Microstructure evolution of Al_(0.6)CoCrFeNi high entropy alloy powder prepared by high pressure gas atomization

The influence of cooling rate on the microstructure of Al0.6CoCrFeNi high entropy alloy（HEA） powders was investigated. The spherical HEA powders（D50≈78.65 μm） were prepared by high pressure gas atomization. The different cooling rates were achieved by adjusting the powder diameter. Based on the solidification model, the relationship between the cooling rate and the powder diameter was developed. The FCC phase gradually disappears as particle size decreases. Further analysis reveals that the phase structure gradually changes from FCC＋BCC dual-phase to a single BCC phase with the increase of the cooling rate. The microstructure evolves from planar crystal to equiaxed grain with the cooling rate increasing from 3.19×10^4 to 1.11×10^6 K/s.

Dynamic indentation response of porous SiC/Ti-based metallic glass composite

Porous SiC/Ti-based metallic glass composite (Ti-BMGC), a new kind of composite, has significant application prospectin the field of light armor. To evaluate the dynamic mechanical response of the composite, dynamic Vickers hardness andindentation-induced deformation behavior were investigated by comparison with that under static indentation. The dynamic hardnesswas measured by a modified split Hopkinson pressure bar (SHPB). The dynamic hardness is obviously greater than the statichardness. The brittleness parameter under dynamic indentation is also greater than that under static indentation. Although thedynamic indentation induced more severe deformation behavior than the static indentation, the deformation and fracturecharacteristics in the two loading cases are nearly the same, both exhibiting extensive cracks in the SiC phase and severe plasticdeformation in the metallic glass phase.

A cluster-plus-glue-atom composition design approach designated for multi-principal element alloys

Multi-principal element alloys(MPEAs)have shown extraordinary properties in different fields.However,the composition design of MPEAs is still challenging due to the complicated interactions among principal elements(PEs),and even more challenging with precipitates formation.Precipitation can be either beneficial or detrimental in alloys,thus it is important to control precipitates formation on purpose during alloy design.In this work,cluster-plus-glue-atom model(CGM)composition design method which is usually used to describe short-range order in traditional alloys has been successfully extended to MPEAs for precipitation design.The key challenge of extending CGM to MPEAs is the determination of center atom since there are no solvent or solute in MPEAs.Research has found that the element type of center atom was related not only with chemical affinity,but also with atomic volume difference in MPEAs,which has inevitable effect on atomic arrangement.Based on experimental data of MPEAs with precipitates,it was found that elements with either stronger chemical affinity or larger volume difference with other PEs would occupy the center site of clusters.Therefore,a cluster index(P_(C)),which considers both chemical affinity and atomic volume factors,was proposed to assist the determination of center atom in MPEAs.Based on the approach,a solid-solution Zr-Ti-V-Nb-Al BCC alloy was obtained by inhibiting the precipitation,while precipitation-strengthened Al-Cr-FeNi-V FCC alloy and Al-Co-Cr-Fe-Ni BCC alloy were designed by promoting the precipitation.Corresponding experimental results demonstrated that the approach could provide a relatively simple and accurate predication of precipitation and the compositions of precipitations were in line with PEs in cluster in MPEAs.The research may open an effective way for composition design of MPEAs with desired phase structure.