【作者】 王明罡；

【导师】 田素贵；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2010， 博士

【摘要】 本文通过对镍基合金进行优化成分设计,并对合金中TCP相的析出倾向进行预测和验证,考察了有/无元素Re镍基合金中TCP相在高温有/无应力时效期间的析出特征及演化规律,研究了元素Re对TCP相形态及合金持久寿命的影响规律。通过测定不同合金在不同条件下的X-ray衍射谱线,计算出不同合金中γ′、γ两相的晶格常数及错配度,研究了元素Re及温度对合金中γ′、γ两相晶格错配度的影响规律;通过对不同镍基单晶合金进行蠕变性能测试及组织形貌观察,研究了不同合金的蠕变行为及影响因素,得出主要结论如下:采用Md法和Nv法可对镍基合金中TCP相的析出倾向进行预测,并确定出含Re镍基合金中有TCP相析出的临界值分别为:Md > 0.98和Nv > 2.1。通过理论预测及验证,元素Re、Mo、W可强烈促进镍基合金中TCP相的析出,确定出析出的TCP相为μ相;在1040℃和1100℃长期时效期间,6%W合金和4.5%Re合金中析出的μ相在{111}晶面沿<110>晶向呈片状生长,其中在{100}晶面μ相呈现相互平行或垂直排列的针状形貌,而在{111}晶面呈现的针状μ相互成60°角排列。在1040℃长期时效期间,无Re的6%W合金中析出的μ相尺寸较短,随时效时间延长不发生球化;而4.5%Re合金在1100℃长期时效期间,随时效时间延长,析出的μ相发生粗化呈现凹凸不平特征,并逐渐转变成球状形态,其中,在片状μ相不同区域的化学位差促使溶质元素向相邻γ′相中扩散,是导致μ相不断溶解及发生球化的主要原因。由于析出μ相可消耗合金中的难溶元素,降低基体的合金化程度和蠕变抗力,因此,可明显降低合金的持久寿命;在施加应力的蠕变期间,析出的针状μ相易于产生应力集中,可加速裂纹的萌生和扩展,是较大幅度降低合金持久寿命的主要原因;而在近球状μ相区域不易产生应力集中,是使合金持久寿命降低幅度减小的主要原因。铸态单晶合金的枝晶干和枝晶间区域,γ′相具有不同的尺寸和形态,并存在明显的元素偏析,元素Re、W、Cr、Mo为枝晶干偏析元素,元素Al、Ta、Co为枝晶间偏析元素,随固溶温度提高,元素在枝晶干/枝晶间的偏析程度减少,并致使合金的持久寿命提高。铸态合金中γ、γ′两相有较大的晶格常数及错配度;经高温固溶及完全热处理后,立方γ′相以共格方式嵌镶在γ基体中,合金中γ′、γ两相的晶格常数及错配度略有减小;经有/无应力的长期时效后,使合金中γ′相粗化,并在两相之间出现界面位错,使合金中γ′、γ两相的晶格常数及错配度的绝对值增加。随元素Re含量提高,单晶合金中γ、γ′两相的晶格常数增加,晶格错配度的绝对值减小,致使蠕变期间合金中γ′相的筏形化速率降低,并较大幅度提高合金的高温持久性能;随温度提高,合金中γ、γ′两相的晶格常数及错配度的绝对值增加。元素Re可明显提高合金的蠕变抗力和持久寿命,与2%Re合金相比,4.2%Re合金具有较好的蠕变抗力和较长的蠕变寿命;在试验的温度和施加应力范围内,测算出两合金的表观蠕变激活能分别为Q1 = 461.5kJ/mol、Q2 = 497.9 kJ/mol。在高温低应力的蠕变初始阶段,单晶合金的变形机制是(1/2)<110>位错在基体通道的八面体滑移系中以交滑移方式运动,在稳态蠕变期间合金的变形机制是位错通过攀移越过筏状γ′相,而在蠕变后期,合金的变形机制是<110>超位错剪切进入筏状γ′相。在中温高应力蠕变期间,合金的变形机制是(1/2)<110>位错在基体通道中运动,并有<110>超位错切入γ′相内,其切入γ′相位错可发生分解,形成不全位错+层错的位错组态,阻碍位错的滑移是使合金具有较好蠕变抗力的主要原因。更多还原

