马氏体转变特征.ppt

,5-,*,单击此处编辑母版标题样式,马氏体及其转变,倪俊杰,聊城大学 材料科学与工程学院,Martensite and Its Transformation,1,6-1,主要内容,6.1,、马氏体概况,6.2,、马氏体转变特征,6.3,、马氏体转变机制,6.4,、马氏体转变热,/,动力学,6.5,、热弹性马氏体与形状记忆效应,6.6,、小结,Chapter 6 Martensite and Its Transformation,2,晶体结构,马氏体形态,力学,/,物理性能,6.1,、马氏体概况,Chapter 6 Martensite and Its Transformation,6-2,3,稳定的奥氏体区,过冷奥氏体区,A,向产,物转变开始线,A,向产物,转变终止线,A,+,转,变,区,产物区,A,1,550,;,高温转变区,;,扩散型转变,;P,转变区。,550,230,;,中温转变,区,;,半扩散型转变,;,贝氏体,(B),转变区,;,230,-50,;,低温转,变区,;,非扩散型转变,;,马氏体,(M),转变区。,时间,(s),300,10,2,10,3,10,4,10,1,800,100,200,500,600,700,温度,(),0,400,A1,Ms,Mf,-100,0,Chapter 6 Martensite and Its Transformation,6-3,马氏体的结构？,4,晶体结构,马氏体是,碳,在,Fe,中的,过饱和固溶体,，用符号,M,表示。,A,M,（,）,fcc,体心正方,成分不变,结构变化,由于碳的过饱和作用,使,Fe,晶格由体心立方变成体心正方晶格。,致使马氏体具有体心正方晶格,(,a,=,b,c,),C,原子,Fe,原子,Chapter 6 Martensite and Its Transformation,6-4,5,碳原子可能分布的位置：,6-5,Chapter 6 Martensite and Its Transformation,6,c,a,碳择优分布在,c,轴方向上的,八面体间隙位置。这使得,c,轴伸长，,a,轴缩短，晶体结,构变为,体心正方,。,轴比,c/,a,马氏体的正方度。,6-6,Chapter 6 Martensite and Its Transformation,7,C%,越高，正方度越大，正方畸变越严重。,当,0.20%C,时，,c/,a,=1,，此时马氏体为体心立方晶格,Chapter 6 Martensite and Its Transformation,6-7,碳含量对正方度的影响,8,c=a,0,+a=a,0,c/a=1+,a=b=c,立方结构,a=bc,正方结构,a,0,Fe,的晶格常数,M,的含碳量,，,，,常数,X,射线结构分析测得含碳量与,M,点阵常数关系,6-8,Chapter 6 Martensite and Its Transformation,9,P,S,T,A1,温度,(),Ms,V,1,P,炉冷,V,2,S,空冷,V,3,油冷,V,4,M,A,R,水冷,V,k,P,S,T,实际生产,连续冷却,Mf,板条状,蝶状,片状,薄片状,位错,孪晶,马氏体形态,Chapter 6 Martensite and Its Transformation,6-9,10,板条马氏体,奥氏体晶粒内包,含几个群，群内,存在位向差时，,会形成几个束,.,群和束都是由板,条组成。群、束,之间均为,大角度,晶界,，板条之间,为,小角度晶界,。,Chapter 6 Martensite and Its Transformation,6-10,11,a low-angle,boundary,large-angle,boundaries,Large-&low-angle boundaries,Chapter 6 Martensite and Its Transformation,6-11,12,组织单元：,群,束,板条,取向关系,：,K-S,惯习面：,111r,光镜下,马氏体束,马氏体群,马氏体群：,同惯习面，形态上呈平行排列的板条集团,马氏体束：,同惯习面，同取向（晶面平行关系）的板条集团,马氏体板条：,马氏体的最基本单元,(,单晶体,),，窄而细长。多数板条宽度,0.1-0.2,微米，长度小于,10,微米，板条间往往存在薄膜状,(,200,nm),的残余奥氏体,Chapter 6 Martensite and Its Transformation,6-12,13,板条马氏体的亚结,构主要为,高密度的,位错,，位错形成位,错网络,(,缠结,),，位错,密度随含碳量增加,而增大，常为,(,0.3,0.9,),10,12,/cm,3,.,故,称位错马氏体。,Chapter 6 Martensite and Its Transformation,6-13,14,蝶状马氏体,6-14,特征：,断面上两翼结合,部分很象片状马氏体中,脊，由此向两侧张成取,向不同的马氏体。立体,形状“,V”,形柱状，断,面呈蝴蝶状。,亚结构：,高密度位错。,Chapter 6 Martensite and Its Transformation,15,片状马氏体,双凸透镜,片状,中脊,第,1,片贯穿,整个晶粒，,互不平行，,愈来愈小。