Copper Interlayer Research Articles

Microstructure and Mechanical Properties of TA2/Q235 Laser Weld Joint with Copper Interlayer.

For the dissimilar metal welding needs of TA2 titanium and Q235 steel, preliminary trials were conducted using laser welding methods, and the results showed that the addition of a copper interlayer and the bias of the laser beam toward the Q235 side allowed for an effective connection. The welding temperature field was simulated using the finite element method, and the optimum offset distance of 0.3 mm was obtained. Under the optimized parameters, the joint had good metallurgical bonding. Further SEM analysis showed that the microstructure of the bonding area between the weld bead and Q235 was a typical fusion weld pattern, while that of the bonding area between the weld bead and TA2 was in brazing mode. The microhardness of the cross-section showed complex fluctuations; the microhardness of the weld bead center was higher than that of the base metal due to the formation of a mixture microstructure of copper and dendritic Fe phases. The copper layer not involved in the weld pool mixing had almost the lowest microhardness. The highest microhardness was found at the bonding site of TA2 and the weld bead, mainly due to the formation of an intermetallic layer with a thickness of about 100 μm. Further detailed analysis revealed that the compounds included Ti2Cu, TiCu and TiCu2, showing a typical peritectic morphology. The tensile strength of the joint was approximately 317.6 MPa, reaching 82.71% of that of the Q235 and 75.44% of the TA2 base metal, respectively. The fracture occurred in the unmixed copper layer.

Electron beam welding of 17-4PH steel and Ti6Al4V alloy with copper interlayer

Electron beam welding of 17-4PH steel and Ti6Al4V alloy with copper interlayer

Study of the brittleness mechanism of aluminum/steel laser welded joints with copper and vanadium interlayers

Intermetallic compounds (IMCs) generated by direct laser welding of aluminum and steel decrease the strength of the joint. To evaluate the effect of alloying elements on the weldability of aluminum/steel dissimilar materials, the copper (Cu) and vanadium (V) were introduced into the interlayer to inhibit the generation of Fe-Al IMCs. Comparing with direct welding, Cu promotes the generation of Al2Cu and V transforms the disordered Fe/Al interface into a continuous Al/V interface to promote the generation of Al3V and Al21V2. In addition, the first-principles calculations were carried out to study the elastic properties and electronic properties of intermetallic compounds. The results show that high brittleness of FeAl, Fe2Al5 and FeAl3 results from strong covalent bonding and antibonding. The Fe(d) orbit hybridizes with Al(s) and Al(p) orbits while resonant peaks and wide pseudogap appear in the density of states. The low brittleness of Al2Cu results from the less count of covalent bonds with 76.2% of weaker antibonding; the low brittleness of Al21V2 results from the lower covalent bond strength with a maximum overlap bond population of 0.265. With the addition of Cu, the strength of the joint was increased to 63 MPa from 31 MPa. Furthermore, the addition of V completely prevents the formation of Fe-Al IMCs, which results in the highest joint strength (93 MPa). The results of the first-principles calculations and experiments are in good agreement.

Enhancement of supercapacitor activity of MoS2 electrocatalyst via incorporation of copper interlayer

In this work, we are reporting the synthesis of MoS 2 nanoparticles prepared using hydrothermal method at 180 °C. We have characterized the phase, morphology, composition, using X-ray diffraction, scanning electron microscopy techniques. We have fabricated two electrodes for electrochemical testing by loading MoS 2 nanoparticles onto (i) bare carbon paper, and (ii) Cu electrodeposited carbon paper. We found that copper interlayer addition increases the electronic conductivity which, in turns, increases the surface energy of the electrocatalyst, leading to an increase in cycle life. Further, the copper interlayer increases the number of active sites via increase of Mo 3+ at the catalyst surface.

