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.     

钎缝间隙对316L不锈钢真空钎焊接头组织的影响

采用镍基钎料BNi2+40%BNi5对316L不锈钢进行真空钎焊。主要通过光学显微镜、电子探针显微分析仪、硬度计等研究了3种钎缝间隙下钎焊接头的显微组织、钎缝成分分布以及钎缝显微硬度。结果表明316L不锈钢的钎焊接头主要由固溶体、共晶组织及网状化合物组成,硼、硅是导致化合物相产生的主要合金元素;随着钎缝间隙的减小,钎焊接头中金属间化合物相的含量逐渐减小,当钎缝间隙为30μm时,接头组织基本为固溶体。     

Vacuum brazing of NiTi alloy by AgCu eutectic filler

Abstract

Joining of NiTi alloy to itself has been realised by vacuum brazing process using AgCu28 eutectic as filler metal. Microstructures, mechanical and shape memory behaviour have been investigated. The shearing strength of the brazed joint exceeds 100 MPa, and rupture occurs at the diffusion layer of parent metal beside brazing metal. The brazed joint will be stronger than parent metal on condition of the specimen with a joint of lap length 10 times of plate thickness. The brazed specimen shows a good shape memory behaviour. From the point of view of practice, the brazing joint design principle and brazing quality improvement have been discussed.     

Cu-P-Sn-Ni钎料真空钎焊MGH956合金的研究

为扩展Cu-P基钎料在连接MGH956合金中的应用,采用新型Cu-P-Sn-Ni钎料对MGH956合金在800~890℃进行了真空钎焊,研究了不同钎焊温度和保温时间对焊缝组织及力学性能的影响.结果表明:在所研究的钎焊温度范围内保温5 min均可获得成形效果良好的钎焊接头,其主要由钎缝中心区和界面反应层组成,其中,钎缝中心区由α(Cu)固溶体基体和化合物Cu_3P+(Fe,Ni)_3P+FeCr组成,反应层由α(Fe)固溶体、Fe_3P和Cu_3P组成;随着钎焊温度的升高,反应层厚度逐渐增加,钎缝中心区中的化合物Cu_3P+(Fe,Ni)_3P+FeCr的形态也随之发生明显改变;各钎焊温度下获得的钎焊接头经室温拉伸,断裂均发生在钎缝中心区,断口形貌呈现韧性和脆性的混合断裂特征.830℃钎焊5 min的接头抗拉强度最大,为510.3 MPa,达到了母材抗拉强度的70.9%.     

Intermetallic compounds formed during brazing of titanium with aluminium filler metals

The effect of aluminium filler metal composition on the formation of AI-Ti intermetallic compounds was investigated in brazed aluminium-to-titanium (Al/Ti) joints and titanium-totitanium (Ti/Ti) joints. The clearance filling ability was also studied. In Ti/Ti joints, the thickness of the intermetallic compound layer was strongly dependent on the aluminium filler metal composition, whereas the clearance filling ability was independent of the composition. The maximum intermetallic compound layer thickness was observed in 99.99% highly pure aluminium filler metal; therefore all additional elements reduced the layer thickness. Above all, the addition of 0.8% Si greatly reduced the thickness. After brazing at 680° C for 3 min, the intermetallic compound formed by Al-0 to 0.8% Si filler metal was found to be of type Al₃Ti. Other compounds, of types Ti₉Al₂₃ and Ti₇Al₅Si₁₂, were also found in joints brazed by Al-3 to 10% Si filler metals. AI-0.8% Si filler metals maintained a higher joint strength than pure aluminium filler metal under brazing conditions of high temperature and long heating time. In Al/Ti joints, AI-Cu-Sn and AI-Cu-Ag filler metal mainly formed Al₃Ti, and Al-10Si-Mg filler metal mainly formed Ti₇Al₅Si₁₂ at the brazed interface of the titanium side after brazing at 600 to 620° C.     

22Ti-78Si高温共晶钎料对SiC陶瓷的钎焊连接

利用非自耗电弧熔融技术制备的22Ti-78Si (wt%)高温共晶钎料实现SiC陶瓷连接. 采用SEM、材料试验机研究了工艺参数对钎焊接头的组织结构、强度和断口形貌的影响规律. 结果表明: 在钎焊温度1380~1420℃、保温时间5~20min、钎料厚度50~200 μm条件下, 均能实现SiC陶瓷连接, 在1400℃、保温时间10min和钎料厚度100μm的条件下, SiC/22Ti-78Si/SiC接头剪切强度最大值可达125MPa.     

