With the development of aero-engine technology， the rising operating temperature makes the service environment of environmental barrier coatings （EBCs） increasingly severe， imposing higher demands on their comprehensive performance. EBCs have evolved from the first-generation mullite/YSZ system to the fourth-generation thermal/environmental barrier coatings （T/EBCs）， among which rare-earth silicates have become a research hotspot owing to their excellent high-temperature stability and matched thermal expansion coefficient. This paper reviews typical EBCs preparation processes including APS， EB-PVD and PS-PVD， analyses the influence of process parameters on coating quality， and elaborates the typical failure mechanisms under water-vapor corrosion， CMAS attack and thermal cycling stress. Future development of EBCs will focus on high-entropy materials， multi-scale structural design and intelligent process optimization to further improve their service performance and lifetime.

The enormous number of vehicles and the industrial system generate large quantities of waste tires， and pyrolysis is considered to be an effective means of treating waste tires. This paper focuses on the current research status of waste tire pyrolysis technology， summarizes the composition and formation mechanism of waste tire pyrolysis products， and analyses the factors restricting the resource utilization of pyrolysis products and the methods to enhance the resource utilization of pyrolysis products， and puts forward the bottleneck problems that need to be broken through for the industrial application of waste tire pyrolysis technology in the future. Pyrolysis of waste tires produces a range of products such as fuel gas， oil and carbon， as well as other valuable chemicals such as limonene， benzene， toluene， ethylbenzene and others. Existing studies have indicated that the distribution of pyrolysis products from waste tires is determined by the degree of primary and secondary reactions in the pyrolysis process， and the degree of primary and secondary reactions is affected by process parameters such as temperature， heating rate， volatile retention time， pressure， reactor structure， catalysts and material particle size， among which temperature has the greatest influence on the distribution of pyrolysis products. The increase of temperature is conducive to the formation of H₂， CH₄， CO， benzene， toluene， ethylbenzene and xylene， and promotes the conversion of limonene to aromatics and the conversion of sulfur from pyrolysis oil and gas to pyrolysis carbon. In order to realize the industrial application of waste tire pyrolysis technology， further research work should be carried out in the accurate construction of pyrolysis kinetic models， the development of highly selective catalysts and the design of pollutant treatment schemes.

Additive manufacturing of nickel-based superalloys holds significant promise for applications in aero-engines and gas turbines. Evaluating the mechanical properties of these materials is crucial for facilitating their use in load-bearing components. This study investigates the high-cycle fatigue performance of the GH3536 alloy， which is fabricated via laser powder bed fusion and then undergoes solution heat treatment， with the assessment carried out at room temperature.By utilizing X-CT technology and performing fracture analysis， the defect characteristics of the material are comprehensively characterized. Furthermore， a quantitative analysis is conducted to explore the relationship between defect size and fatigue limit. The results reveal that the alloy contains porosity and lack-of-fusion defects， with surface and subsurface defects being the main contributors to fatigue fracture. The defect density in vertical samples is lower， leading to a slightly higher fatigue limit compared to that of horizontal samples.By using the effective defect size in the fracture source region of the fatigue sample， a more accurate and conservative prediction of the fatigue limit can be made. This is achieved by enhancing the Kitagawa-Takahashi （K-T） diagram with the El-Haddad model. The fatigue life of the alloy can be predicted by integrating this approach with the fatigue life characterization method based on the ratio proposed by Murakami， in combination with the El-Haddad model. This combined method provides higher prediction accuracy， especially for vertical samples with low defect density.

Selective laser melting （SLM） technology can fabricate components with highly intricate geometries. Nevertheless， due to its layer-by-layer construction process，SLM inevitably leads to variations in microstructures and mechanical properties along the building direction，which in turn undermines the service stability of the fabricated components. Heat treatment is generally employed to enhance the homogeneity of microstructures and reduce the disparity in mechanical properties along the building direction. This study delves into the influence of building heights on the microstructures and mechanical properties of GH4169 alloy produced via SLM and sheds light on the mechanisms governing microstructure evolution during heat treatment. The key findings indicate that the microstructures of the as-built GH4169 alloy consist of the γ phase and Laves phase. The geometrically necessary dislocation density of the alloy demonstrates a decreasing trend as the building height increases， primarily attributable to the thermal cycles and heat accumulation that occur along the building height. After heat treatment， the recrystallization degree of the alloy at the bottom and middle sections reaches approximately 87.8%， while that at the top section is a mere 34.1%. This significant discrepancy in recrystallization is mainly due to the higher dislocation density at the bottom， which boosts the recrystallization driving force. The yield strength of the as-built GH4169 alloy at the bottom and middle sections is around 850 MPa， whereas that at the top section is approximately 780 MPa. Following heat treatment， the yield strengths of the alloy at different heights all approximate 1150 MPa. Owing to the variation in recrystallization， precipitation at the bottom is more pronounced than that at the top， resulting in a stronger precipitation strengthening effect. On the other hand， the finer grain size and higher dislocation density at the top contribute to enhanced grain boundary strengthening and dislocation strengthening. As a consequence， the strength of the alloy at the bottom and top sections after heat treatment is comparable.

