Search

The sulphide stress cracking (SSC) behaviour of a simulated coarse-grained heat-affected zone was investigated under different heat inputs. The microstructure and fracture surfaces were observed. SSC susceptibility was dominated by hydrogen embrittlement (HE) and, to a lesser extent, anodic corrosion. Heat input had a critical effect on the microstructure and material properties. When t8/5 (time taken to cool from 800 °C to 500 °C) was 30 s, the microstructure was mixed lath bainite/granular, with low HE and high SSC resistance. When t8/5 was 100 s, the microstructure was granular bainite, with high corrosion current density and low SSC resistance. The results provide guidance for development of SCC resistant welding procedures.

To explore the effect of integrin β3 (ITGB3) gene silencing mediated mitogen-activated protein kinase (MAPK) signaling pathway on myocardial ischemia-reperfusion injury (MIRI) in mice.MIRI mice model was established, and myocardial tissues of MIRI mice and sham operation group mice were extracted. Hematoxylin-Eosin (HE) staining was used to observe the pathological changes of myocardial tissue; terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) staining was used to detect the apoptosis of myocardial cells; ELISA method was used to detect the levels of interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF)-α in the two groups. The infarct size was measured by TTC staining. Myocardial cells of MIRI model mice were isolated and cultured, and then grouped and transfected. The cells were transfected with the grouping of MIRI group, negative control (NC) group, MAPK signal pathway agonist Anisomycin group, MAPK signal pathway inhibitor SB203580 group, ITGB3-siRNA group, SB203580 + ITGB3-siRNA group. Real-time quantitative polymerase chain reaction (qRT-PCR) and Western blot were used to detect the mRNA and protein expressions of ITGB3, p38MAPK/p-p38MAPK, GSK-3β/p-GSK-3β, Cx43/p-Cx43, pro-apoptotic factor Bax and anti-apoptotic factor Bcl-2. 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay was used to detect cell proliferation and flow cytometry to detect cell apoptosis.The expression of ITGB3 in myocardial tissue of MIRI mice was significantly higher than that of sham operated mice (p0.05). Compared with the sham operation group, the apoptosis rate of myocardial cells in MIRI group was significantly increased, the expression levels of IL-1, IL-6 and TNF-α were significantly increased, and the myocardial infarction area was significantly increased (all p0.05). Compared with MIRI and NC groups, ITGB3 mRNA and protein expression levels in ITGB3-siRNA group and SB203580 + ITGB3-siRNA group were significantly decreased (all p0.05), but no significant change was found in Anisomycin group and SB203580 group (p0.05). Furthermore, ITGB3-siRNA group and Anisomycin group had markedly decreased mRNA and protein expressions of ITGB3 and Bax, increased mRNA and protein expressions of p38MAPK/p-p38MAPK, GSK-3β/p-GSK-3β, Cx43/p-Cx43 and Bcl-2, as well as increased cell proliferation and decreased cell apoptosis (all p0.05); SB203580 group indicated an opposite result with Anisomycin group; while SB203580 + ITGB3-siRNA revealed none significant statistical difference. In addition, compared with ITGB3-siRNA group, SB203580 + ITGB3-siRNA group showed significantly upregulated mRNA and protein expressions of Bax, downregulated mRNA and protein expressions of p38MAPK/p-p38MAPK, GSK-3β/p-GSK-3β, Cx43/p-Cx43 and Bcl-2, as well as decreased cell proliferation and increased cell apoptosis (all p0.05).Silencing ITGB3 gene expression can promote the activation of MAPK signaling pathway, elevate the phosphorylation of GSK-3β and Cx43 in the downstream, promote the proliferation of mouse myocardial cells, inhibit myocardial cell apoptosis and inflammatory reaction, and thus have protective effect on MIRI in mice.

The effect of hydrogen on the fracture toughness of X65 high-frequency welded (HFW) pipelines was investigated both in a hydrogen environment and in air. The hydrogen environment was created by in situ hydrogen charging, using a simulated soil solution as the electrolyte. Four current densities were used, namely 1, 2, 4, and 8 mA/cm2. The fracture toughness was characterized by the crack tip opening displacement (CTOD). The CTOD values of the base metal and weld metal decreased with increasing hydrogen charging current density, and a higher reduction was seen in the weld metal. In addition, the hydrogen permeation and electron backscattered diffraction (EBSD) measurements were also applied to the base metal and weld metal to evaluate the hydrogen-induced cracking (HIC) susceptibility. The results showed that the weld metal had a higher HIC susceptibility than that of the base metal.

