Microstructural,mechanical and shape memory characterizations of Ti–Mo–Sn alloys

As a β stabilizing element in Ti-based alloys, the effect of Mo on phase constitution, microstructure, mechanical and shape memory properties was investigated. Different compositions of Ti–xMo–3Sn alloys (where x=2, 4, 6, at.%) were prepared by arc melting. A binary composition of Ti–6Mo alloy was also prepared for comparison. Ti–xMo–3Sn alloys show low hardness and high ductility with 90% reduction in thickness while Ti–6Mo alloy shows high hardness, brittle behavior, and poor ductility. Field emission scanning electron microscopy (FESEM) reveals round morphology of athermal ω (ω_ath) precipitates. The presence of ω_ath phase is also confirmed by X-ray diffraction (XRD) in both as-cast and solution-treated and quenched conditions. The optical microscopy (OM) and FESEM show that the amount of martensite forming during quenching decreases with an increase in Mo content, which is also due to β→ω transformation. The hardness trends reinforce the presence of ω_ath too. The shape memory effect (SME) of 9% is the highest for Ti–6Mo–3Sn alloy. The SME is trivial due to ω_ath phase formation; however, the increase in SME is observed with an increase in Mo content, which is due to the reverse transformation from ω_ath and the stress-induced martensitic transformation. In addition, a new and very simple method was designed and used for shape memory effect measurement.     

Microstructure and mechanical property of Sn–Ag–Cu solder material

Among the lead-free solder materials,Sn-AgCu alloys have many advantages,such as good wetting property,superior interfacial properties and high creep resistance.In this article,the organization and welding performance of Sn-Ag-Cu material were investigated.The surface morphology of the two alloys was observed by stereoscopic microscope and scanning electron microscope(SEM).Chemical constitution was examined by X-ray energy-dispersive spectroscopy(EDS).The mechanical properties of Sn-Ag-Cu solder were evaluated systematically compared with those of Sn-Cu solder.The results show that Sn-Ag-Cu solder based on different solder pads has different welding properties.The thickness of intermetallic compound(IMC) at the interface increases with aging time.For the gold-plated pads,there are a large number of IMC graphic,and in the welding interface,it can reduce the reliability of electrical connection.The Sn-AgCu solder joints show a superior mechanical property over the traditional Sn-Cu solder.The number of dimples decreases and that of cavities increases for Sn-Cu0.7 alloy and the fracture surfaces of Sn-Ag3.0-Cu0.5 alloy have many small size dimples which are homogeneously distributed.     

Improving the shear strength of Sn–Ag–Cu–Ni/Cu–Zn solder joints via modifying the microstructure and phase stability of Cu–Sn intermetallic compounds

This study focuses on the correlation between high-speed impact tests and the interfacial reaction in Sn-3.0Ag-0.5Cu-0.1Ni/Cu (wt%) and Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints. Adding Ni into the Sn–Ag–Cu solder alters the interfacial morphology from scallop type to layer type and exhibits high shear strength after reflow in both solder joints. However, the shear strength of Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints degrades significantly after thermal aging at 150 °C for 500 h. It is notable that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints still present higher shear strength after aging at 150 °C. The weakened shear strength in Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints is due to stress accumulation in the interfacial (Cu,Ni)₆Sn₅ compound induced by the phase transformation from a high-temperature hexagonal structure (η-Cu₆Sn₅) to a low-temperature monoclinic structure (η'-Cu₆Sn₅). However, doping small amounts of Zn into (Cu,Ni)₆(Sn,Zn)₅ can inhibit the phase transformation during thermal aging and maintain strong shear strength. These experiments demonstrate that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints can act as a stable connection in the micro-electronic packaging of most electronic products at their average working temperatures.     

