Decrease In Fracture Toughness Research Articles

Fracture Toughness Investigations of an Ion‐Irradiated Nanocrystalline TiZrNbHfTa Refractory High‐Entropy Alloy

Refractory high‐entropy alloys (RHEAs) show potential for use in extreme environments, such as advanced nuclear reactors, owing to their high melting temperature, and often outstanding combinations of mechanical properties, corrosion resistance, and irradiation‐damage tolerance. This study evaluates the fracture toughness of a TiZrNbHfTa RHEA across different scales and microstructures, with a focus on the impact of He2+‐ion irradiation. Micro‐ and millimeter‐scale specimens with nanocrystalline (NC) microstructures are compared to existing ASTM standard sized coarse‐grained (CG) specimen data, with critical dimensions spanning over three orders of magnitude, from 10 μm to 12 mm. The ASTM standard sized CG specimens exhibit a fracture toughness 41‐fold greater than their NC microscale counterparts (210–5.1 MPa m1/2), while NC millimeter‐scale specimens show a 7.5‐fold higher fracture toughness than NC microscale specimens (38.1–5.1 MPa m1/2). He2+‐ion irradiation leads to a 27% decrease in fracture toughness in the NC microscale specimens. The results highlight the impact of sample dimensional scale, microstructure, and ion irradiation on the fracture toughness of the RHEA, indicating a need for thorough examination of such factors when investigating the mechanical properties of these materials.

Analysis of Microwave-Induced Damage in Granite Aggregates Influenced by Mineral Texture

The use of microwave energy to recycle high-quality coarse aggregates from waste concrete or assist hard rock breakage in underground building engineering is promising. Controlling or promoting the damage of coarse aggregates, i.e., hard rocks, under microwave irradiation is a crucial issue faced by these techniques. Understanding the damage mechanisms of hard rocks exposed to microwaves is thus urgent. Fracture toughness is a significant mechanical parameter of rocks that reflects their ability to resist crack propagation and damage evolution. In this study, the fracture toughness degradation of microwave-heated granite was investigated by combining experimental investigations and numerical simulations. A three-point-bending (TPB) experiment was conducted on granite specimens after microwave irradiation. A coupled electromagnetic–thermal–mechanical model considering the actual mineral texture of the granite specimen was established. The evolution of the temperature gradient and stress field near the initial notch tip were investigated. The results suggest that the microwave-induced maximum temperature gradient and stress in granite are at the plagioclase–quartz (Pl–Qtz) interfaces or inside the Pl near the boundary. The region of cracking initiation was defined as the damage zone, which could be obtained by comparing the microwave-induced thermal stress with the critical value. The fracture toughness degradation, which corresponds to the evolution of the damage zones, can be divided into two stages. A relatively rapid decrease in fracture toughness in the first stage is primarily caused by the spread of the scattered damage zones along the Pl–Qtz interfaces; subsequently, a gentler fracture toughness degradation results mainly from the extension of the previous damage zones.

Development and characterization of Al2O3/SrAl12O19 reinforced zirconia with high fracture toughness and low-temperature degradation-resistant for dental applications

The low fracture toughness and sensitivity to low-temperature degradation (LTD) are the primary reasons for the suboptimal long-term performance of dental zirconia. Composite ceramics of zirconia have gained popularity due to their ability to combine the benefits of various reinforcements. In this study, Al2O3-SrAl12O19-3Y/4Y/5Y-ZrO2 composite ceramics were fabricated using the Pechini method, and the optimal sintering temperature and time were investigated. The relative density, microstructure, grain size, mechanical properties, and LTD resistance of the samples were characterized. The results indicated that the composite achieved optimal performance when sintered at 1500°C for 3 hours. Al2O3 and SrAl12O19 primarily influence the properties of the zirconia composite ceramics by modulating their density and grain size. With an increase in the content of Al2O3 and SrAl12O19, the relative density first increases and then decreases, while the grain size exhibits an inverse trend, resulting in an initial increase followed by a decrease in fracture toughness. Additionally, the rate of increase in the m-phase fraction of the zirconia composite slowed down, but it reached a similar level after 64 hours of LTD. The incorporation of 8 vol.% Al2O3 and 8 vol.% SrAl12O19 into 3Y-ZrO2 resulted in a ceramic composite with the highest fracture toughness values and acceptable LTD sensitivity, measured at 5.23 ± 0.25 MPa·m1/2 and 48.35 ± 5.70% m-phase (LTD 64 hours), respectively. This composite also exhibited high bending strength (990.09 MPa) and hardness (16.52 GPa), making it a promising alternative to conventional 3Y-TZP ceramics commonly used in dentistry.

