双相不锈钢各组相循环变形行为的纳米压痕试验和有限元表征方法研究

对双相不锈钢的奥氏体相和铁素体相,分别开展了不同加载模式（接触载荷和压入位移）和不同加载波形下的单向、循环纳米压痕试验,对比分析了两相的基本力学性能和压痕循环变形行为的演化规律。基于压痕试验结果和修正ABDEL-KARIM-OHNO非线性随动硬化准则的弹塑性本构模型,提出一套双相不锈钢奥氏体相和铁素体相的塑性和循环塑性行为的本构模型参数表征方法。通过对微结构代表性体积单元整体拉伸和循环变形行为进行模拟,并与宏观试验结果对比,验证了参数表征方法的合理性。研究结果表明,铁素体相的强度、硬度和抗棘轮变形的能力均高于奥氏体相,两相之间通过晶界产生一定的交互作用;在接触载荷控制的循环加载条件下,奥氏体相与铁素体相均产生明显的压痕棘轮现象,且载荷水平越高压痕棘轮变形程度越大;所发展的本构模型参数表征方法可为研究多相材料各组相、小体积材料的循环变形行为提供借鉴和参考。     

多晶硅微悬臂梁断裂失效强度的尺寸效应

为了了解构件尺寸的微型化给材料的强度和弹性模量带来的影响,利用纳米硬度计通过微悬臂梁的弯曲实验来测量其力学特性.该方法可精确测量微悬臂梁纳米级弯曲形变,但必须考虑压头在微悬臂梁上的压入及微悬臂沿宽度方向的挠曲.试验研究表明,多晶硅微悬臂梁的平均弹性模量为156GPa±(4.52～9.83)GPa,其失效断裂强度表现出对构件有效体积和表面积的尺寸效应.由实验测得的失效强度得到KC=1.62MPa*m1/2,计算出的缺陷尺寸a为58～117nm.     

不同成分780MPa级双相钢的显微组织和力学性能

在相同工艺条件下生产了高碳(碳质量分数达到0.157％,高碳系)和低碳并添加铌、钼元素(Nb-Mo系)的2种成分780 MPa级双相钢,对比研究了2种钢的显微组织、拉伸性能、扩孔性能,以及软硬相的纳米压痕硬度.结果表明:2种钢的显微组织均为铁素体和马氏体;与高碳系试验钢相比,N b-Mo系试验钢的铁素体晶粒得到细化,屈服强度和屈强比提升,并具有更高的扩孔率;高碳系试验钢中的马氏体因碳含量较高而硬度较大,且硬度分布更发散,N b-Mo系试验钢中马氏体的硬度分布较集中;N b-Mo系试验钢中铁素体和马氏体两相的纳米压痕硬度差更小,因此扩孔性能更优.     

TiCx/NiAl复合材料界面纳米硬度与弹性模量分布

对C、Ti比x分别为0.6，0.75，0.8和0.9的四种不同TICx/NiAl复合材料进行扫描电镜研究，发现陶瓷颗粒随着C、Ti比的增加而变小，并且Ti元素向金属相存在较强的扩散，而Ni和Al元素几乎没有向陶瓷相中扩散，扩散形成了两相界面处直接的原子结合，提高了复合材料相界面结合的强度和韧性。利用纳米压痕技术得出材料相界面附近的纳米硬度H和弹性模量E呈连续梯度分布，C、Ti比为0.75的复合材料相界面处的纳米硬度和弹性模量值较大。     

高密度聚乙烯/纳米氧化锌共混材料性能研究

采用熔融共混法 ,探寻了高密度聚乙烯 /纳米氧化锌的耐光老化性能和拉伸性能 ,少量纳米氧化锌的加入可使材料耐光老化性能提高 3倍以上 ,同时使材料的拉伸强度和断裂伸长率得到提高 ,纳米氧化锌含量超过 5 %时 ,对力学性能产生不利影响。     

一种析出强化型Fe-C-Mn-Ni奥氏体合金钢的微观组织和力学性能

对Fe-C-Mn-Ni-X(X为铬、钒等元素)奥氏体合金钢锻材进行固溶和时效处理,研究了时效温度(650,700,750℃)和时效时间(0～25h)对合金钢显微组织与力学性能的影响。结果表明:固溶态和时效态合金钢显微组织形态相差不大,时效处理后,合金钢中析出大量与奥氏体基体呈共格或半共格位向关系的纳米VC相;固溶态合金钢表现出很强的时效硬化能力,随时效温度升高,硬度达到峰值的时间缩短,峰值硬度降低;时效处理后,合金钢的屈服强度和抗拉强度显著增加,断后伸长率和加工硬化指数则明显下降,拉伸失效模式由韧性断裂转变为韧脆混合断裂;随时效温度升高和时效时间延长,合金钢的强度有所降低,但加工硬化能力增强。     