Microstructural,mechanical, and electrical characterization of directionally solidified Al–Cu–Mg eutectic alloy

The composition of an Al–Cu–Mg ternary eutectic alloy was chosen to be Al–30 wt% Cu–6 wt % Mg to have the Al₂Cu and Al₂CuMg solid phases within an aluminum matrix (α-Al) after its solidification from the melt. The alloy Al–30 wt % Cu–6 wt % Mg was directionally solidified at a constant temperature gradient (G = 8.55 K/mm) with different growth rates V, from 9.43 to 173.3 μm/s, by using a Bridgman-type furnace. The lamellar eutectic spacings (λ_E) were measured from transverse sections of the samples. The functional dependencies of lamellar spacings λ_E (\({\lambda _{A{l_2}CuMg}}\) and \({\lambda _{A{l_2}Cu}}\) in μm), microhardness H _V (in kg/mm²), tensile strength σ_T (in MPa), and electrical resistivity ρ (in Ω m) on the growth rate V (in μm/s) were obtained as \({\lambda _{A{l_2}CuMg}} = 3.05{V^{ - 0.31}}\), \({\lambda _{A{l_2}Cu}} = 6.35{V^{ - 0.35}}\), \({H_V} = 308.3{\left( V \right)^{ - 0.33}}\); σ_T= 408.6(V)^0.14, and ρ = 28.82 × 10^–8(V)^0.11, respectively for the Al–Cu–Mg eutectic alloy. The bulk growth rates were determined as \(\lambda _{A{l_2}CuMg}^2V = 93.2\) and \(\lambda _{A{l_2}Cu}^2V = 195.76\) by using the measured values of \({\lambda _{A{l_2}CuMg}}\), \({\lambda _{A{l_2}Cu}}\) and V. A comparison of present results was also made with the previous similar experimental results.     

Comments on “A numerical method to determine interdiffusion coefficients of Cu6Sn5 and Cu3Sn intermetallic compounds”

Li et al. (Intermetallics 2013; 40:50–59) [1] published a paper on “A numerical method to determine interdiffusion coefficients of Cu₆Sn₅ and Cu₃Sn intermetallic compounds”. In section 5.1 of this paper, they stated that the Wagner's method can be used to calculate the integrated interdiffusion coefficients for an incremental diffusion couple only under the assumption of “constant molar volume” for all phases. They gave a detailed derivation. In this comments, we show however that one of the assumptions in their derivation is unphysical, which made them give wrong conclusions. We propose a modified derivation of Wagner's equation without the assumption of “constant molar volume”.     

Influence of Cu content on microstructure,grain orientation and mechanical properties of Sn–xCu lead-free solders

The effect of Cu content on the microstructure, grain orientation and mechanical properties of Sn–xCu (x=0–4.0 wt.%) lead-free solder was studied. Results showed that added Cu induced the formation of intermetallic phases. Only the η-Cu₆Sn₅ and ?-Cu₃Sn phases were present in the β-Sn matrix. For all contents, the strongly preferred orientation of the β-Sn phase was formed on the {001} plane. In Sn doped with 1.0 wt.% Cu, the η-Cu₆Sn₅ phase exhibited the preferred orientation of {0001} plane, whereas doping with 3.0 or 4.0 wt.% Cu transformed the preferred orientation to the {010} plane. In addition, only the {0001} and planes were present in the ?-Cu₃Sn phase. The high Cu contents contributed to an increased number of low-angle boundaries, high residual strain, tensile strength and microhardness.     

Rate-dependent behavior of Sn alloy–Cu couples: Effects of microstructure and composition on mechanical shock resistance

Solders serve as electrical and mechanical interconnects in electronic packaging. The mechanical shock behavior of a Pb-free solder joint is quite complex, since the influences of solder microstructure, intermetallic compound (IMC) layer thickness, and strain rate on the overall dynamic solder joint strength need to be quantified. Dynamic solder joint strength is hypothesized to be controlled by two factors. At low strain rates it should be controlled by the bulk solder, whereas at high strain rates it may be controlled by the brittle intermetallic compound layer. In this paper, the dynamic solder joint strength of Sn–3.9 Ag–0.7 Cu solder joints was experimentally measured over the strain rate range 10^?3–12 s^?1. The influences of changes in solder microstructure and IMC layer on dynamic solder joint strength were quantified, and visualized in three dimensions. Fracture mechanisms operating in the solder-controlled and IMC layer-controlled dynamic strength regimes are discussed. Finally, qualitative numerical simulations were conducted, which accurately depict the experimentally observed fracture behaviors.     

