FGH95粉末镍基合金蠕变期间位错网的形成与分析

采用TEM观察和衍衬分析研究了FGH95粉末镍基合金蠕变期间的位错组态.结果表明,蠕变初期,1/2〈110〉位错在γ基体{111}晶面开动,使位错不断增殖.蠕变稳态阶段,2组不同Burgers矢量的位错可能滑移至同一晶面并相遇,反应后形成六角位错网络,或在不同滑移晶面相交.形成具有四边形特征的位错网络.位错网的形成可降低位错可动性并抑制位错交滑移,提高合金蠕变抗力.蠕变后期变形特征是形变位错在γ/γ′界面位错网损坏处切入γ′相,切入γ′相的位错可发生分解,形成不全位错和层错的位错组态.     

第五章 钛及钛合金的塑性变形

众所周知:钛在低于882℃是六角密排结构的α相,但是Ti、Zr、Hf与其他密排金属所不同的是具有很高的塑性,甚至在很低的温度下仍有很高的塑性。这是由于Ti,Zr,Hf具有很多的滑移系而其余的六角密排金属则滑移系较少。晶体的范性变形是以滑移的方式进行的。所谓滑移:就是晶体的一部份相对于另一部份沿着晶面作相对的平动。实验表明:滑移通常是沿一定的结晶面和结晶方向发生,而不受外加负荷的影响,仅与结晶结构有关。这一定的结晶面和结晶方向,称为滑移而和滑移方向,是晶体的两个滑移要素。一般滑移面总是原子排列最密的面。例如面心立方金属中的滑移面为{111}。而六角密排金属通常是它的基面(0001)。实验表明,原子排列最密的方向是唯一的滑移方向。如面心立方金属的(110),六角金属则为     

ON THE DISLOCATION SLIP MECHANISM OF THE MARTENSITIC TRANSFORMATION OF STEELS

根据实验证据提出:在钢的马氏体转变过程中,fcc→bcc(或bct)晶格改组时所需的原子相对位置变化是通过畸变fcc奥氏体晶格内的偏位错运动实现的,其方式有两种:一种是偏位错沿(1/m)〈112〉_f/{111}_f中的一个滑移系运动导致的主剪切原子位移;另一种是不同共轭{111}_f滑移面内偏位错同时或先后开动联合造成的M=(1/n)[〈112〉_(f1)/{111}_1+〈112〉_(f2)/{111}_2]复合原子位移。由此出发提出了钢淬火时奥氏体向马氏体转变的偏位错滑移共轭复合原子位移机制,并按此机制对马氏体与奥氏体之间的位向关系,马氏体惯析面及淬火马氏体中的一些特有现象给出了晶体几何学的解释。     

钢中马氏体转变的位错滑移机制

根据实验证据提出:在钢的马氏体转变过程中,fcc→bcc(或bct)晶格改组时所需的原子相对位置变化是通过畸变fcc奥氏体晶格内的偏位错运动实现的,其方式有两种:一种是偏位错沿(1/m)〈112〉_f/{111}_f中的一个滑移系运动导致的主剪切原子位移;另一种是不同共轭{111}_f滑移面内偏位错同时或先后开动联合造成的M=(1/n)[〈112〉_(f1)/{111}_1 〈112〉_(f2)/{111}_2]复合原子位移。由此出发提出了钢淬火时奥氏体向马氏体转变的偏位错滑移共轭复合原子位移机制,并按此机制对马氏体与奥氏体之间的位向关系,马氏体惯析面及淬火马氏体中的一些特有现象给出了晶体几何学的解释。     

THE BEHMAVIORS OF (1/2)〈110] DISLOCATIONS IN γ-TiAl SINGLE CRYSTALS

[021]取向的γ—TiAl单晶（Ti—56％Al,原子分数）在－196－1000℃温度范围内压缩变形时主要形变方式为｛111｝（110］普通位错的滑移低温时,（1／2）（110］普通位错大多沿螺型及60°交角两种方向排列,井倾向于成组出现;而在反常屈服温度区域内,（1／2）（110］普通位错大多平行于其螺型方向,且形成许多位错拐点,其数目随温度的升高而增加;在反常屈服峰温以上,普通位错不具有特殊的方向性,且倾向于通过攀移向其它滑移面运动     

双相层片型TiAl基合金的室温变形及断裂

TEM原位拉伸研究表明，尽管双相层片型TiAl基合金中与α2相共存的γ层片相的（1／2）＜110]位错具有良好的可滑移性，并在一些γ层片中（1／6）＜112]形变孪生也较为活跃，但对变形有贡献的滑移系统及孪生系统数目少是室温塑性差的重要原因提高多晶体双相TiAl基合金室温塑性的关键在于促使（1／2）＜110]{111）以外的滑移系开动.     

