Browsing by Author "Yaqub, Talha Bin"
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- Ceramic-reinforced HEA matrix composites exhibiting an excellent combination of mechanical propertiesPublication . Mehmood, M. Adil; Shehzad, Khurram; Mujahid, M.; Yaqub, Talha Bin; Godfrey, Andy; Fernandes, Filipe; Muhammad, F. Z.; Yaqoob, KhurramCoCrFeNi is a well-studied face centered cubic (fcc) high entropy alloy (HEA) that exhibits excellent ductility but only limited strength. The present study focusses on improving the strength-ductility balance of this HEA by addition of varying amounts of SiC using an arc melting route. Chromium present in the base HEA is found to result in decomposition of SiC during melting. Consequently, interaction of free carbon with chromium results in the in-situ formation of chromium carbide, while free silicon remains in solution in the base HEA and/or interacts with the constituent elements of the base HEA to form silicides. The changes in microstructural phases with increasing amount of SiC are found to follow the sequence: fcc → fcc + eutectic → fcc + chromium carbide platelets → fcc + chromium carbide platelets + silicides → fcc + chromium carbide platelets + silicides + graphite globules/flakes. In comparison to both conventional and high entropy alloys, the resulting composites were found to exhibit a very wide range of mechanical properties (yield strength from 277 MPa with more than 60% elongation to 2522 MPa with 6% elongation). Some of the developed high entropy composites showed an outstanding combination of mechanical properties (yield strength 1200 MPa with 37% elongation) and occupied previously unattainable regions in a yield strength versus elongation map. In addition to their significant elongation, the hardness and yield strength of the HEA composites are found to lie in the same range as those of bulk metallic glasses. It is therefore believed that development of high entropy composites can help in obtaining outstanding combinations of mechanical properties for advanced structural applications.
- Design and development of NbTiVZr porous high entropy alloys for energy applicationsPublication . Siddique, Ayesha; Abid, Talha; Akram, M. Aftab; Yaqub, Talha Bin; Karim, M. Ramzan Abdul; Fernandes, Filipe; Khan, Rizwan; Yaqoob, KhurramPorous NbTiVZr refractory high entropy alloys have been developed by a novel method that is based on the addition of yttrium to the base high entropy alloy and its subsequent removal by electrochemical dealloying process. Microstructure and crystal structure characterization of as-cast alloys confirmed the segregation of yttrium at interdendritic regions. Successful removal of yttrium from interdendritic region has been confirmed by microstructure and crystal structure characterization of dealloyed samples. NbTiVZr foams with varying levels of porosity were successfully developed and characterized. Electrochemical performance of the developed foams was investigated by cyclic voltammetry (CV), galvanostatic charge discharge (GCD), and electrochemical impedance spectroscopy (EIS). High areal capacitance of 82.66 mF cm 2 at scan rate of 2 mV s 1 was exhibited by one of the developed electrodes. The electrode displayed capacitance retention of 104 % after 5000 cycles at current density of 1 mA cm 2. The excellent electrochemical performance demonstrated by the NbTiVZr refractory high entropy foams highlights their potential as suitable candidates for supercapacitor electrode.
- Development of eutectic high entropy alloy by addition of W to CoCrFeNi HEAPublication . Abdullah, M.; Mukarram, Muhammad; Yaqub, Talha Bin; Fernandes, Filipe; Yaqoob, KhurramHigh entropy alloys have shown a remarkable combination of physical and mechanical properties. The introduction of eutectic microstructure, consisting of a tough fcc phase, and a hard-intermetallic phase, can help in obtaining even better synergy of strength and ductility. The presence of multiple principal alloying elements in HEAs and absence of corresponding multicomponent phase diagrams makes designing of eutectic high entropy alloys a tedious task. In the present study, systematic investigation of CoCrFeNi-Wx system has been carried out for the development of eutectic microstructure. Experimental results validated the presence of eutectic reaction in the calculated phase diagram. CoCrFeNi-Wx HEAs remained single fcc phase alloys at smaller amount of W (x = 0.1) but changed to hypoeutectic (x = 0.25, 0.5, 0.75) and hypereutectic alloys (x = 1.0) with increase in the amount of tungsten. It has been shown that calculated pseudo binary phase diagrams can provide a very good starting point for the development of eutectic HEAs. Mechanical characterization of the developed HEAs revealed that development of eutectic mixture of a soft (fcc) and a hard phase (intermetallic/bcc) can help in obtaining outstanding combination of mechanical properties.
- Effect of Annealing Heat Treatment on the Composition, Morphology, Structure and Mechanical Properties of the W-S-N CoatingsPublication . Yaqub, Talha Bin; Al-Rjoub, Abbas; Khalid, Hafiza Ayesha; Yaqoob, Khurram; Fernandes, Filipe; Cavaleiro, AlbanoAlloyed-transition metal dichalcogenide (TMD) coatings have been under investigation as multi-environment lubricants for the past few decades. These coatings display very low coefficient of friction properties at elevated temperatures. Studies on the annealing of these low-friction coatings are missing in the literature. For the first time, in this study, the annealing of the W-S-N dry lubricant coatings was carried out to study its effects on the composition, morphology, crystal structure and hardness of the coatings. The W-S-N coatings were deposited by direct current (DC) reactive magnetron sputtering. The analysis was carried out for as-deposited, 200 °C and 400 °C annealed coatings. The as-deposited coatings have N content in the range of 0–25.5 at. %. The coatings are compact and the densification increased with the increase in N-alloying. All the coatings are crystalline except the highest N-alloyed coating which is X-ray amorphous. A maximum hardness of 8.0 GPa was measured for the coating alloyed with 23 at. % N. Annealing did not affect the composition and morphology of the coatings, while some variations were observed in their crystal structure and hardness. The maximum hardness increased from 8 GPa to 9.2 GPa after 400 °C annealing of the 23 at. % N-alloyed coating.
