Copper Diffusion Research Articles

Oxidation resistance mechanism of copper wire regulated by nano-palladium coating

The microstructure characteristics of palladium coating are the key to the oxidation resistance of palladium-coated copper wire. In this paper, the microstructure characteristics of palladium coating thickness, nanocrystalline size and amorphous band width were controlled by adjusting the process parameters of micro-area coating. The relationship between microstructure characteristics of palladium coating and oxidation resistance was studied. The results show that the wire has good oxidation resistance when the deposition temperature is 400℃ and the copper wire/mold clearances are 2.5 μm. The surface of the copper wire has a palladium coating with a thickness of 74 nm, and the palladium particles are composed of amorphous encapsulated nanocrystals. The relationship between the thickness of palladium coating and the copper wire/mould clearances is y=0.012x+44, and the increase of palladium coating thickness can inhibit the migration of copper ions. The increase in the size of the nanocrystalline and the width of the amorphous band has a certain inhibitory effect on the lattice or grain boundary diffusion of copper to the palladium coating. The multi-stage distorted nanotwins in the amorphous palladium coating can reduce the strain difference at the palladium-copper bonding interface, reduce the diffusion driving force of copper outward, and thus improve the oxidation resistance of palladium-coated copper wires.

Diffusion mechanisms and corrosion resistance of nanostructured ZrN-Cu coating obtained by hybrid HiPIMS-DCMS

Globalisation has brought numerous benefits regarding the cost-effective transportation of goods. Still, the shipping industry faces challenges such as corrosion, biofouling, and restrictions on heavy pollutant products used in paintings. This study proposes a solution using a multifunctional coating based on zirconium nitride and copper nano-structured coating, applying high-power impulse and direct current magnetron sputtering processes (i.e., HiPIMS and DCMS, respectively). The coating’s morphological, structural, and chemical features were analysed using advanced characterisation techniques (SEM, EDX, STEM, SAED and EELS). Potentiodynamic polarisation (PP) and Electrochemical Impedance Spectroscopy (EIS − up to 30 days) were employed to study the corrosion resistance in saline solution (3.5 wt% NaCl). Besides, activated ZrN-Cu exhibited a corrosion rate decrease from ∼ 354 x 10−4 to 52 x 10−4 mm/yr when compared to its inactivated counterpart. Besides, a ∼ 3.5-fold impedance increasing was exhibited by activated ZrN-Cu after 30 days of exposure to saline solution, meaning an increase in corrosion resistance compared to the non-activated ZrN-Cu. SEM micrographs revealed that the copper diffusion in ZrN-Cu can be provoked by a strong oxidising agent (NaOCl) or by an electrical potential. Based on the chartered evidence, a diffusion mechanism is proposed for the biocidal release (Cu) in the obtained ZrN-Cu films. The present study depicts a solution that offers a controlled biocide release and corrosion resistance, opening the possibility of its application in the maritime industry.

Exploring W-EUROFER brazed joints: S/TEM and nanoindentation analysis following post-brazing tempering treatment

Tempering treatments are essential for restoring the hardness and microstructure of EUROFER steel when W-EUROFER joints are formed at temperatures exceeding the steel's austenitization point (890 °C). This post-brazing heat treatment can, however, alter the microstructure and thereby affect the mechanical properties. This study explores the microstructural and nanomechanical effects in the brazed area of W-EUROFER joints following this heat treatment, utilizing copper as an intermediate filler material. Using Scanning Transmission Electron Microscopy (STEM) with Energy Dispersive Spectroscopy (EDS) on FIB lamellae and nanoindentation techniques we examined the stability and phase characteristics of the post-tempered microstructure in two lamellae that covers the whole phases of the braze microstructure.The tempering process enhances copper diffusion and the growth of copper precipitates without significantly altering the joint's overall microstructure. Despite the general stress-relief effects of tempering, which typically lower mechanical properties, the diffusion phases formed during brazing maintained high hardness and modulus, indicative of a complex, element-rich composition. A reduction in mechanical properties was observed in the iron-rich phase near the W-braze interface and the EUROFER base material, aligning with the purpose of the heat treatment. However, the copper braze and tungsten base material largely retained their stability and resilience to thermal treatments.This research provides vital insights into the behavior of these material systems under thermal processing, highlighting the necessity of optimizing heat treatment parameters to preserve joint integrity in high-performance applications such as nuclear fusion reactors. The findings contribute significantly to the development of durable and reliable materials for fusion energy, emphasizing the importance of controlled tempering processes to enhance material properties.

