Ti-6Al-4V钛合金表面纳米化机制研究

借助X射线衍射仪、透射电镜及显微硬度仪等先进仪器,研究了经超音速微粒轰击( SFPB)形变热处理Ti-6Al-4V合金表面自身纳米化晶粒尺寸演化及纳米化机制.研究结果表明:超音速微粒轰击使Ti-6Al-4V合金表面获得了纳米组织,并发生显著的加工硬化,表面显微硬度比基体硬度提高了1倍多;随着SFPB处理时间的延长,纳米结构层厚度不断增加,晶粒尺寸逐步细化,当SFPB处理30 min后晶粒尺寸趋于稳定,在表层形成了晶粒尺寸约为20 nm具有随机取向的纳米等轴晶.Ti-6Al-4V合金表面自身纳米化是由于位错运动、孪晶的形成及交割共同作用的结果;在多方向载荷的重复作用下,在塑性变形区产生了大量的由位错线和高密度位错缠结分割的位错胞,并在位错寨集处产生应力集中,进而形成孪晶;孪晶自身相互交割和位错的滑移相互协调,形成了细小的孪晶和胞状组织;晶胞组织转变为细小多边形亚晶;当孪晶尺寸细化到亚纳米级时,位错的滑移起主导作用,最终通过位锗的湮灭和重组形成了具有随机取向的等轴状纳米晶粒.     

室温ECAP变形纯钛孪生行为研究

室温下对纯钛进行多道次等径弯曲通道变形（ECAP）,分别采用光学显微镜（OM）、透射电镜（TEM）、电子背散射衍射仪（EBSD）、室温拉伸和显微硬度观察,测试纯钛变形过程组织演变和力学性能变化规律,探讨纯钛室温变形机制和孪生行为。结果表明,纯钛ECAP变形过程中出现■拉伸孪晶和■压缩孪晶,随着挤压道次的增大,孪晶数量先增大后减小。孪晶的出现有效改变晶格取向,激发进一步位错滑移,辅助塑性变形过程,使纯钛显微组织有效细化,经过4道次ECAP变形,平均晶粒尺寸由约63.79μm细化至约2.81μm。1道次变形后晶粒细化效果最显著,平均晶粒尺寸比变形前减小约94%;随着变形道次的增加,晶粒细化效果减弱,4道次变形后平均晶粒尺寸累积减小约95.6%。同时,大量位错、孪晶和亚晶的形成,使得位错、孪晶以及亚晶之间的相互作用加强,显著提高了纯钛的屈服强度和显微硬度,4道次变形后,屈服强度从215 MPa增加到600 MPa,增幅为179%;显微硬度从HV 129增加到HV 200。由于1道次变形后晶粒细化效果最显著,并且出现大量孪晶和位错,屈服强度与硬度的增幅也最大。     

工业纯钛ECAP变形组织与织构演变的EBSD分析

利用电子背散射衍射(EBSD)对采用90°模具以C方式制备的等径弯曲通道变形(ECAP)各道次工业纯钛(CP-Ti)试样的组织及织构演变进行表征。结果表明:1道次变形后,ECAP组织并不均匀,既有拉长的粗晶,又有细小的等轴晶。随着道次的增加,组织变得细小均匀,从而达到细化晶粒的效果;工业纯钛ECAP变形初始阶段,粗大的晶粒破碎,产生位错缠结和位错胞,使小角度晶界增加。随着道次的增加,位错不断地向亚晶界运动,亚晶间产生相对滑动和转动,最终形成具有大角度晶界的超细晶组织,使小角度晶界减少,大角度晶界增加。工业纯钛原始试样具有双峰基面织构,晶体的c轴由法向方向(ND)向挤出方向(ED)偏转约15°,4道次变形后变为剪切织构,晶体的基面与剪切面平行,最终形成织构组分为(1120)[1101]。     

剪切变形方式下低碳钢表面纳米结构的形成

对低碳钢板材进行表面球磨处理，利用电子显微术研究剪切变形方式下深度方向的组织演变。结果表明，低碳钢的纳米化过程包括：位错通过增殖、运动、湮灭和重组形成位错墙；位错墙逐渐转变成小角度和大角度晶界，将原始粗晶分割成亚微晶；亚微晶内重复上述过程使晶粒继续细化，最终形成等轴状、取向接近随机分布的纳米晶组织。外力作用方向并未改变...     

