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Carbon fibers (C f) were incorporated into Al 2 O 3 –C refractories to enhance their toughness in this work. The results indicated the 0.3 wt% C f -adding improved the high-temperature bending strength to 1.93 MPa from 1.07 MPa, and led to a 55 % enhancement in thermal shock resistance. The above enhancement could attributed to the in-situ formed SiC coating which was observed on the carbon fiber's surface and strengthened the interface bonding between the carbon fiber and refractory matrix. A solid-liquid diffusion reaction was employed to describe the formation process of in-situ SiC layer on the carbon fibers. Furthermore, the wedge-splitting test with digital images was carried out to investigate the crack-growth trajectory during the splitting process. It was confirmed that C f -adding could enhance the strength and reduce brittleness with the crack-bridging, pullout, and interlock behaviors of carbon fibers in the refractory matrix. [ABSTRACT FROM AUTHOR]

Thermal decomposition behaviors and microstructure evolution of porous Cr 2 AlC pellet samples in a graphite bed (65% N 2 and 35% CO) between 1100 °C and 1500 °C were investigated to explore its potential slag-contact application. A walnut-like structure made of a porous chromium carbides core and Al 2 O 3 shell was confirmed on the original Cr 2 AlC particle because of the formation of Al-depleted Cr 2 Al 1-x C in the graphite bed atmosphere. After heat treatment at 1300 °C, depletion of Al within the Cr 2 AlC particle caused to generate a ∼650 μm thickness CrCx-enriched layer on the sample's surface and a highest Vickers hardness of 13.7 GPa. When the temperature rose to 1500 °C, cracks occurred in the sample because of the volumetric expansion from further decomposition. The degradation mechanism of fine-Cr 2 AlC particles in the range from 1100 °C to 1500 °C was proposed in detail. • The degradation process of the porous Cr 2 AlC samples in a graphite bed between 1100 and 1500 °C was investigated. • A walnut-like core-shell structure, made of porous chromium carbide and dense Al 2 O 3 was confirmed on the original Cr 2 AlC particles. • The porous Cr 2 AlC samples processed a CrCx-enriched shell with a depth of ∼650 μm after being fired at 1300 °C and endowed it with a high Vickers hardness of 13.7 GPa. [ABSTRACT FROM AUTHOR]

CaZrO3 samples were prepared by in situ decomposition pore forming technology in this paper. The influence of calcia/zirconia molar ratio and heating treatment on the microstructure and thermal conductivity of the sintered samples were investigated. The phase analysis of CaZrO3 samples was detected by X‐ray diffraction, and the microscopic morphology of CaZrO3 was observed by scanning electron microscope combined with energy dispersive spectrometer for microzone composition analysis. The results showed that a satisfied CaZrO3 sample could be obtained by in situ decomposition pore forming technology with calcium/zirconium molar ratio of 1:1.02. The CaZrO3 grains were developed better when the samples were preheated at 200°C first and then heated at 1600°C for 3 h. The apparent porosity of CaZrO3 samples were increased to 28.5%, and the thermal conductivity reduced to 1.219 W/(m·K) compared with the heavy CaZrO3 samples, which could be used as CaZrO3 refractory aggregates with the lower thermal conductivity. [ABSTRACT FROM AUTHOR]

The incomplete nitriding and heterogeneity structure of large-size Si 3 N 4 -bonded SiC refractories limited its application in refractories industry. The objective of this work was to provide a way that adding carbon in matrix with the expectations of carbon could reacted with free-Si and transformed into SiC after nitridation. The effects of carbon sources on the bonded morphologies and nitridation process of Si 3 N 4 bonded SiC refractories were investigated. Results indicated the strength and Young’s-modulus of specimen with carbon black increased to 39.4 MPa and 103.89 GPa from 29.8 MPa and 73.43 GPa, respectively. The residual Young’s-modulus also improved from 44.13 GPa to 62.9 GPa after 9-quenching cycles. For specimen with graphite, residual graphite after nitridation resulted in a definite strength decline, but residual strength after quenching was improved. Moreover, analysis results on N-elements indicated surprisingly improvement in the nitriding degree for specimen with carbon black. The microstructure evolution and mechanism associating with the enhanced nitriding process was discussed. [ABSTRACT FROM AUTHOR]

