Cu-1 mass%Co合金におけるCo粒子のオストワルド成長

Flip-chip devices with Sn-3.8Ag-0.7Cu solder on electroless Ni (EN) without immersion Au were studied after aging at different temperatures. The (Cu,Ni)6Sn5 intermetallics (IMCs) growth was volume diffusion controlled and Kirkendall voids were found in the Ni3P layer even at the initial stage of high-temperature aging due to the faster diffusion of Ni in the Ni3P layer via its column structure boundaries. The Ag3Sn IMCs were distributed in the bulk solder, existing as plate- or lamella-like phases or as small particles around the β-Sn dendrites, and the (Cu,Ni)6Sn5 IMCs existed as facet-like phases. The plate- and lamella-like Ag3Sn phases break up into small parts and these broken parts, together with small Ag3Sn particles, coarsen into pebble-like phases during high-temperature aging. Shear tests showed that all the solder bumps fractured in the bulk solder. The shear strength of solder bumps decreases at the initial stage of aging at 150°C and 175°C, and the strength degradation during aging may be caused by the coarsening of small Ag3Sn particles.

This paper discussed the coarsening behavior of the γ′ phase in Waspaloy during heat treatment at different aging times under the temperatures of 960 °C and 1000 °C. The morphology of γ′ phase is obtained by scanning electron microscopy and it is measured by the software Image Pro Plus 6.0 in a variety of aging conditions. The volume fraction of the γ′ phase is decreasing with the increase of the temperature. The radius of the γ′ phase is subject to involve the coarsening process during aging treatment, and the coarsening rate decreases with the extension of the aging time at certain temperature. Besides, the coarsening kinetics of γ′ phase in Waspaloy is adequately characterized by the Lifshitz–Slyozov–Wagner (LSW) theory model as the particle size distribution and coarsening behavior show excellent agreement with the LSW model. According to the experimental results and LSW model, the coarsening rate coefficients were determined to be 27.23 nm3/s and 58.67 nm3/s under the aging temperature of 960 °C and 1000 °C respectively. Meanwhile, on the basis of the experimental statistics analysis and the LSW model, the mathematical model of the coarsening behavior of the γ′ phase in Waspaloy was developed. Mathematical model developed in this paper can be used to evaluate the coarsening process of the γ′ phase during thermal exposure. The interfacial energy between the γ′ phase and the γ matrix was determined to be 56.04 mJ/m2 and 44.27 mJ/m2 at the temperature of 960 °C and 1000 °C respectively.

The kinetics of carbide precipitation in a fully processed 2.3 wt Pct silicon, 0.66 wt Pct aluminum electrical steel with carbon contents of 0.005 to 0.016 wt Pct were investigated over the temperature range from 150 to 760 °C and times from 30 seconds to 240 hours. The size, morphology, and distribution of the carbide phases, as functions of aging time and temperature, were determined by optical and transmission electron microscopy. The 1.5T core loss was also evaluated and correlated with the changes in precipitation. Distinct C curves were observed for the formation of grain-boundary cementite at temperatures above 350 °C and a transition carbide ({100} α habit plane) at temperatures below 350 °C. Grain-boundary cementite had a relatively small effect on core loss. The large increases in core loss that accompanied transition carbide precipitation peaked at specific aging temperatures depending on the carbon content of the steel. Once a transition carbide dispersion was initially established at a given aging temperature, particle coarsening and core loss changes were generally insensitive to aging time. The influence of a combined addition of silicon and aluminum on the solubility of cementite and the transition carbide in iron was estimated and discussed.

The effect of deformation on the microstructure of a Al-4wt.%Cu alloy has been investigated. Evaluation of the microstructural changes was made by comparing results after both static annealing and tensile testing (deformed and non-deformed regions) at 450 °C. Uniaxial perturbed-rate tests showed that the Al-4wt.%Cu has a low value of the strain rate sensitivity index (m ~ 0.22) and cannot be considered as a superplastic material. It was found that in the deformed regions, specimens showed a significant increase in the grain and particle size. These changes were accompanied by an increase in the aspect ratio of the matrix grains. Tensile tests carried out at constant strain rates and stopped at intermediate strains helped to estimate the rate of the grain and particle growth and the contribution of deformation to it. To examine in detail the mechanism of the particle coarsening during deformation, additional tensile tests were made using the Al-4wt.%Cu alloy annealed at temperature conditions leading to abnormal grain size. Results of these tests also showed strain-induced particle coarsening, so that dynamic particle coarsening was not simply caused by boundary migration effects.