Deterioration of dynamic fracture properties of granite under the coupled effects of hydrochemical solutions and freeze-thaw cycles

Fractured rock mass is a kind of complex rock mass widely existing in engineering projects, which is often subjected to erosion by different pH hydrochemical solutions such as surface water, acid rain, acidic and alkaline wastewater discharge, and deicing salts. When the rock project in a cold region suffers from the coupled effects of hydrochemical solutions and freeze-thaw (FT) cycles, the frost-heave-thaw-shrinkage characteristics of rocks are different from ordinary FT under dynamic loads, and the effect of FT cycles may be enlarged or reduced in different hydrochemical solutions. How to determine the effect of FT cycles on the expansion and changes of rock fractures, which is related to the safety and stability of many engineering rock masses in cold regions. In this study, the microstructure changes of specimens induced by hydrochemical solutions and cyclic FT were measured using nuclear magnetic resonance (NMR) and X-ray diffraction (XRD). The dynamic fracture tests were conducted using single cleavage triangle (SCT) granite specimens. Crack propagation gauge (CPG) was applied to examine crack propagation speed (CPS). The findings indicate that the mineral composition of the granite did not vary large with the hydrochemical solutions and FT cycles, but the maximum diffraction intensity of each mineral composition changed. For the granite under the coupling effect of hydrochemical solutions and FT cycles, the granite specimen in NaOH solution with 100 FT cycles has the highest dynamic fracture toughness and is 10.76 MPa·m1/2, dynamic fracture toughness of H2O, HNO3 and Na2SO4 solutions are only 0.94, 0.91 and 0.93 of that of NaOH solution. With increasing FT cycle times, the dynamic fracture toughness and crack speed decrease, whereas the porosity increases. For the specimen in NaOH solution and 100 FT cycles, dynamic fracture toughness decreased by 18.12 % without FT cycles and crack speed decreased by 34.18 %, the porosity increases by 26.42 %.

Investigation of the mechanical, thermal and wear properties of eggshell/PLA composites

Abstract The current study investigated the potential application of agricultural waste chicken eggshell (CES) as a reinforcement in composites made of poly (lactic acid) (PLA). With the use of twin extruder and injection molding machine, polymer composites have been developed. The performance of the composites was assessed with respect to its mechanical, thermal, and wear properties. It was shown that the increase in eggshell content led to the increase in void content and water absorption. Despite the increase in void content, the mechanical properties, in particular, micro-hardness, tensile strength and flexural strength were significantly improved. Conversely, when the eggshell content increased from 0 to 30 wt%, the impact strength was decreased. A slight decrease in fracture toughness was observed. Thermal properties, such as thermal stability and thermal degradation temperature, were improved with an increase in eggshell content. PLA, PLA-CES-10, PLA-CES-20, and PLA-CES-30 composites exhibited increase in erosion rate by 13.8 %, 10 %, 9 %, and 6 %, respectively, when the impact velocity was increased from 30 m/s to 50 m/s. Data were analyzed statistically with one-way ANOVA and post hoc Tukey’s HSD test (α < 0.05). Overall, PLA/eggshell based polymer composites performed exceptionally well, in addition to their environmental benefits, pollution control, waste utilization, and reduced production cost.

Creep and fracture of UHSC — A microindentation study

Creep and fracture behaviour of normal strength concrete was investigated by various researchers whereas, research on creep and fracture of Ultra-High-Strength Concrete (UHSC), i.e., concrete with 28-day compressive strength greater than 100MPa is scanty. Also, a detailed investigation of the creep–fracture interaction of UHSC has not been conducted.This study aims at examining creep and fracture of UHSC cement paste mixes (w/b = 0.20) with varying levels of silica fume (SF) replacement (0%, 20%, and 40%) at different ages (3d, 7d, 28d, 90d) using microindentation technique. Two different holding durations, namely 5 s and 180 s, were considered in the indentation test. The findings revealed a noteworthy variation in estimated fracture toughness (Kc) between the two dwelling periods. Longer sustained loading times (180s) indicated a decrease in fracture toughness for all ages considered, suggesting progressive internal cracking during creep phase. Attempt has been made to investigate the interaction effect.