时效时间对表面机械研磨处理Cu-4.5Ti合金组织和硬度的影响

采用表面机械研磨法使Cu-4.5Ti合金表面形成纳米晶,利用X射线衍射分析,透射电子显微镜观察和显微硬度测量等手段研究时效时间对表面机械研磨处理Cu-4.5Ti合金组织和硬度的影响。结果表明:经过表面机械研磨处理后的Cu-4.5Ti合金发生了塑性变形,表层塑性变形明显,试样中出现了纳米晶结构,形成大量交割状态的机械孪晶;经过8 h时效处理后,试样中形成了更加致密的孪晶组织,并产生了更多孪晶区域。经表面机械研磨处理合金试样的显微硬度由表层向基体内部表现为先增大后减小的趋势,并最终达到稳定状态;经过8 h时效处理后试样到达峰值硬度,此时合金表层硬度增大至HV 213,并在离表层深度约50μm处获得HV 278的峰值硬度。     

3％无取向硅钢薄板的表面纳米化结构与性能

为了探索金属薄板表面纳米化制备方法,本工作选取3％无取向硅钢热轧板进行表面机械研磨处理(SMAT)和异步轧制(CSR),研究深度方向结构和硬度的变化.结果表明:SMAT过程中,3％无取向硅钢通过位错的演变,在表面形成了等轴状、尺寸约为10 nm的、取向呈随机分布的纳米晶,纳米晶层厚度约为20 μm; SMAT样品经过C...     

等径角挤压变形奥氏体不锈钢的组织演变

 用实验方法研究了奥氏体不锈钢在等径角挤压冷变形(路径RC)过程中组织变化。实验结果表明：当剪切方向与孪晶带方向成一定角度时，在剪切力的作用下，孪晶逐渐由大块孪晶→由剪切带分割的孪晶(楼梯状)→小块状→奥氏体亚晶或马氏体晶粒；部分孪晶在剪切力作用下，剪切带可直接碎化成具有大角度位向差的细小晶粒(奥氏体亚晶+马氏体晶粒)，可发生马氏体相变；当剪切方向与孪晶带方向相同时，孪晶带区域也可发生马氏体转变；3道次变形后，具有明显特征的孪晶已很少，此后继续进行剪切变形，孪晶碎化组织(含马氏体)和奥氏体剪切滑移带(含碎化晶粒)的变形以剪切滑移方式进行，当奥氏体的滑移遇到阻力时，可局部形成局部形变孪晶来协调变形；随变形道次的增加，马氏体转变也越多，在多次剪切以及道次中的交叉滑移作用下，马氏体板条逐渐被高密度位错墙分割而碎化成细小的晶粒；8道次变形后，可获得60~230 nm的等轴晶粒。     

表面纳米化工业纯钛组织性能研究

采用表面机械研磨处理(SMAT)实现工业纯钛的表面纳米化,利用金相显微镜(OM)、显微硬度计对其微观组织及显微硬度进行表征、测定;利用动电位极化曲线和电化学阻抗谱(EIS),结合X射线光电子能谱分析(XPS)技术,研究了表面纳米化工业纯钛在Hank's人工模拟体液中的腐蚀行为。结果表明:SMAT处理工业纯钛表层晶粒尺寸达到纳米级,从表层到基体晶粒尺寸由小到大呈梯度分布,其表层显微硬度明显提高,并由表层逐步降低至基体硬度。SMAT处理工业纯钛的自腐蚀电位较原始工业纯钛正移,腐蚀电流密度较原始工业纯钛低,其EIS高频容抗弧半径较原始试样大,表现出更稳定的钝化现象。表面纳米化过程中产生的高密度晶界和位错为Ti~(4+)提供了更多的扩散通道,有助于表面产生稳定的保护钝化膜,提高其耐蚀性。XPS分析结果表明,SMAT处理工业纯钛钝化膜的主要成分为Ti O_2。     

高能球磨法对TiAl基合金表面的纳米化改性

采用常规高能球磨机对TiAl基合金进行表面纳米化改性。利用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)和X射线衍射分析仪(XRD)对试样表层的微观结构和相组成进行观察分析,研究表面纳米化过程中表层晶粒细化的机制;并采用纳米压痕仪测定试样表层的显微硬度,研究表面纳米化改性对合金表面性能产生的影响。结果表明:高能球磨技术能够实现TiAl基合金表面的纳米化改性。改性后试样表层晶粒尺寸约为10 nm。晶粒主要通过孪晶交割和位错缠结重组进行细化;表面显微硬度提高至920 HV,约为未处理试样的2.8倍。     