Migration of copper(II) ions in humic systems—effect of incorporated calcium(II), magnesium(II), and iron(III) ions

The mobility of heavy metals in natural soil systems can be affected by the properties and compositions of those systems: the content and quality of organic matter as well as the character of inorganic constituents. In this work, the diffusion of copper(II) ions in humic hydrogels with incorporated calcium(II), magnesium(II), and iron(III) ions was investigated. The methods of instantaneous planar source and of constant source were used. Experimental data yielded the time development of the concentration in hydrogels and the values of effective diffusion coefficients. The coefficients include both the influence of the hydrogel structure and the interaction of diffusing particles with the hydrogel. Our results showed that the presence of natural metal ions such as calcium, magnesium, or iron can strongly affect the diffusivity of copper in humic systems. They indicate that the mobility of copper ions depends on their concentration. The mobility can be supported by higher contents of copper in the system. While the incorporation of Ca and Mg resulted in the decrease in the diffusivity of copper ions, the incorporation of Fe(III) into humic hydrogel resulted in an increase in the diffusivity of Cu(II) in the hydrogel in comparison with pure humic hydrogel.

Study on interface diffusion and welding strength of Cu/Sn dissimilar metal electromagnetic pulse welding based on molecular dynamics simulation

The electromagnetic pulse welding (EMPW) method stands out for its rapid welding time, superior precision, and high automation, making it ideal for materials with significant melting point differences, specifically copper and tin, which often struggle to form robust joints. Utilizing molecular dynamics simulations, this study aims to investigate the interface evolution patterns under varying collision velocities and assess the welding strength of joints subjected to distinct tangential velocities. The findings reveal a profound correlation between the diffusion coefficient, system temperature, and the collision velocity during the simulated EMPW vertical collision. Specifically, at a collision velocity of Vz = 500 m/s, the interface tends to be linear, suggesting an unstable bonding state. However, when the collision velocity exceeds 700 m/s, a more intense diffusion of copper and tin atoms is observed, resulting in a wavy interface indicative of enhanced bonding capabilities. Furthermore, the study examines the shear behavior of welded joints subjected to oblique collisions with varying tangential velocities. The analysis reveals a transition in fracture locations from the joint-joint interface to the joint-base material interface and ultimately to the base material itself, as the tangential velocity increases from 50 m/s to 100 m/s and surpasses 200 m/s. This comprehensive evaluation of EMPW process variables provides a theoretical foundation for optimizing the mechanical properties of copper-tin EMPW joints.

Interlayer design for strong adhesion in the double-layer flexible copper clad laminate via HiPIMS deposition

By designing different interlayers (Al, Si/SixNy and Cr interlayer) and oxygen plasma pretreatment of the substrate, strong adhesion was realized for the double-layer flexible copper clad laminate on polyimide (PI) substrate via high power impulse magnetron sputtering (HiPIMS) technology. The microstructures and properties of Cu films on PI substrate were characterized by an X-ray powder diffractometer (XRD), X-ray photoelectron spectroscope (XPS), atom force microscopy (AFM), scanning electron microscope (SEM), nano-scratch test, scotch tape test and four-probe detector. With the introduction of interlayer and oxygen plasma pretreatment, the critical load of Cu film (300 nm thick) peaked at 43.5 mN and the sheet resistance ranged from 124 to 227 mΩ/sq. The oxygen plasma pretreatment resulted in the drastic oxidation to generate functional groups on the PI substrate surface, which contributed to the improvement of adhesion strength by chemical interaction in terms of the film with Si/SixNy or Cr interlayer. Besides, for the Cu film with Si/SixNy interlayer, the resistance against copper diffusion by the SixNy layer can also promote the enhancement of adhesion strength.

