Room Temperature Compressive Strength Research Articles

The synergistic mechanism of ultrasonic and heat treatment on the composite structure and mechanical properties of Nb-Si-Zr based in-situ composites

Ultrasonic assisted solidification (UST), heat treatment and alloying are all effective methods to control the microstructure of materials and improve their properties. In this paper, the Nb-16Si-20Zr-2C-xW composites were prepared using ultrasonic assisted solidification technology of high temperature melt (≥1800℃) and heat treatment. The influence mechanism of ultrasonic, the W element, and the synergistic regulation mechanism of ultrasonic and heat treatment on the material were studied. Nb-16Si-20Zr-2C-xW(UST) alloys are mainly composed of Nbss phase and γNb5Si3 phase, and their microstructures are mainly divided into strong active zone(SZ) and weak active zone(WZ). In the Nb-Si superalloy melt treated by ultrasonic wave, the area near the ultrasonic sound source is the strong active zone, while the area far away from the ultrasonic sound source is the weak active zone. The features of faceted primary phases and non-faceted primary phases in the SZ and WZ are explained by the equation of undercooling degree at different interfaces and effect of ultrasonic on component undercooling. As the W element content in the alloys (UST) increases, the content of the Nbss phase increases, the median diameter of the primary γNb5Si3 phase decreases, and the room temperature fracture toughness and compressive strength show an upward trend. When the addition amount of W element reaches 2 at%, there are more crack deflections, crack bridging and secondary cracks in the crack propagation path. Through the special arrangement of primary γNb5Si3 phase in the ultrasonic field, the energy density of ultrasonic waves in the melt is calculate to be 33.5 kW/m2. The microstructure of Nb-16Si-20Zr-2C-xW alloys(UST+HT) became more uniform and spheroidize. It is worth mentioning that there are plenty of long strip γNb5Si3 phases with different orientations in the Nb-16Si-20Zr-2C-0.1W(UST+HT) alloy and the long strip γNb5Si3 phases with the same orientation are arranged in a periodic manner. This special composite structure induces crack deflections and branching cracks when cracks propagation, so the room temperature fracture toughness of Nb-16Si-20Zr-2C-0.1 W (UST+HT) alloy reaches 15.66 MPa·m1/2.

Effect of carbon content on the microstructure and mechanical properties of Ti2AlC/TiAl composites with network architecture

In the present work, using pre-alloyed Ti-48Al-2Cr-2Nb powders and graphite powders with different contents as raw materials, the Ti2AlC/TiAl composites with network architecture were fabricated by spark plasma sintering (SPS). The effect of carbon content on the microstructure and mechanical properties of Ti2AlC/TiAl composites with network architecture was investigated. The results have shown that with the increasing carbon content from 0.5 wt% to 2 wt%, the network continuity of Ti2AlC particles gradually transforms from semi-continuous network into quasi-continuous and nearly-continuous network, and the network thickness transforms from 5 to 10 μm into 10∼15 μm and 20∼30 μm. The Ti2AlC/TiAl composite with 1 wt% C shows a better balance of compressive strength and ductility, which the room-temperature compressive strength is 2051 MPa and compressive strain is 30.9 %. The quasi-continuous network structural Ti2AlC particles in Ti2AlC/TiAl composite with 1 wt% C could effectively deplete the crack propagation energy by deflecting the crack, and passivate the crack to hinder further propagation, which facilitates the improvement of the strength and ductility in the Ti2AlC/TiAl composite.

Study on Preparation of Porous Light Refractory from Waste Electric Porcelain

AbstractIn the process of the development of the ceramic industry, a large amount of ceramic solid waste is generated, and how to make high‐value reuse of ceramic solid waste has also become a problem of common concern. In this article, a new method of making porous thermal insulation materials reusing waste electric porcelain was successfully developed. In this work, a porous light refractory with bulk density of 0.99 g/cm3 and apparent porosity of 59% was prepared by the novel method. Which room temperature flexural and compressive strengths are 11.52 MPa and 1.84 MPa, respectively. These properties makes the waste electric porcelain‐based porous light refractory can be applicated as lightweight heat insulation materials for high‐temperature kilns, high‐temperature catalyst carriers, high‐temperature phase‐change heat storage support materials, etc., which will create higher application value and research significance.

