Interfacial Microstructure Evolution Research Articles

Surface and interfacial microstructure evolution of isothermally oxidized thermal barrier coating system

Novel multilayer functionally graded thermal barrier coating (TBC) system consisting of a newly developed glass-ceramic based bond coating, glass-ceramic-25% yttria stabilized zirconia (YSZ) composite coating and 100% 8-YSZ top coating. Since TBC is a layered system property matching between each layer is a major concern. Therefore, thermal properties of the developed glass-ceramic coating and composite coating were studied in detail. The developed system was exposed to static oxidation at 1100 °C for 100 h. To assess the efficacy of the TBC system, XRD phase analysis and also mechanical properties like Young's modulus and nanohardness was performed at each layer for both before and after isothermal oxidation. From the surface and interfacial microstructure evolution it was observed that there was crack development at composite coating-top coating interface, which was due to zirconia phase transformation from tetragonal to monoclinic crystal structure, confirmed by the presence of monoclinic zirconia XRD diffraction peaks in XRD analysis. Additionally, Raman spectroscopy was also carried out on the isothermally oxidized specimen, which also pointed out the presence of monoclinic crystal structure. Even though developed TBC system failed to protect the nimonic alloy (AE435) substrate from thermal exposure at 1100 °C for 100 h the glass-ceramic/substrate had a good interfacial adhesion. Main advantage of using glass-ceramic coating is its ability to tune coating properties by changing the composition. Thus, future works are being carried out to alter the glass-ceramic composition to develop a potential TBC system.

Interfacial microstructure evolution and mechanical properties of carbon fiber reinforced Al-matrix composites fabricated by a pressureless infiltration process

In this study, unidirectional carbon fiber reinforced aluminum-matrix (CF/Al) composites were successfully fabricated by using a pressureless infiltration process to infiltrate Ni-coated CFs with Al. The evolution of the interfacial microstructure was investigated. The results showed that the Al–Ni reaction provided the main driving force for infiltration of Al melt into CF bundles by the significantly improving wettability. As the infiltration time increased from 0 min to 8 min, the infiltration behavior gradually improved with fewer defects and better fiber dispersion. Furthermore, the Al–Ni intermetallic compounds (IMCs) transformed from the large-sized primary Al3Ni phase to fine Al3Ni phase with eutectic structure, and were uniformly distributed around the CFs, which was beneficial for transferring the load and preventing the crack propagation. However, the harmful Al4C3 phase grew up at the interface. The ultimate tensile strength (UTS) of the CF/Al composites with the optimal infiltration time of 6 min was 135 ± 4 MPa, which was 121.3 % higher than that of the Al matrix.

Reliability improvement of SnAgCu interconnections under extreme temperature condition by TiO2 nanoparticles doping: Experiments and first principles calculations

Electronic components of the spacecraft during their service may endure intricate and extreme temperature environments. In this study, the interfacial microstructure evolution and reliability of Cu/Sn-3.0Ag-0.5Cu (SAC305)/Ni and Cu/Sn-3.0Ag-0.5Cu-0.05TiO2 (SAC305–0.05TiO2)/Ni interconnections under thermal shock from −196 °C to 150 °C are investigated. Short-column-type (Cu,Ni)6Sn5 intermetallic compounds (IMCs) are developed at the solder/Ni interface for both interconnections after the reflow process, and their morphology changes to long-rod type after 200 cycles. Extremely thin and discontinuous (Ni,Cu)3Sn4 phases are generated between (Cu,Ni)6Sn5 and Ni only in SAC305 interconnections after 200 cycles. The rate of interfacial IMCs growth in SAC305–0.05TiO2 interconnections is slower than that in the SAC305 interconnections. Cracks are formed in the IMC layer of the SAC305 interconnection after 200 cycles, which propagate through the whole IMC layer after 250 cycles. While for the SAC305–0.05TiO2 interconnection, no crack is observed until after 250 cycles. TiO2 nanoparticles doping could suppress the interfacial IMC growth, leading to an enhancement in the interconnection reliability under thermal shock. First-principles calculations are performed to further understand the mechanism for phase transformation of Ni-Cu-Sn IMCs and the reliability improvement of interconnections.

