Diffusion-bonded Interface Research Articles

Thermal conduction and strength of diamond-copper composite sandwich obtained by SPS diffusion bonding with Ti interlayer

Complex diamond/Cu composites prepared using diffusion bonding by spark plasma sintering (SPS) can realize the full potential of such composites. However, a high thermal conductivity (TC) cannot be achieved due to the diffusion-bonded interface's low bond strength and acoustic mismatch. An intermetallic compound Cu2Ti and a carbide TiC were generated on the diffusion-bonded interface after adding a titanium (Ti) interlayer. The intermetallic compound Cu2Ti and carbide TiC change the mechanical bonding into chemical bonding between diamond and Cu, significantly improving the interfacial bond strength as the diffusion-bonded interface's shear strength increased from 44.94 to 61.23 MPa. And the shear fracture changes from brittle to ductile approximately to that of the Cu matrix. In the meantime, the phonon-regulating effect of the carbide TiC enables interfacial TC in the diamond/TiC/Cu structure to be stronger than that in the diamond/Cu structure. The Ti interlayer can improve the bond strength of the SPS diffusion-bonded interface and acoustic matching of diamond/Cu composites as the TC increased from 347.73 W/(m·K) to 483.37 W/(m·K), which is 86.47% of the base metal.

Microstructural evolution and mechanical response of 304 stainless steel joint diffusion-bonded with micro-deformation

This study explicates the microstructural evolution and mechanical response of the joints of 304 stainless steel developed through micro-deformation diffusion bonding. The diffusion-bonded interface comprised the refined grains embedded with the intergranular M23C6 carbides and complex oxides, which was induced by dynamic recrystallization at 950 °C. The refined grains persisted at the bonding temperature of 950 °C due to the dynamic equilibrium of dislocations and pinning effect of intergranular particles. As the bonding temperature was raised to 1000 °C, the combination-grow up of grains was initiated caused by sufficient thermal activation and complete dissolution of M23C6 carbides. The interface was entirely migrated at 1050 and 1100 °C, and notably, the migration of interfacial grain boundaries played a greater role in diffusion bonding with an increase of bonding temperature. The interface with refined grains permitted a high joint strength (or impact load), while was incompetent to enhancing plasticity and particularly impact toughness. The migrated interface, in contrast, was provided with exceptional plasticity and impact toughness, attributed to its enhanced resistance to crack propagation. The joint prepared at 1050 °C for 60 min exhibited the optimum combination of ultimate tensile strength, fracture elongation, and impact toughness, and the ductile fracture was observed passing through the substrate instead of along the interface. In addition, the comprehensive performance of joints was degraded when the grains were excessively coarsened at 1100 °C for 60 min.

On the study of tailorable interface structure in a diamond/Al12Si composite processed by selective laser melting

Aluminum-diamond composites were produced using selective laser melting (SLM) from mechanically mixed diamond and Al12Si powders for use in thermal management applications. The feasibility of SLM for both interface tailoring and simultaneously densification, which are the key for determining the overall thermal conductivity (TC) of the composites, has been investigated. The results indicate that the interface structure of the as-built composites can be controlled, despite the complex physical and chemical nature of SLM. A ‘clean’ diffusion-bonded interface revealed at the micron scale, which is desirable for enhancing TC, was obtained at a laser energy density of 95.2 J/mm3. This demonstrates a possible new potential of SLM in creating metal matrix composites for functional applications. However, despite manipulation of the processing parameters, it was not possible to achieve a relative density above 90%. Thus, how to realize near full density, while maintaining such a ‘clean’ interface during SLM remains a key technical problem for the future. The complex metallurgical mechanisms responsible for interface evolution and microstructure formation are discussed in detail with the aid of finite element analysis, and further densification strategies are proposed.

