Interstitial Solid Solution Strengthening Research Articles

Effect of Cr addition on the microstructure and mechanical properties of MoNbVTa0.5Crx refractory high-entropy alloys

To increase strength and decrease density of traditional refractory high-entropy alloys (RHEAs), the MoNbVTa0.5Crx RHEAs were synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). The effect of Cr content on microstructure and mechanical properties of the MoNbVTa0.5Crx RHEAs was systematically studied. The results showed the addition of Cr could refine the microstructure, decrease density and increase strength of RHEAs. The microstructure of the sintered alloy was composed of BCC phase and a small amount of oxide phase (Ta2VO6), and Ta2OV6 (200) has a semi-coherent relationship with BCC phase (110), with a lattice mismatch degree of 7.34 %. The compressive yield strength of the MoNbVTa0.5Crx RHEAs initially increased and then decreased with increasing Cr content. The MoNbVTa0.5Cr0.75 RHEAs demonstrated the best mechanical properties, and the compressive yield strength and ultimate compressive strength at room temperature were 3180 MPa and 3596 MPa, respectively, which were far higher than traditional WNbMoTaV RHEAs. And the density of MoNbVTa0.5Cr0.75 RHEAs was 21 % lower than that of sintered WNbMoTaV RHEAs. The strengthening mechanism of sintered MoNbVTa0.5Crx RHEAs involved O/C atoms interstitial solid solution strengthening, grain boundary strengthening, and metal atoms solid solution strengthening, while the contribution of oxide precipitation strengthening was negligible.

Effect of sintering temperature on microstructure and mechanical properties of MoNbVTa0.5Cr high-entropy alloys fabricated by powder metallurgy method

To address the challenges posed by the high density and low plasticity at room temperature of traditional refractory high entropy alloys (RHEAs), the MoNbVTa0.5Cr RHEA was synthesized through a combination of mechanical alloying (MA) and spark plasma sintering (SPS) techniques. The effects of different sintering temperatures on the microstructure and mechanical properties of the alloy were systematically studied. The MoNbVTa0.5Cr RHEA milled up to 60 h was found to have a metastable dual-phase containing a major BCC (a = 3.1474 Å) and Nb-Ta (a = 3.3058 Å) phase. The sintered MoNbVTa0.5Cr RHEA was composed of BCC phase and a small amount of Ta2VO6 at different sintering temperatures. There were a lot of edge dislocations in the BCC matrix near the BCC/Ta2VO6 interface. With the increase of sintering temperature, the grain size of sintered MoNbVTa0.5Cr RHEA gradually increased, while the mechanical properties gradually decreased with the increase of sintering temperature. When the sintering temperature was 1500 °C, the grain size of the alloy was 2.33 μm, the yield strength was 2783 MPa, the compressive strength was 3346 MPa, and the fracture strain was 20.45 %, showing the best comprehensive properties. And the density of MoNbVTa0.5Cr RHEA was 9.11 g·cm−3 and 26 % lower than that of WNbMoTaV RHEA. The specific yield strength of MoNbVTa0.5Cr RHEA prepared in this research was 295.28 kPa·m3·kg−1, which was superior to most RHEAs reported so far. This sintered MoNbVTa0.5Cr RHEA showed an excellent room temperature compression performance, which can be attributed to the co-existence of BCC phase along with the minor Ta2VO6 phases. The high yield strength of MoNbVTa0.5Cr RHEA was mainly attributed to the substitutional solid solution strengthening of metal atoms, the interstitial solid solution strengthening of O atoms and the grain boundary strengthening of ultrafine grains, with contributions to yield strength of 41 %, 28 %, and 24 %, respectively.

The effect of nitrogen on the tensile strength of Ti–22Al–25Nb alloy using laser beam powder bed fusion

Titanium-aluminum (TiAl) based alloys have a wide application prospect in aerospace and auto-industry fields due to low density, good physical and mechanical performances. However, the mechanical strength of TiAl-based alloys is also put forward more stringent requirements with the complexity of the application conditions. In this work, an argon-nitrogen (Ar–N2) reactive atmosphere was designed to achieve nitrogen interstitial solid-solution strengthening of Ti–22Al–25Nb alloy during the laser beam powder bed fusion (PBF-LB) process. An in-depth microstructure and mechanical performance analysis for the as-printed sample under various atmosphere conditions were performed via scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The nitrogen atoms can be dissolved in the octahedral gap of the β phase through the PBF-LB in the Ar–N2 atmosphere, and a small amount of nitride was detected when the volume ratio of Ar to N2 was 95:5. Compared with 100 vol% Ar atmosphere condition, finer grains of the β phase can be obtained after using the mixed gas atmosphere, and the ratio of the O phase was significantly reduced. The yield strength and ultimate tensile strength can be increased from 932 MPa to 947 MPa–1080 MPa and 1099 MPa at room temperature, respectively. At the same time, the elongation reaches ∼11 % while obtaining higher tensile strength. The strength of as-printed Ti–22Al–25Nb alloy was improved by adopting a practical methodology without sacrificing plasticity.