Fracture Toughness Investigation of AL6082-T651 Alloy under Corrosive Environmental Conditions

The crack initiation and propagation in an aluminium alloy in a corrosive environment are complex because of the loading parameters and material properties, which may result in a sudden failure in real-time applications. This paper investigates the fracture toughness of aluminium alloy under varying environmental and corrosion conditions. The main objective of the work is to link the interdependencies of humidity and temperature for an AL6082-T651 alloy in a corrosive environment. This study investigates AL6082-T651alloy's fracture behaviour and mechanism through microstructure and fractographic studies. The results show that a non-corroded sample, at room conditions, provided more load-carrying capacity than a corroded sample. Additionally, an increase in temperature improves fracture toughness, while an increase in humidity results in a decrease in fracture toughness.

Capacity fading and inter/intra-granular fracture of polycrystalline cathode particle induced by charge/discharge cycles: A numerical study

The capacity fading of Lithium-ion batteries (LIBs) containing polycrystalline cathode materials can be attributed to the degradation of secondary particles caused by inter- and intra-granular fractures occurring during charging and discharging cycles. In this work, a diffusion-induced stress (DIS) analysis method based on the finite-discrete element method (FDEM) is developed for studying the fracture behaviors of polycrystalline cathodes. The analysis of lithiation and delithiation processes shows that C-rate and interfacial fracture toughness have significant effects on inter-granular crack morphologies. Our method enables precise analysis of the competition between intra- and inter-granular cracks and the effect of crack-impeded diffusion on crack morphologies. We compared numerical simulation results for scenarios where fracture toughness changes with the number of cycles, and demonstrated that the decreasing fracture toughness with cycle number is an important factor contributing to the slow crack growth. Additionally, we established the relationship between crack length and capacity loss, which agreed well with experimental results.

The mode I fracture toughness and acoustic emission characteristics of hot dry rock under temperature effects

The application of liquid nitrogen fracturing technology exhibits promising potential in the exploitation of hot dry rock (HDR). Therefore, studying the variation in granite's fracture characteristics under rapid cooling with liquid nitrogen is highly significant. In this study, the mode I fracture characteristics and acoustic emission (AE) characteristics of thermally treated granite under liquid nitrogen cooling were investigated experimentally. The results indicate that as the temperature increases, both the natural cooling group and liquid nitrogen cooling group exhibit a gradual decrease in granite's fracture toughness, and the cooling effect of liquid nitrogen will further damage the granite. When heated from 25 °C to 600 °C, the natural cooling fracture toughness decreased from 1.089 MPa·m1/2 to 0.1631 MPa·m1/2, with a reduction of 85.0 %; the liquid nitrogen cooling fracture toughness decreased from 1.089 MPa·m1/2 to 0.1493 MPa·m1/2, with a reduction of 86.3 %. Additionally, both the peak load and fracture energy are reduced; intragranular fracture behavior is observed within the granite, resulting in a rougher fracture surface. The integration of a crack classification method based on the rise angle (RA) and average frequency (AF) of AE parameters with the kernel density estimation (KDE) method effectively validates the fracture mechanism of semi-circular bend (SCB) specimens. Meanwhile, based on the AE results during granite fracturing, a method is proposed to discriminate crack types using RA and AF thresholds.

Research on the Fracture Behavior of Ultra-fine Dredged Sand Concrete Based on the Microstructure Characteristics

Abstract The dredged sand generated by the dredging projects has been abandoned and reclaimed from designated areas. It meets the requirements of environmental construction and resource utilization, if the dredging sand can be used as building material in construction. In order to investigate the fracture behavior of dredged sand concrete, five kinds of concrete with different dredged sand replacements (0 %, 12.5 %, 25 %, 37.5 %, 50 %) were designed in this article. Three-point bending fracture tests were carried out on the concrete. The test results show that with the increase of dredged sand replacement, the initiation load, peak load, fracture toughness, and fracture energy first decrease and then increase. Computerized tomography scan and mercury intrusion porosimetry tests show that with the increase of dredged sand replacements, the porosity, pore volume, and pore surface area increase first and then decrease. Dredged sand can improve the pore structure, increase the compactness of concrete, and improve the fracture behavior of concrete. Scanning electron microscopy and X-ray diffraction tests show that dredged sand mainly plays the role of physical filling, and proper dredged sand can improve the compactness of concrete.

