MICROSTRUCTURE, PHASE TRANSFORMATIONS AND MECHANICAL PROPERTIES OF SOLUTION TREATED BI-MODAL  TITANIUM ALLOY

The effect of heat treatment conditions on the microstructure, phase transformation and mechanical properties of Bi-modal b titanium alloy was investigated. The heat treatment process comprises of solution treated at various temperatures of 640, 680, 720 and 760 °C for 30 min followed by water quenching and aged at 500 °C for 30 min then air cooling. This study was carried out using X-ray diffraction analysis (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), differential thermal analysis (DTA), compression universal testing machine and Vickers hardness tester. The results show that the microstructure of investigated alloys consists of b phase, as a matrix, primary a phase, small precipitates of secondary a phase in addition to orthorhombic martensite (a”) phase found only in the solutionized samples at 720 and 760 °C. Transus temperature for the b phase found to be around 865 °C at heating rate of 10 °C/min. The a/b phase zone is ranging from 650 to 865 °C at the same heating rate for all samples. The formation temperature of nanometer α phase and/or disappearing of wiso phase are almost constant at 385 °C. The formation of primary α phase was detected at a temperature more than 400 °C. Hardness measurements increased as the solution temperature increase. The highest ultimate compression strength, 2680 MPa, achieved with solution temperature of 680 °C. However the maximum yield stress, 1725 MPa, obtained with 760 °C solution temperature. The highest contraction was attained with the solutionized sample at 640 °C for 30 min

Effect of Aging Treatment on the Electrochemical and Corrosion Behavior of NiTiRe Shape Memory Alloy

In this study, Ni52Ti47.7Re0.3 shape memory alloy was subjected to solution treatment at 1000 degrees C for 24h (the tested alloy), followed by ageing at 300, 400, 500 and 600 degrees C for 3h. The objective is to investigate the effect of ageing temperature on the uniform and pitting corrosion characteristics of Ni52Ti47.7Re0.3 alloy. Measurements were conducted in 1.0 M H2SO4 solutions without and with 0.2 M NH4F, using polarization, impedance, and chronoamperometry measurements. Morphologies of the corroded surfaces were examined by SEM/EDX examinations. Results obtained from the employed electrochemical techniques were in good agreement and showed that the rates of the uniform and pitting corrosion processes of the tested alloy decrease with increase in the aging temperature, reaching their minimum values at an aging temperature of 400 degrees C. Further increase in the aging temperature up to 600 degrees C led to an obvious increase in the rates of corrosion. Experimental finding were interpreted adopting the effect of the aging temperature on the microstructure of the tested alloy.In this study, Ni52Ti47.7Re0.3 shape memory alloy was subjected to solution treatment at 1000 &deg;C for 24h (the tested alloy), followed by ageing at 300, 400, 500 and 600 &deg;C for 3h. The objective is to investigate the effect of ageing temperature on the uniform and pitting corrosion characteristics of Ni52Ti47.7Re0.3 alloy. Measurements were conducted in 1.0 M H2SO4 solutions without and with 0.2 M NH4F, using polarization, impedance, and chronoamperometry measurements. Morphologies of the corroded surfaces were examined by SEM/EDX examinations. Results obtained from the employed electrochemical techniques were in good agreement and showed that the rates of the uniform and pitting corrosion processes of the tested alloy decrease with increase in the aging temperature, reaching their minimum values at an aging temperature of 400 oC. Further increase in the aging temperature up to 600 oC led to an obvious increase in the rates of corrosion. Experimental finding were interpreted adopting the effect of the aging temperature on the microstructure of the tested alloy.</p

Electrochemical and Corrosion Behavior of cast Re-containing Inconel 718 Alloys in Sulphuric Acid Solutions and the Effect of Cl-

The effect of Rhenium (Re) additions (2.4, 3.5, and 6%) to a standard Inconel 718 alloy (IN718) on the uniform and pitting corrosion processes of IN718 was studied. Measurements were conducted in 1.0M H2SO4 solutions without and with 0.1M, 0.3M, or 0.6M NaCl at 25 degrees C, employing various electrochemical techniques, complemented with SEM/EDS and AFM examinations. The corrosion behavior at equilibrium (corresponding to immersion of samples without polarization) was studied as a function of alloy composition by monitoring the open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS) measured at the corrosion potential (E-corr), and by polarization studies around E-corr (E-corr +/- 250 mV). The anodic behavior of the tested alloys was also studied in 1.0M H2SO4 solutions without and with Cl-, based on potentiodynamic anodic polarization measurements. A potentiostatic technique (current vs. time measurements at a given potential) was also employed to access the role of the alloyed Re in the kinetics of pit initiation and growth induced by Cl-. Experimental findings showed that the rates of the uniform and pitting corrosion processes decreased when Re content increased from 2.5% to 3.5%. However, further increase in alloyed Re content (up to 6%) has resulted in an obvious enhancement in the rates of uniform and pitting corrosion processes. Potentiostatic measurements in presence of Cl- showed that nucleation of pit (initiated by Cl- at anodic potentials very close to and beyond the pitting potential, E-pit) takes place after an incubation time (t(i)). The rate of pit nucleation (t(i)(-1)) increases with increase in Cl- concentration and applied anodic potential (E-a). The results of potentiostatic measurements also revealed that t(i)(-1) suppressed when Re content in the alloy increased up to 3.5%, but enhanced in presence of 6% Re.The effect of Rhenium (Re) additions (2.4, 3.5, and 6%) to a standard Inconel 718 alloy (IN718) on the uniform and pitting corrosion processes of IN718 was studied. Measurements were conducted in 1.0M H2SO4&nbsp;solutions without and with 0.1M, 0.3M, or 0.6M NaCl at 25&nbsp;oC, employing various electrochemical techniques, complemented with SEM/EDS and AFM examinations. The corrosion behavior at equilibrium (corresponding to immersion of samples without polarization) was studied as a function of alloy composition by monitoring the open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS) measured at the corrosion potential (Ecorr), and by polarization studies around&nbsp;Ecorr&nbsp;(Ecorr&plusmn;250 mV). The anodic behavior of the tested alloys was also studied in 1.0M H2SO4&nbsp;solutions without and with Cl-, based on potentiodynamic anodic polarization measurements. A potentiostatic technique (current&nbsp;vs.&nbsp;time measurements at a given potential) was also employed to access the role of the alloyed Re in the kinetics of pit initiation and growth induced by Cl-. Experimental findings showed that the rates of the uniform and pitting corrosion processes decreased when Re content increased from 2.5% to 3.5%. However, further increase in alloyed Re content (up to 6%) has resulted in an obvious enhancement in the rates of uniform and pitting corrosion processes. Potentiostatic measurements in presence of Cl-&nbsp;showed that nucleation of pit (initiated by Cl-&nbsp;at anodic potentials very close to and beyond the pitting potential,&nbsp;Epit) takes place after an incubation time (ti). The rate of pit nucleation (ti-1) increases with increase in Cl-&nbsp;concentration and applied anodic potential (Ea). The results of potentiostatic measurements also revealed that&nbsp;ti-1&nbsp;suppressed when Re content in the alloy increased up to 3.5%, but enhanced in presence of 6%Re.</p