The effects of interstitial oxygen on mechanical properties of TiZrNb medium-entropy alloy over a wide temperature range

Interstitial oxygen plays an important role in the microstructure and mechanical properties of recently developed refractory high-entropy or complex concentrated alloys. However, the mechanical properties of the oxygen-doped complex concentrated refractory alloy over a wide temperature range remain unclear. In this work, the effect of interstitial oxygen on the mechanical behavior of TiZrNb medium-entropy alloys (MEAs) has been investigated. At room temperature (RT), the interstitial oxygen improves the yield strength and tensile ductility owing to interstitial solid-solution strengthening and strain-hardening enhancement. However, simultaneous improvement of the RT strength-ductility by adding interstitial oxygen comes at the expense of increasing the ductile-brittle transition temperature (DBTT). Furthermore, the high-temperature yield strength of TiZrNb alloy can be improved up to 800 °C with the addition of 2 at% oxygen. The results above provide valuable insight into the mechanical properties of TiZrNb MEA, which would contribute to optimizing the high-performance refractory complex concentrated alloys in various applications.

Synergistic strengthening and toughening of eutectic CxCoCr3Fe5Ni high entropy alloy

CxCoCr3Fe5Ni (x=0, 0.1, 0.2 and 0.3, at.%) high entropy alloys (HEAs) were prepared via vacuum induction melting. The effects of carbon content on the microstructures and mechanical properties of the HEAs were intensively investigated. With the increase of the carbon content, the phase structure transforms from a dual-phase (FCC+BCC) to a eutectic mixture (FCC phase + M23C6 carbide). Compared to CoCr3Fe5Ni base alloy, the C0.2CoCr3Fe5Ni eutectic HEA exhibits a significantly improved yield strength (from 307.5 to 378.9 MPa), ultimate tensile strength (from 646.5 to 837.1 MPa), and ductility (from 55.4% to 56.1%). It is shown that these comprehensive enhancements of strength and ductility result from the effect of interstitial solid solution strengthening by carbon alloying and second phase strengthening via the eutectic structure.

Effects of Nd and B contents on property evaluation of (CoCrNi)100-x-yBxNdy medium entropy alloy films

To modify the microstructures and enhance the mechanical properties of CoCrNi medium-entropy alloys films (MEAFs), multiple strengthening will be multiple strengthening methods will be introduced in this study. We will add rare-earth, neodymium, and metalloid, boron, elements into the MEAFs system to introduce precipitation and solid solution strengthening. (CoCrNi)100-x-yBxNdy MEAFs will be deposited onto silicon wafers using magnetron three-target co-sputtering of CoCrNi, B and Nd targets. Nd and B concentrations in CoCrNi-based films were controlled by various sputtering powers. The influences of Nd and B contents on the microstructure of MEAFs were studied by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Meanwhile, mechanical properties were examined by a nanoindentation. The (CoCrNi)100-xBxNdy MEAFs showed an increase in Nd content, rising from 1.37 to 9.70 at.% as the Nd target power increased from 25 to 100 W. The B content began at 0.94 at.%, increasing slightly to 1.59 at.% as the Nd content reached 4.25 at.%. The maximum hardness of 13.28 GPa is exhibited by MEAFs with minor B doping and no Nd, due to interstitial solid solution strengthening. The presence of an amorphous structure initially caused a decreased hardness of 9.81 GPa in MEAFs with 1.50 at.% B and 1.37 at.% Nd. The presence of a small-radius boron atom as interstitial atoms and a large atom of Nd could be the main mechanisms for strengthening, resulting in both solid solution strengthening effects and grain refinement.

