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A powder-processed hot-extruded high-performance Mg-0.5 wt.% Cu alloy has been developed by solid-state diffusion of elemental copper into commercially pure magnesium powder. Copper, in nanoparticle form, was blended to form a dry-coat layer on micrometer-size magnesium particles, which subsequently homogeneously diffused, forming a single-phase solid solution during the sintering process. Copper as a solute atom did not act as a grain refiner. Investigation of the mechanical properties revealed that the strength properties of commercially pure magnesium were significantly improved (macrohardness by 32.5%, microhardness by 42.7%, tensile yield strength by 114%, tensile strength by 69%, compressive yield strength by 46%, and compressive strength by 48%) due to the dissolution of copper as solute atoms. The ductility of the magnesium suffered marginal loss despite the fracture mode being ductile, which was due to decohesion at the magnesium interparticle boundaries induced by the relatively higher copper concentration. [ABSTRACT FROM AUTHOR]

A magnesium-based metal matrix composite incorporated with 2.5 wt.% TiB2 has been fabricated using spark plasma sintering for the first time. The Taguchi design approach was used to analyze the significant influences of sintering parameters such as the temperature, pressure, and time on the physical and mechanical properties of Mg-based composites. Analysis of variance was used to investigate the effect of each sintering parameter. X-ray diffraction and field-emission scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy were used for structure and microstructure analysis. Rockwell hardness (HR) and Vickers hardness (HV) were used to evaluate the mechanical properties of the composite. The results showed that, in the case of microhardness, all the sintering parameters were controlling factors, and the sintering temperature was the most significant factor. The maximum values obtained for the densification, Rockwell hardness, and Vickers hardness were 100%, 62.18 HR, and 58.6 HV, respectively. [ABSTRACT FROM AUTHOR]

Al 2 O 3 /SiC and Al 2 O 3 –CNT nanocomposites have been fabricated by spark plasma sintering (SPS). Thermal properties (e.g., thermal diffusivity, specific heat capacity, and thermal conductivity) of the nanocomposites have been investigated at room temperature and at elevated temperatures for different nanophase contents and SPS temperatures. The field emission scanning electron microscopy with energy-dispersive spectroscopy, and transmission electron microscopy has been used to investigate the microstructure of nanocomposites. The thermal properties of the nanocomposites as well as those of pure alumina were investigated using direct measurement methods. The results showed that a maximum thermal conductivity of 34 W/m K was achieved on alumina after SPS at 1400 ∘ C , while alumina containing 5 wt% SiC and 1 wt% MWCNTs nanocomposites have maximum thermal conductivities of 24.15 W/m K and 29.62 W/m K, respectively, at a SPS temperature of 1500 ∘ C . The thermal properties of alumina decrease with the addition of the SiC and MWCNT nanophases, increasing its suitability for electro-discharge machining and fabrication of affordable products with intricate parts. The thermal behaviors of pure alumina and of the nanocomposites at elevated temperatures showed a decrease in the thermal diffusivity and thermal conductivity of alumina–SiC nanocomposites with increasing measurement temperature, while the specific heat capacity increased with increasing measuring temperature. The measurement properties correlated with the microstructure, and various transport phenomena were clearly explained. [ABSTRACT FROM AUTHOR]

A biocompatible dicalcium phosphate dihydrate (DCPD) brushite coating of flake-like crystals was developed on AZ91D and AZ31 magnesium (Mg) surfaces to control and slow down the rapid degradation rate of the substrates. The electrochemical behavior of the DCPD-coated substrates was examined in a simulated body fluid (SBF) with uncoated substrates as the control. Fabrication of the coating was achieved via chemical immersion technique by modifying the surfaces with Ca(NO3)2·4H2O and KH2PO4 in addition to heat treatment. The morphology of the DCPD coating is uniform and dense with a flake-like crystal structure. After in vitro tests, the DCPD coating would have exhibited excellent corrosion resistance with more biomineralization of the active calcium phosphate (CaP). Moreover, the DCPD coating induced CaP formation after immersion in the SBF, indicating excellent bioactivity upon increasing the coating. Hence, the two-step chemical treatment enhances the bioactivity of DCPD coatings on Mg alloys, making them better implant materials. [ABSTRACT FROM AUTHOR]

The effect of thermal treatments on the microstructure, hardness, and electrochemical performance in a simulated body fluid were studied for the newly developed (β + α) Ti20Nb13Zr alloy (TNZ) for biomedical applications. The alloy was heat-treated for 1 h at 900 °C and then cooled at different cooling rates. Then, the solution-treated samples were aged at 400, 500, or 600 °C for 5 h. The phase evolution and microstructure of the treated alloy were examined using XRD and SEM/EDX analysis. The mechanical properties were assessed using microindentation. The surface protection performance against corrosion was assessed by potentiodynamic polarization and electrochemical impedance spectroscopic analysis. The obtained results showed that the wide range of microstructure with varied volume fraction and morphology of β and α were obtained with different heat treatment conditions. The different phases' sizes and distributions influenced the microstructure obtained during the heat treatment, thereby affecting the mechanical properties. The corrosion performance significantly altered with variations in the microstructure of the TNZ alloy as a result of the different thermal treatments. The heat treatment of TNZ conferred enhanced combination of mechanical and corrosion protection compared to that of the commercial Ti6Al4V alloy. [ABSTRACT FROM AUTHOR]

