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Joining Mg to Al is challenging because of the deterioration of mechanical properties caused by the formation of intermetallic compounds (IMCs) at the Mg/Al interface. This study aims to improve the mechanical properties of welded samples by preventing the fracture location at the Mg/Al interface. Friction stir welding was performed to join Mg to Al at different rotational and travel speeds. The micro structure of the welded samples showed the IMCs layers containing Al12Mg17 (γ) and Al3Mg2 (β) at the welding zone with a thickness (> 3.5

Plates of AL6XN super-austenitic stainless steel with a single-V groove preparation were gas metal arc welded (GMAW) with and without electromagnetic interaction of low intensity (EMILI) during welding using an ER-NiCrMo3 filler wire and 97% Ar + 3% N2 as shielding gas. The fatigue behavior of the welded joints was evaluated under constant stress amplitude (Δσ/2) between 135 and 170 MPa (R = 0.1) and uniaxial load. The Wohler diagram indicated that for stress amplitude of 170 MPa, 4.19 × 105 and 2.96 × 105 cycles were required for failure without and with EMILI, respectively, whereas for 135, 140, and 145 MPa, 1 × 107 cycles were reached without failure. Welding with EMILI was found to have a positive effect nearby fatigue limit. Observation of the fractures indicates that failures started on the surface of the specimens in the weld metal (WM) due to the stress concentration induced by the abundant presence of precipitates located along the interdendritic spaces in this zone of the welded joint. These particles acted as crack-nucleating agents and then the crack propagated throughout the WM. Fractography revealed brittle fracture associated to cleavage.

In this study, austenitic stainless steel 316L and titanium alloy (ASTM grade 5) were welded together by micro-resistance spot welding at different combinations of welding parameters and by using specifically designed electrode geometry. The welded joints were subjected to tensile shear strength test in order to determine the strength of the welded zones. In addition, micro-hardness and microstructural examinations of the fracture mode (failure analysis) were carried out in order to examine the influence of welding parameters on the welded joints. The results showed that using a combination of 2.0 kN welding current, 100 ms welding time, and 241 N welding force yield the highest load value, 378.25 N by using full factorial design of experiment (DOE). Welding current is the most significant parameter which is obtained through analysis of variance (ANOVA). However, the increase in welding current should be controlled to avoid weld metal expulsion. The microstructure of these resistance-welded metals are detailed and investigated by using SEM and EDS mapping analysis. Based on the SEM observations, columnar dendritic structures can be seen at the fusion zone (FZ) of the welded nugget.

Severely deformed aluminum sheets were processed by friction stir processing (FSP) with SiC nanoparticles under different conditions to improve the mechanical properties of both the stir zone and the heat affected zone (HAZ). In the case of using a simple probe and the same rotational direction (RD) of the FSP tool between passes, at least three FSP passes were required to obtain the appropriate distribution of nanoparticles. However, after three FSP passes, fracture occurred outward from the stir zone during transverse tensile tests; thus, the strength of the specimen was significantly lower than that of the severely deformed base material because of the softening phenomenon in the HAZ. To improve the mechanical properties of the HAZ, we investigated the possibility of achieving an appropriate distribution of nanoparticles using fewer FSP passes. The results indicated that using the threaded probe and changing the RD of the FSP tool between the passes effectively shattered the clusters of nanoparticles and led to an acceptable distribution of SiC nanoparticles after two FSP passes. In these cases, fracture occurred at the HAZ with higher strength compared to the specimen processed using three FSP passes with the same RD between the passes and with the simple probe. The fracture behaviors of the processed specimens are discussed in detail.

Effect of mean stress on fretting fatigue behavior of 304 austenitic stainless steel has been investigated by conducting fretting fatigue tests at a constant contact pressure of 100 MPa under three different mean stresses i.e., 0, 350 and 450 MPa. For comparisons, plain fatigue tests were also carried out. The influence of tensile overload on fretting fatigue life was also investigated. The results showed that with an increase in mean stress, the reduction in fatigue strength due to fretting increased drastically from 51% at 0 MPa mean stress to 71% at 450 MPa mean stress. The application of tensile overload during fretting fatigue had significant influence on the fretting fatigue lives when the tensile overload was above yield strength. The fretting variables, i.e., tangential stress and relative slip amplitude were measured during fretting fatigue tests. Fracture surfaces were examined using scanning electron microscope. The results have been discussed based on the tangential stress measurement, relative slip amplitude evaluation during fretting fatigue and fracture surface examinations.