Enhancing the strength-ductility synergy in hot-forged Fe50Mn30Co10Cr10 high entropy alloy (HEA) through carbon additions

In this work, we systematically investigated the effect of carbon additions on the microstructure and room temperature mechanical properties of hot-forged Fe50Mn30Co10Cr10 HEA. The different carbon contents were introduced to Fe50-xMn30Co10Cr10Cx (x = 1, 2.5, 6 at.%, hereinafter, referred as C1, C2.5 and C6, respectively) HEAs to enhance the strength-ductility synergy by triggering the multiple strengthening mechanisms. The results showed that the grain sizes were decreased with increasing of carbon content, while a high fraction of mechanical twins ∼45% were generated in C2.5 HEA, and their fractions were ∼35% in C1 and C6 HEAs. Moreover, the discrete nano-sized M23C6 carbides in C2.5 HEA were transformed into continuous mico-sized M23C6 carbides along the grain boundaries in C6 HEA. Therefore, C2.5 HEA possessed high yield strength of 584 MPa, tensile strength of 1.03 GPa and outstanding ductility of 68%, i-e., breaking the strength-ductility paradox. A highest yield strength of∼662 MPa and tensile strength of more than 1 GPa were observed for C6HEA with refine grains, although the ductility was only ∼10%, which indicated that the massive carbon addition could effectively enhanced the strength of HEA but at the cost of ductility due to the presence of coarse M23C6 carbide precipitation. The enhanced mechanical properties of studied HEAs are mainly ascribed to the contribution of multiple strengthening mechanisms including precipitation, grain boundary, dislocation and interstitial solid solution strengthening.

Phase formation and unusual interstitial solid-solution strengthening behavior of (CoCrFeMnNi)Nx high-entropy ceramic films

High-entropy ceramic films (HECFs) have become promising industrial materials due to their excellent mechanical and functional properties. Achieving the precise design of HECFs has been a hot topic in recent years. Herein, the CoCrFeMnNi alloy, one of the most classic high-entropy systems, is chosen as the model to reveal the phase formation, growth, and properties of HECFs. Films were fabricated by magnetron sputtering at various N2-to-total (N2 + Ar) flow ratios (RN). Results show that the phase structure transformed from a semi-crystal phase to a single face-centered cubic (fcc) structure with increasing RN. Atomic migration ability affected by RN drives different growth processes, thereby constructing different microstructures, such as loose fiber structure and stacked particle structure. Moreover, the hardness exhibits a nonlinear relationship with interstitial solid solubility. Such unusual interstitial solid-solution strengthening behavior is attributed to the offset between solid-solution strengthening and grain boundary weakening as RN increases. A high hardness of 13.71 GPa and Young's modulus of 203.3 GPa are obtained in the (CoCrFeMnNi)Nx film deposited at RN = 20 %. This work not only explores an unusual interstitial solid-solution strengthening behavior, but also sheds light on the future HECFs design.

Effects of silicon and neodymium additions on microstructures and mechanical properties of CoCrNi medium entropy alloy films

A series of (CoCrNi)100–x–ySixNdy medium entropy alloy films (MEAFs) with manipulated metalloid element, Si, and rare earth element, Nd, was synthesized using magnetron three-target co-sputtering. A transition from single FCC phase to the coexistence of FCC CoCrNi, HCP CoCrNi and HCP NdNi5 phases was observed in XRD and TEM diffraction patterns with the increasing Nd content for Si content of ∼0.7 at.%, and the SEM and TEM images showed the refined columnar grains. The hardness and compressive yield strength reached the maxima of 10.29 and 4.27 GPa, respectively, in Si0.61Nd5.14 film due to the solid solution strengthening, grain refinement and precipitation strengthening. However, The films exhibited a transition from fully crystalline to crystalline within the amorphous matrix in XRD and TEM results with the increasing Si content for Nd content of ∼2.6 at.%, and the columnar structure disappeared in the SEM and TEM images. The hardness and yield strength increased slightly to the maxima of 9.75 and 4.10 GPa, respectively, in Si0.76Nd2.91 film attributed mainly to the interstitial solid solution strengthening. Discussion on (CoCrNi)100–x–ySixNdy MEAFs showed the optimized mechanical properties in Si0.61Nd5.14 film, indicating that precipitation strengthening and grain refinement could be the major strengthening mechanisms in this system.

