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.
The present investigation has been made to assess the influence of B4C reinforced with Ti-6Al-4V matrix prepared by powder metallurgy route. High energy ball milling was used to prepare the composites. Cylindrical preforms were prepared using suitable die set assembly. The green preforms were sintered in the muffle furnace at 900°C for 1 h. Further the preforms were cooled inside the furnace till the room temperature has attained. SEM with EDS mapping analysis was used to evaluate the morphology and elemental confirmation of the prepared composite. The density and hardness of the samples are determined using Archimedes principle and Rockwell hardness testing machine. The wear resistance of the samples was determined by employing a pin on disc apparatus. The hardness of the composites (Ti-6Al-4V /10B4C) was increased while comparing to the base material (Ti-6Al-4V) which is attributed to the presence of hard ceramic phase. Response Surface Methodology (RSM) five level central composite design approach was accustomed and it minimised the amount of experimental conditions and developed mathematical models among the key process parameters namely wt. % of B4C, applied load and sliding distances to forecast the abrasive response of Specific Wear Rate (SWR) and Coefficient of Friction (CoF). Analysis of variance was used to check the validity of the developed model. The optimum parameters of specific wear rate and coefficient of friction were identified.
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.
The low adherence of diamond-like carbon (DLC) films on titanium (Ti) alloys can be improved by using interlayer coatings. In this study, DLC (a-C:H) films were deposited using radio-frequency plasma-enhanced chemical vapor deposition (rf-PECVD), and a TiCN interlayer was applied between the extra low interstitial (ELI) grade of Ti-6Al-4V alloy and a-C:H film. The characteristics of the a-C:H-coated Ti-6Al-4V ELI alloy were investigated using field emission scanning electron microscopy, Vickers hardness, and scratch and wear tests. The DLC (a-C:H) films deposited by rf-PECVD had a thickness of 1.7 µm, and the TiCN interlayer had a thickness of 1.1 µm. Vickers hardness of the DLC (a-C:H) films were increased as a result of the influence of the TiCN interlayer. The resulting friction coefficient of the a-C:H-coated Ti-6Al-4V with the TiCN interlayer had an extremely low value of 0.07.
In this research work, Ti6Al4V alloy material was subjected to electric discharge machining (EDM) and its fatigue life was investigated at low cycle fatigue mode. In order to evaluate the influence of recast layer generated during the machining process on the fatigue life, samples prepared using end milling process were also subjected to similar tests and a comparative analysis is presented. Data were observed in the fully reversed fatigue mode at room temperature using samples fabricated as per ASTM standard E606. The specimen were machined on a spark electric discharge die sink machine which were subjected to fatigue, and the recorded fatigue lives were compared with the fatigue life of end milled specimen. The machined surfaces were examined through optical and scanning electron microscopes, and the roughness was measured with a standard profilometer. It was observed that when the discharge current is augmented, the recast layer formed was in the range of 20 to 70 µm thick. From the results, it is being concluded that fatigue life of the samples fabricated by EDM is less for various load conditions when compared with that of the end milled sample. The milled sample at 160 MPa load exhibited 2.71×105 cycles, which is 64% more when compared to EDM sample.
In this research work, the Ti-6Al-4V material was used for the investigation of machining parameters by means of hybrid micro electrical discharge machining to improve the machining process and reduce the negative effects of debris accumulation in the drilled hole. L9 orthogonal array was used in the Taguchi based grey relational analysis to optimize the parameters such as material removal rate and diametrical accuracy of the machining process for Ti-6Al-4V. This work encompasses the design, development, and calibration of the work piece vibration platform and experimental analysis of the process parameters by means of the hybrid micro electrical discharge machining process. The maximum material removal rate and minimum surface roughness was observed at the current value of 2.5 A, pulse on time is 2 µs and pulse off time is 14.5 µs. The maximum material removal rate was observed for the increase in pulse on time with 14.4 µs and 4 A current level. The diametrical accuracy of the microholes was increased while increasing the pulse off time and decreasing the pulse on time. The fluid flow simulation has been conducted to find out the pressure drop and to know the velocity of the flow inside the hole for the effective flushing of the debris during machining.