Yb–Cu–Sn system: the isothermal section at 400°C

Phase equilibria in the ternary system Yb–Cu–Sn have been studied by X-ray powder diffraction analysis, optical and scanning electron microscopy and electron probe microanalysis. The isothermal section has been analysed at 400°C: 10 ternary compounds have been confirmed or determined and the corresponding tie-triangles defined. The ternary compounds are YbCu_4.4Sn_0.6, Yb₃Cu₁₃Cu₄, Yb₁₄Cu₆₀Sn₂₆, YbCu₉Sn₄, Yb₃₀Cu₃₉Sn₃₁, YbCuSn, Yb₅CuSn₃, Yb₂₃Cu₄₂Sn₃₅, Yb₃Cu₄Sn₄, Yb₃₆Cu₁₈Sn₄₆.     

Influence of Cu addition on intermetallic compound formation and microstructure of Sn–3Ag–1˙5Sb–xCu solder joints

Abstract

This study investigates the influence of 0–1˙5 wt-%Cu addition on the microstructure and the intermetallic compound (IMC) formation of the as soldered Sn–3Ag–1˙5Sb–xCu (wt-%) solders and following thermal storage at 150°C for 0, 25, 200 and 600 h, with the intention of identifying the optimum Cu addition for industrial applications. The experimental results show that the melting point of Sn–3Ag–1˙5Sb–xCu solder decreases with Cu addition. For Cu additions of 1˙0 wt-% or higher, an IMC of Cu₆Sn₅ particles is dispersed throughout the matrix, resulting in a dispersion strengthening effect, and its size increases with the levels of Cu addition increasing. The coarsened long strip like Cu₆Sn₅ with a length of more than 100 μm growing from the upper interface of IMC layer into the solder matrix is observed in the solder with 1˙5 wt-%Cu addition after thermal storage. Cu₆Sn₅ grains in the IMC layer develop the ripening grains with a more hexagonal or polygonal shape and smooth edged flat surfaces instead of scallop shape. Additionally, the microhardness of each solder increases with Cu addition and decreases with increasing time of thermal storage at 150°C.     

Microstructural evolution and mechanical properties of Cu–Al alloys subjected to equal channel angular pressing

Ultrafine-grained (UFG) or nanocrystalline (NC) Cu–Al alloys were prepared using equal-channel angular pressing (ECAP) to investigate the influence of stacking fault energy (SFE) on the microstructural evolution during deformation and the corresponding mechanical properties. The grain refinement mechanism was gradually transformed from dislocation subdivision to twin fragmentation by tailoring the SFE of alloys. Meanwhile, homogeneous microstructures and nanoscale grains were readily achieved in the low-SFE Cu–Al alloys and the equilibrium grain size was decreased by lowering the SFE. Moreover, in the Cu–Al alloy with extremely low SFE, shear fracture occurred during ECAP at strain levels higher than two due to the formation of macroscopic shear bands. In addition, the normalized deformation conditions at large strain were qualitatively discussed. More significantly, the strength and uniform elongation were simultaneously improved by lowering the SFE. This simultaneity results from the formation of profuse deformation twins and microscale shear bands, and their extensive intersections.     

Response to comments on “A numerical method to determine interdiffusion coefficients of Cu6Sn5 and Cu3Sn intermetallic compounds”

Comments have recently been made by Yuan et al. [1] to deny one statement in our paper [2], Eq. (21) in Wagner's paper [3] can be used to accurately calculate the integrated interdiffusion coefficient for an incremental diffusion couple only under the assumption of constant Molar volume for all phases. We respond here to explain how they misunderstood our mathematical deduction, made a mistake in deriving a couple of equations, falsely cited our work and employed unjustifiable assumption. As a result, we believe that their comments are invalid to deny our statement.     

