完整高熵合金课件.ppt
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1、FeCoNiCrMn 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Acknowledgements? 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” Progra
2、m (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 alloysIn 2004, Multicomponent FeCoNiCrMn alloy firstly reported by Cantor B. with a simple
3、 fcc solid-solution structure.Cantor B et al. MSE A, 2004, 375-377: 213-218. Definition of high entropy alloysStill in 2004, the concept of high entropy alloy was firstly introduced by Yeh JWYeh JW et al. Adv Eng Mater, 2004, 6: 299-303. Simple phase formation but complex metallurgical phenomenonCu-
4、Zr binary alloy systemThe Gibbs Phase RuleP=N+1-FWhen N=5, P=6FeCoNiCrMnActually HEAs alloy have a simple solid-solution structure (mainly fcc or bcc) !Features of HEAs severe lattice distortionLattice distortionLattice distortionSolution Solution strengthening effectstrengthening effectZhou, et al.
5、 Appl Phys Lett, 2008, 92: 241917Senkov ON, et al. Intermetallics, 2011,19:698Features of HEAs sluggish diffusion?Constituent 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 constituentsTsai et al. Act
6、a Mater 2013; 61:4887Features of HEAs high phase stability1400oC19hAs-castAfter compression at 1073 KSenkov et al. Intermetallics 2011; 19: 698-706?Formation of a single bccphase?The bccphase is highly stable up to 1600 oCFeatures of HEAs cock tail effect?the effect indicates thatthe unexpected prop
7、erties can be obtained after mixing many elements, which could not be obtained from any one independent element.Extremely high toughness of a typical fcc HEA ?The fracture toughness of Bernd Gludovatz et al. Science 2014,345:1153FeCoNiCrMn exceeds 210 MPam-1/2Abnormal low-temperature mechanical prop
8、erties?With the decrease of testing temperature, both tensile strength and ductility are increased;?The fracture toughness kept almost unchanged;Promising high-temperature mechanical properties of bcc HEAsSenkov et al. Intermetallics 2011; 19: 698-706?High yield strength at temperatures up to 1600o?
9、CThe strong resistance to high-temperature softening, as compared to the superalloysInteresting physical properties of HEAs: discovery of superconductivity?Ta34Nb33Hf8Zr14Ti11HEA possesses an body-centered cubic structure of lattice parameter a 3.36 ?.?It is a type II superconductor with a transitio
10、n temperature Tc 7.3 KP. Ko?elj et al. PRL 2014 ,113: 107001 Diffusion barrier materials?High phase stability -no interaction with substrates;?Low diffusion kinetics- -high diffusion resistance at elevated temperatures 15The research activities on HEAs at USTB Progress in Materials Science, 2014; 61
11、:1-93Our purposeDesign the FeCoNiCrMn based HEAs for high-temperature applicationsContent?Phase formation and stability ?Grain growth at elevated temperatures?Deformation behavior?Alloying effects (to enhance high-T mechanical performance)1.Phase formation and stability are influenced by not only ch
12、emistry but also processing conditions2.Effects of alloying additions on phase formation, stability and properties are not as simple as expectedPhase formation in the as-cast FeCoNiCrMn?Basically the alloy has a single fcc phase but with a small fraction of unidentified phase (Cr2Mn oxide ?)The FeCo
13、NiCrMn high entropy alloy showed high phase stability (a)(b)(c)?Thesingle fcc phase in the FeCoNiCrMn alloy is stable even after 30 days annealing at 950 oC The FeCoNiCrMn high entropy alloy showed high phase stability (b)(c)?Texture seems changed with the processing conditions?No second phase was f
14、ormed during the rolling/annealing processes Content?Phase formation and stability?Grain growth at elevated temperatures?Deformation behavior?Alloying effectsGrain growth behavior of the FeCoNiCrMn high entropy alloy was studied in detail70% cold rolled850C/1h850C/2h850C/2h925C/1h925C/2h925C/3.5hGra
15、in coarsening exhibited a classical power law behavior in the FeCoNiCrMn alloy?n = 3 and D0 = 1.0 m m?n is larger than 2 which is for Liu et al., Scripta Materialia 2013;68:526the “ideal” grain growth in single-phase pure materialsThe apparent activation energy for grain growthsuggests that sluggish
16、 diffusion indeed occurred?The Q value is much higher than that for AISI 304LN -1stainless steels, which is only about 150 kJ molThe hardness values at different temperatures closely follow the classical Hall Petch relationship ?The softening mainly from grain coarsening?The KHPis larger than 600 Mp
17、a m m-0.5(the upper-bound for fcc metals) , suggesting that grain boundary hardening efficiency is obviously higher Content?Phase formation and stability?Grain growth at elevated temperatures?Deformation behavior?Alloying effectsIn-situ neutron diffraction study of deformation behavior of the FeCoNi
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