耐热相关金属学问题

1、耐热的相关金属学问题材料结构在高温环境中的演化及其对力学性能的影响北京科技大学 杨善武内 容 范性变形的一般机制与强化措施 改善材料高温力学性能的主要措施 高温力学行为及其对应的结构演化范性变形的一般机制与强化措施 范性变形的微观机制 金属与合金的宏观范性变形在微观上对应位错的滑移（包括螺型位错在高温的交叉滑移）、攀移（发生于高温）、晶体的孪生（主要发生于低温）和多晶体沿晶界的滑动（发生于高温），其中以位错滑移为最常见的方式。 刃型位错滑移孪生刃型位错攀移“趁热打铁”的道理 升高温度导致钢的变形抗力（位错运动阻力）减弱 温度超过一定值后，钢基体由体心立方结构转变为面心立方结构，更易于变形 升温

2、导致的软化效应（回复、再结晶、析出相粗化、晶粒长大等）可以抵消变形导致的硬化（加工硬化）T金属单晶体的切变强度随温度的变化趋势原因：热激活可以帮助位错克服短程阻力，但对长程阻力无作用。硬度时间回复过程中硬度随时间的变化再结晶体积分数时间再结晶体积分数随时间的变化范性变形的一般机制与强化措施 强化金属的主要措施 以阻碍位错运动为基本出发点，强化措施主要包括：位错强化、细化晶粒的强化、固溶强化（高温适用） 、析出强化（高温适用） 和相变强化（为前几类强化方式的综合）。改善材料高温力学性能的主要措施 强化晶界 降低界面能 增加位错运动的晶格阻力（P-N力） 在材料内部引入稳定的应力场度度强强晶界与晶

3、内强度随温度的变化晶界工程-降低界面能的有效途径 利用面心立方结构的金属易于发生退火孪生这一现象，通过反复进行的变形和退火处理，可以在材料中得到大量=3, 9, 27的重位点阵晶界，从而降低界面能，提高晶界的热稳定性。Grain boundary character distribution of the as-received (AR) and GBE-treated samples as a function of initial percentage reduction in thickness (5%, 9%, and 13%). The symbols in open, diagon

4、al cross, cross, and single horizontal bar denote the number of thermomechanical cycles from 1 to 4 applied to the samples. Fraction of low-R CSLBs of the as-received and GBE treated samples, GBE1 and GBE2. L. Tan et al.Effect of thermomechanical processing on grainboundary character distribution of

5、 a Ni-based superalloy. Journal of Nuclear Materials 371 (2007) 171175Deviation angle from exact R3 of the as-received and GBE-treated samples, GBE1 and GBE2.Thermal stability of the grain boundary character distribution of GBE-treated samples, GBE1 and GBE2, after exposure at 850 for 672 h.位错运动的晶格阻

6、力（P-N力）)1 (2exp12)4exp(12babp其中)1 (2a为位错半宽度由上式可以看出，位错运动的晶格阻力与温度无关，在高温仍能得到维持。高温力学行为及其对应的结构演化在材料内部引入应力场的途径 固溶强化 主要是利用低固溶度元素的过饱和固溶 析出强化 主要依赖于弥散、细小的共格或半共格析出相产生的共格应力场( d ) 不同类型的相界面(a)完全共格；(b)部分共格；(c)切变共格；(d)非共格An illustration for the concept to lengthen thermal fatigue lives. N. Fujita et al. Changes of

7、microstructures and high temperature properties during high temperature service of Niobium added ferritic stainless steels. Materials Science and Engineering A351 (2003) 272/281Effects of Nb and Mo on the 0.2% proof strength at 900 for 13Cr steels.Relationship between addition contents and amounts i

8、n solid solution of Nb and Mo for 13Cr steels.Relationship between 0.2% proof strength at 900 and Nb addition contents of 13Cr steels as annealed and aged at 900 for 500 h.Relationship between Nb amounts in solid solution and Nb addition contents of 13Cr steels as annealed and aged at 900 for 500h.T

9、ransmission electron micrographs and their analysis results by electron diffraction of 0.01C/13Cr/0.5 Nb steels as annealed (a) and aged at 900 for 500 h (b).Corresponding EDS results of (a) and (b)Transmission electron micrographs and their analysis results by electron diffraction and EDS of 0.01C/

