Interfacial Microstructure Evolution Research Articles

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.

Multi-wire arc additive manufacturing of TC4/Nb bionic layered heterogeneous alloy: Microstructure evolution and mechanical properties

The performance improvement of wire arc additive manufacturing component relies on structural innovation and tailored printing, and the naturally optimized structure can provide inspiration for design and manufacturing. In this work, a layered TC4/Nb multi-material alloy component inspired by the biological structure of the Crysomallon squamiferum shell was designed and fabricated by multi-wire arc additive manufacturing (MWAAM). The interfacial reaction, phase composition, microstructure evolution, crystal growth, mechanical properties and crack propagation of MWAAM-processed bionic heterogeneous TC4/Nb multi-material alloy component were investigated by EDS, SEM, EBSD and mechanical tester. The results indicated that the good metallurgical bond was formed between the different layers of MWAAM TC4/Nb multi-material alloy sample. The Ti/Nb multi-material alloy component was mainly composed of α-Ti, β-Ti and (Nb, Ti) solid solution phases. The morphology of phase underwent a continuous transformation process from TC4 layer to G1 layer with the increase of Nb content: Lamellar α + β →Thin lamellar α + Short rod α + β → Acicular α + β → Thin acicular α + β. In addition, the grain size of TC4/Nb multi material alloy component from TC4 layer to G2 layer gradually from 3.534 μm decreased to 2.904 μm with the increase of Nb content. The microhardness of TC4/Nb multi-material alloy from TC4 layer to G2 layer ranged from 404.04 HV to 245.23 HV. The relatively high compression strength and ultimate tensile strength of TC4/Nb multi-material alloy sample were 2162.64 ± 26 MPa and 663.39 MPa, and corresponding strain were 31.99% and 17.77%, respectively. The excellent mechanical behavior was mainly contributed to the excellent combination of gradient transition of grain size and microstructure evolution between layers. Crack propagation was mainly dominated by crack deflection and multistage cracking during the tensile test process. The strength of TC4 layer was the highest than G1 and G2 layer in the TC4/Nb multi-material alloy component.

Interfacial microstructure evolution and mechanical properties of Al2O3/Al2O3 joints brazed with Ti–Ni–Nb filler metal.

Herein, prepared Ti40–Ni40–Nb20 (at. %) alloy was utilized as a filler metal to join Al2O3 ceramic. The effect of brazing temperature and holding time on the interfacial microstructure evolution and shear strength of joints were analyzed systematically. The results demonstrated that AlNi2Ti, Ni6Nb7 and layered Ni2Ti4O formed adjacent to Al2O3 ceramic. The microstructure of Al2O3 joint brazed at 1200 °C for 10 min was Al2O3/AlNi2Ti + Ni6Nb7 + Ni2Ti4O/Ti2Ni/TiNi + Nb solid solution (Nbss) eutectic + (Ti,Nb)2Ni/Ti2Ni/Ni2Ti4O + Ni6Nb7 + AlNi2Ti/Al2O3. As brazing temperature or holding time raised, the Ni2Ti4O layer nearby Al2O3 ceramic, AlNi2Ti and Ni6Nb7 developed tremendously whereas TiNi + Nbss eutectic structure gradually increased and tended to coarsen. Eventually, the TiNi + Nbss eutectic structure and (Ti,Nb)2Ni in brazing seam were replaced gradually by bulk Ni6Nb7 because of the depleted Ti element. The shear strength of joints was first increased and then decreased with the increasing of the temperature/holding time. The Al2O3/Al2O3 joints brazed at 1200 °C for 10 min received the maximum shear strength of 93.2 MPa, and the joints fractured primarily at the brazing seam/Al2O3 interface.

Effect of interfacial microstructure evolution on the peeling strength and fracture of silicon nitride/oxygen-free copper foil joints brazed with Ag-Cu-TiH2 filler

Gas-pressure sintered silicon nitride (Si3N4) ceramic was brazed to oxygen-free copper (OFC) foil using 20.22 ± 0.93 mg/cm2 of Ag-Cu-TiH2 filler at 875 ◦C for 0.5 h. The effect of TiH2 content on the 3D morphology, including the cross-section microstructure and etched surface morphology of Si3N4 ceramic/OFC foil joints, was analyzed. An evolution model of the interfacial microstructure for joints was proposed based on 3D morphological analysis. The reaction between the brazing alloy and Si3N4 ceramic formed the interfacial reaction layer and the inside reaction zones during brazing. The growth mechanism of the interfacial reaction layer was discussed in detail. The peeling test was used to evaluate the bonding strength of the Si3N4 ceramic/OFC foil joints, and the optimum peeling strength of 25.1 N/mm was achieved at 5 wt% TiH2 content. The interfacial microstructure of the joints changed with TiH2 content, leading to different main fracture mechanisms and corresponding peeling strengths.

