氧化钛涂膜玻璃的纳米压痕实验及有限元模拟

采用纳米压痕法测定了涂覆不同厚度溶胶-凝胶TiO2纳米薄膜的玻璃基体表面的力学性能,讨论了薄膜厚度对膜-基复合系统的硬度和弹性模量的影响.结果表明:膜-基复合系统的硬度和弹性模量与TiO2薄膜的厚度无关.同时采用有限元法对压痕过程进行了数值模拟,通过与实验及文献结果相比较证明了有限元模拟的有效性.     

氧化钛涂膜玻璃的纳米压痕实验及有限元模拟

采用纳米压痕法测定了涂覆不同厚度溶胶-凝胶TiO2纳米薄膜的玻璃基体表面的力学性能，讨论了薄膜厚度对膜-基复合系统的硬度和弹性模量的影响。结果表明：膜-基复合系统的硬度和弹性模量与TiO2薄膜的厚度无关。同时采用有限元法对压痕过程进行了数值模拟，通过与实验及文献结果相比较证明了有限元模拟的有效性。     

纳米压痕技术及其在薄膜/涂层体系中的应用

综述了纳米压痕技术的发展历程及其在薄膜领域的应用。介绍了当前实验室条件下主要采用的电磁驱动式纳米压痕仪的构造和工作过程。为了保证测试结果的准确性,要在合适的温度、湿度下进行压入实验,借助保载来消除一些可以避免的误差。阐述了压头的分类和选择原则,玻氏压头相比于维氏压头具有更小的中心线与棱面夹角,避免了尖端横刃对于压入结果准确性的影响,因此最常用的压头为玻氏压头;表征断裂韧性最合适的压头为立方角压头;表征微机电系统的弯曲采用楔形压头。总结了通过最大载荷和压入面积得到涂层力学参量的分析流程。归纳了将纳米压痕法应用于表征薄膜涂层的硬度和弹性模量、室温下蠕变性能、断裂韧性、残余应力、塑性性能等力学量的研究,如表征硬度和弹性模量的Oliver-Pharr法的应用,识别蠕变柔量的Lee-Radok模型的应用,分析断裂韧性的Lawn-Evans-Marshall模型的应用。在涂层制备过程中,制备参数的改变可以使得涂层具有不同的力学性能,涂层厚度远小于表面尺寸,硬度和弹性模量仍然存在各向异性,非晶态结构涂层具有更高的硬度和弹性模量。采用碳纳米管强化可以提高涂层的断裂韧性,涂层内存在适量的残余应力数值和合...     

基于原子力显微镜的薄膜原位压痕力学性能研究

基于原子力显微镜(AFM)和扫描电子显微镜(SEM)建立了一套原位纳米压痕测试系统。该系统可以实现控制带有金刚石(Cube corner)压头的AFM微悬臂梁对样品进行压入实验,并得到载荷-位移曲线,同时可以对压痕过程进行原位SEM实时观察。发展了一种基于AFM微悬臂梁加载和原位SEM压痕图像分析的力学性能测试方法,通过测量压入最大载荷和原位SEM测量压痕残余面积得到塑性薄膜的硬度和弹性模量。利用此方法对磁控溅射硅衬底上纳米晶银薄膜进行了压痕实验,并与Nanoindenter G200型纳米压痕仪实验进行对比研究。结果表明,原位AFM压痕方法具有高的载荷和位移分辨率,可以实现纳牛至微牛级的压痕实验,通过测量压痕面积得到塑性薄膜的硬度值,减小了使用Oliver-pharr方法中软膜硬基底上凸起(Pile-up)效应的影响,计算结果也具有好的测试精度和可靠性。     

纳米压痕技术在工程材料研究中的应用

纳米压痕技术具有高灵敏度、操作简单等优点,可以在微纳尺度上获得块体材料、薄膜以及涂层等的多种力学性能参数。尤其随着材料基因组技术的推广,其将成为应用越来越广泛的力学性能表征方法。本研究介绍了纳米压痕技术的Oliver-Pharr方法原理,以及其在载荷-位移、硬度、弹性模量、断裂韧度、蠕变性能、残余应力、纤维界面性能表征方面的应用。在使用过程中仍存在一些问题需要注意和进一步研究:纳米压痕技术获得的力学性能参量需要考虑其测试模型的适用性;材料表面加工过程需要很高的技术及一致性,以最大减小甚至消除材料表面状态及物理特征对测试结果准确性和重复性的影响;由于测试位置较难精确定位,标准压头外形尺寸存在偏差以及设备本身的热漂移,纳米压痕测试重复性差。     

