Search

Compared with the Ti–C system, the additions of metals (Fe, Al, and Cu) can increase the lattice parameter and stoichiometry of TiC x by forming metal–Ti intermediate phases (for C/Ti≤0.8). But for C/Ti>0.8, the Fe addition can decrease the lattice parameter and stoichiometry of TiC x by the formation of Fe–C solid solutions due to the hindrance of atom diffusion and the decrease of combustion temperature, while the additions of Al and Cu can increase them by the formation of Al–Ti and Cu–Ti solid solutions due to the dilution of Al and Cu. [ABSTRACT FROM AUTHOR]

Abstract The present work revealed a potential to control the static recrystallization kinetics through regulating the feature of pre-existing Mg 17 Al 12 particles in Mg-Al-Zn alloys. The AZ31 (Mg-3Al-1Zn) with rarely dispersoids exhibits the fastest recrystallization rate, while the AZ61 (Mg-6Al-1Zn) with only fine particles (∼100 nm) recrystallizes slower than AZ91 (Mg-9Al-1Zn) containing Mg 17 Al 12 precipitates with scattered size distribution (ranging from less than 100 nm to above 0.6 μm). Especially, we found that coarse Mg 17 Al 12 particles in AZ91 are easier to trigger particle stimulated nucleation (PSN) at 275 °C than 175 °C, which compensates the strong recrystallization inhibition of fine dispersoids, leading to the recrystallization dramatically transforms from retarded to accelerated. Graphical abstract Image 1 Highlights • The precipitate feature notably affects the kinetics of static recrystallization. • Recrystallization of alloys with mixed particle size is sensitive to temperature. • Coarse particles in Mg-9Al-1Zn accelerate recrystallization at high temperature. • The study shows an efficient route to control the static recrystallization process. [ABSTRACT FROM AUTHOR]

Al−7Si−5Cu/Al 2 O 3 −ZrO 2 composites with nacre-like structures were prepared via ice-templating and gas pressure infiltration techniques. The composites were subsequently heat-treated at 850 °C for 0, 30, 60, 90 and 120 min to regulate the interfacial reaction between Al and ZrO 2 . The yield of larger (Al 1−m , Si m ) 3 Zr and ZrSi 2 phases increased with longer dwell times. The compressive strength initially increased and then decreased. The highest strength was observed in composites treated for 60 min and reached 1600±40, 1261±30 and 1033±22 MPa at temperatures of 20, 150 and 300 °C, respectively. These values increased by 30−40% as compared to those of the non-treated counterparts and were 2-, 5- and 12-fold more than those of the matrix alloy, respectively, which is demonstrative of the material's excellent load-bearing capacity, particularly at elevated temperatures. [ABSTRACT FROM AUTHOR]

Insufficient performance, especially at high temperatures, limits the extensive application of cast Al–Cu alloys. This study proposes a novel method of direct reaction synthesis (DRS) for the simultaneous synthesis and dispersion of hybrid-sized in situ TiC–TiB 2 particles in the melt to prepare a trace-particle-reinforced high-performance cast Al–Cu 5.5 –Mn 0.45 –Ti 0.3 –V 0.3 –Cr 0.2 –Zr 0.14 –B 0.04 alloy. The particulate-reinforced alloy achieved strength–ductility synergetic enhancement at room and high temperatures. In comparison to the Al–Cu matrix alloy, the yield strength of 0.7 wt% (TiC–TiB 2)/Al–Cu alloy at 298 K (529 MPa), 493 K (214 MPa), and 533 K (183 MPa) had an increase of 28%, 18% and 35%, meanwhile their elongation increased by 4%, 50% and 62%, respectively. The yield strength enhancement primarily benefited from the thermal mismatch between the particles and matrix, and Orowan strengthening. The strength–ductility performance improvement is due to the optimization of the microstructure: significantly refined α-Al grains with smaller and more dispersed θʹ precipitates. Further, the improvement mechanism of the microstructure is due to the action of the nanoparticles on the heterogeneous nucleation stimulation and dendrite growth inhibition of α-Al during the solidification process. Meanwhile, the segregation of the Cu atoms was inhibited by the particles. The precipitation was significantly promoted because of more uniformly distributed Cu atoms, and more defects induced by particles improved diffusion of the Cu atoms the number and density of the precipitation sites. The results of this study provide an economical and accessible synthesis strategy for industrial manufacturing. [ABSTRACT FROM AUTHOR]