Enhanced interfacial microstructure evolution and mechanical properties of CF/Al–Mg composites with optimal interconnected coating

In the present study, the Ni coatings on the surface of carbon fibers (CFs) were purposely regulated to provide the enhanced interfacial microstructure evolution and mechanical properties of CF reinforced Al–Mg matrix (CF/Al–Mg) composites. With increasing the pH value and deposition time, the coating thickness increased with the formation of island-like agglomeration as the pH value was 4.5. Based on the stable electroless plating process, different thicknesses of interconnected coatings were applied in the CF/Al–Mg composites fabricated by a semi-solid rolling process in open space. With the optimal thickness of 2.15 μm, the relative density of the composites increased from 89.7 % to 98.1 %, compared with that of the composites with the thickness of 0.54 μm due to eliminated un-infiltration defects. Simultaneously, optimized fiber dispersion and interfacial behavior were obtained, leading to effective load transfer, more energy absorption and consequently significant enhanced mechanical properties. The ultimate tensile strength (UTS) of the composites was 183 MPa with the largest improvement, which was 96.8 % higher than that of the matrix.

Interfacial microstructure and mechanical properties of diffusion bonded joints of additive manufactured 17-4 PH stainless steel and TC4 titanium alloy

A novel atomic diffusion additive manufactured 17-4 PH stainless steel and TC4 titanium alloy was successfully joined by vacuum diffusion bonding with Cu foil + Ni foil interlayers at the temperature range of 880°C–960 °C for 60 min with 2 MPa pressure. The interfacial microstructural evolution, interfacial diffusion of elements, and mechanical properties of joints were analyzed. The results indicated that the interfacial transition zone was composed of diffusion affect zone (DAZ) and interface reaction zone (IRZ). With Cu foil + Ni foil composite interlayers, reaction layers such as DAZ 1/IRZ 1/IRZ 2/DAZ 2 were formed in the transition zone, and the interface consisted of CuTi + CuTi2 eutectic phase, CuTi2, Ti (Cu, Ni) and α-Ti. Striped Ti (Cu, Ni) phases were surrounded by serrated CuTi2 phases, which contained Cu-poor, Ni poor areas, and the segregation of Ti atoms. The maximum microhardness of 693 HV0.1 and the maximum shear strength of 163 MPa were obtained at the bonding temperature of 920 °C and 960 °C, respectively.

Enhancing interfacial strength of T-joint for vacuum-brazed thin-walled structures comprising TiAl and GH3536 alloys via in-situ synthesis of Al2TiO5 ceramic coatings

The joining of dissimilar materials to fabricate lightweight components of thin-walled structures for aerospace applications has garnered significant interest. A pioneering technique has been proposed to achieve an optimal interfacial microstructure and fillet of brazed joints. This technique involves a layer of Al deposited on the surface of TiAl base metal, which aids in the brazing process of the thin-walled structure comprising TiAl and GH3536 alloys. Notably, the addition of the Al layer has a significant impact on the spreading area of molten brazing filler metal, the size of the fillet, and the interfacial microstructure evolution. Consequently, these factors contribute to a substantial increase in the load-bearing capacity of the structure. A comprehensive analysis and discussion are conducted to explore the impact of the Al layer on both the interfacial microstructure and mechanical performance. Under the brazing parameters of 1040 °C/5 min, the peak tensile load reaches a peak value of 362 N, which is 100% higher compared to the joints without Al layer. It is worth noting that fracture occurred in the GH3536 foil after undergoing tensile testing. The dimension of fillet can be controlled through the in-situ synthesis Al2TiO5 ceramic phase on the surface of TiAl alloy. This research offers valuable insights into the production of engineered biomimetic materials and devices, specifically focusing on honeycomb-inspired structures.

Operando Investigation of Solid Electrolyte Interphase Formation, Dynamic Evolution, and Degradation During Lithium Plating/Stripping.

