Mixed Ductile-brittle Fracture Research Articles

Effect of rapid thermal shock cycle on the thermomechanical reliability of 20Sn-80Pb solder bumps

The influence of rapid thermal shock(RTS) cycles on 20Sn-80Pb solder bumps was studied. In the study, 20Sn-80Pb solder bumps were prepared by desktop nitrogen lead-free reflow soldering machine. The prepared 20Sn-80Pb solder bumps were used for RTS test in the temperature rang of 0°C ~ 150°C. One cycle of RTS is 24 seconds, and the temperature rise and fall rate of RTS is 12.5 C/s. The result indicated that when the cycle of RTS reached 1500T (here T is cycle, the same below), the shear strength of Sn-80Pb solder bump dropped by drastically 48.6%. Whereas, when the cycle of RTS reached 5500T, 20Sn-80Pb solder bumps’ shear strength decreased to 18.35 MPa, which increased by 7.5% compared with that of l6.97 MPa at 4500T. With the increase of RTS cycles, 20Sn-80Pb solder bumps’ shear strength was a decreasing trend and the fracture mechanism changed from ductile fracture to ductile-brittle mixed fracture, which could be subject to the thickening of the interfaical IMCs and the stress concentration caused by the growth of interfacial IMCs. To understand the changes of the mechanical properties of 20Sn-80Pb solder bumps, the influences of RTS on the crack and interfacial IMC of 20Sn-80Pb solder bumps were studied in details.

Role of microstructural heterogeneities in damage formation and fracture of oligocrystalline Mg under tensile loading

This paper describes the main results from in-situ and ex-situ testing and characterization studies to reveal the effects of microstructural heterogeneities that develop during plastic deformation of coarse-grained Mg on damage formation and fracture of the material. Experiments are carried out using a micro-test tensile stage in and outside a scanning electron microscope in combination with electron backscatter diffraction (EBSD), micro X-ray computed tomography (μXCT), and optical microscopy. It is seen that the micro-specimens exhibit significant macroscopic shape changes upon interrupting the tests. Such shape changes result from microstructural changes and underlying relaxation of inter-granular back-stress accumulated during loading. Twins with low Schmid factor (SF) for basal slip in grains with low SF for basal slip are observed to de-twin. Upon de-twinning, dislocations are found to remain in the structure as is evident by increase in the kernel average misorientation (KAM). Interestingly, twins nucleate in these regions again with continuous forward straining. In contrast, twinned domains favorably oriented for basal slip do not de-twin but thicken with plastic straining. These twins soften the material leading to localization of deformation and damage nucleation. At the interface between twinned domains and parent grains voids are observed. Voids nucleate due to lack of slip transfer causing pile-ups, as is evident from high KAM. Additionally, twins are observed to induce a substantial surface roughness. Large twins accommodating significant shear strain form surface ridges. Such significant heterogeneities also result in nucleation of voids from the surface. In addition to twinning induced voids, damage accumulates and voids form and propagate along high-angle grain boundaries between grains with low SF or those with disparate SF for basal slip. μXCT reveals voids away from the fractured surface highlighting the extent of heterogeneous deformation and fracture behavior of Mg. Fracture surfaces exhibit characteristics of mixed ductile-brittle fracture with signs of trans-granular cleavage and fluted facets with minor content of inter-granular fracture.

Effect of La addition on microstructure and mechanical properties of hypoeutectic Al-7Si aluminum alloy

The effect of La addition (0, 0.1, 0.2, 0.4, wt.%) on the microstructure, tensile properties and fracture behavior of Al-7Si alloy was investigated systematically. It is found that the La appears in the Al-7Si alloy in the form of Al4La and Al2Si2La phases. La addition can refine the secondary dendrite arm spacing (SDAS) and eutectic Si particles, which are decreased by 7.9% and 7%, respectively, with the optimal La content of 0.1wt.%. Because when 0.1wt.% La is added, a relatively higher nucleation undercooling of 37.47 °C is observed. Higher undercooling degree suggests that nucleation is accelerated and subsequent growth is restrained. After T6 heat treatment, compared with the without La, the ultimate tensile strength of the alloy with 0.1wt.% La is enhanced by 5.2% from 333 MPa to 350.2 MPa and the elongation increases by 73% from 7.37% to 12.75%, correspondingly. The fracture mode evolves from the ductile-brittle mixed fracture to ductile fracture mode. However, when La element content reaches a certain value of 0.4wt.%, serious segregation takes place during the solidification process. The formed brittle phases deteriorate the tensile properties of the alloy and the fracture mode of Al-7Si-0.2/0.4 La changes to mixed ductile-brittle fracture mode.

