Nano-meter scale plasticity in KBr studied by nanoindenter and force microscopy

The early stages of plasticity in KBr single crystals have been studied by means of nano-meter-scale indentation in complementary experiments using both a nanoindenter and an atomic force microscope. Nanoindentafion experiments precisely correlate indentation depth and forces, while force microscopy provides high-resolution force measurements and images of the surface revealing dislocation activity. The two methods provide very similar results for the onset of plasticity in KBr. Upon loading we observe yield of the surface in atomic layer units which we attribute to the nucleation of single dislocations. Unloading is accompanied by plastic recovery as evident from a non-linear force distance unloading curve and delayed discrete plasticity events.

Effect of porosity on the indentation behaviour of nanoporous alumina films

Anodising aluminium in an acid electrolyte results in a porous alumina film. The pores are uniformly distributed and their structure can be controlled by varying the anodising parameters. In this study, the pore structure of the anodic alumina films is varied systematically by varying the anodising time and a subsequent pore widening chemical etch. The indentation behaviour of the resulting film is studied using a depth sensing nanoindenter. The hardness of the films was found to be decreasing with decreasing solid area fraction. Understanding the deformation behaviour of nanoporous alumina would help tailoring the mechanical properties by tuning the geometry.

Relationship Between Physical Structure and Tribology of Single Soot Particles Generated by Burning Ethylene

Ethylene gas is burnt and the soot generated is sampled thermophoretically at different heights along the flame axis starting from a region close to the root of the flame. The morphology and crystallinity of the particle are recorded using high resolution transmission electron microscopes. The hardness of a single particle is measured using a nanoindenter. The frictional resistance and material removal of a particle are measured using an atomic force microscope. The particles present in the mid-flame region are found to have a crystalline shell. The ones at the flame root are found to be highly disordered and the ones at the flame tip and above have randomly distributed pockets of short range order. The physical state of a particle is found to relate, but not very strongly, with the mechanical and tribological properties of the particles.

A new method for fracture toughness determination of graded (Pt,Ni)Al bond coats by microbeam bend tests

A novel method is proposed for fracture toughness determination of graded microstructurally complex (Pt,Ni)Al bond coats using edge-notched doubly clamped beams subjected to bending. Micron-scale beams are machined using the focused ion beam and loaded in bending under a nanoindenter. Failure loads gathered from the pop-ins in the load-displacement curves combined with XFEM analysis are used to calculate K-c at individual zones, free from substrate effects. The testing technique and sources of errors in measurement are described and possible micromechanisms of fracture in such heterogeneous coatings discussed.

Solubility-Hardness Correlation in Molecular Crystals: Curcumin and Sulfathiazole Polymorphs

Curcumin and sulfathiazole exist as three and five polymorphs, respectively. We correlate solubility and mechanical properties in these polymorphic systems. It is seen that hardness (H) is inversely proportional to the solubility of a polymorph. H of the polymorphs is explained on the basis of slip planes in the crystal structure, the Schmid factor (m), and the relative orientation of molecules with respect to the nanoindenter direction. Effectively, H is a useful parameter (compared to melting point, T-m, and density, rho) that correlates well with the solubility of a polymorph. Such a correlation is helpful in systems like curcumin and sulfathiazole in which the Gibbs free energy of the polymorphs are close to one another. To summarize, a softer polymorph is more soluble.

Study on Microstructure and Nanomechanics Properties of Antibacterial Bone China

Fracture appearance, surface and nanomechanics properties of antibacterial ceramics contairing rare earth phosphate composite antibacterial materials were characterized and measured by SEM, AFM and Nanoindenter, respectively. Results show that grain of fracture surface of antibacterial ceramics grows uniform refinement topography of bubble break-up appears at the surface, which is flat and has liquid character, by adding the phosphate composite containing rare earth, nevertheless needle-like crystal and granular outgrowth form at fracture surface and surface of common ceramics, respectively. Young's modulus of antibacterial ceramic film is 74. 397 GPa and hardness is 8. 134 GPa, which increses by 4.4﹪ and 1.6﹪ comparing with common ceramics, respectively. Loading curves of two kind of ceramics have obvious nonlinear character under 700 nm and linear character between 700 ～ 1000 nm, and unloading curve have obvious linear character.

The mechanical properties of an aluminum alloy by plasma-based ion implantation and solution-aging treatment

The age-strengthening 2024 aluminum alloy was modified by a combination of plasma-based ion implantation (PBII) and solution-aging treatments. The depth profiles of the implanted layer were investigated by X-ray photoelectron spectroscopy (XPS). The structure was studied by glancing angle X-ray diffraction (GXRD). The variation of microhardness with the indenting depth was measured by a nanoindenter. The wear test was carried on with a pin-on-disk wear tester. The results revealed that when the aluminum alloys were implanted with nitrogen at the solution temperature, then quenched in the vacuum chamber followed by an artificial aging treatment for an appropriate time, the amount of AIN precipitates by the combined treatment were more than that of the specimen implanted at ambient temperature. Optimum surface mechanical properties were obtained. The surface hardness was increased and the weight loss in a wear test decreased too.