一种单晶镍基合金蠕变初期的位错组态

利用ＴＥＭ研究了单晶镍基合金平行于应力轴的（１００）晶面拉伸蠕变初期的位错组态,表明：形变特征是错在γ相八面体滑移系中运动,在基体通道中,１／２〈１１０〉型位错运动相遇,发生反应而增殖;由于（１００）晶面的基体通道受压应力,位错运动阻力大,密度小,位错运动多以交滑移和Ｏｒｏｗａｎ弓入方式进行;当受拉应力通道中弓出的位错环经交滑移进入压应力通道后,入口两侧被钉扎,位错可定向弓入成为形貌类似于双端Ｆ－     

元素Re对镍基单晶合金中温蠕变行为的影响

通过对有/无元素Re合金进行蠕变曲线测定及组织形貌观察,研究了元素Re对镍基单晶合金中温蠕变行为的影响。结果表明:与无Re合金相比,4.5%Re合金在中温/高应力条件下具有良好的蠕变抗力。蠕变期间无Re合金中的#’相转变成串状,而4.5Re合金中的#’相仍保持立方体形貌,有/无元素Re合金在中温蠕变期间的变形机制均为<110>超位错剪切#’相,切入#’相的超位错可在{111}面滑移,或在{111}面分解形成{112}超肖克莱不全位错+(SISF)的位错组态,抑制其交滑移;其中,4.5%Re合金中切入#’相的<110>超位错可由{111}面交滑移至(100)面,形成K-W锁,是使合金具有良好蠕变抗力的重要原因之一。     

组织和温度对Cu表面氧化速率的影响

利用扫描电镜、X射线衍射仪和氧化称重实验对铜表面氧化速率进行研究,分析了不同组织、晶粒和温度对铜氧化性能的影响。结果表明：铜的组织结构是影响其氧化性能的主要因素,非密排的（100）晶面上界面能高、晶面原子堆垛相对疏松和原子尺度上粗糙,且氧化膜生长连续,氧化速率高于密排的（111）晶面;温度升高,铜表面的内能增大,铜原子较易成为活化原子与氧气发生反应,同时增大了铜原子在氧化膜中的扩散速率,加速了铜的氧化;铜试样经过等径角挤压（ECAP）后,（111）晶面铜表面的面积增大,氧化速率降低,晶界不是影响铜氧化速率的主要因素,能量较小的晶面原子所占的面积增大,铜的氧化速率减小。     

一种无铼二代镍基单晶高温合金蠕变机制研究

通过对一种镍基单晶合金中温高应力条件下的蠕变曲线的测定和微观组织及断裂后合金中位错组态的衍衬分析,研究中温高应力条件下单晶合金的组织演化及变形特征。结果表明:在中温高应力条件下,该合金的蠕变激活能Q为(462±20)kJ/mol,表观应力指数na=4.34。表明在试验温度和应力范围内,合金具有较好的蠕变抗力。位错组态衍衬分析表明,蠕变期间切入相内的<110>超位错既可在{100}立方体滑移系中运动,也可在{111}八面体滑移系中运动;位错在运动中相遇发生位错反应,形成的超位错可交滑移至{100}立方体滑移面。位于2个不同{100}六面体滑移面的位错在运动中相遇,可发生位错反应,生成的位错可在{111}八面体滑移系中运动。     

