《徐先生相變會議》PPT課件.ppt

1、相變研究及材料形態(tài)學(xué),徐祖耀 上海交通大學(xué)材料科學(xué)與工程學(xué)院,形核理論,除籍特殊條件下，直接由起伏長大的Spinodal分解外，材料相變均以形核為開端。在均勻形核理論中，對起伏形核，按統(tǒng)計熱力學(xué)， (Landau和Lifshitz)獲得n個原子組成新相集團(tuán)的幾率Pn，決定于形核集團(tuán)的最低可逆功Gn，即 PnexpGn/kT 其中k為Boltzman常數(shù)。由此式得每摩爾平衡集團(tuán)的大小分布，Nne： Nne =NAexp Gn/kT 其中NA為Avagadro常數(shù),固態(tài)相變一般以母相中的缺陷（晶界，位錯等）形核，屬非均勻（非均質(zhì)）形核。經(jīng)典形核理論在近百年來被廣泛應(yīng)用，頗見成效，但也頻受質(zhì)疑。其形

2、核率的基本方程不但難于求解，所得結(jié)果也往往不符合實(shí)驗(yàn)數(shù)據(jù)。非均勻形核由于實(shí)驗(yàn)情況難于描述清楚，形核率的計算頗有難度。Kelton在1991年的論文（Solid State Physics）中瞻望研究“非穩(wěn)態(tài)形核率”（按數(shù)學(xué)，形核率為時間的函數(shù)時即為非穩(wěn)態(tài)形核,上世紀(jì)末，歐洲興起同步輻射強(qiáng)X射線衍射三維儀、以測定一個晶粒（亞晶）內(nèi)的相變。Offerman等（Science,2002）以此設(shè)備測得鋼中奧氏體鐵素體相變非均勻形核（晶界形核）相界能要比經(jīng)典理論預(yù)測的小二個數(shù)量級或以上，即小于經(jīng)典理論中二倍數(shù)量級的驅(qū)動力即能晶界形核。本文作者對此及時給以關(guān)注（2004年全國相變及凝固學(xué)術(shù)會議的大會報告,

3、2007年 他們又發(fā)表兼具理論分析和實(shí)驗(yàn)的論文（ Acta Mater）,闡明C35鋼（0.364C-0.656Mn-0.305Si）中，當(dāng)達(dá)一定過冷度（如30度）1003K時呈顯無形核能壘的晶界形核, 宜予重視 。 其他如相變熱力學(xué)，新相長大理論，動力學(xué)（包括相場理論），晶體學(xué)和形態(tài)學(xué)等均有待深入、創(chuàng)新，衷心盼望我國學(xué)者多作貢獻(xiàn),Relative Gibbs free energy c(n) = DG(n)/kBT for a cluster of the ferrite phase in C35 steel as a function of the cluster size n at se

4、veral temperatures. Both the maximum relative Gibbs free energy c* and the critical cluster size n* significantly decrease for larger values of the undercooling A3T,發(fā)展材料形態(tài)學(xué),材料組織對性質(zhì)的影響是材料科學(xué)與工程的核心。材料科學(xué)的發(fā)展和材料的實(shí)際應(yīng)用都需要材料形態(tài)學(xué)（Materials Morphology）,其內(nèi)容包括： 材料中不同組織形態(tài)的歸納和表征 不同組織形態(tài)的成因 組織形態(tài)對性質(zhì)的影響，這對應(yīng)用緊密相關(guān)，宜制成軟件供

5、材料設(shè)計者參考運(yùn)用,鋼中珠光體的形態(tài)對力學(xué)性質(zhì)的影響,設(shè)珠光體的片間距為S，高度為，向長大方向推進(jìn)距離dx時，形成珠光體體積應(yīng)為Sdx,質(zhì)量為Sdx（為密度）。設(shè)Fe3C/間的表面能為，形成珠光體時新增表面面積為2dx，則新增界面能2dx,Zener（1946）假定相變驅(qū)動力用于所需的界面能，則可求得S與過冷度T之間的線性關(guān)系。結(jié)合Kramer等工作，拙著金屬材料熱力學(xué)（P.281-282）中列出： ST=610-4 cm. (1) 根據(jù)Marder和Bramfitt， 得： ST=8.026104 (2) 由他們的實(shí)驗(yàn)，得珠光體鋼的屈服強(qiáng)度ys和斷裂強(qiáng)度fs為： ys（MPa）=139+46

6、.4S-1（S：m） fs（MPa）=436.4+98.1S-1（S：m） 代入（1）或（2）式則可算得T對ys和fs的影響,馬氏體形態(tài)對鋼的力學(xué)性質(zhì)的影響,R. A. Grange, Strengthening steel by austenite grain refinement, Trans. ASM., 1966, 59(1):26-48 對8650，4340和4310鋼作出馬氏體屈服強(qiáng)度和原奧氏體晶粒大小的-1/2方呈線性Hall-Petch關(guān)系，見拙著馬氏體相變與馬氏體第二版圖3-99,條狀馬氏體顯微組織的示意圖 圖錄自H. Kitahara, R. Ueji, N. Tsuji,

