Jialie Ren

Microstructures and mechanical properties of Ti–24Al–17Nb (at.%) laser beam welding joints

Abstract Laser beam welding of Ti–24Al–17Nb (at.%) alloy was conducted to investigate the microstructures and the mechanical properties of its joints. The results indicated that the weld microstructure consisted primarily of retained ordered β phase (namely B2 phase) and was independent of the laser welding parameters, while the size and the orientation of the weld solidification structures and then the bend ductility of the joints were related to the welding conditions. The microstructures became coarser and the strains of inducing crack and fracturing decreased as the heat input increased. The fracture occurred in the base metal when the transverse tensile test of the joints was conducted. The tensile strength of the joints was equal to that of the base material and the tensile ductility could reach 12∼17%, which was near to that of the base material.

Low Temperature Bonding of Cu Metal through Sintering of Ag Nanoparticles for High Temperature Electronic Application

Lead-based solders bring pollution to the environment and result in health threat to humans. The preparation and application of metallic nanoparticles provide a potential method to develop Pb-free bonding materials. In this article, bonding of Ag-coated Cu bulks was realized through low temperature sintering by directly using the chemically-reduced Ag nanoparticle paste and baked nanoparticle powders at 60 o C, respectively. The results indicate that the capillary flow of paste caused a ring-like deposit on substrate coating, while this phenomenon disappeared when using the powders. Increasing bonding temperature facilitated the sintering, and shear strengths of 20 MPa and 84 MPa was obtained at bonding temperature of 250 o C for 30 min under 20 MPa when using the Ag paste and powders, respectively. High joint strength value of bonded region using paste is due to the high effective bonding pressure and small effective bonded area. Finally, for the extensive application in packaging industry especially for high temperature electronics, challenges such as the improvement of screen and stencil printing ability of paste, avoiding bonding pressure and lowering the cost were pointed out based on our and other researchers achievements. Cu nanoparticle or Cu-containing nanoparticle mixture pastes are promising but the problems of oxidation and bonding stability must be resolved urgently.

Polymer-Protected Cu-Ag Mixed NPs for Low-Temperature Bonding Application

A simple method has been proposed to prepare polymer-protected Cu-Ag mixed nanoparticles (NPs), which are suitable for use as low-temperature bonding materials. The polymer coated on the Cu-Ag mixed NPs can protect them from oxidation effectively when heated in air at temperature lower than 280°C. The low-temperature bonding process utilizing Cu-Ag mixed NPs as the bonding material is investigated. The bonding experiments show that robust joints are formed using Cu-Ag mixed NPs at 160°C in air. The shear test shows that addition of copper to silver is helpful for improving joint strength. This novel sintering-bonding technology using Cu-Ag mixed NPs as an interconnection material has potential for application in the electronics packaging industry.

Effect of PVP on the low temperature bonding process using polyol prepared Ag nanoparticle paste for electronic packaging application

There has been an increasing interest in developing low temperature interconnection process using metal nanoparticles. In this study the Ag nanoparticles (NPs) for this low temperature bonding process applications were prepared based on the polyol method using polyvinylpyrrolidone (PVP) as the protecting agent. The effect of PVP on the Ag nanoparticle size, nanoparticle solution viscosity and the bondability of the Ag nanoparticle paste were studied. The silver nanoparticle with diameter of 90 nm, 40 nm and 20 nm were synthesized by adjusting PVP concentration. The bonding processes using different kind of Ag nanoparticle paste were conducted. The joint with shear strength of 50 MPa were formed using Ag nanoparticle (NP) paste prepared with appropriate PVP concentration.

effect of post-weld heat treatment on microstructure and properties of ti-23al-17nb alloy laser beam welding joints

Abstract The mechanical properties of Ti-23Al-17Nb (mole fraction, %) laser beam welding alloy joint at room temperature are comparable to that of the base materials. However, the strength and ductility of the as-welded joint deteriorate seriously after high temperature circulation. The effect of post-welded heat treatment on the microstructure and mechanical properties of the joint was investigated. The heat treatment was taken at 980 °C for 1.5 h, then furnace cooling and air cooling were performed separately. The results indicate that proper post-welded heat treatment improves the ductility of the joint at high temperature.

Temperature and force response characteristics of friction stir welding on Invar 36 alloy

Abstract The temperature and force response during friction stir welding of Invar 36 alloy were investigated by experimental measurement and numerical simulation. The effect of welding parameters was studied. The temperature and force characteristics were roughly discussed. It is indicated that an elevation rotational speed results in increasing temperature and decreasing axial force, whereas rotational speed has no obvious influence on the longitudinal force. An elevation travelling speed produces increasing axial force and longitudinal force, and a decreased trend of temperature out of stir zone centre. Friction stir welding of Invar 36 alloy produced relatively high peak temperatures, high axial and longitudinal forces, and a narrow temperature distribution compared with those of the other reported high melting temperature materials.

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.

Bending properties and fracture behavior of Ti-23AI-17Nb alloy laser beam welding joints

Ti-23Al-17Nb alloy is an important high temperature structural material used in the space and aerospace fields. Welding of this alloy is an indispensable processing method, so the microstructures and mechanical properties of these welded joints must be studied to improve the welds. Longitudinal three-point bending tests were conducted to measure the bending ductility of laser beam welded joints. The crack distribution and fracture surface were investigated to further analyze the fracture behavior. The results indicate that the bending ductility decreases as the heat input by the laser beam welding increases. The crack inducing strain reaches 4.24%, while the fracturing strain exceeds 5% when the heat input is below 316 J/cm. If the columnar crystal grain of the weld metal exhibits a uniform orientation, the bending ductility is worse. The fractography analysis shows that the cracking propagates transgranularly and the fracture surface has a cleavage mode.