高锰钢加工硬化

利用传统的喷丸技术对高锰钢表面喷丸处理,研究材料表层的组织结构特征.结果表明,纳米晶的演化,通过奥氏体粗晶内部位错增殖、湮灭和重组、位错缠结逐渐向位错胞过渡;应变量和应变速率的增加,诱发机械孪生,单系孪晶逐渐向多系孪晶过渡;同时多系孪晶之间的交割作用使晶粒尺寸不断细化;晶粒在位错运动和机械孪生的重复作用下,最终形成等轴状、取向呈随机分布的纳米晶组织.喷丸处理高锰钢表层明显强化.随层深减小,硬度急剧增加.高锰钢表层的加工硬化主要是由于晶粒细化、位错硬化和孪晶硬化,而与相变硬化无关.     

高能量冲击接触载荷下高锰钢磨损机理的研究

位错、孪晶,微晶和非晶态组织是高能冲击接触载荷下高锰钢变形的主要组织形态,高密度变形条带相互交叉,阻滞或截割,使奥氏体组织严重细化为微晶甚至是纳米晶,同时发生严重的点阵畸变,使晶体的自由能升高,晶体变成非晶态;微晶与非晶态的产生是高能量冲击载荷下,高锰钢加工硬化的一种机制,微晶和非晶的产生及其镶嵌分布是高锰钢在高能冲击接触载荷下具有较高综合机械性能,优越耐磨性的一个很重要的原因。     

高能量冲击接触载荷下高锰钢组织形态与加工硬化机制

滑移和孪生仍然是高能量冲击接触载荷下高锰钢变形的方式;位错,孪晶,微晶和非晶态组织是高锰钢变形的主要组织形态,位错胞是高锰钢在冲击载荷下特有的亚结构;高密度变形条带相互交叉、阻滞或截割,使奥氏体组织严重细化,变为微晶甚至是纳米晶,同时发生严重的点阵畸变,使晶体的自由能升高,晶体变成非晶态,微晶与非晶态的产生是高能量冲击载荷下,高锰钢加工硬化的一个很重要的机制。     

纳米孪晶金属塑性变形机制

本文综述了纳米孪晶金属材料的塑性变形机制.通过分析纳米孪晶二维结构变形时可启动的滑移位错类型,揭示纳米孪晶金属塑性变形的3种位错机制,即位错塞积并穿过孪晶界机制,Shockley不全位错诱导孪晶界迁移机制以及贯穿位错在孪晶片层内受限滑移机制.通过改变加载方向与孪晶界面的相对取向可实现这3类位错机制的可控转变.     

深度轧制高锰钢的组织演变及性能研究

利用常规轧制设备,采用热轧与冷轧及热处理相结合的方法,对铸态高锰钢进行了可控轧制处理。试验结果表明,经预变形的高锰钢奥氏体晶粒急剧细化,内部出现大量的高密度孪晶、位错缠结及层错等组织,加工硬化性能大大提高,耐磨性也随之提高。     

高压扭转大塑性变形Al-Mg铝合金中的层错和形变孪晶

利用高分辨透射电镜研究高压扭转大塑性变形纳米结构Al-Mg铝合金中的位错、层错和形变孪晶。结果表明:在纳米晶和超细晶内均存在高密度的层错和形变孪晶;形成层错的Shockley部分位错可分别由0°纯螺型位错和60°混合位错分解得到;纳米孪晶既可由晶内层错动态叠加而形成,也可由晶界向晶内不断发射部分位错而向晶内长大,从而分别实验证实了分子动力学模拟预测的均质和非均质形核长大的孪生机制;观察到了由4层层错动态叠加而形成的特殊纳米孪晶。此外,高分辨透射电镜观察表明:在不同滑移面上的层错相交时,形成层错而产生的拖曳部分位错相遇可反应生成压杆位错和Lomer-Cottrell位错锁。依据经典位错理论和晶界发射部分位错的机制,提出了描述超细晶面心立方金属和合金中层错和形变孪晶形核长大的新模型。     

