S32750双相不锈钢相界与晶界特征对其力学性能和耐蚀性能的影响EI北大核心CSCD

通过固溶处理获得不同初始组织状态的S32750双相不锈钢样品,然后进行厚度压下量80%的冷轧变形和1050℃的退火处理,采用SEM-EBSD和XRD技术研究合金相界与晶界特征以及相组成分布情况,并利用拉伸实验、纳米压痕和双环电化学动电位再活化法(DL-EPR)分析不同初始状态样品的组织对力学性能与耐晶间腐蚀性能的影响规律。结果表明:高温固溶处理的合金样品经冷轧退火后晶粒细小均匀,两相分布接近1∶1,且相界占内界面(晶界+相界)比例较高,同相晶粒团簇程度最低,表现出优异的综合力学性能。合金样品经敏化处理后,σ相易沿α相晶界析出,高温固溶并经轧制退火后的样品中,由于α晶界比例较少且满足K-S取向关系的相界比例较高则又表现出良好的晶间腐蚀抗力。因此,通过适当的工艺来调控合金的相界与晶界分布可以实现材料强度和晶间腐蚀抗力的同步改善。     

锻造、轧制变形对2519A铝板抗腐蚀性能的影响

为改善2519A-T87铝合金的腐蚀性能并探求其影响因素,采用金相显微镜、透射电镜及X射线衍射仪研究了锻造以及轧制两种变形方式对该合金板晶界无沉淀带、析出相、晶粒取向与抗腐蚀性能的影响.结果表明:锻造板中晶界无沉淀带(PFZ)较轧制板的宽,晶界析出相粒子间距大,较难形成连续腐蚀通道,其抗晶间腐蚀与剥落腐蚀性能优于轧制板;PFZ与基体,析出相与PFZ构成两对电偶发生反应,而晶界上不连续分布的、大的第二相之间的间距有利于提高合金的抗应力腐蚀性能,锻造板的应力腐蚀性能(KISCC=32.1 MPa.m1/2)比轧制板(KISCC=22.1 MPa.m1/2)高;锻造板的{100}晶粒取向密度较低;第二相的大小及分布是决定该合金腐蚀性能的关键..     

无取向硅钢中第二相的析出行为

使用扫描电镜(SEM)和能谱仪(EDS)等手段并结合热力学和动力学计算,研究了无取向硅钢900～1000℃常化处理过程第二相的析出行为。结果表明,无取向硅钢中的第二相主要为AlN和少量MnS。AlN和MnS在不同基体相(α相、γ相及(α+γ)两相）中有三种析出形核机制(均匀形核、晶界形核和位错形核),其临界形核半径(d*)都随常化温度的提高而增大。在同一温度下,相对于其他基体相AlN在(α+γ)两相区中晶界形核的临界形核功最小,相对形核率最大,因此以晶界形核为主;而MnS在α相中位错线上临界形核半径最小,相对形核率大,开始析出温度低,因此以位错形核为主。     

冷却方式对热连轧GH4169合金组织与蠕变行为的影响

通过对不同方式冷却的热连轧GH4169合金进行直接时效处理、蠕变性能测试和组织形貌观察,研究了冷却方式对热连轧GH4169合金的组织结构与蠕变行为的影响。结果表明:"水冷"HCR-GH4169合金经直接时效后,其组织由细小晶粒组成,大量细小γ′,γ″相在晶内弥散析出,可提高合金蠕变抗力,而"空冷"热连轧合金晶粒尺寸较大,且在基体中析出的γ′,γ″两相的数量明显减少;在实验条件下,"水冷"热连轧合金经直接时效后具有较好的蠕变抗力和较长的蠕变寿命;热连轧及直接时效合金在蠕变期间的变形机制是位错在基体中发生单、双取向滑移和孪晶变形,在蠕变后期,裂纹在晶界处萌生和扩展,并发生沿晶断裂是合金的蠕变断裂机制。     

FGH95粉末镍基合金的组织结构与蠕变特征

通过蠕变曲线的测定及组织形貌的观察,研究了FGH95粉末镍基合金的蠕变行为及变形特征.结果表明:FGH95粉末镍基合金在试验的温度和应力范围内,具有明显的施加温度和应力敏感性,并测算出合金的蠕变激活能和应力指数.合金的组织结构由一次、二次、三次γ'相及弥散分布的碳化物组成,在粉末颗粒之间具有较宽的晶界.蠕变期间,在合金晶粒内的变形以单取向或双取向滑移方式进行,并在滑移迹线附近有细小碳化物析出,而较宽的晶界由于剧烈变形可发生碎化形成细小晶粒.合金在蠕变期间的微观变形机制是位错发生双取向滑移,其中(1/2)《110》位错在γ基体相中运动,《110》超位错存在于γ'相内,而层错的形成是由于《110》超位错分解为(1/3)《112》超肖克莱不全位错所致.     