The Effect of Sintering Temperature on Phase-Related Peculiarities of the Microstructure, Flexural Strength, and Fracture Toughness of Fine-Grained ZrO2–Y2O3–Al2O3–CoO–CeO2–Fe2O3 Ceramics

The lifetime of products made of ceramic materials is related to their mechanical characteristics such as strength, hardness, wear resistance, and fracture toughness. The purpose of this work was to study the effect of sintering temperature on the phase-related peculiarities of the microstructures, causing changes in the flexural strength and fracture toughness of fine-grained ZrO2–Y2O3–Al2O3–CoO–CeO2–Fe2O3 ceramics. Flexural strength and fracture toughness tests were carried out using ceramics sintered in three modes (2 h at 1550 °C, 1580 °C, and 1620 °C in argon), and thorough phase, microstructure, and fractographic analyses were performed. For the ceramic sintered at 1550 °C, a mixed mechanism of intergranular fracture of the t-ZrO2 phase particles and cleavage fracture of the Ce–Al–O phase particles was found, which is reflected in its comparatively low fracture toughness. For the ceramic sintered at 1580 °C, a fracture developed along the boundaries of the aggregates, made of completely recrystallized fine ZrO2 grains with a high bond strength between adjacent t-ZrO2 grains; this corresponds to the highest fracture toughness (5.61 ± 0.24 MPa·m1/2) of this ceramic. For the ceramic sintered at 1620 °C, a transgranular fracture of the t-ZrO2 phase and Ce–Al–O phase particles and crack propagation along the t-ZrO2/Ce–Al–O interface were revealed; this caused a decrease in fracture toughness.

Physics informed ensemble learning used for interval prediction of fracture toughness of pipeline steels in hydrogen environments

Hydrogen embrittlement leads to a loss of plasticity and a decrease in fracture toughness in pipeline steels. Fracture toughness is a critical factor in the design and safety assessment of hydrogen-carrying pipelines. However, conducting large-scale fracture toughness testing on hydrogen-charged materials is time-consuming and expensive. Analytical approaches based on micromechanics often involve numerous undetermined (or assumed) parameters. Therefore, this study presents an approach that combines physical information and ensemble learning for predicting the fracture toughness range under hydrogen environments. Initially, detailed experimental data are gathered from a series of fracture tests conducted on pipeline steels under hydrogen environments, as published in the literature. Subsequently, Given the limited availability of experimental data, a feature space was constructed, taking into account the physical information as well as the distributions of yield strength and tensile strength. Furthermore, a predictive model based on Population-Based Training (PBT) optimization and Category Boosting (CatBoost) methodology was developed. Comparative experimentation substantiated its superior predictive accuracy in comparison to Random Forest, Adaptive Boosting (AdaBoost), Gradient Boosting Decision Tree (GBDT), Light Gradient Boosting Machine (LightGBM), and Extreme Gradient Boosting (XGBoost). The MAE, MSE, R2, VAF, a20_index and MAPE, was 0.02139, 0.00096, 0.98741, 98.98%, 0.83 and 0.1552. Building upon these foundations, this study proposes an interval prediction method by combining Monte Carlo simulation with point prediction results to obtain fracture toughness interval prediction results with different confidence intervals (80%, 85%, 90% and 95%).

High-temperature mechanical properties and fracture mechanism of A6B2O17 (A= Hf, Zr; B= Ta, Nb) high-entropy ceramics

A6B2O17 (A= Hf, Zr; B= Ta, Nb) high-entropy ceramics are prepared by a solid reaction method, and the temperature-dependent mechanical properties are in situ determined by a high-temperature three-point bending combined with the digital image correlation method. The results show that (Hf1/2Zr1/2)6(Ta2/3Nb1/3)2O17 (H1Z1T2N1) ceramics exhibit superior high-temperature mechanical properties. As the temperature increases from 25 °C to 1200 °C, the fracture toughness and fracture strength decrease from 3.19 MPa·m1/2 to 2.37 MPa·m1/2 and from 97.38 MPa to 72.48 MPa, respectively. The H1Z1T2N1 ceramics still maintain impressive mechanical properties at high temperatures due to the moderate grain size, low porosity and intergranular fracture. Furthermore, the higher entropy (9.61 R J/mol·K) of this ceramic leads to a significant high entropy effect, and the lattice distortion effects cause high-density dislocation regions, inducing a dislocation toughening mechanism.

