Materials Science Forum Vol. 846

Abstract: Electrochemical migration (ECM) of solder joining can result in the growth of a metal deposit with dendrite structure from cathode to anode. In electronic device, this phenomenon potentially leads to the incompetence or failure of whole devices. In this paper, the ECM behaviour of printed circuit boards (PCBs) with SAC 0307, one of the low-cost lead-free solder alloys with less silver content, has been studied. The corrosion behaviour of SAC 0307 has been investigated by using sodium chloride solution in different concentrations which is between 0.01 M to 1.0 M as a medium. A Water Drop Test (WDT) was carried out and the time-to-failure of each sample has been recorded. After WDT test, the dendrite phase was identified using Variable Pressure Scanning Electron Microscope (VPSEM) with Energy Dispersive X-ray Spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) to investigate its surface morphology and corrosion products. As results, it has been found that the corrosion susceptibility of SAC 0307 is greatly influenced by the concentration of the medium solution used. The voltage drop occurred was due to the dendrite grew at the cathode electrode on the PCBs and expanded to the anode electrode, indicating a significant effect of aggressive behaviour of the medium used. The rate of the dendrite growth was affected by the concentration of the medium used. The main element found in the dendrites on the SAC 0307 on PCBs was Tin as it is more mobile than Cu.

Abstract: Phase formation, microstructure, and hardness properties of FeCrNiMnCoTa_x and Al_0.5 FeCrNiMnCoTa_x high-entropy alloys (HEA) have been investigated and reported. In this study, FeCrNiMnCoTa_x and Al_0.5FeCrNiMnCoTa_x high-entropy alloys (HEA) were synthesized using arc-melting technique in argon (Ar) atmosphere from high purity elements (x in molar ratio, x=0.2, x=0.4 and x=0.6). Ingots from arc-melting were homogenized for 24h at 900°C in Ar atmosphere. Dominant dendritic and inter-dendritic phases were identified from the electron micrographs of these HEA. The area of inter-dendrite region increased for both FeCrNiMnCoTa_x and Al_0.5FeCrNiMnCoTa_x alloys with the increasing of Ta content. The major phases in both FeCrNiMnCoTa_x and Al_0.5FeCrNiMnCoTa_x alloys were identified as FCC and BCC solid-solutions. Addition of Al in Al_0.5FeCrNiMnCoTa_x alloys has resulted in precipitation of a minor phase which was identified as FCC-TaCr₂ Laves phase. As the Ta content increased, hardness of FeCrNiMnCoTa_x and Al_0.5FeCrNiMnCoTa_x alloys increased from 200.34 Hv to 345.10 Hv and 385.22 Hv to 570.86 Hv respectively. Furthermore, presence of Laves phase in Al_0.5FeCrNiMnCoTa_x alloys has resulted in higher hardness values compared to Al free sample, and this higher hardness could be attributed to precipitation strengthening effect by Laves intermetallic phase formation.

Abstract: High Entropy Alloy (HEA) with at least 5 elements with equimolar ratios were developed to investigate the characteristics of Zr added in FeNiAlCoCrZr_x (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0). HEAs were prepared by arc melting technique in Ar atmosphere and were remelted five times to ensure homogeneity. The microstructure and phase constitution of these alloys are examined by X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM). The results show that addition of Zr to FeNiAlCoCr HEA resulted in multiple solid solution phases viz., BCC1, BCC2, FCC1 and FCC2 as evidenced by XRD patterns. Furthermore, presence of both BCC and FCC phases at higher Zr additions suggests that Zr did not preferentially promoted the solidification of either BCC or FCC phase. It can be observed from the FESEM micrographs that with different Zr additions, solidified microstructures of FeNiAlCoCrZr_x alloys varied between completely eutectic microstructures to proeutectic and eutectic phase mixtures. From FESEM micrographs it can be suggested that different Zr contents have resulted in different solidification modes. Hardness of Zr added samples is higher compared to base HEA which is FeNiAlCoCr. It was observed that hardness values are higher when proeutectic phases were present compared to completely eutectic FeNiAlCoCrZr alloy (x=0.1).

