Microstructure evolution, mechanical properties, and fractography of AA7068/ Si3N4 nanocomposite fabricated thorough ultrasonic-assisted stir casting advanced with bottom pouring technique

Ceramic particulate embedded aluminum metal matrix nanocomposites (AMNCs) possess superior mechanical and surface properties and lightweight features. AMNCs are a suitable replacement of traditional material, i.e., steel, to make automotive parts. The current work deals with developing Si3N4 strengthened high strength AA7068 nanocomposites via novel ultrasonic-assisted stir casting method advanced with bottom pouring setup in the proportion of 0.5, 1.0, 1.5, and 2 wt.%. Planetary ball milling was performed on a mixture of AA7068 powder and Si3N4 (in the proportion of 3:1) before incorporation in aluminum alloy melt to avoid rejection of fine particles. Finite element scanning electron microscope (FESEM), Energy dispersive spectroscopy (EDS), X-Ray diffraction (XRD), and Elemental mapping techniques were used in the microstructural investigation. Significant grain refinement was observed with increasing reinforcing content, whereas agglomeration was found at higher weight %. Hardness, Tensile strength, ductility, porosity content, compressive strength, and impact energy were also examined of pure alloy and each composite. Improvement of 72.71%, 50.07%, and 27.41 % was noticed in hardness value, tensile strength, and compressive strength, respectively, at 1.5 weight % compared to base alloy because of various strengthening mechanisms. These properties are decreased at 2wt.% due to severe agglomeration. In contrast, nanocomposite's ductility and impact strength continuously decrease compared to monolithic AA7068. Fracture analysis shows the ductile and mixed failure mode in alloy and nanocomposites.

Mechanical and Microstructural Anisotropy of Laser Powder Bed Fusion 316L Stainless Steel

This paper aims at an in-depth and comprehensive analysis of mechanical and microstructural properties of AISI 316L austenitic stainless steel (W. Nr. 1.4404, CL20ES) produced by laser powder bed fusion (LPBF) additive manufacturing (AM) technology. The experiment in its first part includes an extensive study of the anisotropy of mechanical and microstructural properties in relation to the built orientation and the direction of loading, which showed significant differences in tensile properties among samples. The second part of the experiment is devoted to the influence of the process parameter focus level (FL) on mechanical properties, where a 48% increase in notched toughness was recorded when the level of laser focus was identical to the level of melting. The FL parameter is not normally considered a process parameter; however, it can be intentionally changed in the service settings of the machine or by incorrect machine repair and maintenance. Evaluation of mechanical and microstructural properties was performed using the tensile test, Charpy impact test, Brinell hardness measurement, microhardness matrix measurement, porosity analysis, scanning electron microscopy (SEM), and optical microscopy. Across the whole spectrum of samples, performed analysis confirmed the high quality of LPBF additive manufactured material, which can be compared with conventionally produced material. A very low level of porosity in the range of 0.036 to 0.103% was found. Microstructural investigation of solution annealed (1070 °C) tensile test samples showed an outstanding tendency to recrystallization, grain polygonization, annealing twins formation, and even distribution of carbides in solid solution.

The Effect of Salinized Nano ZrO2 Particles on the Microstructure, Hardness, and Wear Behavior of Acrylic Denture Tooth Nanocomposite

The wear of acrylic denture teeth is a serious problem that can change the vertical dimensions of dentures. This study evaluates the effect of adding salinized nano ZrO2 particles on the microstructure, hardness, and wear resistance of acrylic denture teeth. Heat polymerizing polymethyl methacrylate resin was mixed with salinized ZrO2 at concentrations of 5 wt% and 10 wt%. Acrylic resin specimens without filler addition were used as a control group. SEM/EDS analyses were performed and the Vickers’ hardness was evaluated. Two-body wear testing was performed using a chewing simulator with a human enamel antagonist. After subjecting the samples to 37,500 cycles, both height loss and weight loss were used to evaluate the wear behavior. The microstructural investigation of the reinforced-denture teeth indicates sound nanocomposite preparation using the applied regime without porosity or macro defects. The addition of zirconium oxide nanofillers to PMMA at both 5% and 10% increased the microhardness, with values of up to 49.7 HV. The wear mechanism in the acrylic base material without nanoparticle addition was found to be fatigue wear; a high density of microcracks were found. The addition of 5 wt% ZrO2 improved the wear resistance. Increasing the nanoparticles to 10 wt% ZrO2 further improved the wear resistance, with no microcracks found.

Low Cycle Fatigue Performance of Additively Processed and Heat-Treated Ti-6Al-7Nb Alloy for Biomedical Applications

In biomedical engineering, laser powder bed fusion is an advanced manufacturing technology, which enables, for example, the production of patient-customized implants with complex geometries. Ti-6Al-7Nb shows promising improvements, especially regarding biocompatibility, compared with other titanium alloys. The biocompatible features are investigated employing cytocompatibility and antibacterial examinations on Al2O3-blasted and untreated surfaces. The mechanical properties of additively manufactured Ti-6Al-7Nb are evaluated in as-built and heat-treated conditions. Recrystallization annealing (925 °C for 4 h), β annealing (1050 °C for 2 h), as well as stress relieving (600 °C for 4 h) are applied. For microstructural investigation, scanning and transmission electron microscopy are performed. The different microstructures and the mechanical properties are compared. Mechanical behavior is determined based on quasi-static tensile tests and strain-controlled low cycle fatigue tests with total strain amplitudes εA of 0.35%, 0.5%, and 0.8%. The as-built and stress-relieved conditions meet the mechanical demands for the tensile properties of the international standard ISO 5832-11. Based on the Coffin–Manson–Basquin relation, fatigue strength and ductility coefficients, as well as exponents, are determined to examine fatigue life for the different conditions. The stress-relieved condition exhibits, overall, the best properties regarding monotonic tensile and cyclic fatigue behavior.

Optimization of a Solution Treatment in the Al-Cu-Mg-Ag Alloy via a Microstructural Investigation

We investigated the effect of solution temperature (Tsol. = 440–530 °C) on the mechanical properties of the Al–3.4Cu–0.34Mg–0.3Mn–0.17Ag alloy, finding that the investigated Al alloy showed the highest mechanical strength of σUTS = ~329 MPa at a Tsol. value of 470 °C. The microstructural investigation demonstrates that the mechanical properties for different Tsol. values stem from grain growth, precipitation hardening, and the formation of large particles at the grain boundaries. On the basis of Tsol. = 470 °C, the effect of each microstructural evolution is significantly different on the mechanical properties. In this study, the relationships between the microstructural evolution and the mechanical properties were investigated with respect to different values of Tsol.

Microstructure and phase composition of bronze Montefortino helmets discovered Mediterranean seabed to explain an unusual corrosion

Two Monterfortino helmets, recovered in the Mediterranean seabed, show unusual features with respect to the more common helmets of the same period and found in underwater environments. Hence, they were investigated by a multi-analytical approach, which allowed us to identify the compounds constituting the helmets and to make some considerations about their metallurgy, although all the metal was converted to degradation products. The helmets, originally made in bronze, have maintained their original shape because of copper sulphides formation. The observed differences in composition between the two helmets were attributed to the position modification, of one of them, into the seabed along centuries. For the first time, a microstructural investigation permits to reconstruct the history of the aging processes involved in the total oxidation of roman bronze helmet metal.