High Entropy Alloy Matrix Composites Research Articles

Additive manufacturing of TiB2-containing CoCrFeMnNi high-entropy alloy matrix composites with high density and enhanced mechanical properties

Near-fully dense CoCrFeMnNi high-entropy alloy (HEA) matrix composites reinforced with 5 wt% TiB2 nanoparticles were successfully additively manufactured via the laser-engineered net shaping technique. Compared to the monolithic CoCrFeMnNi printing process, a higher energy density input is shown to produce a synergic combination of Marangoni flow and capillary force in the laser-generated melt pool. It facilitates the enhancement of wettability, and hence a more uniform distribution of the reinforcement material and a high degree of densification of 99.72%, which are able to delay the early fracture of the material. The as-deposited composites exhibit improved yield strength, surpassing that of the monolithic HEA by 42%. The enhanced strength is mainly ascribed to dispersion strengthening. Besides, the refined grain size, the increased dislocation density, and the additional load transfer effect also contribute to the strength enhancement. Furthermore, the wear resistance properties of the CoCrFeMnNi/TiB2 composite are also shown to be superior to those of the CoCrFeMnNi, indicating a decrease in friction coefficient by 22.4%. The enhanced tribological properties are attributed to the synergic effect of high-hardness and self-lubrication of TiB2 nanoparticles. The findings provide guidelines for achieving high-performance HEA-matrix composites.

Effect of ZrO2 particles on the nanomechanical properties and wear behavior of AlCoCrFeNi–ZrO2 high entropy alloy composites

AlCoCrFeNi-x ZrO2 (x = 0, 5, and 10 (wt. %)) high entropy alloy (HEA) matrix composites were prepared by mechanical alloying (MA) and spark plasma sintering (SPS) methods. Microstructural studies showed that the prepared samples mainly consisted of FCC and BCC phases. Also, small contents of Al-rich and Cr-rich phases were observed. According to microhardness analysis, the addition of 10 wt% monoclinic zirconia enhanced the hardness of FCC and BCC phases from 3.42 to 4.48 GPa and 7.00 to 8.52 GPa, respectively. The wear rate calculations showed that using 5 wt% monoclinic zirconia only slightly improved the wear resistance compared to AlCoCrFeNi HEA sample, due to a balance between the positive effect of zirconia addition and the negative effect of BCC phase decrement. However, the wear resistance was considerably enhanced with increasing zirconia content to 10 wt%. Improved H/E ratio of BCC and FCC phases and the reinforcing effect of zirconia particles in this sample are the main effective factors in the enhancement of wear resistance of AlCoCrFeNi-10 wt% ZrO2 sample. In all samples, there were four wear mechanisms including abrasive, adhesive, oxidation, and delamination.

Processing, microstructure and mechanical properties of Ni1.5CoFeCu0.8Al0.2V0.5 high entropy alloy matrix composites reinforced by in-situ synthesized vanadium carbides

Three in-situ synthesized vanadium carbides (in the volume fraction of 5%, 10% and 15%, respectively) reinforced Ni1·5CoFeCu0·8Al0·2V0.5 high entropy alloy (HEA) matrix composites were prepared by adding V and C in equal molar ratio using mechanical alloying and spark plasma sintering techniques. The formation and evolution of vanadium carbide reinforcements as well as their influences on the microstructure and mechanical properties of HEA matrix composite were investigated intensively. The results show that after milling of 70 h part of V and C from raw materials reacted incompletely through the mechanism of solid-state diffusion at the interface, resulting in the generation of V2C and [VC] in the composite powders. Subsequently, owing to the enhanced atomic diffusion during sintering V2C in the intermediate state was further carbonized into [VC] and partial [VC] was transformed to ordered V8C7 in the consolidated composites. The addition of 5 vol% and 10 vol% vanadium carbides resulted in the significant refinement of grains in the HEA matrix due to the grain boundary pinning effect induced by in-situ generated fine reinforcements. However, grains of the composite containing 15 vol% vanadium carbides are coarser than those of the base HEA due to the serious agglomeration of in-situ synthesized reinforcements. With the increase of vanadium carbides content, mechanical properties of the HEA matrix composite do not change monotonously. The composite reinforced by 10 vol% vanadium carbides performs best among the three and its yield strengths at room temperature, 500 °C, 600 °C and 700 °C are about 1.2, 1.4, 2 and 2.5 times, respectively, than those of the base HEA. The improvement in mechanical properties of composite are attributed to grain boundary strengthening and dispersion strengthening caused by in-situ synthesized vanadium carbide nanoparticles.