7、 Y. Minamino，Crystallographic features of lath martensite in low-carbon steel，Acta Mater.， 2006, 54:1276-1288中，P1283， Fig.4,圖錄自S. Morito, H. Tanaka, R. Konishi, T. Furuhara, T. Maki， The morphology and crystallography of lath martensite in Fe-C alloys，Acta Mater.，2003， 51：1789-1799， P1797. Fig.10,Ma

8、rder和Krauss(A. R. Marder, G. Krauss, 2nd Inter. Conf. The Strength of Metals and Alloys, Alisomar, 1970, vol.3, ASM., 822,見馬氏體相變與馬氏體的圖3-98)以及Swarr和Krauss（T. Swarr, G. Krauss, The effect of structure on the deformation of as-quenched and tempered martensite in an Fe-0.2 pct C alloy, Metall. Trans. 19

9、76, 7A:41-48）對Fe-0.2C和Roberts(R. J. Roberts, Metall. Trans. 1970, 1:3287-3294)對Fe-Mn得到，馬氏體屈服強(qiáng)度與馬氏體領(lǐng)域直徑的-1/2方呈線性關(guān)系，如圖（圖錄自G. Krauss, Martensite in steel: strength and structure, Mater. Sci. Enger. A, 1999, 273-275:40-57, P. 556, Fig. 33,Yield strength as a function of packet size, D, of lath martensit

10、e in an Fe0.2 wt.% C FeC alloy and an FeMn alloy,Inoue等顯示領(lǐng)域大小影響馬氏體鋼的韌性。 T. Inoue, S. Matsuda, Y. Okamura, K. Aoki，The Fracture of a Low Carbon Tempered MartensiteTrans. JIM., 1970, 11:36-43, The packet size affects the toughness of martensitic steel J. L. Nilles和W. S. Owen, Deformation twinning of m

11、artensite， Metall. Trans. 1972, 3: 1877-1883, 顯示溫度及領(lǐng)域大小對Fe-25%Ni形變方式的影響。如77K時，領(lǐng)域較小，屈服應(yīng)力小于孿生應(yīng)力，以滑移進(jìn)行形變；當(dāng)4K時才全部以孿生形變。如馬氏體相變與馬氏體第二版圖3-9及3-97,2005年ICOMAT上，Morito等提出馬氏體領(lǐng)域內(nèi)馬氏體束（block）的大小為決定條狀馬氏體強(qiáng)度的主要因素。我國鋼研總院先顯示奧氏體晶粒及馬氏體領(lǐng)域大小對馬氏體力學(xué)性能的影響，后得出束(block)的寬度為強(qiáng)度的控制因素;并顯示原奧氏體晶粒及馬氏體領(lǐng)域細(xì)化更有利于韌性的提高,S. Morito, H. Yoshid

12、a, T. Maki, X. Huang, Effect of block size on the strength of lath martensite in low carbon steels, Mater. Sci. Eng, A, 2006, 438-440: 237-240 The block size is the key structural parameter controlling the strength of lath martensite(by using optical microscopy, SEM, electron backscattered diffracti

13、on(EBSD) and TEM,Fig .1 Relationship between the prior austenite grain size and the packet size in quenched martensite in the Fe0.2C and the Fe0.2C2Mn alloys,Fig.2 Relationship between the prior austenite grain size and the block width in quenched martensite in the Fe0.2C and the Fe0.2C2Mn alloys,Ha

14、llPetch type plots of yield strength vs. reciprocal square root of the packet size, (b) similar plot in terms of the block size, for the Fe0.2C and the Fe0.2C2Mn alloys,Prior austenite grain size (dg), sub-block width (ds), lath width (dl), mean misorientation angle of sub-block boundaries (s), mean

15、 misorientation angle of lath boundaries (l), and dislocation density within laths (0) measured in Fe0.2C2Mn alloy Fe-0.2C-2Mn: Fe-0.206C-0.011Si-2.017Mn-0.004P-0.0007S Fe-0.2C:Fe-0.18C-0.006Si-0.02Mn-0.001P-0.004S,Prior austenite grain size has a strong effect on the scale of packets and blocks in

16、the quenched lath martensite, but little effect on the dependent of the substructure within the blocks, implying that the substructure hardening is basically independent of the grain size. Comparison of Fig.1 and Fig.2 shows that the block width is much smaller than the packet size, indicating that

17、the high angle boundaries in the structure are dominated by the block boundaries. Similar Hall-Petch slopes are obtained when the yield strength is analyzed in terms of the block size for two alloys with 0.2C as shown in Fig.3b, in consistent with the present shown that the Mn addition, does not cha