Design for Ti-Al-V-Mo-Nb alloys for laser additive manufacturing based on a cluster model and on their microstructure and properties

In this study, α+β Ti-Al-V-Mo-Nb alloys with the addition of multiple elements that are suitable for laser additive manufacturing (LAM) were designed according to a Ti-6Al-4V cluster formula. This formula can be expressed as 12[Al-Ti12](AlTi2)+5[Al-Ti14]((Mo, V, Nb)2Ti), in which Mo and Nb were added into the alloys partially instead of V to give alloys with nominal compositions of Ti-6.01Al-3.13V-1.43Nb, Ti-5.97Al-2.33V-2.93Mo, and Ti-5.97Al-2.33V-2.20Mo-0.71Nb (wt.%). The microstructures and mechanical properties of the as-deposited and heat-treated samples prepared via LAM were examined. The sizes of the β columnar grains and α laths in the Nb-containing samples are found to be larger than those of the Ti-6Al-4V alloy, whereas Mo- or Mo/Nb-added alloys contain finer grains. It indicates that Nb gives rise to coarsened β columnar grains and α laths, while Mo significantly refines them. Furthermore, the single addition of Nb improves the elongation, whereas the single addition of Mo enhances the strength of the alloys. The simultaneous addition of Mo/Nb significantly improves the comprehensive mechanical properties of the alloys, leading to the best properties with an ultimate tensile strength of 1,070 MPa, a yield strength of 1,004 MPa, an elongation of 9%, and micro-hardness of 355 HV. The fracture modes of all the alloys are ductile-brittle mixed fracture.

Effect of surface nano-crystallization induced by supersonic fine particles bombarding on microstructure and mechanical properties of 300M steel

Supersonic fine particles bombarding (SFPB) technology opens a new territory for engineering materials towards improved performances. Owing to its merits and emerging applications, 300M steel (tensile strength ≥1800 MPa) was treated with SFPB to create surface gradient nanostructures. The time dependent SFPB process was implemented on various 300M steel surface to investigate the microstructural evolution and mechanical property. 300M steel surface grains were sufficiently refined down to nanometer scale under high energy SFPB. In the subsurface layer, acicular martensite was found to be bent and broken, resulting in the high-density dislocation. At the early stage of SFPB, the impact affected area of 300M steel surface was deepened with increasing SFPB time, and the grains were constantly refined, which further lead to higher strength and improved hardness. However, after longer treatments of more than 90 s, bombardment energy accumulated at 300M steel surface resulted in grain growths and deteriorations of hardness. In particular, the newly formed microcracks substantially reduced the tensile strength. After SFPB treatment, the dimple size of the 300M steel surface fracture decreased significantly, and a large area of cleavage plane appeared, showing typical characteristics of ductile-brittle mixed fracture.

Fracture Behavior of an AlMgMnSc Alloy at Different Temperatures

An Al-4.57Mg-0.35Mn-0.2Sc-0.09Zr (wt. %) alloy was studied in the fine-grained state obtaining after equal channel angular pressing. The mechanical behavior of alloy at the temperatures 173 K, 298 K and 348 K and at strain rate 1×10–3 s–1 is studied. Increase of the temperature testing from 173 K to 348 K decreases the yield stress by 80 MPa, the ultimate tensile strength by 60 MPa while elongation-to failure increases by a factor of 1.4. It was found that at temperatures of 298 and 173 K, the studied alloy mainly demonstrates the mode of ductile fracture, and at a temperature of 348 K the mechanism can be described as mixed ductile-brittle fracture. It was also established that of the studied alloy is the temperature dependence of the size of the dimples on the fracture surface. The formation of smaller dimples in the samples deformed at 298 K was observed.