微桥结构镍膜的弹性模量和残余应力研究

采用MEMS(MicroelectromechanicalSystems)技术研制了宽度在微米尺度的镍(Ni)膜微桥结构试样。采用纳米压痕仪(Nanoindenter)XP系统的楔形压头测量了微桥载荷与位移的关系,并结合微桥力学理论模型得到了Ni膜的弹性模量及残余应力,分别为190GPa和87MPa。与采用纳米压痕仪直接测得的带有硅(Si)基底的Ni膜弹性模量(186.8±7.5)GPa相符合。

A Study of the Tribological Behavior of Carbon-Nanotube-Reinforced Ultrahigh Molecular Weight Polyethylene Composites

The tribological properties of the high-strength and high-modulus ultrahigh molecular weight polyethylene (UHMWPE) film and the UHMWPE composites reinforced by multiwalled carbon nanotubes (MWCNT/UHMWPE) were investigated using a nanoindenter and atomic force microscope (AFM). The MWCNT/UHMWPE composites films exhibited not only high wear resistance but also a low friction coefficient compared to the pure UHMWPE films. We attribute the high wear resistance to the formation of the new microstructure in the composites due to the addition of MWCNTs.

Caracterização mecânica e tribológica de dois glazeadores disponíveis comercialmente e uma composição experimental

O objetivo desse estudo, in vitro, foi avaliar através de testes mecânicos e tribológicos, a aplicação de dois glazeadores disponíveis comercialmente e uma composição experimental como material de cobertura em restaurações de resina composta com relação à rugosidade superficial, à dureza e à resistência ao desgaste. Foram confeccionados 24 corpos de prova (CP) do compósito Z350XT (3M/ESPE) e divididos em 4 grupos. O grupo controle (GC) não recebeu selamento, o grupo Biscover LV (GB) recebeu aplicação do Biscover LV (Bisco), o grupo Natural Glaze (GN) recebeu aplicação do Natural Glaze (Nova DFL) e o grupo Experimental (GE) recebeu aplicação de um glazeador experimental contendo nanopartículas (1% em peso). Posteriormente, os CP foram submetidos à análise da rugosidade superficial utilizando um perfilômetro e avaliação da dureza através de um nanoindentador, que fornece também o módulo elástico do material. Em seguida, os CP foram submetidos ao teste de desgaste linear alternado, durante 15.000 ciclos, com carga de 5N, em água destilada. A profundidade máxima de desgaste foi avaliada através de um perfilômetro. A análise dos dados relativos à rugosidade superficial (m) foi realizada utilizando ANOVA/Duncan (p-valor = 0,000). As médias e desvio padrão foram: GC-0,12(0,01); GB-0,06(0,01); GN-0,13(0,02); GE-0,13(0,01). A análise da dureza (GPa) e módulo elástico (GPa) foram avaliados aplicando o teste não-paramétrico de Kruskal-Wallis. As médias e desvio padrão para dureza foram: GC-1,10(0,24); GB-0,31(0,004); GN-0,08(0,004); GE-0,12(0,008) para carga de 1,25mN; GC-1,08(0,139); GB-0,32(0,004); GN-0,08(0,003); GE-0,13(0,006) para carga de 2,5mN; GC-1,10(0,101); GB-0,33(0,003); GN-0,09(0,002); GE-0,13(0,056) para carga de 5,0mN. As médias e desvio padrão para módulo elástico foram: GC-17,71(1,666); GB-5,44(0,084); GN-3,484(0,114); GE-4,55(0,178) para carga de 1,25mN; GC-17,5(1,449); GB-5,18(0,065); GN-3,38(0,078); GE-4,55(0,12) para carga de 2,5mN; GC-17,69(1,793); GB-5,04(0,041); GN-3,63(0,066); GE-4,85(0,104) para carga de 5,0mN. A análise dos dados relativos à profundidade de desgaste (m) foi realizada utilizando ANOVA/Dunnett (p-valor = 0,000). As médias e desvio padrão foram: GC-12,51(0,89); GB-0,59(0,07); GN-1,41(0,12); GE-1,84(0,18). A partir dos resultados apresentados pode-se concluir que apenas o Biscover LV foi capaz de reduzir a rugosidade superficial da resina composta testada. Os demais, Natural Glaze e Experimental, não alteraram a rugosidade superficial e foram estatisticamente semelhantes entre si e com o grupo controle. Todos os glazeadores testados reduziram a dureza e o módulo elástico da resina composta quando comparados com o grupo controle, diferindo entre si, apresentando uma ordem crescente de dureza e módulo elástico (Natural Glaze < Experimental < Biscover < Controle). Todos os glazeadores testados foram capazes de reduzir o desgaste da resina composta, quando comparados com o grupo controle, diferindo entre si, apresentado uma ordem crescente de desgaste (Biscover < Natural Glaze < Experimental < Controle).