Effect of Al Content on Microstructure and Properties of AlxCr0.2NbTiV Refractory High-Entropy Alloys.

High-temperature creep refers to the slow and continuous plastic deformation of materials under the effects of high temperatures and mechanical stress over extended periods, which can lead to the degradation or even failure of the components' functionality. AlxCr0.2NbTiV (x = 0.2, 0.5, or 0.8) refractory high-entropy alloys were fabricated by arc melting. The effects of Al content on the microstructure of AlxCr0.2NbTiV alloys were studied using X-ray diffraction, scanning electron microscopy, and electron backscatter diffraction. The microhardness, compression properties, and nanoindentation creep properties of AlxCr0.2NbTiV alloys were also tested. The results show that the AlxCr0.2NbTiV series exhibits a BCC single-phase structure. As the Al content increases, the lattice constant of the alloys gradually decreases, and the intensity of the (110) crystal plane diffraction peak increases. Adding aluminum enhances the effect of solution strengthening; however, due to grain coarsening, the microhardness and room temperature compressive strength of the alloy are only slightly improved. Additionally, because the effect of solution strengthening is diminished at high temperatures, the compressive strength of the alloy at 1000 °C is significantly reduced. The creep mechanism of the alloys is predominantly governed by dislocation creep. Moreover, increasing the Al content helps to reduce the sensitivity of the alloy to the loading rate during the creep process. At a loading rate of 2.5 mN/s, the Al0.8Cr0.2NbTiV alloy exhibits the lowest creep strain rate sensitivity index (m), which is 0.0758.

Effect of ball milling and solid solution treatment on microstructure and mechanical properties of ZrMgMo3O12p/2024Al composites

The 10 vol% ZrMgMo3O12/2024Al composites were fabricated using the powder metallurgy process and consolidation via vacuum hot pressing. The effects of the ball milling process and solution treatment time on the composites’ microstructure, Vickers hardness, and compressive properties were studied. Increasing the ball milling speed and extending the ball milling duration reduce the size of ZrMgMo3O12 particles, resulting in a more uniform dispersion within the aluminum matrix. Extending the solution treatment duration facilitates the dissolution of more primary Al2Cu phase into the aluminum matrix reducing the presence of coarse primary Al2Cu phase and increasing the number of fine Al2Cu precipitates formed during the aging process. The results indicated that an appropriate increase in ball milling speed, extension of ball milling duration, and solution treatment time can enhance the Vickers hardness and room temperature compressive strength of the composites. Specifically, the composites processed with a ball milling speed of 350 rpm for 6 h, a solid solution treatment at 495 °C for 24 h, and an aging treatment at 190 °C for 8 h exhibited a Vickers hardness of 277 HV and a compressive yield strength of 687 MPa, along with a compressive strain of 7.8 %.

Microstructure, Compressive Properties and Oxidation Behaviors of the Nb-Si-Ti-Cr-Al-Ta-Hf Alloy with Minor Holmium Addition

In the present research, the Nb-Si-Ti-Cr-Al-Ta-Hf alloys with different Ho addition were prepared. Their microstructure, compressive properties and oxidation behaviors were investigated preliminarily. The results exhibit that the Nb-Si-Ti-Cr-Al-Ta-Hf alloy has coarse microstructure which is mainly composed of Nb solid solution, Nb5Si3 and Ti5Si3 phases. The minor Ho addition could refine the microstructure and suppress the precipitation of Ti5Si3 phase. Moreover, the Ho addition also leads to the formation of Ho2Hf2O7, which prefers to precipitate along the Nbss/Nb5Si3 phase interface. Compared with the Nb-Si-Ti-Cr-Al-Ta-Hf alloy, the minor Ho addition improves the room-temperature and high-temperature compressive properties of the alloy. Its room-temperature compressive strength and ductility obtain the maximum value of 1825 MPa and 16.5% when the Ho content is 0.1 at.%. Moreover, its best compressive strength at 873 K, 1273 K and 1473 K is 1495 MPa, 765 MPa and 380 MPa, respectively, when the Ho addition is 0.1 at.%. The oxidation behavior of the Nb-Si-Ti-Cr-Al-Ta-Hf alloy is diversified with the Ho addition. The oxidation rate of the alloy with 0.1 at.% Ho addition is the lowest while the alloy with 0.2 at.% Ho addition is the highest. Therefore, the 0.1 at.% Ho would be the appropriate content for the Nb-Si-Ti-Cr-Al-Ta-Hf alloy.