TWIP钢在不同应变量下的亚结构

采用静态拉伸、金相、TEM等方法,对两种不同锰含量Fe-Mn-Si-Al系TWIP钢进行表征,研究了成分、应变速率以及应变量对孪晶、位错、层错等亚结构的影响.结果表明:孪晶形成的临界应变量εc与层错能、原始晶粒尺寸以及应变速率有关;两种钢在以10-4s-1的应变速率加载时孪晶体积分数的增长曲线符合Boltzmann模型S曲线关系,孪晶增长速度先增大后减小,Fe25Mn3Si3Al钢在ε＝0.2时孪晶增长速率达到最大,Fe30Mn3Si3Al钢在ε＝0.27时孪晶增长速率最大.Fe25Mn3Si3Al钢以10-2s-1的应变速率加载时,孪晶体积分数呈线性上升;TEM观察发现孪晶总是在高密度位错与层错区产生,位错、层错的塞积,位错、层错以及孪晶间的交互作用共同引起材料强度的提高.     

LNG储罐用高锰钢中厚板生产技术开发

为实现高锰钢良好的强韧性能匹配，对高锰钢中厚板进行了控轧控冷工艺试验，通过金相显微镜、扫描电镜和透射电镜观察了高锰钢中厚板的显微组织，采用拉伸和冲击试验机测定了高锰钢中厚板的综合力学性能。结果表明：高锰钢中厚板显微组织为单相奥氏体，奥氏体晶粒尺寸为10～20μm,碳化物弥散分布在奥氏体晶界处，且奥氏体晶粒内部存在较大尺寸的孪晶；高锰钢中厚板纵向屈服强度、抗拉强度、断后伸长率和-196℃冲击功分别为508 MPa、862 MPa、50.07%和124 J,高锰钢中厚板横向屈服强度、抗拉强度、断后伸长率和-196℃冲击功分别为511 MPa、856 MPa、51.67%和97 J;奥氏体晶界处弥散分布的硬相(Cr, Mn)₂₃C₆型碳化物，可有效提高高锰钢中厚板的强度；孪晶诱导塑性(TWIP)效应产生大量形变孪晶，增加了均匀伸长率，是高锰钢主要的增塑机制；软相奥氏体中形成的机械孪晶促进位错滑移和增殖，同时产生较强的晶粒细化效应，是高锰钢主要的韧化机制。     

高锰钢爆炸硬化机理分析

对爆炸后高锰钢的表层和亚表层的物相进行XRD分析,对爆前、爆后衍射花样进行标定,对显微组织进行对比分析.结果表明:爆炸硬化处理后高锰钢的组织仍为奥氏体,未发生马氏体转变.爆炸硬化的微观机理为:在炸药爆炸产生的巨大爆轰压力作用下,爆后高锰钢晶体各晶面的晶格常数增大,加剧了晶格畸变,在高锰钢内部形成大量位错和层错,这些高密度的位错和层错阻碍位错运动,使高锰钢硬化.     

机械研磨诱导316L不锈钢表层组织的演变

选取具有中等层错能的316L不锈钢进行表面机械研磨处理(SMAT)，制备出纳米结构表层，用X射线衍射(XRD)和透射电镜(TEM)研究横截面组织的演变过程．晶粒细化机理如下：奥氏体粗晶内部通过位错湮灭和重组形成位错胞；应变量和应变速率的增加诱发了机械孪生，形成了片层状孪晶；孪晶内部通过位错的运动使显微组织逐渐由片层状向等轴状转变，且晶粒尺寸逐渐减小、取向差逐渐增大；最终形成等轴状、取向呈随机分布的纳米晶组织．同时，对层错能对微观变形方式和纳米化行为的影响进行了讨论。     

Nanocrystallization process and mechanism in a nickel alloy subjected to surface severe plastic deformation

Bulk components made of a Ni-base C-2000 alloy with a face-centered cubic crystal structure and a very low stacking fault energy have been severely plastically deformed at the surface region to attain a grain size gradient ranging from nanocrystalline at the surface to coarse grained in the bulk. The evolution of microstructural characteristics has been studied as a function of the processing time employing a variety of analytical techniques, including extensive conventional and high-resolution transmission electron microscopy analyses. The thickness of the nanocrystalline surface layer is found to increase with the processing time. Deformation twinning is ubiquitous and occurs at the earliest stage of deformation and the deepest region of the material where plastic deformation has taken place in the surface severe plastic deformation process. A grain-refinement mechanism led by deformation twins and complemented by dislocation activity has been put forth to explain the nanocrystallization of the coarse-grained material employed in this investigation.     