Formation of small particles of gold on alumina support films and their behaviour in oxygen and hydrogen atmospheres

Formation of Ultrafine particles (UFPs) in the urban atmosphere is expected to be less favored than in the rural atmosphere due to the high existing particle surface area acting as a sink for newly-formed particles Despite the large condensation sink (CS) values, previous comparative studies between rural and urban site reported higher frequency of new particle formation (NPF) events over urban sites in comparison to background sites as well as higher particle formation and growth rates attributed to the higher concentration of condensable species. The present study aims to better understand the environmental factors favoring, or disfavoring, atmospheric NPF over Lille, a large city North of France and to analyze their impact on particle number concentration using a long-term dataset (4 years : 1st July 2017 to 31st December 2020). The results highlight a strong seasonal variation of the NPF occurrences with a maximum observed during spring (27 events) and summer (53 events). It was found that high temperature (T > 295 K), low RH (RH < 45 %) and high solar radiation are ideal to observe NPF events over Lille. Relatively high values of condensation sink (CS ~ 2.10-2 s-1) are reported during event days suggesting that high CS does not inhibit the occurrence of NPFt over our site. Moreover, the particle Growth Rate (GR15.7-30 nm) was positively correlated with the temperature most probably linked to the higher emissions of precursors. Finally, the nucleation strength factor (NSF) was calculated to highlight the impact of those NPF events on particle number concentrations. NSF15.7-100 reaches a maximum of 4 in summer, indicating an enormous contribution of NPF events to particle number concentration at this time of the year.

An attempt was made to evaluate nondestructively the degradation of thermally aged 2.25Cr-1Mo steel by electrical resistivity measurement. Artificial aging was performed to simulate the microstructural changes in 2.25Cr-1Mo steel arising from long time exposure at 540 C. Microstructural parameter (amount of dissolved Mo in the matrix), mechanical property (ductile-brittle transition temperature) and electrical resistivity were measured to investigate the relationship among these parameters. Both the amount of dissolved Mo and the electrical resistivity decreased rapidly in the initial 1000 hours of aging and then changed little thereafter. On the other hand, the ductile-brittle transition temperature (DBTT) increased rapidly in the initial stage of aging and then saturated afterward. Electrical resistivity was found to have linear correlation with the amount of dissolved Mo and DBTT, respectivley. Electrical resistivity was suggested as a potential nondestructive evaluation parameter for assessing DBTT of the thermally degraded 2.25Cr-1Mo steel.

The variation of the hardness of a complex Al alloy, of the L70 type, (Al 4% Cu 0.8% Si 0.8% Mg 0.7% Mn 0.5% Fe) with ageing time at 130, 160 and 190° C was measured and correlated with transmission electron microscope observations of preciptate morphology. It was established that the peak hardness, after both 160 and 190° C ageing, was associated with coherentθ′ precipitate particles with a diameter of ∼ 700 A and the subsequent limited overageing at these temperatures was controlled by the slow growth ofθ′ particles. Measurements ofθ′ particle coarsening at 220° C suggested that the process occurred by Ostwald ripening. In contrast, ageing at 130° C gave a series of hardness—time plateaus, which were ascribed to the sequential precipitation of zones,θ′' andθ′ precipitates.

The kinetics of the coarsening of bcc Fe-Co boundary particles has been examined for various [001] twist and symmetric tilt boundaries in Cu-Fe-Co bicrystals aged at 673, 698 and 723K. The particle growth obeys the r 4 =Kt law (where r is the average particle radius, K is a constant and t is the aging time), irrespective of misorientation angle and aging temperature. The measured activation energy Q and calculated pre-exponential factor D 0 of grain-boundary diffusivity against misorientation curves display several cusps and these curves are similar to the grain-boundary energy against misorientation angle curve. A lower-energy boundary has a lower diffusivity with a larger value of Q and a larger value of D 0 .