Effect of cobalt addition on the corrosion behavior of near equiatomic NiTi shape memory alloy in normal saline solution: electrochemical and XPS studies

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Boost the Crystal Installation and Magnetic Features of Cobalt Ferrite/M-Type Strontium Ferrite Nanocomposites Double Substituted by La3+ and Sm3+ Ions (2CoFe2O4/SrFe12&minus;2xSmxLaxO19)

Spinel cobalt ferrite/hexagonal strontium hexaferrite (2CoFe2O4/SrFe12&minus;2xSmxLaxO19; x = 0.2, 0.5, 1.0, 1.5) nanocomposites were fabricated using the tartaric acid precursor pathway, and the effects of La3+&ndash;Sm3+ double substitution on the formation, structure, and magnetic properties of CoFe2O4/SrFe12&minus;2xSmxLaxO19 nanocomposite at different annealing temperatures were assayed through X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. A pure 2CoFe2O4/SrFe12O19 nanocomposite was obtained from the tartrate precursor complex annealed at 1100 &deg;C for 2 h. The substitution of Fe3+ ion by Sm3&ndash;+La3+ions promoted the formation of pure 2CoFe2O4/SrFe12O19 nanocomposite at 1100 &deg;C. The positions and intensities of the strongest peaks of hexagonal ferrite changed after Sm3+&ndash;La3+ substitution at &le;1100 &deg;C. In addition, samples with an Sm3+&ndash;La3+ ratio of &ge;1.0 annealed at 1200 &deg;C for 2 h showed diffraction peaks for lanthanum cobalt oxide (La3Co3O8; dominant phase) and samarium ferrite (SmFeO3). The crystallite size range at all constituent phases was in the nanocrystalline range, from 39.4 nm to 122.4 nm. The average crystallite size of SrFe12O19 phase increased with the number of Sm3+&ndash;La3+ substitutions, whereas that of CoFe2O4 phase decreased with an x of up to 0.5. La&ndash;Sm co-doped ion substitution increased the saturation magnetization (Ms) value and the subrogated ratio to 0.2, and the Ms value decreased with the increasing number of double substitutions. A high saturation magnetization value (Ms = 69.6 emu/g) was obtained using a La3+&ndash;Sm3+ co-doped ratio of 0.2 at 1200 for 2 h, and a high coercive force value (Hc = 1192.0 Oe) was acquired using the same ratio at 1000 &deg;C

The Influence of Microstructure on the Passive Layer Chemistry and Corrosion Resistance for Some Titanium-Based Alloys

The effect of microstructure and chemistry on the kinetics of passive layer growth and passivity breakdown of some Ti-based alloys, namely Ti-6Al-4V, Ti-6Al-7Nb and TC21 alloys, was studied. The rate of pitting corrosion was evaluated using cyclic polarization measurements. Chronoamperometry was applied to assess the passive layer growth kinetics and breakdown. Microstructure influence on the uniform corrosion rate of these alloys was also investigated employing dynamic electrochemical impedance spectroscopy (DEIS). Corrosion studies were performed in 0.9% NaCl solution at 37 &#176;C, and the obtained results were compared with ultrapure Ti (99.99%). The different phases of the microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Chemical composition and chemistry of the corroded surfaces were studied using X-ray photoelectron spectroscopy (XPS) analysis. For all studied alloys, the microstructure consisted of &#945; matrix, which was strengthened by &#946; phase. The highest and the lowest values of the &#946; phase&#8217;s volume fraction were recorded for TC21 and Ti-Al-Nb alloys, respectively. The susceptibility of the investigated alloys toward pitting corrosion was enhanced following the sequence: Ti-6Al-7Nb &lt; Ti-6Al-4V &lt;&lt; TC21. Ti-6Al-7Nb alloy recorded the lowest pitting corrosion resistance (Rpit) among studied alloys, approaching that of pure Ti. The obvious changes in the microstructure of these alloys, together with XPS findings, were adopted to interpret the pronounced variation in the corrosion behavior of these materials