Ultrastrong steel strengthened by multiple shearable nanostructures

Precipitation of multiple strong nanoprecipitates is crucial for the development of ultrahigh-strength structural materials with a strength of 2.5 GPa or above.Nevertheless,the ductility usually loses rapidly with strength due to limited dislocation mobility and high cracking tendency if coarse non-deformable precipitates are employed.Herein,we report a 2.5 GPa maraging steel strengthened by an ultrahigh den-sity of intermeshed shearable nanostructures consisting of Ni(Al,Fe)nanoprecipitates and Mo-rich(∼30 at.%)disordered clusters,both of which assume coherent interfaces.The fully coherent B2-Ni(Al,Fe)par-ticles precipitate in an extremely fast fashion,effectively accelerating local aggregation of low-diffusivity Mo atoms and promoting the formation of Mo-rich clusters surrounding them.This elemental partition was found to be further enhanced by Co addition via depleting both residual Al and Mo within the ma-trix,leading to the formation of copious yet fine intermeshed nanostructures.During plastic deformation,the interlocked nanostructures not only enhance local cutting stress by combining long-range elastic and short-range chemically ordering effects but also improve dislocation activity and resist shear-induced plastic instability.The multiple shearable nanostructures endow decent ductility(>6%)of the 2.5 GPa steel,suggesting a new paradigm for designing ultrastrong steels.

Microstructural stability and aging behavior of refractory high entropy alloys at intermediate temperatures

Several body-centered-cubic(BCC)refractory high entropy alloys(HEAs),i.e.,Hf Nb Ta Ti Zr,Nb Ta Ti Zr,Hf Nb Ti Zr and Nb Ti Zr,were annealed at intermediate temperatures for 100 h,and their microstructures and aging behaviors were studied in detail.All these HEAs start to decompose into multiple phases at around 500°C,but reenter the single-phase region at significantly different temperatures which were determined to be 900,1000,1100 and above 1300°C for Hf Nb Ti Zr,Nb Ti Zr,Hf Nb Ta Ti Zr and Nb Ta Ti Zr,respectively.Our analysis indicates that the onset decomposition temperature in these four HEAs is closely related to the elemental diffusion rates while the ending decomposition temperature is strongly dependent on the elemental melting points.Our findings are important not only for understanding phase stability of HEAs in general,but also for adjusting processing parameters to optimize mechanical properties of these HEAs.

New insight into fabrication of shaped Mg-X alloy foams with cellular structure via a gas release reaction powder metallurgy route

Shaped Mg alloy foams with closed-cell structure are highly interested for a great potential to be utilized in the fields where weight reduction is urgently required.A powder metallurgical method,namely gas release reaction powder metallurgy route to fabricate Mg-X(X=Al,Zn or Cu)alloy foams,was summarized.The principles on shaped Mg-X foams fabrication via the route were proposed.In addition,the effects of alloying elements,sintering treatment and foaming temperatures on fabrication of shaped Mg-X alloy foams were investigated experimentally.The results show that the key to ensure a successful foaming of Mg-X alloy foams is to add alloying metals alloyed with Mg to form lower melting(<600℃)intermetallic compounds by the initial sintering treatment.The foaming mechanism of Mg-X alloy foams also has been clarified,that is,the low-melting-point Mg-based intermetallic compounds melt first,and then reactions between the melt and CaCO_(3),a foaming agent,release CO gas to make the precursor foamed and finally shaped Mg-X alloy foam with a promising cellular structure is prepared.This route has been verified by successful fabrication on shaped Mg-Al,Mg-Zn and Mg-Cu foams with cellular structure.