Effect of heat treatment on microstructural evolution and mechanical properties of the TiAlV0.5CrMo refractory complex concentrated alloy

Ultra-fine grain TiAlV0.5CrMo refractory complex concentrated alloy (RCCA) was prepared by using mechanical alloying (MA) and spark plasma sintering (SPS), and the effects of heat treatment temperature on phase composition, microstructural evolution and mechanical properties were investigated. The results indicate that the phase composition of as-SPSed alloy comprises disordered BCC1 and BCC2 solid solution phases, along with a minor amount of Al2O3 phase. The system demonstrates exceptional microstructural and phase stability after the heat treatment at 1200 °C for 6 h, with only a slight decrease in hardness to a value of 9.86 GPa. With the increase in heat treatment temperature, the volume fraction of recrystallized grains gradually increases, leading to an initial growth and subsequent refinement in grain size. Under heat treatment at 800 °C and 1000 °C, the increase in volume fraction of Al2O3 was found to enhance the room temperature compressive yield strength of the alloy while deteriorating the plasticity. Specifically, the strength-plasticity trade-off was achieved after heat-treated at 1200 °C for 2 h, with a compressive yield strength of 2667 MPa and a plastic strain of 10.7% at room temperature. The excellent mechanical properties were attributed to the synergistic effects of lattice distortions, reduced dislocation density, weakened texture and refined grain structure. Furthermore, this alloy demonstrated a compressive yield strength of 153 MPa at a temperature of 1100 °C without fracturing at a strain of 50%. The flow stresses exhibited typical dynamic recrystallization (DRX) characteristics at elevated temperatures.

Microstructure and characteristics of Cu-W composite prepared by W-coated Cu powder with different W contents

In this study, nanometer W particles were added to Cu matrix as reinforcement phase, aiming to maintain the excellent electrical conductivity of Cu matrix while significantly improving the mechanical performance of Cu-W composite. Cu-W composite powder with W nanoparticle coated Cu was prepared after spray drying and two-step hydrogen reduction. Cu-W composite with different W contents (0 wt%, 5 wt%, 10 wt%, and 20 wt%) were fabricated by spark plasma sintering (SPS). The coating structure can refine Cu particle size and inhibit Cu grain growth during sintering. The impact of W nanoparticles on microstructure, physical and mechanical performance of Cu-W composite was studied. The average size of the W particles dispersed in Cu matrix ranged from 71.89 nm to 106.90 nm. Electron back-scatter diffraction (EBSD) statistics indicated that Cu-5 wt%W, Cu-10 wt%W, and Cu-20 wt%W composite had a mean grain size of 0.76 μm, 0.71 μm, and 0.57 μm, respectively. Cu-20 wt%W composite had a uniform W network-Cu pool structure. The room-temperature tensile strength of Cu-20 wt%W composite was up to 421.98 MPa, with an elongation of 10.91 %; and the room-temperature compressive yield strength reached 313.83 MPa, an increase of 71.76 % compared to pure Cu. Although adding W nanoparticles caused the decrease of electrical conductivity, the conductivity of all Cu-W samples exceeded 81 %. The (111) of Cu and (110) of W showed a semi-coherent relationship with a calculated mismatch parameter δ of 0.077 and good interfacial bonding. The strength of Cu-W composite was improved by the pinning effect of W nanoparticles as a result of the combined effect of fine grain and dispersion strengthening.

