الفهرس 
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Abstract
The aim of the present thesis basically is to investigate the effect of adding Zn as a fourth addition and GONSs as a fifth addition on the thermal, structural and mechanical characteristics of Sn-1wt%Ag-0.5wt%Cu (SAC105) solder alloy. Also, the present work mainly covers studying the effect of strain rate ε•, and testing temperatures, Tt on the stress-strain and stress relaxation characteristics of SAC105 plain, SAC105-1wt%Zn and SAC105-1wt%Zn-0.2wt%GONSs composite wire samples. The effect of different levels of stress and testing temperature on creep characteristics of the three solder alloys was studied.
To study the thermal characteristics, thermal analysis of SAC105, SAC105-Zn and SAC105-Zn-GONSs were discussed. Thermal properties of the selected solder alloys have been studied by using the differential scanning calorimetry (DSC). The results showed that the observed endothermic peaks of the SAC105 plain solder, SAC105-Zn containing and SAC105-Zn-GONSs composite solder were found shifted from two peaks at 494.23 K and 501.21 K for plain solder to one peak at 487 K for composite solder. Thus, the addition of Zn and GONSs influences the melting point of the SAC105-Zn and SAC105-Zn-GONSs solder alloys.
To study the structure characteristics, the microstructure was examined by X-ray diffractometry (XRD), optical microscope (OM), energy dispersive X-ray spectrometer (EDS) and scanning electron microscopy (SEM). XRD pattern for GONSs and bright field transmission electron microscope for GONSs showed an average length of nano-scale with ~20 nanometers. EDS and SEM analysis for the plain and composite solder alloys confirmed that the solder used was SAC105 and SAC105-Zn-GONSs, and the founded inter-metalic compounds (IMCs) were Ag3Sn, Cu10Sn3 and Cu6Sn5. Microstructural analysis revealed that Cu10Sn3, Ag3Sn and Cu6Sn5 IMC particles and the β-Sn phase were detected in SAC105 plain. Addition of Zn into SAC105 promotes the formation of Cu5Zn8 IMC. The Addition of 0.2 wt% GONSs to the Zn-containing solder showed a new IMC Ag5Zn8. OM investigations revealed that addition 1 wt% Zn modified the microstructure of the β–Sn grains of the plain SAC105 solder while the addition of GONSs to the Zn-containing decreased the thickness of β-Sn dendrites and modified its orientation.
Stress-strain, stress relaxation and creep tests have been conducted to study the mechanical characteristics. Stress-strain tests for the three solder alloys were performed under the effect of different strain rates (ε• ) ranged from 5.4 x 10-5 to 179 x 10-5 S-1 at different testing temperatures Tt in the range from 300 to 393 K. The results showed that increasing strain rates, decreasing the testing temperatures and the existence of Zn element and/or GONSs resulted in increasing the work hardening parameter: ultimate tensile stress uts, yield stress y, fracture stress f, Young modulus Y and work hardening coefficient χp. The activation energy Q of 0.42 eV is obtained for the plain, Zn-containing and composite solder alloys. This value was close to those reported for the dislocation motion in Sn-based alloys.
Stress relaxation curves for the plain SAC105, SAC105-Zn and composite SAC105-Zn samples heat treated at 400 K for 30 min and performed at different strain rates ε• (5.4 x 10-5, 54.9 x10-5, 103x10-5 and 179x10-5 s-1) and different testing temperatures Tt (300, 333, 353, 373 and 393 K). The results showed that increasing strain rates and testing temperatures increased the relaxation rate (drel./dt) for the three solder alloys whereas the existence of Zn element and GONSs reduced the relaxation rate. The critical relaxed-stress was found to increase with increasing the strain rates and/or testing temperature for all solder samples. Relaxed activation energy Qrel. ranged from 0.5 to 0.66 eV were detected for the three solder alloys. These values were close to those reported for the dislocation climb and grain boundary diffusion mechanisms in Sn-based alloys
Tensile creep tests of the SAC105 plain, SAC105-Zn containing and SAC105-Zn-GONSs solder alloys were carried out at testing temperatures ranging from 300 to 373 K under different applied stresses ranged for 7.8 to 11.7 MPa. It can be noticed that, with increasing testing temperature and/or applied stress the isothermal creep curves of the three solders showed a monotonic shift towards higher strains and lower fracture times. Moreover, the level of creep strain for SAC105-Zn and SAC105- Zn composite is generally lower than that of SAC105 plain solder under the same testing conditions. Steady state creep strain rate ε•st was found to be increased with increasing temperature. Under the same test conditions SAC105-Zn-GONSs composite yields the lowest creep rates compared with those of both other solders. This means that the composite solder has longer creep life time while retaining higher creep resistance. This can be rendered to: (i) the decrease of the grain sizes in the composite solder, (ii) the finer microstructure of the IMCs and (iii) the covering of edges of the GONSs by a thin film of fine IMC (nano-scale) grains. The obtained activation energy Q was found to be 0.6 eV for the three solder alloys. This value suggests that the creep process is controlled by dislocation climb.