FGH95粉末镍基合金的组织结构与蠕变断裂特征

通过对不同工艺处理FGH95合金进行组织形貌观察及持久性能测试,研究了组织结构对合金持久性能的影响规律。结果表明:经1150℃固溶和时效处理后,合金中有粗大γ′相在较宽的边界区域不连续分布,其周围存在γ′相贫化区;经1160℃固溶及时效处理后,合金中粗大γ′相完全溶解,在晶内弥散分布高体积分数的γ′相,并有粒状(Cr,Nb)23(C,B)6硼碳化合物在晶内及沿晶界不连续析出;经1165℃固溶和时效后,合金的晶粒尺寸明显长大,并有硬而脆的碳化物膜沿晶界连续析出。在650℃、1034MPa条件下,经1160℃固溶和时效合金具有较高蠕变抗力和较长持久寿命,蠕变期间的变形机制是位错以Orowan机制饶过γ′相、或位错剪切γ′相,其中晶界处不连续析出的粒状碳化物可有效阻碍位错滑移,是使合金具有较好蠕变性能的主要原因。蠕变后期,合金的变形特征是晶内发生单取向滑移,随蠕变进行位错在晶界处塞积,并引起应力集中,致使裂纹在晶界处萌生及扩展是合金的蠕变断裂机制。     

Fe-Ni基合金中次生η相的析出机理

针对奥氏体合金中次生η相与基体位向关系存在的不同看法，研究了铁镍基奥氏体合金大量次生η相的析出机理，结果表明，η相与基体之间有良好的共格关系：{001}η／／{111}γ，（110）γ／／（210）η．晶界η相首先在一般无规晶界γ＇相处通过不全位错滑移产生堆垛层错带的方式形核，之后通过原子控制长程扩散机制的台阶方式在基体中长大，进入晶界另一侧与之匹配差的晶粒中，晶界随之一起迁动．η相的析出伴随着附近区域γ＇相的溶解和消失．     

电弧离子镀NiCoCrAlY涂层的透射电镜研究

采用透射电镜技术对电弧离子镀制备的NiCoCrAlY涂层的微观组织结构进行了研究,结果表明,电弧离子镀沉积后,在DSM11高温合金基体γ′相中析出大量的弥散纳米γ相颗粒,析出的γ相与γ′相取向相同.γ′晶胞内部出现大量的堆垛层错,涂层与基体界面之间的应力处于一个较低的水平.电弧离子镀方法沉积的NiCoCrAlY涂层具有纳米晶体的结构,且涂层比较致密.真空退火后涂层内部的结合更致密,晶粒明显长大,部分晶粒有孪晶出现,并伴随β-NiAl或CoAl相析出.     

热轧过程中高纯钴微观组织及织构演变

金属钴具有同素异构转变特性。为探究热轧工艺对高纯钴的微观组织及织构演变规律的影响,对纯度为99.99%(质量分数)的高纯钴进行500 ℃(高于同素异构转变温度)下的热轧,并采用电子背散射衍射(EBSD)技术对样品进行表征。结果表明:初始态板材由密排六方相(HCP相)和面心立方相(FCC相)构成,且以HCP相为主;HCP相晶粒的晶体取向较为集中,而FCC相晶粒的晶体取向较为分散;HCP相中的相变孪晶和FCC相中的退火孪晶含量较高。经过热轧,不同道次下的水冷板材中仍含有HCP相和FCC相,HCP相和FCC相在不同轧制板材中含量略有不同,但FCC相的相对含量均高于HCP相;HCP相晶粒的细化效果尤为显著。两相的小角度晶界含量较初始态大幅度上升,大角度晶界含量大幅度下降;轧制水冷板材中HCP相形成了特殊的择优取向,{0001}基面法向偏离ND方向朝向RD方向35°,且{10-12}取向较为分散;而FCC相呈现出较为随机的晶体取向特征。     

