Influences of oxide content and sintering temperature on microstructures and mechanical properties of intragranular-oxide strengthened iron alloys prepared by spark plasma sintering

How to increase strength without sacrificing ductility has been developed as a key goal in the manufacture of high-performance metals or alloys. Herein, the double-nanophase intragranular yttrium oxide dispersion strengthened iron alloy with high strength and appreciable ductility was fabricated by solution combustion route and subsequent spark plasma sintering, and the influences of yttrium oxide content and sintering temperature on microstructures and mechanical properties were investigated. The results show at the same sintering temperature,with the increase of yttrium oxide content, the relative density of the sintered alloy decreases and the strength increases. For Fe–2wt%Y_(2)O_(3)alloy, as the sintering temperature increases gradually, the compressive strength decreases, while the strain-to-failure increases. The Fe–2wt%Y_(2)O_(3)alloy with 15.5 nm Y_(2)O_(3)particles uniformly distributed into the 147.5 nm iron grain interior sintered at 650℃ presents a high ultimate compressive strength of 1.86 GPa and large strain-to-failure of 29%. The grain boundary strengthening and intragranular second-phase particle dispersion strengthening are the main dominant mechanisms to enhance the mechanical properties of the alloy.

Advances in ultra-high temperature ceramics,composites,and coatings

Ultra-high temperature ceramics(UHTCs)are generally referred to the carbides,nitrides,and borides of the transition metals,with the Group IVB compounds(Zr&Hf)and TaC as the main focus.The UHTCs are endowed with ultra-high melting points,excellent mechanical properties,and ablation resistance at elevated temperatures.These unique combinations of properties make them promising materials for extremely environmental structural applications in rocket and hypersonic vehicles,particularly nozzles,leading edges,and engine components,etc.In addition to bulk UHTCs,UHTC coatings and fiber reinforced UHTC composites are extensively developed and applied to avoid the intrinsic brittleness and poor thermal shock resistance of bulk ceramics.Recently,high-entropy UHTCs are developed rapidly and attract a lot of attention as an emerging direction for ultra-high temperature materials.This review presents the state of the art of processing approaches,microstructure design and properties of UHTCs from bulk materials to composites and coatings,as well as the future directions.

Natural selection on various sites of ribosomal proteins: a cladistic view

Deducing the function of certain sites within a protein necessitates a priori recognition of the strength of selective pressure. Currently, statistical method is the only option to evaluate the degree of conservation. In the statistical framework, the types of selective pressure can be divided into classifications of negative, nearly neutral and positive. However, such quantitative methods may omit some crucial amino acid sites among the nearly neutral results. In this study, we propose that the cladistic information can be also important to evaluate the functional importance of various amino acid sites. The ribosomal proteins of 62 eukaryotic species were chosen as the case for statistical and cladistic analysis. The evolutionary changes of each site in the aligned sequences were matched on a currently well-accepted cladogram of eukaryotes. Hundreds of synapomorphic sites were discovered in various clades, in which only part of them were suggested to be potentially significant in the statistical framework. Notably, the mutation on His213 of RPL10 in human beings, which are synapomorphic in vertebrates but only be identified as being under neutral selection, is account for the disease Autism. Therefore, the cladistic information can be complementary to the statistical framework in understanding lineage-specific selection event. Additionally, the bias in the accumulation of apomorphic amino acids is significant when going from the Chordata to the Mammalia lineages. This study emphasizes the value of analyzing transcriptomic and proteomic data in a cladistic way to recognize the presence of group-specific selection on various sites in proteins.