Papers by Keyword: Nanoindentation

Abstract: With the growing application of wide-bandgap semiconductors such as SiC in power electronics, efficient and low-damage machining of large-diameter, high-quality 4H-SiC wafers has become a critical research priority. This study systematically compares the grinding behavior of the C-and Si-faces of laser-sliced 4H-SiC wafers and reveals the effect of crystallographic anisotropy on tool wear. In the experiments, a picosecond laser was used to induce internal crystal modification, and multiple pairs of 12-inch high-purity semi-insulating crystals and wafers were obtained through ultrasonic separation. These wafers were subsequently ground using #800/#8000 resin-bonded diamond wheels. Material removal and wheel wear were recorded in real time, and the wheel wear ratio (W/M) was adopted as the key evaluation metric. Nanoindentation and white-light interferometry were further employed to characterize the mechanical properties and surface morphology of the two crystal faces. Results show that in both rough and fine grinding, the C-face demonstrates superior material removal performance despite its higher hardness, whereas the Si-face is more prone to wheel degradation. For thin wafers, residual laser focus near the surface further aggravates wheel wear. These findings establish a link between crystallographic anisotropy, laser-modified layer position, and wheel wear behavior, providing an experimental foundation for clarifying the underlying mechanisms and developing face-specific grinding strategies for high-quality SiC wafer fabrication.

Abstract: This research explores the effect of elevated extrusion ram speed—achieved through die cooling with liquid nitrogen—on the mechanical behavior of 6060-aluminum alloy profiles. Mechanical characterization was conducted via tensile testing and nanoindentation, with the latter also employed to assess the alloy’s creep response. Results reveal that while the increased ram speed exerts minimal impact on Ultimate Tensile Strength (UTS) and Yield Tensile Strength (YTS), it notably enhances elongation. Furthermore, the study demonstrates a significant influence of ram speed on creep displacement as the dislocations generated by higher ram speeds seems to improve the creep resistance of the material. Keywords: 6060 Aluminum Alloy; Liquid Nitrogen Cooling; Nanoindentation; Tensile Testing; Creep Behavior.

Abstract: The nucleation of dislocations in sapphire of various structural perfection has been investigated by nanoindentation. The studies were carried out on crystallographic planes С(0001), a(1 1 2 0), R (0 112). In the curve of indentation of a Berkovich indenter into the single crystals, an abrupt transition from elastic to plastic deformation has been observed at a depth of about 75 nm due to the nucleation of dislocations in the initially dislocation free region under the contact. Deterioration of structural perfection results in a decrease in shear stresses under which dislocations nucleated. It is shown that the anisotropy of sapphire nanohardness is less pronounced than the static one.

Abstract: Nanoindentation, an advanced technique employed for characterizing materials, facilitates the precise determination of their hardness and Young's modulus by applying a specific, controlled force through an indenter, enabling highly localized deformation and measurement at nanometer scales. The nanoindentation gives us the view of the isotropic and anisotropic features of the materials by analyzing the zone beneath the indenter. The application of Bulk Metallic Glass (BMG) alloy, renowned for its unique combination of high strength, exceptional elasticity, and superior corrosion resistance, spans diverse industries including aerospace, biomedical, and consumer electronics. The study focuses on conducting nanoindentation analysis on the BMG alloy, aiming to characterize its deformation behavior. This involved utilizing Scanning Electron Microscopy (SEM) to discern deformation characteristics, followed by validation of the findings through simulations, ensuring robustness and reliability of the results. The modulus, determined to be 227GPa, provided insight into the material's structural rigidity, and the hardness 14.8GPa offered an indication of its resistance to localized plastic deformation. The results have been compared with the simulation results where the modulus was 242GPa and the hardness was 16.1GPa.

Abstract: The instrumented nanoindentation technique is widely used to investigate the local mechanical properties of cementitious composites. Due to its high-resolution load control and displacement sensing capabilities, this technique is increasingly being used to measure hardness, elastic modulus, creep parameters, and residual stresses that have been explored at micro and nanolevel. During the indentation of brittle materials, cracks may be generated around the impression, which depend on load conditions, material and indenter geometry. This work presents a simulation of the three-dimensional nanoindentation model established with finite element method and modified constitutive relation. The model is created to simulate on single phase (homogeneous) materials such as cement clinker (C3S and C2S separately) and the hydrated phase – Low Density CSH and High Density CSH separately that constitute the primary phases of cementitious matrix. Then numerical modelling (FEA) of indentation is conducted using the concrete damage plasticity (CDP) material model, with the constants calibrated for hardened cement paste. At the end, there was a good agreement when comparing the differences between the simulated and literature experimental results.