10、14Cr/0.1Ti/0.3Nb/0.5Mo steels asannealed (a) and aged at 900 for 500 h (b).Changes of Nb and Mo amounts in solid solution with agingtime at 900 for 0.5Nb and 0.3Nb/0.1Ti/0.5Mo steels.Changes of 0.2% proof strength at 900 with aging time at900 for conventional 19Cr/0.4Nb and 14Cr/0.3Nb/0.1Ti/0.5Mo st

11、eels.Comparison of thermal fatigue lives between conventional19Cr/0.4Nb and 14Cr/0.3Nb/0.1Ti/0.5Mo steels. The thermalfatigue tests were performed with sheet specimens with 2 mm thick which were heated and cooled repeatedly between 200 and 900 in a constraint ratio of 100% of thermal expansion.Chang

12、e in yield strength at 700 with aging time. G.M. Sim et al. Effect of Nb precipitate coarsening on the high temperature strength in Nb containing ferritic stainless steels. Materials Science and Engineering A 396 (2005) 159 165Change of Nb amount in precipitates measured by ICP with aging time.Relat

13、ionship between high temperature strength and Nb content in solid solution in Nb containing steels.Average diameter of precipitates with aging time in Nb containing steels.(a) NbC particle after aging for 60,000 min in 0.01C0.38Nb steel, (b) HR-TEM micrograph showing interface between NbC and the Fe

14、 matrix, (c) SAD pattern of interface (arrows indicate overlapped spot) and (d) schematic illustration of SAD pattern.(a) Fe2Nb particle after aging for 60,000 min in 0.01C0.38Nb steel, (b) HR-TEM micrograph showing interface between Fe2Nb and the Fe matrix, (c) SAD pattern of interface (arrows indi

15、cate overlapped spot) and (d) schematic illustration of SAD pattern.小结 对于铁素体不锈钢而言，Nb的固溶强化是提高其高温强度的有效机制。但是，Nb的析出与析出相的粗化会导致钢的高温强度迅速下降。而适当降低Nb含量并复合添加Mo、Ti有利于得到持久稳定的强化。析出类型及析出基体界面的共格程度对析出相的长大、粗化速度有重要影响。0246810121416182022130140150160170180190200210220230240250260270280HvTempering Time/h No relaxation Re

16、laxed for 30s Relaxed for 60s Relaxed for 200s Relaxed for 1000s（a）0246810121416182022100120140160180200220240260280HvTempering time/h Relaxed for 60s Relaxed for 1000s（b）含Nb钢在850变形25%后弛豫不同时间的样品在650（a）和700（b）重加热过程中的硬度变化 0246810121416182022150160170180190200210220230240250260270280HvTime/h No Relaxat

17、ion Relaxed for 60s Relaxed for 1000s真应变真应变0.4弛豫不同时间的样品在弛豫不同时间的样品在650重加热过程中的硬度变化重加热过程中的硬度变化b0.1 me0.5 maa)a)0.5 mc0.5 md0.1 mf0.1 m不同弛豫时间的样不同弛豫时间的样品重加热等温前的品重加热等温前的透射电镜形透射电镜形(a),(b) 弛豫弛豫0s；(c),(d) 弛豫弛豫60s；(e),(f) 弛豫弛豫1000s(a)(b)0.1 m(c)弛豫不同时间的样品弛豫不同时间的样品650重加热等温重加热等温0.5h后的位错组态后的位错组态 (a)弛豫弛豫0s；(b) 弛豫弛

18、豫60s；(c) 弛豫弛豫1000s0.2m0.3m变形奥氏体中的位错网络在贝氏体相变后的形态 (b)0.1 m(a)0.1 m 弛豫60s的样品650重加热等温3h后的位错和析出形态 (a)明场像 (b)暗场像； (a)0.15 m(b)0.15 m弛豫弛豫60s的样品的样品650重加热等温重加热等温10h后的位错和析出形态后的位错和析出形态 (a) 明场像明场像 (b) 暗场像暗场像(b)0.5 m(a)0.5 m弛豫弛豫60s的样品的样品700重加热等温不同时间的位错形态重加热等温不同时间的位错形态 (a)重加热等温重加热等温 5h；(b) 重加热等温重加热等温7h(a)0.75 m(d)0.1 m(c)0.25 m(b)0.25 m弛豫弛豫60s的样品的样品700重加热等温重加热等温10小时后板条边界形态小时后板条边界形态(a)1m0.3m(b)(c)0.1m弛豫弛豫60s的样品的样品700重加热等温重加热等温20小时后板条边界的再结晶形态小时后板条边界的再结晶形态 (a), (b), (c)为同一位置不同放大倍数的形貌为同一位置不同放大倍数的形貌10m(d