A study on fracture behavior of SEN natural hybrid composite specimen under tensile load

In this work, two reinforcements (natural jute fiber and glass fiber) hybridized with different volume fractions, are reinforced with a constant volume epoxy resin through hand layup method. The ASTM standard tensile specimen of jute natural epoxy composite of different volume fractions and orientations of fibers, with varied single edge notch (SEN) size were subjected to uniaxial tensile load in universal testing machine. Effect of jute volume fraction, notch size and fiber orientation on tensile strength and fracture toughness has been studied through experimental results. Increased percent of jute fibre showed decrease in tensile strength and fracture toughness. Also, with the increase in notch size, the tensile strength decreased and the fracture toughness increased. Further, the tensile strength and fracture toughness were superior in 0°/90° fiber orientation specimen than those with ±45° fiber orientation. Furthermore, experimental results were validated by conducting statistical and fractographic analysis. The jute fiber percentage was ranked as best level factor affecting the fracture behavior as per taguchi method. Morphological features of fractured surfaces were analyzed through scanning electron microscopic (SEM) images with respect to nature of jute fiber failure under uniaxial loading conditions.

Design of a double-layer composite ceramic and its brazing with niobium

A double-layer composite ceramic incorporating excellent mechanical and joining properties was designed by optimizing the composition of the TiB2–TiC–SiC ceramic. First, the ceramic composition that optimized the mechanical properties was explored by fabricating TiB2–TiC–SiC ceramics with four different compositions. The results showed that the flexural strength of the composite ceramics increased with the increase of TiC component in the composite ceramics, albeit with a slight decrease in fracture toughness. The TiB2–20TiC–20SiC (vol. %) ceramic exhibited excellent mechanical properties with a hardness of 20.6 GPa, fracture toughness of 6.21 MPa ·m1/2, and flexural strength of 486 MPa. Then, the four TiB2–TiC–SiC composite ceramics were brazed with Nb to investigate the ceramic composition that optimized the joining performance. As the TiC component in the composite ceramics increased, the reduction of the Nb3B2 phase and the increment of the (Ti, Nb)2Ni phase within the reaction zone along the ceramic side can be noticed, and the width of this reaction zone decreased from 29 μm to 15 μm. The TiB2–5TiC–20SiC (vol. %) ceramic demonstrated promising joining performance with a maximum shear strength of 229 MPa for its brazed joint with Nb. Finally, a double-layer composite ceramic with the surface composition of TiB2–5TiC–20SiC and base composition of TiB2–20TiC–20SiC was prepared. The maximum shear strength of 248 MPa was achieved by brazing the double-layer composite ceramic with Nb at a temperature of 1433 K for 10 min, representing a 39 % improvement over the unoptimized condition.

Microstructure and properties of intercritically reheated coarse-grained heat affected zone in X65 pipeline steel with pre-strain

The properties of the intercritically reheated coarse-grained heat affected zone (ICCGHAZ) in X65 pipeline steel with large deformation are studied. The ICCGHAZ is composed of acicular ferrite, granular bainite and lath bainite. With the increasing t8/5 (the time for specimens to cool from 800 °C to 500 °C), the sulfide stress corrosion cracking (SSCC) resistance with and without pre-strain both increases, and the secondary cracks propagate along the necklace-type martensite-austenite (M-A)/matrix interface or near the M-A constituents, and the fracture toughness decrease. When t8/5 = 30 s, ICCGHAZ has the most ideal performance on fracture toughness and stress corrosion resistance.

The influence of water-saturation on the strength of volcanic rocks and the stability of lava domes

