Interdiffusion Of Elements Research Articles

Effect of deposition sequence on interfacial characteristics of Inconel–copper functional bimetallic structures fabricated by directed energy deposition-arc

Interfacial bonding reliability is a critical issue in bimetallic structures. To understand the effect of deposition sequence on interfacial characteristics, bimetallic structures of Inconel and copper alloys were fabricated by directed energy deposition arc (DED-Arc). The interfacial element diffusion behaviors and formation mechanisms were investigated in detail. The bimetallic structure of C18150 on GH4169 exhibits a sound metallurgical bonding interface with a wide interfacial region (∼400 μm), which is attributed to Marangoni convection and intense elemental interdiffusion. The study highlights the feasibility of fabricating large Inconel–copper functional bimetallic structures with sound metallurgical bonding using DED-Arc and it provides a theoretical reference for design and fabrication of bimetallic structures with material-property mismatches.

High temperature performance and interface evolution of a NiCoCrAlY coating with Pt modification and Re-based diffusion barrier

The cyclic and early isothermal oxidation behaviors at 1050 °C of the NiCoCrAlY, Pt-modified NiCoCrAlY and Pt-modified NiCoCrAlY with Re-based diffusion barrier (DB) have been evaluated. The atomic immigration and electron location function (ELF) at the Ni-Re interface were simulated by density function theory (DFT) calculations. After isothermal oxidation for 1 h, island NiCoCrAlY particles with extremely poor Al were observed in the oxide scale of normal NiCoCrAlY coating, and then the oxide scale transformed into a double-layer structure after oxidation for 20 h. The initial “island-oxide” scale model was proposed to illustrate the oxidation mechanisms for normal NiCoCrAlY coating. The oxide scale of Pt-modified NiCoCrAlY coating was single-layer Al2O3 with rapid coverage at the surface, because the modification of Pt changed the initial oxidation mechanism by promoting the uphill diffusion of Al. The Re-based DB reduced the thickness of the secondary reaction zone (SRZ) by inhibiting the element interdiffusion between the NiCoCrAlY coating and the substrate, thus the Pt-modified NiCoCrAlY with Re-based DB exhibited the lowest interdiffusion extent. Interestingly, the thermal stability of Re-based DB in NiCoCrAlY coating system was poorer than that in NiCrAlY system. The DFT simulation shows that the incorporation of Co made the energy difference more negative, which confirmed that Co promoted the diffusion of Re in the NiCoCrAlY coating, thus accelerating the degradation of Re-based DB.

Architecting “Li-rich Ni-rich” core-shell layered cathodes for high-energy Li-ion batteries

Li-rich or Ni-rich layered oxides are considered ideal cathode materials for high-energy Li-ion batteries (LIBs) owing to their high capacity (> 200 mAh g–1) and low cost. However, both are suffering from severe structural instability upon high-voltage cycling (> 4.5 V). Here, “Li-rich Ni-rich” Li1.08Ni0.9Mn0.1O2 oxides with core-shell architecture are designed and synthesized to improve their high-voltage cyclability. These oxides are determined to be composed of a less reactive “Li-rich Mn-rich” shell and a high-capacity “Li-rich Ni-rich” core. As Li-ions gradually enter into the core-shell precursor during high-temperature lithiation reaction, the interdiffusion of elements across the interphase between the Mn-rich shell and the Ni-rich core successively occurs. Such thermally-driven atomic interdiffusion could lead to a thickness-controllable “Li-rich Mn-rich” shell, which can guarantee an exceptional structural reversibility for the layered “Li-rich Ni-rich” core upon long-term cycling. As a consequence, the optimized core-shell Li1.08Ni0.9Mn0.1O2 achieves a capacity retention of 96% at 0.1 C after 100 cycles in the voltage range of 2.7–4.6 V. These findings might open up a new avenue for rational design of advanced cathode materials for LIBs and beyond.

Choosing Carbon Conductive Additives for NMC-LATP Composite Cathodes: Impact on Thermal Stability

One of the main technological challenges oxide-based solid-state batteries face today is the densification of their components to reach good interfacial contact. The most common approach requires co-sintering of the different components (electroactive material, catholyte and conducting additive) at high temperatures which often results in the inter-diffusion of elements that deteriorate the overall cathode performance. In this work, the impact of different carbon grades in the thermal response of LATP-NMC622-Carbon electrodes is evaluated and shown to significantly influence the chemical compatibility between components. By means of a combination of bulk and surface characterization techniques including gas adsorption, X-ray diffraction, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and thermogravimetric analysis, it is shown that carbons with low surface area are more adequate as result in higher oxidation temperatures and hence are less reactive.

