The effect of oxygen on the microstructure,mechanical properties and deformation behaviours of as-cast biocompatible Ti40Zr25Nb25Ta10Ox(x=0.5,1.0 and 2.0 at.%)high entropy alloys(HEAs)was investi-gated.All three oxyge...The effect of oxygen on the microstructure,mechanical properties and deformation behaviours of as-cast biocompatible Ti40Zr25Nb25Ta10Ox(x=0.5,1.0 and 2.0 at.%)high entropy alloys(HEAs)was investi-gated.All three oxygen-doped HEAs solidified as a single body-centred cubic(BCC)phase grain structure with predominantly high-angle grain boundaries following the Mackenzie prediction.Increasing oxygen content significantly increased tensile strength at a rate of about 180 MPa/1.0 at.%,but decreased ten-sile ductility.However,at the addition level of 0.5 at.%O,the as-cast Ti40Zr25Nb25Ta10O0.5 HEA can achieve a yield strength(σ_(0.2))of 947±44 MPa and an elongation at break(ε_(f))of 9.5%±1.8%.These properties make this HEA comparable to medical grade Ti-6Al-4V(wt.%)alloy(ASTM Grade 23 titanium)(σ_(0.2)≥759 MPa;ε_(f)≥10%)in itsability to absorbenergy in plasticdeformation,whileoffering greater resistance to permanent shape changes.Due to the possible strong interaction between oxygen atoms and dislocations through pinning and de-pinning,all oxygen-doped HEAs exhibited discontinuous yield-ing,whereas the low oxygen base HEA underwent normal yielding.No oxygen clusters were detected through atom probe tomography(APT)analysis.The deformation mechanism depends on oxygen con-tent.The plastic deformation of the Ti40Zr25Nb25Ta10O0.5 HEA occurred through the formation of pri-mary and secondary shear bands.In contrast,planar slip bands and a limited number of primary shear bands(without secondary shear bands)were observed in the Ti40Zr25Nb25Ta10O2.0 HEA.To ensure suf-ficient ductility,the oxygen content should be limited to 0.5 at.%.Furthermore,at this oxygen content,the corrosion resistance of the Ti40Zr25Nb25Ta10O0.5 HEA in Hank’s solution is comparable to that of Ti-6Al-4V.展开更多
Alpha-beta(α-β)titanium alloys such as Ti-6Al-4V(wt.%,here-after the same)and Ti-6Al-2Sn-4Zr-2Mo fabricated by fusion-based additive manufacturing(AM)typically exhibit a strong columnar prior-βgrain structure.These...Alpha-beta(α-β)titanium alloys such as Ti-6Al-4V(wt.%,here-after the same)and Ti-6Al-2Sn-4Zr-2Mo fabricated by fusion-based additive manufacturing(AM)typically exhibit a strong columnar prior-βgrain structure.These columnar prior-βgrains with their001along the build direction not only lead to solidification tex-ture but also cause subsequentα-phase textures[1].The forma-tion of theseα-phase textures is a consequence of theβ→αtransformation obeying the Burgers orientation relationship(BOR)[1-5],which results in[0001]of theα-phase being orientated at about either 45°or 0°relative to the horizontal.They affect the deformation behaviour and mechanical properties[1,6].Defined by the BOR,a singleβ-phase grain can bring forth 12α-phase vari-ants[2,7],leading to significant microstructural intricacy.Theseα-phase variants do not form randomly in eachβ-phase grain.Rather,their formation displays specific crystallographic features,known asα-variant selection,which is common in Ti alloys.In an extreme case,α-variant selection can lead to the formation of a singleα-phase crystal through anα→β→αtransformation cy-cle[8,9].展开更多
Mechanical metamaterials are architectured cellular materials with unusual properties.Herein we report another type of metal mechanical metamaterials-their elastic admissible strain(EAS)is on the order of 0.1,compared...Mechanical metamaterials are architectured cellular materials with unusual properties.Herein we report another type of metal mechanical metamaterials-their elastic admissible strain(EAS)is on the order of 0.1,compared to about 0.01 for common metallic materials.Four conditions are required for a metal mechanical metamaterial to achieve this super EAS:(i)bending-dominated deformation;(ii)low density;(iii)an appropriate lattice topology,and(iv)an intrinsically high EAS for the lattice strut constituent material.The findings of this work extend perspectives on metal mechanical metamaterials.展开更多
