一种[011]取向镍基单晶合金拉伸蠕变中的组织演化

在1040℃,137MPa下对[011]取向镍基单晶合金进行蠕变曲线测定,采用SEM观察热处理及蠕变后样品不同晶面的组织形貌,研究了[011]取向镍基单晶合金在蠕变期间的组织演化特征,并分析了组织演化的规律及影响因素。结果表明:取向差为4°的[011]取向镍基单晶合金经完全热处理后,组织是立方γ′相以共格方式嵌镶在γ基体相中,并沿<100>取向规则排列;在拉伸蠕变期间,合金中γ′相转变成与[001]取向平行的纤维状筏形组织。由于施加拉伸载荷,使立方γ′相中的(100)晶面及γ基体相承受挤压力,可排斥较大半径的Al、Ta原子,而在(001)晶面产生较大的晶格扩张应变,可诱捕较大半径的Al、Ta原子,因而促使γ′相沿[001]取向定向生长成为纤维状筏形组织。在外加应力作用下,不同晶面γ′/γ两相界面的应变能密度变化是促使发生元素扩散和γ′相定向粗化的驱动力。     

[111]取向镍基单晶合金在蠕变期间组织演化的有限元分析

采用弹塑性应力-应变有限元方法计算了[111]取向镍基单晶合金中γ/γ′两相共格界面的von Mises应力及应变能密度分布,研究了施加拉应力对γ/γ′两相界面von Mises应力分布及γ′相定向粗化规律的影响.结果表明:[111]取向镍基单晶合金经热处理后,组织结构是立方γ′相以共格方式嵌镶在γ基体相中,沿(100)方向规则排列.当沿[111]取向施加拉应力蠕变期间,与近(010)γ′晶面的基体通道相比,近(001)γ′和(100)γ′晶面的基体通道有较大的von Mises应力,在主应力分量的作用下,(100)和(001)晶面分别沿[001],[010]和[010],[100]方向发生较大的晶格扩张应变,可诱捕较大半径的Al和Ti原子,这是促使γ′相在(010)面沿[001]和[100]方向定向生长成为层片结构的筛网状筏形组织的主要原因.     

[011]取向镍基单晶合金在压应力蠕变期间的组织演化与有限元分析

采用弹/塑性应力-应变有限元方法计算了[011]取向单晶镍基合金中γ /γ’ 两相共格界面的von Mises应力及应变能密度分布特征,研究了施加压应力对γ /γ’ 两相界面von Mises应力分布及γ’相定向粗化规律的影响。结果表明:[011]取向单晶镍基合金经热处理后,组织结构是立方γ’相以共格方式嵌镶在γ基体相中,并沿<100>γ方向规则排列。当沿[011]方向施加压应力时,(100)晶面沿[001]γ和[010]γ方向发生晶格收缩,其晶格收缩的挤压作用可排斥半径较大的Al、Ti原子,而在(010)和(001)晶面则分别沿[100]取向发生晶格扩张应变,可诱捕半径较大的Al、Ti原子,是促使γ’相在(100)晶面交错生长成网状结构,并沿[010]和[001]取向扩散连接,生长成为相互垂直的层片网状筏形组织的主要原因。     

Microstructure Evolution of A Pre-compression Nickel-Base Single Crystal Superalloys During Tensile Creep

采用预压应力处理使镍基单晶合金中的γ’相转变成P-型筏状结构, 通过拉伸蠕变曲线测定和组织形貌观察, 研究了该合金拉伸蠕变中的组织演化. 结果表明: 在拉伸蠕变初期, 合金中的P-型筏状γ’相转变为N-型筏状结构. 由于高温拉应力导致γ’/γ两相中元素平衡浓度发生变化及P--型筏状γ’相的不均匀粗化, 促使P-型筏状γ’相发生分解出现沟槽; 沟槽区域溶质元素化学位的提高引起的元素定向扩散是γ’相逐渐溶断成类立方体结构的主要原因. 切应力分量使立方γ’相与应力轴垂直界面的晶格收缩可排斥较大半径的Al和Ta原子, 拉伸张应力使平行于应力轴界面的晶格扩张可诱捕较大半径的Al和Ta原子, 是促使γ’相定向生长成为N--型筏状的主要原因. 其中, 在拉应力作用下类立方γ’相不同界面的应变能密度变化是元素扩散及γ’相定向粗化的驱动力.     