18、nge that the Hall-Petch slope, and the block size dominates the yield strength,惠衛(wèi)軍 , 董瀚 , 翁宇慶42CrMoVNb 細(xì)晶高強(qiáng)度鋼的力學(xué)行為材 料 熱 處 理 學(xué) 報, 2005, 26(5):57-61,對0.43C-1.10Cr-0.52Mo-0.30V-0.03Nb鋼，細(xì)化奧氏體晶粒及馬氏體packet寬度、提高馬氏體的屈服強(qiáng)度及韌性（脆性轉(zhuǎn)變溫度） 細(xì)化奧氏體晶粒對馬氏體條寬無影響,Chunfang Wang, Maoqiu Wang, Jie Sui, Weijun Hui and Han Don

19、g，Effect of Microstructure Refinement on the Strength and Toughness of Low Alloy Martensitic Steel, J. Mater. Sci. Technol., 2007,23(5):659-664,The prior austenite grain size and martensitic packet size in a 0.17C-1.8Cr-1.58Ni-0.23Mo steel follow the Hall-Petch relationship with the yield strength a

20、nd the microstructure refinement is more effective in improving the resistance to cleavage fracture than in increment of the strength,Chunfang Wang, Maoqiu Wang, Jie Shi, Weijun Hui, Han Dong, Effect of microstructural refinement on the toughness of low carbon martensitic steel, Scritpa Mater., 2008

21、, 58:492-495,Electron backscattered diffraction(EBSD) analysis of the cleavage crack path in an as-quenched and tempered 0.17C-0.21Si-0.55Mn-1.80Cr-1.58Ni-0.25Mo-0.011P-0.002S steel shows that the packet boundary can strongly hinder the fracture propagation, implying that the packet size controls th

22、e impact energy and fraction appearance transition temperature(FATT) Table. 1 Microstructural features, LSE, mean cleavage facet size, fracture stress and yield strength for the steel austenitized at various temperatures,a) Variation of Charpy impact energy with test temperature in the range 77373 K

23、 for specimens with various packet sizes and (b)50% FATT as a function of the martensitic packet size for the steel,The average lath width of various samples is about 0.3m, being independent of the prior austenite grain size. Lower shelf energy(LSE) decreases with the increment of packet size. From

24、table 1, it seems that the yield strength of martensitic steel is not so strongly related to the prior grain size rather than the toughness does,L. A. Norstrom, Scand. J. Metall., 1976, 5:159- 165,An equation for the yield strength of the low carbon martensitic structure was developed as: y=0+1+kyD-

25、1/2+KSd-1/2+Gb0+Kl%C where 0 is the friction stress of the pure iron, 1 is the solid solution strengthening from Mn and Ni, d is the lath width, D is the packet size, 0 is the dislocation density of martensitic pure iron,Y. Tomita and K. Okabayashi, Effect of Microstructure on Strength and Toughness

26、 of Heat-Treated Low Alloy Structural Steels. Metall. Trans. A., 1986, 17A:1203-1209,The packet diameter is the primary microstructural parameter controlling yield stress and ductile-brittle transition temperature. The mechanical properties are also improved to a lesser degree with decreasing width

27、of the lath within the packet,Table .1 Values ofi and ky in the Relation, 0.2=i+1+kydp-1/2, for Martensitic Steels,0.2=i+1+kydp-1/2,Effect of the lath width on ky parameter in the Hall-Petch equation,D. W. Smith and R. F. Hehemann, Influence of Structural Parameter on the Yield Strength of Tempered

28、Martensite and Lower Bainite, J. Iron and Steel Inst.,1971,June,476-481 The change in yield strength that occur when martensite and bainite in 4340 steel are tempered at temperatures in the range from 315-540(from 1500MPa to 1200MPa) can be attributed to coarsening of carbide precipitates and to inc

29、rease in size of the cellular substructure(lath width). The Langford-Cohen model for cell-size hardening, which relates the yield strength with the reciprocal of the average cell width, providing a better correlation of the experimental data than does the Hall-Petch model,0.2=0+1.2610-2w-1+4.21 10-3

30、 p-1,0 :the sum of peierls stress, solution harderning, work hardening, and the effect of dislocation substructure. W: The average cell size(lath width) p :The average planar interparticle spacing, in mm,J. P. Naylor, The Influence of the Lath Morphology on the Yield Stress and Transition Temperatur

31、e of Martensitic-Bainitic Steels, Metall. Trans., 1979, 10A,861-73. In 0.065C-0.97Mn-2.32Cr-0.83Ni-0.19Mo-0.31Si steel, the tensile strength increases with the reduction of lath width(l) of martenstie,And the ductitle-brittle transition temperature(DBTT) can be related to a logarithmic function of the produ