Due to excellent mechanical properties and corrosion resistance, the carbon steel/nickel-based alloy has huge potential for using in oil and gas industry. The pipes are usually joined by welding. Hence, it is significant to study the effect of welding on the corrosion properties. A literature search indicates that few studies have been conducted on the corrosion properties. Accordingly, in the present work, electrochemical measurements together with immersion tests were used to analyze the corrosion properties of Inconel 625 clad layers and butt-weld metal. The hardness was also determined. The microstructures, morphological features, and the changes observed in the surface composition were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), together with energy-dispersive spectroscopy (EDS). The microstructures of Inconel 625 clad layers and butt-weld metal consist of primary γ-Ni solid solution dendritic, γ/laves interdendritic eutectic. Because of the heat effect induced by multi-pass welding, element segregation and more participation of carbide were observed in the butt-weld metal, which could account for higher hardness and inferior corrosion resistance of the butt-weld metal as compared to the clad layer.

This paper exhibits a novel in situ remediation technique named friction hydro-pillar process overlap welding (FHPPOW) to repair the through crack of the structures and components in the harsh environments. In the present work, the effects of welding parameters on the microstructures and mechanical properties of the welding joints are investigated. The defect-free joints can be obtained in a large process window with the rotational speed of 6000–7000 rpm and welding force of 20–40 kN. In the heat-affected zone (HAZ), the interface between the substrate and lap plate can be clearly distinguished. The microstructure of the weld is mainly consisted of the upper bainite. The hardness value in the welding zone is highest and is the lowest in the base material. The pull-out tests of all welds are failure in the stud. Results indicate that the good welding quality can be obtained in these welding conditions. The best results of the cruciform uniaxial tensile and the shear tests are 662.8 and 552 MPa, respectively. The favorable Charpy impact absorbed energy is 68.75 J at 0 °C. The fracture characteristic of Charpy impact tests is brittle fracture with a large area of cleavage.

This paper presents the results for the indentation size effect (ISE) on the creep stress exponent and hardness of 0.03 wt.% Ag-modified graphene nanosheet Sn-Ag-Cu solder alloys, using constant loading/holding and multi-cycle (CMC) loading methods, respectively. At each maximum load, with increasing indentation depth, the creep exponent first decreased and then increased. At the same strain rate, the stress exponent also showed the same tendency, increasing as the indentation depth (peak load) increased and then decreased. The hardness was measured continuously with increasing indentation depth by the CMC loading method. The hardness did not exhibit a decrease as the indentation depth increased, which differs from the classical description of the ISE. After an initial decrease, the hardness then increased and finally decreased as the indentation depth increased. This study reviews the existing theories and formulations describing ISE with hardening effects. The experimental results fit well with the empirical formulation. The phenomenon of ISE accompanied by hardening effects has been explained physically via the interaction between geometrically necessary dislocations and grain boundaries.

This paper exhibits a novel in situ remediation technique named friction tapered stud overlap welding (FTSOW) to repair a through crack in structures and components in extremely harsh environments. Furthermore, this paper presents variations in process data, including rotational speed, stud displacement, welding force, and torque for a typical FTSOW weld. In the present study, the effects of welding parameters on the microstructures and mechanical properties of the welding joints were investigated. Inapposite welding parameters consisted of low rotational speeds and welding forces, and when utilized, they increased the occurrence of a lack of bonding and unfilled defects within the weld. The microstructures with a welding zone and heat-affected zone mainly consisted of upper bainite. The hardness value was highest in the welding zone and lowest in the base material. During the pull-out tests, all the welds failed in the stud. Moreover, the defect-free welds broke at the interface of the lap plate and substrate during the cruciform uniaxial tensile test. The best tensile test results at different depths and shear tests were 721.6 MPa and 581.9 MPa, respectively. The favorable Charpy impact-absorbed energy was 68.64 J at 0 °C. The Charpy impact tests revealed a brittle fracture characteristic with a large area of cleavage.