AZ31镁合金室温拉伸微观变形机制EBSD原位跟踪研究

利用电子背散射衍射(EBSD)技术,原位跟踪AZ31镁合金轧制板材室温下沿轧向拉伸时的晶粒取向变化。对变形过程的滑移系和孪晶启动机进行分析。结果表明:变形过程主要由〈a〉基面和柱面滑移系开动而实现,晶粒取向无明显变化,大量〈a〉位错滑移的产生,使得变形后小角度晶界增加明显。晶粒中拉伸孪晶是试样在拉伸变形过程中产生的,而非在试样拉伸后的卸载过程中产生。     

Grain growth and grain orientation distribution of Al-Mg alloys

Grain growth behaviour of Al–Mg alloys containing 0.3, 2.7 and mass% Mg was investigated focusing on the spatial distribution of grain orientation and grain boundary character. In Al–0.3 mass% Mg alloy the cube texture developed at the first stage and then the texture declined accompanied with abnormal grain growth of non-cube grains at the second stage. The development of cube grains was suppressed by an increase of solute Mg atoms. The texture change depended strongly on spatial distribution of grain boundary character and cube clusters.     

Isothermal decomposition of the ß′ phase in a Cu-Zn-Al alloy

The isothermal decomposition of theβ′ phase in a Cu-25 wt % Zn-6 wt % Al alloy was investigated using transmission electron microscopy and electron probe microanalysis. The ordering of theβ phase was too rapid to be suppressed during quenching from the solution annealing temperature. On ageing the alloy in the temperature range 603 to 703 K, theβ′ phase was found to decompose into a mixture of α+γ phases by the precipitation of fine and equiaxed γ-phase particles distributed uniformly throughout the matrix of α. The orientation relationship between α and γ was identified as $$\begin{gathered} (001)_\alpha ||(001)_\gamma \hfill \\ [010]_\alpha ||[010]_\gamma \hfill \\ \end{gathered} $$ The growth rate of the γ phase precipitates exhibited a maximum at 653 K. Electron probe microanalysis showed that the γ phase precipitates were enriched in aluminimum and depleted in zinc, compared to the α matrix. In addition to the uniform distribution of intragranular γ phase precipitates, heterogeneous precipitation of the α phase was observed along the grain boundaries indicative of a direct transformation ofβ′ to α in these regions: this reaction was found to be pronounced as the ageing temperature was increased up to 773 K.     

In-situ observation of interaction between precipitates and austenite during δ→γ phase transformations

The δ-ferrite to γ-austenite phase transformation in duplex stainless steels was observed using ultra high-temperature confocal laser scanning microscope, and the orientation relationship between the γ phase, and precipitate is discussed. Owing to mutual promotion action, the γ phase was observed at δ/δ grain boundary at the beginning of δ-ferrite→γ-austenite transformation, followed by two-dimensional γ-phase growth at the same speed (0.625?µm?s^?1) along the grain boundary and into the δ grain matrix. The γ-phase growth rate decreases to 0.244?µm?s^?1 when precipitate stops growing. In the process of grain growth at high temperature, the precipitated pinning grain boundary will slow the movement speed of the grain boundary.

The mutual promotion action leads to preferential nucleation of the γ phase, and the nucleation and growth of the austenite also promoting the growth of MnS the growth.     

Stability of trapped lattice dislocations on interphase boundaries in duplex stainless steel

Abstract

Differences in the thermal stability of trapped lattice dislocations in interphase boundaries and grain boundaries in austenitic–ferritic steel have been studied. It was found that the distribution of diffusional properties of α/γ interphase boundaries depends on the mutual orientation of phases and differs significantly from the distribution of diffusional properties of α/α and γ/γ grain boundaries, which stems from the fact that interphase boundaries include a substantial fraction of boundaries of particularly low diffusivity. These are interfaces of austenite grains which nucleated inside ferritic grains and demonstrate Kurdjumov–Sachs or Nishiyama–Wassermann relationship with respect to the ferritic matrix.

