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An interstitial solute strengthened high entropy alloy (iHEA), Fe49.5Mn30Co10Cr10C0.5 (at.%), was successfully additively manufactured via selective laser melting. The as-built iHEA exhibits a hierarchically heterogeneous microstructure with length scales across several orders of magnitude, which engenders an enhanced strength–ductility combination relative to those fabricated by conventional processing routes. The high yield strength mainly stemmed from the dislocation strengthening besides the friction stress and grain boundary strengthening. The joint activation of multiple deformation mechanisms involving dislocation slip, deformation twinning and phase transformation can maintain the steady work-hardening behavior at high stress levels, leading to a high ductility. A hierarchical interstitial high entropy alloy, Fe49.5Mn30Co10Cr10C0.5 (at.%), was successfully additively manufactured via selective laser melting. Its exceptional strength–ductility synergy surpasses that of the most SLM processed conventional alloys. [ABSTRACT FROM AUTHOR]

In the present study, 0.05 wt.% of Ni-coated multi-walled carbon nanotubes (Ni-CNTs) were successfully incorporated into the 95.8Sn-3.5Ag-0.7Cu solder using the powder metallurgy technique, to synthesize a new lead-free composite solder. Its mechanical property (in terms of hardness) was investigated at room temperature using the nanoindentation method. The results revealed that the nanoindentation hardness increased by 14.3% with the incorporation of 0.05 wt.% of Ni-coated CNTs. This observation is in good agreement with the microhardness test results. Moreover, the addition of Ni-CNTs improved the creep resistance of the composite solder. The test results established that nanotechnology coupled with composite technology in electronics solders can result in the enhancement of mechanical properties. These advanced interconnect materials will thus benefit the microelectronics assembly and packaging industry. [ABSTRACT FROM AUTHOR]

The creep behavior and hardness of Sn-3.5Ag-0.7Cu solder were studied using Berkovich depth-sensing indentation at temperatures of 25°C to 125°C. Assuming a power-law relationship between the creep strain rate and stress, an activation energy of 40 kJ/mol and stress exponents of 7.4, 5.5, and 3.7 at 25°C, 75°C, and 125°C, respectively, were obtained. The results revealed that, with increasing temperature, the creep penetration and steady-state creep strain rate increased whereas the stress exponent decreased. The stress exponent and activation energy results also suggested that the creep mechanism is dislocation climb, assisted by diffusion through dislocation cores in Sn. Furthermore, the hardness results exhibited a decreasing trend with increasing temperature, which is attributed to softening at high temperature. [ABSTRACT FROM AUTHOR]

In the present study, nanoindentation studies of the 95.8Sn-3.5Ag-0.7Cu lead-free solder were conducted over a range of maximum loads from 20 mN to 100 mN, under a constant ramp rate of 0.05 s-1. The indentation scale dependence of creep behavior was investigated. The results revealed that the creep rate, creep strain rate and indentation stress are all dependent on the indentation depth. As the maximum load increased, an increasing trend in the creep rate was observed, while a decreasing trend in creep strain rate and indentation stress were observed. On the contrary, for the case of stress exponent value, no trend was observed and the values were found to range from 6.16 to 7.38. Furthermore, the experimental results also showed that the creep mechanism of the lead-free solder is dominated by dislocation climb. [ABSTRACT FROM AUTHOR]

In the present study, copper at the nanometer length scale is integrated with Sn-3·5Ag using the technique of powder metallurgy incorporating energy efficient microwave sintering. Superior mechanical characteristics were realised for the formulations containing nanometer length scale copper in excess of 1 vol.-%. Sn-3·5Ag reinforced with 2.5 vol.% nanosize copper particulates exhibited the best overall mechanical characteristics. Particular emphasis is placed on studying the effect of the increasing presence of nanosize copper particulates on the microstructure and property evolution of the Sn 3·5Ag matrix. [ABSTRACT FROM AUTHOR]