Mechanical Properties and Stacking Fault Energies of NiFeCrCoMn High-Entropy Alloy

Materials with low stacking fault energies have been long sought for their many desirable mechanical attributes. Although there have been many successful reports of low stacking fault alloys (for example Cu-based and Mg-based), many have lacked sufficient strength to be relevant for structural applications. The recent discovery and development of multicomponent equiatomic alloys (or high-entropy alloys) that form as simple solid solutions on ideal lattices has opened the door to investigate changes in stacking fault energy in materials that naturally exhibit high mechanical strength. We report in this article our efforts to determine the stacking fault energies of two- to five-component alloys. A range of methods that include ball milling, arc melting, and casting, is used to synthesize the alloys. The resulting structure of the alloys is determined from x-ray diffraction measurements. First-principles electronic structure calculations are employed to determine elastic constants, lattice parameters, and Poisson’s ratios for the same alloys. These values are then used in conjunction with x-ray diffraction measurements to quantify stacking fault energies as a function of the number of components in the equiatomic alloys. We show that the stacking fault energies decrease with the number of components. Nonequiatomic alloys are also explored as a means to further reduce stacking fault energy. We show that this strategy leads to a means to further reduce the stacking fault energy in this class of alloys.     

TEM STUDY OF MECHANISM OF STRAIN-AGE HARDENING OF INITIALLY DISORDERED (Co,Fe)_3V ALLOY

TEM study was made to explore the mechanism of the strain-age hardening of initially-dis-ordered (Co_(78)Fe_(22))_3V,which was found to be attributed to the formation of a special disloca-tion-stacking fault configuration in company with disorder-order transformation-disloca-tions extended to stacking faults on{111}planes and got connected with each other throughpartial dislocation reaction at intersections of{111}planes,leading to dense networks withcells bounded by stacking fault tetrahedrons.The results also indicated that ordered(Co_(78)Fe_(22))_3V has very low stacking fault energy on{111}planes and relative high andisotropie antiphase boundary energy,which implies that it is most likely to be Lomer-Cottrelllocks,not Kear-Wilsdof locks,that are responsible for the high strength at high temperaturesof this alloy.     

连续升温、降温过程中纯Fe的微观结构分析

通过分子动力学模拟,采用较先进的键型指数法HA及原子团类型指数法CTIM-2,对Fe连续升温、降温过程中微观结构进行模拟研究.结果表明:连续升温过程,Fe的微观结构变化是bcc→fcc\hcp→bcc→液体；连续降温过程,Fe的微观结构变化是液体→fcc\hcp.Fe凝固结束没有形成大量的高温bcc晶体,原因是在高温液态中bcc结构原子稳定性较差,fcc和hcp结构原子更易稳定存在.此外,温度变化速率过快,可诱导晶体生长过程中发生层错,促使Fe在升温、降温过程出现fcc和hcp晶体的交替分层分布,这与fcc和hcp晶体的原子能量相近、晶体的致密度相同、原子空间堆垛方式局部相同有关.     

预变形对Fe-Mn合金层错几率和阻尼性能的影响

探讨了Fe-Mn合金的高阻尼机制并采用G-L位错脱钉模型对其进行描述,同时通过测定层错几率,揭示了预变形(0-10%)对Re-Mn合金阻尼性能影响的本质.采用倒扭摆测试合金的阻尼性能,SEM和TEM观察显微组织,XRD测定物相体积分数和层错几率.结果表明,Fe-Mn合金的高阻尼性能来源于层错界面上Shockley不全位错的脱钉运动,实验结果很好地符合G-L位错脱钉模型;预变形量小于4%时,预变形处理虽然对合金的ε马氏体量没有太大影响,但明显增加了其层错几率,即Shockley不全位错的数量,合金的阻尼性能随变形量增加逐渐提高;预变形量大于4%时,由于ε马氏体和层错的相互交割,增大了Shockley不全位错的脱钉难度,所以合金的阻尼性能随变形量增加逐渐下降.     