预压缩镍基单晶合金拉伸蠕变期间的组织演化

采用预压应力处理使镍基单晶合金中的γ'相转变成P-型筏状结构,通过拉伸蠕变曲线测定和组织形貌观察,研究了该合金拉伸蠕变中的组织演化.结果表明:在拉伸蠕变初期,合金中的P-型筏状γ'相转变为N-型筏状结构.由于高温拉应力导致γ'/γ两相中元素平衡浓度发生变化及P-型筏状γ'相的不均匀粗化,促使P-型筏状γ'相发生分解出现沟槽;沟槽区域溶质元素化学位的提高引起的元素定向扩散是γ'相逐渐溶断成类立方体结构的主要原因.切应力分量使立方,γ'相与应力轴垂直界面的晶格收缩可排斥较大半径的Al和Ta原子,拉伸张应力使平行于应力轴界面的品格扩张可诱捕较大半径的Al和Ta原子,是促使γ'相定向生长成为N-型筏状的主要原因.其中,在拉应力作用下类立方,γ'相不同界面的应变能密度变化是元素扩散及γ'相定向粗化的驱动力.     

镍基单晶合金在压缩蠕变期间的组织演化与有限元分析

通过[001]取向镍基单晶合金压缩蠕变性能测试及组织形貌观察,确定出合金经压应力蠕变后的组织结构是γ'相沿平行于应力轴方向形成P-型筏状组织。采用三维应力应变有限元方法计算出立方γ/γ'两相共格界面的Von Mises应力分布,研究了施加应力对应力分布及γ'相定向粗化规律的影响。结果表明,施加压应力可改变立方γ/γ'两相的应力分布,γ'相的定向粗化取向与γ基体通道的Von Mises应力分布密切相关,其中,在施加压应力作用下,立方γ'相的(001)晶面产生较大的Von Mises应力及应变能密度变化是使其发生组织演化的主要原因。并进一步提出压应力蠕变期间,合金中发生元素定向扩散和γ'相定向生长的驱动力。     

晶体取向对镍基单晶合金蠕变行为的影响

通过蠕变曲线测定及组织形貌观察,研究[001]、[011]取向镍基单晶合金在蠕变期间的组织演化及变形特征。结果表明:经完全热处理后,[001]和[011]取向合金中立方γ′相均以共格方式镶嵌在γ基体相中,并沿〈100〉取向规则排列。蠕变期间,[001]取向合金中γ′相沿垂直于应力轴方向形成N-型筏状组织,而[011]取向合金中γ′相沿[001]取向形成纤维状筏形组织,且在(100)晶面的筏状γ′相与施加应力轴方向呈45°角排列,其中,立方γ′相不同晶面中扩张晶格的法线方向是筏状γ′相的生长方向。在试验温度和应力范围内,与[011]取向合金相比,[001]取向合金具有较好的蠕变抗力。在高温蠕变后期,两取向合金中的筏状γ′相均发生粗化和扭折,其中,[001]取向合金在蠕变后期的变形机制是位错剪切γ′相,而[011]取向合金的变形特征主要是形变位错在基体通道中滑移。     

一种单晶镍基合金压缩蠕变期间γ′相的定向粗化

对［001］取向单晶镍基合金恒温恒载压缩蠕变不同时间的组织形貌进行SEM和TEM观察表明：蠕变初期,两立方γ′相沿平行于应力轴方向扩散相连定向生长成为条形筏结构;垂直通道中基体[001］晶向共格应变量减小,应变能降低是合金元素定向扩散形成γ′相筏结构的驱动力;压缩与拉伸蠕变相比较,γ′相形筏所需要的时间较长,应力较大     

