氧化铝基复合陶瓷-金属钎焊界面的热应力

用Ag-Cu-Ti钎料钎焊SiCw／Al2O3复合陶瓷和金属时，陶瓷与钎料发生化学反应，在陶瓷表面形成由TiO、TiC等物相组成的反应层。采用有限元法，对SiCw／Al2O3复合陶瓷／反应层界面的热应力进行了计算。结果表明，复合陶瓷／反应层界面的残余应力变化急剧，最大拉应力位于晶须、基体和反应层交界处；晶须内部及其表面存在较高的双向压应力，Al2O3基体主要承受垂直于界面的拉应力；SiC晶须／反应层界面及其附近的反应产物TiC内具有较高的平行于界面的拉应力，当连接界面承受剪力作用时，SiC晶须／反应层界面和TiC处极易破坏。借助TEM和SEM观察了复合陶瓷／反应层界面区的精细结构和剪切断口形貌，并利用计算结果对观察到的现象进行了分析。     

Al2O3/SUS304 Brazing via AgCuTi-W Composite as Active Filler

Alumina ceramic (α-Al₂O₃) was brazed to stainless steel (SUS304) using an Ag-Cu-Ti + W composite filler and a traditional active brazing filler alloy (CuSil-ABA). Then, the effects of the presence of W particles and of the brazing parameters on the microstructures and mechanical properties of the brazed joints were investigated. The maximum tensile strength of the joints obtained using Ag-Cu-Ti + W composite filler was 13.2 MPa, which is similar to that obtained using CuSil-ABA filler (13.5 MPa). When the joint was brazed at 930 °C for 30 min, the tensile strengths decreased for both kinds of fillers, although the strength was slightly higher for the Ag-Cu-Ti + W composite filler than for the Ag-Cu-Ti filler. The interfacial microstructure results show that the Ti reacts with W to form a Ti-W-O compound in the brazing alloy. When there are more W particles in the brazing alloy, the thickness of the Ti _X O _Y reaction layer near the alumina ceramic decreases. Moreover, W particles added to the brazing alloy can reduce the coefficient of thermal expansion of the brazing alloy, which results in lower residual stress between the Al₂O₃ and SUS304 in the brazing joints and thus yields higher tensile strengths as compared to those obtained using the CuSil-ABA brazing alloy.     

Cf/SiC复合材料与304不锈钢钎焊接头组织与性能

采用Ti-Zr-Be活性钎料作为连接层,在一定工艺参数下真空钎焊C_f/SiC复合材料和304不锈钢.利用SEM,EDS,XRD和俄歇谱仪分析接头微观组织结构,利用剪切试验检测接头力学性能,分析了工艺参数对接头抗剪强度的影响.结果表明,在复合材料附近形成ZrC+TiC+Be₂C/Ti-Si反应层,连接层中主要包含FeZr₂,锆基固溶体,BeTi,Ti-Zr固溶体等反应产物,304不锈钢附近形成FeTi/αFe反应层.在连接温度为950℃,连接时间为60min时,接头室温抗剪强度最高为109.3 MPa,断裂位置为C_f/SiC复合材料与中间层连接界面靠近复合材料端.     

Microstructure and mechanical properties of ZrB2–SiC ultrahigh temperature ceramic composite joint using TiZrNiCu filler metal

Abstract

ZrB₂–SiC ceramic composite was brazed by using TiZrNiCu active filler metal. The microstructure and interfacial phenomena of the joints were analysed by means of SEM, energy dispersive X-ray spectroscopy and X-ray diffraction. The joining effect was evaluated by shear strength. The results showed that the reaction products of the ZrB₂–SiC ceramic composite joint were TiC, ZrC, Ti₅Si₃, Zr₂Si, Zr(s,s) and (Ti, Zr)₂ (Ni, Cu), and the microstructure was separately ZrB₂–SiC/Zr(s,s)/Ti₅Si₃+Zr₂Si+TiC+ZrC+(Ti,Zr)₂(Ni,Cu)/Zr(s,s)/ZrB₂–SiC. A conceptual interface evolution model was established to explain the interface evolution mechanism. The maximum shear strength of the brazed joints was 143·5 MPa at the brazing temperature T of 920°C and the holding time t of 10 min.     