This work was carried out to investigate the relationship between microstructures and mechanical properties of extruded Al–20Mg 2 Si–4Cu alloys unmodified and modified with 0.5 wt% Sb addition at room and high temperatures. Various techniques including metallography, field emission scanning electron microscope, differential thermal analysis and scanning electron microscopy were used to characterize the microstructure, tensile behavior and fracture mechanism of the alloys. It was found that 0.5 wt% Sb additions were highly effective in refining microstructures by changing the morphology of primary Mg 2 Si from coarse dendrite into smaller polyhedral shape with average size less than 20 µm. Tensile test showed that ultimate tensile strength (UTS) of the modified alloy increased dramatically to 283 MPa at room temperature and 213 MPa at 150 °C, evidently higher than the 220 MPa and 185 MPa for the unmodified alloy, respectively. Fracture surface examinations revealed a transition from particle fracture of primary Mg 2 Si in the unmodified alloy to particle–matrix interface debonding in the modified alloy. The transformation of primary Mg 2 Si from coarse dendrites to refined polygonal shapes contributes to the enhanced strength and ductility of the modified alloy, since the polygonal primary Mg 2 Si particles dispersed uniformly in modified alloy, impeding dislocation motions and freeing stress concentrations. A schematic map was established to further elucidate the mechanisms of fracture behavior during stretching process. [ABSTRACT FROM AUTHOR]

• 66 wt% carbon fiber reinforced PEEK composite with strong interface was prepared. • The composite has ultra-high specific strengths exceeding majority of polymer or metal matrix composites. • The wear rate of composite is 1–2 orders of magnitude lower than materials with lubricating particles. • Excellent properties are attributed to high-mass carbon fibers and self-lubricating of composite. • A new idea is provided for the application of high-strength resin-based composite. It remains challenging to incorporate high-content fibers in fiber-reinforced polymer matrix composites to significantly enhance their mechanical properties. This work prepared polyether ether ketone (PEEK) matrix composite reinforced with 66 wt% carbon fibers with 0°/90° prepreg layer by compression molding, with aim to further increase the carbon fibers content in PEEK-based composites to improve the mechanical and wear properties at different temperatures, especially high temperature. The composite exhibits tensile and flexural strength of both exceeding 1000 MPa at room temperature, 810 ± 10 MPa and 521 ± 12 MPa at 200 °C and 458 ± 22 MPa and 290 ± 18 MPa at 300 °C, respectively. Especially at 300 °C, the composite demonstrates specific strength of 290 MPa/(g/cm3), which is superior to many magnesium or aluminum alloys (18–86 MPa/(g/cm3)). Further, the composite has a lower wear rate (5.47–12.80 × 10−7 mm3/Nm) at 200 °C by 1–2 orders of magnitude that of some materials with lubricating particles, and the wear surface is dominated by mild adhesive wear instead of abrasive wear at room temperature. The ultra-high mechanical and friction wear properties are attributed to the high content of staggered 90° carbon fibers, great interface bonding between the fibers and PEEK matrix, and self-lubricating effect of fibers and PEEK particles in the composite. This opens up a new performance level and provides a new idea for high-temperature applications of high-strength fiber-reinforced resin matrix composites. [ABSTRACT FROM AUTHOR]