单晶Ni基合金高温蠕变期间γ''''定向粗化驱动力的有限元分析

为研究γ＇相定向粗化现象,采用有限元方法（ＦＥＭ）计算了单晶 Ｎｉ基γ和γ＇双相合金有／无外加载荷时的热错配应力及应变能密度．结果表明：外加载荷改变了γ和γ＇相内的ｖｏｎ Ｍｉｓｅｓ应力及应变能密度分布,与弹性应变相联系的共格应变能变化是γ＇相定向粗化的驱动力．外加拉伸或压缩应力,引起立方γ＇相不同界面晶格发生挤压或扩张应变,晶格的挤压应变可排斥γ＇相中原子半径较大的ＡＩ,Ｔａ等溶质元素;扩张的晶格可诱捕这些元素,以促进γ＇相的定向生长,因此,沿（１００）方向扩张晶格的法线方向是γ＇相形筏的生长方向．随γ＇相弹性扩张晶格应变及γ相粘滞塑性流变的增加,元素扩散及γ＇相形筏速率提高。     

单晶Ni基合金高温蠕变期间γ''相定向粗化驱动力的有限元分析

为研究γ‘相定向粗化现象,采用有限元方法（ＦＥＭ）计算了单晶Ｎｉ基γ和γ’双相合金有／无外加勒荷时的热错配应力及应变能密度。结果表明：外加载荷改变了γ和γ‘相内的ｖｏｎＭｉｓｅｓ应力及应变能密度分布。与弹性应变相联系的共格应变能变化是γ’相定向粗化的驱动力,外加拉伸或拉缩应力,此起立方γ‘相不同界面晶格发生挤压或扩张应变,晶格的挤压应变可排斥γ’相中原子半径较大的Ａｌ,Ｔａ等溶质元素;扩张的晶格可     

[011]取向镍基单晶合金在拉伸蠕变期间的组织演化与有限元分析

采用弹性应力-应变有限元方法计算了[011]取向单晶镍基合金中γ/γ'两相共格界面的von Mises应力及应变能密度的分布特征,研究了施加拉应力对γ/γ'两相界面von Mises应力分布及γ'相定向粗化规律的影响.结果表明:[011]取向单晶镍基合金经热处理后,组织结构是立方γ'相以共格方式嵌镶在γ基体相中,并沿〈...     

Structure Evolution and Creep Behavior for a Nickel-Base Single Crystal Alloy along [011] and [001] Orientations

研究980 ℃,200 MPa拉伸蠕变期间[001]和[011]取向镍基单晶合金中γ′相的形貌演化及蠕变特征,在相同拉伸条件下晶体取向的变化对合金的应变和应变速率产生明显影响。结果表明：沉淀相的定向粗化方向取决于合金的晶体取向,沿[001]取向拉伸,γ′相从最初的立方形态转化为与拉伸应力轴垂直的筏形;当拉伸轴平行于[011]取向时,γ′ 相沿[010] 和[100] 方向扩散生长,演化成与拉伸轴倾斜45o角的筏形。[011]取向合金的蠕变强度随其基体通道宽度的增大而快速下降,蠕变前期[001]与[011]取向的应变速率相近,蠕变后期合金表现出明显的蠕变各向异性     

Phase chemistry of the superalloy SC16 after creep deformation

The local chemical concentrations of the elements in the nickel-based single crystal superalloy SC16 were examined by atom probe field ion microscopy (APFIM) after standard heat treatment and after creep strain of 1.35% at 1223 K. The measurements were carried out along the [001] direction parallel to the applied creep stress. An enrichment of Al and a slight depletion of Ti in the γ′ precipitate near the γ′/γ interface were observed in both states, the as-prepared and the creep-deformed. The average chemical composition of the γ′ precipitates had hardly been changed during the creep deformation. However, the average Cr content decreased in γ channels perpendicular to the applied stress significantly. Its enrichment was detected near the interface. Contrary to Cr, the average Ni concentration increased in these γ channels and depleted near the interface. Both Ti and Ta seem to be depleted in γ channels near the interface after creep deformation. According to the results, the long range diffusion for directional coarsening of γ′ precipitates is suggested to take place mainly in γ channels.     