In this study, varying amounts of Ag-modified graphene nanosheets (Ag-GNSs) were added to Sn–Ag–Cu (SAC) solders to synthesize composite solders. Then, the morphology and thickness of the intermetallic compound (IMC) layers were investigated during the liquid–solid reactions and isothermal aging. The test results revealed that the IMCs were scallop-shaped after soldering, but they changed from scallop-shaped to an irregular shape with increasing aging time. The IMC thickness and diffusion coefficients of the composite solders were both found to be lower than those of the plain solders. Moreover, it is worth noting that with the same amount of reinforcement, the composite solders reinforced with Ag-GNSs exhibited thinner IMC layers and lower diffusion coefficients than the solders reinforced with GNSs alone. Furthermore, Ag-GNSs prepared using ball milling yielded thinner IMC layers and lower diffusion coefficients than the same amount of Ag-GNSs prepared via mechanical mixing using a blender. Our results indicate that Ag-GNSs are more influential on delaying the growth of IMC layers than GNSs alone and that ball milling has advantages over mechanical mixing using a blender for the preparation of Ag-GNS composite solders.

The effects of deep cryogenic treatment (DCT) on the residual stress and mechanical properties of electron beam (EB)-welded Ti–6Al–4V(TC4) joints were investigated. In addition, the effect of different DCT soaking times was analyzed to obtain the optimal time. The results indicated that with a soaking time of 24 h, perpendicular to the welding direction, the residual stress declined by 31.2% for the longitudinal stress and 46.5% for the transverse stress, and along the welding direction, the residual longitudinal and transverse stress declined by 25.1% and 17.2%, respectively. More than 24 h, the effect of increasing the soaking time on eliminating residual stress is not obvious. Meanwhile, the effect of DCT on the tensile strength of the EB-welded TC4 joint was also investigated, which showed that the strength increased by 4.3% and the elongation rate increased by 46.8% when the soaking time was longer than 24 h. The hardness test indicated that values at the weld were higher than that in the base metal, and the average values of hardness increased with DCT. Particular focus was given to the changes in the quantity, size, and morphology of the α and β phases as the main reasons for the above results.

In this paper, welding residual stress in socket weld of 304L stainless steel pipe was investigated using numerical simulation and validated by X-ray stress measurement. From the simulation results, the maximum tensile residual stresses were located at weld root and weld toe on both sides of the weld along pipe, which led to the fatigue failure. Pre-bevelling and low transformation temperature (LTT) dressing could decrease tensile residual stress both in hoop and axial direction at weld root and weld toe. After LTT dressing, compressive residual stress was generated throughout weld toe. Compressive stress can delay fatigue crack initiation and propagation. Therefore, pre-bevelling and LTT dressing can improve the fatigue life of socket weld.

In this study, Sn–Ag–Cu solder alloys and Sn–Ag–Cu solder alloys reinforced with 0.1 wt% Ag-graphene nanosheets (Ag-GNSs) by mechanical mixing (H for abbreviation) and ball milling (Q for abbreviation), which were referred as SAC, H/0.1Ag-GNSs, and Q/0.1Ag-GNSs, respectively, were used to form solder joints. The creep behavior of the above solder joints was investigated by conducting nanoindentation tests. A method for calculating the strengthening stress generated by the load transfer and orientation of the Ag-graphene nanosheets was proposed. The method considers the geometry and grain data of the Ag-graphene nanosheets, which were obtained through scanning electron microscopy and electron back scattering diffraction. Considering other strengthening stresses generated by the dislocation strengthening, fine grain strengthening, Orowan strengthening for intermetallic compounds and metal matrix nanocomposites, and strengthening stress generated by Ag-graphene nanosheets, a modified constitutive model was proposed to investigate the constitutive behavior for creep performance of solder joints formed by SAC, H/0.1Ag-GNSs and Q/0.1Ag-GNSs. The results show good agreement with the experimental data.