Microstructure and mechanical properties of in-situ TiC reinforced FeCoNiCu2.0 high entropy alloy matrix composites

FeCoNiCu2.0 high entropy alloy matrix composites reinforced with different TiC volume fraction (0 vol%, 5 vol% and 10 vol%) were prepared by induction melting. The reaction mechanism in TiC/FeCoNiCu2.0 HEA was studied by thermodynamic analysis and the microstructure of the composites was observed to study the effect of different volume fraction of TiC reinforcement on the mechanical properties of the composites. The results show that all the composites matrix was a solid solution of FCC phase. The reaction mechanism of Ti–C–Cu revealed the formation process of TiC in the HEAs. With the increase of the volume fraction of TiC, the number and size of TiC particles increase and the morphology becomes more uniform. When the volume fraction of TiC reached 10 vol%, the composite has the optimal ultimate tensile strength of 698 MPa, which is 47.6% higher than that of the matrix.

Effect of multiple oxides on the mechanical properties of CoCrFeMnNi high-entropy alloy matrix composites

ABSTRACT This study investigates the oxide formation behaviour and mechanical properties of oxide-dispersion-strengthened (ODS) CoCrFeMnNi high-entropy alloy (HEA) matrix composites produced via powder metallurgy. Grain boundary strengthening, solid solution hardening, and precipitation hardening were controlled by varying the duration of mechanical milling and heat treatment durations. The grain size decreased significantly upon milling and it increased to the range of hundreds of nanometres with the heat treatment. Although ex situ-added Y2O3 nanoparticles were uniformly dispersed in the HEA matrix regardless of the milling duration and heat treatment time, different types of in situ oxides, such as Cr- and Mn-oxides, were formed during the heat treatment. Longer milling times led to more crystal defects (e.g. grain boundaries and dislocations) and stored energy in the HEA matrix, thereby stimulating second phase precipitation and oxide formation. Under optimal conditions, the ODS-HEA composites exhibited a good balance between yield strength and elongation in compression.

In-situ development of MB2 and their effect on microstructure and mechanical properties of refractory Hf0.5Mo0.5NbTiZr high entropy alloy matrix composites

To improve the room temperature comprehensive mechanical properties of the refractory high entropy alloy Hf0.5Mo0.5NbTiZr, boron element is added to form the boride phase as the strengthening phase. The Hf0.5Mo0.5NbTiZrBx (x = 0.1, 0.3, 0.5, 0.7, and 0.9) were produced by vacuum arc melting and effect of boron element on the microstructure and room temperature mechanical properties of Hf0.5Mo0.5NbTiZr alloy was investigated. The boride MB2 phase form and the volume fraction of boride phase increases with the addition of boron element. The microstructure exhibits the evolution from the hypoeutectic structure to the eutectic structure, and then to the hypereutectic structure with the increase of boron element. Because of the difference of the formation path, the morphology and chemical compositions of MB2 phase is different. The lamellar or needlelike MB2 phase forms through the eutectic reaction and is rich in Zr element but poor in Mo and Nb elements. The agglomerated or block sexangle MB2 phase forms as the proeutectic phase and is enriched with Nb element and are depleted with Mo and Zr elements. When the content of the boron is x = 0.1 and 0.3, both the strength and ductility are improved due to the refined structure, the clean interface between the BCC solid solution phase and MB2 phase and the precipitated strengthening of boride phase. And the strength increases dramatically at the expense of the decrease of the ductility with more addition of boron element, which is attributed to the formation of more brittle boride phase

In Situ TiC Particle-Reinforced FeCoCrNiCu High Entropy Alloy Matrix Composites by Induction Smelting

High entropy alloy is a new type of high-performance metal material with high strength, high wear resistance and other characteristics, which has been widely concerned by scholars at home and abroad. In this study, in situ TiC particle-reinforced FeCoCrNiCu high entropy alloy matrix composites were prepared successfully via vacuum induction melting method. X-ray diffraction and scanning electron microscope equipped with energy-dispersive spectrometer were used to analyze the phase, composition and micromorphology of the samples, and tensile properties of the samples were tested at room temperature. The experimental results show that the FeCoCrNiCu high entropy alloy matrix has an equiaxed grain structure, and the TiC-reinforced high entropy alloy matrix composite has a single FCC phase structure. The generation of in situ TiC-reinforced phase makes the composite tensile strength increase, but the elongation decreases. After adding 10 vol% TiC-reinforced phase, the tensile strength of the sample increases from 560.3 to 705.2 MPa, and the elongation decreases from 53.3 to 23.3%.

