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• An alumina dispersion strengthened copper alloy exhibits the highest softening temperature of 1203 K and was fabricated by in-situ internal oxidation and reduction method. • The strong pinning effect of the nanometer-scaled Al 2 O 3 particles helps increase the dislocation density and the grain boundary stability even at elevated temperatures. • A modified Hall-Petch relationship was established by introducing the integration of the grain size distribution, which can describe the correlation between softening behavior and the pinning effect of Al 2 O 3 particles. An Al 2 O 3 dispersion strengthened (ADS) alloy with an ultra-high softening temperature of ∼1200 K was fabricated by the in-situ internal oxidation and reduction methods. The evolution of the nanometer Al 2 O 3 particles, grain size, and consequently the softening behavior of this ADS alloy, were investigated by conducting the annealing treatments in the range from 673 K to 1273 K for 60 min. These refined nanometer Al 2 O 3 particles were found to be highly stable at elevated temperatures, leading to the high dislocation density and grain boundary stability of the matrix. The average grain size was found to increase extremely slowly from ∼0.60 μm to ∼0.74 μm with increasing annealing temperatures from 773 K to 1273 K. A criterion for grain boundaries migration and softening was established based on the competition between grain growth and pinning effect of Al 2 O 3 particles. The strong pinning effect of Al 2 O 3 particles was found when the grain size was between the lower limit (about 0.4–0.5 μm) and upper limit (2.18 μm). The occurrence of softening behavior was attributed to the rapid increase of the proportion of grains larger than the upper limit. A modified Hall–Petch relationship was established by introducing the integration of the grain size distribution, which can describe this correlation between softening behavior and the pinning effect of Al 2 O 3 particles. The current study not only sheds light on the further understanding of the softening mechanism of ADS copper alloy but also provides a useful route for designing copper alloy with high softening resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, in-situTiB2/AlSi7Mg composites were successfully fabricated using TiB2decorated AlSi7Mg alloy powder synthesized via salt-metal reaction and gas atomization, followed by powder metallurgy and hot extrusion. Microstructure and mechanical properties were investigated by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and tensile tests. The results show that the formation of fine grains and homogeneous subspherical silicon particles in as-extruded composites with high ductility (elongation of 21.7%) is achieved by perfect metallurgical bonding during severe plastic deformation. The covering effect of TiB2aggregates around silicon particles as particle shells has hindered the dissolution of silicon in the composite. After T6 treatment, the ultimate strength, yield strength and elongation at fracture of the 2 wt% TiB2/AlSi7Mg composite reach up to 344 MPa, 298 MPa and 8.6%, respectively. The excellent mechanical properties are mainly attributed to grain refinement, silicon optimization and precipitation strengthening. This study provides a good solution for improving the strength and toughness of Al–Si alloy.

Al2O3dispersion-strengthened (ODS) copper has an excellent comprehensive performance due to the strong hindrance of the high concentration nano-Al2O3to the dislocations inside copper grains. However, the processability of ODS copper is seriously deteriorated, which is caused by the presence of unfavorable microlevel Al2O3particles along powder particle boundaries. In this study, a strategy of ball-milling-induced impurity removal is adopted to surmount the dilemma. It was found that the ball milling process can significantly weaken the formation of large Al2O3particles in the primary boundaries. However, due to the activation of the powder particle surface, the metallurgical bonding between the powder particles is strengthened. The results showed that the ball-milled samples exhibited the optimal properties, including the ultimate tensile strength of 488 ± 3 MPa, elongation of 18.7 ± 0.7%, reduction in the area of 46.8 ± 1.2%, 82.2 ± 0.3 Rockwell Hardness measured on the B scale (HRB), and electrical conductivity of 77.2 ± 0.1% International Association of Classification Societies (IACS).

An investigation on the microstructure of as-cast Al-Mg-Cu composites reinforced by in situ nano-sized Al2O3dispersoids with ultrasonic treatment showed that ultrasonic treatment of the melt prior to casting had a significant effect on the size and sphericity of α-Al dendrites as well as on the size, continuity and sphericity of intermetallic particles (Al2CuMg) formed during cooling and solidification of the composite. More importantly, Al2O3nanoparticles were uniformly distributed inside the grains, which were in situ produced by the displacement reaction between Al and CuO in the melt under ultrasonic treatment. The microstructural effects were mainly attributed to the cavitation and streaming phenomena which took place during ultrasonic treatment in the melt. The mechanical properties were investigated by tensile tests and hardness measurements. Ultrasonic treatment caused a significant increase in the yield strength (~43%), ultimate tensile strength (~32%) and hardness (~13%), and simultaneously slight improvement in the ductility.

In-situ (10 vol%) TiB/Ti-Al-4V composites were prepared by employing cold isostatic pressing and vacuum sintering. The “pinning” effects of TiB whiskers on the hot deformation behavior and dynamic recrystallization of composites in the temperature range of 1000–1200°C with strain rates from 0.01 to 10 s-1were investigated in terms of flow behavior, hot-processing maps, and microstructural evolution. No flow instability region within the specified range was found. The dominant deformation mechanisms of the composites were CDRX and DDRX in the (α+β) and β regions, respectively. Owing to the “pinning” effect, prior-α could generate more grain boundaries by HAGB immigration to move through TiB whiskers. In the β region, owing to the deformation incompatibility and the “pinning” effect, more bulging of grain boundaries induced by TiB whiskers resulted in more nucleation sites for DDRX. On account of the “pinning” effect, TiB whiskers enhanced microstructural refinement by restricting grain growth.