The behaviour and kinetics of cell growth in a secondary coarse lamellar pearlite reaction in Cu-22.6 at%Be alloy have been studied principally by metallographic observations. The variations in cell radius, interlamellar spacing and volume fraction of γ phase in pearlite cells with ageing time have been determined by quantitative metallographic measurements of the specimens aged at temperatures from 673 to 823 K.The results obtained are as follows:(1) After initial, fine lamellar pearlite reaction has almost completed, coarse lamellar pearlite reaction occurs wherein the fine pearlite is replaced by the coarse pearlite.(2) Cell growth rate of coarse pearlite decreases, and the interlamellar spacing increases with ageing time.(3) Interlamellar spacing of coarse pearlite is 4∼5 times larger than that of fine pearlite in every ageing time.(4) Be concentration of α phase in fine pearlite is supersaturated at the initial ageing stage, then decreases with ageing time and attains an equilibrium value prior to the occurrence of a coarse pearlite reaction. Then it is considered that there are no chemical free energy changes during the cell growth of coarse pearlite.(5) Grain boundary diffusivities, evaluated from the discontinuous coarsening model proposed by Livingston and Cahn are reasonable. Therefore, it can be concluded that the cell growth of coarse pearlite occurs by the discontinuous coarsening mechanism.

Abstract. New particle formation (NPF) and growth are a major source of atmospheric fine particles. In polluted urban environments, NPF events are frequently observed with characteristics distinct from those in clean environments. Here we simulate NPF events in urban Beijing with a discrete-sectional model that couples cluster dynamics and multicomponent particle growth. In the model, new particles are formed by sulfuric acid–dimethylamine nucleation, while particle growth is driven by particle coagulation and the condensation of sulfuric acid, its clusters, and oxygenated organic molecules (OOMs). A variable simulation domain in the particle size space is applied to isolate newly formed particles from preexisting ones, which allows us to focus on new particle formation and growth rather than the evolution of particles of non-NPF origin. The simulation yields a rich set of information including the time-dependent NPF rates, the cluster concentrations, the particle size distributions, and the time- and size-specific particle chemical compositions. These can be compared with the field observations to comprehensively assess the simulation–observation agreement. Sensitivity analysis with the model further quantifies how metrics of NPF events (e.g., particle survival probability) respond to model input variations and serves as a diagnostic tool to pinpoint the key parameter that leads to simulation–observation discrepancies. Seven typical NPF events in urban Beijing were analyzed. We found that with the observed gaseous precursor concentrations and coagulation sink as model inputs, the simulations roughly captured the evolution of the observed particle size distributions; however, the simulated particle growth rate was insufficient to yield the observed particle number concentrations, survival probability, and mode diameter. With the aid of sensitivity analysis, we identified under-detected OOMs as a likely cause for the discrepancy, and the agreement between the simulation and the observation was improved after we modulated particle growth rates in the simulation by adjusting the abundance of OOMs.

Effect of Aging Time at High Temperature on Microstructural Evolution Behavior of a Nickel-Based Single Crystal Superalloy

Cu-C70 nanocomposite thin films were deposited on glass, silicon and TEM grids by thermal co-evaporation; the thin films were irradiated by 350 keV Ar ions and 120 MeV Ag ions at different fluences, ranging from 1 × 1013 to 3 × 1016 ions cm−2 in a high vacuum chamber. Rutherford backscattering (RBS) of pristine film verified that the thickness and copper content of thin films were 30 nm and ∼10 at%, respectively. The modifications in structure and optical properties of irradiated thin films were studied by UV-visible absorption spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS); the results were compared with those of pristine film. Raman spectroscopy gave evidence of transformation of fullerene C70 matrix into amorphous carbon after irradiation by 350 keV Ar ions at a fluence of 3 × 1014 ions cm−2. At 1 × 1015 ions cm−2 fluence, a surface plasmon resonance band due to Cu nanoparticles appeared at ∼627 nm in the visible absorption spectrum. This band was seen to undergo blue shift at higher fluence values. TEM confirmed that increasing fluence brings about the coarsening of Cu nanoparticles (from 2.4 to 6.6 nm). Moreover, XPS study ruled out the possibility of formation of any Cu compound due to irradiation. In contrast, irradiation by 120 MeV Ag ion led to amorphization of Cu (10%) C70 nanocomposite thin films at higher fluences. The SPR band intensity at 627 nm was appreciably enhanced at a fluence of 3 × 1013 ions cm−2. The amorphization of C70 due to irradiation by 120 MeV Ag ion at fluence 3 × 1013 ions cm−2 was confirmed by the appearance of D and G band in the concerned Raman spectra. Moreover, this brings about a small increase in particle size. Both particle coarsening and amorphization of C70 were responsible for the emergence of SPR band due to copper.

