Microstructural Examination and Thermodynamic Analysis of Sn-1.5Ag-0.5Cu-x mass% Ni Lead-Free Solder Alloys

Abstract

The diminutive additions of nickel (Ni) element have been fused to Sn-1.5Ag-0.5 mass% Cu (SAC155) lead-free solder alloy. The study was examined experimentally and computationally (using JMatPro software program) the microstructural features, thermal behavior, density, thermal diffusivity, and conductivity as well as tensile stress strain of the Sn-1.5Ag-0.5Cu-x mass %Ni (x = 0.00, 0.05, 0.10, 0.20, and 0.50) solder alloys (SAC155-xNi). The fusing additions of Ni have a little impact on the melting point of SAC155 alloy which increasing from 502 to $$504.2 K$$ 504.2 K . The microstructure of SAC155 solder alloy included coarse grains of β-Sn besides, large eutectic regions, and embedded IMCs of Ag3Sn and Cu6Sn5. The computed values of Gibbs free energy (G) during solidification of the β-Sn phase, Ag3Sn, and Sn3Sn4 IMCs show the stability at $$- 130.7 \times 10^{3} {\text{J}}{\text{.kg}}^{ - 1}$$ - 130.7 × 10 3 J .kg - 1 , $$- 157.7 \times 10^{3} {\text{J}}{\text{.kg}}^{ - 1}$$ - 157.7 × 10 3 J .kg - 1 , and $$- 377.13 \times 10^{3} {\text{J}}{\text{.kg}}^{ - 1}$$ - 377.13 × 10 3 J .kg - 1 , respectively. The SAC155-xNi alloys involved finer β-Sn grains, large fibrous eutectic regions, (Cu,Ni)6Sn5 and (Cu,Ni)3Sn4 IMCs. The G of Cu6Sn5 decreased from $$- 233.1 \times 10^{3} {\text{J}}{\text{.kg}}^{ - 1}$$ - 233.1 × 10 3 J .kg - 1 to $$- 317.9 \times 10^{3} {\text{ J}}{\text{.kg}}^{ - 1}$$ - 317.9 × 10 3 J .kg - 1 when Ni content increased up to 0.25 mass %, then stable and steady at $$- 318.4 \times 10^{3} {\text{J}}{\text{.kg}}^{ - 1}$$ - 318.4 × 10 3 J .kg - 1 with more addition of Ni element. The formation of the (Cu, Ni)6Sn5 and (Ni, Cu)3Sn4 IMCs is motivated by the lowest Gibbs free energy, especially when Ni mass% is added to a sufficient level. The measured and computed values of specific heat at constant pressure (Cp) of SAC155-xNi alloys show a good matching especially at lower temperatures and a little mismatch at high temperatures which decreases with increasing Ni content. The activation energy of atomic arrangement (Q) increased from 11.36 to $$13.41 {\text{kJ}}{\text{.mole}}^{ - 1}$$ 13.41 kJ .mole - 1 with increasing Ni content in SAC155-xNi alloys. Thermal diffusivity (α) and conductivity (κ) of SAC155-xNi gradually decreased with increasing temperature in the range from 303 to 423 K and/or Ni content in alloys. The measured values of (κ) are slightly lower than the computed value at similar temperatures of the SAC155-xNi alloys. The decrease in (κ) may be assigned to scattering the electrons or reducing the phonon contributions due to the presence of various solute atoms and different IMCs. The results of stress-strain graphs reveal the enhancement of YS and UTS for all Ni-containing alloys. The improvement of the yield stress (YS) and ultimate tensile strength (UTS) of Ni-containing alloys is attributed to the uniform distribution of the IMCs, the reduction of β-Sn grain size, and the smoothed enlargement of the eutectic region.