E. A. Eid

Microstructure analysis, thermal behavior, and tensile creep characteristics of the Sn-1.5Ag-0.5Cu-x wt.% Ni (SAC155-xNi, x = 0, 0.05, 0.1, 0.2, and 0.5 wt.%) solder alloys have been examined. The Ni additions have greatly modified the microstructure of Ni-free alloy into bulky fibrous eutectic regions and included the contemporary (Cu, Ni)₆Sn₅, and (Ni, Cu)₃Sn₄ IMCs. Ni additions slightly increased solidus temperature and melting temperature of them. The results of tensile creep resistance have shown dependence on Ni content and testing temperatures due to bulky fibrous eutectic regions and finer IMCs. Creep rates vary with Ni content across all temperatures and stresses. The SAC155-0.05Ni alloy has the lowest and the SAC-0.0Ni alloy has the highest creep rates at all tested conditions. The delicate dispersed IMCs of Ag₃Sn and Cu–Ni–Sn resulted in a significant increase in stress exponent (n $$\approx $$≈ 5–8), enhancing its deformation resistance. The $$n$$n values of alloys decrease as the testing temperature rises due to a change in the dominant creep mechanism. The average values of activation energy (Q) of SAC155-xNi alloy ranged from 60.20 to 68.02 kJ/mol. These Q values are coherent to the process of pipe self-diffusion through dislocation cores.

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 (C_p) 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.