PLASTIC DEFORMATION AND DISLOCATION STRUCTURE IN γ'-PHASE OF A DIRECTIONALLY SOLIDIFIED Ni-BASE SUPERALLOY

The dislocation structure of directionally solidified(DS)Rene 80 superalloy during tensileand creep deformation has been studied by TEM.In tensile deformation,γ'shearing occurs byslip of APB-coupled(1/2)<110>dislocation pairs on{111}planes at temperatures below760℃.and by slip of SISF-seperated(1/3)<112>superpartials which have dissociated on{111}planes into a(1/2)<110>screw superpartial and a(1/6)<112>edgesuperpartial with an APB in between at temperatures equal to or above 760℃.In creepdeformation,γ'shearing occurs again by slip of SISF-seperated(1/3)<112>superpartialswhich have not dissociated on{111}planes and by diffusive slip of APB-coupled(1/2)<110>dislocation pairs at 760℃,618 MPa.However,no γ'shearing occurs at 980℃,190MPa.During secondary creep at 760℃,618 MPa or at 980℃,190 MPa,2-dimensional net-works have formed at γ/γ'interfaces,and the strain is mainly the result of diffusion control-led climb of dislocation networks at γ/γ'interfaces.The dependence of secondary creep rate εupon size a and volume fraction v_■ of cubic γ' has been found to be ■∝α/v_f~(2/3).     

COLD-ROLLING AND RECRYSTALLIZATION OF (110)[110] IRON-SILICON SINGLE CRYSTALS

After70-90% cold-rolling,strong{111}〈110〉and weak {111},〈112〉 cold-rolled tex- tures and perfect{111}〈112〉 recrystallization texture were obtained in Fe-Si single crys- tals.The cold-rolled textures with different orientations possesses different ability for recov- ery because of the difference of dislocation structure and store energy alter cold-rolling.The recovery taking place at{111}〈112〉orientation region was prior to that at{111}〈110〉 orientation region.hese subgrains with{111}〈112〉 orientation became recrvstallization nuclei during their growth at expending the surrounding matrix which was sluggish in recovery process.The development of recrystallization textures may be suggested as a process of “nucleation in-situ-selective growth”.The formation of(111)textures in low carbon steel sheets has been discussed in the light of this suggestion.     

MICROSTRUCTURE AND MECHANICAL BEHAVIOR OF Nb-（10, 15）A1-20V ALLOYS

Compression tests at room and high temperature and creep tests at high temperature have been performed on B2 Nb15A120V and Nb10A120V alloys. At room temperature, in the as-cast state, both alloys exhibited significant ductility in compression. The Burgers vectors of the dislocations were found to be 1/2(111) slipping on {112}. The dislocations showed good mobility. Dislocation clusters also triggered the formation of pseudotwins, which resulted in serrated yielding. In steady state creep, deformation occurred by a combination of dislocation glide and climb, giving a homogeneous microstructure. The dislocations in Nb10A120V were determined to be 1/2(111) slippingon {110} with some (100) segments. After creep at 1100℃, Nb15A120V showed a two phase structure with a few dislocations in the A15 phase but no dislocations in the A2 phase.     

DISLOCATION PINNING IN HIGH TEMPERATURE DEFORMED Ni3(Al,Ti) SINGLE CRYSTALS CONTAINING DISORDERED γ PRECIPITATES

A transmission electron microscopy (TEM) investigation has been performed on the dislocation pinning in LI2-ordered Ni3(Al, Ti) containing disordered γ precipitates. The morphology of deformation induced dislocations in the γ' base alloys containing fine dispersion of disordered γ was investigated by means of weak-beam electron microscopy. The superdislocations are strongly attracted to the disordered particles and dissociate on the (111) plane in the γ particles, while they dissociate on the (010) plane in the γ' matrix. The disordered γ precipitates play an important role as a pinning point during the cross-slip of superdislocations from (111) to (010) planes in the γ'matrix and restrain the cross-slip of superdislocations. The interaction of superdislocations with disordered particles causes the formation of superkinks, jogs and closed loops.     

In situ TEM observation of dislocation motion in thermally strained Al nanowires

Al thin films deposited epitaxially on (0001) -Al₂O₃ substrates, have been thinned cross-sectionally to form Al nanowires. The Al wires, consisting of two Σ3 twin variants, have been strained in situ by differential thermal expansion between the Al wires and the Al₂O₃ substrate during transmission electron microscopy heating. Dynamical observations show that maximum dislocation activity occurs in the first heating cycle up to 400°C, with decreasing activity during further cycles. The {111} Al || (0001) -Al₂O₃ interface acts as a source of dislocation half-loops. The motion of threading dislocations along the wires generates long trailing dislocation segments parallel to, and offset from, the {111} Al || (0001) -Al₂O₃ interface. Dislocation multiplication occurs by the reaction of half-loops and extended threading dislocation segments at the wire boundaries and substrate interface. The Σ3 twin grains bisecting the wires are observed to be stable during thermal cycling to 400°C, and their { } boundaries are weak pinning sites.     