This work studies the microstructure and mechanical properties of K439B nickel-based superalloy castings with a wall thickness of 1-10 mm. The results show that the melt feeding capacity in thin-walled castings is poor， there are many shrinkage porosity in the 1 mm and 3 mm thin-walled castings， and the 10 mm thick-walled casting has the lowest porosity. Due to the increase of melt solidification rate， all of the secondary dendrite arm spacing， grain size and γ' phase size of the castings increase with the increase of thickness. The tensile tests at room temperature show that the mechanical properties of thin-walled castings are significantly affected by the evolution of microstructure. Due to the synergistic effect of the fine grain strengthening mechanism and precipitate shearing mechanism， the 1 mm thick casting exhibits the highest ultimate tensile strength （1037 MPa） and elongation to fracture （5.6%）.The 3 mm thick casting shows the poorest tensile strength and ductility，with values of 890 MPa and 4.1%， respectively， which can be attributed to its highest porosity level and the resulting severe stress concentration. Although the coarsening of grains and γ' phase reduces the grain boundary strengthening effect of the 10 mm thick casting， the reduced porosity and limited dislocation localization effectively impede the crack propagation，thereby preventing a pronounced deterioration in elongation to fracture.

The grain-boundary microstructure of Inconel 617 alloy hot-rolled rods during cold drawing and subsequent solution treatment is investigated using the electron backscattering diffraction （EBSD） technique. The results reveal that the microstructure of the hot-rolled rods contains a substantial number of coincidence site lattice （CSL） grain boundaries， predominantly Σ3 grain boundaries. Following cold drawing， the proportion of CSL grain boundaries decreases significantly， while the proportion of low-angle grain boundaries experiences a sharp increase. After solution treatment at 1120 ℃， low-angle grain boundaries are almost entirely replaced by high-angle and CSL grain boundaries. As the solution temperature rises， the proportion of Σ3 grain boundaries increases， whereas the proportions of Σ9 and Σ27 grain boundaries decline. Within a specific grain-size range， the proportion of Σ3 grain boundaries rises with an increase in grain size. During the solution treatment process， annealing twin boundaries with “cluster” and “island” morphologies emerge， and there exists a Σ3 ⁿ orientation relationship between adjacent grains.

The Al-6Si-0.75Mg-0.2Sc-0.15Zr-0.12Sb alloy is prepared using the smelting process. This study investigates the impacts of solution and aging temperatures， as well as their durations， on the microstructure and mechanical properties of the alloy. Additionally， it analyzed the morphology， size， and distribution of Si and precipitated phases.It is observed that the as-cast microstructure comprises α-Al， eutectic Si， Mg₂Si， Al₃Sc， and Al₃（Sc， Zr） phases. As the solution and aging temperatures and times increase， the morphology of the Si phase transforms from plate-like and fibrous to worm-like and nearly spherical. Prolonged holding times lead to the segregation and coarsening of the Si phase， which turns into short rod-like structures. The tensile strength and elongation initially rise and then decline with increasing solution temperature. During single-stage aging at 170 °C， the strength and hardness first increase and then decrease with the extension of the holding time， eventually reaching a stable state. The interface between the β´´ and α-Al phases evolves from coherent to semi-coherent and then incoherent， and the fracture mechanism shifts from intergranular fracture to typical dimple fracture.Pre-aging at 110 ℃ promotes the precipitation of β´´ and Al₃（Sc， Zr） phases， significantly spheroidizes the morphology of the Si phase， and refines its size. The length and precipitated surface density of the β´´ phases are （29 ± 1.8） nm and 3.52 × 10³ μm⁻²， respectively. After dual-stage aging at 110 °C/2 h + 170 °C/6 h， the tensile strength， yield strength， and elongation can reach 363， 301 MPa， and 7.9%， respectively.