In the refractories processing, developing low cost methods and simplifying the existing technology for manufacturing refractories are always desirable. In this perspective, heat treating in a graphite bed in combination with ferrosilicon sintering additive were used to fabricate self-reaction silicide/nitride-bonded SiC refractories. The influence of ferrosilicon (0–5 wt%) on the microstructure evolution and mechanical properties was investigated. On the one hand ferrosilicon presented between the SiC aggregates boundaries, which indicated that ferrosilicon played a dominant role in the densification of materials. On the other hand the formation of Si 3 N 4 whiskers with tips was encouraged in the presence of ferrosilicon; which suggested that ferrosilicon had catalytic effects on the formation of Si 3 N 4 whiskers via a vapor-liquid-solid (VLS) mechanism. Furthermore, the cold modulus of rupture (CMOR) increased with ferrosilicon content up to 2.5 wt% followed by slight decrease in strength after further increase in the amount of additive. The observed improvement can be attributed to the densification and formation of a new reinforced phase (Si 3 N 4 whiskers with tips). At last, a SiC x O y bonding layer between SiC aggregate and matrix could be distinguished, and a mechanism to explain the formation was suggested. [ABSTRACT FROM AUTHOR]

Al 2 O 3 -Ti 3 AlC 2 -C refractories with different carbon content were prepared by using Ti 3 AlC 2 as substitute for partially graphite. The influences of Ti 3 AlC 2 on microstructure and thermal mechanical properties of Al 2 O 3 -Ti 3 AlC 2 -C refractories were investigated. The drastic deterioration in thermal mechanical properties of Al 2 O 3 -Ti 3 AlC 2 -C refractories was effectively prevented by reducing carbon content from 10 to 4 wt%. Particular attention was paid to the microstructure evolution of Ti 3 AlC 2 , the formations of Al 2 TiO 5 , SiAlON and Al-Si-C-O whiskers were developed to explain the limited fall in strength after thermal shock test in our works. The formation mechanism of the new bonded phases in the specimen with Ti 3 AlC 2 was explained in this paper. [ABSTRACT FROM AUTHOR]

The microstructure evolution of the 7050 Al alloy treated by age-forming was studied using a designed device which can simulate the age-forming process. The grain shape, grain boundary misorientation and grain orientation evolution of 7050 Al alloy during age-forming have been quantitatively characterized by electron backscattering diffraction technique. The results show that age-forming produced abundant low-angle boundaries and elongated grains, which attributed to stress induced dislocation movement and grain boundary migration during the age-forming process. On the other side, the stress along rolling direction caused some unstable orientation grains to rotate towards the Brass and S orientations during the age-forming process. Hence, the intensity of the rolling texture orientation in age-formed samples is enhanced. But this effect decays gradually with increasing aging time, since stress decreases and precipitation hardening occurs during the age-forming process. [ABSTRACT FROM AUTHOR]

The porous MgO–Al 2 O 3 refractory aggregates containing 30–92 wt% Al 2 O 3 were prepared via an in-situ decomposition pore-forming route using magnesite and Al(OH) 3 as starting raw materials. The phase compositions, pore characteristics and mechanical strengths were characterised by means of X-ray diffractometry (XRD), scanning electron microscopy (SEM), and mercury porosimetry measurements, etc. The results showed that the Al 2 O 3 contents in the porous refractory aggregates strongly affected the spinel formation, change of the neck bonds between the particles, pore structure (porosity, average pore size and pore size distributions), and then affected the strengths. The porous MgO–Al 2 O 3 refractory aggregates of 62–72 wt% Al 2 O 3 showed the best combination of high apparent porosities of 42.1–44.2%, high compressive strengths of 51.1–52.0 MPa, high flexural strengths of 17.7–18.6 MPa and small average pore size of 10.81–12.07 μm. [ABSTRACT FROM AUTHOR]