Investigation of microstructure evolution and mechanical properties of cold crucible directional solidification Nb-Si alloy

In this work, the microstructure and properties of Nb-16Si-24Zr alloy directionally solidified by electromagnetic cold crucible under different process parameters were investigated. As the pulling rate increases, the size of both primary Nbss and eutectic Nbss decreases, resulting in a straighter primary dendrite γ-Nb5Si3 and a fishbone like Nbss/γ-Nb5Si3 coupling structure of secondary eutectic. As the power supply increases, the size of the nascent Nbss and γ-Nb5Si3 increases, and the coupling growth trend of Nbss and Nb5Si3 weakens. As the pulling rate and power supply increase, the toughness shows a trend of first increasing and then decreasing, while the room temperature compressive strength gradually increases.

Effect of Graphite Powder Addition on Microstructure and Room Temperature Mechanical Properties of Ti-45Al-8Nb Alloys

The enhancement of the mechanical properties of TiAl alloys through the introduction of a second-phase reinforcement is highly essential. In this paper, using graphite powder as a carbon source, the Ti2AlC phase is introduced to improve the compression and friction properties of the TiAl alloy. Concurrently, the effects of graphite powder additions on the microstructure and room-temperature mechanical properties of Ti-45Al-8Nb-xC (mass%) alloys are investigated. The results show that as the volume fraction of Ti2AlC and the interdendritic γ phase increases, the length–diameter ratio of the Ti2AlC phase decreases with increases in the graphite powder addition. The addition of graphite powder results in a refining effect on the grain size and lamellar spacing of the Ti-45Al-8Nb-xC (mass%) alloys. As the graphite powder content increases from 0 to 0.9 mass%, the microhardness increases from 557 HV to 647 HV. The room-temperature compressive strength and strain of the Ti-45Al-8Nb-xC (mass%) alloys first increase and then decrease with the addition of graphite powder. Specifically, when the content of graphite powder is 0.6 mass%, the alloy exhibits a maximum compressive strength and strain of 1652 MPa and 22.2%, respectively. Compared with the alloy without the graphite powder addition, the compressive strength and strain are improved by 37.7% and 62.1%, respectively. The wear resistance of the alloys is improved through the addition of graphite powder and the wear rate decreases from 5.062 to 2.125 × 10−4 mm3·N−1·m−1 as the content of graphite powder increases from 0 to 0.9 mass%.

Improving the mechanical properties and oxidation resistance of Nb-16Si-20Ti alloys with B4C addition

Nb-Si-based alloys, as one of the candidate materials which may replace nickel-based alloys for the next generation aero-engines, its low fracture toughness (KQ) and poor oxidation resistance severely limited their application and development. Research has shown that Nb-Si-based alloys with a refined microstructure usually have good fracture toughness, whereas B and C elements are good microstructure refinement elements. So, the effects of B4C on the microstructure evolution and properties of Nb-16Si-20Ti alloys were studied. The results showed that the microstructure of Nb-16Si-20Ti was composed of Nb-based solid solution (Nbss) and Nb3Si phases. With the addition of B4C, the coarse Nb3Si decomposed and transformed into (α, γ)-Nb5Si3 + Nbss eutectic structure, refining the microstructure of the alloys. The room temperature fracture toughness and compressive strength of Nb-16Si-20Ti alloy were improved by adding B4C, among which the fracture toughness of 0.50B4C alloy was up to 11.5 MPa·m1/2, which increased by 98.3% compared with that of the 0B4C alloy. The improvement of the fracture toughness was mainly due to the increment of the ductile Nbss content in the alloy and the refinement of the microstructure. In addition, the addition of an appropriate amount of B4C (≤0.5 at.%) also improved the oxidation resistance of Nb-Si-based alloys.