The texture development during friction stir processing (FSP) of 1050 aluminum severely deformed at the strain magnitude of 2.32 was comprehensively discussed. It was observed that the component $$ \bar{B} $$ of the ideal shear texture along with the cube texture was developed in the severely deformed base metal. The effects of base metal texture on the texture development of stir zone, thermo-mechanically affected zone, and heat-affected zone during FSP were examined. Also, the developed texture components in the vicinity of the FSP tool and the stir zone were correlated to the deformation induced by the rotating tool which consisted of pin and shoulder. The observed texture components in the longitudinal section of the stir zone were found coincided with the ideal shear ones, but different from those observed in the severely deformed base metal. It could be responsible for the fact that the material beneath the FSP tool is predominantly deformed and stirred by the shoulder rather than the pin. The independency of texture development in the stir zone from pin-induced deformation was also consistent with the observation associated with the stir zone geometry which was independent of the pin geometry. Microstructural evolutions in the regions located ahead of the FSP tool manifested the incident of static recovery and recrystallization as a result of the stored strain in the severely deformed base metal. These led to the development of almost random texture and the deterioration of base metal texture in this region. This suggested the independency of texture development in the stir zone from the texture of severely deformed base metal.

Fretting fatigue behavior of IMI 834 titanium alloy has been investigated at room temperature, 400 and 590 °C. For comparison plain fatigue tests were also carried out. Finite element analysis was done to evaluate the tangential stress coefficient and relative slip amplitude during fretting fatigue at room temperature and high temperatures. The fracture surface and fretting contact surface were examined using scanning electron microscope. The result showed that, the fatigue strength has reduced due to fretting both at room temperature and high temperature. With an increase in temperature the fretting fatigue strength reduced. It reduced significantly at 400 °C and drastically at 590 °C, due to the increase in severity of damage in fretting contact surface with an increase in test temperature. The results were discussed based on the relative slip amplitude values, tangential stress coefficient values and the surface damage observations.

In the present study, fatigue crack growth tests of Pb-containing [Sn-37Pb (wt.%)] and Pb-free [Sn-3.0Ag-0.5Cu (wt.%)] solders were performed under cycle/time-dependent step loading at a constant J-integral range (ΔJ). The C* parameter was also estimated for discussing time-dependent crack growth behavior. The experimental results indicated that acceleration of the crack growth rate at the beginning of the second loading step was induced when the C* value for the first loading step was high, regardless of time- or cycle-dependent crack growth and for both Sn-37Pb and Sn-3.0Ag-0.5Cu solders. The length of the acceleration region of the crack growth rate for both solders was in good agreement with the creep damage zone size estimated by the creep zone model proposed by Riedel and Rice.

Adhesion is an important and basic property for thermal spray coatings. The standard tensile test method “ISO 14916” is usually used to evaluate the adhesive strength of coatings. On the other hand, the indentation test method has some advantages to evaluate the interfacial fracture toughness as the adhesive strength, arising from the following reasons: the test procedure and the specimen preparation are easy in comparison with the typical testing method. Collaborative research has been conducted by “Committee on Standard Development” in the Japan Thermal Spray Society to establish a standard test method for evaluating interfacial fracture toughness of thermal spray coatings using a conventional Vickers indenter. This article reports the differences among collaborators in round-robin tests performed in this committee and discusses the validity of the test method and test conditions with respect to the test results and finite element analyses. Comparison among collaborators reveals that interfacial fracture toughness can be obtained with a small scattering from the indentation test under constraints found on the basis of the results.

