The activation energy of the β → α/ω phase transformation increased monotonously with the application of a continuous heating process to a Ti-15Mo-2.7Nb-3Al-0.2Si alloy. Precipitation behaviour of the alloy aged at different temperatures were analysed with scanning electron microscopy, electron backscattered diffraction and transmission electron microscopy. Selected-area diffraction patterns of the ω, ω/α and α phases in the alloy aged at different temperatures indicated that the type of phase transformation was influenced by the precipitation process. Precipitate-free zones in the alloy aged at 450 °C for 8 h were harmful to the mechanical performance. Fine α precipitates with an obvious texture were obtained in the alloy aged at 500 °C. A good combination of tensile properties with an ultimate tensile strength of 1310 MPa and an elongation of 13.5% were obtained due to the expected microstructure and texture of the precipitates that transformed in the specimen when it was aged at 500 °C for 8 h. The size of the precipitates increased with increasing aging temperature. Furthermore, the amount of precipitates and their degree of texture decreased substantially in the alloy aged at 600 °C. The investigation of the tensile properties and fractures also revealed a correlation between the mechanical properties and precipitation behaviour in the Ti-15Mo-2.7Nb-3Al-0.2Si alloy aged at different temperatures.

MOF–derived porous carbon is a type of promising catalyst to replace expensive Pt–based catalysts for oxygen reduction reaction (ORR). The catalytic activity for ORR depends closely on pyrolysis conditions. In this work, a Co–doped ZIF–8 material was chosen as a research object. The effect of pyrolysis conditions (temperature, heating rate, two–step heating) on the ORR performance of ZIF–derived carbon catalysts was systematically studied. The Co–ZIF–8 catalyst carbonized at 900 °C exhibits better ORR catalytic activity than that carbonized at 800 °C and 1000 °C. Moreover, a low heating rate can enhance catalytic activity. Two–step pyrolysis is proven to be an effective way to improve the performance of catalysts. Reducing the heating rate in the low–temperature stage is more beneficial to the ORR performance, compared to the heating rate in the high–temperature stage. The results show that the Co–ZIF–8 catalyst exhibits the best performance when the precursor was heated to 350 °C at 2 °C/min, and then heated to 900 °C at 5 °C/min. The optimum Co–ZIF–8 catalyst shows a half–wave potential of 0.82 V and a current density of 5.2 mA·cm⁻² in 0.1 M KOH solution. It also exhibits high content of defects and good graphitization. TEM mapping shows that Co and N atoms are highly dispersed in the polyhedral carbon skeleton. However, two–step pyrolysis has no significant effect on the stability of the catalyst.

The effect of heat treatment on the microstructures and mechanical properties of a novel β-solidifying Ti–43Al–2Cr–2Mn–0.2Y alloy was investigated. A fully lamellar (FL) microstructure with a colony size of about 100 μm was obtained by heat treatment at 1320 °C/10 min/furnace cooling (FC). A duplex (DP) microstructure with globular γ grains and γ/α₂ lamellae was obtained by heat treatment at 1250 °C/4 h/FC. The residual hard–brittle β₀ phase was also eliminated after heat treatment. The mechanical properties of the β-solidifying TiAl alloy depended closely on the heat treatment. The FL alloy had better fracture toughness, and the fracture toughness (K_IC) value was 24.15 MPa·m^1/2. The DP alloy exhibited better ductility, and the room temperature (RT) elongation of the alloy could reach 1%. The elongation of the alloy with different microstructures sharply increased when the temperature increased from 700 to 750 °C, indicating that the microstructure had no effect on the ductile–brittle transition temperature of the β-solidifying TiAl alloy. The fracture morphologies of different tensile specimens were observed. Interlamellar and translamellar fractures were the main fracture features of the FL alloy. Intergranular, translamellar, and interlamellar fractures were the main fracture features of the DP alloy.

This study systematically investigated the influence of multi-directional forging (MDF) on the microstructural evolution, hot deformation behavior, and tensile properties of a β-solidifying TiAl alloy. The initial lamellar microstructure of an as-cast alloy was remarkably refined and homogenized by three-step MDF. High temperatures and multi-pass deformations were conducive to the decomposition of lamellae. A crack-free billet was obtained through three-step MDF, with a deformation temperature of 1250 °C and a forging speed of 0.1 mm/s, indicating that MDF can be applied to β-solidifying TiAl alloys by the proper control of the alloy composition and process parameters. Microstructural observation showed that the billet mainly consists of fine and equiaxed γ grains and a small amount of β phase. The tensile properties of the multi-directional forged alloy were also significantly improved, due to microstructure refinement. The ultimate tensile strength (UTS) and elongation (δ) at room temperature were 689.4 MPa, and 0.83%, respectively. The alloy exhibits excellent ductility at 700 °C. When the temperature was increased to 700 °C, the UTS decreased to 556 MPa and δ increased to 5.98%, indicating that the alloy exhibits excellent ductility at 700 °C. As the temperature further increased to 750 °C, δ dramatically increased to 46.65%, indicating that the ductile-brittle transition temperature of the alloy is between 700 °C and 750 °C.

Titanium alloys are widely used in marine engineering and other industries. To broaden their application, a novel (α + β) titanium alloy Ti−6Al−3Mo−2Zr−2Fe was studied in this work. A tube with an outer diameter of 60mm, inner diameter of 38 mm, and length of 500 mm was produced by ingot metallurgy and hot extrusion. The microstructure, mechanical properties, and corrosion resistance of the tube were systematically analyzed. The as−extruded Ti−6Al−3Mo−2Zr−2Fe alloy exhibited a typical duplex microstructure. EBSD observation showed that a strong <$10 \overline{1}0$>//RD fiber texture of an α phase with a close−packed hexagonal structure was formed in the radial direction. The transformation temperature T_β was determined to be 880–890 °C. A duplex microstructure with fine α platelets was obtained when the alloy was solution−treated at 850 °C for 1 h and underwent an aging treatment at 550 °C for 6 h. The room−temperature tensile strength and elongation of the aged alloy reached 1081.5 MPa and 6.5%, respectively. The corrosion resistance was tested by open circuit potential and a potentiodynamic polarization curve. The results show that the corrosion resistance of the Ti−6Al−3Mo−2Zr−2Fe alloy was better than that of the commonly used TC4 alloy in both a 3.5% NaCl solution and an acidic solution.