,残余奥氏体,分布在马氏体片间,Chapter 6 Martensite and Its Transformation,6-15,16,Chapter 6 Martensite and Its Transformation,6-16,17,高碳钢,W,C,1.0%,中,出现,亚结构,孪晶,Chapter 6 Martensite and Its Transformation,6-17,18,a coherent twin boundary,an incoherent twin boundary,f,Chapter 6 Martensite and Its Transformation,6-18,19,薄片状马氏体,-,马氏体,特征：,立体形状为薄片状，其金相形态呈很细的带状,、并且相互交叉、分枝、曲折等形态。,亚结构：,孪晶，但无中脊,(,与片状马氏体区别,),点阵结构：,密排六方（其它马氏,体均为体心立方或体心正方点阵,结构）,特征：,薄片状,亚结构：,高密度层错,原因：,奥氏体的层错能较低形成,Chapter 6 Martensite and Its Transformation,6-19,20,显微裂纹,高碳钢,Chapter 6 Martensite and Its Transformation,6-20,21,混合马氏体,Chapter 6 Martensite and Its Transformation,6-21,22,最主要的两个因素是：,奥氏体中碳含量和马氏体形成温度。,马氏体形态和亚结构的因素,Chapter 6 Martensite and Its Transformation,6-22,23,HRC,C%,A,r,硬度,/HRC,Ar(%),0 0.2 0.4 0.6 0.8 1.0 1.2 1.4,70,60,50,40,30,20,10,70,60,50,40,30,20,10,3,2,1,曲线,3,马氏体的硬度,曲线,2,高于,Ac1,淬火后,钢的硬度,曲线,1,高于,Ac3,或,Accm,淬火后钢的硬度,马氏体强度和硬度,碳含量分数对马氏体和淬火钢硬度及残余奥氏体的影响,Chapter 6 Martensite and Its Transformation,6-23,24,1,2,3,4,马氏体高硬高强的本质,固溶强化,相变强化,时效强化,细晶强化,Chapter 6 Martensite and Its Transformation,6-24,25,过饱和碳原子溶入马氏体间隙引起强烈点阵畸变，形成以碳原,子为中心应力场，并与位错发生交互作用，使碳原子钉扎位。,。,固溶强化,马氏体的碳浓度,Wc,100,50,70,40,60,20,30,10,0.1,0.3,0.2,0.4,0,0.5,0.6,0.7,0.8,0.9,1.0,硬度,(HRC),Chapter 6 Martensite and Its Transformation,6-25,26,相变强化,：马氏体相变时，在晶体内造成晶格缺陷密度,很高的亚结构,(,位错,/,孪晶,),，这些缺陷阻碍位错的运动,，使马氏体得到强化。,孪晶对,M,的强度硬度有附加贡献。,C%,相同时，孪晶,M,硬度,位错,M,Chapter 6 Martensite and Its Transformation,6-26,27,马氏体在淬火后室温停留期间、,或在外力作用下，使碳原子通过,扩散，发生碳原子偏聚和析出、,甚至以碳化物弥散析出，使马氏,体晶体内产生超显微不均匀，引,起时效强化,Chapter 6 Martensite and Its Transformation,6-27,时效强化,28,b,slip plane,precipitate,b,b,Dt,r,Chapter 6 Martensite and Its Transformation,6-28,29,1)M,形成能松弛塑变所造的局,部应力集中，防止裂纹形成或,裂纹扩展。,2),发生塑性变形区，有形变诱,发,M,产生，使已塑变区继续变,形困难，抑制缩颈的形成。使,塑性和韧性提高,在马氏体转变过程中塑性有所增加,-,相变诱发塑性。,马氏体相变塑性,Chapter 6 Martensite and Its Transformation,6-29,30,Chapter 6 Martensite and Its Transformation,6-30,31,马氏体韧性,C%:,0.4%,，韧性低，硬而脆,Chapter 6 Martensite and Its Transformation,6-31,0.2,0.2,32,马氏体韧性主要决定于,亚结构,Chapter 6 Martensite and Its Transformation,6-32,33,Chapter 6 Martensite and Its Transformation,6-33,34,马氏体强度和硬度主要取决于其含,C,量。,马氏体塑性和韧性主要取决于其亚结构。,位错型马氏体具有较高强度，硬度和良好的塑韧性（强韧性）,孪晶型马氏体强度，硬度很高，但塑韧性较低。,故在保证足够强度，硬度前提下，应尽量减少孪晶,M,的数量。,小 结,Chapter 6 Martensite and Its Transformation,6-34,35,(1),比容,马氏体比容比奥氏体大,;,(2),磁性,铁磁性,(,可用磁性法测量马氏体转变量,),、高矫顽力；,(3),电阻,电阻比珠光体大。