Lung cancer is one of the most common malignancies worldwide, the morbidity and mortality of which have been on rising in recent years. Moreover, lncRNAs have been implicated in the development of various cancers, as well as cancer treatment and prognosis. In this study, long non-coding RNA (lncRNA) MEG3, an identified tumor suppressor, was explored for its role in the chemotherapy of lung cancer.All cases were divided into (I+II) group and (III+IV) group according to different stages of tumor node metastasis (TNM), and were divided into sensitive group and insensitive group according to chemotherapy sensitivity. A549 and H292 cells were selected as the resistant cell and non-resistant lung cancer cells. Quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) was performed to detect the expression of MEG3. After transfection with overexpression plasmid pcDNA-MEG3 or/and different concentrations of vincristine, cell viability and proliferation were measured by cell counting kit-8 (CCK-8) assay and plate cloning assay, respectively. Western blotting was used to analyze the expressions of autophagy-related proteins.In vivo, lncRNA MEG3 was significantly lower in III+IV group and insensitive group than that in I+II group and sensitive group. In vitro, MEG3 expression in resistant cells was significantly lower than that in non-resistant cells. Overexpression of MEG3 significant inhibited the viability and proliferation of both resistant and non-resistant lung cancer cells. Western blot results showed that autophagy level was higher in resistant cells than that in non-resistant cells, while overexpression of MEG3 significantly reduced the expression of autophagy-related proteins. CCK-8 results also indicated that the cell viability was negatively correlated with the dose of vincristine, while the viability of drug-resistant cells was higher than that of non-drug resistant cells after the treatment of vincristine. The vitality of both cells decreased in a concentration-dependent manner after combined treatment with vincristine and MEG3.Our data indicated that lncRNA MEG3 showed a low expression in chemotherapy-sensitive lung cancer tissues, and overexpression of lncRNA MEG3 attenuated autophagy level, thus increasing the sensitivity of vincristine in chemotherapy of lung cancer.

With the aim of developing highly conductive ink for flexible electronics on heat-sensitive substrates, Ag nanospheres and nanoplates were mixed to synthesize hybrid inks. Five kinds of hybrid ink and two types of pure ink were written to square shape on Epson photo paper using rollerball pens, and sintered at a low temperature (100 °C). The microstructure, electrical resistivity, surface porosity, hardness and flexibility of silver patterns were systematically investigated and compared. It was observed that the optimal mixing ratio of nanospheres and nanoplates was 1:1, which equipped the directly written pattern with excellent electrical and mechanical properties. The electrical resistivity was 0.103 μΩ · m, only 6.5 times that of bulk silver. The enhancement compared to pure silver nanospheres or nanoplates based ink was due to the combined action of nanospheres and nanoplates. This demonstrates a valuable way to prepare Ag nanoink with good performance for printed/written electronics.

The eutectic 80Au/20Sn solder alloy is widely used in high power electronics and optoelectronics packaging. In this study, low cycle fatigue behavior of a eutectic 80Au/20Sn solder alloy is reported. The 80Au/20Sn solder shows a quasi-static fracture characteristic at high strain rates, and then gradually transforms from a transgranular fracture (dominated by fatigue damage) to intergranular fracture (dominated by creep damage) at low strain rates with increasing temperature. Coffin-Manson and Morrow models are proposed to evaluate the low cycle fatigue behavior of the 80Au/20Sn solder. Besides, the 80Au/20Sn solder has enhanced fatigue resistance compared to the 63Sn/37Pb solder.

In this study, the effect of graphene nanosheets (GNSs) on the corrosion resistance of 96.5Sn–3Ag–0.5Cu (SAC) solder at ambient temperature in a 3.5 wt% NaCl solution was investigated using the potentiodynamic polarization method . The corrosion products were analyzed by field emission-scanning electron microscope, energy dispersive spectroscopy , and X-ray diffraction. The results showed that the GNSs affect the anodic polarization behavior of the solders. Adding GNSs enhanced the corrosion resistance of the SAC solder, as GNSs content increased to 0.03 wt%, the corrosion resistance peaked and then declined with further increment in the wt% of the GNSs. Overall, the corrosion resistance of SAC/GNSs was found to be more superior than that of the pure SAC. The mechanism of the corrosion resistance improvement can be explained by the formation of a compact corrosion layer of the GNSs. This provides an inert physical barrier to the initiation and development of corrosion. As the GNSs content further increased (more than 0.03 wt%), the corrosion resistance of the SAC/GNSs solder decreased.

