,确定最佳钎焊工艺为590℃、30 min.     

Microstructure and strength of brazed joints of Ti3Al-base alloy with different filler metals

The interfacial microstructure and properties of brazed joints of a Ti₃Al-based alloy were investigated in this paper to meet the requirements of the use of Ti₃Al-based alloy in the aeronautic and space industries. The effects of different brazing fillers on the interfacial microstructure and shear strength were studied. The relationship between brazing parameters and shear strength of the joints was discussed, and the optimum brazing parameters were obtained. The brazed joints were qualitatively and quantitatively analyzed by means of EPMA, SEM and XRD. The results showed that using a AgCuZn brazing filler, TiCu, Ti(Cu,Al)₂ and Ag[s,s] were formed, the shear strength of the joint was decreased because of the formation of TiCu and Ti(Cu,Al)₂; using a CuP brazing filler, Cu₃P, TiCu and Cu[s,s] were formed at the interface of the joint, the former two intermetallic compounds decreased the shear strength. The analysis also indicated that using the TiZrNiCu brazing filler, the optimum parameters were temperature T=1323 K, joining time t=5 min, and the maximum shear strength was 259.6 MPa. For the AgCuZn brazing filler, the optimum parameters were joining temperature T=1073 K, joining time t=5 min, and the maximum shear strength was 165.4 MPa. To the CuP brazing filler, the optimum parameters were joining temperature T=1223 K, joining time t=5 min, and the maximum shear strength is 98.6 MPa. Consulting the results of P. He, J.C. Feng and H. Zhou [Microstructure and strength of brazed joints of Ti₃Al-base alloy with NiCrSiB, Mater. Charact., 52(8) (2004) 309–318], relative to the other brazing fillers, TiZrNiCu is the optimum brazing filler for brazing Ti₃Al-based alloy.     

Joining of carbon/carbon composites for nuclear applications

Using hot pressing, carbon/carbon composites were joined using a Ti₃SiC₂/SiC interlayer which was in situ synthesized by the reaction of TiC and Si. Phase composition of the interlayer was characterized by X-ray diffraction. Morphologies of the joints before and after shear test were determined by scanning electron microscope and energy dispersive spectroscopy. The mechanical strength of the joints was assessed by shear strength test. Phase analysis reveals that the interlayer was mainly composed of ternary Ti₃SiC₂, SiC, and little TiC. The microstructure observation results show that the dense and uniform interlayer adheres firmly to the C/C composites. A composition gradient reaction layer was formed at the joining interface between C/C substrates and interlayer. The room temperature average shear strength of the joints is about 38.9 ± 3.6 MPa. The joining mechanism and failure behavior of the joints were also discussed.     

Joining of C/C composite to TC4 using SiC particle-reinforced brazing alloy

Silicon carbide particles were used as reinforcement in the Ag-26.7Cu-4.6Ti (wt.%) brazing alloy for joining C/C composite to TC4 (Ti-6Al-4V, wt.%). The mechanical properties of the brazed joints were measured by shear strength testing. The effects of the volume percentage of SiC particles on the microstructures of the brazed joints were investigated. It is shown that the maximum shear strength of the joints is 29 MPa using 15 vol.% SiC in the brazing alloy which is greater than that with Ag-26.7Cu-4.6Ti brazing alloy alone (22 MPa). Ti is reacted with SiC particles, forming Ti–Si–C compound in the particle-reinforced brazing alloy. Due to this, more SiC particles in the brazing alloy, the thickness of TiC/TiCu reaction layer near C/C composite decreases. Moreover, SiC particles added to the brazing alloy can reduce the CTE of the brazing alloy which results in lower residual stress in the C/C composite-to-metal joint. Both of the above reasons lead to the increasing of the shear strength of the brazed joints. But excessive SiC particles added to the brazing alloy lead to pores which results in poor strength of the brazed joint.     

Transient liquid-phase insert metal bonding of Al2O3 and AISI 304 stainless steel

Transition liquid-phase insert metal bonding of Al2O3 and AISI 304 stainless steel based materials is investigated. This joining technique allows the continuous replenishment of the active solute which is consumed by the chemical reaction that occurs at the ceramic/filler metal interface. Replenishment is facilitated by employing a sandwich of filler materials comprising tin-based filler metal and amorphous Cu50Ti50 or NiCrB interlayers. During Al2O3/AISI 304 stainless steel bonding, the highest shear strength properties are produced using a bonding temperature of 500 °C. Thick reaction layers containing defects form at the ceramic/filler material interface when higher bonding temperatures are applied. Bonding at temperatures above 500 °C also increases the tensile residual stress generated at the periphery of Al2O3/AISI 304 stainless steel joints. The shear strength of joints produced using NiCrB interlayers markedly increased following heat treatment at 200 °C for 1.5 h. Heat treatment had little influence on the shear strength of the joint produced using Cu50Ti50 interlayers. This revised version was published online in November 2006 with corrections to the Cover Date.