Microstructure and mechanical properties of friction stir lap welded dissimilar zirconium-steel joint

Friction stir lap welding (FSLW) was employed to weld dissimilar joints of zirconium and stainless steel for the first time. The microstructure, evolution mechanism of intermetallic compounds (IMCs) and mechanical properties of joint were investigated. Discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occurred in zirconium, while DDRX occurred in stainless steel during FSLW. The formation sequence of IMCs at the interface was FeZr3, FeZr2, Fe2Zr, and Fe23Zr6. The crack nucleated at the hook zone on the advancing side (HookAS), and IMCs in the Zr/SS mixed zone accelerated crack propagation. The fracture surface exhibited ductile-brittle mixed fracture characteristic.

Effect of Heat Treatment on Microstructure and Mechanical Properties of As-Forged ZYK530 Mg Alloy

In the paper, the microstructure and mechanical properties of ZYK530 Mg alloy with different aging heat treatment processes were analyzed and studied by OM, SEM, EDS and XRD. The results show that after heat treatment at different temperatures and aging times, the hardness of the alloy first decreases, then increases in a wave-like manner, and then decreases in a wave-like manner after reaching its peak value. The optimum aging process of ZYK530 alloy is T5-220°C×5h, and the maximum hardness is 88.34HRE, which tensile strength, yield strength and elongation are 335MPa, 305MPa and 13.5% respectively. Compared with the untreated forged alloy, the mechanical properties are increased by 6.3%, 4.8% and 35%, which its fracture mechanism is mainly ductile-brittle mixed fracture.

High strength (~2000 MPa) or highly ductile (~11%) additively manufactured H13 by tempering at different conditions

H13 is a typical high-performance tool steel, and has a wide application in the mold making industry. To optimize mechanical properties of additively manufactured H13, a detailed investigation on tempering was conducted at 600 oC and 700 oC. Tensile testing, transmission electron microscopy (TEM) and atom probe tomography (APT) were utilized in the present study. It was found that the selective laser melted H13 showed unsatisfactory tensile properties in the as-printed condition, especially in terms of the elongation at fracture (~2.42%). After tempering at 600 oC, the tensile properties, including the ultra-high yield strength (1483 ± 48 MPa), ultimate strength (1938 ± 62 MPa) and ductility (~5.8%), were significantly improved, which was attributed to the strengthening effect mainly from the presence of a large number of fine V8C7 precipitates and the high density of dislocations. After tempering at 700 oC, the material showed a high ductility (~10.95%) and moderate tensile strength (1076 ± 21 MPa). The fracture mode was a mixed ductile-brittle fracture for the specimen after tempering at 600 oC, and became a ductile fracture for the specimen after tempering at 700 oC. It is clarified that a transition in the microstructure explains the difference in the mechanical behavior between the specimens tempered at 600 oC and 700 oC. The present study provides a basis for manipulating the SLM-fabricated H13 for applications requiring either high strength or high ductility.

Microstructure and shear property of In-Sn-xAg solder joints fabricated by TLP bonding

Transient liquid phase (TLP) bonding was applied to prepare Cu/In-Sn-xAg/Cu (x = 20, 30, 40, 50, 60, 70 wt%) solder joints, and the effect of Ag particle content on joint microstructure, shear property and growth mechanism of intermetallic compound (IMC) was studied. The results indicated that the microstructure of solder joint consists of interfacial diffusion reaction zone and particle in situ reaction zone. The IMC in interfacial diffusion reaction zone is Cu3(In, Sn) phase and the IMCs in in situ reaction zone is composed of In-rich phase + Ag particle + ζ-Ag3In + Ag3(In, Sn). With the increasing Ag particle content, the thickness of IMC layer in diffusion reaction zone is decreased, the total amount of In-rich phase and Ag3(In, Sn) phase in in situ reaction zone is decreased, the quantity of Ag particles and ζ-Ag3In phase is grew. The AgIn2 phase is a stable IMC formed as a preferential reaction because it requires less Gibbs free energy than Sn-Ag phase, and it is transformed to ζ-Ag3In phase with increasing bonding time to 10 min. The void ratio of solder joints is decreased firstly and then increased with increasing Ag content. The shear strength of the joint is increased firstly and then decreased with increasing Ag particle content, and the maximum shear strength 22.2 MPa is obtained by Cu/In-Sn-50Ag/Cu solder joints. The shear fracture mechanism of solder joints is changed from ductile–brittle mixed fracture to brittle fracture.