This paper focuses on the effects of stud and hole configurations on weld defects in friction hydro-pillar processing (FHPP). Various configurations of the stud and hole are designed and all welds are performed by using a self-developed high-performance platform with the same welding parameters. The experimental results indicate that the defects usually appear at the bottom of the hole, but the upper region bonds well. The quality of welded joints is deeply affected by the bottom filling which is called initial stage. Therefore, the finite-element method (FEM) is employed to simulate the initial stage of FHPP. The simulated results agree well with those of the experiments. The results indicate that the geometry of the hole influences the welding quality more strongly than the shape of the stud and that weld samples with a rounded corner at the bottom of the hole bond well. Moreover, different shapes of the studs cause different stress states and temperature distributions, which also influence the quality of welded joints.

In this study, mechanical mixing and ball milling were used to mix a variety of different mass fractions of Ag nanoparticle-modified graphene nanosheets (Ag-GNSs) and Sn-Ag-Cu solder alloys to form composite solder alloys. We found that the latter was superior to the former, as the ball-milled samples showed better mechanical properties through nanoindentation tests. The mechanical properties of solder alloys reinforced with Ag-GNSs were compared with those reinforced with unmodified GNSs, and we found that Ag-GNSs were more beneficial for reinforcement. When the amount of Ag-GNSs increased, the composite solders showed improved Young's modulus, hardness, and creep resistance with the exception of 0.2 wt%. The indentation morphologies were observed by scanning electron microscope (SEM), while the microstructure of the composite solder alloys were analyzed by transmission electron microscope (TEM) and electron back scattering diffraction (EBSD). Due to grain boundary and dislocation strengthening, the mechanical properties of the composite solder alloys have been improved. A modified constitutive creep model considering microstructural strengthening showed great agreement with the experiment data.

Sn96.5Ag3.0Cu0.5 (SAC305) is one of the most promising lead-free solder alloys and bismuth telluride-based compounds are the best known thermoelectric materials. Interfacial reactions of the SAC305/Bi0.5Sb1.5Te3 and SAC305/Bi1.8Sb0.2Se0.15Te2.85 couples at 260 °C are studied to investigate the effect of reaction on the efficiency and reliability of thermoelectric device. Initially, the major products in SAC305/Bi0.5Sb1.5Te3 couple reaction for a short time are a strip-type Ag-rich IMC layer and a dense SnTe–SbSn mixture layer. With the reaction time increasing, a two-phase layer, which is SnTe–SbSn mixture with pores with 200–500 nm size which are occupied by solder originally, appears next to the dense layer. However, the reaction products do not change significantly. It is observed that the growth rate of reaction phase layer is about 4.05 μm/min. As for the SAC305/Bi1.8Sb0.2Se0.15Te2.85 couple reaction, besides SnTe phase, Bi–Te phase is also formed at the solder/Bi1.8Sb0.2Se0.15Te2.85 interface. As the reaction time increases, the morphology of IMC layer becomes rough, and then the stable scallop-type IMC appears; the growth rate of reaction phase layer is about 0.39 μm/min.

In this study, the effect of Ni-coated carbon nanotubes (Ni-CNTs) on the corrosion resistance of 95.8Sn-3.5Ag-0.7Cu (SAC) solder at ambient temperature in 3.5 wt.% NaCl solution was investigated using the potentiodynamic polarization method. The corrosion products were analyzed by field-emission scanning electron microscopy (S4800), energy-dispersive spectroscopy, and x-ray diffraction. The results showed that addition of Ni-CNTs enhanced the corrosion resistance of the SAC solder and that increasing the content of Ni-CNTs made the effect more evident. The mechanism of the corrosion resistance improvement is the formation of a compact corrosion layer of Ni-CNTs that provides an inert physical barrier to the initiation and development of corrosion. Furthermore, in the corrosion microcell produced by the Ni-CNTs dispersed in the SAC solder, the Ni-CNTs act as a third phase (electrode) which contributes to reducing the galvanic corrosion between Sn anode and Ag3Sn cathode. Hence, the corrosion resistance of the composite solders was improved.

Varying weight fractions of graphene nanosheets were successfully incorporated into lead-free solder using the powder metallurgy route. The effects of graphene nanosheets on the physical, thermal, and mechanical properties of a SnAgCu solder alloy were investigated. With the increasing addition of graphene nanosheets, the nanocomposite solders showed a corresponding improvement in their wetting property but an insignificant change in their melting point. The thermomechanical analysis showed that the presence of graphene nanosheets can effectively decrease the coefficient of thermal expansion (CTE) of the nanocomposites. Furthermore, an improvement in UTS and a decrease in ductility were recorded with the addition of graphene nanosheets. The reinforcing mechanism of the graphene nanosheets on various properties obtained was also analyzed in this study.

