Al(CON₂H₄)₆Cl₃ was firstly synthesized as a precursor with urea and AlCl₃·6H₂O as a nitrogen source and an aluminum source, respectively, and then the precursor was calcined at 1 000 ℃ to prepare spherical h-AlN nanoparticles. The effects of atmosphere pressure and sintering time on the morphology and the nucleation-growth mechanism of AlN were investigated. The results show that spherical AlN particles with the sizes of 320-460 nm are formed by equiaxed fine grains of smaller than 10 nm and amorphous phase under N₂ pressure of 0.1-0.2 MPa. As the N₂ pressure increases to 0.5 MPa, the diameter of spherical AlN increases to 650 nm, and rod-shaped AlN crystals appear in the aggregates. The size and number of rod crystals increase as the sintering time increases. AlN nanoparticles are formed by the reaction of AlCl₃ and NH₃ due to the decomposition of the precursor. The gas phase saturation in the crucible increases as N₂ pressure increases, promoting the nucleation and growth of AlN, reducing the amorphous phase content, and enhancing the crystallinity of AlN.

Copper-iron matrix composites containing mullite were prepared by powder metallurgy. By adding 0-25% (volume fraction) industrial mullite and high purity mullite respectively, the effects of mullite contents on the mechanical properties and tribological performances of the composites were compared. Furthermore, the influences of graphite content and mullite particle size on the friction performance of the composite were studied as well. With the increase of mullite content, the relative density and bending strength of the composites decreased, although the hardness increased. The coefficient of friction (COF) rose to the highest when mullite content was 15% and the wear rate showed smallest when mullite content was 5%. Compared with high-purity mullite, industrial mullite with wide particle size distribution and various particle shapes had a negative impact on the bending strength and wear rate of the composites. With 15% (volume fraction) graphite addition, the friction coefficient of the composite containing 15% industrial mullite was 0.3-0.4, with a lower wear rate. The industrial mullite with large particle size after sieving selection were beneficial to increase the friction coefficient. However, the industrial mullite with small particle size after ball milling had little effect on increasing the friction, and the wear rate was higher.

Si₃N₄ ceramics were prepared by an oscillating pressure sintering technique when Al₂O₃, Y₂O₃ and TiC additives were introduced into Si₃N₄ powders. The microstructure, grain size and mechanical properties of silicon nitride ceramics at different temperatures (i.e., 1 700, 1 725, 1 750 and 1 775 ℃) were analyzed. The effect of TiC additive on the particle densification and interface bonding of the ceramics were discussed. The results show that Si₃N₄ ceramics can be fully densified at 1 725 ℃ in the oscillating pressure sintering process, thus obtaining a high bending strength of (1 421±59) MPa and the Vickers hardness of (16.1±0.3) GPa, respectively. The aspect ratio of the sample also firstly increases and then decreases with the increase of temperature, and the maximum grain aspect ratio reaches at 1 725 ℃. The aspect ratio decreases and the grains become coarser when the temperature further increases to 1 775 ℃. The flexural strength and the Vickers hardness of silicon nitride decrease with the decrease of length-diameter ratio when the temperature higher than1 725 ℃.

Magnesium alloy has good potential application in bone tissue repair, but it is extremely susceptible to corrosion in the human physiological environment and loses its original mechanical properties, causing the implant material to fail during service. In order to improve its corrosion resistance and ability to rapidly induce apatite in vitro, a one-step hydrothermal method was used to prepare a micro-nano structured hydroxyapatite coating on magnesium alloys. The polarization resistance of the sample reached 138.680 kΩ·cm², indicating that the sample has excellent electrochemical performance. The degradation performance of the sample was tested in simulated body fluids. During the 30 d immersion time, the pH value of the simulated body fluids were maintained in the range of 7.10-7.60, and the corrosion rate was lower than 0.400 mm/y. And when immersed for 3 d, hydroxyapatite mineralization were formed on the coating surface, indicating that the micro-nano structural coating can quickly induce the formation of Ca-P products and has good mineralization ability.

SiC/Al composites were prepared by a pressureless infiltration process using SiC powder and aluminum alloy (3%Mg (in mass fraction), 5%Mg, 7%Mg, and 10%Mg) as main raw materials. The phase composition, microstructure, mechanical properties and thermal properties of SiC/Al composites were characterized. The effect of Mg content in aluminum alloy on the phase composition, microstructure, mechanical properties and thermal properties of SiC/Al composites was investigated. The results show that Mg can improve the impregnation properties of aluminum alloys and promote the occurrence of interfacial reaction in SiC/Al composites. The main crystalline phases of the prepared SiC/Al composites are both SiC and Al. The presence of Si, Mg₂Si and MgAl₂O₄ phases is also detected. After comparison, the sample with 5% Mg performs the better properties. The optimum performance of the sample prepared with 5%Mg (i.e., flexural strength of (366.36±14.37) MPa, fracture toughness of (9.2±0.27) MPa·m^1/2 and thermal conductivity of 178.81 W/(m·K) can be obtained when the porosity is 0.13% and the bulk density is 2.94 g/cm³.