钛基非晶态钎料钎焊高强石墨与铜的界面特征

石墨在核工业中得到广泛应用,铜与其连接起到加强散热的作用,二者间的连接问题成为必须要解决的技术关键.采用非晶态TiZrNiCu钎料箔真空钎焊紫铜与普通高强石墨,研究了工艺参数对接头界面组织的影响.结果表明,接头室温剪切和拉伸时均断于石墨母材侧,经接头微观组织分析,认为高强度的结合界面是由于钎料与石墨反应生成了TiC薄层,钎缝主要是以固溶体为基,由金属间化合物相间其中的组织结构形成的.     

C_f/SiC复合材料与钛合金Ag-Cu-Ti-C_f复合钎焊

采用Ag-Cu-Ti-Cf(Cf:碳纤维)复合钎料作中间层,在适当的工艺参数下真空钎焊Cf/SiC复合材料与钛合金,利用SEM,EDS和XRD分析接头微观组织结构,利用剪切试验检测接头力学性能.结果表明,钎焊时复合钎料中的钛与Cf/SiC复合材料反应,在Cf/SiC复合材料与连接层界面形成Ti3SiC2,Ti5Si3和少量TiC化合物的混合反应层.复合钎料中的铜与钛合金中的钛发生互扩散,在连接层与钛合金界面形成不同成分的Cu-Ti化合物过渡层.钎焊后,形成碳纤维强化的致密复合连接层.碳纤维的加入缓解了接头的残余热应力,Cf/SiC/Ag-Cu-Ti-Cf/TC4接头抗剪强度明显高于Cf/SiC/Ag-Cu-Ti/TC4接头.     

Joining of C<Subscript>f</Subscript>/SiC Ceramics to Nimonic Alloys

C_f/SiC ceramic composites have been brazed to Nimonic alloys using TiCuAg filler metal. In order to improve wettability and to provide compatibility between ceramic and metal, the C_f/SiC surface was metallized through the deposition of a chromium layer. Subsequent heat treatments were carried out to develop intermediate layers of chromium carbides. Excellent wetting of both the composite ceramic and the metal from the filler metal is observed in the fabricated joints. Shear tests show that failure occurs always within the ceramic material and not at the joint. In the filler region depletion of Ti and formation of Ag and Cu rich regions are observed. At the C_f/SiC-filler interface a layered structure of the filler metallic elements is observed. Titanium interacts with the SiC matrix to form carbides and silicides.     

Graphite-to-304SS Braze Joining by Active Metal-Brazing Technique: Improvement of Mechanical Properties

In the present investigation, an attempt has been made to improve the mechanical strength of graphite-stainless steel-brazed joint. Due to high capillary action, the liquid filler alloy usually tends to percolate into the pores of graphite causing severe stress in the graphite near the joint interface resulting in poor joint strength of 10-15 MPa. In the present investigation, a thin coating of SiC was applied on graphite before the joining process to avoid the penetration of liquid filler alloy into the pores of the graphite. Active filler alloy Ag-Cu-Ti was used to braze the substrates. The brazing was carried out at 850, 900, 950, and 1000 °C. The characterization of the interfaces of the brazed joints was carried out using scanning electron microscopy attached with energy dispersive spectroscopy and x-ray diffraction analysis. From the correlation between the microstructural and mechanical properties, shear strength of approximately 35 MPa for graphite-304SS-brazed joint produced at 900 °C was demonstrated. After the shear tests, the fracture surfaces were analyzed by SEM-EDS.     

AgCuTi-Al钎焊C_f/SiC与TC4接头分析

采用AgCuTi-Al混合粉末作为中间层,在适当的工艺参数下真空钎焊Cf/SiC复合材料和钛合金,利用扫描电镜,能谱仪和X射线衍射对接头的微观组织结构进行分析,利用剪切试验测定接头的力学性能.结果表明,在钎焊过程中,钎料中的钛与Cf/SiC复合材料中的基体SiC,碳纤维发生反应,在Cf/SiC复合材料侧形成了TiC,T...     

