The Effect of Silicon on the Electronic Structure and Corrosion–Electrochemical Behavior of Austenitic Steels1

The regularities of the effect produced by alloying with silicon (up to 6% Si) on the corrosion–electrochemical behavior of austenitic stainless steels of various structure types (single-phase or with the precipitation of second phases) in a solution of 1 mol/l HClO₄ + 0.25 mol/l NaCl at 22°C and in 27 and 65% HNO₃ at 70°C and at the boiling point are clarified. Nuclear -resonance (Mössbauer) spectroscopic studies enabled us to develop a mechanism of enhancing the passivability of the steels studied at potentials corresponding to their active–passive transition and accelerating the transpassivation process by silicon. The hypothesis proposed is based on the change in the electron density distribution around iron nuclei induced by silicon and accordingly the change in the chemisorption interactions between the surface iron atoms and the polar molecular and ionic components of the solution.     

The Effect of Silicon on the Electronic Structure and Corrosion–Electrochemical Behavior of Boron-Containing X20H20 Steels

The effect of silicon (0.06 to 4.89%) on the electron density distribution around ⁵⁷Fe nuclei in quenched boron-containing X20H20 steels is studied with the use of -resonance spectroscopy. Computer treatment of the spectra provided the estimates of the isomeric (chemical) shifts (mm/s) and half-widths (mm/s) of the singlet and doublet spectral lines, as well as the area parts S (%) of each constituent in the summary spectrum and the quadrupole electric splitting eq (mm/s) of the doublet. On the basis of these estimates, both new and earlier obtained experimental data on the peculiarities of the corrosion–electrochemical behavior of silicon-containing austenitic stainless steels are discussed.     

Effects of Microstructure and Rare-Earth Constituent on the Oxidation Behavior of Ti–5.6Al–4.8Sn–2Zr–1Mo–0.35Si–0.7Nd Titanium Alloy

The isothermal oxidation behavior in air of high-temperature titanium alloy Ti–5.6Al–4.8Sn–2Zr–1Mo–0.35Si–0.7Nd with bimodal and lamellar microstructures was investigated at 600–800 °C. The results revealed that the alloy with lamellar microstructure has better oxidation resistance than that with bimodal microstructure. The porous oxide scales that form mainly contain TiO₂. A noticeable observation concerns the preferential attack around rare-earth particles, associated rapid oxygen diffusion along the incoherent rare-earth precipitate/matrix interface and cracks formed during oxidation. The resulting internal attack caused fragmentation of rare-earth particles and further oxidation of substrate to form TiO₂ scale with some fine dispersoids of Al₂O₃. Tensile tests showed that the ultimate strength and ductility of the specimens with removed surface were higher than that with a surface scale.     

Thermal Behavior of Mn- and P-containing Anodic–Spark Coatings on Titanium

Differential thermogravimetric, and x-ray photoelectron spectral, as well as diffraction, analyses were applied to investigate anodic coatings formed under electric-breakdown conditions in electrolytes containing polyphosphate manganese complexes. It is shown that annealing at temperatures of up to 1000°C does not affect the concentration of elements in coatings, but is conducive to crystallizing Na_0.23TiO₂-bronze, manganese pyrophosphate Mn₂P₂O₇, sodium, as well as manganese, titanophosphates NaTi₂(PO₄)₃ and Mn(II)Mn(III)Ti(PO₄)₃, respectively.     

Effect of HIP Treatment on Fatigue Crack Growth Behavior of Ti–6Al–4V Alloy Fabricated by Electron Beam Melting

The effect of hot isostatic pressing treatment on the fatigue crack growth behavior of Ti–6Al–4V alloy fabricated by electron beam melting was investigated.The results indicate that the fatigue crack growth rate of the HIPed samples is higher than that of the as-fabricated one under certain stress intensity factor(DK18 MPa m~(1/2)).With further increase in DK,the fatigue crack growth rates of the studied two samples become similar.The variation of a lamella thickness and the pore defects distribution have an effect on the fatigue crack growth rates in the studied samples,and the latter plays the dominant role.     

Effect of Intergranular Precipitation on the Internal Oxidation Behavior of Cr–Mn–N Austenitic Stainless Steels

The effect of intergranular precipitation on the internal oxidation behavior of Cr–Mn–N austenitic steels at 1000 °C in dry air atmosphere was investigated using scanning electron microscope, transmission electron microscope, and X-ray diffraction analysis. The results show that intergranular M23C6 carbide morphologies play an important role on the internal oxidation behavior of Cr–Mn–N steels. During the period of the oxidation, both discontinuous chain-shaped and continuous film-shaped intergranular M23C6 carbides precipitated along the grain boundaries. Internal oxides of silica preferentially intruded into the matrix along grain boundaries with discontinuous M23C6 carbide particles, while silica was obviously restricted at the interfaces between the external scale and matrix on the occasion of continuous film-shaped M23C6 carbides. It is seemed that reasonable microstructure could improve the oxidation resistance of Cr–Mn–N steels.     