Joining of SiC fibre reinforced borosilicate glass matrix composites to molybdenum by metal and silicate brazing

The brazing of SiC fibre reinforced borosilicate glass matrix composites with Mo plates has been investigated. Molybdenum was chosen as the metallic partner under consideration of system requirements, e.g. thermomechanical stability at temperatures of interest (500–750^∘C), and physical properties, e.g. coefficient of thermal expansion close to that of the glass matrix composite. Two brazing filler materials were investigated: a glass braze (Schott G018-174) and an active filler metal (Incusil ABA, brazing temperature = 740^∘C). When using the glass braze the surface of the metal had to be roughened to ensure a bond of significant strength. Vacuum brazing with the active filler metal resulted in joints with high strength, which allows to fully utilise the mechanical competence of the glass matrix composite when the joint configuration is adapted to the relevant loading conditions. A novel design of a tool for hot glassware handling, made of glass matrix composite/Mo joints, is presented.     

铝基钎料在SiC及SiC_p/6061复合材料上的润湿性研究

对多种铝基钎料在SiC、6 0 6 1及SiCp 6 0 6 1复合材料上进行了润湿性试验。结果表明 :炉中钎焊时 ,钎料与钎剂的成分、加热温度与保温时间、钎料与钎剂熔化温度的匹配等是影响铝基钎料润湿性的主要因素 ;真空钎焊时 ,镁含量不同的各种含镁Al 2 8Cu 5Si钎料在Al基复合材料连接的温度范围内都不能润湿SiC陶瓷表面 ;配合QJ2 0 1钎剂 ,Al 2 8Cu 5Si 2Mg钎料对 15 %SiCp 6 0 6 1Al复合材料具有良好的润湿性 ,但对 30 %SiCp 6 0 6 1Al复合材料却润湿不良 ;在加钎剂的情况下 ,钎料中的镁反而对在铝合金及铝基复合材料上的润湿性有不利影响 ;在Al 2 8Cu 5Si 2Mg钎料和 15 %SiCp 6 0 6 1Al复合材料的钎焊界面处存在SiC颗粒的偏聚现象     

Preliminary investigation on joining performance of SiCp-reinforced aluminium metal matrix composite (Al/SiCp–MMC) by vacuum brazing

The present study has investigated the joining performance of SiC particulate reinforced aluminium metal matrix composite (Al/SiC_p–MMC) by vacuum brazing process. After the joints brazed with Al–Si–Mg foil brazing filler metal at different brazing batches, both the mechanical properties and the microstructures of brazed joints were estimated. Moreover, the influence of SiC_p size, SiC_p volume percentage and the brazing parameters on bonding quality of the joints have also been discussed in detail. The results have revealed that the bonding quality either in SiC_p/Al interface or in SiC_p/SiC_p interface belongs to weak bonding, and the results also show that under the same brazing parameters condition, the strength of brazed joints decreases along with increasing the SiC_p volume percentage. In addition, the results also indicate that for a constant SiC_p volume percentage the strength of brazed joints decreases when SiC_p size increases. These results are very useful for the joining design of discontinuously reinforced metal matrix composites and further for the optimum design of composition of composites.     

Infrared brazing Inconel 601 and 422 stainless steel using the 70Au-22Ni-8Pd braze alloy

Infrared brazing Inconel 601 and 422 stainless steel using the 70Au-22Ni-8Pd braze alloy is performed in the experiment. The brazed joint is primarily comprised of Au-rich and Ni-rich phases, and there is no interfacial intermetallic compound observed in the joint. The (Ni,Fe)-rich phase is observed at the interface between 422SS and the braze alloy, and the Ni-rich phase is found at the interface between the braze alloy and IN601. With increasing the brazing temperature and/or time, the microstructures of the brazed joint is coarsened. For the infrared brazed joint at 1050^∘C for 180 s shows the highest average shear strength of 362 MPa. In contrast, the shear strength of the infrared brazed joint is higher than that of the furnace brazed specimen due to coarsening of the microstructure in the furnace brazed joint.     

Interface characteristics and mechanical properties of the induction brazed joint of magnesium alloy AZ31B with an Al-based filler metal

In this paper, wrought magnesium alloy AZ31B sheets were brazed by means of high-frequency induction heating device using a novel Al-based filler metal in argon gas shield condition. The interfacial microstructure, phase constitution and fracture morphology of the brazed joint were studied. The experimental results show that α-Mg solid solution and β-Mg₁₇Al₁₂ phase were formed in brazing region. Moreover, the homogeneous Mg₃₂(Al, Zn)₄₉ phase in the original Al-based filler metal disappeared entirely after the brazing process due to the fierce alloying between the molten filler metal and the base metal during brazing. Test results show that the shear strength of the brazed joint is 45 MPa. The fracture morphology of the brazed joint exhibits intergranular fracture mode and the crack originates from the hard β-Mg₁₇Al₁₂ phase.     