STUDY ON FRICTION AND WEAR PROPERTIES OF HARVESTING BLADE BASED ON TiC/FeCoNiCuTi HIGH ENTROPY ALLOY MATRIX COMPOSITE

FeCoNiCuTi high entropy alloy (HEA) and TiC/FeCoNiCuTi high entropy alloy matrix composites were prepared by induction electromagnetic melting. The microstructure and composition of the composites were identified by XRD, SEM and EDS. The results show that the composite is FCC crystal form, and square TiC particles are dispersed on the matrix. The wear rate and friction coefficient of the composites were tested by wear resistance testing machine. The effects of friction speed and load on the wear properties of the composites were discussed and the wear mechanism was analyzed. When the load is 200N and the sliding speed increases from 0.2m/s to 0.4m/s, the wear rate of the matrix increases, the wear rate of the composite increases first and then decreases, and the value of the friction coefficient decreases. When the sliding speed is 0.3m/s and the load increases from 100N to 200N, the wear rate of the matrix and the composite increases and the friction coefficient decreases. The wear mechanism is combined wear, with abrasive wear as the main wear at high load and oxidation wear as the main wear at high sliding speed.

Preparation and Mechanical Property of the Ceramic-reinforced Cr0.5MoNbWTi Refractory High-entropy Alloy Matrix Composites

Preparation and Mechanical Property of the Ceramic-reinforced Cr_0.5MoNbWTi Refractory High-entropy Alloy Matrix Composites

Microstructures and mechanical properties of in-situ FeCrNiCu high entropy alloy matrix composites reinforced with NbC particles

A series of NbC/FeCrNiCu high entropy alloy matrix composites (2.5, 5, 7.5 and 10 vol% of NbC) were prepared by vacuum induction melting. The microstructures and mechanical properties of the composites were investigated using X-ray electron diffraction, scanning electron microscopy, transmission electron microscopy, tensile and hardness tests. The results show that the FeCrNiCu high entropy alloy matrix composites are composed of FCC solid solution embedded with NbC particles. A coherent relationship was identified between the alloy matrix and reinforcement phase. The formation of NbC particles increases the hardness from 337.6 HV to 591.3 HV. Moreover, compared with the base alloy, the tensile yield strength, ultimate tensile strength and ductility of the new composite first increases and then decreases with the increase of NbC content. The tensile yield strength, ultimate tensile strength and ductility reaches maximum for the composites containing 5 vol% of NbC, which is 458.2 MPa, 691.6 MPa and 24.7%, respectively. The strengthening mechanisms of the composites are discussed and the contributions of dislocation strengthening, load bearing effect and Orowan mechanism are quantified.

Synergistic strengthening of FeCrNiCo high entropy alloys via micro-TiC and nano-SiC particles

Adding reinforcing phases is an effective method to improve the mechanical performance of high entropy alloys. The strengthening effect of single reinforcement type has thus been studied to a great extend. Here FeCrCoNi high entropy alloy matrix composites embedded with micro-scale TiC and nano-scale SiC particles were fabricated via vacuum inductive melting method. The combined volume fraction of TiC and SiC particles was 10%, while the volume fraction of each particle was varied namely, 10 : 0, 7: 3, 5 : 5, 3 :7, and 0 : 10. The results show that the composite matrix has FCC structure, and the micro- TiC and nano- SiC particles were developed in the matrix through in-situ reactions. When the volume ratio of TiC and SiC particles is 7: 3, the mechanical properties reach the optimal combination. The yield tensile strength of the composite is 498.0 MPa, which is 207.2% higher than that of the matrix. The percent elongation is 41.2%. The strength increase stems from a synergy of grain refinement, thermal mismatch, solid solution, load bearing effect, and Orowan effect.

A powder-metallurgy-based fabrication route towards achieving high tensile strength with ultra-high ductility in high-entropy alloy

The strength-ductility trade-off dilemma is perennially problematic in the materials science community. In particular, the attainability of high tensile strength and large elongation is ambitious in alloys fabricated by powder metallurgy. Here, we demonstrate a powder-metallurgy-based fabrication route to achieve a high synergy of tensile strength and ductility through cold-consolidation of CoCrFeMnNi high-entropy alloy powder using high-pressure torsion followed by annealing. This approach has resulted in an exceptional synergy of high yield strength of 754 MPa with an ultra-high tensile elongation of 58%% which has never been achieved in alloys fabricated by powder metallurgy routes. Additionally, the microstructure can be tuned by annealing treatment to achieve a range of strength and ductility that are highly sought after in industries for a specific application. The present fabrication route can be applied for fabrication of high-entropy alloy-matrix composites using alloys, metals, and ceramic powders to achieve controllable microstructure and eminent tensile properties.

