纳米压痕硬度计测方法的研究进展

针对纳米尺度下的材料硬度测量,利用纳米硬度计得到压痕的载荷-压深曲线,并用原子力显微镜得到压痕的三维形貌图.通过载荷-压深曲线和压痕形貌图,以及相应的计算方法,可以得到纳米压痕硬度.纳米压痕硬度计测方法不同,得到的材料硬度值也不同.分析现有的几种纳米压痕硬度计测方法,找出它们的优缺点,并对未来发展方向做了展望.     

Li_2O-Al_2O_3-SiO_2微晶玻璃超光滑表面纳米划痕产生机理及抑制实验研究

对Li2O-Al2O3-SiO2微晶玻璃超光滑表面进行了纳米划痕实验,测得微晶玻璃超光滑表面弹性-塑性与塑性-脆性转变的临界载荷分别为3.906 mN和29.78 mN.通过对微晶玻璃超光滑表面划痕产生机理进行分析,得出在纳米尺度的抛光加工过程中,抛光颗粒的载荷越接近弹塑转变临界载荷,则样品表面产生的划痕越少,越易获得无划痕的超光滑表面.通过对比抛光工艺优化前后的实验结果,可以看出优化后的抛光工艺对超光滑表面划痕的抑制效果较明显,证实了上述研究结果的正确性.该研究结果对于Li2O-Al2O3-SiO2微晶玻璃超光滑表面加工具有一定的指导意义.     

化学强化铝硅酸盐玻璃表面微观力学行为的有限元模拟

采用有限元方法研究化学强化铝硅酸盐玻璃的表面硬度、模量等微观力学行为,并与纳米压痕实验结果进行对照.结果表明,通过有限元计算获得的纳米压痕载荷-位移曲线与实验结果吻合度良好,根据有限元模拟得到的载荷-位移曲线,采用Oliver和Pharr方法计算出的硬度和杨氏模量值与实验得到的硬度和杨氏模量值非常接近.模拟过程中采用了根据Larsson塑性公式计算出的铝硅酸盐玻璃屈服强度与塑性区域的应力应变关系,模拟结果与实验结果吻合度高说明根据Larsson塑性公式获得的铝硅酸盐玻璃塑性参数准确度较高.根据有限元模拟得到的应力分布情况,分析了铝硅酸盐玻璃在化学强化前后的弹塑性变形行为,结果表明化学强化产生的表面压应力层对铝硅酸盐玻璃的弹性区影响较大,对塑性区影响较小.     

基于EBSD方法测定单晶Cu纳米压痕的各向异性实验

为研究单晶Cu材料的各向异性力学特性,针对单晶连铸技术制备的单晶Cu,采用电子背散射衍射(EBSD)法对其3个不同晶粒的晶面进行定向,利用原位纳米压痕仪在不同晶面进行不同压入载荷的纳米压痕实验.通过EBSD分析,发现用单晶连铸技术制备的单晶Cu在拉拔方向上具有较强的择优取向,单个晶粒较大,且晶粒内部没有(亚)晶界存在.纳米压痕实验结果表明单晶Cu样件在各种压痕载荷下的约化模量为50 GPa～120GPa,材料的晶体取向对纳米压痕载荷-位移曲线和约化模量有很大影响,面(032)比面(119)和面(041)有更大的约化模量.不同载荷下,硬度值在0.8 GPa左右变动,晶体取向对硬度的影响较小.实验所得单晶Cu各晶面约化模量与采用金属弹性力学理论计算所得数值吻合较好.     

两种微纳米硬度测试方法的比较

在对材料微纳米硬度测试中,可利用纳米压痕方法得到载荷-位移曲线,并用相关算法得到接触面积和硬度值;也可通过原子力显微镜测出压痕残余面积,由残余面积和最大载荷得到材料的硬度值.利用这两种方法对塑性材料单晶铝和脆性材料单晶硅做微纳米硬度测试试验,经过比较分析,这两种方法各有优势和不足,得到的材料微纳米硬度都有压痕尺寸效应,但第二种方法得到的微纳米硬度尺寸效应比第一种明显.     

