退火对表面纳米化后IF钢结构和织构影响

通过组织观测和织构ODF测试,研究了退火对表面机械研磨处理后的冷轧IF钢结构和织构的影响。结果表明:表面机械研磨处理后的冷轧IF钢表面层纳米晶组织具有良好的热稳定性,经850℃真空退火后,样品表面依然为晶粒取向呈随机分布的纳米晶组织。SMAT样品退火前的晶粒取向对IF钢退火织构的形成具有重要影响,取向处于a-丝织构中的晶粒是再结晶形核和长大的源泉;退火前a-丝织构组分越强,退火后形成的再结晶织构也就越强。     

表面纳米晶化处理中碳钢的组织与力学性能

采用高能表面处理技术在40Cr钢的表面制备出具有纳米晶体特征的表面层.用扫描电子显微镜和透射电子显微镜研究了表面纳米层的微观结构,并利用纳米压入法测定了表面纳米层的硬度.结果表明,经过高能表面处理后,样品表面层的晶粒细化为纳米晶,平均晶粒尺寸约为11 nm,表面纳米层的硬度明显提高.     

表面纳米化处理对IF钢电化学析氢行为的影响

利用阴极极化曲线、交流阻抗谱,对超音速微粒轰击（USPP）表面纳米化处理（SNC）的IF钢在30%NaOH溶液中的析氢行为进行了研究,同时利用XRD和SEM分析了表面纳米化前后IF钢的晶粒度和表面形貌。试验证明,经SNC处理后,IF钢析氢过电位比基材降低200 mV;SNC＋1%平整的IF钢比基材析氢过电位低300 mV以上;经处理后IF钢真实表面积比原IF钢板分别增大18倍和21倍,其表观析氢活化自由能分别由51.7 kJ/mol降低为26.5 kJ/mol和21.7 kJ/mol,仅为原IF钢板的50%。     

表面机械研磨工业纯锆的疲劳性能研究

采用表面机械研磨工艺对工业纯锆进行处理,利用四点弯曲疲劳试验对试样的疲劳性能进行研究,并利用透射电子显微镜(TEM)和光学显微镜(OM)对试样的微观组织进行观察,利用纳米压痕仪测试处理试样从表层到基体的硬度分布,采用X射线衍射(XRD)方法分析表层晶粒尺寸、微观畸变以及残余应力分布特征。结果表明:经表面机械研磨处理工业纯锆的疲劳极限为195 MPa,而原始试样的疲劳极限为159MPa,表面机械研磨处理使工业纯锆的疲劳极限提高了23%,疲劳性能的改善可归因于表面机械研磨引入的纳米化表层、加工硬化以及残余压应力。本文进一步研究发现,应力幅大于270 MPa,表面机械研磨处理试样的疲劳寿命低于原始试样;应力幅低于270 MPa,表面机械研磨处理试样的疲劳性能比原始试样优异。     

IF钢晶体取向与纳米力学性能的原位分析

为了研究材料微区力学性能与多晶体取向之间的直接定量联系,以IF钢(无间隙原子钢)为例,分析了不同晶体取向与纳米力学性能之间的关系。首先利用高温激光扫描共聚焦显微镜(HLSM)对IF钢样品进行退火处理,以保证原位分析的有效性,然后通过电子背散射衍射(EBSD)对退火前后的标定区域进行晶体取向分析,得出晶体取向的原位变化规律,最后利用纳米压痕仪测试标定区域的微观力学性能。结果表明,不同晶体取向晶粒的杨氏模量不同,在原子间距较小的<111>晶体学方向上,杨氏模量值较高,在原子间距较大的<001>晶体学方向上,杨氏模量值较低,并通过理论计算验证了试验结果。退火后,不同晶体取向的晶粒硬度没有明显的规律性,但晶粒内位错密度显著降低,硬度比冷轧态明显下降,随着退火温度的升高,硬度降低速度变缓。     

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。     

低碳钢的表面纳米化组织及其性能

对低碳钢进行表面机械研磨处理(SMAT),研究组织变化及其对性能的影响.结果表明:经过SMAT后,低碳钢上形成了厚度约为40 μm的纳米组织表层,在深度为40～80 μm处获得亚微晶组织;表面纳米化不仅提高了低碳钢表面的硬度和耐磨性,而且在不明显降低韧性的前提下提高了板材的整体强度;在纳米到微米量级的范围内,晶粒尺寸与硬度之间满足Hall-Petch关系.     