The copper interlayer tunes the reactivity of cobalt oxide towards the oxygen evolution reaction

The activity of the cobalt-based material towards the oxygen evolution reaction can be enhanced via the metal interlayer. The metal interlayer, not only enhances the activity, it can also hamper the activity. The role of copper interlayer for activity changing depends on the fabrication method of the host material. In this study we have investigated the influence of Cu interlayering on the electrochemical properties of Co 3 O 4 nanoparticles. For this, we have initially synthesized the cobalt oxide nanoparticles employing the solution combustion method using cobalt nitrate and ascorbic acid as precursors. The ratio of cobalt nitrate and ascorbic acid plays a crucial role in determining the morphology and hence the electrochemical characteristics. Co 3 O 4 nanoparticles prepared with optimized amount of precursor (i.e., when ratio of cobalt nitrate and ascorbic acid is 1:1) showed the increased activity towards oxygen evolution reaction. While the samples prepared using lower/higher amounts of these precursors, showed the detriment in activity with copper interlayer. This effect is due to the presence of Co +3 at the surface. The polarization analysis showed that for optimized sample, the Co +3 content is highest while for high and low fuel content sample the Co +3 is low. The above analysis is further supported via the Tafel and electrochemical impedance analysis. The Tafel analysis showed the optimized sample showed the Tafel slope 100.26 mV/dec, while the high and low fuel content sample showed the 170.2 mV/dec and 219.72 mV/dec Tafel slope. Finally, the EIS analysis showed the lowest polarization resistance for optimized sample and high polarization resistance for high and low fuel content sample.

Effect of rotational speed and copper interlayer on the mechanical and fracture behaviour of friction stir spot welds of 5754 aluminium alloy

The application of joining processes requires advanced mechanical tests to control the joints’ quality. Generally, welded sheets are verified using tensile shear tests. However, few studies also recommend conducting tension peel and cross-tension tests. The present work evaluates the mechanical behaviour of 5754 aluminium sheets jointed by friction stir spot welding (FSSW). The influence of the rotational speed on joint strength was first compared to riveted assemblies. Then, sheets welded with pure copper interlayers were compared to the precedents. The results indicated that, without an interlayer, lower and intermediate rotational speeds lead to higher mechanical strength under tensile shear tests compared to riveted assembly. However, it performed worse under tension peel and cross-tension tests at all studied rotational speeds. By adding copper, the strength of welded sheets is globally improved under tensile shear tests. Nevertheless, under tension peel and cross-tension tests, it performed worse, although a slight improvement was observed for increasing rotational speeds. Two different failure morphologies and four fracture modes were observed regarding the different tested samples. Microhardness tests were also conducted, to relate the influence of the studied parameters on the joint’s strength.

Quality Diagnostics of Parts Produced by Combined Additive Manufacturing Technology

The work is focused on the combined process of obtaining bimetallic parts that involve laser-directed energy deposition (LDED) additive technology and the conventional casting process. In this research, molybdenum powder was deposited by LDED on a cast 25L steel substrate. The choice of materials is motivated by demands for replacing the traditional technique of brazing molybdenum with a copper interlayer on low-carbon steel to eliminate shortcomings. The influence of powder particle morphology on the quality of deposited layers was studied. Spherical molybdenum powder PMS-M99.9 facilitated stable deposition of good layers and was found to be suitable for the LDED. Quality diagnostics were performed by studying microstructure, hardness, and wear resistance properties. Preferential parameters of the LDED of molybdenum were found through parametrical analysis. Microstructural studies showed that LDED of PMS-M99.9 powder results in a homogeneous stable layer with a strong bond to the steel substrate, which was confirmed by mutual diffusion of Mo and Fe in the boundary. It is also demonstrated that the found working parameters of LDED assure high hardness, wear, and fretting wear resistance. The three studied coatings (LDED of powders PMS-M99.9 and PM-M; VM1 brazing) had the same friction coefficient value of ~0.25. Compared to others, PMS-M99.9 coating had the lowest volumetric wear, while abrasive wear was measured to be the highest.