MST/1005     

无取向硅钢形变储能取向依赖性及其对再结晶织构的影响

采用晶体塑性有限元模拟与实验相结合的方式,研究无取向硅钢冷轧过程中不同初始织构组分的取向流动与形变储能累积。结果表明:冷轧后形成了较强的α,γ形变织构和较弱的λ形变织构。再结晶织构由γ,α,η和λ织构组成,其取向密度依赖于冷轧压下率。随冷轧压下率增大,λ再结晶织构逐渐增强,η织构先增强后减弱,γ织构先减弱后增强,α织构稍有弱化。冷轧过程中形变储能累积具有明显的初始取向依赖性,初始γ取向储能累积速率在低于50%压下率时与初始α取向接近,高于50%压下率时则明显大于后者,初始λ取向储能累积速率始终显著低于γ和α取向,转至同一形变取向的不同初始取向间的储能累积也会产生差异。冷轧过程中不同初始织构组分的取向流动与形变储能累积规律,决定了无取向硅钢再结晶织构组分的发展。     

Ta掺杂对γ-TiAl基合金块状组织和力学性能的影响

研究了Ti-48Al-2Nb-2Cr-xTa(x=0,1.0,2.0)(原子分数,%)合金α单相区淬火,块状组织(γ_m相)的演变规律,采用EBSD(电子背散射衍射)技术对晶粒取向进行表征。结果表明,在快速冷却条件下,微量Ta元素的添加能够促进γ_m相的析出,促进(体积分数大于50%)或者抑制(体积分数小于50%)γ_m相析出的Ta元素临界含量为2%(原子分数)。Ta元素能够细化γ_m相亚颗粒,同时,不同种类γ_m变体可直接在α₂晶粒内以BOR形核,在生长过程中发生了沿着{111}γ密排面的变体选择,使得第二代γ_m变体偏离BOR。     

Influences of Thermal Martensites and Grain Orientations on Strain-induced Martensites in High Manganese TRIP/TWIP Steels

Strain-induced martensites in high manganese TRIP/TWIP steels were investigated in the presence of thermal martensites and under the influence of austenitic grain orientation by X-ray diffraction(XRD),scanning electron microscopy(SEM) and electron backscattered diffraction(EBSD).Before deformation,the morphology of α’-M depended mainly on the number of variants and growing period.Regardless of martensite morphologies and deformation,the Kurdjumov-Sachs(K-S) orientation relationships always maintained.The 6 α-M variants formed from a plate of ε-M were of 3 pairs of twins with a common axis <110> α’ parallel to the normal of {111} γ habit plane to minimize transformation strain.When α’-M could be formed only by deformation,it nucleated at the intersection of ε-M variants and grew mainly in thick ε-M plates.Thick ε plates promoted significantly the α’-M and weakened the influence of grain orientations.During tension,the transformation in <100>-oriented grains was observed to be slower than that in <111>-oriented grains.Deformation twins promoted ε-M formation slightly and had no apparent effect on α’-M.Deformation increased the number of ε-M variants,but reduced that of α’-M variants.     

Microstructure and Phase Transformation of a Niobium-rich TiAl-based Alloy Containing Boron and Carbon

Microstructure and phase transformation of Ti46Al8Nb0.5B0.2C alloy have been investigated.X-ray diffraction (XRD),optical microscopy (OM),scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show that as-cast and hot isostatic pressing (HIP) alloy mainly composed of γ and α 2 phase have fully lamellar microstructure with point-like or ribbon-like TiB 2 distributing in lamellar colony or at grain boundary.The mean size of lamellar colony is about 150 and 450 μm for as-cast and HIP alloy,respectively.The lamellar spacing is about 550 and 600 nm for as-cast and HIP alloy,respectively.It has been found that cooling rates and quenching temperatures have significant effect on phase transformation of Ti46Al8Nb0.5B0.2C alloy.When the alloy is treated at 1380℃ for 1 h and cooled from α domain,water cooling leads to complete α→α 2 transformation,oil cooling leads to predominant α→α 2 and part α→γ m transformation,air cooling leads to α→α + γ p2 →L(α + γ) →L(α 2 + γ) transformation,and furnace cooling leads to α→α + γ p3 →L(α + γ) →L(α 2 + γ) transformation.However,when the alloy is treated at 1400℃ for 1 h and cooled from α domain,water cooling leads to predominant α→α 2 and part α→α + γ p4 →γ m transformation,oil cooling leads to α→α + γ p5 →γ m transformation,air cooling leads to α→α + γ p6 →L(α + γ) →L(α 2 + γ) transformation,and furnace cooling leads to α→α + γ p7 →L(α + γ) →L(α 2 + γ) transformation.Microstructural evolution of the alloy during various heat treatments has been examined and the phase transformation mechanisms have been elucidated.Based on the experimental observation,schematic CCT diagrams for the alloy have been given.