,马氏体的物理性能,Chapter 6 Martensite and Its Transformation,6-35,36,6.2,、马氏体转变特征,Chapter 6 Martensite and Its Transformation,6-36,(1),马氏体转变的非恒温性,(2),马氏体转变的无扩散性,(3),马氏体转变的可逆性,(4),马氏体转变的位向关系和关系面,(5),马氏体转变的表面浮凸效应和共格性,37,(1),转变的非恒温性,Chapter 6 Martensite and Its Transformation,6-37,马氏体的转变是在一个温度范围内进行的,38,马氏体转变开始的温度称,上马氏体点，,用,Ms,表示。,马氏体转变终了温度称,下马氏体点，,用,M,f,表示,.,只要温度达到,Ms,以下即发生马氏体转变。,在,Ms,以下，随温度下降，转变量增加，冷却中断，转变停止。,马氏体转变量是在,Ms,M,f,温度范围内，通过不断降温来增加的，,即马氏体转变量是温度的函数，与等温时间无关,。,Chapter 6 Martensite and Its Transformation,6-37,39,原子切变变化位置,界面推移,M,共格切变,A,母相点阵上原子从一种排列转变到另一种排列,原来相邻两个原子在相变后仍然相邻,它们之间相对位置不超过一个原子间距。即碳原子没有经过扩散就可进行马氏体转变。,(2),转变的无扩散性,只有点阵改组，没有成分变化,Chapter 6 Martensite and Its Transformation,6-39,40,马氏体无扩散性证据：,a,.,碳钢中马氏体转变前后碳浓度没有发,生变化，仅发生晶格切变；,b.,马氏体转变可以在超低碳合金中发生,，而且转变速度极快，说明无碳扩散参,与。,c.,转变可在极低的温度进行（,4K,），此,时相变已不可能以扩散方式进行,Chapter 6 Martensite and Its Transformation,6-40,41,(3),转变的可逆性,马氏体加热变为奥氏体,(,一般碳钢不可以,),As/Af(Fe-Ni:As,比,Ms,高,410,;,Au-Cd:As,比,Ms,高,16,),热弹马氏体是创作形状记忆合金的基础,6-41,42,(4),位向关系及惯习面,马氏体转变时马氏体与奥氏体存在着严格的晶体学关系,位向关系和惯习面,Chapter 6 Martensite and Its Transformation,马氏体是在母相的一定晶面上开始形成的，这个晶面就是,惯习面,。,111,A,、,225,A,、,259,A,。,通常：碳含量,0.5%,时，惯习面为,111,A,；,碳含量,0.51.4%,，惯习面为,225,A,；,碳含量,1.51.8%,，惯习面为,259,A,6-42,43,位向关系,相变时，整体相互移动一段距离，相邻原子的相对位置无变化。作小于一个原子间距位置的位移，因此,奥氏体与马氏体保持一定的严格的晶体学位向关系。,(1,）,KS,关系,晶向：,111,M,011,A,（,2,）西山关系,晶向：,110,M,112,A,（,3,）,GT,关系,晶向：,111,M,101,A,Chapter 6 Martensite and Its Transformation,6-43,44,(5),表面浮凸效应和共格性,马氏体转变产生的表面浮凸,Chapter 6 Martensite and Its Transformation,6-44,马氏体转变时在预先磨光试样表面上形成有规则的表面,浮凸,(,切变使马氏体表面出现一边凹陷、一边凸起，并带动,附近奥氏体也发生弹性切变,),。,说明马氏体形成,与母相奥氏体宏,观切变密切相关。,45,Chapter 6 Martensite and Its Transformation,6-45,界面上原子为马氏体与奥氏体共有,马氏体切变方式,46,Chapter 6 Martensite and Its Transformation,6-46,47,Chapter 6 Martensite and Its Transformation,6-47,6.3,、马氏体转变模型,(1),Bain,模型,(2),K-S,切变模型,(3),G-T,模型,48,f.c.c,可看作体心正方,其轴比,c/,a,=1.414,A,点阵只需适当变形，调整轴比，使之达到与含碳量对应的,M,正方度时，,A,即可转变成,M,。,(1)Bain,模型,Chapter 6 Martensite and Its Transformation,6-48,49,（,111,）,A,(011),M,X,M,Y,M,Z,M,X,A,Y,A,Z,A,模型不能解释表面浮凸效应和惯习面。,Chapter 6 Martensite and Its Transformation,6-49,50,(2)K-S,模型,如何由,fcc,转变为,bcc,点阵？,先看奥氏体,111,面,Chapter 6 Martensite and Its Transformation,6-50,51,第一层,第二层,第三层,将三层相邻,(111),A,晶面对某一层作垂直投影,120,Chapter 6 Martensite and Its Transformation,6-51,52,马氏体,011,面,Chapter 6 Martensite and Its Transformation,6-52,53,第一层,第二层,第三层,将三层相邻（,011,）面对某一层作垂直投影,109,28,Chapter 6 Martensite and Its Transformation,6-53,54,第一层,第二层,第三层,120,111,A,第二层原子沿,方向做第一次切变沿,方向做第二次切变,110,M,109,28,Chapter 6 Martensite and Its