Microstructure and high-temperature mechanical properties of Cu-W composite prepared by hot isostatic pressing

In current work, Cu-20wt%W (Cu-20W) composite of near theoretical density (99.69 %) and high electrical conductivity (86.78 %IACS) was fabricated by spray drying technique and hot isostatic pressing (HIP), aiming to enhance the mechanical properties of Cu-W composite while maintaining high conductivity. The impacts of W nanoparticles on the microstructure and properties of Cu-20W samples were evaluated. Adding W nanoparticles can remarkably refine the grain of Cu and strengthen the Cu-W composite through a pinning effect. Room temperature tensile strength and compressive yield strength of Cu-20W composite were 380 MPa and 304.49 MPa, which are 117.14 % and 616.95 % higher than that of pure Cu (175 MPa and 42.47 MPa), respectively. Tungsten nanoparticles can promote the high-temperature reliability of Cu-W samples. Tensile strength of pure Cu and Cu-20W sample gradually decreased with increasing test temperature, but the percentage increment of tensile strength increased. The tungsten particles pinned at grain boundaries during hot deformation inhibit recrystallization grain growth and hinder dislocation movement, thereby contributing to the high-temperature properties of Cu-20W composite. The peak stress of Cu-20W sample is 146.60 % higher than pure Cu, even at close to the melting point of Cu (940 °C). The strength of Cu-20W composite is heightened by combining fine-grain strengthening and dispersion strengthening due to the introduced W nanoparticles.

Design and coherent strengthening of ultra-high strength refractory high entropy alloys based on laser additive manufacturing

The WNbMoTa-based refractory high entropy alloy (RHEA) is expected to become a new generation of high-temperature materials due to its high thermal stability, which can be used in aerospace, nuclear energy and other fields. In this paper, TN10 (TN is the abbreviation of Ti and Ni elements), TN15, TN20 and TN25 non-equimolar WNbMoTa-based RHEAs were designed based on phase engineering and formed by laser powder bed fusion (LPBF) technology. The solidification thermodynamics, microstructure and mechanical properties (compressive strength at 25 °C) of the four alloys were analyzed, and the strengthening mechanism of TN20 alloy was studied. The compressive yield strength of the four alloys exceeds 2050 MPa, the ultimate compressive strength exceeds 2550 MPa, and the elongation exceeds 9%. The compressive yield strength of TN20 alloy is 2513 MPa, the ultimate strength is 3127 MPa, and the elongation is 11.38%. The room temperature (25 °C) compressive yield strength of TN20 alloy is the highest among the high entropy alloys studied so far. TN20 alloy is composed of BCC matrix phase and grain boundary phase containing three different structures, which are B2 TiNi phase, Ni55Nb25Ti15Ta5 phase generating stacking faults and Ni70Ti20Nb10 secondary precipitated phase. The micrometer matrix phase and nanometer grain boundary phase of TN20 alloy show a network distribution in fine crystal region. After the matrix phase cracks due to high thermal stress, the flow TiNi-rich grain boundary phases precipitate to fill the cracks. The grain boundary phase with high proportion in this region is enhanced by the secondary phase and its nanoprecipitated phase. In other regions, stacking faults are generated by the Ni55Nb25Ti15Ta5 phases, which convert the thermal stress that induces crack into lattice defects of the crystal. On the other hand, the content of B2 phase is the highest in grain boundary phase, and the grain boundary between B2 phase and matrix phase is a coherent grain boundary, which realizes the high quality combination of grain boundary phase and matrix phase. The design and strengthening of WNbMoTa-based non-equimolar RHEAs are studied in this paper, which is expected to provide a reference for the design of a new generation of high entropy alloy.

Investigation of Severe Plastic Deformation Effects on Magnesium RZ5 Alloy Sheets Using a Modified Multi-Pass Equal Channel Angular Pressing (ECAP) Technique.

The present study investigates the effects of multiple passes of equal channel angular pressing (ECAP) on magnesium alloy sheets with the assistance of an Inconel plunger along with a die setup having a channel angle of 120° and corner angle of 10° operating at a temperature of 200 °C followed by the required heat treatment processes. The microstructural analysis of the sheet samples at various stages of the multi-pass hot ECAP has shown evidence of ultrafine grain refinement (UFG) due to the occurrence of severe plastic deformation. X-ray diffraction analysis has also exhibited the presence of phases like MgZn and CeZn3 which is supposedly responsible for the enhancement of the mechanical properties. As a result, the room temperature tensile and compressive strengths have improved by 6.12% and 6.63%, respectively, after the second pass, and 11.56% and 15.64%, respectively, after the fourth pass of ECAP. Additionally, the hardness of the sheets has increased by 6.49% and 16.64% after the second and fourth pass of hot ECAP, respectively, mainly attributed to the drastic decrease in grain size from 164 μm to 12 μm within four ECAP passes, all these with a negligible change in ductility. This success in the thermomechanical processing of Mg-RZ5 alloy sheets using a die channel angle of 120° with a minimal number of passes of hot ECAP under a controlled equivalent strain, further opens doors for incorporating optimizations and/or additional aspects so as to achieve even better grain refinements, and consequently, mechanical strength improvements thereby catering to the industrial needs of aerospace and construction areas.