Numerical Modelling of Thermo-Mechanical Effects Developed in Resistance Spot Welding of E304 Steel with Copper Interlayer

Resistance spot welding is a technique applied to join two or more similar or dissimilar metals, by applying pressure and electric current to the spot-weld area. Based on the electrical resistance property of metals, a great amount of heat is generated and used to carry out materials joints, by creating a molten metal nucleus between the components to be welded. The influence of an interlayer material, positioned between the parent materials, on the strength of similar or dissimilar welded joints was studied by researchers worldwide. In most cases, by optimising the process parameters, an increase in the welded joint strength was achieved. In this paper, the resistance spot welding of 1mm thick E304 stainless steel sheets, both with and without a copper foil interlayer, was investigated, by applying, in all cases, the same process parameters. The tensile test of the joints showed a decrease in the strength of joints performed with interlayer metal. A method to control the deterioration level of the joint’ mechanical properties is the Finite Element Analysis which allows to optimise the process parameters so that the negative effects of the process on the joint quality to be limited. It was found that an increase in amperage is needed to compensate for the addition of the interlayer metal and to obtain an adequate melting in the spot-weld area. This modification causes an increase of the molten core diameter that will lead to improvement of the welded joint strength, while no significant influence on the internal stress level was noticed in the processing and numerical analysis of the output data.

High frequency ultrasonic inspection of the bonded interface between a divertor monoblock and a cooling pipe

This study evaluated the applicability of a high-frequency ultrasonic test to the inspection of the bonded interfaces between a divertor monoblock and a cooling pipe. This study prepared a tungsten block bonded with 1 mm of oxygen-free copper and 1.5 mm-thick CuCrZr plates, which simplifies one of the fundamental designs of a divertor: a tungsten monoblock bonded with a cooling pipe with a copper interlayer. The samples were fabricated using a high-temperature vacuum furnace for diffusion bonding. A high-frequency ultrasonic immersion test using a 30 MHz probe was performed from the CuCrZr surface to simulate inspecting the interface from inside the pipe. Ultrasonic images obtained by the test were consistent with the actual bonding condition revealed by sectioning the samples; whether a flaw exists on the interface between CuCrZr and the oxygen-free copper or that between the oxygen-free copper and tungsten was clearly distinguished. The results of this study also suggested the possibility of detecting the growth of crystal grains caused by improper bonding such as too high bonding temperature.

Effect of the thickness of Cu interlayer on dissimilar laser welding of 304 stainless steel to tantalum

304 stainless steel (304SS) tube and tantalum (Ta) cylinder were successfully joined by laser welding with copper (Cu) interlayer. The influence of Cu interlayer thickness on the microstructure and mechanical properties of joints was clarified. The intermetallic compounds (IMCs) generated between the 304SS and Ta were determined as Fe2Ta and FeTa in the joint without Cu interlayer. The addition of Cu interlayer could effectively inhibit the atomic diffusion between the base metal and the generation of IMCs. In addition to other laser welding parameters, the thickness of the Cu interlayer also has an extremely important effect on the amount of IMC at the fusion zone (FZ)/Ta interface and the heat input on Ta side. As a result, the formation of Fe2Ta and FeTa was reduced and the weld consisted of Fe-based solid solution and Cu-rich phases. Joints produced with a 0.4 mm thick Cu interlayer exhibited the highest tensile strength of 288.7 MPa, which was 54.1% higher than that without Cu interlayer, due to the excellent metallurgical bond and few IMCs at the FZ/Ta interface. A large amount of IMCs was found at the FZ/Ta interface of the joint with a 0.2-mm Cu interlayer, which reduced the strength of the joint. A weak metallurgical bond was formed due to insufficient heat input, as the thickness of the Cu interlayer reached 0.6 mm. Thermodynamic calculations of the Fe-Ta-Cu ternary system explain the diffusion behavior of Cu atoms at the FZ/Ta interface and its effect on the formation of Fe-Ta reaction layer.

Diffusion Bonding of Al7075 to Ti-6Al-4V by Spark Plasma Sintering and Using a Copper Interlayer

Sheets of aluminum 7075 and titanium Ti-6Al-4V alloys were successfully joined using the spark plasma sintering (SPS) process. A copper foil was placed as an interlayer between the two surfaces. The bonding was made at 480 °C, 500 °C, and 520 °C with a holding time of 10 min and under a uniaxial pressure of 5 MPa and 10 MPa. The obtained bonds were analyzed by scanning electron microscopy, energy dispersive spectroscopy (SEM/EDS), and wavelength dispersive spectroscopy (WDS). It was found that copper diffused away through Al7075 and formed Al2Cu intermetallics but was not present at the joint region. The investigation of the fractured surfaces using X-ray diffraction (XRD) showed that the joint region contained TiAl3, TiAl2, and Ti3Al intermetallic compounds. The presence of the Cu foil was believed to hinder the formation of Al3Ti observed in previous studies by allowing more Ti to diffuse into the Al side.