Effect of oxygen doping on the corrosion behavior of nanocrystalline coating under the synergy of solid NaCl deposit and water vapor

Nanocrystalline coating with the same chemical composition as the nickel-based superalloys was proved to possess high resistance to oxidation and scale spallation, meanwhile avoid notable elements interdiffusion. It opens up a new direction for the development of protective coatings. However, in a worse environment containing chlorine and water vapor, the ultrafine grains act like a double-edged sword, which can promote the formation of a protective scale of Al2O3 or Cr2O3, but also favor the inward diffusion of Cl and H2O to accelerate corrosion. In order to solve this problem, moderate amount of oxygen was doped into nanocrystalline coating during magnetron sputtering. Then, corrosion behavior of the two nanocrystalline coatings with or without oxygen doping was studied in the O2 + 38% H2O environment with solid NaCl deposit. Results indicated that the doped oxygen can attract active elements of Ti and Al to form TiO2 and θ-Al2O3, which pinned at grain boundaries to keep the ultrafine grains stable at high temperature while prevent inward diffusion of the corrosive media. Accordingly, a dense and pure chromia scale was formed quickly at surface, ensuring that the oxygen-doped nanocrystalline coating provided the highest corrosion resistance under the synergy of solid NaCl deposit and water vapor. In contrast, the coating without oxygen doping suffered from severe internal corrosion.

Microstructure and properties of TiC particles planted on single crystal superalloy by electrospark discharging

The formation mechanism of the surface and cross-sectional morphology of the TiC particles planted on single crystal superalloy by the electrospark discharging process, as well as the effect of pulse energy on the microstructure and shear force of the planted particles were investigated. The results show that, the surface of the planted particles can be categorized as 3 regions: spreading region, flushing region and oxidation region. The cross sectional microstructure is formed by 3 synergistic processes: the electrospark discharging process, the particle breakage process, and electro-capillary rise process. Because of these processes, micro-cracks and merged pores are formed in the particle, which are quickly filled with the molten substrate metal, resulting in the element interdiffusion and metallurgical bonding between TiC particles and the metal substrate. With increasing pulse energy, the effect of these processes on the surface and cross-sectional morphology is changed, leading to the change of shear force.

Porous bio-high entropy alloy scaffolds fabricated by direct ink writing

Porous tantalum-titanium-niobium-zirconium (Ta-Ti-Nb-Zr) bio-high entropy alloy (bioHEA) scaffolds are fabricated using direct ink writing 3D printing technology in this study. A composite ink is prepared using four metal powders as raw materials: Ta, Ti, Nb and Zr. Ink extrusion is used to build 3D scaffolds with interconnected porous structures at room temperature, which are then sintered in a vacuum environment. The interdiffusion of metal elements yields porous bioHEA scaffolds with a body-centered cubic (BCC) structure. The fabricated scaffolds have uniform compositions with a significant alloying effect and good biocompatibility. The scaffolds have a compressive strength of 70.08-149.95 MPa and an elastic modulus of 0.18-0.64 GPa, indicating that the mechanical properties can be controlled over a wide range. The scaffolds have a compressive strength close to that of human cortical bone and thus meet the requirements for porous structure characteristics and biological and mechanical properties of orthopedic implants.

Unbalanced thermal field assisted thermo-compensated resistance brazing welding 6061 aluminum alloy to 304 stainless steel

The reliable Al/steel resultant welded joint with a large contact area was of great significance in electrolysis cells to produce aluminum. Herein, a large-area 6061 aluminum alloy/304 stainless steel dissimilar welds were successfully obtained by unbalanced thermal field assisted thermo-compensated resistance brazing welding(abbreviated as UTC-TC-RBW). In the present study, the heating distribution conditions of the joint were adjusted based on the introduction of the auxiliary welding current, forming an unbalanced temperature field. The whole welding temperature field of the joint was improved significantly with the increase of the auxiliary current, which promoted the interdiffusion of Al and Fe elements at the interface. Hence, the connection area between Al alloy and steel was increased gradually. The final interface between Al alloy and steel was changed to the Al(s.s) diffusion layer and Fe2Al5 layer. XRD results proved the presence of these phase compositions. When the auxiliary current was 0.3 kA, the maximum thickness of the Al(s.s) diffusion layer and Fe2Al5 layer reached 5.25 μm and 0.86 μm. The final load of the obtained joint with the auxiliary current of 0.3 kA was the maximum and reached 1789.7N, which was approximately 3 times that of the joints without auxiliary current.