Fabrication and Tailoring Interface Structure of Diamond/Al(and Al12Si) Composites for Heat Sink Applications by Vacuum Hot Pressing and Selective Laser Melting

Al and Al12Si matrix composites reinforced with synthetic diamond particles have been developed by using conventional powder metallurgy and emerging additive manufacturing techniques, i.e. vacuum hot pressing (VHP) and selective laser melting (SLM), respectively. Relative density and interface structure have been evaluated to relate to measured thermal conductivity (TC) of the composite. Despite very different physical and metallurgical mechanisms (VHP vs. SLM), the diamond/Al interface can be tailored allowing to form a ‘clean’ and tightly-adhered interface at the micrometer scale in both cases. This so-called diffusion-bonded interface is the most favorable for enhancing overall TC which demonstrates the potential of SLM for processing multifunctional Al matrix composites. However, how to realize full densification and simultaneously maintain such an interface structure during SLM remains a key technical problem to figure out.

Tailoring interfacial bonding states of highly thermal performance diamond/Al composites: Spark plasma sintering vs. vacuum hot pressing

Interfacial configurations of the diamond/Al composites fabricated by vacuum hot pressing (VHP) and spark plasma sintering (SPS) have been investigated to evaluate feasibility of both techniques for tailoring interfacial bonding states, namely non-bonded, diffusion-bonded, partially and fully reaction-bonded interfaces. Multiscale interfacial characterization reveals that the unique diffusion-bonded interface at the micrometer scale, being very favorable for enhancing global thermal conductivity (TC), has been achieved by conventional VHP technique due to its large processing window and homogenous thermal field. Comparatively, micrometer-scale and, even macroscopic (radial and axial) thermal gradients can be inevitably generated during the SPS process in rapid heating-cooling mode. As a result, the mixed interfacial bonding states have always been introduced in the SPSed samples which reduce the effectiveness of TC enhancement. The formation mechanisms of nanoscale interfacial Al2O3 and Al4C3 at the diamond/Al interface are also discussed.

Diffusion Bonding of Ti-6Al-4V Sheet with Ti-6Al-4V Foam for Biomedical Implant Applications

Advanced metallic bone implants are designed to have a porous surface to improve osseointegration and reduce risks of loosening. An alternative approach to existing surface treatments to create a porous surface is to bond separately produced metallic foams onto the implant. To assess the feasibility of this approach, a Ti-6Al-4V foam was diffusion bonded onto bulk Ti-6Al-4V in an argon atmosphere at temperatures between 1173 K and 1223 K (900 °C and 950 °C) for times between 45 and 75 minutes. These specimens were tested in tension to determine bond quality: failures occurred in the foam, indicating a strong diffusion-bonded interface. The quality of the bond was confirmed by metallographic studies, indicating that this approach, which can also be applied to creating of sandwich with porous cores, is successful.

In situ synthesis and bonding of Ti TiAl TiC/Ni functionally graded materials by field-activated pressure-assisted synthesis process

Employing reactive synthesis and consolidation and using elemental powders as reactants, TiC/Ni cermets were formed and bonded to Ti substrates in one step by a field-activated method. Microstructural observations and EDS analyses revealed well-formed, crack-free bonds between the layers. Bonding between the TiC/Ni cermet and the Ti substrate was facilitated by the formation of TiAl as an intermediate layer, which also formed from the elements during the on-step process. Shear strength and thermal shock evaluations were made on the resulting samples. The diffusion-bonded interface has a shear resistance of as high as 70.98 MPa and has a good thermal shock resistance. Crack propagation observations indicate high interface strength. The interface between Ti and TiAl has a higher bonding strength than that between the TiC/Ni cermet and TiAl.

Study of microstructure and XRD diffraction near interface of diffusion bond between Mg/Al dissimilar materials

The microstructure and phase constitution near the interface of diffusion bonding in Mg/Al dissimilar materials were researched by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The test results indicated that an obvious diffusion zone was formed near the Mg/Al interface during the vacuum diffusion bonding. The diffusion transition zone near the interface consists of MgAl, Mg3Al2 and Mg2Al3 phases. The transition region on the Mg side mainly consists of Mg crystals, and the new phase formed was Mg3Al2 with a face-centered cubic lattice. This is favorable for improving the combination strength of the Mg substrate and the diffusion transition zone.