超声表面滚压加工纯钛梯度材料的力学性能反演与有限元分析

对TA2纯钛进行超声表面滚压加工,研究了其截面显微组织和残余应力分布;采用纳米压痕试验测定距表面不同距离处的载荷-压入深度曲线并反演得到应力-应变曲线,将该应力-应变关系作为材料属性,采用有限元方法模拟得到载荷-压入深度曲线,通过与试验曲线进行对比对反演方法进行验证,并且研究了初始屈服应力和应变硬化指数对载荷-压入深度曲线的影响.结果表明:试样表层形成晶粒尺寸逐渐增大的梯度结构,残余压应力随着距表面距离的增加先增大后减小;载荷-压入深度模拟曲线与试验曲线基本一致,最大压入深度的相对误差在8％以内,说明反演方法可靠;随着初始屈服应力和应变硬化指数增大,载荷-压入深度曲线加载段曲率增大,塑性功与总功之比减小,初始刚度变化不明显.     

改性纳米SiC粉体强化球墨铸铁的耐磨损性能

采用改性纳米SiC粉体对球墨铸铁进行了强韧化处理,研究了不同的纳米SiC粉体加入量对球墨铸铁的微观组织、力学性能以及耐磨损性能的影响。结果表明,经改性纳米SiC粉体强韧化处理后,球墨铸铁中的石墨球尺寸减小,圆整度提高,铁素体含量增多,球墨铸铁的韧性和耐磨损性能提高。当粉体加入量为0.1%（质量分数）时,其延伸率和冲击功分别增加了19%和194%。耐磨损性能提高的原因是石墨球形态的改善和基体组织韧性的提高。     

干法室温振动制备纳米铜粉

将粒径为1～5μm的原料铜粉置入辊压振动磨中,经振动研磨后得到纳米铜粉,通过X射线多晶衍射仪和扫描电子显微镜对其进行了分析.结果表明:得到的纳米铜粉晶格类型仍为面心立方晶格,结构参数和化学成分没有发生变化;随着研磨时间的增加,粉末的平均粒径越来越小,粒度分布趋于均匀,研磨6 h以后,平均粒径在100 nm左右.     

热老化过程中焊态和热处理态核级316L不锈钢焊缝的组织演变

采用国产核级E316L焊条对20mm厚奥氏体不锈钢板进行多层多道填充焊接,之后对焊缝进行610℃×16h热处理和400℃下不同时间(400,2 000,3 500h)的加速热老化处理,研究了在热老化过程中焊态和热处理态焊缝中铁素体及析出相的演变。结果表明:焊态和热处理态焊缝的组织均由奥氏体、铁素体和析出相组成;随着热老化时间的延长,焊缝中铁素体的数量呈先增多后减少的趋势,铁素体形貌由断续网状变为较连续网状,再变为断续网状;焊态焊缝中铁素体的含量高于热处理态的;在热老化过程中,焊缝中的析出相主要为Cr_(23)C_6相和σ相,热处理态焊缝比焊态的更容易形成析出相;随着热老化时间的延长,Cr_(23)C_6相和σ相优先在晶界处析出并聚集,随后铁素体晶内也有Cr_(23)C_6和σ相的析出和聚集。     

Scratch and indentation tests on seashells

In this work, the scratch and indentation properties of the outer and inner (nacre) layers of green mussel shells under dry and water-soaked conditions were investigated. In micro-scratch tests with increasing normal load, it was found that the scratch hardness of the inner and outer shell surfaces tended to decrease rapidly at lower loads as compared to the changes in hardness at higher loads. The readings varied in the ranges of 1.5-2.4 and 0.8-2.0 GPa for inner and outer surfaces, respectively. In nano-indentation tests, the responses of inner nacre were not affected by prior soaking as much as those of the outer shell surfaces. The outer shell surfaces showed a significant drop in nano-hardness from 4.5 to 2.8 GPa, while the Young's modulus increased from 62 to 84 GPa after soaking. However, the average nano-hardness and modulus of elasticity of nacreous inner layer only varied slightly in the range of 4.5-4.1 and 64-61 GPa, respectively. In addition, Vickers hardness readings showed that there was a detectable steady increase in micro-hardness of nacre as soaking time increased, although the differences were small. The reverse trend was observed for the outer layer. Analysis of the shells using Fourier transform infrared (FTIR) in reflectance mode gave strong evidence of the presence of sulphated saccharides, polyglycine and hydro-complex in the organic phase of the shell. Their interaction with calcium carbonate of the shell during scratch and indentation tests could be affected with the permeation of water due to soaking of shells.     

