Microstructure tailoring in nanostructured thermoelectric materials

Progresses in thermoelectric(TE)materials will contribute to solving the world's demands for energy and global climate protection.It also calls for higher ZT to achieve ideal commercial conversion efficiency.As an effective way,nanostructuring can reduce the thermal conductivity by the selective scattering of phonons or enhance Seebeck coefficient via modification of the density of the states,resulting in good ZT value.Meanwhile,TE properties of nanostructured materials should depend on the size and morphology of the microstructure features.This review emphasizes the developments in the TE bulk materials at the nanoscale in the past several years and summarizes the understanding in this active field.

Recent advances and influencing parameters in developing electrode materials for symmetrical solid oxide fuel cells

This article delivers a robust overview of potential electrode materials for use in symmetrical solid oxide fuel cells(S-SOFCs),a relatively new SOFC technology.To this end,this article provides a comprehensive review of recent advances and progress in electrode materials for S-SOFC,discussing both the selection of materials and the challenges that come with making that choice.This article discussed the relevant factors involved in developing electrodes with nano/microstructure.Nanocomposites,e.g.,non-cobalt and lithiated materials,are only a few of the electrode types now being researched.Furthermore,the phase structure and microstructure of the produced materials are heavily influenced by the synthesis procedure.Insights into the possibilities and difficulties of the material are discussed.To achieve the desired microstructural features,this article focuses on a synthesis technique that is either the most recent or a better iteration of an existing process.The portion of this analysis that addresses the risks associated with manufacturing and the challenges posed by materials when fabricating S-SOFCs is the most critical.This article also provides important and useful recommendations for the strategic design of electrode materials researchers.

Microstructural tailoring,mechanical and thermal properties of SiC composites fabricated by selective laser sintering and reactive melt infiltration

Poor flowability of printable powders and long preparation cycles are the main challenges in the selective laser sintering(SLS)of chopped carbon fiber(C_(f))reinforced silicon carbide(SiC)composites with complex structures.In this study,we develop an efficient and novel processing route in the fabrication of lightweight SiC composites via the SLS of phenolic resin(PR)and Cr powders with the addition of a-SiC particles combined with the one-step reactive melt infiltration(RMI).The effects of a-SiC addition on the microstructural evolution of the C_(f)/SiC/PR printed bodies,C_(f)/SiC/C green bodies,and derived SiC composites were investigated.The results indicate that the added a-SiC particles play an important role in enhancing the flowability of raw powders,reducing the porosity.increasing the reliability of the C/SiC/C green bodies,and contributing to improving the microstructure homogeneity and mechanical properties of the SiC composites.The maximum density,flexural strength,and fracture toughness(Kic)of the SiC composites are 2.749±0.006 g·cm^(3),266±5 MPa,and 3.30±0.06 MPa-m,respectively.The coefficient of thermal expansion(CTE,a)of the SiC composites is approximately 4.29×10^(-6)K^(-1)from room temperature(RT)to 900℃,and the thermal conductivity(x)is in the range of 80.15-92.48 W·m^(-1)·K^(-1)at RT.The high-temperature strength of the SiC composites increase to 287±18 MPa up to 1200℃.This study provides a novel as well as feasible tactic for the preparation of high-quality printable powders as well as lightweight,high-strength,and high-x SiC composites with complex structures by the SLS and RMI.

Effect ofαphase on fatigue crack growth of Ti-6242 alloy

Fatigue crack growth as a function ofαphase volume fraction in Ti-6Al-2Sn-4Zr-2Mo（Ti-6242）alloy was investigated using fatigue testing,optical microscopy,scanning electron microscopy,and transmission electron microscopy.Theα＋βannealing treatments with different solid solution temperatures and cooling rates were conducted in order to tailor microstructure with differentαphase features in the Ti-6242 alloy,and fatigue crack growth mechanism was discussed after detailed microstructure characterization.The results showed that fatigue crack growth rate of Ti-6242 alloy decreased with the decrease in volume fraction of the primaryαphase（αp）.Samples with a large-sizedαgrain microstructure treated at high solid solution temperature and slow cooling rate have lower fatigue crack growth rate.The appearance of secondaryαphase（αs）with the increase of solid solution temperature led to crack deflection.Moreover,a fatigue crack growth transition phenomenon was observed in the Paris regime of Ti-6242 alloy with 29.8% αp（typical bi-modal microstructure）and large-sizedαgrain microstructure,owing to the change of fatigue crack growth mechanism.