Tuning the secondary reaction zone between PtAl coating and nickel based single crystal superalloy during high-temperature oxidation through regulating aluminizing time

Microstructure degradation caused by interdiffusion between coating and superalloy is an important factor affecting the performance of thermal barrier coatings. Tuning the interdiffusion microstructure of PtAl Coatings/Superalloys interface is the key to preparing high performance thermal barrier coatings. In this paper, two β-(Ni, Pt)Al coatings with different compositions and thicknesses were first deposited on the same nickel-based single-crystal superalloy by regulating the aluminizing time. After the isothermal oxidation at 1100 °C, a typical two-layer structure forms in the two different coating/superalloy specimens but with different interdiffusion microstructures. It was found that a noticeable secondary reaction zone (SRZ) with topologically close-packed (TCP) precipitates develop in the specimen with 6 h aluminizing after oxidation for 36 h and its thickness continuously increase. By contrast, no SRZ forms in the specimen with 4.5 h aluminizing after oxidation for even 100 h, but only the microstructure transformation of the interdiffusion zone (IDZ) occurred. That is mainly due to the existence of an incomplete transformed sublayer in the as-prepared specimen with a short aluminizing time, which may affect the subsequent interdiffusion of Al, Ni, and refractory elements. It is highly expected that regulating the aluminizing time is an effective strategy to tune the interdiffusion structure between coating and substrate, which should be helpful for designing the coating/substrate system with better performance.

Effect of rhenium on corrosion behavior of electrodeposited Co-Cu alloy coating at room temperature and high temperature

Rhenium (Re) is a high-performance refractory metal. Adding rhenium to the alloy can significantly improve the overall performance of the alloy. This paper proposes a simple way to prepare rhenium alloy coatings. The microstructure and XRD results show that the addition of rhenium has a certain effect on the alloy coating. Co-Cu-Re alloy coating had a corrosion current density of 3.2 10−6 (A/cm2) in a solution of 3.5% NaCl, which was 3.4 times lower than that of the mild steel substrate and 2.4 times lower than that of the Co-Cu alloy coating. The charge transfer resistance (Rct) is 4512 (Ω·cm2), which is 6 times larger than that of the mild steel substrate and 1.1 times larger than that of the Co-Cu alloy coating. The electrochemical test results show that the addition of rhenium element can enhance the corrosion resistance of the alloy coating. In the high-temperature oxidation experiment, the oxidation rate constant of the rhenium-containing coating was calculated to be the smallest compared with the mild steel substrate and the Co-Cu alloy coating, and it was observed that the addition of rhenium can effectively inhibit the interdiffusion of elements, indicating that the rhenium-containing coating has stronger high-temperature oxidation resistance. Finally, through the XPS characterization of the alloy coating, the mechanism by which rhenium protects the alloy coating in a high-temperature environment is explained. The addition of rhenium has a broader significance in improving the overall performance of the alloy coating, and will promote its wide application in various fields.

Microstructure and magnetic property optimization for Co-rich dual-main-phase Nd-(Fe, Co)-B sintered magnet

High-Co-containing RE-(Fe, Co)-B (RE, rare earth) sintered magnets by dual-main-phase route (DMP, sintering the mixture of Co-free and Co-containing RE2Fe14B powders) were developed in this work, which effectively suppresses the formation of Co-rich intergranular phases and significantly increases the Co-substitution level in Nd-Fe-B magnets. Magnetic properties of Br = 13.74 kGs, Hcj = 13.09 kOe, and (BH)max = 44.32 MGOe were obtained even when 35 at. % Co substitutes for Fe in the dual-main-phase magnets. Phase components analysis indicated that the typical RE(Fe, Co)2 and RE(Fe, Co)4B were detected until the relative concentration of Co up to 35 at. %, which are commonly conceived as harmful to magnetic properties. Microstructural analysis revealed the distribution of each intergranular phase at grain boundaries and the inhomogeneous distribution of RE in the core and shell of the grain. Compared to the addition of Co through alloying, introducing Co by mixing RE-(Fe, Co)-B and RE-Fe-B allows a metallurgical reaction between Co-rich intergranular phases and 2:14:1 matrix phase, accompanied by dramatical elemental interdiffusion during the sintering, thus the formation of Co-rich intergranular phases can be suppressed to a certain extent. These efforts provide another possibility to obtain Nd-Fe-B magnets with higher Co content and achieve better thermal stability.