The microstructure evolution in Al8.79Zn2.16Mg2.11Cu0.12Zr alloy ingot during the one-step low-temperature homogenization and three-steps high-temperature homogenization is investigated by the scanning electron microscopy （SEM）， differential scanning calorimetry （DSC）， X-ray diffraction （XRD）， and the transmission electron microscopy （TEM）. The results indicate that the microstructure of the cast Al8.79Zn2.16Mg2.11Cu0.12Zr alloy is similar to that of traditional commercial Al-Zn-Mg-Cu alloys， consisting of η′（Mg（Zn， Cu， Al）₂）， η（MgZn₂）， and Fe-rich （Al₇Cu₂Fe） phases. The θ（Al₂Cu）， T（Al₂Mg₃Zn₃），and S（Al₂CuMg） phases are not present. The redissolution effect of the second phases is not enough after one-step homogenization heat treatment at low temperature（380 ℃/2，8，16，24 h） and the change of redissolution effect is not obvious even if the homogenization heat treatment time is prolonged. A large number of the eutectic organization of the second phases still remains in the original mesh structure. However， the redissolution effect is improved by increasing the homogenization heat treatment temperature to 475 ℃（430 ℃/12 h+470 ℃/4 h+475 ℃/15 h）， except for a small amount of Fe-rich （Al₇Cu₂Fe） phases that are difficult to redissolution， the other phases are almost completely redissolution， no η′ phase transformation of S phase is detected during the one-step low-temperature homogenization and three-steps high-temperature homogenization heat treatment processes. The appearance of quench cracks occurs during the three-steps homogenization heat treatment at 475 ℃， which severely deteriorated the mechanical properties of the region near the crack in the alloy.

Based on the in-situ fatigue test technique of scanning electron microscope （SEM），the small crack behavior of selective laser melting （SLM） TC4 alloy is studied. The focused ion beam （FIB） technique is used to manufacture the simulative initial defects in the process of additive manufacturing，and the initiation and propagation behavior of small cracks induced by defects are observed under cyclic loading. The results show that under cyclic loading，small cracks are easy to initiate at the surface defect，and the crack fatigue initiation life is short. The fatigue life of SLM TC4 alloys is mainly consumed in the small crack propagation stage. Affected by the microstructure，the small cracks are more likely to propagate along the α/β interface. Due to the random orientation of α laths，the path of small cracks is deflected several times in the initial propagation stage，exhibiting a mixed mode of propagation along α lamellae and through α lamellae within grains， resulting in significant scatter in crack growth rates. At the stable crack propagation stage，the plastic slips of the crack tip are obvious，the influence of microstructure is reduced，and the propagation path tends to straighten. Comparative analysis with long crack growth data indicates that SLM TC4 alloy exhibits a significant “small crack effect”.

The microstructure， tensile fracture morphology and initial residual stress of ZTC4 titanium alloy repair welding are analyzed by stereomicroscope， optical microscope （OM）， scanning electron microscope （SEM）， X-ray residual stress analyzer and tensile testing machine， and their effects on room temperature/high temperature tensile properties and fatigue properties are studied. The results show that the microstructure of ZTC4 titanium alloy after repair welding is mainly composed of equiaxed grains （with a grain size of about 1.5 mm） and grains with a large aspect ratio （5∶1）. Different repair welding diameters and annealing treatment can affect the properties of residual stress， thus affecting the mechanical properties. The residual stress at the center of the original state of the room temperature/high temperature tensile and fatigue specimens is mainly tensile stress， which is 115.9， -24.6 MPa and 55.6 MPa， respectively. In the high temperature （350 ℃） tensile test， the larger the initial residual tensile stress （173.3 MPa） at the center of the repair welding diameter 4 mm specimens， the lower the tensile strength （710.7 MPa）； the larger the initial residual compressive stress （-159.1 MPa） at the center of the repair welding diameter 4 mm and annealing specimens， the higher the tensile strength （749.3 MPa）.The residual tensile stress significantly shortens the fatigue life of titanium alloy， whereas residual compressive stress increases it. The initial residual stress at the center of the original state， repair welding diameter of 2 mm， repair welding diameter of 2 mm and annealing， repair welding diameter of 4 mm， and repair welding diameter of 4 mm and annealing specimen is 55.6，109.9， -189.1，61.4 MPa， and -64.3 MPa， respectively. The fatigue properties of the specimens with initial residual compressive stress is better.