• The novel layered CNTs/Al composites with Cu decorated on CNTs are designed and prepared. • The strength and ductility of CNTs/Al composites are simultaneously remarkable improved. • The enhanced mechanism of Cu nanoparticles on the interfacial structure in CNTs/Al composites is revealed. • A new strategy for overcoming the contradiction between strength and ductility of CNTs/Al composites is proposed. Interfacial bond and structure as key points significant restrict the mechanical properties of carbon nanotubes (CNTs) reinforced aluminum matrix composites (CNTs/Al composites). In order to further enhance the interfacial bond of CNTs/Al composites, this paper proposed a novel fabrication process of CNTs/Al composites with Cu nanoparticles decorated CNTs, which results in the remarkable improvement of strength and ductility of CNTs/Al composites. The in-depth study results from microstructure of layered CNTs/Al composites show that: Cu nanoparticles can repair CNTs structural defects, and passivate the reaction activity of the defect points, which successfully inhibit producing big Al 4 C 3 phase. On the other hand, Cu nanoparticles as a bridge connecting Al and CNTs, can improve the interface wettability, and produce an "Al-Cu-CNT" interlocking effect. Due to the improvement of the interfacial bond and structure between CNTs and Al matrix, the strengthening and toughening effect of CNTs is effectively exerted in the Al matrix composites. Additionally, this work avoids the traditional mismatch relationship between strength and ductility in CNTs/Al composites. [ABSTRACT FROM AUTHOR]

Optimization binding system for refractory castables is significant to enhance the service performance. Hydrotalcite has been considered a promoter for high-temperature performance of basic castables, however, its binding property remains to be improved before practical application. In this work, the thermal activated Mg–Al hydrotalcites were incorporated in magnesia castables, and the mutual influence of pre-calcination temperature on the hydration, microstructure, and strength of castables was investigated. The obtained results indicated that the reconstruction of calcined hydrotalcite took place in the hydration process and effectively motivated the hydrolysis. Hydrate was thus promoted and a relatively dense microstructure of magnesia castables was confirmed by X-ray computed tomography analysis. Hydrotalcite pre-calcinated at 300 °C contributed to the highest early strength for castable, and the high-temperature properties also performed better than that of other pre-calcinated hydrotalcite-adding. The enhancement mechanisms of calcined hydrotalcite were attributed to the two following reasons: (ⅰ) the modified microstructure of magnesia castables from the early stage by hydration process, (ⅱ) the further enhanced sinterability inspired by the appropriate thermal activation effect. [ABSTRACT FROM AUTHOR]

High-purity magnesia refractories were fabricated by brine magnesium hydroxide from the salt-lake brine (Qinghai Salt Lake) and Y 2 O 3 as an additive at 1780 °C. It avoided the substantial CO 2 emissions and ultra high temperature sintering process (＞1900 °C) when compared with the conventional magnesite-calcination technical approach. The results confirmed that Y 2 O 3 was dispersed on the MgO grains boundaries in the fabricated MgO aggregates, resulting in a decrease in apparent porosity and enhancing the grains' boundaries. With 3 wt% addition of Y 2 O 3 , the apparent porosity and bulk density of the sample reached to 15.9 % and 3.10 g/cm3 from 37.9 % to 2.30 g/cm3 of blank control group, respectively. Compared to the blank control without Y 2 O 3 -adding, the sample with 5 wt% Y 2 O 3 exhibited a 54.17 % increase in the resistance to molten slag. SEM results indicated that the incorporation of Y 2 O 3 in samples increased the porosity of small pores and enhanced grains boundaries, thereby suppressing slag's penetration. Furthermore, the Y 2 O 3 -adding was employed to disperse the MgO grains boundaries and existed as separate phases for grains boundaries enhancement. The slag attack of the fabricated MgO–Y 2 O 3 refractory raw materials were controlled by an inter-crystalline corrosion process. [ABSTRACT FROM AUTHOR]