Ag-Cu+WC复合钎料钎焊ZrO2陶瓷和TC4合金

采用新型Ag-Cu+WC复合钎料进行ZrO₂陶瓷和TC4合金钎焊连接,探究了接头界面组织及形成机制,分析了钎焊温度对接头界面结构和力学性能的影响. 结果表明,接头界面典型结构为ZrO₂/TiO+Cu₃Ti₃O/TiCu+TiC+W+Ag_(s,s)+Cu_(s,s)/TiCu₂/TiCu/Ti₂Cu/TC4. 钎焊过程中,WC颗粒与Ti发生反应,原位生成TiC和W增强相,为Ti-Cu金属间化合物、Ag基和Cu基固溶体提供了形核质点,同时抑制了脆性Ti-Cu金属间化合物的生长,优化了接头的微观组织和力学性能. 随钎焊温度的升高,接头反应层的厚度逐渐增加,WC颗粒与Ti的反应程度增强. 当钎焊温度890 ℃、保温10 min时,复合钎料所得接头抗剪强度达到最高值82.1 MPa,对比Ag-Cu钎料所得接头抗剪强度提高了57.3%.     

Influence of In Situ Reaction on the Microstructure of SiC<Subscript>p</Subscript>/AlSi7Mg Welded by Nd:YAG Laser with Ti Filler

The effect of in situ reaction on the microstructure of Nd:YAG laser welded joints of aluminum matrix composite SiC_p/AlSi7Mg was studied. Results showed that the laser welding with Ti filler improved the tensile strength of welded joints. Moreover, the laser welding with in situ reaction effectively restrained the pernicious Al₄C₃ forming reaction in the interface between aluminum matrix and reinforcement particles. Simultaneously, the reaction-formed TiC phase distributed uniformly in the weld. This permitted SiC_p/AlSi7Mg composite to be successfully welded by Nd:YAG laser.     

Interfacial Behavior and Its Effect on Mechanical Properties of C<Subscript>f</Subscript>/SiC Composite/TiAl6V4 Joint Brazed with TiZrCuNi

In order to characterize the interfacial behavior of brazed joints and offer theoretical basis for the applications of TiZrCuNi-based composite fillers, C_f/SiC composite and TC4 were brazed by TiZrCuNi filler, and the microstructures of joints versus temperature and versus holding time were systematically studied in this paper. The mechanical properties of brazed joints were measured and analyzed. The results showed that Ti(Zr)C, Ti₅Si₃, Ti₂Cu, TiNi, TiZrCu₂, Ti₂(Cu,Ni) and Ti(s,s) were the predominant compounds in the joints. Brazing temperature had a distinct effect on the microstructures of joints: with the increase of brazing temperature, the structure of brazed joints was reduced from four parts to three parts, and the wavy reaction layer became continuous and much thicker. While holding time had a similar but weaker effect on microstructures: with the extension of holding time, the reaction layer became thicker, but it was difficult to induce the decrease in the structural parts of joint. The thickness of reaction layer determined the mechanical properties of joints. The results were beneficial for the selection of reinforced phases and the design of composite fillers to obtain better mechanical performances. When the brazing temperature was 940 °C and the holding time was 25 min, the maximum shear strength of brazed joints attained a value of 143.2 MPa.     

Using coated ceramic particles to increase wear resistance in high-speed steels

The use of chemical-vapor-deposition (CVD)-coated ceramic particle reinforcements in metal-matrix composites allows the control of reactivity at the particle/matrix interface. Wear-resistant, high-speed, steel-based composites containing uncoatedAl₂O₃ uncoated TiC, and CVD-coated A1₂O₃ were liquid-phase sintered and characterized using pin-on-disk wear testing. TiC or TiN CVD coating of Al₂O₃ resulted in a porosity decrease at the particle/matrix interface in addition to better ceramic/metal cohesion due to improved wettability. Lower wear rates were obtained with the composites containing TiC-or TiN-coated Al₂O₃.     

