Study of high-speed-impact-induced conoidal fracture of Ti alloy layer in composite armor plate composed of Ti-and Al-alloy layers

In order to understand the mechanism of conoidal fracture damage caused by a high-speed fragmentsimulating projectile in titanium alloy layer of a composite armor plate composed of titanium-and aluminum-alloy layers,the ballistic interaction process was successfully simulated based on the Tuler eButcher and GISSMO coupling failure model.The simulated conoidal fracture morphology was in good agreement with the three-dimensional industrial-computed-tomography image.Further,three main damage zones(zones I,II,and III)were identified besides the crater area,which are located respectively near the crater area,at the back of the target plate,and directly below the crater area.Under the high-speed-impact conditions,in zone II,cracks began to form at the end of the period of crack formation in zone I,but crack formation in zone III started before the end of crack formation in zone II.Further,the damage mechanism differed for different stress states.The microcracks in zone I were formed both by void connection and shear deformation.In the formation of zone I,the stress triaxiality ranged from2.0 to1.0,and the shear failure mechanism played a dominant role.The microcracks in zone II showed the combined features of shear deformation and void connection,and during the formation process,the stress triaxiality was between 0 and 0.5 with a mixed failure mode.Further,the microcracks in zone III showed obvious characteristics of void connection caused by local melting.During the zone III formation,the triaxiality was 1.0e1.9,and the ductile fracture mechanism was dominant,which also reflects the phenomenon of spallation.

Data-driven mapping-relationship mining between hardness and mechanical properties of dual-phase titanium alloys via random forest and statistical analysis

In order to accelerate the research on the property optimization of titanium alloy based on high-throughput methods,it is necessary to reveal the relationship between hardness and other mechanical properties which is still unclear.In this work,taking Ti20C alloy as research object,almost all the microstructure of dual-phase titanium alloys were covered by traversing over 100 heat treatment schemes.Then,massive experiments including microstructure characterization and performance test were conducted,obtaining 51,590 pieces of microstructure data and 3591 pieces of mechanical property data.Subsequently,based on large-scale data-driven technology,the quantitative mapping relationship between hardness and other mechanical properties was deeply discussed.The results of random forest models showed that the correlation between hardness(H)and Charpy impact energy(A_(k))(or elongation,A)was hardly dependent on the microstructure types,while the relationship between H and tensile strength(R_(m))(or yield strength,R_(p0.2))was highly dependent on microstructure types.Specifically,combined with statistical analysis,it was found that the relationship between H and Ak(or A)were negatively linear.Interestingly,the relationship between H and strength was positively linear for equiaxed microstructure,and strength was linked to d^(−1/2)(d,equivalent circle diameter)ofα-grains in the form of classical Hall–Petch formula;but for other microstructures,the relationships were quadratic.Furthermore,the above rules were nearly the same in the rolling direction and transverse direction.Finally,a"four-quadrant partition map"between H and R_(p0.2)/R_(m) was established as a versatile material-screening tool,which can provide guidance for on-demand selection of titanium alloys.

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.