Interfacial Microstructure Evolution Research Articles

Investigation on the microstructure and mechanical properties of large-tube forging manufactured by additive forging

Abstract Large-tube forgings were formed using nine layers of continuous-casting billet made from 15CrNi3MoV alloy steel via additive forging. The interfacial microstructural evolution under different hot-compression bonding temperatures and strains was investigated using optical microscopy, scanning electron microscopy, and electron backscatter diffraction. The tensile properties of the hot-compression-bonded and tube-forged samples were also evaluated. The results showed that as the hot-compression bonding temperature and strain increased, the bonding interface gradually disappeared and the voids at the bonding interface closed. Finally, the interface was replaced with recrystallised grains. The tensile properties of the hot-compression-bonded samples at different temperatures and strains were identical. The tensile properties of the interface and base samples of the tube forging were comparable, and the fracture morphologies were consistent. The fracture position of the large tensile sample with a length of 1000 mm containing three original interfaces is the base, indicating the complete metallurgical bonding of the forging

Effects of recrystallization on interfacial microstructure evolution and shear strength of TiAl alloy joints

The effects of dynamic recrystallization (DRX) and post-bonding heat treatment (PBHT) on the interfacial microstructure evolution and mechanical properties enhancement of Ti-43Al-4Nb-1Mo-0.2B alloy joints, subjected to various bonding parameters, were thoroughly investigated through detailed microstructural characterization and shear performance tests. A strip-like DRX area was observed at the interface when bonding at 1100 °C, ≥30 MPa, for 60 min. Equiaxial- γ grains underwent discontinuous dynamic recrystallization during the bonding process, and tended to form flat grains parallel to the lamellae direction during recrystallization annealing (1000 °C/6 h) owing to the hindrance imposed by the lamellae on both sides. The orientations of lamellae on the both sides of bonding interface affects the lamellae's stress distribution and deformation behavior at the bonding interface, subsequently influencing the DRX behavior and the width of the DRX zone. Static recrystallization (SRX) during the recrystallization annealing treatment can eliminate bonding defects of joints bonding at lower pressures or temperatures. Optimal joints with fully lamellar interfacial microstructure and excellent shear properties can be obtained through single-α phase annealing treatment. Lamellae microstructure tailored through PBHT can significantly enhance the quality of joints, attributed to the homogeneity of the microstructure between the interface and matrix. The highest shear strength of 478 MPa, accounting for 82 % of the matrix strength, was obtained under the bonding parameters of 1100 °C/30 MPa/60 min-1290 °C/15 min. This work provides important DB process parameters for fabricating of complex structural parts of TiAl alloy.

Study on the Influence of Surface Roughness and Temperature on the Interface Void Closure and Microstructure Evolution of Stainless Steel Diffusion Bonding Joints

Study on the Influence of Surface Roughness and Temperature on the Interface Void Closure and Microstructure Evolution of Stainless Steel Diffusion Bonding Joints

Interfacial microstructure evolution and mechanical behavior of W/steel joints diffusion bonded with CoCrFeNi interlayer

In the nuclear industry and military field, diffusion bonding between tungsten (W) and steel has received extensive attention, in which selecting and developing new joining materials is of great significance. In this paper, a high entropy alloy CoCrFeNi with excellent ductility and high melting point, is used as interlayer material for the electric-field assisted diffusion bonding between W and steel. Effects of diffusion bonding time on interfacial microstructure and mechanical performance was investigated. Under the diffusion bonding conditions of 950 °C for 5, 15, 30 and 45 min, no cracks or discontinuities appeared in the joints. Element diffusion occurred at interfaces and metallurgical bonding was realized between interlayer and substrates. At W/CoCrFeNi interfaces, in addition to the solid solution phase, intermetallic compounds were detected for the joint bonded with holding time longer than 30 min. Only solid solution phase formed for all the CoCrFeNi/steel interfaces. The room temperature tensile strength of the W/CoCrFeNi/steel joint was determined to be 270 MPa, exceeding the values documented in prior studies. The elevated temperature (400 °C and 600 °C) tensile strength was found to be higher than that at room temperature. In addition, similar microhardness distribution across the joints bonded for different holding times were observed, and there was no obvious difference in the hardness of the interlayer and metal substrates in these joints.

