《徐先生相变会议》PPT课件.ppt

1、相变研究及材料形态学,徐祖耀 上海交通大学材料科学与工程学院,形核理论,除籍特殊条件下，直接由起伏长大的Spinodal分解外，材料相变均以形核为开端。在均匀形核理论中，对起伏形核，按统计热力学， (Landau和Lifshitz)获得n个原子组成新相集团的几率Pn，决定于形核集团的最低可逆功Gn，即 PnexpGn/kT 其中k为Boltzman常数。由此式得每摩尔平衡集团的大小分布，Nne： Nne =NAexp Gn/kT 其中NA为Avagadro常数,固态相变一般以母相中的缺陷（晶界，位错等）形核，属非均匀（非均质）形核。经典形核理论在近百年来被广泛应用，颇见成效，但也频受质疑。其形

2、核率的基本方程不但难于求解，所得结果也往往不符合实验数据。非均匀形核由于实验情况难于描述清楚，形核率的计算颇有难度。Kelton在1991年的论文（Solid State Physics）中瞻望研究“非稳态形核率”（按数学，形核率为时间的函数时即为非稳态形核,上世纪末，欧洲兴起同步辐射强X射线衍射三维仪、以测定一个晶粒（亚晶）内的相变。Offerman等（Science,2002）以此设备测得钢中奥氏体铁素体相变非均匀形核（晶界形核）相界能要比经典理论预测的小二个数量级或以上，即小于经典理论中二倍数量级的驱动力即能晶界形核。本文作者对此及时给以关注（2004年全国相变及凝固学术会议的大会报告,

3、2007年 他们又发表兼具理论分析和实验的论文（ Acta Mater）,阐明C35钢（0.364C-0.656Mn-0.305Si）中，当达一定过冷度（如30度）1003K时呈显无形核能垒的晶界形核, 宜予重视 。 其他如相变热力学，新相长大理论，动力学（包括相场理论），晶体学和形态学等均有待深入、创新，衷心盼望我国学者多作贡献,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,发展材料形态学,材料组织对性质的影响是材料科学与工程的核心。材料科学的发展和材料的实际应用都需要材料形态学（Materials Morphology）,其内容包括： 材料中不同组织形态的归纳和表征 不同组织形态的成因 组织形态对性质的影响，这对应用紧密相关，宜制成软件供

5、材料设计者参考运用,钢中珠光体的形态对力学性质的影响,设珠光体的片间距为S，高度为，向长大方向推进距离dx时，形成珠光体体积应为Sdx,质量为Sdx（为密度）。设Fe3C/间的表面能为，形成珠光体时新增表面面积为2dx，则新增界面能2dx,Zener（1946）假定相变驱动力用于所需的界面能，则可求得S与过冷度T之间的线性关系。结合Kramer等工作，拙著金属材料热力学（P.281-282）中列出： ST=610-4 cm. (1) 根据Marder和Bramfitt， 得： ST=8.026104 (2) 由他们的实验，得珠光体钢的屈服强度ys和断裂强度fs为： ys（MPa）=139+46

6、.4S-1（S：m） fs（MPa）=436.4+98.1S-1（S：m） 代入（1）或（2）式则可算得T对ys和fs的影响,马氏体形态对钢的力学性质的影响,R. A. Grange, Strengthening steel by austenite grain refinement, Trans. ASM., 1966, 59(1):26-48 对8650，4340和4310钢作出马氏体屈服强度和原奥氏体晶粒大小的-1/2方呈线性Hall-Petch关系，见拙著马氏体相变与马氏体第二版图3-99,条状马氏体显微组织的示意图 图录自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,图录自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,见马氏体相变与马氏体的图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）对Fe-0.2C和Roberts(R. J. Roberts, Metall. Trans. 1970, 1:3287-3294)对Fe-Mn得到，马氏体屈服强度与马氏体领域直径的-1/2方呈线性关系，如图（图录自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等显示领域大小影响马氏体钢的韧性。 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, 显示温度及领域大小对Fe-25%Ni形变方式的影响。如77K时，领域较小，屈服应力小于孪生应力，以滑移进行形变；当4K时才全部以孪生形变。如马氏体相变与马氏体第二版图3-9及3-97,2005年ICOMAT上，Morito等提出马氏体领域内马氏体束（block）的大小为决定条状马氏体强度的主要因素。我国钢研总院先显示奥氏体晶粒及马氏体领域大小对马氏体力学性能的影响，后得出束(block)的宽度为强度的控制因素;并显示原奥氏体晶粒及马氏体领域细化更有利于韧性的提高,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,惠卫军 , 董瀚 , 翁宇庆42CrMoVNb 细晶高强度钢的力学行为材 料 热 处 理 学 报, 2005, 26(5):57-61,对0.43C-1.10Cr-0.52Mo-0.30V-0.03Nb钢，细化奥氏体晶粒及马氏体packet宽度、提高马氏体的屈服强度及韧性（脆性转变温度） 细化奥氏体晶粒对马氏体条宽无影响,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