Abstract: During nanoindentation analysis of cementitious materials, data points with abnormal load-depth curves are often obtained. This study investigates the effect of these abnormal indentation points (AIP) on the micromechanical properties and content of phase in hydrated cement paste calculated by nanoindentation test combined with deconvolution analysis, including the least-square-estimation (LSE) and maximum-likelihood-estimation (MLE) methods. The results indicate that the AIP is mostly associated with phases with low mechanical properties, and the exclusion of AIP significantly affects the volume fractions of micropore phase and low-density calcium silicate hydrate, while the mechanical properties of phases keep stable except that the mechanical properties of micropore phase are slightly increased by the exclusion of the AIP. The phase contents derived based on LSE showed a more significant change than those derived based on the MLE when AIP was excluded from indentation data. In addition, the phase content derived by nanoindentation analysis was compared to that derived by other analysis methods, including mercury intrusion and quantitative x-ray diffraction.

Abstract: Electron-Beam Powder Bed Fusion (EB-PBF) is one of the most important metal additive manufacturing (AM) technologies. In EB-PBF, a focused electron beam is used to melt metal powders in a layer by layer approach. In this investigation two pre-alloyed steel-based powders, stainless steel 316L and V4E, a tool steel developed by Uddeholm, were used to manufacture functionally graded materials. In the proposed approach two powders are loaded into the feeding container, V4E powder on top of 316L one, preventing their mixing. Such type of feeding yields components with two distinct materials separated by a zone with gradual transition from 316L to V4E. Microstructure and local mechanical properties were evaluated in the manufactured samples. Optical Microscopy, Scanning Electron Microscopy and EDX on the polished cross-sections show a gradual microstructural and compositional transition from characteristic 316L at the bottom of the specimens to the tool steel towards the top. Nanoindentation experiments confirmed a consequent gradient in hardness and elastic modulus, which gradually increase towards the top surface of the samples. The achieved results provide great possibilities to tailor the composition, microstructure, mechanical properties, and wear resistance by combining different powders in the powder bed AM technology. Potential applications include the tooling industry, where hard and wear-resistant materials are demanded on the surface with tougher and more ductile materials in the core of the tool.

Abstract: The influence of the processing route on the microstructure characteristics and mechanical properties of high-entropy carbides was investigated. The experimental materials were prepared by a combination of ball milling and spark plasma sintering at the temperature of 2100 °C. The effect of sintering time (5 min, 10 min, and 20 min) on the microstructure development and properties of the investigated systems has been studied. The microstructure analysis was performed using scanning electron microscopy + EDAX analysis on the polished surfaces. Nanoindentation was used for the nano-hardness and Young’s modulus measurements. Micro-hardness was measured using Vickers method and indentation method using a Vickers indenter was used to determine the indentation fracture resistance – fracture toughness. The measured grain size values were in the range from 5 µm to 14 µm. The nano-hardness values changed from 36 GPa to 39 GPa and the indentation modulus of elasticity from 558 GPa to 577 GPa, respectively. The measured micro-hardness values were in the range from 18.93 GPa to 21.95 GPa and the indentation fracture resistance changed from 2.70 MPa.m^1/2 to 3.50 MPa.m^1/2, respectively.

Abstract: Co-28Cr-6Mo alloy (ASTM F75) is widely used in different biomedical applications (dental devices, orthopedic implants, etc.). Casting and metal forming are the two conventional technologies for the fabrication of this alloy. Recently, additive manufacturing has also been adopted. Due to the peculiarities of this technological process, 3D-printed alloys differ from traditionally manufactured alloys in their structure and properties. In the present work, the features of selective laser melted Co-28Cr-6Mo alloy were studied in comparison with its wrought analogue. The study included microstructural characterization (optical and electron scanning microscopy), nanoindentation, and tribological testing. It was shown that the SLM alloy featured the “fish-scale” structure, characteristic of additively fabricated alloys. This structure was composed of fine columnar dendrites. SLM Co-28Cr-6Mo was found equivalent or superior to the wrought alloy in terms of properties, such as hardness, elastic modulus and tribological behavior that makes SLM Co-28Cr-6Mo a promising candidate for implant applications.

Abstract: The low weight and high strength ratio of titanium alloy make TiO₂ nanotubes ideal for biomedical applications. Increasing the oxidation process has recently been studied as a means of encouraging the formation of nanotubes. This study synthesizes the TiO₂ nanotubes with different input voltages. There was an increase in nanotube growth rate as a result of de-ionized water in the electrolyte, as well as an increase in the input potential, which favours oxidation. An analysis of the surface morphology suggests that rib structures were generated in the area where corrosion results were greatly elevated. X-ray diffraction and nanoindentation were used to study phase transformations and nanohardness respectively.