Microstructure Evolution of a Single Crystal Nickel-Base Superalloy During Heat Treatment and Creep

Microstructure evolution of a single crystal nickel-base superalloy during heat treatment and tensile creep at 1010℃ and 248 MPa for 30h was observed and analyzed. Internal stresses because of lattice mismatch between γ and γ‘ phase provided the driving force for γ‘ shape evolution during heat treatment. More than 65 vol. % distorted cubic γ‘ phase keeping coherency with the γ matrix precipitated after solution at 1295℃ for 32h. The shape of γ‘ phase was perfectly cubic with increasing precipitate size during the two-step aging treatment. Due to the applied stress and intemal stress field the continuous γ-γ‘ lamellar structure perpendicutar to the apptied stress was fonmed after 30h tensile creep.     

Pt+g ￠-Ni3Al+g-Ni/CMSX-4涂层结构的透射电镜研究

通过在CMSX-4镍基单晶高温合金表面镀Pt然后采用包埋渗铝的方法成功制备Pt改性的Pt+γ′-Ni3Al+γ-Ni/CMSX-4涂层,采用扫描电镜和透射电镜研究Pt+γ′-Ni3Al+γ-Ni/CMSX-4涂层的微观结构。TEM分析表明Pt主要分布于涂层γ′-Ni3Al相中,且涂层γ′-Ni3Al相里存在{111}孪晶;此外涂层内还发现六方结构富铼的拓扑密堆相(μ相),点阵常数为a=0.473nm和c=2.565nm,首次发现μ相内除了(001)孪晶外还存在(102)孪晶;探讨μ相和孪晶的形成机制。     

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).     

[111]取向镍基单晶合金的组织结构与蠕变行为

通过蠕变曲线的测定及微观组织形貌观察,研究[111]取向镍基单晶合金在高温低应力条件下的组织结构与蠕变行为。结果表明:经完全热处理后,[111]取向单晶合金的组织结构是立方γ′相以共格方式嵌镶在γ基体中,并沿100方向规则排列;在1 040~1 080℃、137~180 MPa的温度和应力范围内,该取向单晶合金表现出明显的温度和施加应力敏感性。蠕变期间,γ′相沿与应力轴呈一定角度形成筏状组织,蠕变后期在近断口区域筏状γ′相发生粗化和扭折。[111]取向单晶合金在蠕变期间的变形特征是位错在γ基体通道中运动和剪切筏状γ′相,由于形变量较大,较多位错切入筏状γ′相后使其形成亚晶结构,其中,蠕变后期大量位错切入筏状γ′相导致合金的蠕变抗力降低,是合金发生蠕变断裂的主要原因。     

Phase field modeling of channel dislocation activity and γ′ rafting in single crystal Ni–Al

Dislocation-precipitate interaction and directional coarsening (rafting) of γ′ precipitates in single crystal Ni–Al alloys under external load are investigated by three-dimensional computer simulations. The simulation technique is based on an integrated phase field model that characterizes simultaneously the spatiotemporal evolution of both precipitate microstructure and dislocations. The initial configurations consisting of cuboidal γ′ particles and dislocations in γ channels are constructed according to experimental observations and phase field simulations of the dislocation filling process in the γ channels. For a given state (sign and magnitude) of the lattice misfit and external load commensurate with experimental values, the predicted morphologies of the rafted γ′ precipitates and the rafting kinetics agree well with experimental observations. This indicates that plasticity plays a dominant role in the rafting process as compared to elastic modulus mismatch between γ and γ′ phases, which has been ignored in the present simulations. The spatial variation of chemical potential of solute atoms caused by the coupling between channel dislocations and misfit stress is evaluated from concentration and stress distributions, from which diffusion fluxes in the γ channels are analyzed.