Structure and mechanical and corrosion properties of new high-nitrogen Cr-Mn steels containing molybdenum

The structure, mechanical properties, and pitting corrosion of nickel-free high-nitrogen (0.8% N) austenitic 06Kh18AG19M2 and 07Kh16AG13M3 steels have been studied in various structural states obtained after hot deformation, quenching, and tempering at 300 and 500°C. Both steels are shown to be resistant to the ?? ?? ?? and ?? ?? ? martensite transformations irrespective of the decomposition of a ?? solid solution (06Kh18AG19M2 steel). Austenite of the steel with 19 wt % Mn shows lower resistance to recrystallization, which provides its higher plasticity (??₅) and fracture toughness at a lower strength as compared to the steel with 13 wt % Mn. Electrochemical studies of the steels tempered at 300 and 500°C show that they are in a stable passive state during tests in a 3.5% NaCl solution and have high pitting resistance up to a potential E _pf = 1.3?C1.4 V, which is higher than that in 12Kh18N10T steel. In the quenched state, the passive state is instable but pitting formation potentials E _pf retain their values. In all steels under study, pitting is shown to form predominantly along the grain boundaries of nonrecrystallized austenite. The lowest pitting resistance is demonstrated by the structure with a double grain boundary network that results from incomplete recrystallization at 1100°C and from the existence of initial and recrystallized austenite in the 07Kh16AG13M3 steel. To obtain a set of high mechanical and corrosion properties under given rolling conditions (1200?C1150°C), annealing of the steels at temperatures no less than 1150°C (for 1 h) with water quenching and tempering at 500°C for 2 h are recommended.     

Solid solution decomposition mechanisms in cast and microcrystalline Al-Sc alloys: III. Analysis of experimental data

The results of experimental studies of the decomposition of the solid solution in cast and microcrystalline (MC) Al-X wt % Mg-0.22 wt % Sc-0.15 wt % Zr (X = 0, 1.5, 4.5) aluminum alloys that were described in part I of this work are analyzed. The data on the electrical resistivity of the alloys are used to determine the volume fraction of Al₃Sc(Zr) particles precipitating in the temperature range 240–400°C. The model developed in part II of this work is used to reveal the mechanism of particle precipitation in the cast and MC alloys. It is shown that the particles in the cast and MC alloys precipitate mainly on dislocations. The differences in the decomposition kinetics of the solid solution in the cast and MC alloys are explained by different mechanisms of dislocation structure recovery mechanisms occurring in them.     

Hardness and electrical resistivity of Al–13 wt % Mg<Subscript>2</Subscript>Si pseudoeutectic alloy

In the present work, effect of growth rates on microhardness, electrical properties and microstructure for directionally solidified Al–13 wt % Mg₂Si pseudoeutectic alloy at a constant temperature gradient were studied. Directional solidification process were carried out with five different growth rates (V = 8.33–175.0 μm/s) at a constant temperature gradient (G = 6.68 K/mm) by using a Bridgman type directional solidification furnace. Microstructure of directionally solidified Al–13 wt % Mg₂Si pseudoeutectic alloy was observed as Mg₂Si coral-like structure phase dispersed into primary α-Al phase matrix. The electrical resistivity for Al–13 wt % Mg₂Si pseudoeutectic alloy, were measured by the d.c. four-point probe method. The dependency ofmicrohardness and electrical resistivity on growth rates were obtained as HV = 135.7 (V)^0.09 and ρ = 17.30 × 10^?8(V)^0.08, respectively for Al–Mg₂Si pseudoeutectic alloy. The results obtained in present work were compared with the previous similar experimental results.     

Microstructure and mechanical properties of Mg-Zn-Y-Nd-Zr alloys

The microstructure and tensile properties of the as-cast and solution treatment Mg-4.5Zn-1Y-xNd-0.5Zr (x=0, 1 wt.%, 2 wt.%, 3 wt.%) alloys were investigated. The results showed that the microstructure of Mg-4.5Zn-1Y-0.5Zr alloy consisted of α-Mg, Zn-Zr, W (Mg₃Y₂Zn₃) and I (Mg₃YZn₆) phases. With the addition of Nd, I-phase disappeared and Mg₃Y₂Zn₃ phase changed into Mg₃(Nd,Y)₂Zn₃ phase. When the content of Nd reached 3 wt.%, T phase, i.e., ternary Mg-Zn-Nd phase, formed. In addition, with the increase of Nd content in the alloys, the secondary dendritic arm spacing decreased, while the amount of intermetallic phases increased. For as-cast Mg-4.5Zn-1Y-xNd-0.5Zr alloys, after solution treatment, microsegregation was eliminated and the shape of eutectic structure of α-Mg+W transformed from lamellar into spherical. The tensile strength and elongation of Mg-4.5Zn-1Y- 3Nd-0.5Zr alloy were increased from 219.2 MPa and 11.0% to 247.5 MPa and 20.0%, respectively.     

Influence of the initial concentration of hydrogen and modes of vacuum annealing on the structure, phase composition, and mechanical properties of sheet billet of the VT6 alloy: Part 1. Influence of the initial hydrogen concentration and modes of vacuum annealing on the phase composition and the average diameter of grain of the VT6 alloy

The possibilities of using reversible hydrogen doping in combination with warm rolling for milling the structural components and the formation of a heterophase structure are shown by the example of the VT6 alloy. Alloy doping with 0.3?C0.7 wt % hydrogen and the formation of a ?? + ?? + ??₂ structure is accompanied by the enhancement of the local nonuniformity of deformation and an increase in the number of recrystallization nuclei during warm sheet rolling. The relation between the initial hydrogen concentration and the temperature of vacuum annealing (VA) with the phase composition and the size of structural components is established.     