Al Cu alloys inoculated by in-situ nano-sized particles crystallized from Ni-Nb-Ti amorphous alloys were prepared by casting method in this work. Different compositions of Ni-Nb-Ti amorphous alloys significantly enhanced heterogeneous nucleation for α-Al and promoted obvious grain refinement of the Al Cu alloys. It was found that 0.05 wt% Ni-Nb-Ti amorphous alloys addition caused a significant and efficient refinement on α-Al (from 200 μm to 39 μm) and θ′ phase (from 146.4 nm to 37.6 nm). The strength and ductility of the inoculated alloy were improved significantly at high temperature. The tensile strength and fracture strain of the alloy inoculated by 0.05 wt% Ni-Nb-Ti amorphous alloy for 20 min at 533 K under the strain rates of 10−1 s−1 were increased by 32.63% and 90.35% respectively, compared to those of the uninoculated alloy. The nano-sized NiTi particles contributed to the grain refinement of α-Al, and grain refinement shortened the solute atomic diffusion distance and refined θ′ phase during heat treatment, resulting in higher strength and plasticity at high temperature. The model developed for this new type Al Cu alloy is found to be efficient in predicting the stress at 453 K–533 K under the strain rates of 10−4 s−1 to 10−1 s−1. • In-situ nano-sized NiTi can serve as efficient heterogeneous nuclei of α-Al. • Inoculation caused a significant refinement on α-Al and precipitation θ′ phase. • The tensile strength and fracture strain were increased by 32.63% and 90.35% respectively at 533 K with 10−1 s−1. • The enhanced tensile property was due to the finer θ′ phase which impeded dislocation motion. • A stress prediction model was presented at 453 K–533 K under the strain rates of 10−4 s−1 to 10−1 s−1. [ABSTRACT FROM AUTHOR]

At high temperatures, the weakened strength and decreased ductility of Al alloys limit their industrial applications. (TiB 2 –TiC)/Al–Cu–Mg–Si composites were synthesized by adding in situ dual-phased and bimodal-sized (TiB 2 –TiC)/Al master alloys to molten Al–Cu–Mg–Si alloys. The addition of minor amounts of TiB 2 and TiC particles (0.05 and 0.1 wt%, respectively) effectively refined the α-Al grains and θ′ and Q′ precipitates and increased the elevated-temperature strength and uniform elongation of the Al–Cu–Mg–Si alloys. The 0.1 wt% (TiB 2 –TiC)/Al–Cu–Mg–Si composite showed the best yield strength (279 MPa), ultimate tensile strength (366 MPa), and uniform elongation (10.6%) at 493 K, with enhancements of 9.4%, 15.1%, and 24.7% compared to the Al–Cu–Mg–Si matrix alloy (255 MPa, 318 MPa, and 8.5%). The simultaneous increases in the elevated temperature strength and ductility of the composites were attributed to the strengthening effects of the bimodal-sized TiB 2 and TiC particles, θ′ and Q′ precipitation strengthening, and the refined partial recrystallization microstructure. [ABSTRACT FROM AUTHOR]

Ni-coated SiC p /Al–Cu nanocomposites with different addition levels (0, 1, 2 and 3 wt% Ni-coated SiC p nanoparticulates) were successfully fabricated by semisolid stir casting combined with hot extrusion. The microstructures of the as-cast and hot-extruded nanocomposites showed that the grain size could be substantially refined. The dispersion mechanism of the SiC p nanoparticulates was discussed. Because the Al 3 Ni that was formed on the SiC p surface improved the wettability, more Ni-coated SiC p nanoparticulates were captured as the solid/liquid interface advanced, causing the Ni-coated SiC p to enter the α-Al interior and reduce agglomeration in the grain boundaries. The strengthening mechanism of the SiC p nanoparticulates at room temperature and high temperatures was studied. At 298 K, the strengthening was attributed to the hindrance of dislocation movement by the uniformly distributed SiC p nanoparticulates, grain size refinement and thermal mismatch strengthening. At 453 K and 493 K, the strengthening effect was ascribed to the impeded dislocation climb by the SiC p nanoparticulates distributed in the grain interior and the pinning effect of nanoparticulates on the grain boundaries. [ABSTRACT FROM AUTHOR]