Impact of W alloying on microstructure, mechanical property and corrosion resistance of face-centered cubic high entropy alloys: A review

Face-centered cubic (f.c.c.) high entropy alloys (HEAs) are attracting more and more attention owing to their excellent strength and ductility synergy, irradiation resistance, etc. However, the yield strength of f.c.c. HEAs is generally low, significantly limiting their practical applications. Recently, the alloying of W has been evidenced to be able to remarkably improve the mechanical properties of f.c.c. HEAs and is becoming a hot topic in the community of HEAs. To date, when W is introduced, multiple strengthening mechanisms, including solid-solution strengthening, precipitation strengthening (μphase,σphase, and b.c.c. phase), and grain-refinement strengthening, have been discovered to be activated or enhanced. Apart from mechanical properties, the addition of W improves corrosion resistance as W helps to form a dense WO_(3) film on the alloy surface. Until now, despite the extensive studies in the literature, there is no available review paper focusing on the W doping of the f.c.c. HEAs. In that context, the effects of W doping on f.c.c. HEAs were reviewed in this work from three aspects, i.e., microstructure,mechanical property, and corrosion resistance. We expect this work can advance the application of the W alloying strategy in the f.c.c. HEAs.

Synergy effect of multi-strengthening mechanisms in FeMnCoCrN HEA at cryogenic temperature

High-entropy alloys(HEAs)have attracted great research interest owing to their good combination of high strength and ductility at both room and cryogenic temperatures.However,expensive raw materials are always added to overcome the strength-ductility trade-off at low temperatures,leading to an increased production cost for the cryogenically used alloys.In this work,a series of nitrogen-doped Fe Mn Co Cr HEAs have been processed by homogenization annealing,cold rolling and recrystallization annealing followed by water quenching.The microstructural evolution and mechanical properties of the alloys are studied systematically.The Fe_(49)Mn_(30)Co_(10)Cr_(10)N1alloy shows excellent mechanical properties at both 293 K and 77 K.Particularly,the yield and ultimate tensile strength of 1078 and 1630 MPa are achieved at the cryogenic temperature,respectively,while a satisfactory uniform elongation of 33.5%is maintained.The ultrahigh yield strength results from the microstructure refinement caused by the activation of athermal martensitic transformation and mechanical twinning that occur in the elastic regime together with the increased lattice friction due to the cryogenic environment.In the plastic regime,the dynamic Hall-Petch effect caused by twinning,martensitic transformation,and reverse transformation together with the high barrier to dislocation motion jointly contribute to the ultrahigh tensile strength.Simultaneously,the transformation induced plasticity(TRIP)and the twinning induced plasticity(TWIP)effects jointly contribute to the ductility.The design strategy for attaining superior mechanical properties at low temperatures,i.e.by adjusting stacking fault energy in the interstitial metastable HEAs,guides the development of high-performance and low-cost alloys for cryogenic applications.

Influence of Shear Banding on the Formation of Brass-type Textures in Polycrystalline fcc Metals with Low Stacking Fault Energy

Texture evolution in nickel, copper and α-brass that are representative of face-centered-cubic （fcc） materials with different stacking fault energy （SFE） during cold rolling was systematically investigated. X-ray diffraction, scanning electron microscopy and electron backscatter diffraction techniques were employed to characterize microstructures and local orientation distributions of specimens at different thickness reductions. Besides, Taylor and Schmid factors of the {111} 〈110〉 slip systems and {111} 〈112〉 twin systems for some typical orientations were utilized to explore the relationship between texture evolution and deformation microstructures. It was found that in fcc metals with low SFE at large deformations, the copper-oriented grains rotated around the 〈110〉 crystallographic axis through the brass-R orientation to the Goss orientation, and finally toward the brass orientation. The initiation of shear banding was the dominant mechanism for the above-mentioned texture transition.