Microstructure and mechanical properties of in situ (TiC + SiC)/FeCrCoNi high entropy alloy matrix composites

In situ (TiC + SiC) particles (5 vol.% and 10 vol.%, respectively)-reinforced FeCrCoNi high entropy alloy matrix composites were fabricated via vacuum inductive melting method, with equal volume fractions of TiC and SiC particles. X-ray diffraction, scanning electron microscope and energy diffraction spectrum were employed to analyze the microstructure and composition of the samples. The results manifested that the FeCrCoNi matrix is composed of FCC phase, and the in situ particles are homogeneously scattered in the matrix. The presence of reinforcements augmented the ultimate tensile strength from 452 to 783 MPa, and raised the yield strength from 162 to 466 MPa at room temperature, whereas the elongation to fracture was reduced from 70.6% to 28.6%. All the tensile fracture surfaces consisted of numerous tiny dimples, indicating that the composites exhibited ductile fracture. Furthermore, the enhancement of strength ascribes to a combination of thermal mismatch strengthening, load-bearing effect, grain refinement, Orowan strengthening and solid solution strengthening effect, which contribute about 58.0%, 2.4%, 12.3%, 11.1% and 16.2% to the improvement of yield tensile strength, respectively.

A Powder-Metallurgy-Based Fabrication Route Towards Achieving High Tensile Strength with Ultra-High Ductility in High-Entropy Alloy

The strength-ductility trade-off dilemma is perennially problematic in the materials science community. In particular, the attainability of high tensile strength and large elongation is ambitious on alloys fabricated by powder metallurgy. Here we demonstrate a powder-metallurgy-based fabrication route to achieve high synergy of tensile strength and ductility through cold-consolidation of CoCrFeMnNi high-entropy alloy powder using high-pressure torsion followed by annealing. This approach has resulted in an exceptional synergy of high yield strength of 754 MPa with an ultra-high tensile elongation of 58% that has never been achieved in alloys fabricated by powder metallurgy routes. Additionally, the microstructure can be tuned by annealing treatment to achieve a range of strength and ductility that are highly sought after in industries for a specific application. The present fabrication route can be applied to fabricate high-entropy alloy-matrix composites using alloys, metals, and ceramic powders leading to a controllable microstructure and eminent tensile properties.

In Situ TiC/FeCrNiCu High-Entropy Alloy Matrix Composites: Reaction Mechanism, Microstructure and Mechanical Properties

In situ TiC particles-reinforced FeCrNiCu high-entropy alloy matrix composites were prepared by vacuum induction melting method. The reaction mechanisms of the mixed powder (Ti, Cu and C) were analyzed, and the mechanical properties of resultant composites were determined. Cu4Ti were formed in the reaction of Cu and Ti when the temperature rose to 1160 K. With the temperature further increased to 1182 K, newly formed Cu4Ti reacted with C to give rise to TiC particles as reinforcement agents. The apparent activation energy for these two reactions was calculated to be 578.7 kJ/mol and 1443.2 kJ/mol, respectively. The hardness, tensile yield strength and ultimate tensile strength of the 15 vol% TiC/FeCrNiCu composite are 797.3 HV, 605.1 MPa and 769.2 MPa, respectively, representing an increase by 126.9%, 65.9% and 36.0% as compared to the FeCrNiCu high-entropy base alloy at room temperature. However, the elongation-to-failure is reduced from 21.5 to 6.1% with the formation of TiC particles. It was revealed that Orowan mechanism, dislocation strengthening and load-bearing effect are key factors responsible for a marked increase in the hardness and strength of the high-entropy alloy matrix composites.