Oxidation behavior of Cu–Ag alloy in-situ manufactured via laser powder bed fusion

The oxidation behavior of copper-silver (Cu–Ag) alloy with the structure of triply periodic minimal surfaces (TPMS) processed by laser powder bed fusion (LPBF) was investigated at 300 °C and 600 °C. The lightweight TPMSs increase surface area, boosting measurement sensitivity in oxidation studies. The presence of silver enhances oxidation resistance of Cu–Ag alloy compared to that of pure copper by slowing down the oxidation process and thinning the oxide layer. This suggests that silver in the alloy potentially suppresses the outward diffusion of copper from the substrate to the oxide layer. This effect is evident in the oxidation rate curves, where the introduction of silver changes the oxidation kinetics from a linear rate in Cu to a parabolic rate in Cu–2 wt.% Ag at 300 °C. Moreover, at 600 °C, silver induces a slower parabolic rate in Cu–2 wt.% Ag compared to Cu.

Material screening for future diffusion barriers in Cu interconnects: Modeling of binary and ternary metal alloys and detailed analysis of their barrier performance

One of the challenges in the semiconductor industry is to find new barrier materials and copper (Cu) alternative solutions in interconnects. In this work, we focused to find alternative diffusion barrier materials. Different binary (CoMo, CoRu, CoTa, CoW, MoRu, RuTa, RuW) and ternary (CoMoTa, CoRuTa, MoRuTa) metal alloys were evaluated theoretically with the Miedema model to find the amorphous phase composition range. Afterward, thin films of the alloys with various compositions were deposited by magnetron sputtering and theoretical values were compared to the experimental results. From the experimental measurements, which included grazing incidence x-ray diffraction analysis and resistivity measurements, suitable binary and ternary alloys were chosen for diffusion analysis. By annealing thin film stacks at temperatures ranging from 500 to 675°C, diffusion was induced and detected by x-ray photoelectron spectroscopy depth profiles. Seventeen alloys were evaluated by their diffusion barrier effectiveness, and five of those, which include Ru60Ta40, Ru45W55, Mo47Ru53, Mo36Ru50Ta14, and Co40Mo35Ta25, showed excellent barrier properties against copper diffusion. Furthermore, all of the stated materials have a lower resistivity than TaN. Last, the adhesion of the best performing alloys to SiCOH and Cu was evaluated by the modified edge lift-off test. Only Ru45W55 had reasonable adhesion at both interfaces. The other materials showed low adhesion strength to Cu, which would make an adhesion promoter (liner), such as cobalt, necessary for the integration.

Self-assembled layer as an effective way to block copper diffusion into epoxy

The reliability of copper/epoxy bonding is important for power semiconductors. It has been found that copper can diffuse into epoxy and accelerate epoxy decomposition at high temperatures, deteriorating reliability. We proposed a way to inhibit copper diffusion into epoxy by using self-assembled layers. Copper substrates with self-assembled layers on their surface were encapsulated with epoxy and placed at 200 °C for 1000 h. The diffusion of copper into epoxy was evaluated by XPS depth profiling, and the decomposition of epoxy was evaluated by ATR-FTIR. The results showed that self-assembled layers can effectively hinder copper diffusion into epoxy. The possible reason is that the existence of the self-assembled layer greatly reduces the formation of copper ions. Also, we found that the self-assembled layer survived the heating, implying its potential for practical power module applications.