Towards ultrastrong and ductile medium-entropy alloy through dual-phase ultrafine-grained architecture

Advanced materials with superior comprehensive mechanical properties are strongly desired,but it has long been a challenge to achieve high ductility in high-strength materials.Here,we proposed a new V 0.5 Cr 0.5 CoNi medium-entropy alloy(MEA)with a face-centered cubic/hexagonal close-packed(FCC/HCP)dual-phase ultrafine-grained(UFG)architecture containing stacking faults(SFs)and local chemical order(LCO)in HCP solid solution,to obtain an ultrahigh yield strength of 1476 MPa and uniform elongation of 13.2%at ambient temperature.The ultrahigh yield strength originates mainly from fine grain strength-ening of the UFG FCC matrix and HCP second-phase strengthening assisted by the SFs and LCO inside,whereas the large ductility correlates to the superior ability of the UFG FCC matrix to storage disloca-tions and the function of deformation-induced SFs in the vicinity of the FCC/HCP boundary to eliminate the stress concentration.This work provides new guidance by engineering novel composition and stable UFG structure for upgrading the mechanical properties of metallic materials.

Revealing the role of site occupation in phase stability,magnetic and electronic properties of Ni-Mn-In alloys by ab initio approach

The effects of site occupation on the phase stability,martensitic transformation,and the magnetic and electronic properties of a full series of Ni-Mn-In alloys are theoretically studied by using the ab initio calculations.Results indicate that the excess atoms of the rich component directly take the sublattices of the deficient components of the Ni2Mn_(1+x)In_(1-x),Ni2-xMn_(1+x)In,and Ni_(2+x)Mn_(1-x)In alloys.Nevertheless,the mixed and indirect site occupations may coexist in the Ni_(2+x)Mn In_(1-x)system.The relevant magnetic configurations of the austenite for the four alloy systems have also been determined.The results show that,except for the austenite in the Ni2-xMn_(1+x)In alloys,which tend to be ferrimagnetic,the other alloys all present ferromagnetic austenite.Thus,the site occupation and associated magnetic states are the crucial influencing factors of the phase stability,martensitic transformation,and the total magnetic moment.The electronic structure of the austenite phase also shows that the covalent bonding plays an important role in the phase stability.The key finding of this work is both Ni2Mn_(1+x)In_(1-x)and Ni_(2+x)Mn In_(1-x)alloys serve as the potential shape memory alloys.

Probing martensitic transformation,kinetics,elastic and magnetic properties of Ni2-xMn1.5In0.5Cox alloys

The martensitic transformation,kinetics,elastic and magnetic properties of the Ni2-xMn1.5In0.5Cox(x=0-0.33)ferromagnetic shape memory alloys were investigated experimentally and theoretically by first-principles calculations.First-principles calculations show that Co directly occupies the site of Ni sublattice,and Co atoms prefer to distribute evenly in the structure.The optimized lattice constants are consistent with the experimental results.The martensitic transformation paths are as follows:PA↔FA↔6MFIM↔NMFIM when 0≤x<0.25;PA↔FA↔6MFM↔NMFIM with 0.25≤x<0.3 and PA↔FA↔NMFM with 0.3≤x≤0.33 for Ni2-xMn1.5In0.5Cox(x=0-0.33)alloys.The fundamental reasons for the decrease of TM with increasing Co content are explained from the aspects of first-principles calculations and martensitic transformation kinetics.The component interval of the magnetostructural coupling is determined as 0≤x≤0.25 by first-principles calculations.Furthermore,the origin of the demagnetization effect during martensitic transformation is attributed to the shortening of the nearest neighboring distances for Ni-Ni(Co)and Mn-Mn.Combining the theoretical calculations with experimental results,it is verified that the TM of the Co6 alloy is near room temperature and its magnetization differenceM is 94.6 emu/g.Therefore,magnetic materials with high performance can be obtained,which may be useful for new magnetic applications.

