(完整ppt)高熵合金课件.ppt

1、FeCoNiCrMnFeCoNiCrMn高熵合金的组织稳定性高熵合金的组织稳定性及变形行为及变形行为吕昭平吕昭平 教授教授北京科技大学北京科技大学 新金属材料国家重点实验室新金属材料国家重点实验室AcknowledgementsAcknowledgements Students:W.H.Liu,S.Y.Li,H.L.Huang and Z.F.Lei Collaborators:H.Wang,Y.Wu,and X.J.Liu National science foundation of China(Nos.51010001,51001009,and 51271212)“111”Program(

2、B07003)Program for Innovative Research Team in UniversityTraditional alloys are mostly based on one primary elementSteels(Fe),Al alloys,Ti alloys,Mg alloys,Supper alloys(Ni)Discovery of high entropy alloysCantor B et al.MSE A,2004,375-377:213-218.In 2004,Multicomponent FeCoNiCrMn alloy firstly repor

3、ted by Cantor B.with a simple fcc solid-solution structure.Yeh JW et al.Adv Eng Mater,2004,6:299-303.Definition of high entropy alloysStill in 2004,the concept of high entropy alloy was firstly introduced by Yeh JWSimple phase formation but complex metallurgical phenomenonCu-Zr binary alloy systemAc

4、tually HEAs alloy have a simple solid-solution structure(mainly fcc or bcc)!The Gibbs Phase RuleP=N+1-FWhen N=5,P=6FeCoNiCrMnFeatures of HEAssevere lattice distortionLattice distortionLattice distortionZhou,et al.Appl Phys Lett,2008,92:241917Senkov ON,et al.Intermetallics,2011,19:698Solution strengt

5、hening Solution strengthening effecteffectTsai et al.Acta Mater 2013;61:4887Constituent elements in the HEA matrix diffuse much slowly over the entire temperature range The diffusion coefficient of Ni is the smallest among that of all constituentsFeatures of HEAssluggish diffusionSenkov et al.Interm

6、etallics 2011;19:698-706 As-castAfter compression at 1073 KFormation of a single bcc phaseThe bcc phase is highly stable up to 1600 oC1400oC19hFeatures of HEAshigh phase stabilityFeatures of HEAscock tail effectthe effect indicates thatthe unexpected properties can be obtained after mixing many elem

7、ents,which could not be obtained from any one independent element.Extremely high toughness of a typical fcc HEA Bernd Gludovatz et al.Science 2014,345:1153The fracture toughness of FeCoNiCrMn exceeds 210 MPam-1/2Abnormal low-temperature mechanical propertiesWith the decrease of testing temperature,b

8、oth tensile strength and ductility are increased;The fracture toughness kept almost unchanged;High yield strength at temperatures up to 1600oCThe strong resistance to high-temperature softening,as compared to the superalloysPromising high-temperature mechanical properties of bcc HEAsSenkov et al.Int

9、ermetallics 2011;19:698-706 Ta34Nb33Hf8Zr14Ti11 HEA possesses an body-centered cubic structure of lattice parameter a 3.36.It is a type II superconductor with a transition temperature Tc 7.3 KP.Koelj et al.PRL 2014,113:107001 Interesting physical properties of HEAs:discovery of superconductivity15Di

10、ffusion barrier materialsHigh phase stability-no interaction with substrates;Low diffusion kinetics-high diffusion resistance at elevated temperatures The research activities on HEAs at USTB Progress in Materials Science,2014;61:1-93Our purpose Design the FeCoNiCrMn based HEAs for high-temperature a

11、pplicationsContentPhase formation and stability Grain growth at elevated temperaturesDeformation behaviorAlloying effects(to enhance high-T mechanical performance)1.Phase formation and stability are influenced by not only chemistry but also processing conditions2.Effects of alloying additions on pha

12、se formation,stability and properties are not as simple as expectedPhase formation in the as-cast FeCoNiCrMnBasically the alloy has a single fcc phase but with a small fraction of unidentified phase(Cr2Mn oxide?)The FeCoNiCrMn high entropy alloy showed high phase stability The single fcc phase in th

13、e FeCoNiCrMn alloy is stable even after 30 days annealing at 950 oC The FeCoNiCrMn high entropy alloy showed high phase stability Texture seems changed with the processing conditionsNo second phase was formed during the rolling/annealing processes ContentPhase formation and stabilityGrain growth at

14、elevated temperaturesDeformation behaviorAlloying effects850C/1h850C/2h850C/2h70%cold rolled925C/1h925C/2h925C/3.5hGrain growth behavior of the FeCoNiCrMn high entropy alloy was studied in detailGrain coarsening exhibited a classical power law behavior in the FeCoNiCrMn alloyn=3 and D0=1.0 m mmn is

15、larger than 2 which is for the“ideal”grain growth in single-phase pure materialsLiu et al.,Scripta Materialia 2013;68:526The apparent activation energy for grain growth suggests that sluggish diffusion indeed occurred The Q value is much higher than that for AISI 304LN stainless steels,which is only

16、 about 150 kJ mol-1The hardness values at different temperatures closely follow the classical HallPetch relationship The softening mainly from grain coarseningThe KHP is larger than 600 Mpa m mm-0.5(the upper-bound for fcc metals),suggesting that grain boundary hardening efficiency is obviously high