The Effects of Alloying Elements on the Continuous Cooling Transformation Behavior of 2¼Cr-1Mo Steels

The continuous cooling transformation (CCT) behavior of eight 2¼Cr-1Mo steels from a statistically designed matrix was determined. These steels contained two levels of carbon (0.07 and 0.16 wt.%), manganese (0.35 and 0.85%), chromium (1.5 and 2.8%), and molybdenum (0.3 and 1.25%). Each steel was tested in a quenching dilatometer at five to six cooling rates between 725 and 1.2 °C/min. For each CCT sample, the change in length, microstructure, and macrohardness were determined. The ferrite content was also measured for samples cooled near the ferrite nose. Pearson correlation and multiple regression analyses were performed for various CCT diagram parameters. The correlation analysis showed that carbon and chromium contents significantly affected the critical temperatures and the bainite and martensite transformation temperatures. Increasing carbon content significantly increased the hardness for the bainite and martensite range of cooling rates, but hardness at slower cooling rates was unaffected by alloying elements. Regression equations were obtained for the critical temperatures and the ferrite nose cooling rate.     

Effects of Microalloying and Heat-Treatment Temperature on the Toughness of 26Cr–3.5Mo Super Ferritic Stainless Steels

The effects of Ni content and heat-treatment process on the toughness of a super ferritic stainless steel with 26 wt% Cr and 3.5 wt% Mo were investigated. It was found that with the increase of Ni content, the Charpy impact toughness improved remarkably, and transformed from cleavage brittle fracture to the most ductile fracture. There were no obvious differences between the high- and low-Ni contents on the microstructure and mechanical properties since the addition of Ni did not influence crystal structure, phase composition, and precipitation of ultra pure ferritic stainless steels. Meanwhile, the heat-treatment process was a key point to maintain a high level of toughness by optimizing structure and removing detrimental precipitation, i.e., chi phase.     

Influences of the Welding Heat Input and the Repeated Repair Welding on Ti–3Al–2.5V Titanium Alloy

The primary purpose of this study was to determine the effects of gas tungsten arc welding heat input on the high-temperature tensile properties, toughness, and microstructural features of titanium alloy Ti–3Al–2.5V. The secondary objective was to examine the effect of the repeated repair welding on the properties of the alloy. It was also found that the mechanical properties progressively decreased with increasing the repair welding cycles, especially in the case of the weldment after the first welding repair. It was observed that the sizes of the acicular α' and prior β grain boundaries as well as the volume fraction of the acicular α' phases increased with increasing the welding heat input. In addition, the amount and size of the acicular α' phases were found to increase with increasing the repair welding cycles.     

Effects of Ga,Sn Addition and Microstructure on Oxidation Behavior of Near-α Ti Alloy

We investigated the effects of adding Ga or Sn, with almost the same Al equivalent, on the oxidation behaviors of near-α Ti alloy with the bimodal structure and lamellar structure. The replacement of Sn with Ga decreased the alloy weight gain during oxidation, suppressed oxide growth, and improved adherence between the oxide and substrate. A lamellar alloy structure showed a lower weight gain during oxidation compared to the bimodal structure. Unlike conventional near-α alloys, recrystallization occurred near the oxide/substrate interface in Ga-modified alloy, which may contribute to the release of stress, improvement of the adherence between the oxide and substrate, and prevention of oxide-scale spallation from the Ga-modified alloy. A possible mechanism for the recrystallization in the Ga-modified alloy was also discussed.     

Effects of Ce and Ti on the microstructures and mechanical properties of an Al-Cu-Mg-Ag ahoy

The effects of Ce and Ti additions on the microstructures and mechanical properties of an Al-Cu-Mg-Ag alloy have been studied, It has been shown that either Ce or Ti can decrease the as-cast grain size of the Al-Cu-Mg-Ag alloy, increase the nucleation ratio for Ω phase as heterogeneous nucleation centers, inhibit the growth of Ω phase during aging, and thus increase the volume fraction and decrease the spacing of Ω phase. These microstructures increase the yield strength and tensile strength. However, if both Ce and Ti are added to the alloy, they form （Ce,Ti）-contained compounds and increase the grain size during casting, but have no effects on the nucleation and the growth of Ω phase during aging. The alloy containing both Ce and Ti has a relatively lower Vicks hardness and strength compared to the alloy containing either Ce or Ti.     

Effects of Ce and Ti on the microstructures and mechanical properties of an Al-Cu-Mg-Ag alloy

1. Introduction Heat-treated aluminum alloys are required for several structural applications. Several efforts have been made to improve the mechanical properties of the alloys that are currently in use and also to de-velop a novel series of alloys. The approaches used are: alloy modification, or processing modification, or both. The strength of aging-hardenable alloys such as Al–Cu–Mg series relies upon the strength-ening precipitates that are formed during aging after quenching. The agin…     

Features of the Anode Behavior of the Combined Iron–Titanium Electrode in Halide-Containing Electrolytes

Protection of Metals and Physical Chemistry of Surfaces - The electrochemical behavior of a combined iron–titanium electrode in aqueous halide solutions has been studied. The distribution of...     