The effect of processing variables on the microstructures and properties of aluminum brazed joints

Aluminum brazed joints are used extensively in the automotive and aircraft industries. In order to insure the integrity of the bond, the effects of processing variables on the quality of the bond must be understood. The effects of brazing period and joint thickness on the microstructure, tensile properties, microhardness and micromechanisms of failure of two aluminum alloy 3003 plates connected by a layer of 4047 aluminum filler material were investigated. It was found that the amount of aluminum-silicon eutectic microstructure in the reaction zone decreased with increasing brazing period and decreasing joint thickness. This was attributed to silicon diffusion from the joint material and dissolution of base metal and its entrance into the liquid joint. The amount of shrinkage porosity in the reaction zone was found to increase with increasing brazing period due to base material solutioning. The ultimate tensile strength of joints decreased with increasing brazing period and decreasing joint thickness. This was attributed to the joint microstructure and shrinkage porosity formed in the joint. Shrinkage porosity was found to be the primary cause of decreased joint strength. Joints with 10 minutes brazing period failed within the base material, while for brazing periods greater than 10 minutes, joints failed within the aluminum-silicon eutectic microstructure of the reaction zone. This indicated that the joint strength was greater than the base material for joint with brazing period of 10 minutes. Finite element analysis was performed to determine the effect of joint material yield strength and joint thickness on the stress and strain field in the brazed joint. Finite element analysis results supported experimental observations.     

Ni-Cr-P焊膏钎焊C/C复合材料的组织和性能

用真空熔炼、惰性气体雾化法制备Ni-Cr-P金属粉末,再加入有机黏结剂高速搅拌,制备Ni14Cr10P膏状活性钎料。用制备好的焊膏真空钎焊C/C复合材料,测试钎焊接头的剪切强度,通过OM,SEM,EDS,XRD等对钎焊接头界面组织结构进行分析。结果表明:在钎焊温度1000℃、保温时间0.5 h条件下,获得的接头剪切强度达到28.6 MPa,然后随着钎焊温度上升或保温时间延长,钎焊接头强度下降;通过界面组织结构分析发现焊膏可以增加钎料层与C/C复合材料表面的接触面积,有利于堵塞C/C复合材料表面的孔隙。焊后在界面处形成了交错分布的Cr碳化物相缓冲层,使得界面呈现热膨胀系数梯度增加的结构,有助于缓解热失配,提高C/C复合材料钎焊接头强度。     

Effect of holding time on vacuum brazing for a stainless steel plate–fin structure

This paper presents a vacuum brazing of 304 stainless steel plate–fin structures with nickel-based BNi-2 filler metal. The effect of brazing holding time on tensile strength and microstructure has been investigated, aiming to obtain the optimal brazing holding time. The microstructure in brazing joint consists of diffusion-affected zone (DAZ), interface reaction zone (IRZ), isothermally solidified zone (ISZ) and athermally solidified zone (ASZ). The structure in the fillet is composed of solid solution, nickel silicon, nickel boron compound and a mixture with nickel silicon and nickel boron. The tensile strength increases along with the increase of holding time, but decreases when the holding time is over 25 min. A maximum tensile strength of 65.1 MPa is obtained with 25 min holding time. Too short holding time will make boron diffuse insufficiently and generate a great deal of brittle boride components, and too long holding time will make the base metal dissolve into the filler metal excessively and creates more corrosion voids.     

BCu50ZnMnNiSi多元铜基钎料的研究

提出了一种含Ｎｉ、Ｓｉ的适合钎焊合金白口铸铁的Ｃｕ基ＣｕＺｎＭｎ多元钎料,并对ＢＣｕ５０ＺｎＭｎＮｉＳｉ钎料的熔化特性、钎焊工艺性能、钎料组织以及力学性能进行了研究。研究结果表明,与普通ＣｕＺｎ合金钎料比较,ＢＣｕ５０ＺｎＭｎＮｉＳｉ钎料钎焊冶金特性优异,界面冶金结合致密,尽管钎料中含有多元合金元素,钎焊后钎缝仍有较好的塑必     

Modellierung der Stängelkristallitbildung beim Hartlöten von Kohlenstoffstählen mit Kupfer