17、er ContentPhase formation and stabilityGrain growth at elevated temperaturesDeformation behaviorAlloying effectsIn-situ neutron diffraction study of deformation behavior of the FeCoNiCrMn alloy was conductedWu et al.,Appl.Phys.Letts.2014;104:051910VULCAN system at Spallation Neutron Scattering,Oak R

18、idge National LaboratoryModulus:GPaStrong elastic anisotropy was observed during the tensile loadingThe lattice strain change is strongly dependent on the grain orientationsThe 200 planes have the lowest elastic modulus while the 331 planes have the highestYoungs modulus anisotropy(E111/E100)is 1.98

19、,close to that of Ni(2.17)but smaller than that of typical fcc steels(3.20)Development of a textured structure during the tensile deformationThe peak intensity of the 220 and 200 reflections decreased,while that of the 111 reflections increasedTextural evolution of the current HEA during tension app

20、ears to be similar to those of typical FCC metals and alloys,for example,polycrystalline copper with columnar grainsThe single crystal elastic constants of the current HEA were determined by the Kroners modelThe cubic elastic anisotropy factorThe shear anisotropy was calculated as 2.84,much smaller

21、than that of the ternary FeCrNi alloy(3.77),but close to that of the pure FCC-Ni(2.51),manifesting that the elastic anisotropy behavior of the current HEA is close to that of its FCC component,i.e.,pure Ni.The experimentally determined peak broadening data can reveal the dislocation types during def

22、ormationThe slope in the above plot is 2.189,which seems like a balancing value for the edge(1.492)and screw(2.298)dislocations,but close to that of the screw dislocationA representative bright field image with wiggled dislocations in a deformed specimen,suggesting a mixed dislocation characteristic

23、sFlow behavior at different temperatures and strain rates were investigated The temperature is in between 1023 and 1123 KThe strain rate ranges from 6.410 10-7 to 8.013 10-4 s-1He et al.,Intermetallics 55,2014;9-14.The Norton EquationSteady-state deformation behavior of FeCoNiCrMnRegion II with a hi

24、gh stress exponent at the high strain rates(or stresses)while Region I with a low stress exponent at the low strain rates(or stresses)The activation energy in two regions are comparable to that for lattice diffusion.For example,Ni(317.5 kJ/mol),Cr(292.9 kJ/mol),and Mn(288.4 kJ/mol)The normalized plo

25、t indicates that the data obtained at various temperatures(1023-1123 K)collapse into one single master curve In the high strain rate regime,n is 5 and the activation energy is 330 kJ/mol,suggesting a dislocation-climb mechanism and the slowest diffusing species Ni controls the rate process.In the lo

26、w strain rate regime,n is 3 and the activation energy is 280 kJ/mol,suggesting that the mechanism is the dislocation gliding and the deformation rate is controlled by the diffusion of one of the constituent elements which acts as the solute atom.ContentPhase formation and stabilityGrain growth at el

27、evated temperaturesDeformation behaviorAlloying effectsAl effects1.Relatively lower steady state flow stress than super alloys2.Oxidation resistance is low due to highly active element MnAddition of Al in the(FeCoNiCrMn)100-xAlx alloys induced a phase transition from fcc to bcc starting at Al8He et

28、al.,Acta Mater.2014;62:105.Microstructure observation further confirms the phase transition resulted from the Al additionBcc phase becomes dominant in alloy Al13,Al14 and Al16,and the minor fcc phase mainly lies in the bcc grain boundaries.The cubic-shaped particles are ordered B2 while the inter-pr

29、ecipitate area is disordered A2.fcc:74.6%.TEM characterization reveals the detailed phase characteristics The cubic-shaped precipitates become slightly smaller but more close-packed.fcc:11%Al are too brittle to be deformed due to formation of ordered BCC structures.Summary FeCoNiCrMnalloyPhase forma

30、tion and stability-high(homogenization,long term aging,rolling)Grain growth at high temperatures-slowAl effects-solution strengtheningDeformation behavior-RT:similar to Ni,mix dislocationsHT:high strain rate,dislocation climb low strain rate,dislocation glideHigh-T materials Secondary phase hardenin

31、g resulted from bcc phases(NiAl B2)in FeCoNiCrMn is not very satisfactory.Based on previous studies in steels and superalloys,L12 phase(phase-Ni3Al)is a desirable secondary phase for a fcc matrix,both at room and elevated temperature.Hardening mechanisms urgently needed in the FeCoNiCr HEA system金属学

32、报，金属学报，1978,14(3):227-237金属学报金属学报.2014,50(10):1260-12GH984G合金中球形Ni3Al型 沉淀相颗粒The L12 precipitates was observed in the fcc Al0.3FeCoNiCr The tensile strength is only increased slightly after aging due to the fact that the precipitates distribute inhomogeneously.More work has been done for precipitatio

33、n in HEAs.Shun TT et al.JAC 2009;479:157160Addition of Al alone cannot effectively promote precipitation of a large density of nanosized particles uniformly dispersed in the matrixUnsolved scientific problems/Key research topicsPhase formation and stability(why solid-solutions&under what conditions,phase transition,enthalpy effects,etc.)Alloy design and preparation(alloying effects,structures&properties optimization,processes,etc.)Deformation mechanism and mechanical propertiesPhysical and chemical propertiesApplications:different service temperatures