C 3 A-containing CaO specimen was prepared and the evolution of its microstructure during hydration process was investigated to clarify the protective mechanism of tricalcium aluminate (C 3 A) on hydration resistance of CaO specimen. The slit-shaped micropores were formed on the grain boundary of CaO due to the stacking of lamellar C 4 AH 13 formed by the hydration of C 3 A. The contact area of residual C 3 A with the moisture was reduced by the porous C 4 AH 13 layer at the original site, which resulted in a slower dissolution rate of C 3 A grain through the porous layer. In addition, the crack propagation and the formation of macropores were inhibited by the pinning effect of C 4 AH 13 , which was beneficial to the improvement of hydration resistance. [ABSTRACT FROM AUTHOR]

The stability of the thermo-mechanical properties of magnesia castables is critical for both the service life of castables and the steel cleanliness. In this study, simultaneous use of magnesium-aluminum hydrotalcite and hydratable alumina was determined to improve the mechanical strength and volume stability of magnesia castables. Hydrotalcite was decomposed to magnesium aluminate spinel and reactive MgO below the medium temperature, which accelerated sintering reactions in magnesia castables and further promoted the formation of spinel and forsterite at high temperature. Suitable volume stability was presented as a consequence of the improved sinterability. The thermo-mechanical properties of magnesia castables were also enhanced. A modified three-dimensional microstructure with the fewer and smaller pores in this optimized magnesia castable at the same time was verified by X-ray micro-computed tomography technology. A correlation analysis identified bending strength and compressive strength of castables having the strongest relationship with the spatial porosity and the number of pores in a diameter range of 0.3–0.5 mm. [ABSTRACT FROM AUTHOR]

• Corroded microstructure of a Cr 2 O 3 -Al 2 O 3 -ZrO 2 refractory brick used in a gasifier was fully characterized, revealing four separate layers. • Behaviors of the main corrosive constituents (Fe, Si) involved in the corrosion process were examined. • An isolation layer comprising (Mg, Fe2+)(Cr, Fe) 2 O 4 complex spinel was formed on the refractory's surface. • A corrosion model was introduced to discuss corrosion behaviors of Cr 2 O 3 -Al 2 O 3 aggregates under different slag concentration gradients. Corroded microstructure of a Cr 2 O 3 -Al 2 O 3 -ZrO 2 refractory brick after 4200 h service in a gasifier was investigated. An isolation layer comprising mainly (Mg, Fe2+)(Cr, Fe) 2 O 4 complex spinel was formed on the refractory's surface, which effectively suppressed the infiltration of main corrosive constituents in the slag (Fe X O, MgO). Furthermore, a quantitative analysis of main corrosive elements in the corroded/uncorroded interface was carried out based on EDS mapping. The results indicated that the overall corrosion depth was dependent on the penetration distance of Fe X O. Finally, the corrosion behavior of Cr 2 O 3 -Al 2 O 3 aggregates in the refractory was investigated, and a dissolution-phase separation-crystallization mechanism proposed. [ABSTRACT FROM AUTHOR]

In this study, two kinds of MgO ceramic filters were prepared by using porous magnesia powder and fused magnesia powder as raw material, respectively. The microstructures, mechanical properties and purification efficiency on the molten steel of two MgO ceramic filters were investigated by mercury porosimetry measurement, SEM, EDS and immersion test with molten steel, etc. The results demonstrate that compared with the filter FM prepared from the fused magnesia powder, the rheological property of the slurry of the filter PM was improved via the finer and uniformly distributed nano-sized Mg(OH) 2 particles generated by the hydration of the porous magnesia powder, which not only optimized the macropore structure but also promoted the growth of the sintering neck between the microparticles of the skeleton. Therefore, the MgO filter skeleton with a microporous structure was obtained, which elevated the strength and thermal shock resistance of the filter PM. According to the immersion tests with the molten steel, both filters significantly reduced the number of inclusions with size < 5 µm2 in the molten steel as well as their total oxygen contents, and the filter PM had better purification efficiency than the filter FM. The reason for the better purification efficiency of the filter PM was related to its smaller micro-sized pores, larger surface roughness, and certain high-temperature liquid phase in their skeletons. In general, the porous magnesia powder resulted in higher compressive strength, better thermal shock resistance and superior purification efficiency on the molten steel of the filter compared with the fused magnesia powder. [ABSTRACT FROM AUTHOR]