Transformation,6-54,55,Chapter 6 Martensite and Its Transformation,6-55,56,Chapter 6 Martensite and Its Transformation,(3),G-T,模型,相变经一次宏观均匀切变和一次宏观非均匀切变,57,Chapter 6 Martensite and Its Transformation,6-57,58,Chapter 6 Martensite and Its Transformation,6-58,59,Chapter 6 Martensite and Its Transformation,60,Chapter 6 Martensite and Its Transformation,6-60,6.4,、马氏体转热,/,动力学,61,Chapter 6 Martensite and Its Transformation,6-61,马氏体转变热力学条件,为什么有热滞？,62,驱动力：,阻力：,Chapter 6 Martensite and Its Transformation,63,Chapter 6 Martensite and Its Transformation,6-63,M,转变自由能变化,64,Chapter 6 Martensite and Its Transformation,6-64,M,s,点的因素,65,Chapter 6 Martensite and Its Transformation,66,Chapter 6 Martensite and Its Transformation,6-66,67,Chapter 6 Martensite and Its Transformation,6-67,68,Chapter 6 Martensite and Its Transformation,6-68,应力：,在奥氏体状态下施加拉应力或单向压应力会促进马氏体形成，,M,s,升高。,在奥氏体状态下施加多向压应力会阻碍马氏体形成，,M,s,下降。,塑性变形：,1,、若在,M,s,M,d,温度范围内经塑性变形会促进奥氏体在该温度下向马氏体转变，使,M,s,升高，产生应变诱发马氏体。,2,、若在,M,s,M,f,温度范围内的某一温度进行塑性变形也会促进奥氏体在该温度下向马氏体转变。,3,、若在,M,d,以上某一温度范围内经塑性变形不会产生应变诱发马氏体。,69,Chapter 6 Martensite and Its Transformation,6-69,用外力能否改变马氏体转变？,70,71,Chapter 6 Martensite and Its Transformation,6-71,72,73,Chapter 6 Martensite and Its Transformation,6-73,马氏体形成动力学特点,74,Chapter 6 Martensite and Its Transformation,6-74,75,Chapter 6 Martensite and Its Transformation,6-75,为什么,Ms,温度,在,300,摄氏度？,76,Chapter 6 Martensite and Its Transformation,6-76,77,Chapter 6 Martensite and Its Transformation,6-77,为什么呈,C,形,?,78,Chapter 6 Martensite and Its Transformation,6-78,79,Chapter 6 Martensite and Its Transformation,6-79,80,Chapter 6 Martensite and Its Transformation,6-80,81,Chapter 6 Martensite and Its Transformation,6-81,82,Chapter 6 Martensite and Its Transformation,6-82,83,Chapter 6 Martensite and Its Transformation,6-83,84,Chapter 6 Martensite and Its Transformation,6-84,85,Chapter 6 Martensite and Its Transformation,6-85,86,Chapter 6 Martensite and Its Transformation,6-86,87,Chapter 6 Martensite and Its Transformation,6-87,88,Chapter 6 Martensite and Its Transformation,6-88,6.5,热弹性马氏体与形状记忆效应,89,Chapter 6 Martensite and Its Transformation,6-89,(3),母相弹性极限要高,90,Chapter 6 Martensite and Its Transformation,6-90,91,Chapter 6 Martensite and Its Transformation,6-91,92,Chapter 6 Martensite and Its Transformation,形状记忆效应的应用,93,Chapter 6 Martensite and Its Transformation,6-93,6.6,小结,94,