Synthesis of Ti-Al-xNb Ternary Alloys via Laser-Engineered Net Shaping for Biomedical Application: Densification, Electrochemical and Mechanical Properties Studies

The lives of many people around the world are impaired and shortened mostly by cardiovascular diseases (CVD). Despite the fact that medical interventions and surgical heart transplants may improve the lives of patients suffering from cardiovascular disease, the cost of treatments and securing a perfect donor are aspects that compel patients to consider cheaper and less invasive therapies. The use of synthetic biomaterials such as titanium-based implants are an alternative for cardiac repair and regeneration. In this work, an in situ development of Ti-Al-xNb alloys were synthesized via laser additive manufacturing for biomedical application. The effect of Nb composition on Ti-Al was investigated. The microstructural evolution was characterized using a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS). A potentiodynamic polarization technique was utilized to investigate the corrosion behavior of TiAl-Nb in 3.5% NaCl. The microhardness and corrosion behaviour of the synthesized Ti-Al-Nb alloys were found to be dependent on laser-processing parameters. The microhardness performance of the samples increased with an increase in the Nb feed rate to the Ti-Al alloy system. Maximum microhardness of 699.8 HVN was evident at 0.061 g/min while at 0.041 g/min the microhardness was 515.8 HVN at Nb gas carrier of 1L/min, respectively.

Islamic Copper-Based Metal Artefacts from the Garb Al-Andalus. A Multidisciplinary Approach on the Alcáçova of Mārtulah (Mértola, South of Portugal)

A multidisciplinary approach has been applied to investigate the production technology of a collection of copper-based artefacts found during archaeological excavation campaigns carried out in the Almohad neighbourhood of Mārtulah, the Islamic name of modern Mértola (South of Portugal). In stark contrast to other Islamic materials found in the same site such as common and finely decorated pottery, glass, and bone artefacts, metal objects have received less attention despite the number of artefacts recovered. This study focuses on the chemical characterisation of 172 copper-based artefacts dating back to the 12th and the first half of the 13th centuries. The artefacts are daily use objects and consist of personal ornaments (earrings, rings, and casket ornaments), tools (spindles, spatulas, and oil lamp sticks) and artefacts with unknown functions. X-ray fluorescence Spectroscopy (XRF) and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM/EDS), provided information not only about technological issues, as well as on the socio-economic implications of metal consumption at Islamic Mértola. The results revealed that metals were produced with a variety of Cu-based alloys, namely unalloyed copper, brasses, bronzes, and ternary alloys, by mixing Cu, Zn and Sn and Pb without any apparent consistency, as a likely result of recurrent recycling and mixing scrap metals practices or use of minerals available locally.

SPECIFIC STRUCTURE OF EFFECTIVE MEMBRANE ALLOYS BASED ON NIOBIUM, VANADIUM AND ZIRCONIUM

Аморфные, нанокристаллические мембранные сплавы на основе элементов V группы с уникальными механическими и функциональными свойствами и с матричной дуплексной микроструктурой активно способствуют развитию водородной энергетики. Имеются еще не вполне разрешенные проблемы для этих новых сплавов -их низкая термическая стабильность, недосточная механическая прочность (пластичность, твердость), а также охрупчивание интерметаллидное и гидридное. Для эффективного применения разрабатываются сплавы с тройным составом - в которые помимо элементов V группы входят и легирующие металлы никель и титан. Получают не только аморфные и нанокристаллические сплавы, применимые в электронике и электроэнергетике, а также мембранные сплавы с дуплексной матричной структурой, объединяющей аморфные, так нано- и квазикристаллические дендритно упрочняющие фазы, как упрочняющие аморфную матрицу. В специализируемых мембранных тройных сплавах формируются соединения NiTi и NiTi, стабилизирующие и предохраняющие нано- и кристаллические мембраны от хрупкого разрушения. Установлено, что интенсивное образование гидридов в этих альтернативных мембранных сплавах столь же не желательно, как и для традиционных сплавов на основе палладия. Рассматриваемые сплавы действительно позволяют получить газообразный водород высокой чистоты с применением новых составов взамен дорогостоящих мембран на основе сплавов Pd - Au / Ag / Cu. With unique mechanical and functional properties, amorphous, nanocrystalline and matrix duplex microstructure membrane alloys based on group V elements actively contribute to the development of hydrogen energy. There are still not completely resolved problems for these new alloys - their low thermal stability, insufficient mechanical strength (plasticity, hardness), and intermetallic and hydride embrittlement. For effective use, alloys with a triple composition are being developed - which, in addition to the elements of group V, also include nickel and titanium as alloying metals. Not only amorphous and nanocrystalline alloys are obtained that are applicable in electronics and power engineering, as well as membrane alloys with a duplex matrix structure that combines amorphous, nano-and quasicrystalline dendritic-hardening phases strengthening the amorphous matrix. In specialized membrane ternary alloys, NiTi and NiTi compounds are formed, which stabilize and protect nano-and crystalline membranes from brittle destruction. It has been found that the intense formation of hydrides in these alternative membrane alloys is as undesirable as for palladium-based compounds. The alloys under consideration actually make it possible to obtain high-purity gaseous hydrogen using new compositions instead of expensive membranes based on Pd - Au / Ag / Cu alloys.

EFFECT OF CU CONTENT AND GROWTH VELOCITY ON THE MICROSTRUCTURE PROPERTIES OF THE DIRECTIONALLY SOLIDIFIED AL-MN-CU TERNARY ALLOYS

In this work, influences of composition (Cu content) and growth velocity (V) on the microstructure (dendritic spacing) of Al–Mn–Cu ternary alloys have been investigated. Al–1.9Mn–xCu (x=0.5, 1.5 and 5 wt. %) alloys were prepared using metals of 99.90% high purity in the vacuum atmosphere. These alloys were directionally solidified upwards under various growth velocities (8.3–978 m/s) using a Bridgman-type directional solidification furnace at a constant temperature gradient (7.1 K/mm). Measurements of primary dendrite arm spacing () of the samples were carried out and then expressed as functions of growth velocity and Cu content. Especially, cell-dendritic transition was detected for low growth velocity (41.6 m/s) for alloys containing 0.5 and 1.5Cu. It has been found that the values of  decrease with increasing V and decreasing Cu content. Keywords: Aluminum alloys, Solidification, Cell-dendritic transition, Dendrite arm spacing

Effect of Ti on the Structure and Mechanical Properties of TixZr2.5-xTa Alloys

To determine the effects of Ti and mixing entropy (ΔSmix) on the structure and mechanical proper-ties of Zr-Ta alloys and then find a new potential energetic structural material with good me-chanical properties and more reactive elements, TixZr2.5−xTa (x = 0, 0.5, 1.0, 1.5, 2.0) alloys were investigated. The XRD experimental results showed that the phase transformation of TixZr2.5−xTa nonequal-ratio ternary alloys depended not on the value of ΔSmix, but on the amount of Ti atoms. With the addition of Ti, the content of the HCP phase decreased gradually. SEM analyses revealed that dendrite morphology and component segregation increasingly developed and then weakened gradually. When x increases to 2.0, TixZr2.5−xTa with the best mechanical properties can be ob-tained. The yield strength, compressive strength and fracture strain of Ti2.0Zr0.5Ta reached 883 MPa, 1568 MPa and 34.58%, respectively. The dependence of the phase transformation and me-chanical properties confirms that improving the properties of Zr-Ta alloys by doping Ti is feasible.