Transient liquid phase (TLP) bonding of Ti–6Al–4V/AISI 304 stainless steel using Cu/CNT composite interlayer

This paper investigates the idea of using Cu/CNT composite interlayer in the transient liquid phase (TLP) bonding of Ti–6Al–4V/AISI 304 stainless steel. In this investigation, initially TLP was carried out using a pure copper interlayer at 900, 950 and 1000 °C with the holding time 60 min. The TLP joining was then carried out at 900 °C with Cu/CNT interlayer, with the CNT weight percent, ranging from 0 to 3%. CNT was deposited on Cu foils, using electrophoretic deposition technique. Microstructure and mechanical properties of the joints were investigated with optical/electron microscopes, microhardness, and shear tests. Results showed that the interface microstructure can be divided into athermal solidification zone, isothermal solidification zone, and diffusion affected zone. The phase structure and compositions in CNT-containing samples are relatively similar to TLP samples with pure Cu interlayer. Results showed that CNT addition has expanded the diffusion areas and facilitated the diffusion across the interface. CNT addition up to 3 wt. % resulted in a significant increase in hardness up 500 VHN. The increase in hardness in the joint area can be related to the presence of various intermetallic compounds at the TLP region. The correlations between mechanical properties and microstructure and the implications of CNTs for mechanical properties of the joints are discussed.

Preparation and Characterization of the Cr-Nanodiamonds/MoN Coatings with Performant Mechanical Properties

This paper presents the results of a study on the preparation and characterization of a Cr-DND/MoN detonation chromium-nanodiamond coating deposited on cemented tungsten carbide (WC–3 wt.% Co) mill blades using Arc-PVD and electrodeposition methods. The physical and mechanical characteristics of the coatings were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), XRD analysis, Raman spectroscopy, micro-identification, and scratch test (evaluation of the coating adhesion). It was shown that the Cr-DND/MoN coating consists of successive layers of Cr-DND (top), Cu (middle) and MoN (bottom) with separate phases of γ-Mo2N, α-Mo, α-Cu, Cr-DND and nanodiamonds. The Cr-DND composite electrochemical coating (CEC) was deposited from the conventional chromium plating electrolyte with the addition of nanodiamonds. The copper interlayer was deposited by the Arc-PVD method on the surface of the MoN coating to improve the adhesion strength of the Cr-DND CEC. The coating showed an optimum microhardness of about 14 ± 1 GPa and good adhesion with a critical load Lc of about 93 N. In addition to the expected experimental results, the coating has high wear resistance, confirmed by scratch tests.

Hybrid additive manufacturing of an electron beam powder bed fused Ti6Al4V by transient liquid phase bonding

Hybrid Additive Manufacturing (HAM) is a production strategy enhancing the flexibility of the already versatile Additive Manufacturing (AM) techniques. AM of Ti6Al4V, on the other hand, has been of great interest to numerous research works, thanks to the unique corrosion, biomedical and mechanical properties of the alloy. Hence, this research marks the first report on the HAM of Ti6Al4V by Transient Liquid Phase (TLP) bonding of an Electron Beam Powder Bed Fused (EB-PBF) sample to a conventional one. A copper interlayer was used for bonding, and the TLP process was performed at 890 °C and 970 °C for 60 min. Shear strength test was carried out and the results showed the highest shear strengths of 579.3 and 662.5 MPa for TLP bonding at 890 °C and 970 °C, respectively. By increasing the bonding temperature to 970 °C, no Cu-rich phases were observed in the microstructure, as opposed to the 890 °C samples, and a complete isothermal solidification without intermetallic phases was achieved. Moreover, the 970 °C TLP sample was featured with a much better microstructural integrity and homogeneity in both the base metals and the bonded zone. TLP bonding at 970 °C resulted in a more ductile fracture surface than that bonded at 890 °C. The strong differences between the two TLP bonds were primarily attributed to the faster diffusion rate of elements along the joint and base metal at higher temperatures.