Simulation of columnar crystallite formation in brazed seams of copper‐brazed carbon steels When brazing steels of different carbon content with copper filler metal, columnar crystallites form on the carbon‐rich iron surface if the width of the brazing gap is smaller than 100 μm. Braze seams with such microstructures were described as early as the 1950ies and it was found out, that the strength of such a joint is significant enhanced, if this crystallites penetrate the entire seam. Extensive experimental investigations in recent years confirm, that the final average length of the crystallite increases superproportionally with decreasing brazing gap width and is almost inversely proportional to the difference in carbon content of the joined steels. Although many attempts to explain this phenomenon are known from literature, the mechanism of columnar structure formation has not been clarified properly until now. The aim of the present work was to develop an appropriate physical model, that describes the growth of crystallites as a function of carbon content in the base materials, the initial brazing gap width and the applied process parameters (temperature, time). The model is an appropriate tool for a general choice and development of filler metal‐base material combinations forming columnar crystallites in the braze seam.     

Relationship between X-ray diffraction and unidirectional solidification at interface between diamond and brazing filler metal

Brazing single crystal diamonds by using silver-copper eutectic filler containing reactive metal: titanium has been carried out. Unidirectional solidification brazing method was tried to obtain stable brazed strength. The diamond specimen was cooled down by contact with copper cooling mass of which temperature was controlled at a room temperature, 470 K and 670 K, respectively. The brazing temperature was 1080 K. The brazing filler was solidified from diamond brazing surface and we called this method as unidirectional solidification brazing. The brazed specimen was examined in shear strength by an original apparatus. In the case of diamond (100), the average shear strength shows more than 120 MPa and maximum shear strength is 240 MPa. These specimens are stronger than that made by usual brazing method. After the strength test, interface orientation between the diamond and the brazing filler was investigated by X-ray diffractometer. In the case of brazing diamond (100), diamond (100) – TiC (111) – Ag (111) orientation can be detected. In the case of brazing diamond (111), diamond (111) – Cu (111) orientation can be detected. Misfits for those orientations were calculated. The value for TiC (111) // diamond (100) is 0.05016, on the other hand the value for TiC (111) // diamond (111) is 0.2125. The brazed interface of diamond (111) is more delicate for thermal stress than diamond (100).     

Microstructural Modification by Redesigning the Chemical Composition of Ni 620 Filler Metal

Ni 620 is a widely used brazing alloy, especially in cases where high-temperature strength and corrosion resistance are required. The formation of undesirable intermetallic phases in the brazing joint due to the addition of boron and silicon as melting point depressants affects the mechanical properties of the joint. Reducing the formation of intermetallic phases during brazing is an important issue in the application of Ni 620. In this study, two approaches, inoculation with Nb and variation of the B and Si content in Ni 620, are pursued to selectively influence the microstructure of the brazed joint. Therefore, the solidus and liquidus temperatures of the new brazing alloys are investigated by means of differential scanning calorimetry measurements. Also, the microstructure of brazed joints is analyzed and evaluated by scanning electron microscope/electron-dispersive spectroscopy as well as the hardness properties using nanoindentaion. It is observed that the addition of Nb, as well as the variation of the B and Si content, leads to a change in the brittle phase band. Especially brittle borides can be reduced in this way. The results contribute to produce brazing joints with more adapted properties, despite low brazing temperatures and short holding times.     

Void formation in wide gap brazing using prepacks of nickel base braze mixes

Abstract

The various types of void formed in wide gap brazed joints of C1023 nickel base superalloy produced using prepacks of nickel base braze mixes have been investigated and systematically categorised. Of particular interest are interfacial and interstitial voids and unwetted pockets, which are features frequently found in joints brazed using such a technique. Examination of brazed joints produced under a wide range of conditions revealed that during heating to the brazing temperature, the braze mix partially sinters together, causing the prepack to shrink towards the centreline, leaving two channels next to the joint faying surfaces. At the same time, relatively large pockets of free space are created within the partially sintered mass of prepack. At the brazing temperature, the filler metal deposited at the gap mouth becomes molten and this molten filler is drawn into the gap preferentially through the fine capillary paths in the partially sintered mass of prepack. The relatively large pockets of free space in the prepacks as well as the channels adjacent to the joint faying surfaces are bypassed by the molten filler metal owing to their lack of capillarity. As a result, the various brazing defects described above will be formed should solidification occur before these empty spaces are filled. The effects of materials and process variables on the formation of various brazing defects are briefly discussed.

MST/1925     

影响铝合金真空钎焊质量的关键因素

通过钎剂、钎料、真空度、工装夹具和钎焊工艺等对铝合金真空钎焊质量的影响实验研究,明确了这些关键因素的影响机理,归纳出了钎焊工艺设计的关键点。工作压强≤1×10-3Pa是铝真空钎焊的必要条件,尽可能减少工装的热容量是基本的设计原则。