Effect of interstitial oxygen /nitrogen on mechanical and wear properties of TiZrHfNb refractory high-entropy alloy

Refractory high-entropy alloy (RHEA), as a kind of promising alloy, has received particular attention in high-temperature applications because of its stability and excellent high-temperature softening resistance. However, most RHEAs are in the strength-ductility trade-off dilemma, which leads to limited applications. In this study, the TiZrHfNb alloy with better ductility is selected as the base alloy, and the strength of the alloy is enhanced by interstitial solid-solution strengthening of O and N atoms, thereby improving the wear resistance of the alloy. All alloys exhibit a body-centered cubic (BCC) structure. The O-doped alloy exhibits a remarkable balance between strength and ductility, while the N-doped alloy displays the highest levels of hardness and yield strength, attributed to the grain boundary strengthening and solid-solution strengthening effects of interstitial atoms. The N-doped alloy has the lowest wear rate at room temperature and 500 ℃, which is attributed to the hardening effect of N atoms. At 25 ℃, the main wear mechanisms are severe abrasive wear, adhesive wear, and oxidative wear. At 500 ℃, the dominant wear mechanisms change to oxidative wear and slight abrasive wear. The oxide layer on the worn surface can decrease the coefficient of friction (COF) and improve the wear resistance.

An exceptionally strong, ductile and impurity-tolerant austenitic stainless steel prepared by laser additive manufacturing

The effective strategy for structural steel with excellent tolerance of impurities is to increase solidification rate to prevent the formation of segregation and intermetallic during fabrication.Carbon (C) and oxygen (O) as impurities in austenitic stainless steel are often controlled at extremely low levels to ease their detrimental effects on toughness and corrosion resistance. Hence, high-quality austenitic stainless steels are poor in impurity tolerance and moderate in strength. Here, we use laser additive manufacturing successfully engineering C, N and O with high contents as interstitial atoms coordinated with Cr in the form of short-range ordered assembly in steel, and develop an impurity-tolerant supersaturated austenitic stainless steel with an ultrahigh strength of 961±40 MPa, a good ductility (37.5 ± 3%), an enhanced corrosion resistance (0.0745 Ecorr/V) and acceptable thermal stability up to 500 °C. First-principles calculations indicate that a coordinated hexahedron C4Cr4, as a stable unit in the austenite, can be assembled via three basic types of stacking. With the presence of N and O, N1C6Cr8, O1C6Cr7 and O1C6Cr8 are also stable coordination assembly units. Such short-range ordered assembly of interstitial atoms can produce significant super-saturated interstitial solid solution strengthening, which is responsible for the enhancement of tensile strength while maintaining ductility. The novel approach in engineering impurities by laser additive manufacturing may open up a new avenue in developing advanced high-impurity-tolerance steels for potential industrial applications at a low cost.

Effect of carbon on microstructure and mechanical properties of Co-free medium-entropy alloys

Effect of carbon content on the microstructure and mechanical properties of a Co-free C x (CrFeNi)100−x (x = 0, 0.5, 1, 1.5, 3, 4.5, and 6 at.-%) medium-entropy alloys were systematically investigated. The increase of carbon content promoted the phase structure of alloys changing from a single FCC phase to an FCC + M23C6 carbides dual-phase structure, accompanied by an apparent increase in yield strength and an uneven decrease in plasticity. The improvement of yield strength was attributed to the interstitial solid solution strengthening of carbon element and the precipitation strengthening of carbides. The decrease of plasticity was related to the formation of coarse carbides. The C1.5(CrFeNi)98.5 alloy exhibited an enhanced yielding strength of 265 MPa while maintained a considerable elongation of 38%.

Insight into the low cycle fatigue deformation mechanisms of minor element doping single crystal superalloys at elevated temperature

The roles of minor elements, usually as grain-boundary strengtheners, in the fatigue properties of single crystal (SX) superalloys have not received adequate attention. Our study reveals that both C and B remarkably increased the stress amplitude, while reduced the cyclic hysteresis energy, under the condition of approximate low cycle fatigue (LCF) lifetime at 980 ºC. In terms of the enhanced fatigue stress, it is considered to be associated with the interstitial solid solution strengthening. Based on the analysis of deformation microstructure, the improved fatigue deformation resistance can be ascribed to the formation of slip bands and a<010> superdislocations in C-containing alloys, whereas, B additions triggered the denser dislocation-tangle at the γ/γ' interface and the homogenization of overall dislocation distribution.

Strengthening of cost-effective Co-free medium entropy alloys by Al/C alloying

The effects of the elemental Al or C addition on the microstructure and room-temperature mechanical properties of a cost-effective Cr12Fe60Mn16Ni12 medium-entropy alloy were investigated. The yield stress of a medium-entropy alloy substantially increased from 230 MPa to 458 MPa following the addition of small amounts of elemental Al (∼2.0 at.%) or C (∼1.0 at.%). Throughout experimentation and theoretical modeling, we were able to systematically show that the improvement in the yield stress following the Al/C addition was attributed to the combination of various strengthening mechanisms, such as grain boundary strengthening, precipitation strengtheing, and solid-solution strengthening mainly caused by the lattice distortion or lattice strain. On the fundamental level, this work provides insights into the effect of the lattice constant on the stress increase for both substitutional and interstitial solid-solution strengthening.