FINE STRUCTURE ANALYSIS OF DEFORMED STEEL 1Cr18Ni9

X-ray diffraction profiles of various deformed steel 1Cr18Ni9 through stepped scanning wereobtained.By profile analysis,some structure parameters such as effective domain size D_(eff),dislocation density in domain,distribution parameterand bulk stored energy densiy(E/V),etc.,were obtained.The results were compared with those of TEM observation.Thetrue domain sizes D_e are comparable,but the minimum and characteristics of width of stack-ing fault are different.This may be resulted from the large fluctuation in width of stackingfault.     

金属材料表面纳米化研究现状

金属材料的表面纳米化处理是近几年表面强化方法研究的热点之一。这种技术将纳米晶体材料的优异性能与传统工程金属材料相结合,在工业应用上具有广阔的应用前景。通过对表面纳米化的基本原理、制备方法、结构特征和功能特性的综述,提出要实现这种新技术的工业应用需要解决的问题,如影响因素,表面纳米化形成动力学等。     

FeMnCoCr系亚稳高熵合金的研究进展

高熵合金是一种原子排列有序,化学无序的新型多主元合金。通过改变合金元素的种类和浓度,能够调控合金系统层错能及显微组织的相稳定性,进而诱发形变孪晶、马氏体相变等塑性变形机制,最终使合金获得突出的综合力学性能。这种高熵合金的设计理念称为“亚稳工程”。亚稳高熵合金的显微组织、相结构及变形机制与合金体系的层错能密切相关。在FeMnCoCr系亚稳高熵合金中,随着系统层错能降低,面心立方结构稳定性下降,从而激活应变诱导马氏体相变(γ→ε),实现了合金强度和塑性的同时提高。本文主要介绍了FeMnCoCr系亚稳高熵合金的成分设计、制备及加工方法、微观结构和力学性能,并对亚稳高熵合金未来的研究方向进行了展望。     

Microstructure evolution ofAZ91D induced by high energy shot peening

A nanostructured surface layer was fabricated on a AZ91D magnesium alloy by using a high-energy shot peening（HESP）. HESP induced structure along the depth of the treated sample surface layer was characterized by means of X-ray diffractometer （XRD）, transmission electron microscope（TEM） and high resolution transmission electron microscopc（HRTEM）. The experimental results show that a deformed layer of about 50 μm has formed after HESP treatment and the average grain size increases from about 40 nm in the surface layer to about 200 nm at the depth of 40 μm. The surface nanocrystallization can realize intercoordination of the dislocations slipping and dynamic recrystallization. The nanocrystalline grains have stacking faults and dislocation in their interiors. The microhardness of the top surface is about triplicate that of the coarse-grained matrix.     

Direct evidence for Suzuki segregation and Cottrell pinning in MP159 superalloy obtained by FEG(S)TEM/EDX

The effects of Suzuki segregation on the plastic flow behaviour of MP159 alloy deformed at high temperature and on the resulting dislocation structure have been examined. Elemental concentration profiles across both stacking faults and slip bands have been measured in a FEG TEM in nano-probe using the line scanning mode and EDX. It was found that Suzuki segregation resulted in continuously serrated plastic flow for deformation at temperatures from 450–670 °C and at a slow strain rate such as 1.0×10⁻⁴/s. TEM examination showed an increased dissociation width for dislocations and larger and more stacking faults after deformation at high temperatures as compared with those after deformation at room temperature. This can be interpreted as being due to the reduction of stacking fault energy by Suzuki segregation and/or Cottrell pinning. The elemental concentration profiles across stacking faults and slip bands showed that Mo and Al were more often found than other solutes to segregate to stacking faults and slip bands. Occasionally, the segregation of Ti and Nb could also be detected at stacking faults and slip bands.