In the present study, a new welding procedure was developed according to the welding difficulties of mechanical clad pipe. The effect of temperature on the corrosion product layer of stainless steel welded joints exposed to a CO2-containing solution was investigated. The measurement techniques, such as scanning electron microscopy with energy dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy, were used to systematically characterize the morphology and composition of the corrosion product layer. The corrosion rates were calculated by weight loss method. The corrosion mechanisms are studied and discussed. The results showed that temperature is an important factor in the corrosion rate of mechanical clad pipe welded joints.

Fatigue related failures of small bore piping caused by vibration of socket welds often occur at nuclear power plants. The purpose of the present study is to evaluate the integrity of the socket weld in nuclear piping under the condition of vibration testing. The specimens were bolted to the shaker table and shaken simultaneously near their resonant frequencies to produce the desired stress. The test results show that the failures at higher stress tend to originate at the toe, while that for the case of lower stress failures tends to occur at the root. The effects of penetration depth and radial gap were also investigated by finite element method. Results show that the higher penetration depth and radial gap can decline the stress distribution in the weld root, which is beneficial to fatigue life. Further, the desired radial gaps can significantly reduce the von Mises stresses, which decrease from 150·4 to 82·7 MPa with the width of radial gap from 0·1 to 0·4 mm.

The non-cyanide silver electroplating on copper substrate has been discussed. Based on the surface morphology by using SEM, the smooth and fine silver layer is obtained. The influences of concentration of silver and plating temperature on the thickness of the plating layer are discussed, the thickness of the silver layer is increasing with silver concentration rising and plating temperature rising.

In this study, the effect of microstructure at the base metal (BM), the fine grain heat affected zone (FGHAZ), the coarse grain HAZ (CGHAZ) and weld metal (WM) under different welding heat input on hydrogen permeation in X80 steel weldments have been investigated. Base metal showed the highest effective diffusivity. With each heat input, the effective hydrogen diffusivity in FGHAZ is comparable to that of the base metal. The effective hydrogen diffusivity in weld metal was lower than that in CGHAZ. With increasing the welding heat input, the effective diffusivity in different zones of the weldment decreased correspondingly. Non-metallic inclusions were not detected in each specimen. Constituents in microstructure under low heat input are likely to agglomerate during accelerated cooling. The retained hydrogen may create an unpredictable susceptibility to hydrogen cracking at the CGHAZ even existing during service.

The electrochemical behavior of corrosion resistance alloys (316L SS, 2205 DSS and Inconel 625) was carried out at ambient temperature in 3.5% NaCl solution using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. Some significant characterization parameters such as Ecorr, Eb, Icorrand △E in polarisation curves were analyzed and compared to reveal the corrosion resistance of corrosion resistance alloys. The ZsimpWin software was utilized to discuss the Nyquist plots of various corrosion resistance alloys. The result shows that the corrosion resistance of the corrosion resistance alloys in 3.5% NaCl solution at ambient temperature follows the sequence: Inconel 625> 2205 DSS > 316L SS.

The electrochemical behavior of welded joints with 308L stainless solid welding wire and low temperature transformation welding wire using different welding processes was investigated at ambient temperature in 3.5% NaCl solution using potentiodynamic polarisation technique. Welded joints exhibited different corrosion potential due to the dilutions of alloy elements such as Cr, Ni, Ti, Nb and Mo. To reveal the corrosion resistance of welded joints using different welding processes, some significant characterization parameters such as Ecorr, Eb, △E and Icorr in polarisation curves were analyzed and compared. The result shows that the corrosion resistance of welded joints using low temperature transformation welding wire is better than that using 308L stainless solid welding wire.

In this paper, varying weight percentages of Ni-coated carbon nanotubes (Ni-CNTs) was incorporated into Sn-Ag-Cu (SAC) solder matrix, to form composite solder. Up to 0.05% of Ni-CNTs were successfully incorporated. After that, the electrochemical behavior of Sn-Ag-Cu with varying weight percentages of Ni-coated carbon nanotubes (Ni-CNTs) composite solder were investigated in 0.3% Na2SO4 solution by using potentiodynamic polarization method. Scanning microscopy was used to characterize the samples after the electrochemical tests. It was observed that the corrosion resistance decreased when the content of Ni-CNTs reached a certain level.