The porous mullite-based ceramics were prepared by a particle-stabilized foam method and a subsequent freeze-drying process with α-Al₂O₃ and SiO₂ as raw materials, propyl gallate (PG) as a surface modifier and gelatin as a binder. The effect of aluminum to silicon (Al/Si) molar ratio on the composition, microstructure and properties of the prepared materials was investigated. The results show that the foam stability after foaming at different proportions is >95%. The sintered material is composed of mullite as a main phase and corundum as a second phase, and the mullite phase content decreases from 93.11% (in mass fraction) to 85.11% with increasing the Al/Si molar ratio from 2.0∶1.0 to 3.0∶1.0. The total porosity and bulk density are 85.51%-86.51% and 0.44-0.48 g/cm³, respectively. The open porosity is 84.34%-84.82%. The compressive strength firstly increases and then decreases (i.e., 2.25-2.86 MPa). The vacuum thermal conductivity increases from 0.15 W/(m·K) to 0.22 W/(m·K). It is indicated that the method could be promising to prepare porous mullite-based ceramics with a high porosity, a high strength and a low thermal conductivity.

The sintered Al₂O₃ blocks with some properties similar to Al₂O₃ inclusions in ingot were investigated, and the fracture behavior of Al₂O₃ during deformation was analyzed by high-temperature compression experiments in a special hot compression device. Based on the analysis of fracture characteristics of crushed samples, a prediction model of high-temperature crushing strength of Al₂O₃ was proposed based on the hyperbolic sinusoidal Arrhenius equation, the region map of crushing mode of Al₂O₃ characterized by Z parameter was constructed, and the crushing mechanism of Al₂O₃ at different deformation parameters was revealed. The results show that the hot compression process of Al₂O₃ has a typical brittle fracture, i.e., its crushing strength is positively correlated to the strain rate and it is negatively correlated to the deformation temperature, and it is more sensitive to the deformation temperature. The crushing mode of Al₂O₃ inclusions gradually changes from transgranular fracture to intergranular fracture when the Z parameter decreases.

The failure mechanisms of SiC, B₄C ceramic and the laminated SiC/BN composite armor under ballistic impacts of 5.8 mm steel bullet at 920 m/s were investigated by the finite element analysis and ballistic experiments. The results show that the fracture toughness of laminated SiC/BN ceramic with weak interfaces is 7.6 MPa·m^1/2. The shear fractures of substrate and interlayer appear on the ballistic impact surface, and the delamination and folding fractures occur at the back. The more transgranular fractures occur when the interlayers increase, compared to the intergranular fractures. The shallower impact craters are generated when the thickness of the SiC substrate layers decreases along the impact direction. SiC/BN laminated ceramic has a better ballistic performance when the mass fraction of BN interlayer is 6.9%, and SiC and B₄C block ceramics exhibit a better ballistic performance under multiple bullet impact condition.

A series of nonstoichiometric (NaBi)_0.47Ba_0.06TiO₃ (NBT-6BT) ceramics were prepared by the conventional solid-state method. The impact of A-site nonstoichiometry on the structural and electrical properties of the prepared ceramics was investigated. The room temperature diffraction patterns and Raman spectra revealed the coexistence of the Cc and P4bm phases for all samples. The experimental results in the present work showed that a deficiency in the Bi³⁺ and Na⁺ contents could lead to a transformation from the Cc to P4bm phase in addition to a variation in the piezoelectric coefficient d₃₃ with the Cc phase fraction. Favorable thermostability for the piezoelectric properties of the ceramics was observed by testing the depolarization temperature (T_d). Among them, the d₃₃ of the N_0.32B_0.32T-6BT ceramics still had a value of 23 pC/N at 160 ℃. These results showed that a deficiency in the Na⁺ and Bi³⁺ contents can significantly enhance T_d and extend the temperature region for the application of NBT-6BT ceramics.

Lead-free single-phase perovskite BaTiO₃-Bi(Al_0.5Sc_0.5)O₃ ceramics as novel high performance BaTiO_3-based energy storage ceramics were synthesized by a solid-state reaction method. Effect of BAS content on the structure, dielectric properties, energy storage of (1-x) BT-xBAS ceramics was investigated. The (1-x)BT-xBAS solid solution transforms from tetragonal (x≤0.05) to cubic (x≥0.1), but is still based on the tetragonal. The T_m moves toward a low temperature range, and the dielectric peak broadens with the BAS content increases, exhibiting a dispersive dielectric behavior with respect to frequency. The long-range ferroelectric order of ceramics is destroyed by BAS. Also, the phase transition of BT-xBAS ceramics is from a typical ferroelectric phase to a relaxor phase. The phenomena both indicate that the BT-BAS ceramics could have the excellent characteristics of relaxor ferroelectrics. The 0.85BT-0.15BAS ceramics show a good temperature stability, and the diffusion coefficient γ is 1.97. There are an energy storage density of 0.684 J·cm^-3 and an energy efficiency of 95% in an electric field of about 105 kV/cm.