Effect of Nitrogen Doping on the Structure and Mechanical Properties of the Fe40Mn40Cr10Co10 High-Entropy Alloy

The structure and mechanical properties of as-cast and thermomechanicaly processed (cold rolling followed by annealing at 700 °C and 900 °C) Fe40Mn40Cr10Co10 (at.%) high-entropy alloys doped with different amounts (0, 0.5, and 2.0 at.%) of N were examined. The as-cast Fe40Mn40Cr10Co10 alloy (N0) contained σ-phase particles at the boundaries of the fcc grains. The addition of 0.5 (N0.5) and 2.0 (N2) at.% of nitrogen suppressed the formation of the σ-phase due to which the alloys consisted of only the fcc phase. Annealing after rolling resulted in the development of static recrystallization and precipitation of additional phases: the σ-phase was found in the N0 and N0.5 alloys, and hexagonal M2N nitrides were found in the N2 alloy. The strength of the as-cast alloys at room temperature increased with increasing nitrogen concentration due to interstitial solid solution strengthening. Cold rolling and subsequent annealing resulted in considerable strengthening of the program alloys. The strength of the alloys increased with the N content and decreased with increasing annealing temperature. The best combination of mechanical properties at room temperature was attained in the N2 alloy after annealing at 700 °C, and at 77 K, was demonstrated by the N0.5 alloy after annealing at 900 °C.

Effects of carbon addition on microstructure and mechanical properties of Fe50Mn30Co10Cr10 high-entropy alloy prepared by powder metallurgy

To improve the mechanical properties of Fe50Mn30Co10Cr10 high entropy alloy (HEA), a series of carbon-containing HEAs based on Fe50Mn30Co10Cr10 were successfully prepared by powder metallurgy. The effects of carbon content on microstructural evolution and mechanical properties of the as-sintered HEAs were investigated. The improved FCC phase stability and the decreased Σ3 twin grain boundary proportion as the increase of carbon content are mainly due to the increased stacking fault energy. As the carbon content increases, the phase structure of the as-sintered HEAs changes from FCC + HCP phases to FCC phase and then to FCC + M23C6 phases, and the deformation-induced martensitic transformation from FCC to HCP weaken gradually. The solid solubility of carbon in the as-sintered Fe50Mn30Co10Cr10 HEAs is below 2 at.%. A large number of carbides can be observed in the microstructure of the alloys at higher carbon content. The yield strength of the alloys increases approximately linearly with carbon content, while the uniform elongation first increases and then decreases. The (Fe50Mn30Co10Cr10)98C2 HEAs with nano-carbides and ultrafine manganese oxide exhibited a yield strength of 362 MPa, an ultimate tensile strength of 792 MPa, and uniform elongation of 36.7%, showing simultaneous improvement in strength and ductility compared with the carbon-free alloy. This is due to the joint contribution of multiple strengthening mechanisms in the carbon-containing HEA. Interstitial solid solution strengthening and grain boundary strengthening act as the dominant strengthening mechanism. Alloying with carbon element is a feasible method to enhance the mechanical properties of HEAs prepared by powder metallurgy.

In-situ interstitial alloying during laser powder bed fusion of AISI 316 for superior corrosion resistance

• L-PBF of a 316L admixed with 2.5 wt% Cr 2 N enhanced the Cr and N contents as compared to 316L. • A nitrogen content of 0.31 wt% in solid solution was obtained. • The parts were fully austenitic, exhibiting the favorable cellular substructure. • The enhanced nitrogen content improved corrosion resistance and hardness as compared to 316L. • The results show an alternative to manufacturing of high nitrogen steels. The present work explores for the first time additive manufacturing of powder mixtures consisting of Chromium Nitride (Cr 2 N) and AISI 316L with laser powder bed fusion (L-PBF). The addition of 2.5 wt% Cr 2 N to an AISI 316L powder resulted in the successful dissolution of both chromium and nitrogen into a fully austenitic stainless steel microstructure. The nitrogen content was augmented from 0.09 wt% in the as-delivered AISI 316L powder to 0.31 wt% in the L-PBF built part, causing a slight expansion of the austenite lattice. Elongated austenite grains with an internal cellular substructure were obtained in both the Cr 2 N modified 316L and the 316L specimens manufactured by L-PBF. The addition of nitrogen (and chromium) from Cr 2 N resulted in a Vickers hardness increase of about 40 HV 0.1 , mainly by interstitial solid solution strengthening. The modification of 316L by the addition of Cr 2 N significantly improved the corrosion resistance. The improved hardness and corrosion resistance while retaining the manufacturability and cellular microstructure illustrate the potential for modifying the composition and properties of L-PBF 316L with targeted dosing with Cr 2 N powders.