【Abstract】 In this dissertation, the precipitation trend of TCP phase are predicted and verified by means of the alloys compositions design of using the Md and Nv methods, and the morphology features and evolution regularity of TCP phase precipitated during high temperature aging of the Re containing/free single crystal nickel-based superalloys are detected, and in the further the influences of the element Re on the TCP phase configuration and stress rupture properties of the alloys are investigated. The lattice parameters and misfits of theγ′,γphases in the different superalloys are calculated by means of measuring X-ray spectrums, and investigating the effecting regularity of the element Re and temperatures on the misfits ofγ′,γphases. And the creep behaviors and effect factors of the different superalloys are investigated by measuring creep properties and microstructure observation.Results show that the precipitated trend of TCP phase in the nickel-based superalloys can be predicted by using Md and Nv method of the alloys design, and the critical values of TCP phase precipitated in the Re containing single crystal nickel-based superalloys are defined as Md > 0.98 and Nv > 2.1. The trend of TCP phase precipitated in the single crystal nickel-based superalloys increases with the amount of the elements W、Re、Mo addition, and TCP phase precipitated in the Re containing/free superalloy is identified as theμp?hase. During long term aging at 1040℃and 1100℃, theμphase precipitated in the 6%W alloy and 4.5%Re alloy is grown along the <110> orientation on {111} planes in the form of the strip-like structure. Thereinto, theμphase on {100} planes displays the strip-like configuration arranged at the parallel or upright each other, and theμphase on {111} planes displays the strip-like configuration arranged at the angle of 60°each other. The element Re has an obvious influence on the morphology ofμphase in alloys.During long term aging at 1040℃, theμphase precipitated in 6%W alloy is shorter in size, no spheroidized feature of the TCP phase is detected. But theμphase precipitated in 4.5%Re alloy during aging at 1100℃is longer in size, and theμphase is regularly coarsened, as the aging time prolongs, for displaying the accidented feature up to transformed into the sphere-like morphology. The difference of the chemical potential at the different regions of the slice-likeμphase promotes the solute elements diffusing to the adjacentγ′phase, which is thought to be a main reason of resulting in theμphase dissolved and transformed into the sphere-like morphology. The refractory elements in the alloys are consumed due to the precipitation ofμphase, therefore the stress rupture lifetimes of the alloys are obviously decreased. The stress concentration is easily generated in the regions near the strip-likeμphase to accelerate the initiation and propagation of the cracks during creep, which is thought to be the main reason of the creep lifetime deterioration, to a great extent, of 6%W alloy. But the stress concentration is not easily generated in the regions near the sphere-likeμphase, which is thought to be a main reason of depressing creep lifetime of 4.5% Re alloy to a smaller extent.The different size and morphology ofγ′phase are displayed in the interdendritic and dendritic areas, which are related to the segregation of the alloying elements in the areas. Thereinto, the elements W, Cr, Mo and Re are richer in the dendritic area, and the elements Co, Ta, Al are richer in the interdendritic area. And the segregation extents of the elements in the areas decrease with the enhancing temperature of the solution treatment, which may obviously improve the stress rupture lifetimes of the alloys.Theγ′,γphases in as-cast single crystal nickel-based superalloy have a bigger lattice parameters and misfit. After high temperature solution and fully heat treated, the lattice parameters and misfits ofγ′,γphases in the alloys is slightly diminished due to the cubicγ′phase embedded coherently in theγmatrix. After long time age under the applied stress/unstress, theγ′phase in alloy is coarsened and the dislocation networks are appeared on the interfaces ofγ,γ′phases, which increases the lattice parameters and misfit ofγ、γ′phases. The lattice parameters increase with the Re content, but the absolute value of the misfit decreases, which decreases the rafting rate ofγ′phase and enhances the creep resistance of the alloys at high temperature. But the lattice parameters and absolute value of misfit increase with temperature.Comparing to 2%Re alloy, 4.2% Re alloy displays the better creep resistance and longer creep lifetime, which indicates that the creep resistance and stress rupture lifetimes of the alloys may be obviously improved by addition the element Re. In the ranges of the applied temperatures and stresses, the activation energies of the alloys during steady state creep are calculated to be Q1 = 461.5kJ/mol and Q2 = 497.9kJ/mol, respectively. During the initial stage of high temperature and low stress creep, the deformation mechanism of the single crystal superalloys is that the (1/2)<110> dislocations activated in the octahedral slip system of the matrix channel in the form of cross-slipping. And the deformation mechanism of the alloy during steady state creep is the dislocations climbing over the raftγ′phase, while the deformation mechanism of the alloy during the later stage of creep is the <110> super-dislocations shearing into the raftedγ′phase, thereinto, the dislocation which shears into theγ′phase may be decomposed to form the configuration of the partial dislocation and stacking fault, which can hinder the cross-slipping of dislocations to improve the creep resistance of the alloy.更多还原