Microstructure and mechanical properties of the SiC/Nb joint brazed using AgCuTi+B4C composite filler metal

The residual stress is considered to be the driving force for the failure of ceramic/metal brazing joint. In this paper, the residual stress in a SiC/Nb joint is alleviated by using AgCuTi+B₄C composite brazing filler. SEM, EDS and XRD are applied to characterised the microstructure of the joint, which is determined to be SiC/Ti₃SiC₂/Ag(s,s)+Cu(s,s)+TiB+TiC/TiCu+ Nb(s,s)/Nb. The effects of the B₄C strengthening phase mass fraction and the brazing temperature on the microstructure and the mechanical properties of the joint are investigated. It is found that the reaction products between B₄C and the brazing filler (TiB whisker and TiC particles) uniformly distribute inside the joint if the mass fraction of the B₄C is not higher than 1.5 wt% and when the amount of B₄C reaches 2 wt%, the reaction products begin to agglomerate. With the rising of the brazing temperature, the thickness of the Ti₃SiC₂ reaction layer next to the ceramic increases and when the brazing temperature reaches 910 °C, another reaction layer of Ti₅Si₃ can be found adjacent to the Ti₃SiC₂ reaction layer. The strength of the joint first increases and then decreases with the increase of both the strengthening phase and the brazing temperature. The highest shear strength of the joint reaches 98 MPa when the joint is achieved at 890 °C using AgCuTi+1.5 wt%B₄C brazing filler.     

α‐Fe layer formation during metal dusting of iron in CO‐H2‐H2O gas mixtures

The formation of an α‐Fe layer between cementite and graphite was observed and investigated during metal dusting of iron in CO‐H₂‐H₂O gas mixtures at both 600°C and 700°C. The condition to form this phenomenon is determined by the gas composition which depends on temperature. The iron layer formation was observed for CO content less than 1 % at 600°C and less than 5 % at 700°C. With increasing CO contents, no α‐Fe layer was detected at the cementite/graphite interface by optical microscopy. In this case cementite directly contacts with the coke layer. The morphologies of the coke formed in the gas mixtures with low CO contents were also analysed. Three morphologies of graphite have been identified with 1 % CO at 600°C: filamentous carbon, bulk dense graphite with columnar structure, and graphite particle clusters with many fine iron containing particles embedded inside. At 700°C with 5 % CO the coke mainly consists of graphite particle clusters with some filamentous carbon at the early stage of reaction. Coke analysis by X‐ray diffraction shows that both α‐Fe and Fe₃C are present in the coke. The mechanism of α‐Fe accumulation between cementite and graphite is discussed in this paper.     

Reaction layer characterization of the braze joint of silicon nitride to stainless steel

This investigation studies the role of titanium in the development of the reaction layer in braze joining silicon nitride to stainless steel using titanium-active copper-silver filler metals. This reaction layer formed as a result of titanium diffusing to the filler metal/silicon nitride interface and reacting with the silicon nitride to form the intermetallics, titanium nitride (TiN) and titanium suicide (Ti ₅Si₃). This reaction layer, as recognized in the literature, allows wetting of the ceramic substrate by the molten filler metal. The reaction layer thickness increases with temperature and time. Its growth rate obeys the parabolic relationship. Activation energies of 220.1 and 210.9 kj/mol were calculated for growth of the reaction layer for the two filler metals used. These values are close to the activation energy of nitrogen in TiN (217.6 kj/mol). Two filler metals were used in this study, Ticusil (68.8 wt% Ag, 26.7 wt% Cu, 4.5 wt% Ti) and CB4 (70.5 wt% Ag, 26.5 wt% Cu, 3.0 wt% Ti). The joints were processed in vacuum at temperatures of 840 to 900 °C at various times. Bonding strength is affected by reaction layer thickness in the absence of Ti-Cu intermetallics in the filler metal matrix.     