Slip patterns and preferred dislocation boundary planes

The planes of deformation induced extended planar dislocation boundaries are analysed in two different co-ordinate systems, namely the macroscopic system defined by the deformation axes and the crystallographic system given by the crystallographic lattice. The analysis covers single and polycrystals of fcc metals in three deformation modes (rolling, tension and torsion). In the macroscopic system, boundaries lie close to the macroscopically most stressed planes. In the crystallographic system, the boundary plane depends on the grain/crystal orientation. The boundary planes in both co-ordinate systems are rationalised based on the slip. The more the slip is concentrated on a slip plane, the closer the boundaries lie to this. The macroscopic preference arises from the macroscopic directionality of the slip. The established relations are applied to (a) prediction of boundary planes from slip patterns and (b) prediction of slip patterns from boundary planes.     

A level set method for dislocation dynamics

We propose a three-dimensional level set method for dislocation dynamics in which the dislocation lines are represented in three dimensions by the intersection of the zero levels of two level set functions. Since the level set method does not discretize nor directly track individual dislocation line segments, it easily handles topological changes occurring in the microstructure. The dislocation dynamics are not limited to glide along a slip plane, but also account for three-dimensional aspects of their motion: cross-slip occurs naturally and climb is included by fixing the relative climb and glide mobility. The level set dislocation dynamics method was implemented using an accurate finite difference scheme on a uniform grid. To demonstrate the versatility, utility and simplicity of this new model, we present examples including the motion of dislocation loops under applied and self-stresses (including glide, cross-slip and climb), intersections of dislocation lines, operation of Frank–Read sources and dislocations bypassing particles.     

AN IN SITU STUDY ON DEFORMATION TWINNING NEAR CRACK TIP IN TWO－PHASE TiAl－BASE ALIOY

ＡＮＩＮＳＩＴＵＳＴＵＤＹＯＮＤＥＦＯＲＭＡＴＩＯＮＴＷＩＮＮＩＮＧＮＥＡＲＣＲＡＣＫＴＩＰＩＮＴＷＯ－ＰＨＡＳＥＴｉＡｌ－ＢＡＳＥＡＬＩＯＹＷＬｉａｎｇ￣１,２）,Ｑ．Ｌｉ￣２）ａｎｄＤ．ＺＹａｎｇ￣２）（ＣｅｎｔｒｅｏｆＭｅａｓｕｒｉｎｇａｎｄＴ...     

Stress-driven migration of simple low-angle mixed grain boundaries

We investigated the stress-induced migration of a class of simple low-angle mixed grain boundaries (LAMGBs) using a combination of discrete dislocation dynamics simulations and analytical arguments. The migration of LAMGBs under an externally applied stress can occur by dislocation glide, and was observed to be coupled to the motion parallel to the boundary plane, i.e. tangential motion. Both the migration and tangential velocities of the boundary are directly proportional to applied stress but independent of boundary misorientation. Depending on the dislocation structure of the boundary, either the migration or tangential velocity of the boundary can switch direction at sufficiently high dislocation climb mobility due to the dynamics of dislocation segments that can climb out of their respective slip planes. Finally, we show that the mobility of the LAMGBs studied in this work depends on the constituent dislocation structure and dislocation climb mobility, and is inversely proportional to misorientation.     

B2结构的铝-镝金属间化合物位错性质的研究

采用截断近似法,研究了B2结构的铝-镝(B2-Al Dy)金属间化合物{110}面的位错性质。结果表明,伯格斯矢量为<110>方向的螺位错、刃位错和混合位错的芯宽度都要比<100>方向窄。它们相应的不稳定层错能存在γus<110>大于γus<001>的关系,可见,不稳定层错能是影响具有B2结构的金属间化合物位错性质的重要因素之一。B2-Al Dy滑移系为<111>{110}的位错,除了位错角为54.7°的位错以外,其他位错角的弹性应变能都要大于失配能,而且在相同周期内看,它们的相位总是相反;位错角为54.7°的位错,失配能比弹性应变能大,而且两者在相同周期内同相位。总体来说,B2-Al Dy的{110}面上<100>、<110>和<111>方向的位错,随着位错角的减小(<111>方向的54.7°的位错角除外),总能量以及相应的应力都依次增大。