Identification of Some Gem-Quality Red and Green Feldspars

Sunstone is a member of the feldspar group. Natural sunstones from Oregon exhibit unique optical effects and hold significant market value. However, since 2008, there has been a persistent issue of diffused red feldspars masquerading as natural sunstones in the market, severely undermining consumer confidence in purchasing natural sunstones. Fluorescence characteristics under 305–335 nm ultraviolet excitation are considered an effective method for distinguishing copper-diffused red feldspars from natural sunstones. In this paper, through detailed analysis and testing of ten market-acquired red and green feldspar samples, including UV-vis spectra, microscopic characteristics, fluorescence spectra, and chemical compositions, we validate the efficacy of fluorescence characteristics in identifying copper-diffused feldspars. The results verify the widespread prevalence of copper diffusion treatment in market-acquired red and green feldspars, shedding light on their treatment history and providing valuable insights for jewelry consumers. This research not only enhances our understanding of sunstone treatments but also strengthens the reliability and applicability of fluorescence spectroscopy in gemstone identification, offering promising prospects for its broader adoption in the jewelry market.

A healable amino silane self-assembled monolayer incorporating polymer capped palladium nanoclusters and its application as the copper diffusion barrier layer on silicon wafer

Self-assembled monolayers (SAMs) with short organic chains terminated with specific functional groups are attractive for modifying surface properties for a variety of applications, including being a copper diffusion barrier layer on Si wafer. However, SAM formation is process-sensitive and ideal SAM is difficult to obtain, both of which need to carefully deal with before practical use. Herein we developed a system to achieve seamless electroless deposited copper (ELD Cu) film on an amino-terminated silane SAM modified Si wafer with the help of a bifunctional polyvinyl alcohol-capped Pd nanocluster (PVA-Pd) catalyst. The PVA-Pd acts as a catalyst for ELD Cu as well as a healing agent to fix defects of the amino silane SAM. The sheet resistance, cross-sectional morphology analysis and adhesion of ELD Cu on the Si wafer are extensively studied. By controlling the abundancy of PVA in PVA-Pd, the diffusion barrier property of a flawed amino-terminated silane SAM remains reliably effective even after a 500 °C rapid thermal annealing (RTA), evidencing the superior healing function of PVA. The whole thickness of the PVA-Pd/amino-terminated silane SAM before and after RTA is 〜6 nm and 〜2 nm, respectively, which is applicable for advanced microelectronic manufacturing.

Wettability and microstructural evolution of copper filler in W and EUROFER brazed joints

In terms of wettability, active systems are characterized by a reduction in interfacial energy as the time at specific conditions is increased. This article aims to investigate the evolution of wettability and microstructure, which undergoes a critical transformation at temperatures and dwell times near brazing conditions due to their significant impact on resultant mechanical properties. The objective is to enhance wettability and prevent the formation of different phases that can occur rapidly within the brazing window conditions. Up to 1105 °C, complete fusion of the filler does not occur. However, once it happens, the expansion of the copper filler in EUROFER increases up to 400%, and the contact angle reduces from 100° to 10°, indicating an active wetting behavior. On the other hand, when copper is used with tungsten, an inert behavior is observed, maintaining the contact angle around 70°. Brazed joints carried out under the most promising wetting conditions demonstrated that at 1110 °C-1 min, various phenomena began to occur. This includes solid-state diffusion of copper in the EUROFER, following the austenitic grain boundaries, and partial dissolution of Fe in the copper braze. Increasing the brazing time from 2 to 5 min achieved high interfacial adhesion properties and controlled the diffusion layer and Fe-rich band formed at the W-braze interface, resulting in the best mechanical results (295 MPa).

Growth of conformal TiN thin film with low resistivity and impurity via hollow cathode plasma atomic layer deposition

Copper has been used as an interconnect material in integrated semiconductor devices because of its excellent conductivity, mechanical strength, and electromigration resistance. Introducing a diffusion barrier layer using transition metals such as Ti, Ta, W, Mo, and their nitrides can effectively prevent copper diffusion into the transistor region. TiN is widely used as the diffusion barrier. Plasma-enhanced atomic layer deposition (PEALD), which uses plasma to activate molecular reactions, can be used to fabricate high-quality thin films at lower temperatures than thermal atomic layer deposition. However, its high electrical resistivity and poor step coverage are disadvantageous for its adoption in highly scaled three-dimensional structures. In this study, TiN thin films were fabricated using PEALD with a hollow cathode plasma (HCP) source. The fabricated TiN exhibited a high density (5.29 g/cm3), which was very close to the theoretical density of TiN. Moreover, it has low electrical resistivity (132 μΩ cm) and excellent step coverage (>98%) in a trench pattern with a high aspect ratio of 32:1. These results suggest the possible application of the PEALD of TiN films using HCP sources in semiconductor device manufacturing.