形变孪晶的消失与退火孪晶的形成机制

 等径角挤压变形奥氏体不锈钢的退火研究表明,层错与形变孪晶是在回复阶段开始退化与消失的,层错的退化与消失主要是由于相邻亚晶以及内部形成的新亚晶以凸出机制逐渐吞并层错的结果。孪晶的退化与消失包括两个方面原因：相邻亚晶以凸出机制逐渐吞并形变孪晶;孪晶板条以合并机制逐渐减少板条数量而使板条扩宽,最终宽板条的孪晶界面由于位错的运动而消失。退火孪晶形成于回复阶段,是大角度界面的迁移结果。     

冷轧IF钢表面纳米化后的组织与性能

利用机械研磨处理（SMAT）在冷轧IF钢表面制备出具有纳米晶体结构特征的表面层．利用金相观察和透射电镜分析研究了表面纳米层的结构特征,测定了硬度沿厚度的变化,并分析了表面纳米化（SNC）对力学性能的影响．结果表明：（1）表面机械研磨处理后,冷轧（CR）IF钢表面形成了平均晶粒尺寸为7～9nm、晶粒取向呈随机分布的纳米晶组织;（2）表面层附近的硬度显著提高;（3）纳米表层的存在使得材料强化的同时成形极限也得到提高．     

Microstructural Evolution of Surface Layer of TWIP Steel Deformed by Mechanical Attrition Treatment

 A nanocrystalline layer was synthesized on the surface of TWIP steel samples by surface mechanical attrition treatment (SMAT) under varying durations. Microhardness variation was examined along the depth of the deformation layer. Microstructural characteristics of the surface at the TWIP steel SMATed for 90 min were observed and analyzed by optical microscope, X-ray diffraction, transmission and high-resolution electron microscope. The results show that the orientation of austenite grains weakens, and α-martensite transformation occurs during SMAT. During the process of SMAT, the deformation twins generate and divide the austenite grains firstly; then α-martensite transformation occurs beside and between the twin bundles; after that the martensite and austenite grains rotate to accommodate deformation, and the orientations of martensite and between martensite and residual austenite increase; lastly the randomly oriented and uniform-sized nanocrystalline layers are formed under continuous deformation.     

温轧表面纳米晶化304不锈钢钢板的多尺度晶粒组织

采用表面机械研磨处理后进行温轧的工艺,制备超细晶粒结构的304不锈钢钢板;采用XRD、TEM分析表征材料的微观组织结构;测试材料的维氏硬度。试验结果表明,所获得的材料晶粒尺寸呈梯度分布,从表层的纳米晶层逐渐过渡为心部的微米晶层,其中微米晶层的体积分数约为40%;同时,此多尺度晶粒分布的304SS板由奥氏体和马氏体双相组成,并同样呈梯度分布,具体为马氏体的体积分数从表层到心部逐渐减少,而奥氏体则反之;所制备的钢板表层维氏硬度显著提高,与原始未处理的304SS相比提高了150%;硬度的大幅度提高源于晶粒细化和应变诱导马氏体相变;维氏硬度分布与微观组织变化一致,表明此样品实现了高强高延性的良好结合。     

无取向硅钢表面纳米结构的渗硅行为

 对3%无取向硅钢进行表面机械研磨处理（SMAT）,获得表面纳米结构,再进行550~650℃、4h固体粉末渗硅处理,用透射电镜（TEM）、扫描电镜（SEM）和X射线衍射仪（XRD）研究表层组织演变。结果表明：经过SMAT后,3%无取向硅钢表面晶粒尺寸降低至10nm左右,纳米晶层厚度约为20μm。经过550~650℃、4h渗硅处理后,SMAT样品表面形成化合物层,其厚度随着渗硅温度的升高由27μm增加到150μm。化合物层由FeSi和Fe3Si两相组成,其中FeSi相随着渗硅温度的升高而逐渐增加。     

Microstructure Evolution of Surface Gradient Nanocrystalline by Shot Peening of TA17 Titanium Alloy

