Plate-like growth in a eutectic Bi–Ni alloy: effects of morphological microstructure evolution and Bi3Ni intermetallic phase on tensile properties

Abstract The development of efficient thermal interface materials (TIMs) has become an emerging demand mainly driven by the continual rise in power dissipation of high-performance microprocessors. In this context, Bi-based alloys are among the promising types of TIMs for electronic packaging applications. However, the influence of the microstructural arrangement on mechanical strength of Bi–Ni alloys remains barely understood. To overcome this issue, this study aims to develop quantitative microstructure features-tensile properties correlations for a Bi–0.28 wt.%Ni alloy solidified in a wide range of cooling rates ( T ˙ ) . In addition to the phase diagram calculated by the Thermo-Calc software (SSOL6 database) and differential scanning calorimetry analysis, the characterization of the Bi3Ni intermetallic compound is carried out using X-ray diffraction and SEM microscopy with energy dispersive X-ray spectroscopy. Wavy instabilities in the plate-like morphology of the Bi matrix are shown to occur for T ˙ ≤ 0.13 ° C / s . Besides that, more significant variations in yield and ultimate tensile strengths, σy and σu, respectively, are associated with a certain range of microstructural spacings between Bi plates (λ) from 47.6 to 135.2 μm. Hence, Hall–Petch type relations are proposed to describe the variation of both σy and σu as a function of λ.