Lead isotopes of prehistoric copper tools define metallurgical phases in Late Neolithic and Eneolithic Italy.

The diffuse presence of small copper ore deposits in the Alpine area, mostly exploited since Late Medieval times, led most scholars to assume that these deposits may actually be active much earlier and that many of the circulating prehistoric metal objects found in the area were produced with local copper sources. This assumption was recently validated for the Recent Bronze Age through the use of lead isotope tracers, and well supported by the archaeometallurgical evidences found in the South-Eastern Alps. However, the scarcity of available lead isotope data for pre-Bronze Age metals precluded to date the reconstruction of the metal flow through the Late Neolithic and Eneolithic (or Copper Age). Based on 49 new analyses of important archaeological objects from the Alpine region, the Po River Valley and Central Italy, mostly axes dated from the Late Neolithic to the Late Eneolithic, here we show that the diffusion of copper in Northern Italy (approximately 4500-2200 BC) includes three major periods of metal use and/or production, each related to specific ore sources. The South Alpine copper was massively used only starting from the middle of the 3rd millennium BC, in connection or slightly earlier than the Beaker event.

Copper diffusion into epoxy under high temperature

High reliability is critical for semiconductors, especially power semiconductors, which usually work in high temperature conditions. One important reliability issue for power semiconductors is the copper diffusion into polymers. Copper diffusion accelerated polymer decomposition. Also, severe copper diffusion even causes short circuits. Although copper diffusion has been identified, the reason for the initiation of copper diffusion is still not well understood. Here, we encapsulated copper substrate with five different epoxies to investigate the reason for the initiation of copper diffusion. The influence of epoxy impurity elements and epoxy cross-link density was investigated. The results show that the initiation of copper diffusion into epoxy is highly related to the impurity elements, sulfur (S) and chlorine (Cl). In contrast, the low cross-link density of the epoxy cannot initiate copper diffusion. It implies that using S-free and Cl-free epoxy is necessary for semiconductors requiring high reliability.

