Papers by Keyword: Instrumented Indentation

Abstract: Metallic infrastructures suffer deterioration during their service life. When the metallic component reaches a limit level of damage, it is replaced by a new one. This generates high costs of maintenance and residues management. However, the deposition of coatings by the cold spray technique would allow the repairing of these damaged components and extent their service life. In this work the effect of the spraying temperature and pressure on the mechanical behavior of 316L stainless steel coatings deposited on carbon steel by the cold-spray technique has been analyzed. Spraying gas temperatures of 800oC, 900oC and 1000oC combined with gas pressures of 50 and 60 bars were selected. Indentation stress-strain curves were determined for each spraying conditions. The results showed a significant effect of both spraying parameters on the work hardening of the coatings.

Abstract: Ti6Al4V alloy is widely used for aeronautical components due to a special combination of high mechanical properties, low density and good corrosion resistance at high temperature. These components are usually damaged by particles impacts during their operating time. When the reliability of these components is compromised, they are replaced with the consequent cost of material and time. Spraying coatings on the damaged surface could reveal as an alternative process to repair these components, increasing their operating life. Traditionally, thermal spray processes are used to repair the aeronautical components. However, the coatings produced by these processes are characterized by high residual stresses, porosity and oxidation. The cold spray technique is revealed as a promising spraying alternative due to the characteristic low temperature of the process. Consequently, residual stresses, oxidation, crack formation, phase transformations and microstructural changes are minimized. In this work, a cold spray technique was used to generate Ti6Al4V coatings onto a bulk of the same material. Three different spraying conditions were studied: Ti6Al4V coatings sprayed at 800oC; Ti6Al4V coatings sprayed at 1100oC; and Ti6Al4V coatings sprayed at 1100oC with a subsequent heat treatment: The wear resistance of these coatings was investigated by solid particle erosion and micro-scratch tests. The wear behaviour was determined under several wear tests conditions. Additionally, instrumented indentation tests were carried out on the coatings to determine their mechanical response. The wear mechanisms of the coatings were identified and compared to their microstructure and mechanical properties.

Abstract: The effect of processing conditions on microstructure and mechanical properties of Fe-Al-Si powders was studied by means of scanning electron microscopy, X-ray diffraction and nanoindentation. Fe-Al-Si alloy powder was prepared from pure elemental powders by mechanical alloying. Microstructure and mechanical properties of powders were characterized after various durations of mechanical alloying. Special sample preparation technique was developed allowing to characterize the properties of individual powder particles after each step of processing in a planetary ball mill. This step-by-step characterization allowed to find the optimum conditions for subsequent spark plasma sintering.

Abstract: The mechanical properties investigation results obtained by tension and indentation tests of RIP (resin impregnated paper) electric insulator are presented. Tension and indentation tests of the RIP electric insulation material in wide temperature range are conducted. The common relations between strength and temperature as well as between hardness and temperature for the RIP electric insulation are established. The ratio of ultimate tensile strength to Brinell hardness is performed to be constant (about 1/3) irrespective of temperature, that means a possibility of the RIP electric insulation mechanical properties evaluation by the instrumented indentation test.

Abstract: Young’s modulus of alumina particles reinforced pure Al-matrix composite is characterized by different methods: the pulse-echo ultrasound method, static three point bending, resonant bending and continuous multicycle measurement by instrumented indentation. Dependency of apparent Young’s modulus on loading amplitude was observed and attributed to the local mechanical properties of both phases, especially to the development of internal damage (local plasticity and particle cracking).

Abstract: Calibration of Berkovich indenter area function was performed on materials with different elastic-plastic behavior resulting in pile-up and sink-in, respectively. Experimentally obtained results were compared with the results obtained by the application of theoretical area function. The values of Young’s modulus and hardness were significantly affected by the calibration function used. Since the effects of pile-up and sink-in are already included in the used area function, this simple method can lead to more accurate results of Young’s modulus and hardness measurements.

Abstract: Mechanical properties of two stainless steels (AISI 316L and AISI 410) processed by spark plasma sintering (SPS) were evaluated by four different types of indentation-based tests: hardness mapping, evaluation of indentation stress-strain curves, instrumented indentation and bonded-interface technique. Obtained results showed that the used combination of relatively simple experiments may provide a deeper understanding of mechanical behavior of materials prepared by SPS.

Abstract: NiTi shape memory alloy thin film sputter-deposited on a large scale silicon wafer was characterized by means of instrumented (depth-sensing) indentation technique. Thickness of deposited thin film was measured by calotest device. Microstructure of thin film was observed using differential interference (Nomarski) contrast. It was shown that the local mechanical properties are different in areas containing different phases (austenite and martensite) according to different deposition conditions (kinetic energy of deposited atoms when impacting the substrate surface).

Abstract: This research presents a developed simple analytical model to estimate the residual stress state and its magnitude in plasma sprayed coating based on the Vickers instrumented indentation results. By means of energy method during a Vickers indentation cycle, it is convenient to compute the stress state and its magnitude without any comparison of load-displacement curves of stress-free reference material. Computed results show that the residual stress in plasma sprayed Al-Si coating mainly ranges between 23-32 MPa in tensile state, which is consistent with the measurement of residual stress in as-sprayed NiCrAlY coating using neutron diffraction.

Abstract: In this study, a method based on finite element (FE) simulation was proposed for characterizing simultaneously residual stresses (RS) and accumulated plastic strain (PP) induced by shot peening process. Through a series of simulations of instrumented indentation, contour plots of several parameters, as maximum load, contact hardness and contact stiffness, were computed. By superposing them pair-wisely, RS and PP mixed together could be characterized simultaneously. In order to verify the method, several simulations with different combinations of RS and PP were performed. Results showed that the method is promising but remains to be tested on experimental acquisitions.