Modification of multi-component Al–Si casting piston alloys by addition of rare earth yttrium

The effects of yttrium (Y) additions (0.2, 0.4, 0.6, 0.8 and 1.0 wt%) on the microstructures and mechanical properties of multi-component Al–Si casting piston alloys were studied in this work. The as-cast specimens were characterized and analyzed using different techniques (SEM, EDS, DSC, XRD, EBSD and TEM) to determine the modification capabilities and better understand the underlying mechanism of adding rare earth Y. The results indicate that the morphology of the α-Al phase could be refined from coarse dendrites to relatively fine cell-like structures and uniform equiaxed grains when adding Y at a concentration of 0.8 wt%. The corresponding mean secondary dendrite arm spacing decreased by 64.6% from 12.7 μm to 4.5 μm. Meanwhile, the rare earth Y effectively modified the eutectic Si structure from coarse flake and needle to fine fibrous structure and partial particles. The average roundness of the eutectic Si decreased by 52% from 9.8 to 4.7. In addition, the fish-bone-like γ-Al7Cu4Ni and δ-Al3CuNi phases gradually transformed into the block-shaped AlCuNiY-Aluminide phase with the addition of rare earth Y. The nanoscale Y-containing compounds adsorbed at the front of the Si phase growth interface to restrain further growth, which changed its growth direction and preferentially promoted the formation of a twin structure along the {111}〈112〉 orientation. With the modification and homogenization of the eutectic structure, the comprehensive mechanical properties were evaluated by the Q-factor increased by 52.6% from 173 MPa to 264 MPa. The fracture model of the multi-component Al–Si alloy gradually transformed from a classical, brittle, trans-granular fracture mode to a mixed ductile-brittle fracture style.

PM versus IM Ti-5Al-5V-5Mo-3Cr Alloy in Mechanical Properties and Fracture Behaviour

The comparisons of mechanical properties and fracture behaviour between as-consolidated PM Ti-5553 alloy and as-cast IM Ti-5553 alloy were investigated through tensile, fracture toughness and impact toughness tests in this research. The slightly higher strength but much higher ductility and toughness can be identified in IM alloy specimens, which is also confirmed by the fracture behaviour of the specimens after mechanical tests. IM alloy specimens always exhibit the ductile dimple fracture mechanism in the different tests, while the fracture mechanism of PM alloy specimens indicates a high loading rate sensitivity, changing from the mixed ductile-brittle quasi-cleavage fracture into the brittle cleavage fracture mechanism accompanied by the remarkable decrease of impact toughness. The relatively low mechanical properties, especially the ductility and the brittle fracture behaviour of as-consolidated PM Ti-5553 alloy, are mainly explained by the differences in the initial microstructures between these two alloys.

Microstructure and Properties of 3D Printed Inconel 718 Joint Brazed with BNi-2 Amorphous Filler Metal

Three dimensional (3D) printing technology has been widely used in metal manufacturing industry. This study focused on the vacuum brazing of 3D printed Inconel 718 superalloy with BNi-2 amorphous filler metal. Interfacial microstructure and element distribution revealed excellent wettability and spreadability of the filler metal as well as favorable brazability of the base material. Brazed joint could be divided into two distinct zones: isothermally solidified zone (ISZ) consisting of γ-Ni solid solution and diffusion-affected zone (DAZ) consisting of a large amount of precipitates besides γ-Ni solid solution. Microhardness reached peak values in DAZ. Although borides filled the gaps of base material’s grains to restrict grain boundary sliding and restrain the expansion of gaps, but its high hardness and brittleness would cause DAZ turn into weaker region when external loads were very large. The complete diffusion of B indicated the completion of isothermally solidified process. Precipitate CrB2 with high hardness and brittleness was the key point of reducing the joint strength. Shear strength of the brazed joint was up to 802 MPa, and fracture morphology presented a mixed ductile-brittle fracture.

