Tiesong Lin

Improvement of mechanical properties of Sn-58Bi alloy with multi-walled carbon nanotubes

Carbon nanotubes (CNTs) reinforced Sn-58Bi composites were successfully fabricated through ball-milling method and low temperature melting process.The influence of multi-walled carbon nanotubes (MWCNTs) on the mechanical strength and ductility of Sn-58Bi lead-free alloy was studied.The mechanical test results show that the bending strength of Sn-58Bi-0.03CNTs (mass fraction,%) composite is increased by 10.5% than that of the Sn-58Bi alloy,which can be attributed to the reduction of Sn-rich segregation and the grain refinement.The toughness of Sn-58Bi-0.03CNTs composite is increased by 48.9% than that of the matrix materials.It is indicated that the influence of CNTs on the strength of Sn-58Bi-xCNTs composite is insignificant.In addition,the fracture mechanism of CNTs reinforced Sn Bi composite was analyzed.The corresponding fracture surface comparison between the Sn-58Bi-0.03CNTs composite and the monolithic Sn-58Bi alloy was made to identify the influence of CNTs on the fracture behavior and the reinforcing effect of CNTs.

Microstructure and shear strength of reactive brazing joints of TiAl/Ni-based alloy

Abstract Reactive brazing of TiAl-based intermetallics and Ni-based alloy with Ti foil as interlayer was investigated. The interfacial microstructure and shear strength of the joints were studied. According to the experimental observations, the molten interlayer reacts vigorously with base metals, forming several continuous reaction layers. The typical interfacial microstructure of the joint can be expressed as GH99/(Ni, Cr) ss (γ)/TiNi (β 2 )+TiNi 2 Al (τ 4 )+Ti 2 Ni (δ)/δ+Ti 3 Al (α 2 )+Al 3 NiTi 2 (τ 3 )/α 2 +τ 3 /TiAl. The maximum shear strength is 258 MPa for the specimen brazed at 1000 °C for 10 min. Higher brazing temperature or longer brazing time causes coarsening of the phases in the brazing seam and formation of brittle intermetallic layer, which greatly depresses the shear strength of the joints.

Effect of bonding parameters on microstructures and properties during TLP bonding of Ni-based super alloy

Abstract Ni-based alloy was transient liquid phase bonded using a BNi-2 interlayer. The effect of bonding parameters on the microstructures and mechanical properties of the joints was investigated. With the increase of bonding temperature or time, the number of Ni-rich and Cr-rich borides and the grain size of precipitation zone decrease. Higher bonding temperature or longer bonding time is beneficial to the diffusion of melting point depressant elements (B and Si) from the PZ to the base metal and atomic interdiffusion between the base metal and the joint. The chemical composition and microstructure of the joints bonded at 1170°C for 24 h are comparable to the base metal. The shear test results show that both the room and elevated temperature shear-strengths of the joints increase with increasing bonding time. However, the effect of bonding time on elevated temperature tensile-shear strength is greater than on room temperature tensile-shear strength.

Microstructure and Mechanical Properties of Tin-Bismuth Solder Reinforced by Aluminum Borate Whiskers

Tin-bismuth solder has emerged as a promising lead-free alternative to tin-lead solder, especially for low-temperature packaging applications. However, the intrinsic brittleness of tin-bismuth solder alloy, aggravated by the coarse bismuth-rich phase and the thick interfacial intermetallic layer, notably limits the mechanical performance of the bonded joints. In this work, the microstructure and mechanical performance of solder joints were improved by adding 3.2xa0vol.% aluminum borate whiskers to the tin-bismuth solder alloy. This whisker-reinforced composite solder was fabricated through a simple process. Typically, 25-μm to 75-μm tin-bismuth particles were mixed with a small amount of aluminum borate whiskers with diameter of 0.5xa0μm to 1.5xa0μm and length of 5xa0μm to 15xa0μm. The addition of whiskers restrained the formation of coarse brittle bismuth-rich phase and decreased the lamellar spacing from 0.84xa0μm to 7.94xa0μm to the range of 0.22xa0μm to 1.80xa0μm. Moreover, the growth rate of the interfacial intermetallic layer during the remelting treatment decreased as well. The joint shear strength increased from 19.4xa0MPa to 24.7xa0MPa, and only declined by 4.9% (average, −5.9% to 15.8%) after the tenth remelting, while the shear strength of the joint without whiskers declined by 31.5% (average, 10.1–44.1%). The solder alloy was reinforced because of their high strength and high modulus and also the refinement effect on the solder alloy microstructure.

An influence of a Glass Braze Composition on the Properties of Li-Ti Ferrite Joints

The influence of the chemical composition of Bi2O3-B2O3-SiO2-ZnO glass brazes on (i) the microstructure, (ii) the mechanical and (iii) the dielectric properties of Li-Ti ferrite joints was systematically investigated. The Bi5(Ti3Fe)O15 whisker and a white block phase consisting of Bi12SiO2 and Bi24B2O39 were observed in the joints of Li-Ti ferrite/Bi25-Ba and Li-Ti ferrite/glass brazes, respectively, containing a higher content of Bi2O3. No crystalline phase was detected in the Li-Ti ferrite/Bi25 and Li-Ti ferrite/Bi20 joints. The joint strength reached the maximum of 48xa0MPa in the Li-Ti ferrite/Bi25-Ba couples. It is assumed that this is mainly due to the strengthening effect of Bi5(Ti3Fe)O15 whiskers. The bonding temperature (700°C) had little effect on the dielectric properties of Li-Ti ferrite. Moreover, compared to the Bi25-Ba glass brazes, the Bi25 and Bi20 glass brazes had a less pronounced influence on the dielectric properties of joints. Different glass brazes can be tailored to different requirements depending on specific application and joint property requirements.

An influence of a glass composition on the structure and properties of Bi 2 O 3 –B 2 O 3 –SiO 2 –ZnO glass system with addition of BaO, CaO and Fe 2 O 3

The Bi2O3–B2O3–SiO2–ZnO glass system with addition of network modifier (BaO, CaO and Fe2O3) were synthesized using the conventional melt quenching method. The effect of chemical compositions on the glass network structure, thermal properties, crystallization characteristics and electrical properties were systematically investigated. With rising the Bi2O3 content, the number of [BiO3] and [BiO6] units increases and a new bridging of Bi–O–B bond forms. Moreover, either the increase of Bi2O3 content or the decrease of SiO2 content induce a progressive conversion of [BO4] into the [BO3] unit. However, the influence of a network modifier on the conversion of [BO4] to [BO3] unit depends on the composition. An addition of network modifier helps stabilize the glass structure against a crystallization. A high content of Bi2O3 and ZnO promotes the formation of Bi-rich and Zn-rich crystals during heat-treated process, respectively. The Bi content of Bi-rich crystal increases and the Zn-rich crystal decomposes with increasing the heat-treated temperature. Both of the glass network structure and the formation of Bi-rich crystal in glass matrixes during testing process combine to determine the change rule of the CTEs (coefficients of thermal expansion). The variation of the Tg (glass transition temperature) only depends on the glass network structure. The dielectric constant of glasses without network modifier decreases with decreasing the Bi2O3 content. Moreover, an addition of network modifier could decrease the dielectric constant. Each glass offers a dielectric loss tangent below 0.005 and an electrical resistivity above 107xa0Ωxa0cm.