Observation of magnetic domain evolution in constrained epitaxial Ni–Mn–Ga thin films on MgO(0 0 1) substrate

Epitaxial Ni–Mn–Ga thin films have promising application potential in micro-electro-mechanical sensing and actuation systems. To date, large abrupt magnetization changes have been observed in some epitaxial Ni–Mn–Ga thin films, but their origin-either from magnetically induced martensite variant reorientation(MIR) or magnetic domain evolution-has been discussed controversially. In the present work, we investigated the evolutions of the magnetic domain and microstructure of a typical epitaxial Ni–Mn–Ga thin film through wide-field magneto-optical Kerr-microscopy. It is demonstrated that the abrupt magnetization changes in the hysteresis loops should be attributed to the magnetic domain evolution instead of the MIR.

Electromagnetic wave absorption performance of Ti_(2)O_(3)and vacancy enhancement effective bandwidth

The microwave absorption properties of Ti_(2)O_(3)were systematically investigated.Experimental results indicate that Ti_(2)O_(3)has microwave absorption performance with a minimum reflection loss value of-37.6 d B at 18.6 GHz and an effective absorption bandwidth(RL<-10 d B)of 2 GHz.Further,vacancy defects were introduced into Ti_(2)O_(3)by carbothermal reduction.Interestingly,the effective absorption bandwidth of Ti_(2)O_(3)with vacancy defects reach 3.2 GHz.First-principles calculations provide evidence that vacancy defects result in the changes of electric dipole state,leading to a wider effective absorption bandwidth.These results have significance in understanding the origin of electromagnetic phenomena and developing electromagnetic wave absorption materials.

Composition-Dependent of 6 M Martensite Structure and Magnetism in Cu-Alloyed Ni-Mn-In-Co by First-Principles Calculations

The composition dependence of the crystal structure and magnetism of the 6 M martensite for the Cu-doped Ni_(43.75)Mn_(37.5)In_(12.5)Co_(6.25) alloy at different site occupations(Cu substitution for Ni, Mn, In, and Co, respectively) is investigated in detail with the first-principles calculations. Results show that the austenite(A) phase exhibits a ferromagnetic(FM) state in all occupation manners, the 6 M martensite possesses an FM state except for the case of Cu substitution at the normal Mn(Mn1) site, and the non-modulated(NM) martensite displays a ferrimagnetic(FIM) state apart from the Cu substitution at the Ni, Mn1, or In sites. The Cu atom destabilizes the A, 6 M, and NM phases regardless of the occupation manner. The one-step martensitic transformation from the A to NM phase occurs in the case of Cu substituting for Mn1, excess Mn(Mn2), or Co;for Cu substituting Ni, a martensitic transformation including 6 M martensite happens, i.e., A → 6 M → NM;however, the martensitic transformation disappears when Cu replaces In site. From the equilibrium lattice constants, it can be speculated that the substitution of Cu for Ni can effectively reduce the thermal hysteresis( ΔT_(Hys)). The magnetic properties are found to be greatly reduced by the substitution of the non-magnetic element Cu for the ferromagnetic Mn atom, whereas the effect is fewer in the remaining cases. It is predicted that the alloy has more favorable properties when Cu replaces Ni. The present results can lay a theoretical foundation for further development of multielement magnetic shape memory alloys.

Investigation of martensitic transformation behavior in Ni-Mn-In Heusler alloy from a first-principles study

Composition dependence of martensitic transformations as well as the magnetic properties for the Ni_2 Mn_(1+x)In_(1-x)(0.25≤x≤0.58)alloys were investigated by using the first-principles calculations.Key results demonstrate that the stability of parent austenite(A)decreases gradually with increasing Mn content whilst it is opposite for the martensitic phase.This causes the total energy difference between the austenite and martensite phases increscent with increasing Mn contents.When x=0.33,the martensite transformation during cooling is PA→FA→NM.When x≥0.42,an intermartensitic transformation occurs from modulated 6 M martensite to non-modulated(NM)martensite with the martensite transformation sequence of PA→FA→6 M→NM.The martensitic transformation from austenite to martensite accompanies the transition from ferromagnetic to ferrimagnetic state.This is a typical magneto-structural coupling transformation.The analysis of the density of states demonstrates that the Ni 3 d state plays an important role in the phase stability.