表面机械研磨处理工业纯锆的组织和拉伸性能研究

对退火态工业纯锆试样分别进行了5,15,30和45 min的表面机械研磨处理,利用光学显微镜和扫描电子显微镜观察了试样的微观组织,对其表层晶粒尺寸进行了X射线衍射分析、采用维氏显微硬度仪测量了沿层厚方向的硬度,并进行了室温拉伸性能测试。实验表明,经过表面机械研磨处理,在强烈塑性变形作用下试样表层晶粒尺寸能够细化到纳米尺度,而且随处理时间增加而进一步降低,经过45 min处理后试样表层晶粒尺寸可以达到25 nm左右;处理后在试样的次表层形成了一定深度的变形层,具有较高的孪晶密度,并且变形层厚度随处理时间延长而提高。试样表层形成的纳米结构使其显微硬度获得了显著提高,并随处理时间增加而进一步提高;沿层厚方向试样显微硬度逐渐降低,与微观组织的变化一致。拉伸试验表明,表面机械研磨能够使试样得到强化。随处理时间的增加,试样屈服强度和抗拉强度能够得到明显改善,而试样的延伸率则随处理时间的增加而降低。对经过45 min处理的试样,其屈服强度和抗拉强度分别为324和414 MPa,相对于原始试样分别提高了11.7%和8.7%,延伸率为23%,降低了30.9%,拉伸断口主要形貌特征为韧窝,处理层和中心层呈现不同的组织特征。     

制样方法对IF钢纳米压入测试结果的影响

 对3种不同方法制备的IF钢试样进行了纳米压入表征,分析了制样方法对IF钢中铁素体纳米压入测试结果的影响。结果表明,制样方法对铁素体杨氏模量平均值影响不大,但对硬度平均值影响显著,机械抛光和机械抛光+化学侵蚀状态铁素体的硬度均高于机械抛光+电解抛光状态的铁素体。这主要是因为机械抛光对试样表面造成了明显的加工硬化层,而化学侵蚀处理不能完全去除硬化层,只有电解抛光才能起到有效消除硬化层的作用。机械抛光+电解抛光处理更有利于IF钢的纳米压入表征。     

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。     

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...     

铝合金表面纳米化——微弧氧化复合涂层摩擦行为

通过表面机械研磨处理在LY12CZ铝合金表面制备表面纳米化(SNC)过渡层,再采用微弧氧化(MAO)技术对纳米晶过渡层进行微结构重构,设计制备出纳米化-微弧氧化(SNC-MAO)复合涂层,并对比研究了铝合金表面微弧氧化涂层及纳米化-微弧氧化复合涂层的摩擦学行为.与微弧氧化涂层相比,纳米化-微弧氧化复合涂层因硬度较高而具有较好的耐磨性.微弧氧化涂层及纳米化-微弧氧化复合涂层与GCr15钢球对磨时具有相同的磨损机理,为对磨钢球向涂层的材料转移和氧化磨损.      

Influence of Surface Mechanical Attrition Treatment Duration on Fatigue Lives of Ti–6Al–4V

This work deals with the influence of surface mechanical attrition treatment (SMAT) duration on fatigue lives of Ti–6Al–4V. The SMAT process was carried out in vacuum with SAE 52100 steel balls of 5 mm diameter for 30 and 60 min at a vibrating frequency of 50 Hz. SMAT treated surface was characterized by electron microscopy. Surface roughness, nano-indentation hardness, residual stress, and tensile properties of the material in both SMAT treated and untreated conditions were determined. SMAT enabled surface nanocrystallization, increased surface roughness, surface hardness, compressive residual stress and tensile strength but reduced ductility. Samples treated for 30 min exhibited superior fatigue lives owing to positive influence of nanostructured surface layer, compressive residual stress and work hardened layer. However, fatigue lives of the samples treated for 60 min were inferior to those of untreated samples due to presence of microdamages or cracks induced by the impacting balls during the treatment.     