单晶氮化镓纳米压痕与划痕实验

为分析单晶氮化镓的微观变形机理,使用纳米压痕仪对单晶氮化镓进行压痕与划痕实验.结果表明单晶氮化镓压痕过程存在弹塑转变过程即"pop-in"现象,分析得出此现象是由材料的位错萌生和扩展导致,压痕周围产生凸起现象导致计算硬度和弹性模量偏大,通过模型修正得到更真实的硬度和弹性模量数据.单晶氮化镓的变载划痕过程发生弹塑转变和脆塑转变,弹塑变形阶段深度-位移曲线波动平稳,表面光滑;而脆性阶段曲线波动幅度较大,表面产生侧向裂纹且朝着划痕方向45°对称分布.得到弹塑转变的临界载荷为389 mN,脆塑转变临界载荷为1227 mN,因此单晶氮化镓塑性加工区域应在389～1227 mN之间,该区域内易加工出光滑表面.通过不同载荷划痕实验,发现划痕压头所受的切削力和摩擦系数随划痕载荷的增大而增大,因此氮化镓加工时应选择合理的加工载荷.     

Li2O-A12O3-SiO2微晶玻璃超光滑表面纳米划痕产生机理及抑制实验研究

对Li2O-A12O3-SiO2微晶玻璃超光滑表面进行了纳米划痕实验,测得微晶玻璃超光滑表面弹性一塑性与塑性．脆性转变的临界载荷分别为3．906mN和29．78mN．通过对微晶玻璃超光滑表面划痕产生机理进行分析,得出在纳米尺度的抛光加工过程中,抛光颗粒的载荷越接近弹塑转变临界载荷,则样品表面产生的划痕越少,越易获得无划痕的超光滑表面．通过对比抛光工艺优化前后的实验结果,可以看出优化后的抛光工艺对超光滑表面划痕的抑制效果较明显,证实了上述研究结果的正确性．该研究结果对于Li2O-A12O3-SiO2微晶玻璃超光滑表面加工具有一定的指导意义．     

基于AFM纳米硬度测量系统的实验

为了解决用AFM自身压痕软件进行纳米硬度测量时无法直接获得载荷-压深曲线和由于受到扫描陶管扫描范围的限制而进行多点压痕实验范围有限的问题,建立了三维微动工作台和原子力显微镜相结合的纳米压痕硬度测量系统.基于该系统,对单晶薄膜材料进行了单点压痕实验,得出该系统适合进行纳米硬度测量的结论;并对薄膜材料的纳米硬度和弹性模量进行了分析,讨论了尺寸效应对两者的影响.另外,进行了40×40的点阵压痕实验,得到了材料整个压痕面的三维形貌图和三维硬度图.     

氟金云母微晶玻璃陶瓷的动态本构关系及断裂机理研究

为了研究氟金云母微晶玻璃陶瓷的动态力学性能及断裂机理,利用高速液压伺服材料试验机进行了动态压缩实验,得到试样中等应变速率下的动态力学参数,结果表明该陶瓷材料具有明显的应变率效应,并基于损伤力学理论,得到了该材料的弹脆性动态损伤本构方程。通过对试样断口微观形貌的SEM观测,并结合纳米压痕实验,分析了材料的断裂机理。从试样断口的宏观和微观形貌可得:材料断裂方式为脆性解理断裂,云母相与玻璃相交界面存在大量沿晶微裂纹;由纳米压痕实验验证了两相之间弱界面的存在,微裂纹最早成核于两相交界处,并沿弱界面扩展,成核载荷为20 mN。     

单晶铝纳米级硬度试验研究

使用纳米硬度计对单晶铝进行了纳米压痕试验,利用原子力显微镜对压痕形貌进行扫描并计算硬度值,重点观察和分析了纳米级条件下单晶铝的硬度性质,结果表明,当压痕深度小于2000nm时,单晶铝纳米硬度存在尺寸效应现象;从材料性质的角度分析了纳米硬度尺寸效应现象;探讨了纳米硬度和传统硬度本质上的区别,指出其根本原因在于不同尺度下人们对材料性质的关注点不同。     

