上海交通大学：《材料加工原理 Principles of Materials Processing》教学资源（课件讲稿）凝固和铸造 Solidification and casting_Solidification of multi phase alloys（2）

先进材料疑固实验室 Laboratory of Advanced Materials Solidification 1896 1920 1987 2006 Solidification of multi phase alloys(2) Dr.Mingxu Xia anced Mate 国 上浒充通大学 SHANGHAI JIAO TONG UNIVERSITY

1896 1920 1987 2006 Solidification of multi phase alloys (2) Dr. Mingxu Xia

先进材料疑固实验室 References Laboratory of Advanced Materials Solidification M.C.Flemings,凝固过程 W.Kuz,凝固原理 介万奇，凝固技术 JA Dantzig,M.Rappaz,Solidification tory of vanced Materials Solid 上浒充通大学 SHANGHAI JIAO TONG UNIVERSITY

References M.C.Flemings, 凝固过程 W.Kurz,凝固原理 介万奇，凝固技术 JA Dantzig, M. Rappaz, Solidification

先进材料疑固实验室 OUTLINE Laboratory of Advanced Materials Solidification Solidification of Eutectics Solidification of Peritectics General considerations of pertitectics Nucleation of peritectics Solidification of peritectics Microstructure control through solidification method Solidification Defects The other defects vanced MaterialsS 上浒充通大学 SHANGHAI JIAO TONG UNIVERSITY

OUTLINE Solidification of Eutectics Solidification of Peritectics • General considerations of pertitectics • Nucleation of peritectics • Solidification of peritectics Microstructure control through solidification method Solidification Defects The other defects

先进材料疑固实验室 General considerations Laboratory of Advanced Materials Solidification Many important industrial alloys exhibit a peritectic transforamtion during solidfiication.The most important systems are steel(Fe-C), Bronze(Cu-Sn)and brass(Cu-Zn).Peritectic invariants are also found in Al-Ti,Al-Ni or high-Tc YBaCuO superconductors. 0+l→B Cper Cper Cper a liquid T品(C) a+l aY 6+ C C B liquid (a) (b) (c) 上游文通大学 SHANGHAI JIAO TONG UNIVERSITY

General considerations Many important industrial alloys exhibit a peritectic transforamtion during solidfiication. The most important systems are steel (Fe-C), Bronze (Cu-Sn) and brass (Cu-Zn). Peritectic invariants are also found in Al-Ti, Al-Ni or high-Tc YBaCuO superconductors. α+l→β

先进材料疑固实验室 Nucleation Laboratory of Advanced Materials Solidification a phase nucleation temperature:T=(Ti(C)-4T) B phase nucleation temperature:=(T(C)-4T, Where,T(Co)T(C)liquidus temperature,4T undercooling T T △T% me Effective liquidus line △T 上浒充通大学 SHANGHAI JIAO TONG UNIVERSITY

Nucleation α phase nucleation temperature: β phase nucleation temperature: Where, liquidus temperature, undercooling

先进材料疑固实验室 Nucleation Laboratory of Advanced Materials Solidification Only when T>,we can conclude a phase will nucleate before βphase. ⊕ In general 4T+4,and thus the a-B transition composition C is shifted with respect to Cper,it is given by C-Cpor ATS -ATE T T B mg -m △TR ⊕ m mf are the liquidus slope of a and B D1 Effective liquidus line △Tn 上浒充通大学 SHANGHAI JIAO TONG UNIVERSITY

Nucleation Only when > , we can conclude α phase will nucleate before β phase. In general , and thus the α→β transition composition Cn α→β is shifted with respect to Cl per, it is given by are the liquidus slope of α and β

先进材料疑固实验室 nucleation Laboratory of Advanced Materials Solidification Consider now a hyperperitectic alloy oc composition close to the peritectic composition Cper,we assume the a/l interface to be at equilibrium,i.e.,that the curvature and kinetic contributions are negligible.Therefore,the undercooling for the nucleation of B for T<Tper is given by 4=(Ga(G)-Ta(G)=(m-m）(G-C) T(C) Since the a phase is already present, the a/liquid interface is the most △ probable site for nucleation of B.There T) is usually a coherency relationship between the phases. 上浒充通大学 SHANGHAI JIAO TONG UNIVERSITY

nucleation Consider now a hyperperitectic alloy oc composition close to the peritectic composition Cper, we assume the α/l interface to be at equilibrium, i.e., that the curvature and kinetic contributions are negligible. Therefore, the undercooling for the nucleation of β for T<Tper is given by Since the α phase is already present, the α/liquid interface is the most probable site for nucleation of β. There is usually a coherency relationship between the phases. Cper β

先进材料疑固实验室 Solidification of peritectics Laboratory of Advanced Materials Solidification Normal growth speed: A quenched peritectic microstructure observed in Sn- 1000 900 bronze,with the B-phase 800 completely surrounding the 700 primary a-phase. 600 10 20 30 Cs [wt6] (a)Cu-Sn phase dingram (b)Cu-Sn microstructure A micrograph of Fe-50wt%Au 1400 alloy with the peritectic phase 1200 has the same crystal structure as the primary phase.The 1000 primary y-phase solidifies first 800 and thin layer y'-phase forms 204060C. 10m around y. (e)Fe-Au phase diagram (d)Fe-Au mierostructure Fig.9.27 Examples of peritectie microstructures and their associated phase dia. grams:(a)The Cu-Sn phase diagram and (b)mierostructure observed in a quenched Cu-20wt%Sn specimen [19).(c)The Fe-Au phase diagram and (d) mierostructure in a quenched Fe-50wt Au specimen.(Courtesy,D.Favez.) 上游文通大学 SHANGHAI JIAO TONG UNIVERSITY

Solidification of peritectics Normal growth speed: A quenched peritectic microstructure observed in Sn￾bronze, with the β-phase completely surrounding the primary α-phase. A micrograph of Fe-50wt%Au alloy with the peritectic phase has the same crystal structure as the primary phase. The primary γ-phase solidifies first and thin layer γ’-phase forms around γ

先进材料疑固实验室 Solidification of peritectics Laboratory of Advanced Materials Solidification Slow growth speed: (a) (b) (c) (d) (e) (D Fig.9.30 A summary of peritectic microstructures observed at very low speed dur ing solidification in a vertical thermal gradient:(a)Bands;(b)Islands;(c)Single transition from a to B;(d)Coupled growth of o-and B-lamellae;(e)Nucleation of in the liquid ahead of a 3-e planar front;(f)Helicoidal structure.(a-d)Hypoperi tectic compositions;(e-f)Hyperitectic compositions.(After Boettinger et al.[61.) 上浒充通大 SHANGHAI JIAO TONG UNIVERSITY

Solidification of peritectics Slow growth speed:

先进材料疑固实验室 Solidification of peritectics Laboratory of Advanced Materials Solidification Cper 1.4 bands plane coupled front 1.0 mixed t118601202 bands yplane front 0.6 6cells dendrites 0.2 Ycells dendrites 3.0 3.5 4.0 4.5 15.0 5.5 CNi [at%] Cper (a)Coupled growth (b)Morphology map Fig.9.31 (a)Coupled (or cooperative)growth of y and 6 phases in Fe-Ni.(b)The G/v-Co diagram showing the various morphologies that can be observed in Fe-Ni. (After Hunziker et al.[15].) 熟 上游文通大学 SHANGHAI JIAO TONG UNIVERSITY

Solidification of peritectics