TiAlN刀具涂层影响因素的研究

通过正交实验获得了Ti50Al50N涂层的最佳工艺参数和各个工艺因素对其性能的影响,在此最佳工艺的同一条件下制备了不同Al含量的TiAlN涂层,利用X射线衍射、扫描电镜、高分辨透射电镜和纳米压痕仪分别对微观结构和力学性能进行了表征和测量。结果表明:随着Al含量的增加,硬度和弹性模量逐渐增加。当Al含量为40%时,硬度和弹性模量达最大值分别达到38、392 GPa;进一步增加Al含量,硬度和弹性模量不断降低。     

纳米晶Ta_2N涂层在模拟人体环境中的耐蚀性能研究

为了改善植入钛合金材料在人体环境中耐蚀性能,采用双阴极等离子反应溅射沉积方法,在医用Ti-6Al-4V钛合金表面制备了厚度为40 mm、平均晶粒尺寸为12.8 nm的Ta_2N纳米晶涂层。采用纳米压入仪、Vikers压痕仪和划痕仪考察了Ta_2N纳米晶涂层的硬度、弹性模量、韧性以及涂层与基体间的结合力。结果表明,Ta_2N涂层的硬度和弹性模量分别为(32.1±1.6)GPa和(294.8±4.2)GPa,涂层与基体的结合力为56 N;在压入载荷为0.49~9.8 N下,Vikers压痕表面以及横断面均未观察到微裂纹,反映其具有较高的压痕韧性。采用动电位极化、电化学阻抗谱、恒电位极化和电容测量(Mott-Schottky)等多种电化学表征技术,对Ta_2N涂层在Ringer's生理溶液中的电化学腐蚀行为进行了深入研究,并从钝化膜组成、致密性和半导体特性3个方面探讨了涂层的腐蚀防护机理。结果表明,在Ringer's生理溶液中,Ta_2N涂层表面形成的钝化膜更加致密,其腐蚀抗力明显优于Ti-6Al-4V合金。XPS分析结果表明,在较低的极化电位下,Ta_2N涂层的钝化膜主要由TaO_xN_y构成,随着外加极化电位的升高,其进一步氧化形成Ta_2O_5;电容测试结果表明,Ta_2N涂层表面所生成的钝化膜具有n型半导体特征,其施主浓度和载流子扩散系数明显低于Ti-6Al-4V合金表面生成的钝化膜。     

CoCrFeMnNi/6061Al复合材料制备及微区力学性能研究

通过放电等离子烧结(SPS)制备了CoCrFeMnNi/6061Al复合材料,采用SEM、XRD和纳米压痕等手段对其界面形貌和微区力学性能进行分析。结果表明,基体和增强颗粒间形成了厚度约为20μm的反应界面层,并生成了BCC固溶体相;复合材料微区的弹性模量和硬度变化趋势相同;界面层上的微纳力学性能高于基体和增强颗粒,界面层对复合材料力学性能的提高起重要的作用。     

纳米压痕技术在材料力学测试中的应用

近年来,材料纳米级力学测试日益引起广大研究者的重视。纳米压痕仪凭借极高的载荷和位移分辨率,广泛应用于材料表面的微纳米级力学性能的测试,包括硬度、弹性模量、塑性应变、薄膜界面结合强度以及材料疲劳特性等。综述了几种纳米压痕和纳米冲击技术测试材料力学性能的方法和原理,介绍了纳米压痕技术在材料力学性能测试方面的若干先进应用实例及其测试机理,以及原子力显微镜和扫描探针显微镜在力学测试方面的原理和应用。最后,提出了纳米压痕仪存在的若干问题,并对纳米压痕技术的发展进行了展望,认为纳米压痕技术结合有限元模拟建立材料疲劳断裂模型,是纳米压痕在力学测试方面发展的必然趋势。     

EB-PVD热障涂层的弹性模量和断裂韧性研究

用压痕法测量EB-PVD热障涂层的弹性模量及断裂韧性。发现热障涂层的Vickers显微硬度和弹性模量随施压载荷增大而减小,当载荷为2.94N时,显微硬度和弹性模量接近稳态值,分别为6.3GPa和172GPa;断裂韧性平均值约为1.81MPa·m1/2。压痕法测得陶瓷层断裂韧性数据波动较大,其主要原因是陶瓷层显微结构不均匀,使压痕裂纹在涂层不同局部区域所遇到的扩展阻力不同。     

Accuracy of Young’s Modulus of Thermal Barrier Coating Layer Determined by Bending Resonance of a Multilayered Specimen