- Insights into the oxidation resistance mechanism and tribological behaviors of multilayered TiSiN/CrVxN hard coatingsPublication . Ju, Hongbo; Athmani, Moussa; Luan, Jing; AL-Rjoub, Abbas; Cavaleiro, Albano; Yaqub, Talha Bin; Chala, Abdelouahad; Ferreira, Fabio; Fernandes, FilipeIn the last decades, vanadium alloyed coatings have been introduced as potential candidates for self-lubrication due to their perfect tribological properties. In this work, the influence of V incorporation on the wear performance and oxidation resistance of TiSiN/CrN film coatings deposited by direct current (DC) reactive magnetron sputtering is investigated. The results show that vanadium incorporation significantly decreases the oxidation resistance of the coatings. In general, two layers are formed during the oxidation process: i) Ti(V)O2 on top, followed by a protective layer, which is subdivided into two layers, Cr2O3 and Si–O. ii) The diffusion of V controls the oxidation of V-containing coatings. The addition of vanadium improves the wear resistance of coatings, and the wear rate decreases with increasing V content in the coatings; however, the friction coefficient is independent of the chemical composition of the coatings. The wear of the V-containing coatings is driven by polishing wear.
- The influence of V addition on the structure, mechanical properties, and oxidation behaviour of TiAlSiN coatings deposited by DC magnetron sputteringPublication . AL-Rjoub, A.; Yaqub, Talha Bin; Cavaleiro, A.; Fernandes, FilipeThe influence of V content on the morphology, structure, hardness (H) and reduced Young's modulus (E), adhesion, and oxidation resistance of TiAlSiN coatings is investigated. The coatings were produced by DC reactive magnetron sputtering, with increasing V contents from 0, 4.8 and 11.0 at.%. All coatings exhibit a fcc type structure. The coating with 4.8 at.% of V shows the highest values of H and E, whereas the values are similar for the reference coating and the coating with 11.0 at.% of V. The coatings adhere well to the substrates and show a dense and compact columnar growth extending from the adhesive interlayer to the top surface of the coatings. The dynamic thermal gravimetric oxidation curves reveal that V additions decreases the onset point of oxidation significantly and degrades the oxidation resistance of the coatings. A dual oxide layer is formed on the top surface of the reference coating: an outer porous Ti–Al–O rich layer with plate-like features on the top, which classified to TiO2 (rutile and anatase) and Al2O3 phases, and an inner Ti–Si–O rich layer with Al depletion that identified as mixture of amorphous Si–O and Ti–Si–O protective oxides. The diffusion of V to the top surface governs the oxidation process of the V-containing coatings, i.e. increasing V concentration leads to disrupt the formation of the protective continuous oxide layers easily.
- Tribological Comparison of Coatings Produced by PVD Sputtering for Application on Combustion Piston RingsPublication . Ferreira, Ney Francisco; Neis, Patric Daniel; Fernandes, Filipe; Poletto, Jean Carlos; Yaqub, Talha Bin; Cavaleiro, Albano; Vilhena, Luís; Ramalho, AmílcarThis article compares the tribological performance of coatings produced by PVD sputtering. Transition metal dichalcogenide (TMD) coatings doped with carbon (WSC and MoSeC) and nitrogen (WSN and MoSeN) and a conventional diamond-like carbon (DLC) coating are compared. The tribological evaluation was oriented towards the use of coatings on piston rings. Block-on-ring tests in a condition lubricated with an additive-free polyalphaolefin (PAO 8) and at temperatures of 30, 60, and 100 °C were carried out to evaluate the coatings in boundary lubrication conditions. A load scanner test was used to evaluate dry friction and scuffing propensity. In addition to WSN, all other TMD coatings (WSC, MoSeC, and MoSeN) exhibited lower friction than DLC in dry and lubricated conditions. The study reveals that WSC, among TMD coatings, offers promising results, with significantly lower friction levels than DLC, while demonstrating reduced wear and a lower risk of metal adhesion. These findings suggest that WSC may be a viable alternative to DLC in piston rings, with potential benefits for reducing fuel consumption and increasing engine durability.
- Vacuum Tribological Properties of W-S-N Coatings Synthesized by Direct Current Magnetron SputteringPublication . Yaqub, Talha Bin; Yaqoob, Khuram; Mukhtar, Amir; Fernandes, Filipe; Bondarev, Andrey; Ferreira, Fabio; Al-Rjoub, Abbas; Cavaleiro, AlbanoThis work deals with the investigation of the tribological performance of DC magnetron sputteredW-S-N coatings under vacuum atmosphere, as part of the exploration of multi-environment sliding properties of W-S-N solid lubricants. This study is part of the systematic testing of W-S-N solid lubricants in different environments, especially vacuum, which is often ignored. The trend is to test sliding properties in dry N2 by considering it as replacement of vacuum environment testing. This approach is not appropriate. In this work, a set of coatings was synthesized with N-alloying content in the range of 0–25.5 at.%. A maximum S/W ratio of 1.47 was observed for the pure WSx coating. A maximum hardness of 8.0 GPa was observed for 23 at.% of N-alloying. The coating with the lowest N content (14.6 at.%) displayed the lowest friction, specific wear rate and wear scar depth under vacuum conditions. Despite superior sliding performance at room temperature (35% humidity), 200 C and dry nitrogen conditions, the performance of the WSN12.5 coating deteriorated vacuum environment.