Ti-Cu alloys have broad application prospects in the biomedical field due to their excellent properties. The properties of Ti-Cu alloys are strongly dependent on Cu content, microstructures, its Ti₂Cu phase and its preparation process. The aim of this work is to investigate the effect of Cu content on the precipitation behaviors, mechanical and corrosion properties of the as-cast Ti-Cu alloys. The microstructures and phase evolution were characterized by SEM and TEM, and the properties were studied by tensile and electrochemical test. The results show that the volume fraction of Ti₂Cu phase increases with the increase of Cu content. The Ti₂Cu phase presents a variety of microscopic morphologies with different Cu content, such as rod, granular, lath and block shaped. The crystal orientation relationships between the Ti₂Cu and α-Ti matrix in Ti-4Cu and Ti-10Cu alloys are (103)_Ti2Cu//(0[1$\overline{1}$11)_α-Ti, [$\overline{3}$01]_Ti2Cu//[2$\overline{1}\overline{1}$0]_α-Ti, and (103)_Ti2Cu//(0002)_α-Ti, [$\overline{3}$31]_Ti2Cu//[1$\overline{2}$10]_α-Ti, respectively. The tensile strength, Vickers hardness and Young’s modulus of the Ti-Cu alloys increase with the increase of Cu content, whereas the elongation decreases. The fracture morphologies of these alloys reveal ductile, ductile-brittle hybrid, and cleavage brittle mode, respectively. The corrosion resistance of the Ti-Cu alloys in SBF solution can be described as: Ti-4Cu alloy > Ti-10Cu alloy > Ti-7Cu alloy. The volume fraction of Ti₂Cu phases and the “protective barrier” provided by the fine lath Ti₂Cu phases strongly affected the electrochemical performances of the alloys.

To improve the heat resistance of titanium alloys, the effects of Y content on the precipitation behavior, oxidation resistance and high-temperature mechanical properties of as-cast Ti-5Al-2.75Sn-3Zr-1.5Mo-0.45Si-1W-2Nb-xY (x = 0.1, 0.2, 0.4) alloys were systematically investigated. The microstructures, phase evolution and oxidation scales were characterized by XRD, Laser Raman, XPS, SEM and TEM. The properties were studied by cyclic oxidation as well as room- and high-temperature tensile testing. The results show that the microstructures of the alloys are of the widmanstätten structure with typical basket weave features, and the prior β grain size and α lamellar spacing are refined with the increase of Y content. The precipitates in the alloys mainly include Y₂O₃ and (TiZr)₆Si₃ silicide phases. The Y₂O₃ phase has specific orientation relationships with the α-Ti phase: (002)Y₂O₃ // ($\overline{1}$$\overline{1}$20)_α-Ti, [110]Y₂O₃ // [$\overline{4}$401]_α-Ti. (TiZr)₆Si₃ has an orientation relationship with the β-Ti phase: (02$\overline{2}$$\overline{1}$)(TiZr)₆Si₃ // (011)_β-Ti, [$\overline{1}$2$\overline{1}$6](TiZr)₆Si₃ // [04$\overline{4}$]_β-Ti. The 0.1 wt.% Y composition alloy has the best high-temperature oxidation resistance at different temperatures. The oxidation behaviors of the alloys follow the linear-parabolic law, and the oxidation products of the alloys are composed of rutile-TiO₂, anatase-TiO₂, Y₂O₃ and Al₂O₃. The room-temperature and 700 °C UTS of the alloys decreases first and then increases with the increase of Y content; the 0.1 wt.% Y composition alloy has the best room-temperature mechanical properties with a UTS of 1012 MPa and elongation of 1.0%. The 700 °C UTS and elongation of the alloy with 0.1 wt.% Y is 694 MPa and 9.8%, showing an optimal comprehensive performance. The UTS and elongation of the alloys at 750 °C increase first and then decrease with the increase of Y content. The optimal UTS and elongation of the alloy is 556 MPa and 10.1% obtained in 0.2 wt.% Y composition alloy. The cleavage and dimples fractures are the primary fracture mode for the room- and high-temperature tensile fracture, respectively.

X2CrNi12 ferritic stainless steel has a wide range of application prospects in the railway transportation, construction, and automobile fields due to its excellent properties. The properties of X2CrNi12 ferritic stainless steel can be further improved by cold-rolling and subsequent annealing treatment. The purpose of this work is to investigate the effect of cold-rolling reduction on the microstructure, texture and corrosion properties of the recrystallized X2CrNi12 ferritic stainless steel by using SEM, TEM, EBSD and electrochemical testing technology. The results show that the crystal orientation characteristics of the cold-rolled sheet could be inherited into the annealed sheet. The higher cold-rolling reduction could promote the deformed grains rotating into the {111} orientation, increasing storage energy and driving force for recrystallization, which could reduce the recrystallized grain size. The orientation densities of α-fiber and γ-fiber were low at 50% cold-rolling reduction. After recrystallization annealing, a large number of grains with random orientation could be produced, and the texture strength was weakened. When the cold-rolling reduction rose to 90%, the γ-fiber texture at {111} was strengthened and the α-fibers, particularly the {112} component, were weakened after recrystallisation annealing, which could improve the formability of the steels. The proportions of special boundaries, i.e., low-angle grain boundaries and low-Σ CSL boundaries, among the grain boundary distribution of the recrystallized X2CrNi12 stainless steel were higher when the reduction was 90%, especially when the annealing temperature was 770 °C. Additionally, the proportion of LAGBs and low-Σ CSL boundaries were 53% and 7.43%, respectively, which improves the corrosion resistance of the matrix, showing the best corrosion resistance.

The formation mechanism of the spheroidal carbide in the ultra-low carbon ductile cast iron fabricated by the metal mold casting technique was systematically investigated. The results demonstrated that the spheroidal carbide belonged to eutectic carbide and crystallized in the isolated eutectic liquid phase area. The formation process of the spheroidal carbide was related to the contact and the intersection between the primary dendrite and the secondary dendrite of austenite. The oxides of magnesium, rare earths and other elements can act as heterogeneous nucleation sites for the spheroidal carbide. It was also found that the amount of the spheroidal carbide would increase with an increase in carbon content. The cooling rate has an important influence on the spheroidal carbide under the same chemical composition condition.

In order to improve the mechanical properties of Mg-Li alloy with single β phase structure, Mg-12Li-3Al-xNd (x=0.3, 0.7, 1.1, 2.0wt.%) alloy was prepared. Subsequently, the as-cast microstructure and mechanical properties were observed and tested. The results showed that the structure of Mg-12Li-3Al-xNd (x=0.3, 0.7, 1.1, 2.0wt.%) as-cast alloy was composed of β phase matrix and Al₂Nd, Al₁₁Nd₃, MgLiAl₂, Al₄Li₉ and AlLi phases. With the increase of Nd content in the alloy, the Al-Nd intermetallic compounds have a trend to change from needle-like Al₁₁Nd₃ to granular Al₂Nd. The hardness of as-cast Mg-12Li-3Al-xNd (x=0.3, 0.7, 1.1, 2.0wt.%) alloy was stable at room temperature. The tensile strength of Mg-12Li-3Al-1.1Nd was as high as 180 MPa, the elongation rate of Mg- 12Li-3Al-0.7Nd reached 53.7%, and the comprehensive mechanical properties of Mg-12Li-3Al-2.0Nd was the best. PLC phenomenon occurred during the tensile process of the alloys at room temperature. Therefore, the β-based Mg-Li alloy with good plasticity as well as enhanced strength can be obtained by a moderate addition of Nd and Al.