Porous spinel (MgAl 2 O 4 ) ceramics were prepared from magnesite and Al(OH) 3 with TiO 2 addition through an in-situ decomposition pore-forming technique. The porous ceramics were characterized through X-ray diffractometer (XRD), scanning electron microscopy (SEM), and mercury porosimetry measurements, etc. The effect of TiO 2 addition on the phase compositions, pore characterizations and strengths was investigated. The results showed that the amount of TiO 2 added (ATA) affected the formation of liquid phase at sintering temperature, changed the porosity, the pore size distribution and the neck bonds, thus affecting the strength of the porous ceramics. With an increase in ATA, the liquid content at sintering temperature increased, the neck bonds developed better, the porosity decreased, and the average pore size and strength increased. The optimized product is a specimen with 1.5 wt% ATA which has a high apparent porosity (53.0%), a small average pore size (5.95 μm), a high compressive strength (21.2 MPa), a high flexural strength (8.5 MPa) and a relatively homogeneous pore size distribution. [ABSTRACT FROM AUTHOR]

Abstract The microstructure, precipitation hardening and magnetic properties of melt-spun Fe 78 Co 11 Mo 11 and Fe 74 Co 11 Mo 11 B 4 alloys were studied. It is shown that B addition increases the precipitation reaction temperature of the supersaturated matrix from 605 °C for the Fe 78 Co 11 Mo 11 alloy to 640 °C for the Fe 74 Co 11 Mo 11 B 4 alloy. In the Fe 78 Co 11 Mo 11 alloy, a cotton-shaped (Fe,Co) 7 Mo 6 precipitate is observed inside the grains of the matrix phase. In the Fe 74 Co 11 Mo 11 B 4 alloy, in addition to the (Fe,Co) 7 Mo 6 phase, spherical MoB 2 precipitates are also observed. Compared to the Fe 78 Co 11 Mo 11 sample, the Fe 74 Co 11 Mo 11 B 4 sample exhibits a finer and more homogeneous microstructure with more equiaxed grains. This finer microstructure explains the enhanced hard magnetic properties in the Fe 74 Co 11 Mo 11 B 4 sample (M r = 60.4 A m2/kg, i H c = 20.8 kA/m) compared to those of the Fe 78 Co 11 Mo 11 sample (M r = 56.5 A m2/kg, i H c = 17.3 kA/m). Furthermore, the Fe 74 Co 11 Mo 11 B 4 sample shows better antioxidant ability than the Fe 78 Co 11 Mo 11 sample, especially when the temperature exceeds 400 °C. Highlights • B addition enhances the hard magnetic properties of the Fe-Co-Mo alloy. • The (Fe,Co) 7 Mo 6 and MoB 2 phases can be observed in the annealed Fe-Co-Mo-B alloy. • B addition leads to the formation of finer and equiaxial grains in the Fe-Co-Mo. • Fe-Co-Mo-B has higher precipitation temperature (640 °C) than Fe-Co-Mo (605 °C). • The Fe-Co-Mo-B alloy shows better antioxidant ability than the Fe-Co-Mo alloy. [ABSTRACT FROM AUTHOR]

