Papers by Keyword: Vickers Microhardness

Abstract: In the present study, the influence of stationary shoulder friction stir processing (SSFSP) tool wear on the processed surface was investigated. SSFSP is a solid-state process that uses a rotating tool plunged in the material to promote microstructure modification, mainly grain refinement, on the workpiece without melting the material itself. It differs from conventional Friction Stir Processing (FSP) since in the SSFSP the tool shoulder does not rotate and simply slides on the surface. The workpiece processed with SSFSP shows a smoother surface without shoulder marks, and with smaller flash than conventional FSP. The tool wear could slightly change the profile of the shoulder and affects process soundness. SSFSP testing made up of 2880 experiments, each one with a path length of 50 mm, was realized on AA 6082 T6 sheets with 3.0 mm thickness using 1500 rpm tool rotation speed and 300 mm/min welding speed. Optical and confocal microscopy analysis and Vickers micro hardness measurements allowed putting in evidence the characteristics of the processed surfaces and their modifications as a function of tool wear.

Abstract: Ultrahigh molecular weight polyethylene (UHMWPE) is used as a key component of total joint replacements (TJR) and its mechanical performance is one of the factors influencing TJR lifetime. Micromechanical properties of three model UHMWPE samples with different molecular weights were evaluated from both non-instrumented and instrumented microindentation hardness testing. The properties were correlated with molecular and supermolecular structure of the samples. We have demonstrated that molecular weight influenced the final micromechanical properties mostly indirectly – it changed the overall crystallinity, which strongly correlated with microhardness, indentation modulus, and also with the elastic part of the indentation work. Only microcreep was influenced predominantly by amorphous phase, in which the higher molecular weight resulted in higher amount of entanglements and slightly higher creep resistance.

Abstract: The present work has investigated precipitation behavior in an Al-17at%Mg alloy isothermally aged at 373K and 473K, by means of Vickers micro-hardness tests, DSC measurements and TEM observations. The present DSC measurements have revealed that the metastable β′-phase precipitates mainly contributed to precipitation hardening of this alloy in isothermal aging at 373K and 473K. The TEM observations have confirmed that the β ' phase precipitates were formed in the {001} planes of Al matrices in platelet shapes.

Abstract: The effect of hydroxyapatite (HA) particle composition on the microstructure, Vickers microhardness, relative density and phases of β titanium nanocomposite prepared by powder metallurgy method were investigated experimentally. Hydroxyapatite particle in the range of 5 wt% to 25 wt% were mixed with Ti-35Nb-2.5Sn particles. The samples were pressed at 111 MPa and sintered at 900°C for 2 hours in a vacuum furnace. Result shows that by increasing the hydroxyapatite composition from 5 wt% to 15 wt %, the relative density and Vickers mirohardness increased. Phase analysis of raw materials was studied by XRD analysis and microstructure of composite by SEM.

Abstract: Ti-50.8%Ni shape memory alloy was subjected to four passes equal channel angular pressing (ECAP) with angle 120◦ via route B_c at 450°C. The deformation homogeneity was analyzed on planes across the thickness of the deformed sample by Deform-3D software. Two methods were used from the simulation model to quantify deformation homogeneity , including strain standard deviation (SSD) and inhomogeneity index (C_i). In addition, The deformation heterogeneity of ECAP was analyzed experimentally from microhardness inhomogeneity index ( HII) based on Vickers microhardness test results.In the present work, C_i and SSD had been testified to detect which one could give better results experimentally. It was demonstrated that the simulation results of SSD measurements were in good agreement with experimental results .

Abstract: Al7075 and Al₂O₃ powders were synthesized via high-energy ball mill for 15 h. Al7075 powders were mixed with 10 vol. % Al₂O₃, compacted by cold uniaxial compaction at 400 MPa. The green pellets were degassed at 350 oC for 30 min, and then sintered in the temperature of 600 oC under argon atmosphere for 120 min. It was shown that better density, vickers micro hardness and corrosion resistance were achieved due to refinement of grain size. HRTEM micrographs demonstrated a uniform distribution of Al₂O₃ particles in aluminium alloy and equilibrium η (MgZn₂) precipitates along the grain boundaries.

Abstract: In this study, annealed AL-6063 alloy was processed by the Equal Channel Angular Extrusion (ECAE) up to 6 passes at a temperature of 200^°c following route A with a constant ram speed of 30 mm/min through a die angle of 90^° between the die channels. The influence of ECAE processing on the evolution of microhardness in the material was studied using Vickers microhardness testing. The detailed analysis was carried out on the samples of as-received, one, two, three, four, five, and six pass conditions. The grain diameter reduced from 45μm to 2.8 μm after 6 passes of ECAE. The results indicated around 90% increase in Microhardness after 5 passes. Hardness of the inner surface where the billet was under compression was slightly higher than that of the mid-surface.

Abstract: This work studies the effect of a post-weld heat treatment (PWHT) on the mechanical and microstructure properties of an AA6061 sample welded using Tungsten Inert Gas (TIG) method. TIG method is comparatively flexible and has good economy. The welded samples were divided into as-welded and PWHTs samples. The PWHTs samples were solution heat treatment, water quenching and artificial aging. Both welded samples were cut according to the ASTM E8M-04 standard to obtain the tensile strength and the elongation of the joints. The failure pattern of the tensile tested specimens was analysed using scanning electron microscopy (SEM). A Vickers microhardness testing machine was used to measure the hardness across the joints. From the results, the PWHTs were able to enhance the mechanical properties and microstructure characteristics of the AA6061 joints welded by the TIG method.

Abstract: In this work, the mechanical properties, such as Vickers microhardness H_v, fracture toughness K_c, yield strength σ_v and brittleness index B_i, of <0001> oriented 6H-SiC crystal are systematically evaluated using a microindentation technique under 0.1-2 kg applied load. It is found the H_v is decreased as the applied load is increased which is mainly attributed to the effect of indenter penetration. The H_v value can be effectively presumed by Kicks law and the Meyers index n is determined to be 1.73. However, the K_c value is measured nearly a constant (~0.148 MPa.m^1/2) which reveals the toughness of 6H-SiC₍₀₀₀₁₎ crystal is much weaker than those of Si₍₁₀₀₎ and GaAs₍₁₀₀₎ crystals. The variation of σ_v to the load is similar to that of H_v. The brittleness index B_i also exhibits deceasing tendency as the applied load is added.

Abstract: The present work investigated precipitation behavior in an Al-17at%Mg alloy isothermally aged at 473K, by means of Vickers microhardness tests, DSC measurements and TEM observations. A quantitative analysis of DSC measurements revealed that the metastable β-phase precipitates mainly contribute to precipitation hardening of this alloy aged at 473K. The present STEM-EDX observations confirmed that the metastable β-phase precipitate has a layer structure with a composition similar to the stable phase (Al₃Mg₂)_.