Analysis of the practical force accuracy of electromagnet-based nanoindenters

Two important factors that influence the force accuracy of the electromagnet-based nano-indenters but have not yet attracted much attention are analyzed, and a more reasonable way to estimate the force accuracy is presented in this paper. MTS Nano Indenter (R), with the characteristics of a coil suspended in a uniform magnetic field by two sets of springs acting as an actuator and force measuring unit, is used as an example. One of the two factors is the uniformity of the magnetic field. The other is the stiffness of the supporting spring. Consequently, the practical force accuracy varies considerably from test to test because it firmly depends on the working position of the coil and the displacement stroke. A reasonable estimated accuracy value is of the order of 10 degrees mu N for typical indentation tests with a 10(2) nm indentation depth or a 10 degrees mN test force. (C) 2010 Elsevier Ltd. All rights reserved.

电磁式纳米压入仪的载荷精度研究

纳米压入仪(Nanoindenter)已成为纳米/微米力学测试的基本工具之一,广泛应用于纳米材料、薄膜、MEMS微结构的力学性能测试。目前商业化仪器有MTS NanoIndenter(incorporated into Agi lent in 2008),Hysitron TriboIndenter,CSM NanoHardness Tester,MML NanoTest,and CSIRO UMIS,其中原MTS Nano Indenter、CSMNano Hardness Tester和MML NanoTest都采用电磁驱动兼载荷计量的原理设计。这类仪器主要优点之一是载荷分辨力高,可以达到50nN甚至更小。然而仪器制造商从未明确给出此类仪器的载荷精度。目前对纳米压痕测试技术的研究也主要集中在压头形状、试样表面粗糙度、毛细力等因素对压痕测试结果的影响,尚未见针对仪器载荷精度的研究报道。国际标准ISO 14577-2:2002虽对仪器施加的试验力的允差进行了规定,但由于电磁式纳米压入仪的结构响应和试样力学行为耦合在一起,试样上的载荷并不完全等同于通过电磁转换原理计量的试验力,因此实际测试时试样上的载荷精度仍是未知。

纳米压痕仪的载荷精度研究

<正>以MTS Nano Indenter(?)XP为例,研究发现了影响电磁式纳米压痕仪载荷精度的两个重要因素。其一,磁场的均匀性。在实验位移范围内磁场必须是均匀的,这是电磁计量载荷的理论基础。校准实验结果显示,NanoIndenter(?)XP在0.45mm位移行程内的非均匀性为0.24%。即,在0.45mm位移行程内磁场均匀性给载荷

An ATP-dependent mechanism mediates intercellular calcium signaling in bone cell network under single cell nanoindentation

To investigate the roles of intercellular gap junctions and extracellular ATP diffusion in bone cell calcium signaling propagation in bone tissue, in vitro bone cell networks were constructed by using microcontact printing and self-assembled monolayer technologies. In the network, neighboring cells were interconnected through functional gap junctions. A single cell at the center of the network was mechanically stimulated by using an AFM nanoindenter. Intracellular calcium ([Ca2+](i)) responses of the bone cell network were recorded and analyzed. In the untreated groups, calcium propagation from the stimulated cell to neighboring cells was observed in 40% of the tests. No significant difference was observed in this percentage when the intercellular gap junctions were blocked. This number, however, decreased to 10% in the extracellular ATP-pathway-blocked group. When both the gap junction and ATP pathways were blocked, intercellular calcium waves were abolished. When the intracellular calcium store in ER was depleted, the indented cell can generate calcium transients, but no [Ca2+](i) signal can be propagated to the neighboring cells. No [Ca2+](i) response was detected in the cell network when the extracellular calcium source was removed. These findings identified the biochemical pathways involved in the calcium signaling propagation in bone cell networks. Published by Elsevier Ltd.

Cyclic nanoindentation and nano-impact fatigue characterisation of functionally graded TiN/TiNi shape memory film

This paper investigates the mechanism of nanoscale fatigue of functionally graded TiN/TiNi films using nano-impact and multiple-loading-cycle nanoindentation tests. The functionally graded films were deposited on silicon substrate, in which TiNi films maintain shape memory and pseudo elastic behavior, while a modified TiN surface layer provides tribological and anti-corrosion properties. Nanomechanical tests were performed to comprehend the localized film performance and failure modes of the functionally graded film using NanoTestTM equipped with Berkovich and conical indenter between 100 μN to 500 mN loads. The loading mechanism and load history are critical to define film failure modes (i.e. backward depth deviation) including the shape memory effect of the functionally graded layer. The results are sensitive to the applied load, loading type (e.g. semi-static, dynamic) and probe geometry. Based on indentation force-depth profiles, depth-time data and post-test surface observations of films, it is concluded that the shape of the nanoindenter is critical in inducing the localized indentation stress and film failure, including shape recovery at the lower load range. Elastic-plastic finite element (FE) simulation during nanoindentation loading indicated that the location of subsurface maximum stress near the interface influences the backward depth deviation type of film failure. A standalone, molecular dynamics simulation was performed with the help of a long range potential energy function to simulate the tensile test of TiN nanowire with two different aspect ratios to investigate the theory of its failure mechanism.