文摘The effect of oxygen on the microstructure,mechanical properties and deformation behaviours of as-cast biocompatible Ti40Zr25Nb25Ta10Ox(x=0.5,1.0 and 2.0 at.%)high entropy alloys(HEAs)was investi-gated.All three oxygen-doped HEAs solidified as a single body-centred cubic(BCC)phase grain structure with predominantly high-angle grain boundaries following the Mackenzie prediction.Increasing oxygen content significantly increased tensile strength at a rate of about 180 MPa/1.0 at.%,but decreased ten-sile ductility.However,at the addition level of 0.5 at.%O,the as-cast Ti40Zr25Nb25Ta10O0.5 HEA can achieve a yield strength(σ_(0.2))of 947±44 MPa and an elongation at break(ε_(f))of 9.5%±1.8%.These properties make this HEA comparable to medical grade Ti-6Al-4V(wt.%)alloy(ASTM Grade 23 titanium)(σ_(0.2)≥759 MPa;ε_(f)≥10%)in itsability to absorbenergy in plasticdeformation,whileoffering greater resistance to permanent shape changes.Due to the possible strong interaction between oxygen atoms and dislocations through pinning and de-pinning,all oxygen-doped HEAs exhibited discontinuous yield-ing,whereas the low oxygen base HEA underwent normal yielding.No oxygen clusters were detected through atom probe tomography(APT)analysis.The deformation mechanism depends on oxygen con-tent.The plastic deformation of the Ti40Zr25Nb25Ta10O0.5 HEA occurred through the formation of pri-mary and secondary shear bands.In contrast,planar slip bands and a limited number of primary shear bands(without secondary shear bands)were observed in the Ti40Zr25Nb25Ta10O2.0 HEA.To ensure suf-ficient ductility,the oxygen content should be limited to 0.5 at.%.Furthermore,at this oxygen content,the corrosion resistance of the Ti40Zr25Nb25Ta10O0.5 HEA in Hank’s solution is comparable to that of Ti-6Al-4V.
基金supported by the Australian Research Council (ARC) through DP180103205
文摘Alpha-beta(α-β)titanium alloys such as Ti-6Al-4V(wt.%,here-after the same)and Ti-6Al-2Sn-4Zr-2Mo fabricated by fusion-based additive manufacturing(AM)typically exhibit a strong columnar prior-βgrain structure.These columnar prior-βgrains with their001along the build direction not only lead to solidification tex-ture but also cause subsequentα-phase textures[1].The forma-tion of theseα-phase textures is a consequence of theβ→αtransformation obeying the Burgers orientation relationship(BOR)[1-5],which results in[0001]of theα-phase being orientated at about either 45°or 0°relative to the horizontal.They affect the deformation behaviour and mechanical properties[1,6].Defined by the BOR,a singleβ-phase grain can bring forth 12α-phase vari-ants[2,7],leading to significant microstructural intricacy.Theseα-phase variants do not form randomly in eachβ-phase grain.Rather,their formation displays specific crystallographic features,known asα-variant selection,which is common in Ti alloys.In an extreme case,α-variant selection can lead to the formation of a singleα-phase crystal through anα→β→αtransformation cy-cle[8,9].
基金the China Scholarship Council(CSC)for a CSC scholarship(No.201706230108)Funding from the National Natural Science Foundation of China(No.51971145)and the Australian Research Council(Nos.DP200102666 and No.DE230101344)is acknowledged.
文摘Mechanical metamaterials are architectured cellular materials with unusual properties.Herein we report another type of metal mechanical metamaterials-their elastic admissible strain(EAS)is on the order of 0.1,compared to about 0.01 for common metallic materials.Four conditions are required for a metal mechanical metamaterial to achieve this super EAS:(i)bending-dominated deformation;(ii)low density;(iii)an appropriate lattice topology,and(iv)an intrinsically high EAS for the lattice strut constituent material.The findings of this work extend perspectives on metal mechanical metamaterials.