The rocks forming a volcanic edifice or dome are typically saturated or partially-saturated with water. However, most experiments aimed at better understanding the mechanical behaviour of volcanic rocks have been performed on dry samples, and therefore most large-scale models designed to explore volcano stability have used parameters representative for dry rock. Here, we present a combined laboratory and modelling study in which we (1) quantified the influence of water-saturation on the mechanical behaviour of variably altered dome rocks from La Soufrière de Guadeloupe (Eastern Caribbean) and (2) used these new data to investigate the influence of water on dome stability. Our laboratory data show that the ratio of wet to dry uniaxial compressive strength (UCS) and Young's modulus are ∼0.30–0.95 and ∼0.10–1.00, respectively. In other words, the dome rocks were all mechanically weaker when water-saturated. Further, the ratio of wet to dry UCS decreased with increasing alteration (the wt% of secondary minerals in the rocks). Micromechanical modelling suggests that the observed water-weakening is the result of a decrease in fracture toughness (KIC) in the presence of water. The ratio of wet to dry KIC also decreases with increasing alteration, explaining why water-weakening increased as a function of alteration. To explore the influence of water-saturation on lava dome stability, we numerically generated lava domes in Particle Flow Code using the experimental data corresponding to unaltered and altered rock under dry conditions. The strength of the dome-forming rocks was then reduced to values corresponding to wet conditions. Our modelling shows that, although the stability of the unaltered dome was not influenced by water-saturation, larger displacements were observed for the wet altered dome. Additional simulations in which we modelled a buried alteration zone within an otherwise unaltered dome showed that higher displacements were observed when the dome was water-saturated. We conclude that (1) the water-saturation reduces the UCS and Young's modulus of volcanic rock, (2) larger decreases in UCS in the presence of water are observed for altered rocks, and (3) the stability of a dome can be compromised by the presence of water if the dome is altered, or contains an altered zone. These conclusions highlight that the degree of alteration and water-saturation should be mapped and monitored at active volcanoes worldwide, and that large-scale models should use values for water-saturated rocks when appropriate.

Influence of ZrB2 on Si3N4 ceramics prepared by Si nitridation and hot‐pressing process

AbstractThis work investigated the effect of ZrB2 content on phase composition, relative density, microstructure, and mechanical performance of Si3N4 ceramics prepared by Si nitridation and hot‐pressing method. Si3N4 ceramics were fabricated using Si powder by nitridation and hot‐pressing process. Results showed that the addition of ZrB2 enhanced the transformation of α‐Si3N4 into β‐Si3N4 phase during nitridation, resulting in a greater fraction of β‐Si3N4 (above 90 wt.%) phase in Si3N4 ceramics with ZrB2 after hot‐pressing. In contrast, ceramics without ZrB2 had a lower ratio of β‐Si3N4 (40.4 wt.%). The use of 2.5 vol.% ZrB2 yielded a significant bimodal microstructure and increased fracture toughness to 5.0 ± 0.2 MPa·m1/2, but decreased Vickers hardness to 16.4 ± 0.5 GPa. However, increasing the ZrB2 content to 5 vol.% and 10 vol.% led to a massive formation of equiaxed coarse β‐Si3N4 grains and a significant decrease in Vickers hardness and fracture toughness.

Study on the welding properties of modified N50 CICC jacket for future fusion applications

The modified N50 (N50H) cable-in-conduit conductor CICC jacket developed by China will be applied in China Fusion Engineering Test Reactor (CFETR). Building upon the N50H material, China has developed a corresponding welding material and conducted R&D work on N50H jacket welding. We simulated the N50H jacket welded joint to replicate the entire process of CICC preparation, which includes extrusion, bending, straightening and aging. The magnetic properties of welded joints were evaluated at various temperatures using a physical property measurement system. In addition, the microstructure of the welded joint was studied by various microscopic analysis techniques, and the welded joint showed a stable austenitic structure. Furthermore, mechanical properties of the welded joints were investigated at different temperatures with particular emphasis on their behavior at 4.2 K. The circle-in-square ReBCO conductor jackets welding joint showed a yield strength greater than 1500 MPa, a fracture toughness KIC better than 260 MPa m1/2 and the elongation at break is more than 30 % at 4.2 K. However, a decrease in strength, ductility, and fracture toughness is observed within the welded joints of Nb3Sn conductor jackets after undergoing an aging process. This study will present experimental data on welding joints and discuss the feasibility of N50H as a high-magnetic field jacket material for next-generation fusion reactors.

The Microstructure and Mechanical Properties of High Entropy Alloy CoCrFeNiMn Matrix with Cr3C2 Reinforcement and Ag, BaF2/CaF2 Solid Lubrication

A series of CoCrFeNiMn high-entropy alloy matrix self-lubricating composites were prepared by spark plasma sintering. The composites are composed of an FCC phase, Cr7C3, Ag, and eutectic fluoride BaF2/CaF2 phases. The microstructure of the composites is uniform. The additional phases distribute along the boundary of equiaxed grains of the FCC phase. The compressive yield strength and fracture toughness decrease with the increase of eutectic fluoride BaF2/CaF2. The composites are susceptible to brittle cleavage fracture.