A surface gradient nanocrystalline structure (SGNS) was obtained by shot peening (SP) on the TA17 near α titanium alloy to improve its surface properties. The effect of shot peening time was investigated by characterizing the grain size of the surface nanocrystalline layer, the thickness of the severe plastic deformation (SPD) layer, the microstructure evolution of the SGNS and the hardness change. The experimental results show that the grains of TA17 titanium alloy can be refined to a nano-scale of about 22 to 26 nm when shot peened at 0.6 MPa pressure for 5 to 10 minutes. The thickness of the SPD layer increases from 55 to 88 μm with the SP duration from 5 to 10 minutes and tends to be saturated afterward. The SGNS is composed of a surface nanocrystalline layer and a transition layer. During the SP treatment, the coarse grains are first divided into small blocks by intersection of twins, then dislocation walls, dislocation tangles and dislocation bands lead to the formation of low-angle grain boundaries, which subdivide the subgrains into a finer scale until nanograins with a stable size are obtained. The topmost surface hardness can be improved significantly to twice the hardness of the matrix due to both grain refinement and work-hardening.

     

Effect of Surface Mechanical Attrition Treatment on Corrosion Behavior of 316 Stainless Steel

 The nanocrystalline microstructure of the surface of 316 stainless steel (316SS) induced by surface mechanical attrition treatment (SMAT) was determined by X ray diffraction (XRD) and scanning electron microscopy (SEM). The technique of hydrogen embrittlement was first used to obtain the information of the brittleness cleavage plane. The effects of SMAT and the following annealing process on the corrosion behavior of 316SS were investigated by potentiodynamic polarization curves and potentiostatic critical pitting temperature measurements. The results demonstrated that the nanocrystalline layer with an average grain size of 19 nm was produced. However, there were lots of cracks on the surface, which led to the degradation in the corrosion resistance of 316SS after SMAT. Nevertheless, after annealing treatment, the corrosion resistance of the nanocrystalline surface had been improved greatly. The higher the annealing temperature, the better was the corrosion resistance.     

Effects of High Strain Rate on Properties and Microstructure Evolution of TWIP Steel Subjected to Impact Loading

 The mechanical properties of the TWIP steel subjected to impact loading at various strain rates were analyzed by the Split Pressure Hopkinson Bar. Meanwhile the microstructure of the TWIP steel fore-and-after the dynamic deformation were characterized and analyzed by optical microscopy (OM), X-ray diffraction (XRD), and transmission electron microscope (TEM). The result shows that when the TWIP steel was deformed under dynamic station, the stress, microshardness and work hardening rate increase with the increment of strain and strain rate; there exist stress fluctuation and decline of work hardening rate for adiabatic temperature rising softening. There exist many pin-like deformation twins in the microstructure of the TWIP steel subjected to impact loading, the grain size after deformation is bigger than that before; the interaction of twins with dislocation and twins with twins, especial emergence of high order deformation twins are the main strengthening mechanisms of the TWIP steel. The nucleation mechanism of deformation twins will be “rebound mechanism”; the incomplete deformation twins can be observed when the strain rate is low; when strain rate raises, deformation twins unite together; furthermore, deformation twins become denser because the nucleation rating enhancing with strain rate increasing.     

Nanocrystallization and magnetic properties of Fe-30 weight percent Ni alloy by surface mechanical attrition treatment

A nanostructured surface layer was formed in Fe-30 wt pct Ni alloy by surface mechanical attrition treatment (SMAT). The microstructure of the surface layer after SMAT was investigated using optical microscopy, X-ray diffraction, and transmission electron microscopy. The analysis shows that the nanocrystallization process at the surface layer starts from dislocation tangles, dislocation cells, and subgrains to highly misoriented grains in both original austenite and martensite phases induced by strain from SMAT. The magnetic properties were measured for SMAT Fe-30 wt pct Ni alloy. The saturation magnetization (M _s ) and coercivity (H _c ) of the nanostructured surface layers increase significantly compared to the coarse grains sample prior to SMAT. The increase of M _s for SMAT Fe-30 wt pct Ni alloy was attributed to the change of lattice structure resulting from strain-induced martensitic transformation. Meanwhile, H _c was further increased from residual microstress and superfined grains. These were verified by experiments on SMAT pure Ni and Co metal as well as liquid nitrogen-quenched Fe-30 wt pct Ni alloy.     

多向锻造对超高强度不锈钢组织及力学性能的影响

通过光学显微镜(OM)、扫描电子显微镜(SEM)、背散射电子衍射(EBSD)、透射电子显微镜(TEM)对多向锻造淬火后的马氏体超高强度不锈钢的显微组织进行定量表征,分析多向锻造对试验钢显微组织的影响;同时进行力学性能测试,分析多向锻造对试验钢力学性能的影响,讨论不同强化机制对试验钢强度的贡献.结果 表明,随着锻造道次的...