Interfacial Microstructure Evolution Research Articles

SnAgCu Solder Joint Microstructure Evolution During Thermal Aging: Influence of Flux

An intermetallic layer (IML) between the solder alloy and the soldered surface affects the mechanical and electrical performance of the resulting joints. Numerous studies have explored the possibilities of influencing the IML to achieve more reliable interconnections. However, the type and composition of the used flux, crucial for the proper creation of solder joints, is rarely included as a possible influencing factor. In this article, a comprehensive study on the interfacial microstructure evolution of lead‐free SnAgCu solder joints, accounting for the flux type and the temperature of the preheating phase of reflow soldering, where the flux contained in the solder paste becomes active, is presented. In the results, it is shown that the IML of as‐reflowed and thermally aged solder joints depends significantly on the flux. The IML activation energy is 57% higher for rosin‐based low‐activity (ROL)0 flux compared to ROL1 flux. The ROL0 flux, containing fewer active components, also outperforms the ROL1 flux in both the mechanical and electrical properties of the joints. Furthermore, the temperature profiles also show slight differences in measured properties, with the fluxes responding differently to changes in preheating temperature. In the presented results, importance of the used flux on solder joint microstructure is demonstrated.

Interfacial Microstructure Evolution and Mechanical Properties of TC4/MgAl2O4 Joints Brazed with Ti–Zr–Cu–Ni Filler Metal

Interfacial Microstructure Evolution and Mechanical Properties of TC4/MgAl2O4 Joints Brazed with Ti–Zr–Cu–Ni Filler Metal

Repair of ordinary concrete using basalt fiber reinforced geopolymer: High temperature resistance and micro structure evolution of adhesive interface

Good bonding properties in the interfacial transition zone (ITZ) between the substrate and the repair material are critical to the success of the repair, and a good repair material can act as a protective layer to reduce the impact of fire on the structure. In this paper, Ordinary concrete (OP), geopolymer mortar (GP), and basalt fiber reinforced geopolymer mortar (GPb) were poured as the three repair materials on the roughened surface of the old substrate. The bonded specimens were exposed to temperatures of 23 °C, 200 °C, 400 °C, 600 °C and 800 °C for 1 h. The interfacial bond strength of the bonded specimens was tested by slant shear test, and the physical phase change of the repair material and the microstructure of the ITZ were analyzed by microscopic test. The results showed that the mechanical properties and high temperature resistance of ITZ were best when the old substrate interfaces were grinded and grooved and GPb was used as the repair material. Compared with S-OP, the bond strength of S-GPb was 26.92 %, 27.43 %, 46.50 %, 44.26 %, and 97.02 % higher at different temperatures. The increase in interfacial bond strength can be attributed to three mechanisms: (1) Mechanical interlocking with the old substrate with a rough surface. (2) The increase in temperature accelerates the volcanic ash reaction, and the formation of hydration products further fills the voids at the ITZ, maintaining the strength and compactness of the ITZ. (3) The addition of basalt fibers can form an anchoring effect at the interface, reducing the risk of interfacial spalling and cracking caused by material shrinkage in the ITZ.

Understanding the effect of holding time on interfacial microstructure evolution and mechanical properties of Ti3AlC2/Zr-4 brazed joints

In this work, the brazing of Zircaloy-4 (Zr-4) to Ti3AlC2 ceramic was investigated using a Ti-13Zr-21Cu-9Ni (wt.%) amorphous alloy at 930 °C with a holding time of 5 to 60 min. The typical multilayer structure of the joint was carefully characterized as Ti3AlC2/ZrC/Zr[Ti]ss+ [Zr(Ti)]2[Cu(Ni)]/Zr[Ti]ss/Zr-4. Ti3AlC2 was decomposed into TiCx due to the de-intercalation of Al, and Zr-4 dissolved into the molten amorphous TiZrCuNi fillers to form a Zr-based alloy which reacted with TiCx to form a ZrC particle layer on the Ti3AlC2 side. The microstructures and mechanical properties of the brazed joint were significantly influenced by dwell time, and the underlying evolution mechanisms were addressed based on the considerations of mutual dissolution, diffusion, and reaction among Ti3AlC2, Zr-4, and molten amorphous alloys. With the extension of holding time, the amount of [Zr(Ti)]2[Cu(Ni)] in the brazed joints decreased gradually, while the ZrC layer thickened with (Ti, Zr)ss formed around the ZrC particles. The maximum shear strength of the joint, with an average strength of 187 ± 34 MPa, was achieved by brazing at 930 °C for 5 min. A detailed fracture analysis was conducted to determine the failure mechanism. This work provides a reference for brazing other MAX phase materials and alloys.