The Young’s modulus of individual layer in thermal barrier coating (TBC) system is an important mechanical property because it allows determining the parameters of materials mechanics in the TBC system. In this study, we investigated the accuracy of the evaluation method for the Young’s modulus of a TBC layer according to the first bending resonance of a multilayered specimen comprising a substrate, bond coating, and TBC. First, we derived a closed-form solution for the Young’s modulus of the TBC layer using the equation of motion for the bending vibration of a composite beam. The solution for the three-layered model provided the Young’s modulus of the TBC layer according to the measured resonance frequency and the known values for the dimensions, mass, and Young’s moduli of all the other layers. Next, we analyzed the sensitivity of these input errors to the evaluated Young’s modulus and revealed the important inputs for accurate evaluation. Finally, we experimentally confirmed that the Young’s modulus of the TBC layer was obtained accurately by the developed method.     

Micro mechanical properties of n-Al2O3/Ni composite coating by nanoindentation

A new type of nano test system was introduced, the test principle and the indentation data analysis method were described. It was used to test the micro mechanical properties, such as hardness, elastic modulus and indentation creep property of n-Al2O3/Ni composite coating on steel prepared by brush plating, and the variety of mechanical properties with coating thickness was researched. The results show that the mechanical properties are basically identical within the whole coating, the hardness and modulus decrease in the defect fields, especially within the dendritic crystals, whereas the mechanical properties are not influenced greatly at the interspaces among dendritic crystals. The average hardness and elastic modulus of n-Al2O3/Ni coating are 6.34 GPa and 154 GPa respectively, and the hardness is 2.4 times higher than that of steel and the indentation creep curve of n-Al2O3/Ni coating is similar to that of the uniaxial compression creep, and the creep rate of steady-state is about 0. 104 nm/s. These results will supply useful data for process improvement, new type material development and application expansion.     

Characterization of Heat Treated Titanium-Based Implants by Nondestructive Eddy Current and Ultrasonic Tests

This study presents nondestructive characterization of microstructure and mechanical properties of heat treated Ti, Ti-Cu, and Ti-6Al-4V titanium-based alloys and 17-4 PH stainless steel alloy for biomedical implant applications. Ti, Ti-Cu, and 17-4 PH stainless steel based implants were produced by powder metallurgy. Ti-6Al-4V alloy was investigated as bulk wrought specimens. Effects of sintering temperature, aging, and grain size on mechanical properties were investigated by nondestructive and destructive tests comparatively. Ultrasonic velocity in specimens was measured by using pulse-echo and transmission methods. Electrical conductivity of specimens was determined by eddy current tests. Determination of Young’s modulus and strength is important in biomedical implants. Young’s modulus of specimens was calculated by using ultrasonic velocities. Calculated Young’s modulus values were compared and correlated with experimental values.     

The high-temperature elastic moduli of polycrystalline PbTe measured by resonant ultrasound spectroscopy

The thermoelectric material PbTe has been used in a wide variety of power generator applications. However, there is limited mechanical property data available for PbTe for temperatures above room temperature. This paper reports dynamic elastic moduli measured via resonant ultrasound spectroscopy on undoped and PbI₂-doped polycrystalline PbTe between room temperature and 773 K; in addition, the room temperature carrier concentration was measured by a Hall effect experiment. The Young’s modulus and shear modulus of PbTe decreased linearly with temperature above room temperature, while the Poisson’s ratio exhibited either monotonic increase or decrease with temperature. The Young’s modulus and shear modulus values obtained during heating and cooling agreed to within 1%. The dynamic elastic moduli data obtained in this study compared well in general with literature data. The difference observed between the current study and other literature studies is explained in terms of the carrier concentration effect on elastic moduli.     

Effect of densification distribution on the Young＇s modulus of porous coatings after nano-indentation

Nano-indentation of a porous ceramic coating leads to crushing and densification of the coating under the indenter. In this work, finite element simulations of indentation on the porous coating have been carried out to study the effect of the size and distribution of densification on Young s modulus measured by nano-indentation. Two totally different distribution patterns have been simulated in this work. In the case of gradient densification, the Young s modulus increased by 8.6% when the densification has occurred in the maximum influenced area. While the Young s modulus increased by 2% with a uniformed densification. Examinations of the cross-section of the coatings have suggested that the densification after the indentation is close to the second model. The measured Young s modulus could have differed by 2%. The effect of densification on the Young s modulus measured by using nano-indentation is strongly dependent on the densification patterns of the porous coating.     