Outstanding strength and toughness in graphene reinforced Nb/Nb5Si3 composites with interfacial nano-phases

Graphene was first employed to improve the mechanical properties of Nb/Nb5Si3 composite, which is a critical candidate for the next-generation of high-temperature structural materials for aero-engines. Microstructures and mechanical properties of graphene reinforced Nb/Nb5Si3 composites with interfacial nano-Nb4C3 phase were systematically investigated. The graphene reinforced Nb/Nb5Si3 composite with outstanding room temperature fracture toughness and compressive strength was fabricated successfully via spark plasma sintering. The microstructure of this composite changes from laminated morphology to uniformly distributed equiaxed microstructure, with the increase of fabrication temperature from 1450 °C to 1550 °C. The high compressive strength of graphene reinforced Nb/Nb5Si3 composites is attributed to the load transfer of graphene, and this load transfer efficiency is strengthened due to the anchoring effect of the interfacial nano-scale Nb4C3 phase. The high fracture toughness of this composite is attributed to the pull-out of graphene, as well as the crack deflection and crack bridging induced by graphene. The laminated architecture is also beneficial to improve fracture toughness because it can promote the minor deflection of cracks. The superior combination of strength and toughness of graphene reinforced Nb/Nb5Si3 composites validates that our design strategy can successfully break through the strength-toughness trade-off. This study is expected to offer a new strategy and theoretical basis for the development of Nb/Nb5Si3 composites with outstanding mechanical properties.

Strengthening in gradient TiAl alloys

Gradient structure is emerging as an effective strategy to fabricate metals with remarkable mechanical performance, but have not been verified in intermetallic compounds for high-temperature applications. Through experiments and atomic simulations, we show that a typical intermetallic TiAl alloy with gradient structure has a significant strengthening effect both at room temperature and high temperatures. The room-temperature compressive strength of TiAl alloys with gradient grain obtained by additive manufacturing is 2.57 GPa, which is ∼2.7 times as strong as that with equiaxed grain. The strengthening effect is attributed to more sessile dislocations in gradient structure caused by the intersections of multiple slip systems in gradient grain. More importantly, the strengthening effect is still effective at high temperatures and the compressive strength is 1.28 GPa at 750 °C. The simulation results show that this strengthening effect is due to the increased Hirth dislocation at high temperatures. This study expands the applications of TiAl alloys for load-bearing structures and provides a new strategy for improving the strength of intermetallic compounds at both room temperature and high temperatures.

Defect elimination and microstructure improvement of laser powder bed fusion β-solidifying γ-TiAl alloys via circular beam oscillation technology

To eliminate metallurgical defects and improve microstructures in laser powder bed fusion (LPBF) β-solidifying γ-TiAl alloys, circular beam oscillation technology was used to fabricate a Ti–43Al–9V-0.5Y alloy in this work. The metallurgical defects and microstructures under conventional linear (non-oscillating) scanning and circular oscillating scanning are first studied in comparison. Then, the microstructural evolution and defect suppression mechanisms under circular oscillating scanning are revealed based on the melt flow behavior. In contrast to the non-oscillating scanning, circular oscillating scanning can better eliminate the pores and cracks of LPBFed Ti–43Al–9V-0.5Y alloy. As the oscillating velocity is decreased, the crack density decreases and the microstructure changes from columnar to equiaxed grains. The crack-free samples with a relative density of 99.98% and fine equiaxed grains are obtained as the oscillating velocity is less than or equal to 100 mm/s. The microhardness (473–581 Hv) of the non-oscillating samples is higher than that (440–487 Hv) of the oscillating samples. The room-temperature compressive strengths (∼1222 MPa and ∼1931 MPa) and tensile strength (∼253 MPa) of the crack-free oscillating LPBFed samples are superior to those of the as-cast counterparts. The suppression of pores is ascribed to the improved keyhole stability, enhanced melt convection as well as escape of bubbles under circular beam oscillation. When the oscillating velocity is less than or equal to 100 mm/s, the sufficient stirring effect of the laser beam promotes the formation of fine equiaxed grains and the reduction of brittle B2 phase content, which effectively inhibits cracking.

