The current high entropy alloys' studies are most in block, powder, coating, film and other areas. There are few studies of high entropy alloys in other areas and they are lack of unified classification. According to the current high entropy alloys' research situation, The paper has focused on the classification on all kinds of high entropy alloys having been researched, introduced the selecting principle of elements, summarized the preparation methods, reviewed the research institutions, research methods and research contents of high entropy alloys, prospected the application prospect of high entropy alloys, put forward a series of scientific problems of high entropy alloys, including less research on mechanism, incomplete performance research, unsystematic thermal stability study, preparation process parameters to be optimized, lightweight high entropy alloys' design, the expansion on the research field, etc, and the solutions have been given. Those have certain guiding significance for the expansion of the application of high entropy alloys subjects in the future research direction.
Currently, the utilization efficiency of energy still remains at a low level, although the depletion of fossil fuel is appoaching. Therefore, it is of great significance to develop new materials and technologies for energy-saving and environment protection. Phase-change materials (PCM), which can absorb or release heat through inversible phase change, are very promising in the fields of heat storage and thermal management. In this paper, the characteristics and classification of PCM were introduced briefly in the first section, and then the application and development status of PCM were reviewed and analyzed detailedly. In the third part, the main problems of PCM were pointed out, and the related research work and recent research progress were analyzed and discussed. Finally, it was pointed out that optimizing material properties through new functional composite technology, designing new material system, expanding new application fields are the main development directions of phase change energy storage materials.
The research status on theoretic models and the coupling relationships of Orowan strengthening, dislocation strengthening, load-bearing effect of the reinforcement strengthening and others strengthening are successfully described in this study for particle-reinforced metal matrix composites(MMCs) with a volume fraction lower than 14%. Some conclusions can be obtained:Orowan strengthening and dislocation strengthening stress can be enhanced by increasing volume fraction, decreasing size of reinforcement and improving homogeneous distribution of reinforcement, load-bearing strengthening stress can also be enhanced by increasing volume fraction; yield strength and ductibility of MMCs can be enhanced much more by increasing load-bearing strengthening stress and plastic deformation region and adopting the material design method of metal matrix surrounded by particles with microstructural inhomogenous distribution; grain boundary strengthening and Peierls-Nabarro stress can also affect the yield strength of MMCs as a part of matrix strengthening, solid solution strengthening can be ignored usually; there are three coupling relationships for the sum strengthening contributions:linear summation, multiplicative combination and the root of the sum of the squares. The linear summation and multiplicative combination can be applied to nanoparticle-reinforced MMCs, the linear summation is generally applicable in the case when there are few factors influencing the strength, the multiplicative combination is the most commonly used method. The root of the sum of the squares is applied to micronparticle-reinforced MMCs.
After introducing the principle and classification of 3D printing, methods for metal forming using 3D printing were reviewed in details, including electron beam melting(EBM), selective laser melting(SLM), laser direct melting deposition(LDMD). The application fields of metal 3D printing and research status overseas and domestic were also discussed in this paper. At last, based on the current development of metal 3D printing, this paper summarized the key issues that should be solved, which include the quality of powders, the usage of 3D printing equipments, nondestructive testing for 3D printing components, the failure analysis and prediction of lifecycles for 3D printing components. The standards of nondestructive testing for 3D printing components should be established and the database of comprehensive mechanical properties for 3D printing materials should be built.
Graphene is a single atomic layer structure, which is the thinnest 2-D planar sheet composed of sp2-bonded carbon atoms. The special structure of graphene has excellent properties, such as photoelectric property, heat stability and mechanical properties. There has been increasing attention to preparation, property and application of graphene composites in recent years. In the paper, preparation methods of graphene composites is reviewed, such as graphene/polymer composites, graphene/metal (metal oxide) composites, and ternary composites of graphene. The advances in application of graphene composites are also reviewed, such as in lithium battery, supercapacitors, photovoltaic devices, sensor applications. Furthermore, the important research direction of graphene composites is pointed out.
Perovskite solar cells(PSCs) have been developed rapidly as one of the most remarkably growing photovoltaic technologies in the last five years. The power conversion efficiency(PCE) of the solar cells has been unprecedentedly increased over the relatively short period. It is of great significance to study the perovskite materials in this kind of solar cells for improving the efficiency. The most focused issues as well as the main progress in varied fabrication techniques and synthesis of new materials in recent years were reviewed in this paper. The characteristics and improvements of varied fabrication techniques are introduced in detail, the necessity and the problems facing for new materials synthesis were analyzed. Finally, a perspective view on reducing the toxicity of perovskite, preparing large-scale perovskite solar cells, and the cost reduction was given to provide the direction for the future research of high-efficiency and stable perovskite solar cells.
With the increase of the thrust-weight ratio of the aero-engine, CMC-SiC composites with low density, high strength and toughness, high thermal stability, long lifetime, good ablation resistance and oxidation resistance need to be developed to meet the requirements of the complicated and aggressive environments in the aero-engine. The characteristics, fabrication methods, applications on the hot components of the abroad advanced aero-engines, the domestic research achievements and the open problems of the CMC-SiC composites were introduced. The research tendencies in the high performance fibers, parts design and fabrication, environmental barrier coatings, non-destructive testing technologies, evaluation and verification method and repairing technologies were put forward.