Despite the widespread application of Ti alloy in the biomedical field, surface treatments are typically applied to improve its resistance to corrosion and wear. A newly developed biomedical Ti-20Nb-13Zr at.% alloy (TNZ) was laser-treated in nitrogen environment to improve its surface characteristics with corrosion protection performance. Surface modification of the alloy by laser was performed through a Nd:YAG laser. The structural and surface morphological alterations in the laser nitrided layer were investigated by XRD and a FE-SEM. The mechanical properties have been evaluated using nanoindentation for laser nitride and as-received samples. The corrosion protection behavior was estimated using electrochemical corrosion analysis in a physiological medium (SBF). The obtained results revealed the production of a dense and compact film of TiN fine grains (micro-/nanosize) with 9.1 µm below the surface. The mechanical assessment results indicated an improvement in the modulus of elasticity, hardness, and resistance of the formed TiN layer to plastic deformation. The electrochemical analysis exhibited that the surface protection performance of the laser nitrided TNZ substrates in the SBF could be considerably enhanced compared to that of the as-received alloy due to the presence of fine grains in the TiN layer resulting from laser nitriding. Furthermore, the untreated and treated Ti-20Nb-13Zr alloy exhibited higher corrosion resistance than the CpTi and Ti6Al4V commercial alloys. The improvements in the surface hardness and corrosion properties of Ti alloy in a simulated body obtained using laser nitriding make this approach a suitable candidate for enhancing the properties of biomaterials. [ABSTRACT FROM AUTHOR]

Laser surface melting of hot pressed aluminum composite tile, consisting of 90 % aluminum and 10 % WC, is carried out. Temperature and stress fields developed in the laser-treated region are modeled and predicted using ABAQUS finite element code in line with the experimental conditions. The spiral motion of the laser beam is incorporated at the surface during the laser scanning. This arrangement provides self-annealing effect on the initially formed laser scanning tracks through heat conduction from the lately formed laser scanning tracks. Surface temperature predictions are validated through the thermocouple data. Morphological and metallurgical changes in the laser-treated layer are examined using optical and electron scanning microscopes. It is found that the cooling rates in the central region of the workpiece remain low because of the self-annealing effect of the lately formed laser scanning tracks. This, in turn, lowers von Mises stress levels in this region. Stress peaks are formed below the surface because of the high thermal strain formed in this region during the cooling cycle. The spiral scanning of the laser beam causes oscillating stress levels in the surface region of the laser-treated layer; in which case, its amplitude reduces with the progressing time. Laser-treated layer is free from cracks and crack networks, which is associated with the self-annealing effect of the lately formed laser scanning tracks. [ABSTRACT FROM AUTHOR]

Although casting is commonly used to process aluminum alloys, powder metallurgy remains a promising technique to develop aluminum based materials for structural and functional applications. The possibility to synthesize Al-Mg-Zr alloys through mechanical alloying and spark plasma sintering techniques was explored. Al-10Mg-5Zr and Al-5Mg-1Zr alloyed powders were synthesized through wet ball milling the appropriate amount of elemental powders. The dried milled powders were spark plasma sintered through passing constant pulsed electric current with fixed pulse duration at a pressure of 35 MPa. The samples were vacuum sintered at 450, 500, 550, 600 and 620 °C for 10, 15 and 20 min. The Al-10Mg-5Zr alloy displays poor densification at lower sintering temperatures of 450, 500, 550 and 600 °C. Its sinterability is improved at a temperature of 620 °C whereas sintering temperatures higher than 620 °C leads to partial melting of the alloy. It is possible to sinter the Al-5Mg-1Zr alloy at 450, 500 and 550 °C. The increase of sintering temperature improves its densification and increases its hardness. The Al-5Mg-1Zr alloy displays better densification and hardness compared to Al-10Mg-5Zr alloys. [ABSTRACT FROM AUTHOR]

A duplex treatment of laser gas assisted nitriding and TiN-PVD (physical vapor deposition) coating was carried out on the surface of Ti-6Al-4V alloy. The laser pulse frequency was varied between 2,000 and 1,000 Hz to identify the optimum test conditions. Moreover, nanoindentation technique was utilized to in-situ map mechanical properties and study the wear behavior of the developed dissimilar layers. It was observed that these alloys exhibited transitional properties by employing the duplex treatment; by obtaining the values of individual layers due to the sensitivity of the nanoindentation tests and the possibility of testing small volumes of materials. The hardness and modulus of elasticity values of the sample treated at 2,000 Hz were relatively higher compared to other samples which can be attributed to the increased thickness of the laser affected zone caused by the higher deposited energy per unit area with increased frequency. Wear tests were conducted on the upper TiN layer and the substrate of the alloy to evaluate the improvement in tribological properties. It was observed that the wear resistance of the surface layer was on average 20 times higher than the substrate and the adhesion of the TiN-PVD layer is expected to improve due to the introduction of the laser-irradiated layer underneath which acted like a transitional region. [ABSTRACT FROM AUTHOR]