Microstructure characterization and mechanical properties of the 304SS-(NiTif/FeAl) metal-intermetallic laminate composites

In this work, a novel continuous NiTi Shape Memory Alloy Fiber Reinforced (SMAFR) B2-FeAl based metal-intermetallic laminate (MIL) composite was prepared via two-step vacuum hot pressing combined with “multi-thin foils” stacking configuration. The microstructure characterization of the composite was conducted by using X-ray diffractometer, scanning electron microscopy, electron backscattered diffraction and transmission electron microscopy. The compressive and tensile properties of the composites were measured. Results indicated that the SMAFR MIL composite exhibits multi-layer structure consisting of residual stainless steel layer, newly-formed intermetallic layer and intermediate transition layer. The intermetallic layer is composed of several sublayers with the boundaries of centerlines, and B2-FeAl phase is the main phase in this layer. NiTi fibers locate at the centerlines in the intermetallic layer and show a uniform distribution. A metallurgical interfacial bonding between NiTi fiber and FeAl matrix was obtained through the inter-diffusion of Ni, Ti and Al elements across the interface. In the intermediate transition layer, B2 phase was also the dominant phase, and a large amount of fine Al-rich precipitates dispersed in the matrix. Compared with the MIL composite without NiTi fibers, the SMAFR MIL composite possesses superior compressive and tensile properties, which are mainly attributed to (Ⅰ) high tensile properties of NiTi fiber, (Ⅱ) a good interfacial bonding of NiTi/B2-FeAl, (Ⅲ) strong interfacial reaction products, and (Ⅳ) pullout effect of NiTi fibers.

Cobalt-free nickel-rich cathode materials based on Al/Mg co-doping of LiNiO2 for lithium ion battery

To develop Co-free LiNiO2-based layered cathode materials is crucial for meeting the demands of the lithium-ion batteries with high energy density, long cycling life, and low cost. Herein, the LiNi1-x-yAlxMgyO2 materials are synthesized by the solid–solid interface elemental interdiffusion strategy. It is elucidated that the Mg2+ and Al3+ ions are mainly doped in the Li slabs and transition metal slabs, respectively, leading to the alteration of the crystal lattice. Furthermore, the incorporation of the Mg2+ ions may induce more Ni2+ ions formed in the transition metal slabs, which would have great impact on the electrochemical performance of the materials. The LiNi1-x-yAlxMgyO2 materials with optimized Mg/Al co-doping exhibit much better electrochemical performance than the pristine LiNiO2 and Al-doped LiNiO2 materials, including cycling stability and rate capability. The in-situ XRD characterization and structural analysis show that stabilization of the crystal structure, preservation of the integrity of the secondary particles, and enlargement of the interlayer spacing by the Mg/Al co-doping are the main factors responsible for the superior performance of the materials. The Mg/Al co-doping strategy might be the promising approach for the design of the cobalt-free nickel-rich materials.

In-situ scanning transmission electron microscopy study of Al-amorphous SiO2 layer-SiC interface

Here, we present a comprehensive study on atomic-scale in-situ biasing/heating scanning transmission electron microscopy ((S)TEM) of Al-amorphous SiO2–SiC interface. The investigation includes electrical, chemical, and structural analysis of the interface at different temperatures (25–600 °C). The results show that at ~ 500 °C the electrical (three-orders of magnitude resistivity drop), chemical (dissolution of SiO2 amorphous layer), and microstructural features (e.g. formation of Al2O3, Si and Al4C3) of the interface start to change. According to the results, amorphous SiO2 dissolves in Al, leading to formation of α-Al2O3 and Si within the Al. In contrast, elemental interdiffusion (Al3+ ⇄ Si4+) between Al and SiC occurs resulting in formation of Al4C3. From the results, we can infer that reaction mechanism between Al and crystalline SiC is different with that between Al and SiO2 amorphous phase. It is believed that structural similarities between SiC and Al4C3 play an important role in paving the way for elemental interdiffusion.