(Invited) Reliability Challenges in Advanced 3D Technologies

Customer need for faster electronic products, with enhanced functionalities and smaller form factor is driving the growth of the microelectronic industry. As the traditional more Moore approach is slowing down due to the exponential cost of silicon scaling and the lowers yields [1], a chiplet-based future is being adopted [2, 3]. Chiplets enable modular products by combining chips from various technologies and technology nodes, allowing designs out of reach of the monolithic approach [4, 5]. To tackle the inherent interconnect latency observed in the 2.5D-System-on-Chip (SoC) approach, 3D interconnects technologies are a must.Nevertheless, to enable advanced 3D-SoC circuits, the 3D interconnect pitch needs to be scaled further. This can be achieved using Through Silicon Vias (TSV) [6-8] and wafer-to-wafer (W2W) hybrid bonding [9, 10], in combination with nano-TSVs connecting back-side buried power rails [11]. While TSVs are used to electrically connect the front side to the back side of a silicon wafer, and thus to enable die stacking, W2W hybrid bonding connects directly two wafers through copper pads embedded in a dielectric material which is generally SiO2 [12, 13] or SiCN [14].Unfortunately, these novel technologies come along with key reliability issues. TSV’s aggressive aspect ratios (up to 20:1 [15]) put stringent requirements on the etch and liner deposition process to guarantee the electrical isolation and avoid copper diffusion in the silicon substrate [16]. Additionally, their sole presence has been shown to influence the reliability of the above BEOL layers [17, 18] and near-by transistors [6]. In the hybrid-bonding technologies, the constant pitch down-scaling results in an increased leakage current along the bonding interface [19] which can be further enhanced by pad-to-pad misalignment [20]. While this misalignment can be mitigated with unequal pad schemes [21], the resulting copper-dielectric interface could lead to metal ion drift at elevated temperature and electric fields [19].In this presentation, the reliability issues and failure mechanisms linked to 3D technologies will be discussed and a particular focus will be given on topics which are currently of interest at imec. The controlled-IV methodology, used to assess dielectric material reliability will be reintroduced. Data obtained on 1 x 5 µm TSVs will demonstrate the advantage of imec embedded barrier to mitigate reliability issues arising from copper resputtering during the etch process while the importance of an optimized etch recipe will be shown. Reliability characterizations of SiCN-based hybrid bonded structures, down to a pitch of 700 nm will be presented along with a discussion on the influence of the CMP process on the leakage current and resulting lifetime. The potential influence of copper ion diffusion along the bonding interface will be analyzed. Finally, the impact of electromigration on the copper pads will be presented.[1] Samavedam, S. B. et al., IEDM, 2020.[2] Cao, L., IEDM, 2022.[3] Beyne, E. et al., IEDM, 2021.[4] Su, L. et al., IEDM, 2017[5] Naffziger, S.et al., IEEE ISSCC, 2020.[6] Croes, K., et al., IEEE Design & Test , 2016, Vol. 33, No. 3.[7] Burkett, S. et al., Journal of Vacuum Science & Technology A, 2020, Vol. 38, No. 3.[8] Van Huylenbroeck, S. et al., ECTC, 2019.[9] Jouve, A. et al., SOI-3D-Subthreshold Microelectronics Technology Unified Conference (S3S), 2017.[10] Kim, S-W. et al., ECTC, 2020.[11] Jourdain, A. et al., ECTC, 2022.[12] Utsumi, J., et al., Micro and Nano Engineering, 2019, Vol. 2[13] Ayoub, B et al., EPTC, 2020.[14] Iacovo, S. et al., ECTC, 2022.[15] Van Huylenbroeck, S et al., IEEE 3DIC, 2016[16] Li, Y. et al., Microelectronics Reliability, 2013, Vol. 54, No. 9-10[17] Frank, T. et al., Microelectronics Reliability, 2013, Vol. 53, No. 1[18] Li, Y. et al., IRPS, 2014.[19] Hou, Lin et al., IRPS, 2022.[20] Ayoub, B. et al., IRPS, 2022.[21] Kim, S-W., et al., ECTC, 2020.

Copper Phosphinate Complexes as Molecular Precursors for Ethanol Dehydrogenation Catalysts.

Nowadays, the production of acetaldehyde heavily relies on the petroleum industry. Developing new catalysts for the ethanol dehydrogenation process that could sustainably substitute current acetaldehyde production methods is highly desired. Among the ethanol dehydrogenation catalysts, copper-based materials have been intensively studied. Unfortunately, the Cu-based catalysts suffer from sintering and coking, which lead to rapid deactivation with time-on-stream. Phosphorus doping has been demonstrated to diminish coking in methanol dehydrogenation, fluid catalytic cracking, and ethanol-to-olefin reactions. This work reports a pioneering application of the well-characterized copper phosphinate complexes as molecular precursors for copper-based ethanol dehydrogenation catalysts enriched with phosphate groups (Cu-phosphate/SiO2). Three new catalysts (CuP-1, CuP-2, and CuP-3), prepared by the deposition of complexes {Cu(SAAP)}n (1), [Cu6(BSAAP)6] (2), and [Cu3(NAAP)3] (3) on the surface of commercial SiO2, calcination at 500 °C, and reduction in the stream of the forming gas 5% H2/N2 at 400 °C, exhibited unusual properties. First, the catalysts showed a rapid increase in catalytic activity. After reaching the maximum conversion, the catalyst started to deactivate. The unusual behavior could be explained by the presence of the phosphate phase, which made Cu2+ reduction more difficult. The phosphorus content gradually decreased during time-on-stream, copper was reduced, and the activity increased. The deactivation of the catalyst could be related to the copper diffusion processes. The most active CuP-1 catalyst reaches a maximum of 73% ethanol conversion and over 98% acetaldehyde selectivity at 325 °C and WHSV = 2.37 h-1.