The solid electrolyte interphase (SEI) dictates the stability and cycling performance of highly reactive battery electrodes. Characterization of the thin, dynamic, and environmentally sensitive nature of the SEI presents a formidable challenge, which calls for the use of microscopic, time-resolved operando methods. Herein, we employ scanning electrochemical microscopy (SECM) to directly probe the heterogeneous surface electronic conductivity during SEI formation and degradation. Complementary operando electrochemical quartz crystal microbalance (EQCM) and ex situ X-ray photoelectron spectroscopy (XPS) provide comprehensive analysis of the dynamic size and compositional evolution of the complex interfacial microstructure. We have found that stable anode passivation occurs at potentials of 0.5 V vs Li/Li+, even in cases where anion decomposition and interphase formation occur above 1.0 V. We investigated the bidirectional relationship between the SEI and lithium plating-stripping, finding that plating-stripping ruptures the SEI. The current efficiency of this reaction is correlated to the anodic stability of the SEI, highlighting the interdependent relationship between the two. We anticipate this work will provide critical insights on the rational design of stable and effective SEI layers for safe, fast-charging, and long-lifetime lithium metal batteries.

Evolution of the microstructure of amorphous polyethylene under friction-induced plastic flows: A reactive molecular investigation.

The plastic flow of ultra-high molecular weight polyethylene (UHMWPE) at a frictional interface, which is critical to the wear behavior, was investigated by reactive molecular dynamics simulations. The UHMWPE substrate was found to experience various deformations during the friction process. First, some polyethylene (PE) chains could detach from the substrate because of their rapid movement. Second, the frequent motion of PE chains also resulted in the intermittent formation and breaking of cavities between intermolecular PE chains. These deformations were more obvious on a surface with a convex protrusion, where the plowing effect exacerbated the cavitation and elastic deformation of PE chains. Correspondingly, the plastic flow in turn reconstructed the convex protrusion by displacing the surface atoms on the Fe slab. The plastic flow of PE chains broke the C-C bonds, and the carbon moieties were then chemically bonded onto the metal surface. A rapid change of atomic charge, hence, happened when the bonds broke. Meanwhile, PE chains release short alkyl radicals gradually after bond breakage, indicating gradual wear of the substrate during friction. This work provides molecular insight into the evolution of interfacial microstructure under plastic flow on a UHMWPE substrate.

Interface microstructure evolution and bonding mechanism of low-temperature diffusion bonding of hydrogenated Zr-4 alloy

Zr-4 alloy is widely used as fuel cladding in the nuclear industry. And welding is one of the most significant procedures during the manufacturing of fuel assembly. Bonding at high temperature risks safe operation of nuclear reactors because high temperature deteriorates the properties of Zr-4 alloy. Herein, Zr-4 alloy was hydrogenated to a hydrogen content of 0.2 wt.% before diffusion bonding. Direct diffusion bonding of hydrogenated Zr-4 alloy was performed at various bonding temperatures. The microstructural evolution of the bonding interface and the interface bonding mechanism were systematically investigated. The bonding temperature of the hydrogenated Zr-4 alloy was reduced by 150 °C compared with the corresponding nonhydrogenated alloy. Furthermore, the shear strength of the joints was as high as 257 MPa (4.6 × higher than corresponding joints comprised of the nonhydrogenated alloy) at a bonding temperature of 700 °C. Transmission electron microscopy and electron backscatter diffraction indicate that plastic deformation of the joints increased because of a phase transition of the hydrides (to the β-Zr phase) during bonding, leading to high-density dislocations that accumulated at the bonding interface. The migration of the interface grain boundary was facilitated by high-density dislocations of sufficiently high energy. The bonding interface was no longer evident, enabled by dynamic recrystallization induced by migration of the interface grain boundary. Furthermore, the fracture mode of the joints was initially brittle but became ductile/brittle mixed mode with increasing temperature.