In the present study, the influence of multiwalled carbon nanotubes (CNTs) on the creep performance of 95·8Sn–3·5Ag–0·7Cu lead free solder is investigated. Composite solders containing varying weight percentages of CNTs were synthesised. Solder joints were fabricated and subjected to a series of tests under testing temperatures ranging from 25 to 125°C and applied stresses ranging from 4 to 18 MPa. Creep results revealed that solders containing CNTs exhibited significantly improved creep resistance and also creep time to failure increased. Stress exponents of composite solders were higher than that of monolithic solder. In general, stress exponent was found to increase with increasing applied stress and with decreasing testing temperature. The range of activation energies of composite solder with 0·01 wt-%CNT addition was found to be comparable to that of monolithic Sn–Ag–Cu. However, as the amount of CNT increased to 0·04 wt-%, the range of activation energies increased accordingly. [ABSTRACT FROM AUTHOR]

In this study, the influence of carbon nanotubes (CNTs) on the shear strength and electrical resistivity of 95.8Sn-3.5Ag-0.7Cu lead-free solder was investigated. Composite solders containing various weight percentages of CNTs were synthesized, and electrical resistivity results of the bulk composite solders revealed that the presence of CNTs did not degrade the electrical performance of such solders. Tests conducted on lap-shear solder joint samples showed an improvement in the shear strength of the composite solders. However, at higher amounts of CNT additions (0.04 wt.% and 0.07 wt.%), the strength improvement was only marginal compared to that of the monolithic solder joint. A comparison of yield stress and ultimate stress test results between the solder joint and bulk solder also showed good agreement. Furthermore, the presence of CNTs in the solder matrix had a minimal influence on the thickness of the interfacial intermetallic compound layer formed during soldering. [ABSTRACT FROM AUTHOR]

In this study, Sn-Ag-Cu based nanocomposites with carbon nanotubes (CNTs) as reinforcements were successfully synthesized via the powder metallurgy technique. Lead-free solder powders were firstly blended together with varying weight percentages of CNTs. The materials were then compacted, sintered and finally extruded at room temperature. The extruded materials were characterized for their microstructural, thermal and mechanical properties. The porosity of the nanocomposites was observed to increase with increasing weight percentages of CNTs, accordingly the density of the nanocomposites was reduced. Thermomechanical analysis of the solder nanocomposites showed that the use of CNTs as reinforcements decreased the average coefficient of thermal expansion of the solder matrix. Furthermore, the results of mechanical properties characterization revealed that the addition of CNTs aids in enhancing the microhardness and the overall strength of the nanocomposite solder. An attempt is made in the present study to correlate the variation in weight percentages of the carbon nanotubes with the properties of the resultant nanocomposite materials. [ABSTRACT FROM AUTHOR]

In the present study, three aluminium based functionally gradient materials (FGMs), reinforced with different ceramic particulates (silicon carbide, aluminium oxide, and titanium carbide), were successfully synthesised using the innovative gradient slurry disintegration and deposition (GSDD) technique. The results for Al/SiC and Al/Al[sub 2]O[sub 3] revealed, in common, an increase in the weight percentage of reinforcement along the direction of deposition, to result in an increase in porosity and microhardness. However, for Al/TiC, the reverse trend was observed, with porosity and microhardness decreasing with increasing distance from the base of the ingot. The porosity levels for Al/TiC were also found to be significantly lower than those of the other two FGMs. Thermomechanical analysis of the FGMs showed that the average coefficient of thermal expansion of the high reinforcement end was reduced, as compared to the high aluminium end. Sliding wear test results also revealed that the high reinforcement end was more wear resistant than the high aluminium end, except for the case of Al/Al[sub 2]O[sub 3]. An attempt is made to interrelate the effects of different types of particulates, with microstructural development, microhardness and wear rate results obtained in the present study. [ABSTRACT FROM AUTHOR]