Effects of plastic strain and strain path on youngs modulus of sheet metals

The effects of plastic strain and strain path on Young’s modulus of sheet metals are experimentally investigated using low carbon steel, stainless steel, aluminium, copper and brass sheets of 1 mm thickness. These sheets are firstly deformed to different plastic strains under a few strain paths from balanced biaxial stretching to uniaxial tension. Then, a small uniaxial tension test specimen is cut from each deformed sheet and Young’s modulus is measured using electrical-resistance strain gauges glued to both surfaces of the specimen. The experimental results show that Young’s moduli of the low carbon steel and stainless steel sheets decrease with increasing plastic strain, while those of aluminium, copper and brass sheets hardly change with the plastic strain. In all materials, however, the effect of the strain path on Young’s modulus is not necessarily evident. It is confirmed that Young’s modulus of the low carbon steel sheet can be recovered to the initial value of undeformed sheet by a subsequent annealing. In addition to Young’s modulus, the effects of the plastic strain and the strain paths on Poisson’s ratio of these materials are also shown.     

Mechanical properties of polycrystalline copper and single-crystal LiF initial components for composite system Cu/LiF

The paper deals with an investigation of mechanical properties and deformation features of polycrystalline copper and single-crystal LiF under dynamic nano/microindentation. It is shown that the values of hardness and Young’s modulus depend on the magnitude of the applied load (P_max): when the load is increased, H and E decrease. General regularities of the indenter penetration process in a wide range of loads are revealed: the appearance of a “pop-in” effect at the initial stage of the loading process, the formation of more pop-in steps with the growth in load, and the formation of pileups around the indentations. Such a nature of deformation is the result of sequential activation of different dislocation mechanisms with indenter deepening. Along with a great similarity in the specificity of deformation, some differences are noted at the unloading stage. The results serve to compare the mechanical properties of Cu and LiF individual components with similar parameters of the “coating/substrate” composite systems (CS Cu/LiF) produced on their basis.     

超细氮化硼多孔纤维对WC-ZrO2复合材料力学性能的改善

多孔纤维的研究传统上一般局限于催化和环境化学领域。而本研究将一种超细氮化硼多孔纤维被加入WC-8%ZrO₂(质量分数)复合材料,以期改善其力学性能。结果表明,这种纤维的加入使得材料的杨氏模量、硬度和断裂韧性都得到了改善。然而,加入超细氮化硼多孔纤维样品的杨氏模量的提升并不遵循常用于评价陶瓷基材料杨氏模量的混合法则。个别添加了0.05%超细氮化硼多孔纤维的样品的杨氏模量高达692GPa,已经接近纯WC材料的杨氏模量700GPa。这种现象可以通过基于ZrO₂的超塑性实现的纳米材料的小尺寸效应得到解释。     

On the Early Stage Isothermal Oxidation of APS CoNiCrAlY Coatings

The aim of this study is to analyze the evolution of microstructural and room temperature mechanical properties of air plasma sprayed (APS) CoNiCrAlY coatings before and after early stage high-temperature oxidation. To this purpose, selected samples were isothermally heat treated at 1110 °C for different durations. Phase analysis and oxide scale characterization were performed using x-ray diffraction. Morphological and microstructural features of as-sprayed and oxidized CoNiCrAlY coatings were analyzed by scanning electron microscopy and energy dispersive x-ray spectroscopy. After heat treatment, a duplex oxide scale, composed of an inner α-Al₂O₃ layer and an outer spinel-type oxide layer, was observed on coating top-surface. The nanoindentation technique was employed to study the evolution of the mechanical properties. An increase in Young’s modulus and hardness with increasing the aging time was observed, this effect was mainly addressed to the partial densification of coating microstructure.     

Influence of Deposition Temperature on the Microstructures and Properties of Plasma-Sprayed Al2O3 Coatings

Al₂O₃ coatings were deposited on 1Cr13 substrates by atmospheric plasma spraying at different deposition temperatures of 140, 275, 375, 480, 530, and 660 °C to investigate the effect of coating surface temperature on the lamellar bonding formation. The fractured cross section morphology was characterized by scanning electron microscopy to reveal the lamellar interface bonding. X-ray diffraction was used to characterize the phase contents in the coating. Micro-hardness, Young??s modulus, and thermal conductivity of the deposits were measured for examining the dependency of coating properties on its microstructure. The results show that the interface area bonded through columnar grain growth across splat-splat interfaces was increased with increasing deposition temperature. Moreover, micro-hardness, Young??s modulus and thermal conductivity were increased with the increase of deposition temperature. However, the phase structure of the coating changed little with deposition temperature. The results evidently indicate that the apparent bonding ratio and properties of deposits can be significantly changed in a wider range through controlling the deposition temperature.