Evolution mechanism of interfacial microstructure and its effect on failure in dissimilar metal welds containing ferritic heat resistant steels

This study investigated the behaviour and mechanism of interfacial microstructure evolution during long term high temperature exposure and the effect of interface structure on creep failure in the dissimilar metal welds (DMWs) involving ferritic heat resistant steels with nickel-based filler metal. The welding of nickel-based and ferritic materials led to the formation of interfacial martensite layer in the ferritic steel side of DMW. During long term high temperature exposure, interfacial martensite transformed to ferrite due to C diffusion and migration in the micro-region near the BCC/FCC interface between the martensite layer and the weld metal. The martensite-ferrite transformation was attributed to the large C chemical potential gradient caused by chemical composition gradient. Under creep condition, the failure of DMW was prone to occur along the weld metal/ferritic steel interface, which was related to strain concentration around the interfacial ferrite formed during service. Hence, the relationships between interface structures before and after service and interfacial failure in the DMWs were clarified.

In-plane thermal expansion behavior of M55J carbon fiber reinforced SiC matrix composite

With the rapid development of high-precision ultra-stable spacecraft, the absolute values of coefficients of thermal expansion (CTE) of carbon fiber reinforced SiC matrix composite (C/SiC) are required to be closer to 10−7 K−1 or even lower. In this work, high-modulus and low-expansion M55J carbon fiber was selected to replace T300 carbon fiber as the reinforcement to decrease the CTE of C/SiC. The interfacial region, pore distribution and microstructure evolution during the densification process were investigated. With the replacement of T300 carbon fiber by M55J carbon fiber as the reinforcement, axial thermal residual stress in SiC matrix can increase to 378 ± 26 MPa, resulting in the generation of matrix microcracks. This can reduce the constraint of matrix to carbon fiber and provide expansion space for M55J-C/SiC. Therefore, the average in-plane technical CTE of C/SiC in the range of −20 to 50 °C can be reduced from 1.09 × 10−6 to 0.34 × 10−6 K−1.

Improved Cu/Sn interface reliability using double-layer stacked nano-twinned Cu

The immoderate growth of intermetallic compound (IMC) at the Cu/Sn bonding interface reduces the reliability of bonding joints, leading to the failure of high-density packaging. Herein, we design a double-layer nanotwinned Cu (d-ntCu) structure composed of the perpendicularly aligned nano-twinned Cu (p-ntCu) as the upper layer and horizontally aligned nano-twinned Cu (h-ntCu) as the lower layer. We study the Cu/Sn bonding interface microstructure evolution to reveal the IMC growth inhibition and void suppression ability of d-ntCu. As a comparison, the interface microstructure evolution of single layer h-ntCu/Sn is also studied. After thermal aging, the growth mode of IMC at the Cu/Sn bonding interface can be divided into two stages, which are caused by the in-situ annealing of the p-ntCu. In the initial stage of aging, the main diffusion path of Cu atoms is twin boundary diffusion, causing a rather fast growth of IMC. After 100 h aging, the twins anneal into large grains, which induce a lower growth rate of IMC due to the bulk diffusion of Cu atoms. Compared with the h-ntCu single layer, the IMC thickness of the d-ntCu is suppressed by 20%. Besides, the bonding interface in d-ntCu/Sn is void-free due to the vacancy-sink effect of twin boundaries. Therefore, using d-ntCu as the substrate can not only control the IMC growth rate but also suppress the formation of voids during aging, which is helpful to achieve high bonding reliability.

Development of high thermal conductivity of Ag/diamond composite sintering paste and its thermal shock reliability evaluation in SiC power modules

Diamond has the highest thermal conductivity among naturally occurring materials and a relatively low coefficient of thermal expansion (CTE), making it a promising interconnected material for next-generation semiconductor power devices. In this study, Ag/diamond composite sintering paste was developed. The agglomerated diamond particles were uniformly dispersed in the sintered Ag porous structure, and the thermal conductivity was increased from 171.4 W/(m·k) for pure Ag sintering to 288 W/(m·k) for an Ag@2%diamond (2% of the total weight of Ag) specimen. The interfacial microstructure evolution and fracture behavior were investigated in detail for a SiC/Direct Bond Copper (DBC) joint structure during an extreme thermal shock test (TST) in the range of −50 °C–250 °C. Importantly, with a moderate amount of diamond additive, the microstructural degradation and severe deformation of the DBC substrate were effectively suppressed. This is mainly attributed to the diamond addition, which can block the migration pathways of Ag atoms toward long-term thermal shock and adjust the thermo-mechanical performance of the sintered layer. This detailed study about Ag/diamond composite paste can provide new guidance for strengthening sintered Ag interconnections for SiC power modules.