Correlating lithium-ion transport and interfacial lithium microstructure evolution in solid-state batteries during the first cycle

Correlating lithium-ion transport and interfacial lithium microstructure evolution in solid-state batteries during the first cycle

Interfacial structure and formation mechanism of 90 W-7Ni-3Fe/steel using co-sintering method

In this study, we proposed a powder metallurgy method to develop an interlocking interface in tungsten heavy alloy/steel composites, which is achieved by co-sintering technology using tungsten heavy alloy and steel powders with a large difference in particle size. The interfacial microstructure evolution and mechanical properties of the co-sintered joint as a function of co-sintering temperature were investigated systematically. Results showed that a well-bonded interlocking interface was formed along the steel particles as a result of the tungsten heavy alloy particles filling in the gaps between two neighboring steel particles. The co-sintered joint contains four regions: the W alloy matrix, the Fe3W3C layer, the Ni-affected layer, and the steel matrix. Based on the microstructural characterization, the interface formation mechanism and reaction layer growth behavior are discussed in depth. Benefitting from the interlocking structure, the highest tensile strength of the co-sintered specimen is 265 MPa, which is 66% higher than that of the non-interlayer joint obtained by diffusion bonding method. Moreover, its performance is better than that of some W alloy/steel with an interlayer. This technique offers a potential method for the efficient preparation of a W alloy/steel composite structure with outstanding properties.

Interface microstructures in the wetting of Cu by equiatomic GaInSnBiZn high-entropy alloy

This study investigates the wetting characteristics, interface microstructure evolution of equiatomic GaInSnBiZn HEA on Cu under high vacuum with sessile drop method to extend its electronic packaging applications. Optimal conditions involve a 350 °C temperature maintained for ∼20 min to prevent Bi loss, resulting in a contact angle inversely proportional to temperature and reaching a minimum of ∼15.6°. A dual-layer of Cu9Ga4 and CuGa2 forms at the HEA/Cu interface, consistent with thermodynamic predictions, featuring lower activation energy and growth driven by bulk alloy diffusion. Base on the interface microstructures, Cu9Ga4 and CuGa2 act as diffusion barriers, restricting the movement of other elements while promoting the accumulation of Zn at the interface. The wetting mechanism may be determined by the oxide (Cu2O) removal reaction (i.e., reaction between Ga and Cu2O).

Evolution of the interfacial microstructure in 316L/AlxCoCrFeNi composite material induced by high-velocity impact welding

AlxCoCrFeNi high entropy alloy with various Al contents has been successfully joined to 316L steel. The effect of mechanical properties of AlxCoCrFeNi induced by Al content on the interfacial microstructure in the 316L/ AlxCoCrFeNi has been investigated. All the 316L/AlxCoCrFeNi composite plates showed the typical interfacial microstructure of the high-velocity impact welding—periodic wavy interface. Four areas of the straight smooth area, the small wave area, the wave area, and the large wave area were along the radial direction in the interface orderly. The differences in wavelength, amplitude, ratios of the length in each area to the overall length, and the evolution of interfacial microstructure were discussed. The analysis of grain orientation, grain boundary, recrystallization, and orientation difference in the wave area showed that interfacial differences were caused by the difference in deformation mechanism of AlxCoCrFeNi matrix with different Al content. The deformation mechanism was closely related to the elongation and hardness in the macroscopic mechanical properties, which represented the ability to deformation and resist deformation, respectively. Consequently, the effect of Al content on the evolution of interface morphology was essentially the effect of hardness and elongation of AlxCoCrFeNi matrix. Additionally, all the wavy interfaces of 316L/AlxCoCrFeNi had good bonding strength in the wave area.

Interfacial characteristics, interfacial oxide evolution and bonding mechanism of 2219 aluminum alloy joints manufactured by hot-compression bonding

The bonding joints of 2219 aluminum alloy with different deformations of 30%, 45% and 55% were fabricated using hot-compression bonding, and subsequent subjected to homogenization treatment. The interfacial microstructure and interfacial oxide evolution of the bonding joints were systematically investigated. The results showed that increasing deformation can effectively reduce the formation of interfacial voids and promote the interfacial grain boundary migration (IGBM). As the deformation increased from 30% to 55%, the flat bonding interface transformed into curved grain boundaries, and ultimately being occupied by dynamically recrystallized (DRXed) grains. The development of IGBM and interfacial DRXed grains is crucial for ensuring high-quality bonding joints. At 55% deformation, the interface bonding strength reached 156.2 MPa, corresponding to 98.1% of the matrix bonding strength. In addition, the residual interfacial oxide film Al2O3 reacted with MgO and transformed into MgAl2O4 spinel. The final evolution products at the bonding interface were the mixture of MgO, Al2Cu, Al2O3, and MgAl2O4. The bonding interface at 55% deformation successfully achieved relatively clean atomic bonding after homogenization. Based on interfacial void closure, interfacial oxide film fragmentation and evolution, and interfacial recrystallization, the bonding mechanism of 2219 aluminum alloy joints was proposed. These findings contribute to our understanding of the interfacial bonding process in metal solid bonding.