Oxidation behavior and interfacial microstructure evolution of MoSi2/MoB coatings on Mo1 substrate at 600 and 1400 °C

Boron was incorporated into the MoSi2 coating via BSi co-cementation and a two-step process, i.e., boronizing followed by siliconizing. Compositional and microstructural changes arising from B-doping remarkably improved the performance of the MoSi2 coating. At 600 °C, compositional change caused by B-doping led to the formation of borosilicate scale with lower viscosity relative to vitreous SiO2, which considerably enhanced the oxidation resistance. However, the pores that formed within the middle and lower part of the B-doping MoSi2 coatings during preparation had a negative effect on the development of a continuous borosilicate scale. At 1400 °C, the interfacial reaction between MoB and Mo5Si3 led to the formation of a continuous Mo5SiB2 interlayer, which delayed the inward diffusion of Si within the coating. Accordingly, the growth rate of Mo5Si3 was roughly halved.

Effect of differential temperature on the interfacial microstructure evolution and mechanical properties of asymmetrically rolled Mg/Al composite plates

To investigate the effects of differential temperature on microstructure, interfacial morphology and mechanical properties of Mg/Al composite plates, asymmetric rolling was used to prepare Mg/Al composite plates. The results show that the shear deformation induced slip system at interface is less and the degree of dislocation accumulation is higher in isothermal rolling compared to differential temperature rolling. This results in a higher degree of subgrain in each layer and higher tensile and yield strength of composite plate. However, the plate is prone to stress concentration at interface, which severely reduces elongation and bond strength. The differential temperature rolling can better promote the recrystallization of magnesium alloy and grain refinement of aluminum alloy at interface by introducing temperature gradient. This reduces the occurrence of stress concentrations at interface, resulting in higher elongation and bond strength of composite plate.

Effects of grain size and nano-oxide particles on the healing mechanism of hot compression bonding Fe–9Cr-1.5W-0.3Ti alloy

The hot compression bonding (HCB) in a Fe–9Cr-1.5W-0.3Ti alloy, under three conditions: (i) coarse-grained; (ii) fine-grained hot isostatic pressed (HIP); and (iii) fine-grained nano-oxide dispersion strengthened (ODS), was performed at 800 °C with strains of 10% and 30% and followed by soaking treatment at 1000 °C for 4 h. The effects of grain size and nano-oxide particles on the interfacial microstructure evolution and healing mechanism were systematically investigated. The results showed that grain boundary bulging and small recrystallized grains formed along the straight bonding interface of the coarse-grained alloy were related to discontinuous dynamic recrystallization behavior. In contrast, a layer of fine recrystallized grains was located at the bonding interface of the fine-grained HIP alloy, which was a typical rotation dynamic recrystallization behavior. Although the interfacial recrystallization behavior of the fine-grained ODS alloy was also rotation dynamic recrystallization, nano-oxide particles inhibited interfacial recrystallization and oxide transformation. Based on the interfacial bonding ratio considering different features of HCB, the ranking of interface bonding ability was coarse-grained alloy < ODS alloy < HIP alloy.

Interfacial reaction and microstructure evolution of nanoparticle-added Al/Cu welded interface under direct current treatment

Interfacial reaction and microstructure evolution of nanoparticle-added Al/Cu welded interface under direct current treatment

An in-situ X-ray computed tomography imaging apparatus with stack pressures for rechargeable batteries

Herein, a novel in-situ X-ray computed tomography (CT) imaging apparatus with stack pressures is proposed to detect the micro-structural evolution at the interface during the electrochemical process. And the relationship between the electrochemical performance and the interface morphology of lithium metal batteries has been effectively investigated through this in-situ technology. It can be observed that the growth of Li dendrites and their morphology evolution are directly dependent on the stack pressures. The Li dendrite grows from the needle-structure to the island-structure, accompanied by the tip-growth mode transferring to the base-growth mode in the range of the critical pressure. Moreover, the growth of Li dendrites can also be effectively inhibited when loading a suitable stack pressure. This novel in-situ CT imaging technology provides a feasible way to underlying the interface micro-structure evolution, electrochemical-pressure complexions, and safety of next-generation rechargeable batteries.

Interfacial microstructure evolution and mechanical properties of AlCoCrFeNi2.1 alloy by multilayer additive hot compression bonding

Multilayer additive hot-compression bonding (MAHCB) is an efficient manufacturing method for obtaining a large alloy with a uniform composition and microstructure. In this work, the method was applied to an AlCoCrFeNi2.1 eutectic alloy for the first time. The results show that the bonding temperature significantly affects the interface microstructure, improving dynamic recrystallization (DRX) and interface grain boundary migration (GBM), as well as reducing defects at the interface. Optimal bonding was obtained at a bonding temperature of 1250 °C. The interfacial Vickers hardness reaches 317 HV, and the tensile‒shear strength reaches 894 MPa, which are 9.3% and 16.5% improved, respectively, compared with the as-cast sample. The interface microstructure and fracture morphology are very close to those of the as-cast state. The combination of temperature and strain promote the interfacial bonding process, which mainly include DRX in the FCC phases, element diffusion between the FCC and B2 phases, and transformation of harmful B2–B2 interfaces into those of FCC-B2 type.