复合钎料钎焊Al_2O_3接头剪切应力场的数值模拟

对Al2O3颗粒增强复合钎料钎焊Al2O3/Al2O3接头的残余应力场进行了数值模拟,分析了Al2O3陶瓷颗粒的加入对陶瓷接头残余剪切应力的影响.模拟发现,陶瓷接头的最大应力位于陶瓷-钎缝界面,陶瓷颗粒的加入对钎焊接头应力起到了缓解作用,其缓解程度随陶瓷颗粒体积分数的增加而增大;在陶瓷颗粒百分比一定的情况下,钎缝厚度的...     

碳化硅复合材料与碳钢钎焊接头的抗剪强度及微观结构

采用磁控溅射镀膜技术对碳/碳化硅复合材料(C/SiC)表面进行镀Ti金属化,以AgCu₂₈为钎料,无氧铜为中间层与碳钢进行钎焊连接. 研究无氧铜中间层、Ti膜厚度和钎焊温度对接头组织形貌和力学性能的影响. 结果表明,采用无氧铜中间层可有效降低接头的残余应力,提高接头强度,并阻挡C/SiC复合材料中的Si元素在钎焊过程中扩散至碳钢侧,防止了碳钢界面FeSi_x恶性反应层的形成. 在试验范围内,钛膜厚度和钎焊温度与接头抗剪强度之间均存在峰值关系. 860 ℃,3 μm Ti膜接头平均抗剪强度最高,达到25.5 MPa. 由剪切试样碳钢侧断口,可观察到大量平行断口方向的碳纤维和碳纤维脱粘坑. 断裂发生在C/SiC复合材料内部距界面约300 μm处. C/SiC界面反应产物以Ti₅Si₃为主,含少量TiC. 钎缝中有TiCuSi相生成.     

Microstructure and wear properties of TiC/FeCrBSi surface composite coating prepared by laser cladding

Titanium carbide particles reinforced Fe-based surface composite coatings were fabricated by laser cladding using a 5 kW CO₂ laser. The microstructure, phase structure and wear properties were investigated by means of scanning electron microscopy, transmission electron microscopy and X-ray diffraction, as well as dry sliding wear test. The results showed that TiC carbides were formed via in situ reaction between ferrotitanium and graphite in the molten pool during the laser-clad process. The morphology of TiC is mainly cubic and dendritic form; and the TiC carbides were distributed uniformly in the composite coating. The TiC/matrix interface was found to be free from cracks and deleterious phases. The coatings reinforced by TiC particles revealed higher wear resistance and lower friction coefficient than that of the substrate and FeCrBSi laser-clad coating.     

Microstructural characterization of diamond/CBN grains steel braze joint interface using Cu–Sn–Ti active filler alloy

In order to develop the new generation superhard abrasive tools of diamond and cubic boron nitride (CBN), the brazing joint experiments of diamond/CBN crystals and AISI 1045 steel matrix using Cu–Sn–Ti active filler powder alloy were investigated in vacuum furnace. The brazing temperature was 930 °C and the dwelling time was 20 min. Interfacial characteristics of the brazing joint among the diamond/CBN grains, the active filler layer and the steel substrate were analyzed using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction techniques. The results indicated that Ti element in the Cu–Sn–Ti alloys diffused preferentially to the surface of diamond/CBN grits to form a Ti-rich reaction layer in the brazed joints by microanalyses. Moreover, the TiC, TiN and TiB₂ phases in diamond/CBN interface and Cu–Ti phase in steel interface were confirmed by X-ray diffraction phase analysis. The wetting and bonding reactions on diamond/CBN by melting Cu–Sn–Ti alloy were realized through the interfacial reaction products like TiC, TiN and TiB₂ compounds during the brazing process. The adhesive strength experiments of the joint interfaces revealed that the grains were not pulled out from the bond interface. The reliable bonding strength of brazed diamond/CBN grains to the steel substrate can meet the application requirements of high efficiency machining in the industrial field.