Abstract: Fire accident is considered as the one of most severe environmental hazards to building and infrastructure. Cold formed steel (CFS) beam has been used extensively as primary load bearing structural member in many applications in the building construction due to high efficiency in term of production, fabrication, and assembling in construction. This material must be well perform in fire incident in term of its integrity and stability of structural for a period of time. Hence, the assessment of the material properties of this material is greatly important in order to predict the performance of this structure under fire incident. The tensile coupon tests of CFS are according to BS EN 10002-1:2001. The CFS material G450 with 1.9 mm thickness is used in this study. The elastic modulus, yield stress, correspondent percentage strain at yield stress, ultimate stress, and correspondent percentage strain of ultimate stress was 200.3 GPa, 540.5 MPa, 0.478 %, 618.8 MPa, and 8.701 % respectively. The results of the ambient temperature test have been used to assess the mechanical strength of CFS at elevated temperature. The discussion of material properties is based on EC3-1-2 and proposed model from other researchers. The main material properties discussed is the stress-strain curve, elastic modulus, yield strength at elevated temperature was determined. The actual elastic region is slightly lower than the prediction of EC3-1.2 at ambient temperature, but well fit with two other studies. Besides that, the actual material properties experience strain hardening after yielding and reach a maximum stress up to 618 MPa while EC3-1.2 predict the constant value of the yield stress after yield until 15 % strain,other two study was fit the ambient tensile test up to ultimate stress, and fit until 2 % strain level.

Abstract: In this work, aluminium foams with modified geometry were successfully fabricated with a combination of dense and porous structure The main objective of this study were to determine the initial physical properties of aluminium foam with modified geometry in terms of density, porosity and morphology. Three different NaCl space holder sizes ranging from 1 mm to 3 mm were sieved and used to replicate the final pore size of aluminium foam. The samples were successfully produced through casting replication process. After densification, samples underwent water leaching in ultrasonic bath to remove completely the space holder. Results showed that porosity of the aluminium foam increased from 50 – 62% when the size of space holder was increased from 1 mm to 3 mm. The morphology showed clearly an integrated modified geometry between dense and inter-connected porous structure which is beneficial for applications that require combination properties of structural, thermal and mechanical properties.

Abstract: Optimizing of the spectroscopic features of rare earth (RE) doped inorganic glasses via tuneable growth of metallic nanoparticles (NPs) is demanding in plasmonic based nanophotonics. We report the gold (Au) NPs assisted sizeable enhancements in Er³⁺ luminescence in zinc-sodium tellurite glass. Glasses of the form 70TeO₂-20ZnO-10Na₂O-(x)Er₂O₃-(y)Au (x = 0.0 and 1.0 mol%; y = 0.0-0.6 mol% in excess) are synthesized via melt-quenching method and thoroughly characterized. Au concentration dependent variations in the physical and spectroscopic properties of glasses are determined. XRD data confirms the amorphous nature of all samples. UV-Vis-NIR spectra reveal seven absorption bands corresponding to the transitions from ground state (⁴I_15/2) to ⁴I_13/2, ⁴I_11/2, ⁴I_9/2, ⁴F_9/2, ²H_11/2, ⁴F_7/2 and ⁴F_5/2 excited states of Er³⁺. TEM micrograph manifests the existence of non-spherical Au NPs with average size of 8.6 nm. Prominent surface plasmon band of Au NPs is evidenced around 629 nm. Furthermore, Au NPs display a SPR mediated strong absorption in the visible region. Room temperature visible down-conversion emission (under 425 nm excitation) reveal three significant peaks centred at 532 (moderate green represent ²H_11/2 → ⁴I_15/2 transition), 550 (weak green represent ⁴S_3/2 → ⁴I_15/2 transition) and 588 nm (strong green represent ⁴S_3/2 → ⁴I_15/2 transition). Glass containing 0.4 mol% of Au exhibiting the highest luminescence intensity is ascribed to the NPs local field enhancement and energy transfer between RE ions and NPs. Variations in the physical properties of glass are explained in terms of the alteration in structures and ligand interactions with Au NPs present in the glass network. The intense field amplification discerned in the vicinity of Au NPs is attributed to the charge accumulation at the surface of the NPs. Surface plasmon resonance (SPR) of Au NPs and energy transfer (ET) from NPs to Er³⁺ ions are primarily attributed for the observed spectral modification. It is established that our glass composition displaying such significant enhancement may be beneficial for the development of up-converted solid state lasers and other plasmonic devices.