錫の固相拡散接合界面の酸化皮膜に対するハロゲン化処理の効果

錫の固相拡散接合界面の酸化皮膜に対するハロゲン化処理の効果

Behavior of Superficial Oxide Film at Solid-State Diffusion-Bonded Interface of Tin

The microstructure of the solid-state diffusion-bonded interface of tin has been investigated by TEM observations in order to reveal the evolution of the superficial oxide film of tin with the progress in bonding. The diffusion bonding was carried out in a vacuum chamber at bonding temperatures T j of 373-493 K and at bonding pressures Pj of 90-170 MPa (bonding time = 1.8 ks). The tensile strength of the joint was increased with bonding temperature and pressure: joints having tensile strength comparable with the base metal were obtained at T j = 493 K at P j = 130 MPa and at T j = 443 K at P j = 130 MPa. When the joint strength was much lower than the base-metal strength, an interfacial region ∼500 nm in width was observed where a number of very fine inclusions that could be regarded as tin oxide were distributed. As the joint strength increased with bonding temperature, these inclusions were coarsened, and their number density was decreased. The increase in the bonding pressure enhanced these changes in the inclusion. The rise in the joint strength with bonding temperature corresponded well with the observed change in the size and density of the inclusion.

XRD and TEM analysis on the Fe 3Al/18-8 stainless steel diffusion bonded interface

Fe 3Al intermetallic and 18-8 stainless steel were diffusion-bonded at 1040 °C for 60 min. The reacted phase in the Fe 3Al/18-8 diffusion-bonded interface was determined via X-ray diffractometry (XRD) and the lattice orientation relation between constituent phases was analyzed by transmission electron microscope (TEM). The results indicated that there were Fe 3Al, Ni 3 Al, FeAl, α-Fe (Al) solid solution and Fe 3C in the interface. In addition, the lattice orientation relation between α-Fe (Al) and Fe 3C was (002) α-Fe (Al)(130) Fe 3C . But there were no other brittle phases and micro-defects such as pore and crack, which can ensure the microstructure performance in the Fe 3Al/18-8 diffusion-bonded interface.

Electrical and thermal properties of the interface at diffusion-bonded and soldered 304 stainless steel and copper bimetal

The 304 stainless steel and copper were joined by diffusion bonding and soldering with different bonding conditions. The microstructure of the interfaces of diffusion-bonded bimetal was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrical resistivity of the interface of the diffusion-bonded samples (ERIDB) and electrical resistivity of the soldered interface (ERIS) were measured in the temperature range 260–370 K. By the increase of temperature, ERIDB and ERIS gave different results subject to electrical current direction. It was also seen that, ERIDB started to increase at lower temperatures than ERIS. In addition to the change of electrical resistivity by temperature, the relations between current and potential difference ( I– V) were assessed as function of temperature. According to these results, it was observed that the current obtained on the interfaces of diffusion-bonded sample is more sensitive to voltage than the current measured on the interface of soldered samples. Moreover, the current measured on the interface of diffusion-bonded sample was higher than the value obtained on the interface of soldered bimetal for each current direction. Thermal conductivities of the interface of diffusion-bonded (TCIDB) and thermal conductivities of the interface of soldered bimetals (TCIS) were detected and compared with each other. It has been detected that, TCIDB and TCIS changed according to a linear function by increasing temperature. TCIS did not change by a considerable amount with electrical current direction. However, the intermetallic phases propagated at diffusion-bonded interface changed thermal conductivity values by an excessive amount with the change in electrical current direction.

