Development of Fe-Mn-Si-Cr-Ni shape memory alloy with ultrahigh mechanical properties and large recovery strain by laser powder bed fusion

This work systematically studied the effect of volumetric energy density E on the densification,mi-crostructures,tensile mechanical properties,and shape memory performance of a Fe-Mn-Si-Cr-Ni shape memory alloy(SMA)fabricated by laser powder bed fusion(L-PBF).An E of 90-265 J/mm3 is suggested to fabricate the Fe-Mn-Si-Cr-Ni SMA with minor metallurgical defects and a high relative density of above 99%.The increase in E can promote the formation of the primaryγaustenite and the solid phase trans-formation from the primaryδferrite to theγaustenite,which helps to achieve a nearly complete y austenitic microstructure.The increase in E also contributes to fabricating the Fe-Mn-Si-Cr-Ni SMA with superior comprehensive mechanical properties and shape memory performance by L-PBF.The Fe-Mn-Si-Cr-Ni SMA with a combination of good ductility of around 30%,high yield strength of above 480 MPa,an ultrahigh ultimate tensile strength of above 1 GPa,and large recovery strain of about 6%was manu-factured by L-PBF under a high E of 222-250 J/mm^(3).The good shape memory effect,excellent compre-hensive mechanical properties,and low cost of Fe-Mn-Si-Cr-Ni SMAs,as well as the outstanding ability to fabricate complex structures of L-PBF technology,provide a solid foundation for the design and fabri-cation of novel intelligent structures.

Characterization of Compositionally Complex Hydrides in a Metastable Refractory High-Entropy Alloy

Here,we study the hydride formation in a metastable Ti-33Zr-22Hf-11Ta(at.%)refractory high entropy alloy(RHEA).Deviating to non-equiatomic compositions of RHEAs promotes the formation of transformation-induced plasticity where the body-centered cubic phase transforms to hexagonal close-packed(HCP)phase.It is found that the phase transformation capability assists the hydride formation due to the low solubility of hydrogen within the HCP phase.In this study,hydrogen is charged via electrochemical polishing and the corresponding phase transformation is activated in the metastable RHEAs.The newly formed HCP phase interacts with hydrogen to form a face-centered cubic hydride verified by electron energy loss spectroscopy.This work provides a primary exploration of the formation of compositionally complex metal hydrides in the metastable RHEAs,which are potential candidates for future hydrogen storage material design.

Deformation-induced interfacial-twin-boundary ω-phase in an Fe_(48)Mn_(37)Al_(15) body-centered cubic metastable alloy

Omega(ω)phase has a trigonal or hexagonal crystal structure and was first discovered inβ-type Ti-Cr alloys[1].Since then,theω-phase has been widely reported in numerous group IV transition metal(Ti,Ta,Hf,and Zr)based alloys[2–9].The morphologies ofω-phase could be particle-like(athermalω-phase)[10],ellipsoidal or cuboidal after aging(isothermalω-phase)[11],and plate-like after deformation(stress-relatedω-phase)[12].Amongst,the stressrelatedω-phase is usually located at the twinning boundary,thus also called interfacial-twin-boundary-ω(ITB-ω)phase.The formation of the ITB-ωphase is considered to be related to the formation of{112}bcc<111>mechanical twin(i.e.,{112}bcc twin)in bodycentered cubic(BCC)metals and alloys[13].

In-situ microstructural investigations of the TRIP-to-TWIP evolution in Ti-Mo-Zr alloys as a function of Zr concentration

Aiming at overcoming the strength-ductility trade-off in structural Ti-alloys,a new family of TRIP/TWIP Ti-alloys was developed in the past decade(TWIP:twinning-induced plasticity;TRIP:transformationinduced plasticity).Herein,we study the tunable nature of deformation mechanisms with various TWIP and TRIP contributions by fine adjustment of the Zr content on ternary Ti-12 Mo-xZr(x=3,6,10)alloys.The microstructure and deformation mechanisms of the Ti-Mo-Zr alloys are explored by using in-situ electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).The results show that a transition of the dominant deformation mode occurred,going from TRIP to TWIP major mechanism with increasing Zr content.In the Ti-12 Mo-3 Zr alloy,the stress-induced martensitic transformation(SIM)is the major deformation mode which accommodates the plastic flow.Regarding the Ti-12 Mo-6 Zr alloy,the combined deformation twinning(DT)and SIM modes both contribute to the overall plasticity with enhanced strain-hardening rate and subsequent large uniform ductility.Further increase of the Zr content in Ti-12 Mo-10 Zr alloy leads to an improved yield stress involving single DT mode as a dominant deformation mechanism throughout the plastic regime.In the present work,a set of comprehensive in-situ and ex-situ microstructural investigations clarify the evolution of deformation microstructures during tensile loading and unloading processes.

A kink-bands reinforced titanium alloy showing 1.3 GPa compressive yield strength:Towards extra high-strength/strain-transformable Ti alloys

1.Introduction In structural metallic materials,the occurrence of particular deformation mechanisms such as dislocation slip,deformation twins(DTs)[1,2]deformation kink bands(KBs)[3,4]or stressinduced phase transformations(SIM)[5],are closely related to both their crystal structures[6–8](e.g.FCC,BCC and HCP)and loading conditions(e.g.temperature and/or strain rate).

Compressive deformation-induced hierarchical microstructure in a TWIPβTi-alloy

The deformation mode of{332}<113>twinning(hereafter called 332T)has often been observed under the plastic flow in metastableβtitanium alloys with body-centered cubic(BCC)structure,which contributes to improving the mechanical performance.Herein,we report a structure of compressive deformation-induced primary 332T with hierarchical and/or heterogeneous composite sub-structure in a Twin-Induced Plasticity(TWIP)βTi-alloy under uniaxial compression.The detailed structural characterization after compressive deformation revealed that the sub-structure,including secondary 332T and secondary{112}<111>twinning,formed inside the 332T structure,which constitutes a hierarchical and/or heterogeneous structure at micro-and nano-scale and consequently contributes to the high strength,large ductility and enhanced strain-hardening behavior.