Ecologically clean solder based on Sn–Ag–Cu

A solder is developed, which does not contain harmful components such as lead and shows super performance properties, at the same time the processing behaviour of the solder remains unchanged.     

Effects of Sn additions on microstructure and corrosion resistance of heat-treated Ti–Cu–Sn titanium alloys

The microstructure and corrosion properties of Ti7CuxSn (x?=?0–5?wt-%) alloys after solution treatment have been investigated. The alloys were solution-treated (ST) at 1000°C for 2?h, followed by quenching in water to room temperature. It was found that the microstructure of the ST Ti7Cu alloy had only a martensite structure, and that addition of Sn could refine the microstructure of Ti7CuxSn alloy. Notably, the pseudo dendritic α-Ti phase was formed in ST Ti7Cu5Sn alloys. Potentiodynamic polarisation curves and electrochemical impedance spectroscopy data demonstrated that adding Sn improved the electrochemical corrosion behaviour of the Ti7CuxSn alloy.     

The isothermal section at 400°C of the Nd–Cu–Sn ternary system

The Nd–Cu–Sn isothermal section at 400°C has been investigated by means of X-ray diffraction, optical and scanning electron microscopy and electron probe microanalysis. The following compounds have been identified or confirmed: NdCu₅Sn, Nd₇Cu₃₅Sn₁₁, NdCu₉Sn₄, NdCuSn, Nd₃Cu₄Sn₄, NdCu₂Sn₂, Nd₂Cu₃Sn₆ and NdCu_1−ySn₂, and their crystal structure have been determined or revised. Single crystal structure determination of the phases Nd₇Cu₃₅Sn₁₁ and Nd₃Cu₄Sn₄ and full profile powder refinement of the compound Nd₂Cu₃Sn₆, previously suggested as Nd₂Cu₄Sn₅, are also given. The subdivision of the composition triangle in tie triangles has been nearly completed. Of the predicted 36 three-phase equilibria, thirty have been defined. The general characteristics of the section have been discussed in comparison with those of other R–Cu–Sn systems formed by light rare earths (R= Ce, Pr).     

Microstructures and mechanical properties of homogenization and isothermal aging Mg–Gd–Er–Zn–Zr alloy

The effects of homogenization and isothermal aging treatment on the mechanical properties of Mg–12Gd–2Er–1Zn–0.6Zr(wt%) alloy were investigated. The precipitated long-period stacking order(LPSO) structure and the aging precipitation sequence of the conditioned alloys were observed and analyzed, respectively. The results indicate that the 14H-LPSO structure occurs after the homogenization treatment and the b0 phase forms after the isothermal aging process. These two independent processes could be controlled by the precipitation temperature range. The significant increase in the elongation of the as-cast alloy after homogenization treatment is attributed to the disappearance of the coarse primary Mg5(Gd, Er, Zn) phase and the presence of the 14H-LPSO structure. The precipitation sequence of the investigated alloy is a-Mg(SSS)/b00(D019)/b0(cbco)/b.Furthermore, the yield tensile strength(YTS) and ultimate tensile strength(UTS) values of the isothermal aging alloy have a great improvement, which could be attributed to the high density of the precipitated b0 phase.     

A DSC analysis of thermodynamic properties and solidification characteristics for binary Cu–Sn alloys

The liquidus temperatures and enthalpies of fusion for Cu–Sn alloys are systematically measured across the whole composition range by differential scanning calorimetry (DSC). The liquidus slope vs. Sn content is derived on the basis of the measured results. The measured enthalpy of fusion is related to the Sn content by polynomial functions, which exhibit one maximum value at 55 wt.% Sn and two minimum values around 28.9 wt.% Sn and 90 wt.% Sn, respectively. The undercoolability of those liquid alloys solidifying with primary α (Cu) solid solution phase is stronger and can be further enhanced by increasing the cooling rate. However, other alloys with the preferential nucleation of intermetallic compounds display smaller undercoolings and are not influenced by cooling rate. Microstructural observations reveal that peritectic reactions can rarely be completed. With the increase in undercooling, the primary α (Cu) dendrites are refined in the peritectic Cu–22 wt.% Sn alloy. For the hyperperitectic Cu–70 wt.% Sn alloy, typical peritectic cells are formed in which the peritectic η(Cu₆Sn₅) phase has wrapped the primary ε(Cu₃Sn) phase. The DSC curves of metatectic-type Cu–Sn alloys indicate that the metatectic transformation γ → ε + L upon cooling is an exothermic event, and a large undercooling of 70 K is required to initiate this transformation in metatectic Cu–42.5 wt.% Sn alloy. The metatectic microstructures are characterized by (ε + η) composite structures. The η phase is mainly distributed at the grain boundaries of the coarse ε phase, but are also dispersed as small particles inside ε grains. The volume fraction of the η phase increases with the Sn content.     