Constitutive modeling of Ta-rich particle reinforced Zr-based bulk metallic composites in the supercooled liquid region by using evolutionary artificial neural network

In this study, a series of in-situ Ta-rich particle reinforced Zr-based bulk metallic glass composites were successfully fabricated by arc-melting copper-mold spray casting. The effects of Ta content on the room temperature plasticity, compressive strength and thermoplastic formability were studied. (Zr55Cu30Al10Ni5)94Ta6 showed good comprehensive performance, and it was selected to systematically study the deformation behavior in the supercooled liquid region. Different from the strain softening after stress overshoot in bulk metallic glass, the composites showed work hardening in the late stage. Some classical constitutive models cannot accurately describe these phenomena. The back-propagation artificial neural network optimized by particle swarm optimization and genetic algorithm was used to establish the constitutive model. The particle-swarm-optimization back-propagation network with the optimal topology showed high accuracy and good generalization ability. The results predicted with this model were consistent with the experimental data, providing a powerful approach for describing the hot-deformation behavior of these Zr-based bulk metallic glass composites in the supercooled liquid region.

Synergistic effects of Fe and C on microstructure and properties of Nb-Ti-Si based alloys

Nb-silicide in situ composites have been considered as alternatives applied for nickel-based superalloys in aerospace field. The synergistic effects of Fe and C on microstructural evolution, properties and hot deformation behavior of Nb-24Ti-16Si-2Al-3 V-xFe-yC alloys are investigated. Results show that the microstructure of 4Fe-1 C alloy consists of Nbss/β-(Nb, X)5Si3 eutectics and γ-(Nb, X)5Si3 blocks, while the TiC particles precipitate with the increase of C content. For 6Fe-yC alloys, a new silicide phase Nb4FeSi is formed around the (Nb, X)5Si3 phase. Element Fe is mainly distributed in Nb4FeSi and part of Fe-rich (Nb, X)5Si3, while C is mainly dissolved in TiC particles, followed by Nbss. The orientation relationship of Nbss and TiC in accordance with {110}Nbss//{111}TiC. The room temperature fracture toughness and compressive strength exhibit a trend of enhancing first and then reducing with the co-addition of Fe and C. The KQ value of the 4Fe-3 C alloy reaches the highest with a mean of 14.49 MPa·m1/2. Element C can effectively promote the high temperature compressive strength, and Fe can improve the hot deformability. The initial eutectic coupled structure has evolved into a continuous Nbss matrix with dispersed silicides during hot deformation. Furthermore, the splitting mechanism of silicides during hot deformation is determined.

Anisotropy of mechanical properties in directionally solidified Nb-Si alloys at room temperature compression

The room-temperature compressive strength and deformation mechanisms in directional solidified Nb-Si alloy with different orientations were studied. The Electron Backscattered Diffraction (EBSD) experiment further explained that the orientation relationship between the Nbss phase and the α-Nb5Si3 phase is [001] Nbss // [001] α-Nb5Si3, (110) Nbss // (110) α-Nb5Si3, and the corresponding relationship between the material crystal structure and macroscopic spatial coordinates was established. The anisotropy of mechanical properties and failure mode in the alloys are attributed to the phase structures which are the long rod-like morphology of the α-Nb5Si3 phase growing along [001] and the spatial asymmetry of a single (110) Nbss // (110) α-Nb5Si3 phase interface. The Tsai-Hill criterion was applied to explain the anisotropy of the compressive strength of alloy at an angle to the direction of the heat flow. In addition, phase boundary separation was considered to be an important reason for the higher plasticity exhibited by the [100] compression orientation.