Interfacial bonding and microstructural evolution in Inconel-copper bimetallic structures fabricated by directed energy deposition-arc

Directed Energy Deposition-Arc (DED-Arc) was utilized to fabricate Inconel-copper bimetallic structures, with the aim of improving manufacturing modes and reducing costs for rocket engine thrust chambers. In this paper, bimetallic Inconel superalloy (GH4169) and copper alloy (C18150) structures were deposited using different deposition strategies. The formation mechanisms of grain-size gradients and heterogeneous interfacial microstructural evolution were comprehensive investigated and further discussed. Both strategies produced high-quality bimetallic samples with tensile strength exceeding 260.2 MPa. Fractures occurred within the C18150 metal rather than at the interface, indicating successful interface strengthening of the bimetallic samples. Gradual gradients in grain size distribution and nano-hardness were observed across the interface. The crystal structures of C18150 were unaffected by GH4169, and no new phases were generated in the interfacial region. The crystallographic orientation relationship between Ni and Cu was determined to be [011]Cu//[011]Ni and (111)Cu//(111)Ni, and interfaces were strengthened by grain boundary and dislocation strengthening through. This work demonstrates an approach for fabricating large, high-performance bimetallic structures with tailored grain-size gradients and heterogeneous microstructures, suitable for rocket engine thrust chamber applications.

Evolution of interfacial microstructure and oxides of CLAM steel by hot compression bonding

The development of the joining process is essential for the application of China low activation martensitic (CLAM) steel as the structural material for fusion reactors. In the present study, the hot compression bonding (HCB) for CLAM steel was carried out under different parameters. The effects of different strain rates, temperatures, strains and holding time on the evolution of interfacial microstructure and oxides were investigated. Compressed at 1000 °C with 5% deformation, some micron-size continuous oxides distributed along the flat interface. The interfacial oxides were broken and decomposed as the deformation increased to 20%, their average size was reduced to 400 nm. With the bonding temperature increasing, more interfacial grain boundaries (IGBs) could cross the original bonding interface and flat interface became wavy. Compressed at 1000 °C/20%, the interfacial oxides consisted of fcc-structured spinel MnCr2O4 and enriched in Si and Ta oxides. The MnCr2O4 oxides would decompose preferentially after 0.5 h holding treatment at 1100 °C. Only a small number of oxides rich in Si and Ta elements remained at the original bonding area after 2 h holding treatment. Compressed at 1100 °C/20%, the bonding interface was completely replaced by the migrated grains after 2 h holding treatment and no large-size oxides could be observed. Moreover, the tensile strength and elongation at room temperature of the joint were comparable to those of the base material.

Interfacial microstructure evolution and mechanical properties of FGH98 superalloy TLP joints with BNi-2 interlayer

FGH98 nickel-based powder metallurgy superalloy was successfully bonded via transient liquid phase (TLP) bonding technique with a BNi-2 interlayer. The typical joint consisted of three characteristic zones including: ASZ composed of multiple silicon borides, ISZ with uniform γ solid solution and dispersed small γ′ phases and DAZ containing multiple kinds of borides which exist within and at grain boundaries. With the increase of bonding temperature and holding time, ASZ was gradually replaced by the ISZ, and eutectic structure disappeared. But excessive temperature or time will cause grain coarsening, deteriorating the joint performance. Under the bonding parameters of 1130 °C −60 min, the joint with optimal shear strength was obtained, which is 882 MPa (94% of the base metal strength). The fracture occurs in the DAZ, which is a mixed fracture.

Microstructure evolution and formation mechanism of interfaces in parallel gap resistance welding of stranded Ag-plated Cu conductor to Ag interconnector

In space flexible solar arrays, stranded Ag-plated Cu conductors and Ag interconnectors are preferred materials for energy transmission. Parallel gap resistance welding is a solderless micro-joining process that favors the reliability of joints between stranded Ag-plated Cu conductors and Ag interconnectors. It was found the interfacial microstructure presented diversity and complexity while mechanical and electrical properties showed unusual nonlinear variations with welding voltage. This study aims to clarify the interfacial microstructure evolution and its effects on the joint properties while elucidating the microstructure formation mechanisms. A shift in the bonding mechanism at interfaces from solid-state diffusion to brazing was found as welding voltage reached a critical value (1.5 V). It eliminated micro gaps and built nano-scale interlocking structures, resulting in substantial improvement in mechanical properties. Increasing the welding voltage from 1.2 V to 1.4 V improved electrical conductivity due to the enlarged bonding area at interfaces. However, high welding voltage (1.6 V) led to degradation in the electrical conductivity of joints due to excessive Ag-Cu solid solution formed at interfaces. The key to fabricating high-strength and high-conductivity joints lies in achieving appropriate interfacial melting while reducing alloying by controlling peak temperature and shortening the duration above the Ag-Cu eutectic point.