Deposition, microstructure, performance of diamond-like carbon film with Ni/Cu interlayer

Diamond-like carbon (DLC) films containing single copper (Cu), single nickel (Ni) and double nickel/copper interlayers were fabricated on LY-12 aluminum (Al) alloy by electrodeposition. The influence of different interlayers on the microstructure, microhardness, friction and wear properties and electrochemical behavior of the films was investigated. The morphological results show that the porosity of DLC films was reduced and the particles were refined after the introduction of a double interlayer. Raman and X-ray photoelectron spectroscopy results confirm that the amorphous characteristics of DLC films containing nickel and copper interlayers were enhanced, and the content of sp3 carbon in the films was increased. Besides, an optimal microhardness of 210.67 HV was achieved due to the high sp3 carbon content of the double nickel/copper–DLC film. Meanwhile, the nickel/copper–DLC film possessed excellent wear resistance, which benefits from the synergistic effect of the copper and nickel interlayer. Nickel as the supporting layer and copper as the lubricating layer alleviated the wear and friction of the film. Simultaneously, the deposition of a double interlayer increased the density of the film, which further prevented the invasion of corrosion ions, so the film had superior electrochemical properties.

Effect of Bonding Temperature and Interlayer(s) on Microstructure Evolution, Hardness, and Shear Properties of Diffusion Bonded Ti-6Al-4V Alloys

Abstract The workhorse Ti-6Al-4V alloy has numerous applications under extreme conditions, and there is a necessity to produce metallic joints with the alloy for fabrication of some industrial components. In the present study, the solid-state diffusion bonding (DB) process was used to produce similar metal joints between Ti-6Al-4V alloy sheets with and without copper and nickel interlayers. The effect of the bonding temperature as well as the influence of interlayers on the joint interface microstructure and, subsequently, on the mechanical performance of the bonded joints were investigated. The DB was performed at three different bonding temperatures of 1,023, 1,123, and 1,223 K under high-vacuum conditions using a thermomechanical deformation simulator. The microstructure across interface of the joint was examined using optical and scanning electron microscopes. The joint strength was evaluated using both the nanoindentation technique and the shear test. The findings show the formation of intermetallic phases between titanium and interlayer(s) elements across the interface up to the bonding temperature of 1,123 K. Further increase in the bonding temperature led to a complete diffusion of the interlayers into the base metals, thereby forming the Widmanstätten microstructure across the interface. In the case of direct DB, there was a gradual closure of voids along with a homogenized joint interface with an increase in the bonding temperature. The variation of hardness across the bonding interface and the shear properties were found to be consistent with the resultant microstructural features evolved with the bonding temperature and type of interlayer(s).

Gas pressure casting technique for manufacturing of W/OFHC-Cu monoblock

The important engineering part of the divertor vertical target is the quality of joint between armor materials and heat sink. To reduce the joint interface stresses, a pure copper (Cu) interlayer was provided between the tungsten(W) armor and the CuCrZr cooling tube. Gas pressure casting method was developed to reduce the porosity and improve the mechanical properties of the Cu interlayer of W/Cu monoblock. In the vacuum casting sample without pressure, porosities were found in Cu. These porosities become defects at the interface between W and Cu and decrease the mechanical properties of the Cu interlayer. In the cooling process of casting, argon gas was pressurized into a porous tube inserted in the Cu and tungsten monoblock applying perpendicular force on the joint surface. This method was effective to remove the porosity in Cu generated during the cooling process and to increase the bonding strength between Cu and tungsten. The quality of bonding interface, depth of the Cu diffusion, and hardness of Cu were compared by SEM, EDS, and Vickers hardness measurement. In the samples made by gas pressure casting method, the porosity was decreased in Cu, no defects on the interface between tungsten and Cu, Cu was diffused into tungsten with a depth of 2∼3 μm and the hardness of Cu was increased about 15%.Small mock-ups were manufactured by hot radial pressing (HRP) with gas pressure casted W/Cu monoblock and CuCrZr cooling tube and underwent high heat flux (HHF) of 10 MW/m2 up to 5,000 cycles. The ultrasonic test (UT) results before and after the HHF test showed no defects on interfaces and was confirmed by observation of SEM on the cutting surface of the monoblock mock-up after the HHF test.