Mechanical properties degradation of Sn 37Pb solder joints caused by interfacial microstructure evolution under cryogenic temperature storage

The interfacial microstructure, shear property and fracture behaviors of Sn37Pb joints after cryogenic temperature storage for different durations were investigated in this study, storage test at room temperature (298 K) and thermal aging test at 423 K were also carried out as comparison. The morphology of interfacial Cu6Sn5 IMCs for the joints stored under 77 K and 173 K transformed from scallop-like to column-like, moreover, the IMC layer thickness slowly increased with prolonged storage time. The growth rate of Cu6Sn5 layer in Sn37Pb joint stored at 77 K was slightly faster as compared with that stored at 173 K. However, the morphology and thickness of Cu6Sn5 IMC layer still remained roughly unchanged after storage at 298 K for up to 40 days. The Cu6Sn5 IMC growth of Sn37Pb joint stored at 77 K and 173 K was expected to be caused by Cu atom diffusion from Cu pad towards Sn37Pb solder, which was induced by the stress gradient. Additionally, the shear force declined and fracture position changed from in Sn37Pb solder to primarily in Sn37Pb solder and partly along the interface with the prolonging of storage time at 77 K and 173 K, which were induced by IMC layer growth.

Firing behavior of lead-containing and lead-free metallization silver paste for monocrystalline silicon solar cells

In this work, PbO-TeO2-Bi2O3-SiO2 lead-containing glass and TeO2-Bi2O3-ZnO-Li2O lead-free glass were synthesized in order to investigate the difference between them and find out the reason why lead-free paste can't be used on monocrystalline wafer commercially. Their flowability and reactivity with SiNx were characterized. Lead-free glass presents lower flow temperature, better wettability and stronger etching ability to SiNx than lead-containing glass. Button test was carried out and large white particles was identified on the interface for lead-free glass. These results indicates the excessive flowability and etching to SiNx for lead-free glass. The morphology of grid line and interface between silver electrode and silicon wafer were investigated on dependence of temperature. The lead-containing and lead-free glasses went through similar evolution of silver sintering and interface microstructure with lead-free glass better facilitating silver sintering through liquid phase sintering due to its lower flow temperature. The thicker glass layer and more Ag crystallites with large size can be observed from cross-sectional micrographs for lead-free glass. Therefore, lead-free paste exhibits lower Voc and FF than lead-containing glass owing to its ecxessive corrosion of SiNx, thicker glass layer and large Ag crystallites.

Interfacial microstructure evolution and bonding mechanism transformation of CoCrFeMnNi high-entropy alloy joints fabricated by vacuum hot-compression bonding

Vacuum hot-compression bonding (VHCB) is a promising solid-phase bonding technology, but its feasibility and applicability in high entropy alloy (HEA) are still unclear. Herein, the VHCB process of CoCrFeMnNi HEA was investigated, and the interfacial bonding quality was comprehensively evaluated via microstructure characterization and tensile test. Results exhibit that the VHCB enables to obtain the high-quality CoCrFeMnNi HEA joints, and the excellent bonding performance is attributed to the dissolution of interfacial oxide particles (IOPs) (MnCr2O4) and the migration of interfacial grain boundaries (IGBs). The bonding quality results suggest that the sluggish diffusion of the dissolved elements resulted in partial nanoscale IOPs remaining at the original bonding interface, and the mechanical properties of the joints were not compromised when the IOPs were smaller than 35 nm in size and less than 15/100 μm in amount. Crystallographic analysis indicates that the migration behavior of IGBs is closely associated with the evolution of recrystallized grains and twin boundaries in the interfacial region, and the migration mechanism transformed with the rising bonding temperature. Furthermore, a new interfacial bonding mechanism, i.e., twin-induced interfacial boundary migration, was revealed and its beneficial effect on interfacial bonding quality was demonstrated.