In this study, the effects of CeO2 nanoparticle addition on tensile strength and formation of interfacial intermetallic compound layer for lead-free Sn-3.5Ag-0.7Cu solder joint were investigated. The results showed that the thickness of intermetallic layer was decreased with increasing weight percentages of CeO2 reinforcements, and the growth of the intermetallic layer was remarkably suppressed during isothermal aging at 150 °C. It was also found that the tensile strength of the solder joint gradually increased with the addition of CeO2 particles, reached to the maximum value at 0.5 wt% CeO2 and then decreased drastically with further increase in CeO2 content. Microstructural investigation of 1 wt% CeO2 reinforced solder joint revealed that due to particle pushing under the influence of interfacial tension between the particles and the matrix, the brittle cluster-like regions with high concentration of CeO2 particles were formed inside the joint. These brittle clusters act as preferential site for crack initiation during tensile test which would degrade the tensile strength. Hence, based on the results obtained in this study, addition of CeO2 particles up to 0.5 wt% provide an optimized solder joint with improved strength together with suppressed intermetallic growth and long-term reliability.

High-density, ultrasmall-pitch electronic applications require miniaturized solder bumps with improved thermomechanical performance. In addition, novel techniques which are able to precisely characterize these solder bumps are needed. One approach to meeting both of these requirements is to make use of recently developed nanocomposite solders with enhanced creep resistance, and to characterize these solders using a nanoindentation technique. In the present study, the creep behavior of ceria-reinforced nanocomposite solder foils fabricated by the accumulative roll-bonding process was characterized using a depth-sensing nanoindentation technique. It was found that the creep resistance of the composites increased with increasing volume fraction of CeO2 reinforcement, and it was deduced that the creep deformation of this nanocomposite proceeded by deformation of the matrix, with the role of the reinforcement being to increase the creep resistance by reducing the effective stress acting on the matrix. The values of the creep exponent suggested that the dominant creep deformation mechanisms involved were diffusion creep and grain boundary sliding.

As one of the key technologies for high performance electronic devices, composite solders have been recently developed to improve thermal and mechanical properties of solder joints. In this study, accumulative roll bonding process was used as an effective alternative method for manufacturing high-strength, finely dispersed, void-free and highly uniform Sn–Ag–Cu/CeO2 nanocomposite solders. Microstructural investigation of nanocomposite solders revealed that homogenous distribution of CeO2 nanoparticle has been achieved and the eutectic as-cast morphology of the solder changed to recrystallized fine grained structure. As a result of severe plastic deformation during rolling, brittle and elongated intermetallics crushed into fine particles with an average diameter of a few hundred nanometers and dispersed uniformly in the solder matrix. Mechanical test results showed that the microhardness, 0.2% yield stress, and ultimate tensile strength of the composite solder increased with addition of CeO2 nanoparticles, while the ductility of the composite was decreased.

Bioactive coatings on cp-Ti and Ti-6Al-4V were prepared by a simple chemical technique. Specimens of cp-Ti and Ti-6Al-4V were initially immersed in a 5 M NaOH solution at 60 degrees C for 24 h which resulted in the formation of a porous network structure composed of Na2Ti5O11 and TiO2. The specimens were then immersed in a Ca-rich solution either at 60 degrees C or at 36.5 degrees C for 24 h. During this treatment Na+ was released and Ti-OH groups were formed. Subsequently, TiO2 dissociated from the Ti-OH group and combined with calcium ions to form calcium titanate (CaTiO3), which was embedded in a titania gel layer during the immersion period. The specimens were then immersed in r-SBF at 36.5 degrees C for 1-30 days. After immersion in r-SBF for 3 days, HAp (hydroxyapatite) spheroids began to deposit on the substrates, and within a week the surfaces were covered. The HAp spheroids were 5 microm in size with a Ca/P ratio of 1.68 which was close to bone-like apatite (1.67). The average thicknesses of HAp layer after immersion in r-SBF for 3 days, 1 week, and 2 weeks were 3.8, 5.6, and 6.4 microm, respectively. A scratch test, used to evaluate the adhesive strength of the HAp layer, showed that the HAp layer was not scraped off until the applied load reached 26 N.