Improving strength and toughness of Ti–6Al–4V alloy/pure copper diffusion bonded joint with VCrAl1.86Ni1.86 eutectic medium-entropy alloy interlayer

To solve the metallurgical incompatibility of titanium alloy/copper dissimilar metal joining, a suitable interlayer was used to adjust the interface structure, achieving the strength and toughness of joint. The vacuum diffusion bonding between Ti–6Al–4V alloy (TC4) and pure copper (T2) with VCrAl1.86Ni1.86 eutectic medium entropy alloy (EMEA) foil was investigated. Ti3Al, Al(V, Cr)Ti2, Al(V, Cr, Ni)Ti, and AlNi2Ti phases formed in the TC4/EMEA interface. FCC and BCC double-phase solid solution appeared in the EMEA/T2 diffusion zone, resulting in the high-entropy seam between VCrAl1.86Ni1.86 interlayer and T2. The maximum shear strength of joint made at 880 °C for 90 min reached 215 MPa. The growth activation energy of reaction layers (I-III) in the TC4/EMEA interface were 283 kJ/mol, 379 kJ/mol and 431 kJ/mol, respectively. The Ti3Al/Al(V, Cr)Ti2/Al(V, Cr, Ni)Ti/AlNi2Ti interface was coherent. Nevertheless, the AlNi(V, Cr)2/Al(Cu, Ni)2 and AlNi(V, Cr)2/FCC-Cu interface was non-coherent with high strain energy. All joints broke through the EMEA/T2 interface during test. The fracture surface presented some cleavage ravines and auspicious cloud features. This study provided an effective strategy for the joining of titanium alloy and copper in high precision components of aerospace engines.

Determination of phase equilibria in the CuxZryCr1-ySe2 system by the EMF method

Layered materials ZrSe2, CuZrSe2 and CuCr0.8Zr0.2Se2 were synthesized, and the structure of the obtained compounds was determined. The phase states in CuxZrSe2 and CuxZr0.2Cr0.8Se2 systems were determined by coulometric titration and electromotive force methods. An increase in the potential difference in the electrochemical cells Cu|Cu+|CuxZryCr1-ySe2 upon substituting Zr4+ for Cr3+ (0 < x < 0.5) was also noted. The copper diffusion coefficients for CuZrSe2 and CuCr0.8Zr0.2Se2 were estimated to be 10─9 and 10─10 respectively.

Interdiffusion between 316L Stainless Steel and Copper in Coatings Processed by High Velocity Oxyfuel

Abstract Joining of stainless steel and copper is of interest to a variety of applications that range from heat exchanger to nuclear waste container. Nevertheless, welding of these dissimilar metals is challenging because of the risk of hot cracks and lack of fusion associated with their differences in melting temperatures and thermal conductivities. In this work, joining of 316L stainless steel and copper by high velocity oxyfuel is investigated using two systems of materials, the first consisting of copper coatings on AISI 316 substrates, and the second of 316L coatings on copper substrates. To promote metallurgical bonding, the systems were exposed to 500°C, 700°C, 900°C, and 950°C for 10 h under flowing argon atmosphere. Microstructure was characterized by optical and scanning electron microscopy and energy-dispersive x-ray spectroscopy. Bending tests were carried out to qualitatively investigate the coatings adhesion and cohesion strength. It was found that 316L coatings have a much superior adhesion to copper substrates than copper coatings had to AISI 316 substrates, associated with the ease of 316L incoming particles to embed in the softer copper matrix and with the higher susceptibility of 316L coatings to diffuse into copper substrates. In contrast, in copper coatings, copper oxides formed during deposition decomposed during heat treatment, releasing oxygen that caused porosity and oxidation on the interface with the stainless-steel substrate, preventing the formation of a clean metallurgical bond. Diffusion of iron-rich oxide inward the copper coating was also observed near the interface, indicating that diffusion of steel into copper is more likely than diffusion of copper into steel. Nevertheless, heat exposure was found to increase damage tolerance of copper coatings, associated with a higher coating ductility and compliance.