The critical temperature for the order-disorder transition, T c , and the ordered domain structure of the B2 phase have been investigated by electrical resistivity measurements and electron microscopic observations in Ag-Zn alloys containing 38, 40 and 42 at%Zn. Specimens quenched from the disordered β phase were all found to be ordered in the B2 structure. Resistivity change measured during aging of the B2 phase shows a plateau at the initial stage of aging. This indicates the degree of order reaches the equilibrium value immediately after the start of aging. The B2 domain size as measured after aging and quenching increases as the aging temperature increases. However, it takes a smaller value when the aging temperature is beyond T c . Values of T c were determined by monitoring the domain size as 441, 405 and 367 K for the 42, 40 and 38Zn alloys, respectively. The ragging or fluctuating of anti-phase domain boundaries was recognized in the specimens aged at a temperature just below T c . The activation energy for the domain growth was obtained by measuring growth rates as 49.3 kJ/mol, which was judged to correspond to the migration energy of excess vacancies.

Solder joints provide mechanical support, electrical and thermal interconnection between packaging levels in microelectronics assembly systems. Proper functioning of these interconnections and the reliability of the electronic packages depend largely on the mechanical properties of the solder joints. Lead free solders are common as interconnects in electronic packaging due to their relatively high melting point, attractive mechanical properties, thermal cycling reliability, and environment friendly chemical properties. However, environmental conditions, such as, operating temperature, aging temperature, and aging time significantly affect these properties due to the microstructural evolution of the solder that occurs during aging. Moreover, electronic devices, sometimes experience harsh environment applications including well drilling, geothermal energy, automotive power electronics, and aerospace engines, where solders are exposed to very high temperatures from T = 125 –200°C. Mechanical properties as well as microstructural study of lead free solders at elevated temperatures are limited in literature. Previous investigations on the microstructural evolution mainly emphasized on aging at temperatures up to 125°C. In addition, those studies were limited on investigating the coarsening of Ag3Sn IMC particles within the beta-Sn matrix.In this work, the microstructural evolutions of SAC305 (96.5Sn-3.0Ag-0.5Cu) BGA joints were investigated for different aging conditions utilizing Scanning Electron Microscopy (SEM). In particular, our approach has been to monitor aging induced microstructural changes occurring within fixed regions in selected lead free solder joints and to create time-lapse imagery of the microstructure evolution. Aging was performed at T = 150°C for several durations up to 20 days, and the topography of the microstructure of a fixed region was captured using the SEM system. This process generated several images of the microstructure as the aging progressed. We have also explored the Mechanical behavior, and aging effects of SAC305 solder joints at the extreme high testing temperature of T = 150°C using the method of nanoindentation. To study the aging effects, solder joints were preconditioned for 0, 1, 5, 10, and 30 days at T = 125°C in a box oven. Nanoindentation testing was then performed on the aged specimens at a test temperature of T = 150°C to extract the elastic modulus, hardness, and creep performance of the aged material.As expected, the analysis of the evolving SAC305 BGA microstructure showed a significant amount of diffusion of silver and copper in the beta-tin matrix during aging. In addition, a very remarkable growth of copper-tin layer at solder joint and copper pad interface in the PCB side has been visualized and then measured as a function of aging time and temperature. Quantitative analysis of the evolving microstructure showed that the particles coalesced during aging leading to a decrease in the total number of particles. This caused an increase in the average diameter of the particles with aging time, and a double exponential empirical model was used to fit the observed data. The nanoindentation test results also showed a huge degradation in the mechanical properties with the aging time. The time dependent evolution of the microstructure was compared to the degradation in the modulus during aging, and good correlation was observed.