Zr基氮化物／金属Cu纳米多层膜的强韧化研究

多层结构可以提高材料的强度、弹性模量和韧性。当尺寸减小到纳米量级时,性能将产生飞跃变化。首先探讨了多层结构提高强度、弹性模量和韧性等性能的基本原理,然后阐明了纳米尺度效应及理论,重点以过渡族金属氮化物ZrN纳米多层膜为例,研究了氮化物／金属（ZrN／Cu）纳米多层膜、ZrAIN纳米复合膜以及ZrAIN／Cu纳米多层膜的强韧化性能。结果表明,ZrN／Cu纳米多层膜的断裂韧性约是二元ZrN薄膜的2倍。当纳米多层膜的Cu单层厚度为2013131时,多层膜的K1C值最高。ZrAIN复合膜的断裂韧性与Al含量密切相关,当Al原子分数为23％时,薄膜的KIc值达3．17MPa·m^1/2,其硬度〉40Gpa,Al原子分数为47％的薄膜的K1C值则降低到1．13MPa·m…。,其硬度降低至17．1GPa。与z州／cu纳米多层膜和ZrAlN复合膜相比,以ZrAIN层和cu层为调制结构制备的ZrAlN／Cu纳米多层膜具有最高的硬度和最好的韧性。     

压痕硬度测试法的主要研究内容及其应用

详细分析了压痕硬度测试方法自发展以来所研究的主要内容,即建立不同硬度之间的关系、硬度与弹性性能的关系、硬度与强度的关系、硬度与蠕变性能的关系、材料显微组织对硬度的影响以及硬度在薄膜力学测试中的应用等。其中,研究重点主要集中在建立硬度与力学性能参量之间的数学关系方面,即通过压痕硬度测试中获取的有关数据来得到相关的力学参量。同时提出了压痕硬度测试法的研究现状及存在的主要问题。     

A nano-indentation study on the mechanical behaviour of the matrix material in an AA6061 - Al2O3 MMC

The nano-indentation technique is a suitable technique to measure hardness and elastic moduli profiles of AA6061 reinforced with Al₂O₃ particles, since it allows measurements of mechanical properties on a micrometer range. To investigate possible local variations in mechanical behaviour of the matrix material due to precipitation reactions being affected by the presence of ceramic reinforcements, nano-indentation tests were done on both metal matrix composite (MMC) as well as unreinforced reference material, in three different heat treatment conditions. Matrix response depends on heat treatment condition, but is approximately equal for the MMC and the base reference alloy. Due to the various imposed heat treatments, magnesium enrichment around the ceramic particles was observed, but hardness and elastic modulus of this interfacial layer could not be measured. To confirm the preferential segregation of Mg near the particle/matrix interface, linescans were made with a Scanning Electron Microscope (SEM) equipped with EDS (Energy Dispersive Spectrum) facilities. The limited width of the Mg rich zone explains the absence of typical 'interphase' indentations in this investigation. Hardly any differences in calculated elastic moduli and hardness values were found for the three heat treatment conditions investigated, when comparing results of AA6061 reference material with results of an AA6061 matrix in an MMC. This result is of great importance when modelling the mechanical behaviour of MMCs using the finite element method, since it permits the assumption that the MMC matrix material behaves similar to the same aluminium alloy without ceramic reinforcements.     

超光滑表面纳米压痕硬度测试研究

介绍纳米压痕法常用的Oliver-Pharr方法的计算原理,对硬度的概念做了进一步讨论。通过对三种不同材料的超光滑表面进行硬度测试,得出它们各自的硬度值和弹性模量,分析了结果差异的原因,探讨了在采用Oliver-Pharr方法进行硬度各参数测量时应注意的问题,分析结果对超光滑表面加工也有一定的指导意义。     

Instrumented indentation and scratch testing evaluation of tribological properties of tin-based bearing materials

This paper describes a study of some fundamental tribological behavior of two different tin-based bearing materials using scratch and Martens hardness techniques. The scratch test results obtained from the two different tin-based bearing materials were correlated with a function of scratch hardness and coefficient of friction. It is easily observed that the friction coefficients of WM5 are lower than those of WM2 under all scratch test conditions. Beside this, it is clearly distinguished that both materials give higher friction coefficients at higher normal loads and scratch velocities. Also it is found that scratch hardness values of the WM5 materials are higher than WM2 generally. Moreover, optical microscopy was used to determine the scratch hardness of two different tin-based bearing materials by examining the scratch widths. Scanning electron microscopic observations of two different tin-based bearing materials were performed in order to identify the scratch-deformation mechanisms and trace morphology. Beside scratch tests, Martens hardness tests were carried out to evaluate the indentation of materials by considering both the force and displacement during plastic and elastic deformation. By monitoring the complete cycle of increasing and removal of the test force, hardness values were determined.     