Enhancing mechanical properties of the boron doped Al0.2Co1.5CrFeNi1.5Ti0.5 high entropy alloy via tuning composition and microstructure

High entropy alloys (HEAs) have attracted considerable attention due to their excellent mechanical properties, which provides new insights for designing next generation structural materials. A series of Al0.2Co1.5CrFeNi1.5Ti0.5Bx (x = 0, 0.15, 0.3, 0.45, 0.6, 0.75 and 0.9, in molar ratio) HEAs was prepared by vacuum arc melting to investigate the effect of boron doping on the phase evolution, microstructure transformation and mechanical properties. The results indicated that the HEAs with trace boron doping (x = 0.15) maintained single FCC phase, while it evolved to FCC phase, in-situ borides (TiB2 and Cr2B) and Laves phase when the boron molar ratio higher than 0.3. With the boron molar content increased from 0 to 0.9, the microstructures of the HEAs transformed from complete dendrite to dendrites, irregularly shaped TiB2, needle-shaped Cr2B and lamellar eutectic structure which composed by alternate layers of FCC phase and Laves phase. B doping improved the strength and hardness of the HEAs. The enhanced mechanical properties of the boron doped HEAs was attributed to the synergistic strengthening effect among interstitial solid solution strengthening, second phase strengthening, dislocation strengthening, fine grain strengthening and heterostructure strengthening.

A high-density non-equiatomic WTaMoNbV high-entropy alloy: Alloying behavior, microstructure and mechanical properties

A bulk fine-grained W35Ta35Mo10Nb10V10 (at%) high-density high-entropy alloy (HEA) was successfully fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) with varying parameters. Microstructure evolution and mechanical behavior of the HEA samples in various processing conditions were investigated. The alloying effect in the mixed high-purity powders becomes more significant as the increase of ball milling time during MA. Upon SPS at various temperatures ranging from 1600 to 1800 °C, a supersaturated body-centered-cubic (BCC) matrix prevails with the precipitation of Ta2VO6 oxides. After SPS at 1700 °C for 10 min, the average mass density, ultimate compressive strength and microhardness of the bulk HEA at room temperature are 14.65 g cm−3, 2519 MPa and 6.50 GPa, respectively. The mechanisms responsible for the high strength and hardness include massive substitutional solid solution strengthening by the alloying of multiple principal elements, grain boundary strengthening, precipitation strengthening by Ta2VO6 particles, and interstitial solid solution strengthening by interstitials (e.g., tramp O from processing) in the matrix. The systematic information on the relationships among processing parameters, alloy densities, microstructure characteristics (e.g., grain sizes, volume fractions and sizes of precipitated oxides) and mechanical properties provide useful insights for the development of novel high-density and high-strength materials.

Dual phase equal-atomic NbTaTiZr high-entropy alloy with ultra-fine grain and excellent mechanical properties fabricated by spark plasma sintering

Super-high strength NbTaTiZr high-entropy alloys (NbTaTiZr HEAs) have been successfully fabricated by the mechanical alloying (MA) with spark plasma sintering (SPS) technology, which is 2-fold compared with that of NbTaTiZr HEAs prepared by vacuum arc melting (VAM). After the SPS process, the bulk NbTaTiZr alloy samples are provided with dual-phase body-centered cubic (BCC) structure and nanoscale grain size about 500 nm that is obviously smaller than that of NbTaTiZr HEA fabricated by VAM. When the sintering temperature is 800 °C, the compressive fracture strength is the highest reaching at 2511 ± 78 MPa. When the sintering temperature is 1000 °C, the fracture strain is the highest reaching at 12.8%, and compressive fracture strength and yield strength also reach at 2274 ± 91 MPa and 2172 ± 47 MPa, respectively. The excellent mechanical properties of bulk NbTaTiZr alloy samples are attributed to the merits of MA and SPS, and the collaboration effect of ultra-fine grains strengthening, solid solution strengthening and interstitial solid solution strengthening.