Papers by Keyword: Micro Indentation

Abstract: In this research, the mechanical behavior of a multi-pass nickel-aluminum bronze alloy weld joint is investigated. Macro-tensile testing shows the mechanical behavior difference of the weld and base materials. Micro indentation data is applied to calculate the local mechanical properties in a multi-pass weld and base materials. The indentation loading-unloading cycle and stress-strain calculation model are introduced in the paper. It shows that the micro indentation results are in good agreement with the macro-tensile test data. Both the micro structure and uncertainties within the analysis model affect the discrepancy of two testing methods.

Abstract: Active metal brazing of a new high thermal conductivity SiC-polycrystalline fiber-bonded ceramic (SA-Tyrannohex™) has been conducted using a Ti-containing Ag-Cu active braze alloy (Ticusil®). The brazed joints were characterized using SEM-EDS and Knoop hardness scans across the interfaces. The effects of fiber orientation in the composite on the microstructure, elemental composition, and microhardness are presented. Results show that this material can be successfully joined using judiciously selected off-the shelf active braze alloys to yield metallurgically sound joints possessing high integrity.

Abstract: The recently developed indentation techniques are awfully advantageous as they are performing in determination of hardness and local elasticity modulus for particular conditions; also they are being able to deal with small sample sizes. This technique is well used to characterize mechanical properties as hardness, elasticity and creep for coating thin layers. Experimental comparison of common nano and micro scales for hardness evaluation has been performed on metal samples and discussed in details in the literature review [1-3]. In fact, it was well detailed that instrumented indentation was found advantageous in both repeatability and a number of measured parameters over classical hardness methods for different materials. As far as thin materials are being very used in various industrial fields, the mechanical characterization moves to micro level scale, with micro-indentation tests of thin films and from Newton -to- micro Newton for loading conditions. A big step forward has been reached for load-depth monitoring during loading and unloading in indentation cycle. Nowadays, hardness and Young’s modulus can be easily defined using Oliver-Pharr [4-5] equations based on a micro scratch test of a very thin film. In this paper an experimental study is conducted and has been validated with a numerical FE model based on a micro indentation test of a metal matrix composite material 110A, used in aeronautic applications.

Abstract: Brittle cracking in a residual impression can be observed during micro indentation testing of brittle materials. The formation of these cracks in the residual impression depends upon the nature of materials, geometry of indenter, testing load, dwell time and depth of penetration. The area adjacent to the cracks may be appearing either as raised up or sunk down at the edges. This plastic residual impression can be used to obtain various elastic and plastic properties of brittle materials such as shear strength, fracture toughness, crack resistance, surface strength, etc. In present work Soda Lime Glass was studied by micro indentation test carried on Vickers hardness testing method using diamond pyramid indenter. Indentations were obtained on glass using different loads with different dwell times. These indentations generated micro cracks on surface. It was observed that on low values of load no visible cracks were found but on increasing the load the nucleation of crack started its critical value. On further increasing the load the steady growth of crack was observed. The dwell time also affects the propagation of the crack, as the dwell time increased the crack propagation shifts toward higher values. Results were analyzed in the form of load versus crack size for different dwell times focusing on the onset of crack propagation. The results obtained during study were applied to relate various elastic and plastic properties of Soda Lime Glass.

Abstract: A hybrid experimental-numerical approach, which combines microindentation experiments (where we measure the diagonal of the residual imprint after unloading) and numerical simulations by means of the finite-element method has been developed. The investigated materials in the present work are electrochemically deposited on brass substrates chromium and copper films with known thickness and unknown mechanical properties. Mechanical properties of the brass (CuZn36) substrate are known. Vickers’ microindentation experiments were carried out on the films and as a result the experimental load-displacement curves were obtained. After that the process of microindentation was modelled numerically by means of the finite-element method. Numerically obtained load-displacement curves were compared with the experimental curves. The results show good coincidence between numerical and experimental curves. Additionally it was realized nanoindentation experiment of thin copper film and these two methods (nanoindentation experiment and hybrid experimental-numerical method which combines experiment of microindentation and numerical simulations) for determination of mechanival properties of thin copper films were compared. Results obtained by means of the afore-mentioned two methods almost coincide but the second method is cheaper and gives more information about material properties of the film than the first method. It is shown that the second method is preferable to determine the mechanical properties of thin metal films.

Abstract: This study evaluates the fracture toughness of Fe2B boride layers formed by the paste boriding thermochemical process on an AISI 1018 steel surface. The samples were placed in acrylic molds for the impregnation of boron carbide paste with thickness of 4mm over the sample surfaces to produce the diffusion into the steel. The aforementioned treatment considered one temperature, T= 1273 K, and three exposure times t=5, 6 and 8 h. Later, the borided samples were prepared metallographically to determine the mean values of the layer thicknesses and to produce Vickers microindentations at 45 m from the surface, applying four loads (1.9, 2.9, 4.9 and 9.8 N). The microcracks generated at the corners of the Vickers microindentation were considered as experimental parameters, which are introduced into two Palmqvist cracks models to determine their corresponding fracture toughness KC. As a result, the experimental parameters, such as exposure time and applied load are compared with the resulting fracture toughness of the borided phase.

Abstract: Layered structures of dense porcelain/porous alumina and dense porcelain/porcelainalumina/ porous alumina are designed and their crack propagation behaviors are investigated. As a substrate, the porous alumina, which is prepared by a gel-casting process using the binary slip of alumina powder and PMMA spherical micro-bead, is dried at room temperature for 24 h and then sintered at 1600
for 2 h. Porcelain is coated on the porous alumina substrate and then re-sintered at 987
. Bi- and tri-layered structures are produced by the different dwell times (2 min, 10 min) at re-sintering temperature. There is no delaminating or cracks observed after re-sintering the layered samples. The crack propagation behaviors in the bi- and tri-layered structures are evaluated by micro-indentation. The indentation cracks do not propagate into the porous alumina through interface (porosity; 36~62%) except for another one (porosity; 70%) in the bi-layered samples. In the case of the high porosity bi-layered sample (porosity; 70%), cracks are scattered along the 3-D open-pore channels. However, cracks do not propagate through the interface in the tri-layered samples with a porcelain-alumina buffer layer, because the porcelain-alumina buffer layer plays an important part such as a barrier layer in crack propagation.

Abstract: Berkovich micro-indentation tests with different loading rates have been performed on the ball grid array solder joint with a Pb-free solder, Sn-4.0Ag-0.5Cu alloy. The resulting indentation load-depth curves are rate dependent and have varying creep penetration depths during the same hold time. Creep indentation hardness and rate sensitivity have been defined from the concept of “work of indentation”. The rate sensitivity of BGA solder joint is 0.0574.

Abstract: The grain growth and mechanical properties of nanograined bulk Fe-25at%Ni alloy prepared by an inert gas condensation and in-situ warm consolidation technique were investigated. About 43% high temperature face-centered-cubic (FCC) phase and 57% low temperature body-centered-cubic (BCC) phase were observed in the sample at room temperature, which was significantly different from that of the corresponding conventional coarse-grained alloy. The in-situ X-ray diffraction results show that the start and the finish temperature of BCC to FCC phase transformation are 450°C and 600°C, respectively. The isothermal grain growth exponent n from t k D D n n ¢ = − 1 0 1 for nanograined single FCC phase Fe-25at%Ni alloy is 0.38 at 750 °C . The mechanical properties changing with the grain size were studied by means of microindentation test.