Effect of Ni Addition to Sn0.7Cu Solder Alloy on Thermal Behavior, Microstructure, and Mechanical Properties

The addition of Ni on lead-free solder alloys Sn0.7Cu was tested in this study. A small amount of Ni was added to the solder alloys to evaluate the thermal behavior, microstructure, and mechanical properties of the composite solders after sintering and isothermal aging for 3 days and then compared with the results of the binary Sn0.7Cu solder. The results indicated that the ultimate tensile strength and yield tensile strength changed when adding 0.25 wt.% of Ni. The tested results of the differential scanning calorimeter showed that the addition of Ni (such as 0.5 and 1 wt.%) could obviously increase the solidification temperature of Sn0.7Cu alloys in the cooling process. When the Ni content was increased to 0.25 wt.% in the ternary condition, which includes the Sn0.7Cu-xNi (x = 0, 0.1, 0.25, 0.5, and 1 wt.%) solder alloys for the indentation creep test, the minimum creep rate reached the maximum; however, the trend was reversed as the Ni content was higher than this level. In addition, the microstructure of Sn-0.7Cu-xNi solder alloys was obviously different with the eutectic Sn-0.7Cu solder, such that the Ni gradually accumulated in the (Cu, Ni)6Sn5 IMCs within the Ni-containing solder alloys. Additionally, this process refined the microstructure of the Sn-0.7Cu solder. The fracture surface of the eutectic Sn-0.7Cu solder revealed ductile fracture modes; however, there was no mixed ductile–brittle fracture mode occurred when the Ni content was in the range of 0-1 wt.%.

Influence of Interfacial Intermetallic Growth on the Mechanical Properties of Sn-37Pb Solder Joints under Extreme Temperature Thermal Shock

Solder joints in thermally uncontrolled microelectronic assemblies have to be exposed to extreme temperature environments during deep space exploration. In this study, extreme temperature thermal shock test from −196 °C to 150 °C was performed on quad flat package (QFP) assembled with Sn-37Pb solder joints to investigate the evolution and growth behavior of interfacial intermetallic compounds (IMCs) and their effect on the pull strength and fracture behavior of Sn-37Pb solder joints under extreme temperature environment. Both the scallop-type (Cu, Ni)6Sn5 IMCs at the Cu lead side and the needle-type (Ni, Cu)3Sn4 IMCs at the Ni-P layer side changed to plane-type IMCs during extreme temperature thermal shock. A thin layer of Cu3Sn IMCs was formed between the Cu lead and (Cu, Ni)6Sn5 IMC layer after 150 cycles. The growth of the interfacial IMCs at the lead side and the Ni-P layer side was dominated by bulk diffusion and grain-boundary diffusion, respectively. The pull strength was reduced about 31.54% after 300 cycles. With increasing thermal shock cycles, the fracture mechanism changed from ductile fracture to mixed ductile–brittle fracture, which can be attributed to the thickening of the interfacial IMCs, and the stress concentration near the interface caused by interfacial IMC growth.

Effect of solid fraction on microstructures and mechanical properties of a Mg-Al-La-Ca alloy processed by rheocasting

Morphological evolution of microstructures and tensile properties in Mg-Al alloy containing La and Ca (Mg-6Al-3La-1Ca) processed by rheocasting with different solid fractions (fs) were investigated at this paper. An apparatus for semisolid metal alloy processing was used to melt and to obtain the rheocast material. Isothermal mechanical stirring experiments were carried out with fs = 0.30, 0.49 and 0.61 at 950 rpm for 10 min. A conventional casting (no stirring) was also obtained for comparisons. Results showed that microstructure in conventional casting is composed by α-Mg dendritic matrix and Al11La3, (Al,Mg)2Ca and Mg2Ca compounds. Non-dendritic and globular microstructures were observed in the rheocasting. For fs = 0.30 the acicular Al11La3 phase precipitated at globule boundaries, while for the fs = 0.49 and fs = 0.61 the acicular phase precipitated both inside and at globule boundaries. The ideal rheocasting condition was achieved fs = 0.30 due to the improvement of 76% for the ultimate tensile strength (UTS) and 80% in the strain to fracture when compared to the conventional casting. Fracture surface analysis pointed to a mixed ductile-brittle fracture mode containing dimples and quasi-cleavage facets for the lowest solid fraction (fs = 0.3), and a fully brittle fracture mode consisting exclusively of cleavage planes for the highest solid fraction (fs = 0.61).