Lifetime measurement of a particular deep crack failure on a flat-type divertor mockup under cyclic high heat flux loading conditions

Plasma facing components are key to enduring high heat flux (HHF) loading from high-temperature plasma in nuclear fusion reactors. Understanding their thermal-mechanical behavior and cracking failure mechanisms related to structural designs and fabrication technologies during HHF loading is of great significance for improving their servicing performance and R&D (research and development) levels. In this study, a particular deep cracking failure process on the tungsten layer of a flat-type divertor mockup during 1800 cycles of 10 MW m−2 HHF loadings is completely monitored and measured with a special improved digital image correlation (DIC) technique. It is found that the DIC measurement under the HHF loading environment is improved successfully to capture fine deformation and strain fields with a spatial resolution less than 0.35 mm so that field strain on a 1 mm thick copper interlayer and deep crack initiation at several microns scale on the tungsten layer are measured out. Based on both full field and local strain and displacement measurements of the target divertor mockup, the thermal mechanical behaviors from deformation to crack initiation and propagation are successfully measured and traced. It is revealed that for the baseline copper interlayer design of a flat-type divertor mockup, the accumulation of plastic strain in the copper interlayer during ratcheting damage induces enough tensile stress on the tungsten layer during HHF cycles, leading to cracking and fracture failures even in its elastic state earlier than the copper LCF lifetime. Current Structural Design Criteria for ITER In-Vessel Components rules fail to cover this kind of ratcheting cracking failure mode in the design stage. New design models or mechanical validation rules to resolve this design blind spot should be established in the future.

Role of surface roughness in impulse pressure diffusion bonding of dissimilar steels using copper interlayer

Surface preparation is an important step in diffusion bonding that can’t be eliminated and compromised to achieve a good quality joint. Proper surface preparation becomes time consuming besides being laborious due to polishing requirements. In view of the above, P92 steel and 316L ASS rods were diffusion bonded using pressure pulses introducing copper interlayer and the effect of surface roughness was investigated. The developed bonded bonds were characterized in respect of hardness distribution, tensile properties, and scanning electron microscopy. The effect of surface roughness on joint strength was also studied. It was found that the diffusion bond consists the similar microstructural features as the base metal. However, some microvoids were found at the diffusion bond interface for the diffusion bonds developed at high surface roughness, which influences the mechanical property of the diffusion bonds and gets reduced with the decrease in surface roughness. Room temperature tensile tests were conducted and the tensile strength was found as 329, 372, and 413 MPa for three different surface roughness having failure from the copper interlayer.

Investigating feasibility of interlayers in Resistance Spot Welding of low-carbon steel sheets

In this study, experiments without interlayers and with interlayers of copper and stainless-steel sheets were performed. Design of Experiments based Full-Factorial Method was employed to generate experimental combinations. A total 81 samples were welded and tested in Universal Testing Machine to determine their Breaking Load. To investigate feasibility considering vehicle lightweightness, a novel LTW (Load-to-Weight) ratio has been proposed. Calculated LTW ratio for each experiment clearly showed that samples with stainless-steel interlayer outperformed over samples with copper interlayer and samples without interlayer. For feasibility in terms of machine durability, electrode corrosion has been found as the most auspicious parameter among all. Spot welding electrodes attain air oxidation above 700 °C. An FEA solver has been employed to determine time for electrodes to remain above air oxidation temperature during a single welding cycle through numerical simulation. A novel LTT (Load-to- Time) ratio has been proposed to find experimental combinations considering feasibility regarding electrode corrosion. LTT ratio, applied to experimental combinations with SS interlayer helped in selection of suitable process parameter combinations. Selected combinations through LTW and LTT ratio can be further proposed to industries. Study advocates method to calculate LTW ratio initially, following calculation of LTT ratio and eventually selecting process parameters contemplating feasibility in lightweightness and electrode corrosion.Article HighlightsStudy helps to decide feasibility of interlayer in RSW in terms of weight and electrode corrosion.Load-to-Weight (LTW) ratio is proposed to decide feasibility of interlayer in terms of weight.Load-to-Time (LTT) ratio is proposed to determine feasibility of interlayer against electrode corrosion.