Evolution of interfacial heat transfer, contact behavior and microstructure during sub-rapid solidification of molten steel with different hydrogen contents

Evolution of interfacial heat transfer, contact behavior and microstructure during sub-rapid solidification of molten steel with different hydrogen contents

Repair of ordinary concrete using alkali activated slag/fly ash: High temperature resistance and micro structure evolution of adhesive interface

In this paper, the effect of alkali activated slag-fly ash (AASFA) geopolymer as repairing materials on the high temperature resistance of the new-to-old concrete (NTOC) adhesive interface was studied. The deterioration of splitting tensile strength and shear strength with increasing temperature was investigated when different ratios of slag-fly ash were used as repair materials. The mechanism of AASFA improving the high temperature resistance of the adhesive interface was analyzed from the micro morphology, pore structure, and hydration products. The results showed that GPC50 as repairing materials, the mechanical properties and high temperature resistance of adhesive interface were the best. For OOPC-GPC50, the development of the cracks was inhibited at each temperature, especially at 100 °C and 200 °C. AASFA continued to hydrate under high temperature environment, and the filling effect induced by hydration products inhabited the deterioration of pore structure, which reduces the harmful pores formation around adhesive interface. The regenerated gel could provide additional adhesiveness, thus improving the strength of NTOC. Under high temperature environments, Ca(OH)2 reacted with AASFA at the adhesive interface of OOPC-GPC50. As the temperature increased, the reaction continued to develop, and more Ca(OH)2 was consumed in further.

A novel dynamic self-constrained explosive welding method for manufacturing copper-steel bimetallic tube

This study proposed a dynamic self-constrained explosive welding method to fabricate the copper-steel bimetallic tube without external mold. The mechanical balance of the self-constrained process was carefully revealed by three-dimensional (3D) numerical simulations. Besides, the microstructure evolution, element distribution, and mechanical properties of the copper-steel interface were systematically investigated. Results showed that the dynamic self-constrained system could effectively strike a balance between the inner and outer tubes in terms of stress, velocity, and displacement. The max hoop tensile stress near the outer surface of the base tube was significantly reduced from 535 MPa (in the unconstrained experiment) to 387 MPa avoiding the appearance of radial cracks. The welding interface varied from a nearly straight one via a large wave to an irregularly small wave. Meanwhile, the microhardness test showed a significant increase in the region near the welding interface.

Interfacial microstructure evolution for coordinated deformation of Mg/Al composite plates by asymmetrical rolling with differential temperature rolls

In this work, Mg/Al composite plates with different thickness ratios were prepared by the asymmetrical rolling process with differential temperature rolls and isothermal symmetrical rolling. Microstructural evolution and mechanical properties of matrix and composite materials with different thicknesses were analyzed. Influence of thickness ratios on the coordinated deformability of heterogeneous metals and interface toughness under the action of temperature gradient and shear force was investigated. Results show that the relative deformation rates of matrix and composite materials converge gradually under the influence of work hardening of Mg/Al layer. The Mg layer is mainly DRXed grains and texture intensity gradually weakens with increasing thickness ratio. The Al layer is mostly dominated by subgrains and deformed grains, which have a strong correlation with thickness ratio. Strength and plasticity of composites first increase and then decrease with increasing thickness ratio. Fracture of composite plate occurs in intermetallic compounds (IMCs). Thickness of IMCs has a strong positive correlation with thickness ratio. When the thickness ratio of AZ31B/Al6061 for 5, the relative thickness of IMCs is the largest and the relative bonding strength is the smallest. When the thickness ratio of AZ31B/Al6061 for 3, there is no element aggregation in IMCs, and the comprehensive mechanical properties of composite plate are comparatively better.