An enhanced oxidation resistance in Ti-40Al-8Nb alloys with submicron (ω0+γ) microstructure: A comparative study

Oxidation behavior of Ti-40Al-8 Nb alloys with nearly lamellar structure (as-HIP) and submicron (ω0 +γ) microstructure (as-HT) at 800 °C was comparatively investigated. Results showed that owing to the homogenous refined grains and high γ phase content in as-HT sample, a compact oxide scale with reduced thermal stress formed on its surfaces. Moreover, ω0 phase in the as-HT sample promoted the formation of Nb-rich pegs at oxide scale/substrate interface, which not only inhibited elements interdiffusion but also improved the bonding strength between oxide scale and substrate. As a result, the as-HT sample presented an enhanced oxidation resistance comparing to the as-HIP sample.

Dissimilar diffusion bonding of bulk metallic glass: Amorphous/crystalline atomic-scale interaction

Dissimilar diffusion welding of a copper-based bulk metallic glass (BMG) with a stoichiometry of Cu 50 Zr 43 Al 7 and commercial pure aluminum was performed at evaluated different temperatures (below and higher than the glass transition temperature ~ 440 °C) and holding times (up to one hour). The main goal was to successfully bond these dissimilar materials without crystallizing the BMG part to avoid deteriorating properties. Optimum joining conditions were attained at a temperature of 430 °C (<T g ) and dwell time of 60 min. The diffusion-assisted atomic-scale interactions between the amorphous and crystalline structures were studied using electron microscopy. To this end, the interaction zone at the BMG/Al dissimilar interface was extracted and analyzed by focused ion beam/transmission electron microscopy (FIB/TEM) followed by elemental analysis and high resolution-transmission electron microscopy (HR-TEM) to reveal the nature of the diffused layer and orientation relationships within the structure. Based on microscopy observations, the formation of an interaction layer with a thickness in the range of 1–2 μm was observed, confirmed by diffusion of oxygen to this region. High-resolution atomic-scale observations supposed a gradient transition from crystallinity toward the amorphous state undergoing the formation of some semi-crystalline nano-scale layers. The activation energy for the thermally-assisted diffusion bonding process was estimated at ~486.7 kJ/mol, related to the substitutional diffusion of oxygen through the copper matrix after decomposition of the stable alumina oxide layer on the surface. Accordingly, an increased indentation hardness across the dissimilar interface was observed and attributed to the distribution of elements into the reaction layer and the formation of new phases. • Atomic-scale diffusion bonding of Cu-based BMG to Al was studied by FIB-TEM analysis. • Elemental inter-diffusion in amorphous-crystalline materials interaction characterized. • Decomposition of oxide surface layer and formation of a semi-crystalline phase at the interface associated bonding. • A gradual atomic structure transition from amorphous to crystallinity was revealed across the interface. • The activation energy of the bonding process was estimated at ~486.7 kJ/mol, nearby to substitutional diffusion of oxygen.

Dramatic improvement in the stability and mechanism of high-performance inverted polymer solar cells featuring a solution-processed buffer layer.

In this study, we demonstrate inverted PTB7:PC71BM polymer solar cells (PSCs) featuring a solution-processed s-MoO3 hole transport layer (HTL) that can, after thermal aging at 85 °C, retain their initial power conversion efficiency (PCE) for at least 2200 h. The T80 lifetimes of the PSCs incorporating the novel s-MoO3 HTL were up to ten times greater than those currently reported for PTB7- or low-band-gap polymer:PCBM PSCs, the result of the inhibition of burn-in losses and long-term degradation under various heat-equivalent testing conditions. We used X-ray photoelectron spectroscopy (XPS) to study devices containing thermally deposited t-MoO3 and s-MoO3 HTLs and obtain a mechanistic understanding of how the robust HTL is formed and how it prevented the PSCs from undergoing thermal degradation. Heat tests revealed that the mechanisms of thermal inter-diffusion and interaction of various elements within active layer/HTL/Ag electrodes controlled by the s-MoO3 HTL were dramatically different from those controlled by the t-MoO3 HTL. The new prevention mechanism revealed here can provide the conceptual strategy for designing the buffer layer in the future. The PCEs of PSCs featuring s-MoO3 HTLs, measured in damp-heat (65 °C/65% RH; 85 °C per air) and light soaking tests, confirmed their excellent stability. Such solution-processed MoO3 HTLs appear to have great potential as replacements for commonly used t-MoO3 HTLs.