Carbon Nanotube Reinforced Polyimide Thin-film for High Wear Durability

In this paper, the influence of single walled carbon nano tubes (SWCNTs) addition on the tribological properties of the polyimide (PI) films on silicon substrate was studied. PI films, with and without SWCNTs, were spin coated onto the Si surface. Coefficient of friction and wear durability were characterized using a ball-on-disk tribometer by employing a 4 mm diameter Si₃N₄ ball sliding against the film, at a contact pressure of ∼370 MPa, and a sliding velocity of 0.042 ms⁻¹. Water contact angle, AFM topography, and nano-indentation tests were conducted to study the physical and mechanical properties of the films. SWCNTs marginally increased the water contact angle of PI film. The addition of SWCNTs to PI has increased the hardness and elastic modulus of pristine PI films by 60–70%. The coefficient of friction of PI films increased slightly (∼20%) after the addition of SWCNTs, whereas, there was at least two-fold increase in the wear life of the film based on the film failure condition of coefficient of friction higher than 0.3. However, the film did not show any sign of wear even after 100,000 cycles of rotation indicating its robustness. This increase in the wear durability due to the addition of the SWCNTs is believed to be because of the improvement in the load-bearing capacity of the composite film and sliding induced microstructural changes of the composite film.     

Nano-mechanical and tribological characteristics of ultra-thin amorphous carbon film investigated by afm

The mechanical as well as tribological characteristics of coating films as thin as a few nm become more crucial as applications in micro-systems grow. Especially, the amorphous carbon film has a potential to be used as a protective layer for micro-systems. In this work, quantitative evaluation of nano-indentation, scratching, and wear tests were performed on the 7nm thick amorphous carbon film using an Atomic Force Microscope (AFM). It was shown that AFM-based nano-indentation using a diamond coated tip can be feasibly utilized for mechanical characterization of ultra-thin films. Also, it was found that the critical load where the failure of the carbon film occurred was about 18μN by the ramp load scratch test. Finally, the wear experimental results showed that the quantitative wear rate of the carbon film ranged 10^-9~10^-8 mm³/N cycle. These experimental methods can be effectively utilized for a better understanding the mechanical and tribological characteristics at the nano-scale.     

Nano-mechanical behaviour of the 3rd body generated in dry friction—Feedback effect of the 3rd body and influence of the surrounding environment on the tribology of graphite

Wear particles often agglomerate into cohesive transfer films (so-called 3rd body) during dry friction. Although described in terms of load carrying capacity and velocity accommodation, the 3rd body finally became a kind of black box where the comprehension of the real interactions, which occur in the tribocontact, can be unknown. We study the behaviour and the mechanisms of action of the 3rd body in a graphite/steel dry contact. Our experimental approach simultaneously involves the determination of the mechanical properties, the topography and the microstructure of transfer films in order connecting them to the fundamental tribological parameters (surrounding environment, load carrying capacity, friction and wear). In this paper, a methodology combining nano-indentation and AFM is developed. The results explain the various links between the effect of the environment on 3rd body generation and related friction and wear by taking of account the detachment mechanisms, the agglomeration mechanisms and their evolution during friction.     

Rolling contact fatigue of alumina ceramics sprayed on steel roller under pure rolling contact condition

The rolling contact fatigue of sprayed alumina ceramics with a nominal composition of Al₂O₃–2.3 mass% TiO₂ was studied with a two-roller test machine under a pure rolling contact condition with oil lubricant. The influence of undercoating of sprayed Ni-based alloy on the rolling contact fatigue was investigated. The failure mode of all sprayed rollers was spalling caused by subsurface cracking. The undercoating did not contribute to the improvement of the rolling contact fatigue life. The elastic modulus of the alumina sprayed layer evaluated with the nano-indentation method was around 85 GPa. The depths of the observed subsurface cracks corresponded approximately to the depths where the orthogonal shear stress or the maximum shear stress calculated with two-dimensional FEM became maximum.     