In the present study, the residual stress generated in the crack tip of compact specimens was investigated in order to analyze the effect of residual stress on the creep crack growth. Residual stresses were generated using loading in compression beyond yield and then unloading. The maximum region of residual stress in the crack tip was obtained by numerical simulations which calculated the effect of notch radius and penetrated stress. It was found that a 2.5 mm notch radius with the applied stress at 36 KN could generate the largest extent of residual stress ahead of crack tip in the compact specimen. Further, when the specimen was heated to a high temperature, the value of residual stress reduced while the distribution changed little.

In the present study, nanoindentation studies of the 95.8 Sn -3.5 Ag -0.7 Cu 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.

Eutectic 80Au/20Sn solder alloy is widely used in high power electronics and optoelectronics packaging in which the creep property of the solder joint is essential to meet the global demand for longer operating lifetime in their applications. In this study, the tensile creep behavior of bulk eutectic 80Au/20Sn solder alloy is reported and compared with 63Sn37Pb solder joint. The creep strain rate increases and creep lifetime decreases as the applied stress level and temperature increase. The 80Au/20Sn solder alloy shows a superior anti-creep performance over the 63Sn37Pb solder joint. The experimental data were successfully fit with Dorn model and Garofalo model. However, the application of Garofalo model resulted in a lower estimated variance of error terms as compared to the Dorn model. Grain boundary sliding is the possible creep mechanism within the given stress level and temperature. The nucleation, accumulation and further growth of microvoids lead to the creep rupture.

In this paper, the local approach was used to analyze the geometry dependence of coating specimens for interface brittle fracture initiation, and a definition of the fracture process zone was proposed in the paper. The results showed that the interface fracture behavior of two types of specimens with notch had been predicted from the test results of pre-crack specimens based on the local approach for interface brittle fracture, and the predicted distribution of the critical load for the notched specimens gave a good agreement with the test results. It indicated that the local approach not only can be used to describe the interface fracture behavior, but also can be used in the integrity evaluation for interface between different materials.

Butt-fusion welding is the main technology to join high-density polyethylene (HDPE) plastic pipes, which are widely used in transport the water, gas and corrosive liquid. Investigation shows that one of the failure modes of HDPE pipe is the crack slowly grows across the thick direction and leads to failure at last, so that it is very important to study the resistance to crack initiation of HDPE pipe and its butt-fusion welded joint. In this study, the elastic-plastic fracture mechanics parameter, crack opening displacement (COD) is used to describe the fracture initiation behaviors for the HDPE materials and its butt-fusion welded joints. The resistance to initiation fracture of HDPE pipe materials and butt-fusion welded joints were investigated at different temperature by using multiple specimen resistance curve method and silicon-rubber replica method. The results show that saturation initial crack COD- δis of HDPE pipe materials and butt-fusion welded joints decreases with the decreasing temperature. The δis of butt-fusion welded joints is lower than that of HDPE pipe materials. Investigation also proved that the silicon-rubber replica method is more suitable for HDPE engineering material than the multiple specimen method. At the same time the statistic distribution of the δis of HDPE butt-fusion welded joint was conducted. The results show that the value of the δis has the statistic variance inherently. The optimum fitting distribution of COD is Weibull distribution with three parameters.

With the aim of preparing a method for the writing of electronics on paper by the use of common commercial rollerball pens loaded with conductive ink, hybrid conductive ink composed of Ag nanoparticles (15 wt%) and graphene-Ag composite nanosheets (0.15 wt%) formed by depositing Ag nanoparticles (∼10 nm) onto graphene sheets was prepared for the first time. Owing to the electrical pathway effect of graphene and the decreased contact resistance of graphene junctions by depositing Ag nanoparticles (NPs) onto graphene sheets, the concentration of Ag NPs was significantly reduced while maintaining high conductivity at a curing temperature of 100 ° C. A typical resistivity value measured was 1.9 × 10(-7) Ω m, which is 12 times the value for bulk silver. Even over thousands of bending cycles or rolling, the resistance values of writing tracks only increase slightly. The stability and flexibility of the writing circuits are good, demonstrating the promising future of this hybrid ink and direct writing method.