In this study, we investigated the annealing process of a cold-rolled dual-phase Mg-10Li-3Al-2.8Zn alloy and used the crystal defect strengthening model to explain the strengthening mechanism of the annealed Mg-Li alloy. To maximize the strength of the alloy, it is annealed at 553 K for 1 h and then water quenched. The maximum yield strength is 321 MPa and the ultimate tensile strength is 346 MPa. Compared with the cold-rolled alloy, the yield strength is increased by 145 MPa and the ultimate tensile strength is increased by 139 MPa. The high strength of annealed alloy is the result of solution strengthening, fine grain strengthening, second phase strengthening and dislocation strengthening, in which solution strengthening contributes the most. The size, content and distribution of the second phase AlLi and MgLi 2 Al have significant effects on the strength of the alloy. Higher annealing temperature and rapid cooling are all conducive to the dissolution of AlLi in the matrix, lower temperature and rapid cooling are conducive to the solid solution of MgLi 2 Al, and higher on the contrary, MgLi 2 Al will be precipitated quickly at a high temperature. Hard AlLi and MgLi 2 Al both cause the strengthening of the second phase, but their strengthening effect are far less than that of the second phase solid solution in β-Li. • The maximum yield strength is 321 MPa and the ultimate tensile strength is 346 MPa. • Solution strengthening contributes the most in the high strength of annealed alloy. • The second phase AlLi and MgLi2Al have significant effects on the strength of the alloy. [ABSTRACT FROM AUTHOR]

(TiB/Ti)-Ti 3 Al micro-laminated composites have been successfully produced by reaction annealing using in-house fabricated TiB/Ti composite foils and commercial pure Al foils as starting materials. The resulting (TiB/Ti)-Ti 3 Al composites showed a unique microstructure which was comprised of alternating TiB/Ti composite layers and Ti 3 Al layers. Microstructure of (TiB/Ti)-Ti 3 Al micro-laminated composites was characterized systematically by optical microscopy (OM) and scanning electron microscopy (SEM). Furthermore, formation mechanism of the novel micro-laminated structure was discussed. The (TiB/Ti)-Ti 3 Al micro-laminated composites exhibited a desired combination of the enhanced tensile strength with the superior ductility as compared to monolithic Ti 3 Al. This could be likely attributed to the introduction of ductile TiB/Ti composite layers and the formation of unique micro-laminated structure. It is noteworthy that fracture toughness of the (TiB/Ti)-Ti 3 Al micro-laminated composites had a sharp increase, 1.5 times higher than that of monolithic Ti 3 Al. [ABSTRACT FROM AUTHOR]

With the characterization of microstructure and tensile properties, the feasibility of preparing Fe 50 Mn 30 Co 10 Cr 10 high-entropy alloys (HEAs) via powder metallurgy was explored, and the effect of sintering temperature and deformation temperature on the microstructure and tensile properties of the alloy was investigated. The alloys sintered at different temperatures possessed a dual-phase structure with face-centered cubic (FCC) and hexagonal close-packed (HCP). The average grain size, HCP phase fraction, and twinning boundary fraction increased with the sintering temperature. The best combination of strength and ductility was obtained in the alloy sintered at 1000 °C, which exhibited a strongly temperature-dependent mechanical behavior, i.e., when the deformation temperature decreased from 298 to 77 K, the yield strength and ultimate tensile strength increased from ∼287 to ∼490 MPa and from ∼745 to ∼1107 MPa, respectively, with only a tiny loss of uniform elongation; this is mainly attributed to the deformation mode of the alloy varied with deformation temperature. During tensile deformation at 298 K, dislocation slip, phase transformation, detwinning of annealing twins, and mechanical twinning were the dominant mechanisms, while no mechanical twinning was activated at 77 K. The excellent combination of strength and ductility for the alloy at 77 K relative to 298 K is mainly attributed to a more significant TRIP effect. Powder metallurgy can be used as a promising way for manufacturing metastable high entropy alloys with excellent tensile properties. • The metastable Fe 50 Mn 30 Co 10 Cr 10 HEAs were prepared via powder metallurgy. • The properties of the HEAs can be adjusted by changing the sintering temperature. • A stronger TRIP effect was observed at 77 K than at 298 K. • The strength increased at 77 K relative to 298 K with only a tiny loss of elongation. [ABSTRACT FROM AUTHOR]