表面机械研磨工业纯钛表面纳米化研究

表面机械研磨处理可以使工业纯钛形成纳米表面层, 通过扫描电镜、透射电镜和高分辨电镜观察SMAT处理后的工业纯钛表层组织, 并研究了工业纯钛表面纳米化机制. 工业纯钛表面纳米化机制为: 孪晶的形成和孪晶的交割使得原始晶粒尺寸减小, 同时使晶格取向发生改变, 有利于位错滑移; 孪晶通过自身交割, 以及位错密度增加及其相互作用, 形成了细小的孪晶与胞状组织; 胞状组织转变为多边形亚晶; 亚晶不断吸收位错形成大角度晶界, 亚晶以及取向不同的细小孪晶逐渐转变为随机取向的纳米晶.     

Effect of Surface Mechanical Attrition Treatment on Fatigue Lives of Alloy 718

The effect of surface mechanical attrition treatment (SMAT) and its duration on fatigue lives of alloy 718 has been studied. The SMAT process was carried out in vacuum (?0.1?MPa) with SAE 52100 steel balls of 5?mm diameter for 30 and 60?min at a vibrating frequency of 50?Hz. SMAT resulted in surface nanocrystallization, higher surface roughness, higher surface hardness, higher compressive residual stress, higher tensile strength, reduced ductility and superior fatigue lives. The enhancement in the fatigue lives of treated samples can be attributed to the positive influence of nanostructured surface layer, compressive residual stress and work hardened layer, which surpassed the negative effect of increased surface roughness. There was no significant difference between the fatigue lives of samples treated for 30 and 60?min.     

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.     

High performance nano-structured stainless steel sheet

High-strength steels have been attracting more and more attention of people,Unfortunately.deterioration of ductility limited their applications.To solve this problem,a nano-structured stainless steel sheet is developed to combine high strength and high ductility.Processing of the surface mechanical attrition treatment(SMAT) was introduced to obtain a nano-grain layer on the double surface of the stainless steel sheet.The microstructure of the nanostructured steel sheet is characterized by an alternate distribution of coarse grained layer and nanocrystalline layer.Then the dual surface nano-crystallized stainless steel sheets were co-warm rolled at 500℃.The experimental results reveal that the mechanical properties of the nanostructured steel exhibit high yield strength in the range of 700 -950 MPa and tensi le strength higher than 930 MPa.Moreover,elongation to fracture reaches to 15%-48%, together with a uniform elongation stabilized to 13%-45%.     

Recent developments of the high strength and high ductility nanostructured materials

This talk will summarize the recent work related to a kind of new nanomaterials produced by the SMAT (surface mechanical attrition treatment).The concept of surface nanocrystallization of materials will be presented.In terms of the grain refinement mechanism induced by plastic deformation,a novel surface mechanical attrition(SMA) technique was developed for synthesizing a nanostructured surface layer on metallic materials in order to upgrade the overall properties and performance.The grain refinement mechanism of the surface layer during the SMA treatment will be analyzed in terms of the nanostructure observations in several typical materials.Very high yield stress(5 times of the base material) on the surface layer of the material obtained by the SMAT has been observed.The effect of surface nanostructures on the mechanical behavior and on the failure mechanism of metallic material shows the possibility to develop a new strength gradient composite using co-rolling and nitriding.The role of residual stress induced during the treatment will be investigated and discussed.The developed materials are also porosity free materials which can be used as reference material for the local mechanical behavior investigation technique such as the nanoindentation.A general concept for obtaining high strength and high ductility nanostructured materials will be presented.The exceptional high strength and high ductility steels have developed.The simulation of the mechanisms for improving ductility of high strength nanostructured materials will be presented.The potential applications for the land transportation vehicles(car,bus,train) and wind energy have been investigated.Some examples of concept design for the integration of the advanced nanostructured steels will be presented.     

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。     

表面纳米化AISI H13钢的渗铬处理及其耐磨性

对表面纳米化（SNC）处理后的热作模具钢AISI H13钢进行渗铬处理,用扫描电子显微镜、透射电子显微镜、纳米压痕仪和摩擦磨损试验机研究了渗铬层成分、微观结构、硬度和耐磨性。结果表明,经600及1 050℃的复合渗铬处理后,SNC样品表面形成了厚约30μm的连续渗层,是经相同复合渗铬处理的粗晶样品上渗层厚度的3倍。受益于渗铬层中较小的晶粒尺寸和较高的硬度,加之其成分、结构和力学性能在较大深度范围内较为平缓的梯度变化,SNC H13钢经渗铬处理后耐磨性得到显著提高。