Effects of Solidification Thermal Parameters on Microstructure and Mechanical Properties of Sn-Bi Solder Alloys

Abstract

Samples extracted along the length of directionally solidified (DS) castings of three Sn-xBi alloys (x = 34 wt.%Bi, 52 wt.%Bi and 58 wt.%Bi) were first evaluated metallographically and then subjected to scanning electron microscopy and energy-dispersive x-ray spectroscopy analyses. The characteristic length scale of both eutectic and dendritic phases forming the microstructure were determined and correlated with solidification thermal parameters (growth rate V, and cooling rate T ˙). Tensile and Vickers hardness tests were performed to allow strength and ductility to be discussed as a function of both microstructure features and alloy solute content. The tertiary dendrite arm spacings along the length of the DS Sn-52 wt.%Bi alloy casting are shown to be lower than those obtained for the Sn-34 wt.%Bi alloy casting. The results of mechanical tests show that, with the decrease in the alloy Bi content, both tensile strength and hardness are improved. This is shown to be mainly attributed to the higher density of Bi precipitates decorating the Sn-rich dendrites, which are finer than the equivalent phase developed for the Sn-52 wt.% Bi alloy. However, the ductility is shown to be significantly improved for specimens associated with regions of more refined microstructure of the Sn-52 wt.%Bi alloy DS casting. A microstructure combining much branched dendrites, fine Bi particles within the β-Sn dendritic matrix and an important proportion of very fine eutectic formed by alternate Bi-rich and Sn-rich phase, seems to be conducive to this higher ductility. In this case, the fracture surface is shown to be more finely broken with presence of dimples for this particular condition, i.e., characteristic of a ductile fracture mode.

Sn-Bi(-Ga) TIM Alloys: Microstructure, Tensile Properties, Wettability and Interfacial Reactions

“…This method represents a viable alternative for differential scanning calorimetry (DSC) and has already been used in previous studies. [14][15][16] The thermocouples provided data about the temperature evolution with respect to time, which can be analyzed by Gibbs' rule of phases. 9 The change in the number of phases coexisting in the system influences the temperature variation slope.…”

Microstructure Growth Morphologies, Macrosegregation, and Microhardness in Bi–Sb Thermal Interface Alloys

“…Quantitative processing-microstructure-property correlations have been previously developed for alloys of the Bi-Zn, [34] Bi-Ag, [35] and Bi-Sn [36] systems using a directional solidification technique in transient heat-transfer conditions. This experimental approach has a great advantage of promoting fast and slow cooling conditions experienced along the length of a same alloy casting, allowing, consequently, a wide range of microstructural length scales to be characterized through a single solidification experiment.…”

In-Bi-Cd ÖTEKTİK ALAŞIMININ MİKROYAPISAL DEĞERLENDİRİLMESİ VE MEKANİK DAVRANIŞI

“…Özellikle indiyum, bizmut ve galyum elementleri düşük erime sıcaklıklarına sahip olmaları nedeniyle bu elementlerden oluşturulacak alaşımında erime sıcaklığını düşürmektedir [17]. Literatürde düşük erime sıcaklığına sahip Sn-Bi [15,[19][20][21], Sn-In [22], Bi-Zn [17], Bi-Cd [23], In-Bi-Sn [2,[24][25], In-Bi-Zn [26] lehim alaşımlarının özellikleri birçok araştırmacı tarafından halen araştırılmaktadır.…”