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Abstract

The aeronautical industry is a sector constantly looking for new materials and equipment because of its tendency to expand quickly. The Ti6Al4V titanium alloy is used frequently in the aeronautic, aerospace, automobile, chemical and medical industry because it presents high strength combined with low density (approximately 4.5 g/cm3), good creep resistance (up to 550°C), excellent corrosion resistance, high flexibility, good fatigue and biocompatibility. As a result of these properties, this titanium alloy is considered an excellent material for manufacturing structural parts in the aircraft industry for modern aeronautic structures, especially for airframes and aero-engines. But its use is also problematic because the Ti6Al4V titanium alloy manifests hydrogen embrittlement, by means of hydrides precipitation in the metal. The Ti6Al4V alloy becomes brittle and fractures because of hydrogen diffusion into metal and because titanium hydrides appear and create pressure from within the metal, thus generating corrosion. Because of titanium hydrides, the titanium alloy suffers from reduced ductility, tensile strength and toughness, which can result in fractures of aeronautical parts. This poses a very serious problem for aircrafts. In this paper, rapid hydrogen embrittlement is presented along with XRD, SEM and TEM analysis. Its goal is to detect the presence of titanium hydrides and to spot the initial cracks in the metallic material.
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Abstract

The aim of that work was the evaluation of the quality of welded connections elements (welds) from the 30HGS steel and titanium alloy Ti6Al4V. The metallographic, factographic tests were used, and measurements of microhardness with the Vickers method. In the head weld of the 30HGS steel there were non-metallic partial division and bubbles observed. The average microhardness in the head connection was 320 HV0.1. There was no significant increase/decrease observed of microhardness in the head influence zone of the weld. There was a good condition of head connections observed, in accordance with the standard EN12517 and EN25817. In the head weld of Ti6Al4V titanium alloy there were single, occasional non-metallic interjections and bubbles observed. There were no cracks both on the weld, and on the border of the heat influence zone. The value of microhardness in head connection was in the range 300÷445 HV0.1. Reveal a very good condition of the head connections in accordance with the standard EN12517 and EN25817. The factographic tests prove the correctness of welded connections done and then heat treatment in case of steel and titanium alloy.
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