A novel fatigue life model for MCrAlY coated superalloys considering interfacial microstructure evolution

MCrAlY coatings, extensively utilized for safeguarding turbine blades against oxidation and erosion, encounter impediments due to inter-diffusion between the coating and substrate, thereby exacerbating fatigue life degradation at elevated temperatures. In this study, we introduce a novel approach involving the modification of critical depth in interfacial strain energy density to elucidate the impact of interfacial microstructure evolution on mechanical properties. Building upon this concept, we propose a fatigue life prediction model, which incorporates the dynamic evolution of interfacial structure and mechanical characteristics. Validation against empirical data underscores the commendable precision of the model. Our inquiry not only advances the comprehension of mechanical-chemical coupled behaviors but also yields significant insights for the optimization and maintenance of turbine blades.

Interfacial microstructure evolution and mechanical response of TC19/Ti150 dissimilar joints obtained by diffusion bonding

The structure made by dissimilar titanium alloys can meet the differentiated requirements of performance for different parts, fully exerting their performance advantages during operation respectively, which holds significant technological and economic value. Here, we used diffusion bonding (DB) method to connect TC19 and Ti150 dissimilar titanium alloys in the temperature range of 810 °C–900 °C, and investigated the morphology, forming mechanism, deformation behavior and mechanical properties of the joints. The study showed that the interfacial voids disappeared with the increase of temperature, and the interfacial characteristics gradually evolved from the initial straight shape to a curved shape. The original bond line transformed into βTC19/αTi150 phase boundaries (PBs) and high-angle grain boundaries (HAGBs) formed by αTC19 and αTi150. No harmful intermetallic compounds were formed on the interface. The joint formation can be considered as a combination of three behaviors: plastic deformation, elemental diffusion and interfacial grain boundary migration (IGBM). In addition, it was observed that dislocation slip was the main deformation behavior of the joints. The dislocations generated in the both matrices were obviously accumulated at the interface during tensile deformation of the specimen, and the bonding interface hindered the dislocation transfer between two substrates. The room temperature uniaxial tensile results exhibited that the joints bonded at 810 °C and 840 °C were broken at the interface, showing poor mechanical properties caused by holes and straight interface. And yet the joints bonded at 870 °C and 900 °C occurred fracture on the Ti150 matrix. The strength of joints was comparable to that of the Ti150 matrix, indicating that the two dissimilar titanium alloys achieved a reliable bonding. This work provides valuable inspiration for the diffusion bonding process of titanium alloys with different microstructures.

Microstructure evolution and mechanical performance of roll-bonding interface in HAZ during arc welding of titanium/steel clad plates

Microstructure evolution and mechanical performance of roll-bonding interface in HAZ during arc welding of titanium/steel clad plates

Crystal plasticity-phase–field based analyses of interfacial microstructural evolution during dynamic recrystallization in a dual phase titanium alloy

In this study, an integrated crystal plasticity finite element–phase–field (CPFE–PF) model is developed to examine dynamic recrystallization (DRX) in a dual phase Ti alloy. The CP framework is coupled with PF by updating the free energy density with energy contributions due to plasticity. The evolution of grain boundaries through evolving non-conserved order parameters in the PF model is tracked using the Allen–Cahn equation. Nucleation is allowed to occur if the dislocation density exceeds a critical value. DRX is studied in various Ti morphologies such as an α−Ti single crystal containing a stiff elastoplastic particle, α-Ti bicrystals with low and high misorientation between grains, an α−β bicrystal and a globular α−β Ti structure with β phase at α−α interfaces. For an α−Ti bicrystal, a high misorientation facilitates the onset of DRX at the α−α interface at a significantly lower strain than the bicrystal with low misorientation. In an α−β bicrystal, DRX is only observed at the α−β interface. For the globular morphology, nucleation is observed at both α−β interfaces and inside α grains, which is consistent with previous experimental observations for a similar morphology. Nucleation inside α grains is explained by the correlation between SSD density and misorientation indicators such as KAM and GROD at the nucleus site. To correlate slip activity with nucleation propensity immediately prior to different nucleation events, the dislocation density, shear rate and Schmid factors on different slip systems are evaluated at nucleation sites.

