Papers by Keyword: Nanoindentation

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.

Abstract: Now a days, extensive research has been attracted by the α + β based Ti alloys in biomedical applications due to their low elastic modulus and high strength properties. In order to explore the performance of Ti6AlxMo based alloys, Ti6Al with different amount of Mo-based samples were fabricated by powder metallurgy technique. The mechanical properties of the samples such as elastic energy, total energy and elastic recovery were studied through nanoindentation tests. Designed alloys exhibit elastic recovery values in the range of 25.4% - 33.7% which is higher than commonly used biomaterial such as CP Ti therefore it has good impact resistance properties. Ti6Al15Mo alloy with dominant β phase microstructure shows a high elastic energy as well as elastic recovery values which makes it more advantageous than CP Ti for load bearing implant applications.

Abstract: The influence of Al/Ti and Al/Cr ratios on the structural, mechanical and tribological properties of AlTiSiN and AlCrSiN coatings, deposited by the cathodic arc evaporation PVD method at a temperature of 400°C, was investigated. The remains of the original AlSiN hexagonal phase were observed in the obtained coatings as well as the crystallites of cubic TiN and CrN, respectively. XPS analysis assumes the presence of a substoichiometric SiN. The addition of 11 at.% Ti or 13 at.% Cr in AlSiN led to an increase in both the coating’s resistance to plastic deformation and the plasticity index. The addition of 13 at.% and 24 at.% Cr to the AlSiN coating structure resulted in a decrease in the average coefficient of friction with 18% and 36% against a counterpart of Al₂O₃, respectively, and with 36% for both concentration against steel ball counterpart. The addition of Ti have no influence on the values of the coefficient of friction at using ceramic counterpart, while at steel counterpart decreased it up to 30%. Both element change the abrasion effect of the coating.Keywords: AlCrSiN; AlTiSiN; Cathodic Arc Deposition; Tribological Behaviour; Abrasion Resistance; Nanoindentation

Abstract: Al₂O₃, Al₂O₃-10%CeO₂ and Al₂O₃ – 20% CeO₂ coatings were deposited on Mg AZ91 alloy by High Velocity Oxy Fuel (HVOF) process. The microstructure of deposited coatings was characterized by scanning electron microscopy and x-ray diffraction. Nano-indentation tests were performed on deposited coatings to determine its load bearing capacity and elastic recovery. Al₂O₃ coatings exhibited coarse grain structure with porous sites. While addition of CeO₂ promoted grain refinement in the coatings. A load of 100mN was applied on all the samples for nano-indentation test. Coating with 20%CeO₂ exhibited maximum load bearing capacity of 98.7mN with elastic recovery displacement of 1000 nm.

Abstract: This study discussed the effect of blast exposure distance of lead-free solder on micromechanical properties. Sn-Ag-Cu solder samples were exposed to 1000 g of Plastic Explosive. The soldered samples were placed at a distance of 1 m, 2 m and 4 m distance from the blast source. In order to study micromechanical properties in localized and more details, the nanoindentation approach was used. The indentation was performed at the center of the solder to examine the hardness and reduced modulus properties. The load-depth curve of indentation for 1 m distance from the blast source has apparent the discontinuity during loading as compared to the control sample. The hardness value increased as the distance from the blast source increased. The shortest distance from the blast source gives a high impact on the degradation of hardness properties as compared to others. This result is important in assessing the effect of exposure distance from the blast source.