Effects of Ti and La Additions on the Microstructures and Mechanical Properties of B-Refined and Sr-Modified Al–11Si Alloys

The effects of Ti and La additions on the microstructures and mechanical properties of B-refined and Sr-modified Al–11Si alloys were investigated in the present work. The interactions among Ti, La, B and Sr elements were discussed employing microstructure observation, thermal analysis and tensile test, respectively. It was found that the addition of 0.05 wt% B induces a transformation of eutectic Si from finely fibrous to coarsely plate-like morphology in the Al–11Si alloy with 0.02 wt%Sr modification, owing to the poisoning of IIT mechanism, and the eutectic Si grows only with TPRE mechanism. Both titanium and lanthanum can neutralize the co-poisoning effect between Sr and B in the Al–11Si alloy, but the neutralizing effect of La is dependent on the addition sequence. The combinative addition of La and B elements promotes the effective refinement of α-Al grains, but an inhomogeneous modification of eutectic Si phases is also observed, leading to a slightly decrease in the elongation.     

Effects of Cr and Fe Addition on Microstructure and Tensile Properties of Ti–6Al–4V Prepared by Direct Energy Deposition

The effects of Cr and Fe addition on the mechanical properties of Ti–6Al–4V alloys prepared by direct energy deposition were investigated. As the Cr and Fe concentrations were increased from 0 to 2 mass%, the tensile strength increased because of the fine-grained equiaxed prior β phase and martensite. An excellent combination of strength and ductility was obtained in these alloys. When the Cr and Fe concentrations were increased to 4 mass%, extremely fine-grained martensitic structures with poor ductility were obtained. In addition, Fe-added Ti–6Al–4V resulted in a partially melted Ti–6Al–4V powder because of the large difference between the melting temperatures of the Fe eutectic phase (Ti–33Fe) and the Ti–6Al–4V powder, which induced the formation of a thick liquid layer surrounding Ti–6Al–4V. The ductility of Fe-added Ti–6Al–4V was thus poorer than that of Cr-added Ti–6Al–4V.     

Effects of temperature and initial microstructure on the equal channel angular pressing of Ti–6Al–4V alloy

Equal channel angular pressing of Ti–6Al–4V alloy was successfully carried out isothermally above 600 °C. The equiaxed microstructure presented more uniform material flow than the Widmanstätten microstructure, which was discussed in relation to flow softening behavior of the two microstructures.     

The Influence of the Alloy Microstructure on the Oxidation Behavior of Ti–46Al–1Cr–0.2Si Alloy

The influence of microstructure of the two-phase alloyTi–46Al–1Cr–0.2Si on the oxidation behavior in air between600 and 900°C was studied. The oxidation rate, type of scale, and scalespallation resistance were strongly affected by the type of microstructure,i.e., lamellar in as-cast material and duplex after extrusion at1300°C. The oxidation rate was affected by the size and distribution ofthe ₂-Ti₃Al phase, being faster for the extrudedmaterial with coarse ₂-Ti₃Al. The type of oxide scaledetermines the spalling resistance. Cast material developed a uniform scalethat spalled off after short exposure times at 800 and 900°C when a criticalthickness was reached. The extruded material presented a heterogeneous scalewith predominant thick regions formed on -TiAl-₂-Ti₃Algrains and thin scale regions formed on -TiAl grains. Thistype of scale could permit an easier relaxation in the matrix of stressesgenerated by both thermal-expansion mismatch between scale and alloy andoxide growth, resulting in a higher spallation resistance.     

Effects of Substrate Pulse Bias Duty Cycle on the Microstructure and Mechanical Properties of Ti–Cu–N Films Deposited by Magnetic Field-Enhanced Arc Ion Plating

Ti–Cu–N films were deposited on 316 L stainless steel substrates by magnetic field-enhanced arc ion plating.The effect of substrate pulse bias duty cycle on the chemical composition,microstructure,surface morphology,mechanical and tribological properties of the films was systemically investigated.The results showed that,with increasing the duty cycle,Cu content decreases from 3.3 to 0.58 at.%.XRD results showed that only Ti N phase is observed for all the deposited films and the preferred orientation transformed from Ti N(200) to Ti N(111) plane with the increase in duty cycle.The surface roughness and deposition rate showed monotonous decrease with increasing the duty cycle.The residual stress and hardness firstly increase and then decrease afterwards with the increase in duty cycle,while the variation of critical load shows reverse trend.Except for the film with duty cycle of 10%,others perform the better wear resistance.     

Effects of Sn additions on microstructure and corrosion resistance of heat-treated Ti–Cu–Sn titanium alloys

The microstructure and corrosion properties of Ti7CuxSn (x?=?0–5?wt-%) alloys after solution treatment have been investigated. The alloys were solution-treated (ST) at 1000°C for 2?h, followed by quenching in water to room temperature. It was found that the microstructure of the ST Ti7Cu alloy had only a martensite structure, and that addition of Sn could refine the microstructure of Ti7CuxSn alloy. Notably, the pseudo dendritic α-Ti phase was formed in ST Ti7Cu5Sn alloys. Potentiodynamic polarisation curves and electrochemical impedance spectroscopy data demonstrated that adding Sn improved the electrochemical corrosion behaviour of the Ti7CuxSn alloy.