透過電子顕微鏡観察によるＡｌ合金の拡散接合機構の検討 ６ Ａｌ‐Ｘ２元系合金（Ｘ＝Ｍｇ，Ｓｉ，Ｍｎ，Ｚｎ，Ｃｕ）の接合界面の形成相と接合強さ

The oxides at the diffusion-bonded interfaces of a pure aluminum and Al binary alloys (Al-Mg (0.6-2%), Al-Si (1%), Al-Mn (0.5%), Al-Zn (1%), Al-Cu (1%)) have been investigated by transmission electron microscopy in order to examine the effect of their morphologies on the bond strength of the joint interfaces. As the bonding temperature and Mg content were increased, the strength of the joint interfaces of the Al-Mg alloys increased to levels not less than that of the base metals, and the interfacial oxide altered from continuous amorphous films to dispersed crystalline particles of Al2MgO4, and MgO. For the pure aluminum and the alloys, other than those of the Al-Mg system, the strength of the joint interfaces was much lower than that of the base metals at all bonding temperatures employed, and the interfacial oxide remained as amorphous films. These results suggest that the amorphous oxide film prevents an increase in the strength of the diffusion-bonded interface of the Al alloy and that strengths comparable to those of the base metal can be obtained, when almost all amorphous films alter to crystalline particles. When the foils of the Al-Mg alloys were applied as an intermediate layer, the bond strength of the joints of the pure aluminum and the alloys, other than the Al-Mg alloys, was improved significantly, and the oxides at the bond interface became crystalline particles in the same way as those observed in the joints of the Al-Mg alloys. Considering that the morphological change of the interfacial oxide described above can be explained as a consequence of the reductive reaction with Mg, as reported in a previous paper, it can be concluded that the addition of an element having strong affinity to oxygen, like Mg, into the intermediate layer as well as the base metal can improve the bond strength of the joint interface by changing the morphology of the interfacial oxide from amorphous film to crystalline particle.

HREM of carbon/metal and ceramic/metal interfaces in composite materials

As examples of interfaces between crystals of different type of bonding, interfaces of carbon fibre reinforced metal matrix composite and ceramic/metal diffusion-bonded interface are examined. It is our fundamental interest to understand the nature of hetero-bonding. Various problems originate from the difference of the nature of bonding. A difference in the thermal expansion coefficient alone produces internal stress accumulation that can lead to the fracture of the interface during cooling of the specimen. Stress relief by plastic deformation of metal would operate if no reaction layer is present at the interface. Otherwise, the fracture of the brittle component would result after the fracture of the reaction product itself or the interface between the brittle non-metal components. High resolution electron microscopy of the interface structures should give information useful for the assessment of the mechanism.The first part is the observation of interface between carbon fibre and aluminium. Figure 1 shows the cross sectional view.

Modern practice in the construction and maintenance of rail joints and bonds in electric railways

The 304 stainless steel and copper were joined by diffusion bonding and soldering with different bonding conditions. The microstructure of the interfaces of diffusion-bonded bimetal was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrical resistivity of the interface of the diffusion-bonded samples (ERIDB) and electrical resistivity of the soldered interface (ERIS) were measured in the temperature range 260–370 K. By the increase of temperature, ERIDB and ERIS gave different results subject to electrical current direction. It was also seen that, ERIDB started to increase at lower temperatures than ERIS. In addition to the change of electrical resistivity by temperature, the relations between current and potential difference (I–V) were assessed as function of temperature. According to these results, it was observed that the current obtained on the interfaces of diffusion-bonded sample is more sensitive to voltage than the current measured on the interface of soldered samples. Moreover, the current measured on the interface of diffusion-bonded sample was higher than the value obtained on the interface of soldered bimetal for each current direction.Thermal conductivities of the interface of diffusion-bonded (TCIDB) and thermal conductivities of the interface of soldered bimetals (TCIS) were detected and compared with each other. It has been detected that, TCIDB and TCIS changed according to a linear function by increasing temperature. TCIS did not change by a considerable amount with electrical current direction. However, the intermetallic phases propagated at diffusion-bonded interface changed thermal conductivity values by an excessive amount with the change in electrical current direction.