In the present study, the powder metallurgy route was used to successfully incorporate Ni-coated carbon nanotubes into Sn-Ag-Cu solder, to form a nanocomposite solder. Nanoindentation tests were performed on both composite and Sn-Ag-Cu solder samples to investigate their creep behaviour at room temperature. Characterization results revealed that with the addition of Ni-coated carbon nanotubes, the creep behaviour of composite solder improved significantly as compared to that of the unreinforced solder alloy. Moreover, increasing the maximum load from 20 mN to 100 mN increased the percentage reduction in creep strain rate from 4% to 28%, for the composite compared to its monolithic counterpart after 300 s of holding.Copyright © 2011 by ASME

In this study, varying amounts of Ni-CNTs were incorporated into the Sn-Ag-Cu matrix to form the composite solders. The interfacial intermetallic thickness formed on the Ni/Au metallized Cu substrate was determined under the as-soldered and isothermally aged (at 150°C for up to 42 days) conditions. The results of the interfacial intermetallic thickness showed that for the case of the unreinforced solder joint, the intermetallics grew more significantly than that of the composite solder joints, under both as-soldered and isothermally aged conditions. Moreover, the shear test results revealed that the as-soldered and aged composite solder joints exhibited improved ultimate shear strength as compared to that of their unreinforced counterparts. The improvement was observed to be most significant with the addition of 0.05 wt.% of Ni-CNTs, whereby the ultimate shear strength increased by 29% under the as-soldered condition and by 28% after isothermally aged for 42 days. It was concluded that the presence of Ni-CNTs as reinforcements in the Sn-Ag-Cu solder served to inhibit the growth of interfacial intermetallics and also to enhance its mechanical performance.

With the aim of preparing paper-based writing electronics, a kind of conductive pen was made with nano-silver ink as the conductive component and a rollerball pen as the writing implement. This was used to direct-write conductive patterns on Epson photo paper. In order to decrease the sintering temperature, pressure was introduced to enhance the driving forces for sintering. Compared with hot sintering without pressure, hot-pressure can effectively improve the conductivity of silver coatings, reduce the sintering time and thus improve productivity. Importantly, pressure can achieve a more uniform and denser microstructure, which increases the connection strength of the silver coating. At the optimum hot-pressure condition (sintering temperature 120 ° C/sintering pressure 25 MPa/sintering time 15 min), a typical measured resistivity value was 1.43 × 10⁻⁷ Ω m, nine greater than that of bulk silver. This heat treatment process is compatible with paper and does not cause any damage to the paper substrates. Even after several thousand bending cycles, the resistivity values of writing tracks by hot-pressure sintering stay almost the same (from 1.43 × 10⁻⁷ to 1.57 × 10⁻⁷ Ω m). The stability and flexibility of the writing circuits are good, which demonstrates the promising future of writing electronics.

In this study, the constitutive behaviour for creep performance of 95.8Sn–3.5Ag–0.7Cu lead-free solder joints was investigated. It was observed that the stress exponent (n) can be well defined into two stress regimes: low stress and high stress. A new, improved constitutive model, which considered back stress, was proposed to describe the creep behaviour of SnAgCu solder joints. In this model, the back stress, which is a function of the applied shear stress in the low stress regime (LSR) and a function of the particle size, volume fraction and coarsening of IMC particles in the high stress regime (HSR), was introduced to construct the relationship between the creep strain rate and the shear stress. The creep mechanism in these two stress regimes was studied in detail. In the LSR, dislocations passed through the matrix by climbing over the intermetallic particles, while in the HSR, the dislocations were glide-controlled. According to the different creep mechanisms in both the stress regimes, the back stress was calculated, respectively, and then incorporated into the Arrhenius power-law creep model. It was demonstrated that the predicted strain rate–shear stress behaviour employing the modified creep constitutive model which considered back stress, was in good agreement with the experimental results.

The Pt∕BaTiO3 (BTO) interface was investigated by angle-resolved x-ray photoelectron spectroscopy and x-ray reflectivity technique. It was shown that there exists a transition layer of about 9A at the Pt/BTO interface with electron density lower than that of the BTO film. The transition layer shows a higher binding energy of Ba 3d than that of the bulk BTO. Moreover, neither the interdiffusion of BTO and Pt nor the oxidation of Pt near the interface had been observed. We consider that this layer is caused by “interface-induced relaxation.” This relaxation layer is believed to be the origin of the “dead layer” effect.