Evident tension-compression yield asymmetry limited the potential use of the extruded Mg-4.58Zn-2.6Gd-0.18Zr alloy as a structural material. Pre-torsion deformation (free-end torsion) was conducted on the extruded alloy and its effects on microstructure and tensile-compressive mechanical properties were investigated in this study. It was found that the as-extruded alloy exhibited homogenous microstructure and <100>−<110 > double-peak fiber texture. Gradient structures along the radial direction were formed after pre-torsion, which contained gradient distribution of dislocations, grain size, {102} extension twin lamellas and texture components. <100>−<110 > double-peak fiber texture was gradually weakened with the torsional angle increasing from 90° to 135° and 180°, and it was related with the re-orientation of extension twinning and dislocation movement. Moreover, extension twinning was more easily to be activated in grains with <110> fiber texture component, and this phenomenon was revealed by calculating the global Schmid factor of extension twinning under pure shear stress state. Tensile and compressive yield strength increased monotonically with the increasing torsional angle. Meanwhile, ductility almost remained unchanged. Tension-compression yield asymmetry was gradually reduced, and it was eliminated after 180° pre-torsion, which was attributed to the texture weakening. The studying provided a promising and cost-effective method to enhance yield strength and reduce tension-compression yield asymmetry while also keep ductility for extruded Mg alloys. [ABSTRACT FROM AUTHOR]

In the field of metal materials, deformation and annealing play an irreplaceable role in improving the microstructure and optimizing the properties. In this study, we prepared Al 0.5 CoFeCrNiSi 0.25 dual-phase high-entropy alloys (DHEAs) by vacuum arc melting and investigated their microstructure evolution and mechanical properties at different rolling and annealing temperatures. The results showed that the volume ratio of the FCC phase remained largely unchanged with increasing annealing temperature, with only small recovery for 10% reduction alloy. In contrast, the volume fraction and recrystallization ratio of the FCC phase in a 40% reduction alloy increased, and its recrystallization rate was higher than that of the BCC phase. Annealing the alloys at 900 °C formed the FCC, BCC, σ, L1 2, and B2 phases. As the annealing temperature increased to 1100 °C, the lamellar structure was changed, and the L12 and σ phases dissolved, leading to the gradual increase in the spacing size and volume fraction of the FCC phase. Increasing the annealing temperature reduced the yield strength but enhanced the ductility of DHEAs. Annealing for 1 h at 900 °C after 40% cold rolling enhanced their strength to 1360.61 MPa due to the high dislocation density and presence of σ phases but led to poor ductility. Annealing for 1 h at 1100 °C after 40% cold rolling produced a good combination of tensile strength (∼1267.8 MPa) and ductility (uniform elongation of ∼34.4%). Such remarkable strength and ductility may be attributed to the increased volume fraction of the FCC phase and the dual-phase heterogeneous deformation induction strain hardening effect. [ABSTRACT FROM AUTHOR]

In the present study, FeCoCrNiMnSi x (x = 0, 0.1, and 0.2, molar ratio) high-entropy alloys (HEAs) were prepared via arc melting, and subsequently deformed via cold rolling and annealing (CRA). The effects of Si content and annealing temperature on the microstructural evolution and tensile properties of the alloys were systematically investigated. The results indicate that a single-phase FCC structure of coarse-grained FeCoCrNiMnSix HEAs was obtained after homogenized annealing (HOA), and the distribution of each element was uniform. When the molar ratio of Si was increased from 0 to 0.2, the strength of the HOA HEAs increased by nearly 50%, and the elongation did not decrease, largely due to solid solution strengthening and the reduction in stacking fault energy. Conversely, as Si content increased, the recrystallization ratio decreased during annealing. A heterogeneous grain structure composed of recrystallized and residual deformation regions (high density of dislocations and deformation twinning) was obtained by changing the CRA temperature and Si content. A heterogeneous grain structure of CRA HEAs with an annealing temperature of 700 ℃ and Si content of 0.2 exhibits approximately fourfold higher yield strength (733 MPa) compared to that of HOA FeCoCrNiMn HEAs (185.27 MPa). The structure's tensile strength and ductility were measured at 959 MPa and 29.5%, respectively. The high strength was mainly attributed to the combined effect of multiple strengthening mechanisms. Heterogeneous deformation-induced strain hardening and twinning-induced plasticity provide good ductility. • Si decrease the stacking fault energy of FeCoCeNiMn HEAs. • The strength of the HOA HEAs increased with increasing Si content, and the ductility did not decrease. • A heterogeneous grain structure can be tailored by changing Si content and annealing temperatures. • The yield strength of Si2-CRA-700 HEAs is about 4 times higher than Si0-HOA HEAs. [ABSTRACT FROM AUTHOR]