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

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.

Dissimilar low-temperature diffusion bonding of copper and titanium using a Zn interlayer: Interfacial microstructure and mechanical properties

In this study, a zinc (Zn) interlayer was applied in the diffusion bonding of pure copper (Cu) and titanium (Ti). The interfacial microstructure evolution and metallurgical reaction mechanisms of Cu/Ti joints with Zn interlayer were investigated by SEM, EDS and TEM. The addition of the Zn interlayer facilitated metallurgical bonding between Cu–Zn and Ti–Zn at low temperatures. The shear strength of joints exhibited a gradual increase followed by a sharp decline as the bonding temperature increased. An intimate bonding between Cu and Ti was achieved at 450 °C, and the highest average shear strength of 106.82 MPa was obtained at 490 °C. The weld seam is primarily composed of a β′-CuZn layer, which exhibited excellent plasticity and hindered the formation of brittle Cu–Ti intermetallic compounds. The τ1-Cu2TiZn layer, adjacent to β′-CuZn, demonstrated stronger resistance to crack propagation compared to the brittle TiZn3 and TiZn2 layers. Furthermore, the predominant β′-CuZn layer and τ1-Cu2TiZn layer formed a coherent interface, ensuring a reliable bonding. These results demonstrate that the addition of Zn interlayer is an effective strategy for preparing highly reliable Cu/Ti joints at low temperatures.

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

Effect of extrusion and introduction of Cu wire on the microstructure and mechanical properties of the Mg matrix

Composite extrusion of AZ31 Mg alloy and T2 Cu wire was carried out. The interface characteristics, microstructure evolution and mechanical behavior of as-homogenized, single Mg and Mg/Cu composites were analyzed in detail by various analytical methods. The experimental results show that the interface between Cu wire and Mg alloy matrix is better. With the introduction of extrusion and Cu wire, the grains of Mg matrix are continuously refined, the proportion of LAGBs is gradually reduced, and the texture strength is obviously weakened. The Mg matrix in Mg/Cu composites is more conducive to activating various non-basal slip systems than single Mg. Compared with the as-homogenized Mg alloy sample, the elongation (EL), tensile strength (TS) and yield strength (YS) were improved by extrusion and introduction of Cu wire.

Microstructure evolution of interface and matrix during the preparation of SiCf/Ti60 composites

In this paper, continuous SiC fiber-reinforced Ti60 (SiCf/Ti60) composites were fabricated by preparing SiCf/Ti60 precursor wires from matrix-coated fibers and hot isostatic pressing (HIP) consolidation. The microstructures of the precursor wires and composites were investigated using XRD, SEM, EPMA, EBSD, and TEM, which led to the microstructure evolution of the composites. The conclusions of this study are as follows. 1. A reaction layer (RL) with a thickness of approximately 0.1 μm already exists at the interface of the precursor wires during the preparation. The HIP process accelerates the diffusion of the carbon coating with the Ti60 matrix, resulting in an increase in the thickness of the RL to approximately 0.5 μm. This layer is primarily composed of fine-grained TiC layer || discontinuous silicides || coarse-grained TiC layer. 2. The matrix of SiCf/Ti60 precursor wires contains α-Ti (∼ 1.9 μm), S2 (∼ 50 nm), and β-Ti (∼ 50 nm), in the matrix, β-Ti is precipitated from α-Ti, and HIP makes α-Ti, S2, and β-Ti grow to ∼ 2.4 μm, ∼ 200 nm, and ∼ 300 nm, respectively. 3. There are 〈0001〉//axial direction (AD) and 〈10−10〉//AD fiber textures in the matrix of the precursor wires, and HIP makes the matrix undergo a plastic deformation dominated by dislocation slip, and the pole density of the two kinds of textures are both increased.

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.