Papers by Keyword: Nanoindentation

Abstract: The microstructure, texture and elastic modulus of electron beam welding joint in Ti-6Al-4V titanium alloy were investigated by transmission electron microscopy, X-ray diffraction, electron back scattered diffraction and nanoindentation techniques. The α phase was in the majority, and a {0001} <-2110> texture of α phase was observed in the base material. A very weak {11-23} <-1-122> texture of α phase was in the fuse zone. Most of the α grain boundaries in the fuse zone were high-angle boundaries by electron backscattered diffraction, and it also confirmed that the orientations of α phase had a nearly random distribution in the fuse zone. The maximum average elastic modulus value measured by the nanoindentation techniques was in the base material due to the effect of the {0001} <-2110> texture. The average elastic moduli of three different zones in the joint were 134.8±3.5Gpa, 125.5±5.8Gpa and 123.0±4.7Gpa, respectively.

Abstract: WC-8wt%Co nanopowder was consolidated by spark plasma sintering at process temperatures (T_SPS) from 1100 to 1400 °C. The nanoindentation hardness and Young’s modulus of the consolidated specimens were measured under different peak load levels (P_max). The hardnesses and modulus of WC-8wt% Co shows a clear dependence on the microstructures and peak load levels. At 1200 and 1300 °C, the hardness and modulus were higher than those at 1100 and 1400 °C due to the higher relative density and fine grain size. The relationship of stiffness (S) and contact depth (h_c) of nanoindentation was discussed.

Abstract: We report on the mechanical response of semiconductor substructures formed by InP membranes bonded to silicon. The bonded surfaces are of the order of ~ 1 cm2 and were bonded using oxide-free direct wafer bonding. Both the plastic response of the InP membrane and the InP/Si interface strength have been investigated using instrumented nanoindentation.

Abstract: This study combines nanoindentation experiments, electron backscatter diffraction (EBSD) and atomic force microscopy (AFM) topographic measurements to investigate the material anisotropy contribution to the indentation behaviour of individual grains of various hexagonal-close packed (HCP) polycrystals with different axial ratio (zinc, magnesium and titanium). The grain size was much larger than the indents size to ensure quasi-single-crystal indentation and when, combined with an EBSD mapping, a wide variety of crystal orientations can be probed, which provides mechanical characterization of materials at the micro/nanoscale. Experimental curves can be used to determine the mechanical properties of the indented material. Furthermore, by using data issued from AFM topographic measurements, one can analyze the dislocations arrangements below and around the indentation print, and thus characterize the most probably activated deformation systems.

Abstract: Sapphire single crystal is widely used in many fields because of its excellent properties, as a focus of mechanical test, nanoindentation on sapphire is paid a great deal of attention by researchers. In this manuscript, the maximum load, depth and loading rate effects on the first pop-in event during nanoindentation of sapphire single crystal were discussed, the results indicated that these factors had no effect on the load at which the first pop-in occurred and the extension width of pop-in; the deformation below the first pop-in event was discussed and it could be roughly considered as purely elastic deformation through analyzing.

Abstract: Lateral Diffused Metal Oxide Semiconductors (LDMOS) normally have a Cu-W flange, whose CTE is matched to Si. Low cost Cu substrate material provides 2X high thermal conductivity, and along with a AuSi eutectic solder is recommended for optimal thermal performance. However, the CTE mismatch between Cu and Si can lead to failure of the semiconductor as a result of die fracture, due to thermal stresses developed during the soldering step of the manufacturing process. Introducing a Ag ductile layer is very important in minimizing such thermal stresses and preventing catastrophic failure of the semiconductor. Ag is a ductile material electroplated on the Cu substrate to absorb stresses developed during manufacturing due to the CTE mismatch between Si and Cu. The Ag layer thickness affects the magnitude of the resulting thermal stresses. This study attempts to measure the yield strength of the Ag layer, and examines the optimal layer thickness to minimize die stresses and prevent failure. The yield stress of the ductile layer deposited on a Cu flange was measured by nanoindentation. The Oliver and Pharr method was applied to obtain modulus of elasticity and yield depth of Ag. A finite element analysis of the package was performed in order to map die stress distribution for various ductile layer thicknesses. The analysis showed that increasing the ductile layer thickness up to 0.01 - 0.02 mm, decreases the Si die stresses.

Abstract: A study of the structural and mechanical properties of nanocrystalline TiAlSiN gradient coatings deposited by cathodic arc deposition techniques at 500 °C and post-annealed at 525 °C is presented. Analysis of the coatings, chemical composition and microstructure revealed that the coatings have a structure based on (Ti, Al)N nanocrystals with an average size of 10 nm embedded in an amorphous Si₃N₄ phase. The study of the mechanical properties showed that post-annealing causes improvement and increase of the coatings hardness. A maximum hardness of 48 GPa and elastic modulus of 560 GPa were measured. Also, excellent adhesion to the WC-Co substrate was observed in the post-annealed coatings.

Abstract: The effect of the grain orientation of the stainless steel AISI 304 and the effect of the indenter orientation on the indentation moduli was numerically studied by means of the finite element method. The contact areas were evaluated numerically and the indentation moduli was determined according to the Oliver-Pharr method. As a result, the crystallographic orientations in which the indenter orientation plays the most important role were identified. However, the observed indentation moduli variation is within the scatter of the experimental data in practical applications.

Abstract: The corneoscleral rim of the eye represents a region with unique anatomical properties due to its location between the cornea and sclera / conjunctiva. It further has unique functional properties due to the location of adult corneal epithelial stem cells in the rim structure (limbus) itself. These stem cells are essential for the regeneration of the corneal epithelium and for preventing the conjunctival epithelium from growing onto the corneal surface, which could result in blindness. Survival and self-renewal properties of stem cells are known to depend on specific biological and biomechanical properties of its niche environment. We therefore aimed to measure the local mechanical properties of the human corneoscleral rim using a novel nanoindentation device (Bioindenter CSM Instruments, Neuchâtel, Switzerland) developed for soft tissues evaluation. Nanoindentation was performed using a spherical indenter of 0,5mm radius, a maximal load ranging between 20 μN to 30 μN and a penetration depth of several μm to 60μm. The hold period at maximum load was 180 seconds. Youngs modulus (E) was calculated using a Hertzian fit to the loading data. E of the central cornea was in the range of 19 kPa, while in the scleral region we found 17 kPa and the limbal rim region 10 kPa. Considerable creep relaxation occurred during the hold period at maximum load, which scaled with the elastic modulus of the different structures. These results reveal biomechanical properties of the corneoscleral rim with distinct mechanical properties for the three anatomical regions.

Abstract: The paper serves as an introduction to investigation of mechanical properties of functionally graded materials and deals with elastic nanoindentation numerical models. The models were based on the finite element method. Young's moduli were estimated by Oliver-Pharr method. The indenter geometry for which numerical solutions were accomplished was a rounded cone indenter. The effect of tip sharpness was examined by applying an increasing spherical tip radius. The results show that the apparent Young's modulus and the hardness increase linearly with increasing radius of the tip. The effect of approaching interface between two elastic materials on the apparent hardness and indentation modulus was identified in 3D model. The specimen consisted of two materials. First, the interface was linear and parallel to the direction of indentation, so that the Young's modulus changed suddenly. Second, the Young's modulus was continuously changing. The dependence on various boundary conditions of the specimen was also considered.