Abstract: Modifying the optical characteristics of rare earth (RE) doped inorganic glasses by stimulating surface plasmon resonance (SPR) via controlled growth of metal nanoparticles (NPs) is an outstanding quest in glass plasmonics. Glasses with composition 70TeO₂-20ZnO-10Na₂O-(x)Er₂O₃-(y)Au (x = 0.0 and 1.0 mol%; y = 0.0 and 0.6 mol% both in excess) are synthesized using melt-quenching technique and characterized. Influences of heat treatment temperature on the growth of Au NPs and their subsequent impacts on Raman spectral features modifications are inspected. The amorphous nature of glass is confirmed by using XRD. TEM reveal the non-spherical Au NPs with average diameter vary from 7.4 to 10.3 nm. Surface plasmon band is evidenced around 627 - 632 nm. Raman spectra demonstrate the presence of Er-O and Zn-O bond, anti-symmetric vibrations of Te-O-Te bonds and stretching modes of non-bonded oxygen exists in TeO₃ and TeO₃₊₁ unit. The amplifications in Raman signals by a factor of 1.39, 1.40, 0.88 and 1.29 and 1.25 corresponding to the peak centered at 262, 382, 536, 670 and 725 cm^-1 are attributed to the contribution of a surface plasmon (SP) generating a strong, localized and secondary field. The excellent features of the results suggest that our systematic method of controlled NPs growth may constitute a basis for improving the spectral features of tellurite glasses useful for the development of efficient and economic up-converted lasers.

Abstract: This paper reports on the reactivity study of composite cathode materials that comprises different weight percent of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-α (LSCF) and BaCe_0.54Zr_0.36Y_0.1O_3-α (BCZY). BCZY and LSCF powders are both prepared by a sol-gel method using metal nitrate salts as precursor. In this work, three samples with different weight percent ratios of 30, 50 & 70% of LSCF to BCZY were used and denoted as sample A1, A2 and A3, respectively. The powder mixtures of all samples were calcined at temperature of 1000 °C for 10 hours in an air. The phase formation of the samples was identified by X-ray diffractometer (XRD). As a comparison, XRD measurements for the LSCF and BCZY powders were also conducted individually, and their single-phase XRD pattern was used to identify the formation of undesired secondary reaction of the powdered mixture. The analysis of room temperature XRD data revealed that A1, A2 and A3 samples exhibit a complete solid solution between the crystal structures of LSCF cathode and BCZY electrolyte. The peaks can be indexed to (110), (020), (202), (220), (132), (224), (332) that belong to the LCSF phase and (110), (200), (211), (220), (310), (222) peaks that fit to the BCZY phase. No additional reaction products or secondary phases were observed indicating that up to 1000 °C, the prepared mixture formed a decent LSCF-BCZY composite. The average values of the lattice parameters for all the samples confirmed their phases were stable with the increasing BCZY content. Thus, it found that the LSCF is compatible with BCZY to form LSCF-BCZY composite for potential cathode material.

Abstract: The glass series of samarium nanoparticles (NPs) doped zinc borotellurite glasses were successfully fabricated by using conventional melt-quenching technique. The structural properties of the prepared glasses were investigated by X-ray diffraction (XRD) analysis and FTIR analysis. It was confirmed that the prepared glasses are amorphous in nature. The bonding parameters of the glasses were analyzed by using FTIR analysis and were found the formation of non-bridging oxygen. The density of these glasses were measured and found to be increased with increasing samarium NPs content. The optical absorption spectra of these glasses were revealed that the fundamental absorption edge shifts to higher wavelengths as the content of Sm₂O₃ (NPs) increases. The optical energy band gap are found to be decreased linearly with an increasing samarium NPs concentration which is due to the formation of non-bridging oxygen in the glass system.KeywordsBorotellurite glass; optical band gap, Samarium nanoparticles.