A surface layered structure of the Al 0.5 CoCrFeNiSi 0.25 high-entropy alloys was prepared via laser remelting (LR). The microstructures were characterized via optical microscopy, scanning electron microscopy, and electron backscatter diffraction techniques. The microhardness and wear properties of the LR alloys were evaluated in comparison with the as-cast alloy. The results showed that the microstructure of the surface layers can be tailored by changing laser scanning speed. With increasing the laser scanning speed from 3 mm/s to 7 mm/s, the thickness of the molten pool gradually decreased. Meanwhile, the microstructure of the layers changed from BCC + FCC dual-phase layers to BCC phase layers (BCC + B2 phase). And the thickness of BCC + FCC dual-phase layers gradually decreased. When the laser scanning speed reached 7 mm/s, the microstructure of the surface layer was only the BCC phase and the hardness of the BCC layer was doubled compared with the as-cast alloy, which also resulted in a sequential increase in scratch resistance. The relatively high hardness of the layered structure also led to its macroscopic wear resistance higher than that of the as-cast alloy, and the wear mechanism was mainly abrasive wear. • A layered structure with difference microstructure can be tailored by changing laser scanning speed. • The BCC phase layer is achieved with high laser scanning speed of 7 mm/s and its hardness is doubled than the as-cast alloy. • The hardness and wear resistance is enhanced after remelting. [ABSTRACT FROM AUTHOR]

In order to develop high-strength and high-conductivity copper alloys with better comprehensive properties, the effects of Si addition on the mechanical properties, electrical conductivity and microstructure of CuCrZr alloy were investigated in this paper. The addition of Si element can improve the hardness, strength and ductility of CuCrZr alloy. The optimal peak aging parameter for CuCrZrSi alloy is 430 °C for 3 h, the hardness 228.92 HV, the tensile strength 646.76 MPa, and the elongation after fracture 10.67%. Compared with the CuCrZr alloy under the same process, the mechanical properties are increased by 10.3%, 11.9% and 16.9%, respectively. The conductivity is 4 ± 1%IACS lower than that of the sample without Si addition. The addition of Si element refines the deformation substructure and produces more Σ3n (n = 1, 2, 3) grain boundaries, thus providing more nucleation sites and higher driving forces for the precipitation phases. In both CuCrZr and CuCrZrSi alloys, the fine precipitation phases (<10 nm) fcc-Cr phase and orthorhombic-Cu 8 Zr 3 phase, together with coarse precipitation phases (>100 nm) bcc-Cr phase and hcp-Zr phase can be observed. The orientation relationship among the two fine precipitation phases and the matrix is (1 ¯ 1 ¯ 1) [ 1 1 ¯ 0 ] C u ∥ (1 ¯ 1 ¯ 1) [ 1 1 ¯ 0 ] C r ∥ (133) [ 0 1 ¯ 1 ] C u 8 Z r 3 . The Si element tends to precipitate together with the Cr phase and Zr phase, and acts to refine and spheroidize the precipitation phases. [Display omitted] • The Si addition improves the hardness, strength and plasticity of CuCrZr alloy. • The Si tends to co-precipitate with Cr and Zr from the copper matrix during aging. • The CuCrZrSi alloy has finer deformation substructures and more ∑3n CSL boundaries. • The Si addition can refine and spheroidize the precipitates of CuCrZr alloy. • The precipitation phases are fcc-Cr, bcc-Cr, hcp-Zr and Cu 8 Zr 3 phases in both alloys. [ABSTRACT FROM AUTHOR]