Determination of plastic yield stress from spherical indentation slope curve

The indentation slope curve from a spherical indentation on elastic-plastic materials is examined. By comparing it with that of an linear elastic material of the same elastic properties, we found that the start point of plastic yielding for an elastic-plastic material can be easily located from the indentation slope curve. Based on this analysis, a simple but effective method is proposed to measure the plastic yield stress of very small samples from a spherical nano-indentation slope curve.     

Micromechanical characterization of bulk composite prepared by sintering of mechanically alloyed aluminum-316 stainless steel (35 wt%) powder blend

Present study concerns deformation behavior of the ball milled and consolidated powder blend comprising 316 stainless steel and elemental Al (65 wt%), studied by the micro- and nano-indentation techniques. With an aim to examine the strain hardening behavior of the consolidated samples, nano-indentation measurements have been carried out by applying variable load at multiple spots and cyclic load at the single spot. Similar experiments have been carried out for the bulk 316-stainless steel plate to compare the results with those obtained from the consolidated samples. The consolidated samples exhibited much higher hardness values than the plate along with high elastic recovery and appreciable work hardening.     

Nano-indentation of hybrid silica coatings on surgical grade stainless steel

Hybrid silica-based coatings with tetraethoxysilane (TEOS), methyltrietoxysilane (MTES), hydroxyethyl-methacrylate (HEMA) and methacrylopropyl-trimethoxysilane (γMPS) as precursors, were employed to improve the performance of stainless steel used as orthopaedic material. Mechanical properties of the films, such as Young's modulus and hardness, were studied using the load and depth sensing indentation technique known as nano-indentation. The elastic/plastic and creep behaviours were also analyzed. Coatings with a high proportion of organic components (HEMA, γMPS) presented a more plastic response compared to the more vitreous coatings (containing only TEOS and MTES). They also showed the lowest Young's modulus and hardness. Therefore, the more vitreous coatings presented lower creep deformation that increased with the load applied.     

Fracture Characteristics of Frit Bonding through In-Situ Nano-Indentation Testing

Because frit bonding material is brittle, sudden impacts such as dropping may damage the bonding significantly. Strain-rate-controlled in-situ nano-indentation testing, which can determine localized material properties, was carried out on the frit-bonded specimen, especially on the frit bonding matrix and the filler. The results were compared with the drop-impact fracture behavior to understand the fracture characteristics. Mechanical properties at static condition or low strain rate did not show proper relationship with the fracture tendency of the drop tested result of the frit bonding. From the relationship between fracture toughness and the ratio of modulus/hardness, fracture characteristics at the drop impact situation could be estimated by the values at the high strain rate nano-indentation. The ratio between modulus and hardness on frit matrix showed close relationship with drop impact fracture. Though crack propagation path deflected at filler interface, filler property gave less influence on fracture tendency of drop impact fracture due to its small volume fraction. The properties of frit matrix were crucial to the fracture characteristics of the frit bonding.     

Correlation of elastic properties of melt infiltrated SiC/SiC composites to in situ properties of constituent phases

The ability to correlate the elastic properties of melt infiltrated SiC/SiC composites to properties of constituent phases using a hybrid Finite Element approach is examined and the influence of material internal features, such as the fabric architecture and intra-tow voids, on such correlation is elucidated. Tensile testing was carried out in air at room temperature and 1204 °C. Through-thickness compressive elastic modulus utilizing the stacked disk method was measured at room temperature. In situ moduli of constituent materials were experimentally evaluated using nano-indentation techniques at room temperature. A consistent relationship is observed between constituent properties and composite properties for in-plane normal and shear moduli and Poisson’s ratio at room temperature. However, experimental data for through-thickness compressive elastic modulus is lower than the calculated value. It is hypothesized that the existence of voids inside the fiber tows and their collapse under compressive loads is the cause of such discrepancy. Estimates for the change in elastic moduli of constituent phases with temperature were obtained from literature and used to calculate the elastic properties of the composites at 1204 °C. A reasonable correlation between the in-plane elastic moduli of the composite and the in situ elastic properties of constituent phases is observed.