Effects of Sb Addition on Microstructural Evolution and Mechanical Properties of Mg–9Al–5Sn Alloy

The Mg–9Al–5Sn-xSb(x=0.0,0.3,0.6,1.0,1.5 wt%) alloys were prepared by a simple alloying process followed by hot extrusion with an extrusion ratio of 28.2. The effects of Sb additions on the microstructure and mechanical properties of the Mg–9 Al–5 Sn alloys were investigated by optical microscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer. The results indicated that the phases α-Mg matrix, Mg_2_Sn, Mg_3Sb_2 and Mg_17 Al_12 exist in the as-cast Sb-containing alloys. Sb addition results in the precipitation of Mg_3Sb_2. The dendritic size of these alloys decreases with the addition of Sb. Both their ultimate tensile strength and yield strength of extruded alloys increase, and their elongation decreases gradually with increasing the content of Sb. The better mechanical properties of the as-extruded alloys were achieved due to the refined grains and the formation of dispersive second phases Mg_3Sb_2.     

Interfacial reactions of Sn–Zn–Ag–Cu alloy on soldered Al/Cu and Al/Al joints

This work shows the effect on the soldering process of the addition of Ag and Cu to Sn–Zn alloys. Soldering of Al/Cu and Al/Al joints was performed for a time of 3?min, at a temperature of 250°C, with the use of flux. Aging was carried out at 170°C for Al/Cu and Al/Al joints for 1 and 10 days. During the aging process, intermetallic layers grew at the interface of the Al/Cu joint at the Cu substrate. Intermetallic layers were not observed during wetting of Al/Al joints. On the contrary, dissolution of the Al substrate and migration of Al-rich particles into the bulk of the solder were observed. The experiment was designed to demonstrate the effect of Ag and Cu addition on the dissolution of Al substrate during the soldering and aging processes. In the solder alloys, small precipitates of AgZn₃ and Cu₅Zn₈ were observed.     

Investigation of small Sn–3.5Ag–0.5Cu additions on the microstructure and properties of Sn–8Zn–3Bi solder on Au/Ni/Cu pads

The formation of intermetallic compounds and the shear strength of Sn–Zn–Bi solder alloys with various (0, 1, 3, 5 and 7 wt%) weight percentages of Sn–Ag–Cu were investigated on Au/Ni metallized Cu pads depending on the number of reflow cycles. In Sn–Zn–Bi solder joints, scallop-shaped AuZn₃ intermetallic compound (IMC) particles were found at the interfaces and in the solder ball regions, fine Bi- and needle-shaped Zn-rich phase were observed in the Sn matrix. After Sn–Ag–Cu additions, an additional Ag–Zn intermetallic compound layer was adhered to the top surface of the AuZn₃ layer at the interface and fine spherical-shaped AgZn₃ intermetallic compound particles were detected in the solder ball regions together with Bi- and Zn-rich phase volumes. After the addition of Sn–Ag–Cu, the shear strength of Sn–Zn–Bi solder joints increased due to the formation of the fine AgZn₃ intermetallic compound particles. The shear strengths of Sn–Zn–Bi and Sn–Zn–Bi/7 wt% Sn–Ag–Cu solder joints after one reflow cycle were about 44.5 and 53.1 MPa, respectively and their shear strengths after eight reflow cycles were about 43.4 and 51.6 MPa, respectively.