Effect of ultrasonic vibration on the interfacial IMC three-dimensional morphology and mechanical properties of Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu halogen free solder joints

Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu halogen free solder joints were fabricated by an ultrasonic vibration (USV)-assisted soldering process. The effects of the USV power on the three-dimensional (3-D) morphology of the intermetallic compounds (IMC) and mechanical properties of the halogen free solder joints were characterized systematically. Results showed that the root-mean-square roughness (Rrms) and the mean spacing of adjacent peaks of the profile (λave) of the interfacial IMC were linearly correlated with shear strength of the halogen free solder joints. It was more comprehensive to adopt the λave and Rrms evaluation parameters to characterize the relationship between the interfacial IMC 3-D morphology and shear strength of the halogen free solder joints. With increasing USV power, the eutectic microstructure of the solder seam was refined, and the proportion of eutectic microstructure in the solder seam and microhardness increased. When the USV power increased to 130 W, the Rrms and average thickness of the interfacial IMC decreased (decreases of 37.6% and 56.4%, respectively) and the corresponding λave and shear strength of the solder joint increased (increases of 68.7% and 45.8%, respectively). With increasing USV power, the fracture mechanism of the halogen free solder joint changed from brittle fracture to the ductile–brittle mixed fracture, and the fracture pathway transferred from the interfacial transition zone consisting of the solder seam and the interfacial IMC layer to the solder seam.

Effects of Ti addition on microstructure and mechanical property of spark-plasma-sintered transformable 9Cr-ODS steels

By adding Ti consistent, dual-phase 9Cr ODS steel with martensite and transformed ferrite is fabricated by spark plasma sintering, and M23C6 carbides are identified in transformed ferrite. Although Ti is strong carbide forming element, Ti concentration has a negligible effect on the distribution of M23C6 within ferrite, as well as martensite size. With Ti addition increasing, the amount of ferrite is increased, and more fine Y-Ti-O complex oxides are produced. Annealing treatment will not change the ferrite distribution, but the density and size of oxide nanoparticles in steels will be affected. It is found that Ti addition can effectively improve the tensile strength of 9Cr ODS steels, which is related to the Y-Ti-O oxides with small size. The large-sized ferrite grains will induce ductile-brittle mixed fracture, deteriorating the ductility of transformable 9Cr ODS steels.

Evaluation of fracture toughness in different regions of weld joints using unloading compliance and normalization method

Both unloading compliance method and normalization method specified in ASTM E1820-16 were conducted on the API 5L X70 and X80 pipeline steels. Extensive experimental measures of fracture toughness for different regions of weld joints were carried out. For comparison, the J–R curves and initiation fracture toughness determined using the normalization method are compared with those obtained by the elastic unloading compliance method for two different weld joints. The results show that good agreements exist between the two methods, and an average difference less than 10% is detected. Moreover, the comparison indicates that the J–R curves from the unloading compliance method are lower at the initial stage of crack extension, and as the crack grows, the J–R curves are higher compared with those of the normalization method. For different regions in weld joints, there is clear distinction of differences between the corresponding results from above two methods. A ductile brittle mixed fracture mechanism is found in weld metal and coarse grained heat affected zone, and a corresponding higher deviation is detected.

Thermodynamic characteristics, microstructure and mechanical properties of Sn-0.7Cu-xIn lead-free solder alloy

The microstructure and mechanical properties of Sn-0.7Cu solder alloy and Sn-0.7Cu with 1.0–5.0 wt% indium addition were investigated in this study. With indium added into Sn-0.7Cu solder, the melting temperature decreased and the reaction temperature increased. Coarse grains of Cu6(Sn,In)5 intermetallic compounds (IMCs) were formed in the alloy matrix when the indium content increased to 1.0 wt%. Indium was evenly distributed in the β-Sn phase and Cu6(Sn,In)5 IMCs in as-prepared In-containing solder alloys. After isothermal aging, indium accumulated gradually in the Cu6(Sn,In)5 IMCs while decreasing its content in the β-Sn phase. Tensile test results indicated that the ultimate tensile strength increased obviously and that the elongation decreased significantly with indium addition. Sawtooths were observed in the stress-strain curves of all aged In-containing alloys. A model describing a coherent relationship between the β-Sn phase and the Cu6(Sn,In)5 phase was proposed to explain this phenomenon. The fracture surface of the Sn-0.7Cu alloy exhibited a ductile fracture mode while a mixed ductile-brittle fracture mode occurred when excessive indium was added into Sn-0.7Cu alloys.