Microstructure, mechanical and tribological properties of CoCrFeNiMn high entropy alloy matrix composites with addition of Cr3C2

CoCrFeNiMn high-entropy alloy (HEA) matrix composites with different mass fraction of Cr3C2 are produced by spark plasma sintering. The composites are composed of HEA's face-centered-cubic and Cr7C3 phases. When addition of Cr3C2 increases, the hardness and yield strength of composites increase. The friction coefficients at room temperature (RT), 200 and 800 °C exhibit a decreasing tendency with the increase of Cr3C2 content. The wear rates decrease from RT to 800 °C when adding 10% Cr3C2 in CoCrFeNiMn HEA. The wear mechanisms of CoCrFeNiMn HEA matrix composites are governed by abrasion and adhesive wear from RT to 400 °C, and change to oxidation wear above 400 °C. Combined the mechanical and tribological properties, CoCrFeNiMn-10% Cr3C2 composite possesses the best comprehensive properties.

Tuning composition and microstructure by doping Ti and C for enhancing mechanical property and wear resistance of Al0.2Co1.5CrFeNi1.5Ti0.5 high entropy alloy matrix composites

Abstract Spark plasma sintering was used to prepare in-situ synthesized TiC reinforced Al0.2Co1.5CrFeNi1.5Ti0.5 high entropy alloy matrix composites with adding Ti and C elements by the molar ratio of 1:1. Face-centered cubic (FCC) solid solution and in-situ synthesized TiC were the main components of the composite. The content of nanocrystals which induced by grain boundary pinning effect of TiC increased with increasing of Ti and C content. The micro Vickers hardness increased from 410 HV0.3 to 850 HV0.3 and the yield strength increased from 1080 MPa to 2164 MPa when the C content increase to the molar ratio of 2.0. Interstitial solution strengthening, dispersion strengthening, grain-boundary strengthening and fine grain strengthening were the main strengthening mechanisms for the in-situ TiC enhanced Al0.2Co1.5CrFeNi1.5Ti0.5 high entropy alloy matrix composites. The wear resistance of Al0.2Co1.5CrFeNi1.5Ti2.5C2.0 composite was about 40 times higher than that of Al0.2Co1.5CrFeNi1.5Ti0.5 high entropy alloy. The reinforcing effect of TiC and the protective effect of TiO2 oxide glaze layer which formed by the in-situ tribo-chemical reaction during the friction process were the main reasons for the improvement of wear resistance.

Grain refinement and localized amorphization of additively manufactured high-entropy alloy matrix composites reinforced by nano ceramic particles via selective-laser-melting/remelting

Abstract Nano TiN-particle reinforced CoCrFeMnNi high-entropy alloy (HEA) matrix composites were additively manufactured via selective laser melting (SLM) and that with a remelting laser-scan strategy (RLSS). The RLSS process promoted the reinforcement-dispersity and thus further refined the HEA matrix grains. The generated hybrid amorphous-crystalline microstructure was benefited by RLSS-SLM to enhance strength and regulate plasticity. The dispersion behaviors and effects of nano TiN-particles were expounded. The amorphous formation mechanism was also discussed.

Effect of Si and C additions on the reaction mechanism and mechanical properties of FeCrNiCu high entropy alloy

FeCrNiCu based high entropy alloy matrix composites were fabricated with addition of Si and C by vacuum electromagnetic induction melting. The primary goal of this research was to analyze the reaction mechanism, microstructure, mechanical properties at room temperature and strengthening mechanism of the composites with addition of Si and C. The reaction mechanism of powders containing (Si, Ni and C) was analyzed, only one reaction occurred (i.e., Si + C → SiC) and its activation energy is 1302.8 kJ/mol. The new composites consist of a face centered cubic (FCC) structured matrix reinforced by submicron sized SiC particles. The addition of Si and C enhances the hardness from 351.4 HV to 626.4 HV and the tensile strength from 565.5 MPa to 846.0 MPa, accompanied by a slight decrease in the plasticity. The main strengthening mechanisms of SiC/FeCrNiCu composites were discussed based on dislocation strengthening, load bearing effect, Orowan mechanism and solid solution hardening, whose contributions to the tensile strength increase are 58.6%, 6.3%, 14.3% and 20.8%, respectively.

Excellent mechanical properties of in-situ TiC/FeCrNiCuV0.1 high entropy alloy matrix composites

Abstract It remains a challenge to enhance strength without sacrificing ductility for high entropy alloys. Here, we prepared in-situ TiC/FeCrNiCuV0.1 high entropy alloy matrix composites using vacuum induction smelting. The new composites exhibit an excellent combination of high tensile strength (1006.5 MPa) and good ductility (15.6%). The improved mechanical properties, as compared to the V-free composites, are attributed to a synergy of solid solution strengthening and grain size refinement.