Study of growth kinetics of intermetallic compounds at BAl88Si/Cu interface

• The diffusion behavior of the elements at the interface is investigated. • The diffusion reactions of the interface are analyzed. • The growth kinetics of the interfacial compound are analyzed. • The interfacial microstructure evolution model of BAl88Si/Cu are established. In this study, the growth of the intermetallic compounds (IMCs) at the BAl88Si/Cu interface was analyzed and its growth kinetics was investigated. The results reveal that Cu 3 Al, Cu 9 Al 4 , Cu 3 Al 2 and CuAl, four-layer IMCs are formed at the interface due to the interdiffusion of copper elements and aluminum elements. The thickness of the IMCs increases with increasing temperature and holding time, the transition from Cu 3 Al 2 to Cu 9 Al 4 is also observed at 893 K. The activation energies of the Cu 3 Al, Cu 9 Al 4 and total IMCs layers are obtained from the Arrhenius equation and are 127.10 kJ/mol, 189.68 kJ/mol and 184.93 kJ/mol, respectively, which provide a reference for assessing the ease of growth of IMCs.

Regulation mechanism of in-situ synthesized (Nb,Ta)C/Ni composite cladding coatings by laser shock peening: Microstructure evolution and electrochemical corrosion behavior

The surface microstructure of (Nb,Ta)C/Ni composite cladding coatings containing in-situ synthesized composite carbides (ISSCC-LCed coatings) was regulated by laser shock peening (LSP). The regulation mechanism of laser shock waves (LSW) on the microstructure evolution and electrochemical corrosion behavior of the ISSCC-LCed coatings was emphatically revealed. Correspondence between corrosion morphology and microstructure was established. Meanwhile, the phase evolution and residual stress variation laws were also tested and analyzed. The obtained results indicated that the LSW-induced surface structure exhibited interphase distribution characteristics of large and small grains through plastic deformation mechanisms such as extrusion, slip, folding, fracture, and cracking. Plastic deformation caused the relative movement of (Nb,Ta)C at the subsurface out of the surface, and the large (Nb,Ta)C fractured and extended over the entire carbide. Furthermore, element interdiffusion phenomenon existed between (Nb,Ta)C and Fe–Ni alloy. The coupling effect of LSW-induced surface fine grains and residual compressive stress inhibited corrosion propagation and improved electrochemical corrosion resistance.

Improving the durability of cobaltite cathode of solid oxide fuel cells - a review.

Solid oxide fuel cells (SOFCs) are highly efficient, low-emission, and fuel-flexible energy conversion devices. However, their commercialization has lagged due to the lack of long-term durability. Among several performance degradation mechanisms, cathode degradation and elemental inter-diffusion of the electrolyte and cathode has been identified as the predominant factors. In the most common SOFC systems, a cobalt-based perovskite material is used, for example LSC or LSCF. These cobalt-based materials offer mixed conductivity and higher concentration of oxygen vacancies as compared to LSM at lower operating temperature leading to favorable reduction kinetics. However, the presence of cobalt results in higher cost, higher thermal expansion co-efficient (TEC) mismatch and most importantly leads to rapid degradation. Various elements like strontium, cobalt, cerium, chromium, or zirconium accumulate or deposit at the electrode-electrolyte interface, which results in sluggish reaction kinetics of the oxygen reduction reaction (ORR). These elements react to form secondary phases that have lower ionic and electronic conductivity, cover active reaction sites, and eventually lead to cell and system deterioration. Over the past decade, several studies have focused on preventative and protective measures to prolong SOFC lifetime which includes novel fabrication techniques, introduction of new layers, addition of thin films to block the cation transport. Such efforts to prevent the formation of insulating phases and decomposition of the cathode have resulted in a remarkable improvement in long-term stability. In this review paper, current research on leading mechanisms responsible for the degradation of cobaltite cathode of solid oxide fuel cell has been summarized and durability improvement strategies of cobalt-based SOFC cathodes have been discussed.