Joining of Si3N4 using Ag57Cu38Ti5 brazing filler metal

Hot-pressed Si₃N₄ was joined using Ag₅₇Cu₃₈Ti₅ brazing filler metal at 1103 to 1253 K for 5 min in a vacuum. The interface reactions between Si₃N₄ and the brazing filler metal during brazing are reported. An important event is sufficient interface reaction, characterized by the formation of a layer of TiN with an appropriate thickness at the ceramic-filler interface. The joining strength of the butt joint depends on the interface reaction, and a maximum joining strength of 490 MPa measured by the four-point-bend method is achieved for the Si₃N₄-Si₃N₄ joint brazed at 1153 K for 5 min. It is also discussed how to design the best brazing filler metal for joining ceramic to ceramic or ceramic to metal.     

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).     

Joining of Si3N4/Si3N4 with CuNiTiB paste brazing filler metals and interfacial reactions of the joints

The joining of Si₃N₄/Si₃N₄ was carried out using CuNiTiB paste brazing filler metals. The maximum room-temperature three-point bend strength of the joints is 338.8 MPa. The cross-section microstructures of the joints and the element area distribution were examined by scanning electron microscope (SEM) equipped with wave dispersive X-ray spectroscopy (WDS). The phases appeared on the fracture surfaces of the joints were determined by means of X-ray diffraction analysis (XRDA) method. A model is established of the interfacial reactions between Si₃N₄ and the CuNiTiB brazing filler metals. With this model, the relationship between the joint strength and the interfacial reactions is discussed.     

A TEM analysis of the Si3N4/Si3N4 joint brazed with a Cu-Zn-Ti filler metal

Si₃N₄ ceramic was joined to itself using a filler alloy of (CuZn)85Ti15 at 1123–1323 K for 15 min. TEM observation showed that a reaction zone of TiN and/or Ti₂N exists at the interface between the ceramic and filler alloy, and the center of the joint is composed of Cu-Zn solid solution in which there are Cu₂TiZn and Ti₅Si₃ reaction phases. With increasing brazing temperature, both the thickness of the reaction zone and the amount and size of the Ti₅Si₃ phase increase, while the amount and size of the Cu₂TiZn phase decrease. When the brazing temperature reached 1323 K, the Cu₂TiZn phase disappeared. When the brazing temperature is lower than 1223 K, the interfacial reaction zone is mainly composed of Ti₂N, which has a cylindrical shape and orientates randomly in the zone. There is a crystal orientation relationship between the Ti₂N in the reaction zone and the Cu in the Cu-Zn solid solution, which is: {110}_Ti2N//{420}_Cu, 001_Ti2N//001_Cu. When the brazing temperature is higher than 1223 K, the interfacial zone is composed of TiN, which has a plate shape crossing each other.     

化学镀镍Si3N4陶瓷与金属钎焊接头的分析

利用扫描电镜,能谱仪及射线衍射仪对化学镀镍Ｓｉ３Ｎ－Ｑ２３５钢钎焊接头进行了微观分析,分析表明,接头为多层复合结构,陶瓷／镀镍层间发生了界面反应,但反应区在界面上不连续,机械结合仍为陶瓷与金属界面的主要结合方式。     

FEM simulation of Cu97Si3 filler metal droplets spreading under arc brazing

Abstract

The spreading behaviour of Cu₉₇Si₃ filler metal droplets under arc brazing is studied by finite element method (FEM) simulation using Surface Evolver software. The mathematical model of arc pressure force acceleration added to the droplet microelement as the form of gravity acceleration is used in numerical simulation. The 3D filler metal droplet profile for different welding currents is then simulated. Finally, the simulation results were compared with experimental results, showing good correspondence. It was seen that the spreading height decreases and the diameter increases with increase of the welding current in an approximate linear relation.     

Joining of Al-plasma-sprayed Si3N4ceramics

Aluminium was coated on silicon nitride ceramics by a low-pressure plasma spraying method, in order to form a tight bond between aluminium and the ceramics. Aluminium nitride formed as a interfacial reaction product between the aluminium coating layer and the ceramics. Two pieces of the aluminium-coated Si₃N₄ ceramics were then joined using the aluminium coating layers as filler metal in a vacuum of 1.3×10^–3 Pa at 973 K. The average bending strength and Weibull modulus of the joint are 340 MPa and 6.3 respectively, considerably higher than the 230 MPa and 0.9 of a Si₃N₄ ceramics joint brazed with an aluminum plate under the same condition.     

The metallurgical behaviour during brazing of Ni-base alloy Inconel 600 to Si3N4 with Ag71Cu27Ti2 filler metal

Detailed observations were carried out on the metallurgical behaviour of joint-brazing of nickel based alloy Inconel 600 to Si₃N₄ with Ag71Cu27Ti2 filler metal, with emphasis on the interface between the filler metal and the Inconel 600 and the effects of nickel which was the predominant element in the base metal. Based on the experimental results, the mechanism of bonding Inconel 600 to the filler metal is attributed to the diffusion of silver and copper along the grain boundaries of the Inconel 600, which results in mechanical anchoring. The effects of nickel on the metallurgical behaviour of filler metal are summed up as enhancing the separation of silver- and copper-rich liquid phases from the molten filler metal; combining titanium and decreasing its activity in the reaction with Si₃N₄ at the interface with ceramics; promoting the diffusion of silver and copper into Inconel 600; and facilitating the flow of filler metal over the surface of Inconel 600.     

Mechanical properties of Si3N4/BN fibrous monolithic ceramics at elevated-temperature

The mechanical properties at high temperature of Si₃N₄/BN fibrous monolithic ceramics were tested. The flexural strength of SiC whisker reinforced Si₃N₄/BN fibrous monolithic ceramics from 25°C to 1200°C were investigated. The strength degraded slowly from 1000°C to 1200°C which was different to Si₃N₄ monolithic ceramics. The creep behaviors of the material at different temperatures were characterized. Si₃N₄/BN fibrous monolithic ceramics possess high creep resistance. The chemical composition and microstructure of the composites were analyzed by XRD and SEM.