Papers by Keyword: Vickers Indentation

Abstract: Physical Vapour Deposited (PVD) coatings are used in wide range of industrial applications where requirements differ. For example, in cutting applications adhesive-abrasive wear along with high contact stresses prevail and PVD coating with thickness of ~2 μm are used. In forming applications adhesive wear usually dominates and relatively thick PVD coatings (~5 μm) are preferred. For both the applications coatings are subjected to cyclic stress and therefore it is a point of interest to learn the behaviour of PVD coatings with different thickness under cyclic loading. Cracking resistance and fatigue properties of gradient TiCN on hard metal substrate was evaluated by means of the cyclic Vickers indentation method. Hard metal was chosen as a substrate material to avoid pile-up effect and support the hard coating during indentation. The results of the single indentation Vickers test show that secondary radial and circumferential cracks appear in tested coatings already after the first indent. With increasing cycles the cracks grow up to a critical crack length after which the crack length doesn’t increase further. The tested coating thickness has no significant effect on cracking behaviour.

Abstract: The energy consumption of crushing is directly affected by the mechanical properties of cement materials. The elastic modulus, energy dissipation, recovery resistance and other mechanical properties of cement materials are evaluated based on the depth-sensing indentation method in this work. It is significant and efficient for engineering application. In results, the calculated elastic modulus is close to that measured by dynamic method, being used to verify the correctness of the calculated data. And the calculated energy dissipation of clinker is higher than that of limestone and granite, which can partially be used to explain why the grinding of clinker consumes a lot of energy in cement industry. The recovery resistance of clinker is almost identical to that of granite, more than that of limestone. It is found that the clinker, in contrast to granite and limestone, exhibits better plasticity and greater energy absorption capacity.

Abstract: A three dimensional finite element model for Vickers indentations on brittle materials is presented in order to analyze the stress distribution. The objective of this paper is to study when and where cracks are most likely to initiate and propagate in the indentation cycle based on the analyzed stresses. Therefore the time-dependent stresses around and below the surface of the contact area during the indentation cycle, especially at the end of loading and at the beginning of unloading phase are investigated in detail. The analytical results are shown to be in good agreement and verified with the experimental results.

Abstract: In this work a study on the structural phase transitions of silicon undergone by two different methods were performed. The samples were submitted to high non-hydrostatic pressure applied by cyclic Vickers indentations and by the tool tip during the single point diamond turning. The indentations were performed on virgin surface (polished as received) and on an amorphous surface generated either by the machining process or RF sputtering. The analysis on the machined surface, debris on the diamond tool and around of imprints were also performed using Raman micro spectroscopy. The results indicated the formation of some phases may depend upon the initial structural state of the surface, i.e., amorphous or crystalline.

Abstract: The photoacoustic piezoelectric images of Vickers indented silicon nitride, Al2O3-SiCTiC composite ceramic, nanonickel and nanocopper in unloaded and loaded states are presented. It is demonstrated the influence of mechanical stresses on the photoacoustic images of Vickers indented areas both for ceramics and metals. For Al2O3-SiC-TiC composite ceramic it is also shown that an increase of annealing time is accompanied by the decrease in the photoacoustic response from the radial crack tips. The obtained photoacoustic experimental results are explained within the framework of the model for the photoacoustic effect in stressed solids proposed by us earlier.

Abstract: Structure-property relationships in bovine cortical bone have been characterised using grazing-incidence synchrotron radiation diffraction, Vickers indentation and mechanical testing. Depth profiling results indicated the existence of distinct gradual changes in crystal disorder, phase abundance, and texture of hydroxyapatite whilst the crystallite size was depth-independent.

Abstract: Structure-property relationships in baby and adult teeth have been characterised using grazing-incidence synchrotron radiation diffraction and Vickers indentation. Similarities and differences between both types of teeth have been highlighted and discussed. Depth profiling results indicated the existence of contrasting but distinct gradual changes in crystal disorder, phase abundance, crystallite size and hardness within the baby and adult canine enamel, thus confirming the graded nature of human teeth. When compared to the adult tooth, the baby enamel is softer, more prone to fracture, but has larger hydroxyapatite grains.

Abstract: Thermal shock resistance of the RE-Si-Mg-O-N glasses (RE = La, Nd, Yb, Lu) with 0 and 20 eq.% of nitrogen was investigated by the indentation-quench method based on propagation of Vickers cracks. Crack growth was measured on the same sample for a test series of different quenching temperatures. Thermal shock resistance of the studied materials was determined as a temperature difference resulting in 10 % growth of the initial cracks (∆T10) and by the thermal shock parameter R calculated from the material properties. Although the comparison of ∆T10 and R values as a function of glass composition revealed some differences between these two approaches, also a common trend was observed. Thermal shock resistance increased with the fractional glass compactness resulting from RE type and N content increase.

Abstract: The basic requirement for the use of a ceramic coating is sufficient adhesion to its substrate. A measure of the adhesive properties of a coating is the interfacial fracture toughness. The test method applicable for interfacial fracture toughness measurements depends on the mechanical properties of the material system and the geometry of the test piece. In this work, indentation methods have been evaluated for the estimation of the fracture toughness of ceramic thermal barrier coatings on metallic substrates. Coatings of 100 to 300 µm thickness were applied by electron beam – physical vapour deposition. The performed test types were Vickers indentation at the interface of polished cross sections of the coating system and Rockwell indentation with a brale C indenter, penetrating the coating perpendicular to the surface. Both tests generate delamination, in which the delamination crack length corresponds to the interfacial fracture toughness. Fracture surfaces and cross sections of the fractured coatings were investigated by optical and scanning electron microscope. Determined fracture toughness values are discussed with respect to the loading conditions in the test and the fracture process – i.e. interaction between indenter and coating system and the crack propagation path.

Abstract: The contact fracture behaviors of fine-grained Ti3SiC2 and coarse-grained high purity Ti3SiC2 are examined by the Hertzian indentation and Vickers indentation technique. The Vickers hardness of bulk Ti3SiC2 is as low as 5.3~6.3 Gpa, and the Hertzian contact stress-strain curves for Ti3SiC2 deviate much from linearity, which resembles the fracture behavior of a ductile metal rather than a brittle ceramic. The contact damages by both Vickers indentation and Hertzian indentation reveal a fairly good plastic deformation nature of Ti3SiC2. Un-reacted TiCx in fine-grained Ti3SiC2 may impede the plastic deformation by slip along basal plan inside Ti3SiC2 grain, making Ti3SiC2 less plastic under loading.