单晶铜纳米压印亚表层晶体结构演变机理

为研究纳米压印中单晶铜亚表层晶体结构演变机理,采用分子动力学方法构建纳米压印仿真模型并模拟单晶铜纳米压印过程。采用改进的中心对称参数法分析单晶铜试件位错形核过程及缺陷演化机理,发现纳米压印时位错缺陷在压头下方形核并沿{1 1 1}滑移系向试件内部扩展形成堆垛层错,试件表面有原子台阶残留,试件亚表面损伤层存在V形位错等典型缺陷。针对位错形核区域及位错扩展区域材料晶体结构状态的识别,采用球谐函数法对模拟结果进行分析。由分析结果可知:位错形核区域材料晶体结构由FCC转变为排列更为紧密的HCP和ICO结构;位错扩展区域材料主要转变为DFCC结构。     

KDP晶体三倍频晶面微观力学行为及加工性能

为了揭示磷酸二氢钾(KDP)晶体三倍频晶面微观弹塑性力学行为及加工性能,开展了纳米压痕研究。建立了KDP晶体三倍频晶面各向异性力学模型,基于光滑粒子流体动力学(SPH)方法对纳米压痕进行了数值仿真并完成了纳米压痕测试实验。实验结果表明:实验与仿真计算的载荷-压入深度关系曲线的相关系数为0.996 328,吻合度较高,验证了力学模型的正确性,得出KDP晶体三倍频晶面的屈服强度为240MPa。数值仿真结果显示:由于材料的各向异性,工件内部应力呈不规则圆弧状分布;载荷大小与等效应力影响深度呈近似线性递增关系;材料表面等效塑性应变分布形状与压头投影面几何形状相类似,存在复映效果。当载荷小于2mN时,各压头的残余应力深度差异性较小(小于0.2μm);随着载荷逐渐增大,这种差异不断扩大。得到的结果为实现KDP晶体三倍频晶面的高效低损伤加工提供了理论支撑。     

Wear resistant TiMoN coatings deposited by magnetron sputtering

TiMoN coatings with different Mo concentrations were deposited using a reactive magnetron sputtering technique and characterized by X-ray diffraction, nano-indentation, pin-on-disc testing, SEM/EDS and X-ray photoelectron spectroscopy. Mo alloying of TiN coatings generally enhances hardness. When tested in a pin-on-disc test against WC-Co pin, the coefficients of friction of TiMoN coatings were found to decrease with the increase in Mo atomic fraction, with the lowest values (0.4-0.5) being only one-half that of TiN coating (1.03). The underlying mechanism of the Mo effect is the formation of lubricious MoO₃ on the wear track. The combination of low coefficient of friction and enhanced hardness reduces the wear rate of TiMoN coatings to less than 2.5% of the wear rate of TiN coating.     

基于应变梯度理论的光栅铝膜本构关系表征及纳米压痕实验

基于应变梯度理论,提出了一种玻璃基底光栅铝膜本构关系的表征方法。建立了包含基底参数和铝膜参数的本构关系数学模型,并逐一表征了相关参数。进行了79g/mm中阶梯光栅铝膜的纳米压痕实验,验证了上述本构关系表征过程的正确性。提出了光栅薄膜材料和基底材料都具有尺度效应的假设,并应用纳米压痕实验对铝膜的尺度效应和基底效应进行了实验表征。对光栅铝膜压痕实验与含基底压深实验的结果进行了比较,结果显示,在有无基底条件下,压痕结果在应力方向上相差0.8倍,在应变方向上相差3倍。进行了光栅刻划实验,结果显示压痕实验对刻划实验具有重要的指导作用。研究过程及研究结果表明:理论分析和两种实验可有效地分析光栅刻划过程,有助于在实际光栅刻划过程中减小误差,对光栅刻划的工艺过程具有较好的理论指导意义。     

Highly efficient chemical mechanical polishing method for SiC substrates using enhanced slurry containing bubbles of ozone gas

In this study, a highly efficient method for chemical mechanical polishing (CMP) of silicon carbide (SiC) substrates using enhanced slurry was proposed and developed. The enhanced slurry contains bubbles of ozone gas generated by ozone gas generator in pure water mixed with a conventional commercially available slurry. Therefore, the enhanced slurry has an oxidizing effect on the Si-face of SiC substrates. To confirm the effectiveness of bubbles enclosing ozone gas, both nano-indentation test and X-ray photoelectron spectroscopy (XPS) analysis were conducted. As a result, the hardness decrease of the Si-face of the SiC substrate was confirmed through the nano-indentation test, and the generation of reaction products was confirmed on Si-face of SiC substrate in the XPS analysis. According to a series of experimental results of our proposed highly efficient CMP method for SiC substrates, the removal rate can be increased when the enhanced slurry was applied, comparing with that for the not only conventional commercially available slurry but also commercially available dedicated slurry.