Interfacial microstructure evolution and mechanical properties in laser welded Invar alloy/TC4 dissimilar joints

The present study examined the evolution of interfacial microstructure and its effect on the mechanical properties of Invar/TC4 dissimilar joints by laser welding. The results indicated that various intermetallic compounds (IMCs) were formed in the interface layer of the TC4 side, such as Ti2Cu, TiCu and TiNi phases, while the columnar dendrites grown epitaxially perpendicular to the fusion line were observed on the weld seam (WS). Moreover, the boundary between dendrites growing in different directions within the WS was attribute to the high thermal conductivity of the filler metal and the non-equilibrium rapid cooling facilitated by the composition gradient. Besides, excessive heat input intensified the migration of elements and phase transition behavior, leading to the formation of brittle Ti-Fe phases in the interface layer, which significantly weakened the mechanical properties of the dissimilar joints and resulted in brittle fracture characteristics. The strength of the joint exhibits a parabolic distribution with heat input. When the heat input was below 600 J/cm, the joint fractured in the interface layer of the TC4 side, with a maximum tensile strength of 298.4 MPa at 600 J/cm. However, when the heat input exceeded 600 J/cm, the formation of brittle Ti-Fe IMCs contributed to a decrease in joint strength. The investigation provides an efficient and stable method for achieving high-strength Invar/TC4 dissimilar alloy welding.

Study on the interfacial microstructure evolution of aluminum and CFRTP on FSLW joints: influence of pin length

Polymer/metal hybrid lightweight structures are increasingly employed in automotive, aerospace and electronics industries. Friction stir welding (FSW) is applied for the effective welding of metals and thermoplastic materials. For the welding of dissimilar materials, due to the significant property differences, it is hard to achieve high strength welded joints with smooth appearance. In this article, the influence of pin length is studied by experiments for the friction stir lap welding (FSLW) of Al alloy and carbon-fiber-reinforced thermoplastic (CFRTP). Tensile tests, OM, SEM and EBSD are carried out to evaluate the welding performance. Results indicate that the joint with smooth surface topography is obtained at the pin length of 2.5 mm with a peak temperature of 250.3 °C and the CFRTP matrix PEI thermal decomposition temperature residence time of 47.6 s. From OM and SEM micro analysis, the width of the bonding area is 3.02 mm and a thin uniform interaction layer is formed in the joint. EBSD confirms that the Al alloy in the stirring zone is refined after recrystallization. It is difficult to form a stacked layered structure in the bottom of joint, so the property of the joint is improved. The tensile strength is 32.9 MPa, which is 63.1% of CFRTP.

Interfacial microstructure evolution and mechanical properties of TIG welding joints of AISI 304/Q235B rolled composite plates

This study presents a comprehensive characterization of the microstructure evolution and distribution of interfacial bonding properties in the original rolled plates and a welded AISI 304/Q235B clad plates. The findings reveal that an uneven diffusion layer, rich in chromium (Cr) and nickel alloy elements, is formed at the interface of the heat-affected zone during the welding process. The thickness of the diffusion layer reaches 10 μm in the overheated region. This nonuniformity results from the dilution of alloying elements from stainless steel into carbon steel. The presence of the diffusion layer contributes to the highest microhardness value at the weld metal interface. Tensile-shear experiments indicate a 22% increase in the tensile-shear strength of the overheated zone interface compared to the base metal interface, accompanied by a 30% decrease in elongation. While the diffusion layer enhances the interface shear strength, it reduces the interface plasticity, thereby increasing the risk of fracture. Fracture analysis of the overheated zone interface reveals brittle fracture characteristics, with a small amount of Cr present. In contrast, the interface of original rolled plates displays characteristics of ductile fracture, which emphasizes the intricate interaction between brittle and ductile fracture behaviors at the interface. These observations stem from the nonuniform diffusion layer, distinct microstructure distribution, and varying rates of crack propagation.

The welding kinetics of interface evolution and mechanism in IN718 alloy solid-state welding

The welding kinetics of interface evolution and mechanism inIN718 alloy solid-state welding are investigated systematically by comparing the hot compression behavior of the separated samples and conventional samples in the temperature range of 1000 °C–1160 °C and strain rate range of 0.1/s to 5/s. The separated samples obtain higher peak stress than conventional samples, and the kinetics analysis results show that separated samples provide higher structural factors and deformation activation energy. The activation energy of the interfacial microstructure evolution of the IN718 alloy was calculated to be 29.7948 kJ/mol. The evolution mechanism of the interface microstructure is characterized by the elimination of the interface second phase and the migration of straight interfacial grain boundaries (IGBs), which is inseparable from the occurrence of interfacial dynamic recrystallization. Interfacial dynamical recrystallization helps to regulate the chemical potential around the second phase for a continuous dissociation. The migration mechanism of the IGBs is influenced by the strain rates, which is continuous dynamic recrystallization (CDRX) for high strain rates and discontinuous dynamic recrystallization (DDRX) for low strain rates.

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.