Fatigue crack-growth behavior and mechanical properties of Sn-3Ag-0.5Cu, Sn-3Ag-0.5Cu-1Bi, and Sn-3Ag-0.5Cu-3Bi solders have been investigated at room temperature (20 °C). The tensile strength and hardness of the solders increased with increasing Bi content. However, the yield strengths of Sn-3Ag-0.5Cu-1Bi and Sn-3Ag-0.5Cu-3Bi solders were nearly similar, but the 3Bi solder exhibited the lowest ductility. Fatigue crack-growth behavior of the solders was dominantly cycle dependent in the range of stress ratios from 0.1-0.7 at a frequency of 10 Hz, except for the Sn-3Ag-0.5Cu solder tested at a stress ratio of 0.7. Mixed intergranular/transgranular crack propagation was observed for the Sn-3Ag-0.5Cu solder tested at the stress ratio of 0.7, indicating the importance of creep in crack growth. The Sn-3Ag-0.5Cu-1Bi and Sn-3Ag-0.5Cu-3Bi solders had higher resistance to time-dependent crack growth, resulting from the strengthening effect of the Bi constituent. It appears that the addition of Bi above a certain concentration is harmful to the mechanical properties of Sn-3Ag-0.5Cu.

Low-cycle fatigue (LCF) tests on as-cast Sn-3.5Ag, Sn-3Ag-0.5Cu, Sn-3Ag-0.5Cu-1Bi, and Sn-3Ag-0.5Cu-3Bi solders was carried out using a noncontact strain-controlled system at 20°C with a constant frequency of 0.1 Hz. The addition of Cu does not significantly affect the fatigue life of eutectic Sn-Ag solder. However, the fatigue life was significantly reduced with the addition of Bi. The LCF behavior of all solders followed the Coffin-Manson relationship. The fatigue life of the present solders is dominated by the fracture ductility and can be described by the ductility-modified Coffin-Manson's relationship. Steps at the boundaries of dendrite phases were the initiation sites for microcracks for Sn-3.5Ag, Sn-3Ag-0.5Cu, and Sn-3Ag-0.5Cu-1Bi solders, while for Sn-3Ag-0.5Cu-3Bi solder, cracks initiated along both the dendrite boundaries and sub-grain boundaries in the dendrite phases. The linking of these cracks and the propagation of cracks inside the specimen occurred both transgranularly through eutectic phases and intergranularly along dendrite boundaries or sub-grain boundaries.

Low-cycle fatigue tests of as-cast Sn-Ag eutectic solder (96.5Sn/3.5Ag) were performed using a noncontact strain controlled system at 20°C. The fatigue behavior followed the Coffin-Manson equation with a fatigue-ductility exponent of 0.76. Without local deformation and stress concentration at contact points between the extensometer and the specimen surface in strain-controlled fatigue tests, crack initiation and propagation behavior was observed on the specimen surface using a replication technique. After failure, the longitudinal cross sections were also examined using scanning electron microscopy (SEM). Microcracks initiated from steps at the boundary between the Sn-dendrite and the Sn-Ag eutectic structure and cavities along the boundaries especially around the Ag3Sn particles, Stage II crack propagated in mixed manner with intergranular cracks along the Sn-dendrite boundaries and transgranular cracks through the Sn-dendrites and the Sn-Ag eutectic structure. Propagation of stage II cracks could be expressed by the relation of dac/dN = 4.7 × 10-11[ΔJ]1.5, where ac is the average crack length and ΔJ is the J-integral range. After fatigue tests, small grains were observed in Sn-dendrites near the fracture surface.

Fatigue crack growth behavior of two typical solders 63Sn-37Pb and 95Pb-5Sn has been investigated under room temperature (20°C) and frequency of 10 Hz. Fatigue crack growth behavior of the 63Sn-37Pb specimen tested at stress ratios up to 0.5 and the 95Pb-5Sn specimen tested at stress ratios up to 0.7 were dominantly cyclic dependent. Intergranular crack growth was observed for the 63Sn-37Pb specimen tested at stress ratio of 0.7, which indicates that a crack grows under influence of creep. The difference of effect of stress ratio on crack growth behavior between two solders may results from the difference of homologous temperature. Fatigue crack growth mechanisms for solder materials are summarized as follows: A crack propagates in a transgranular manner at low homologous temperature and low stress ratio, while it propagates along eutectic grain boundaries at high homologous temperature and high stress ratio under influence of creep. At the intermediate homologous temperatures, a crack propagates in a transgranular manner with some region of intergranular fracture.