Hydrogen storage properties of mechanically milled La2Mg17-x wt.% Ni （x=0, 50, 100, 150 and 200） composites

Melting method was used to obtain La2Mg17 alloy,and then Ni powder was added by mechanical alloying method.The kinetics of hydriding process and electrochemical properties of La2Mg17-x wt.%Ni(x=0,50,100,150,200) composites were investigated.X-ray diffraction(XRD) and scanning electron microscopy(SEM) analyses showed that the crystal structure of composite alloy gradually transformed into amorphous phase by the effect of ball milling and Ni powders.The research of hydrogen absorption properties found that La2Mg 17-50 wt.%Ni reached the highest hydrogen absorption than other alloys with more addition of Ni content,reached to 5.796 wt.% at 3 MPa,and up to 5.229 wt.% merely in 2 min,which revealed that the amorphous phase reduced the H occupation of the lattice clearance,resulting in the decline of hydrogen absorption capacity.The electrochemical tests indicated that the maximum discharge capacity increased to 353.1 mAh/g at 30 oC,however,the cycle stability decreased considerably.A series of kinetic measurements demonstrated that the controlling steps of electrochemical process of La 2 Mg 17-x wt.%Ni alloys transferred from hydrogen diffusion on alloy bulk(x=50,100) to hydrogen diffusion on both alloy bulk and surface(x=150,200).     

Influence of CeO2 doping amount on property of BCTZ lead-free piezoelectric ceramics sintered at low temperature

Ba0.85Ca0.15Ti0.9Zr0.1O3(BCTZ) lead-free piezoelectric ceramics co-doped with CeO2(x=0.1 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%) and Li2CO3(0.6 wt.%) were prepared by conventional solid-state reaction method. Influence of CeO2 doping amount on the piezoelectric properties, dielectric properties, phase composition and microstructure of prepared BCTZ lead-free piezoelectric ceramics doped with Li2CO3 were investigated by X-ray diffraction(XRD) and scanning electron microscopy(SEM) and other analytical methods. The results showed that the sintered temperature of BCTZ lead-free piezoelectric ceramics doped with CeO2 decreased greatly when Li2CO3 doping amount was 0.6 wt.%; a pure perovskite structure of BCTZ lead-free piezoelectric ceramics co-doped with Li2CO3 and CeO2 and sintered at 1050 °C could also be obtained. The piezoelectric constant(d33), the relative permittivity(εr) and the planar electromechanical coupling factor(kp) of BCTZ ceramics doped with Li2CO3 increased firstly and then decreased, the dielectric loss(tanδ) decreased firstly and then increased and decreased at last when CeO2 doping amount increased. The influence of CeO2 doping on the properties of BCTZ lead-free piezoelectric ceramics doped with Li2CO3 were caused by "soft effect" and "hard effect" piezoelectric additive and causing lattice distortion. When CeO2 doping amount(x) was 0.2 wt.%, the BCTZ ceramics doped with Li2CO3(0.6 wt.%) and sintered at 1050 °C possessed the best piezoelectric property and dielectric property with d33 of 436 pC/N, kp of 48.3%, εr of 3650, tanδ of 1.5%.     

Effect of Co Addition on the Microstructure, Martensitic Transformation and Shape Memory Behavior of Fe-Mn-Si Alloys

The effect of Co addition has been studied in Fe-30Mn-6Si-xCo (x = 0 to 9 wt pct) shape memory alloys in terms of their microstructure, martensitic transformation and shape recovery. Microstructural investigations reveal that in Fe-Mn-Si-Co alloys, the microstructure remains single-phase austenite (??) up to 5 pct Co and beyond that becomes two-phase comprising ?? and off-stoichiometric (Fe,Co)₅Mn₃Si₂ intermetallic ??-phases. The forward ??-?? martensite transformation start temperature (M _S) decreases with the addition of Co up to 5 pct, and alloys containing more than 5 pct Co, show slightly higher M _S possibly on account of two-phase microstructure. Unlike M _S, the ??-?? reverse transformation start temperature (A _S) has been found to remain almost unaltered by Co addition. In general, addition of Co to Fe-Mn-Si alloys deteriorates shape recovery due to decreasing resistance to plastic yielding concomitant with the formation of stress induced ?? martensite. However, there is an improvement in shape recovery beyond 5 pct Co addition, possibly due to the strengthening effect arising from the presence of (Fe,Co)₅Mn₃Si₂ precipitates within the two-phase microstructure and due to higher amount of stress induced ?? martensite.     

Speciation of vanadium (V) extracted from acidic sulfate media by trioctylamine in n-dodecane modified with 1-tridecanol

The speciation of vanadium (V) extracted from acidic sulfate media by protonated trioctylamine in n-dodecane modified with 5% (wt) 1-tridecanol has been investigated by Fourier transformed infrared spectroscopy (FTIR) and ⁵¹V nuclear magnetic resonance spectroscopy (⁵¹V NMR). In aqueous sulfate solutions, vanadium (V) exists both as VO₂⁺ and VO₂SO₄⁻ ions. The FTIR spectra of 0.2 mol kg^− 1 protonated trioctylamine in n-dodecane modified with 5% (wt) 1-tridecanol, loaded with various concentrations of vanadium (V) by extraction from 1 mol kg^− 1 H₂SO₄, indicate that vanadium (V) exists in organic phases as polyvanadates, likely as decavanadates. The condensed nature of the extracted form of vanadium (V) was neither confirmed nor precluded by ⁵¹V NMR as the micellar structure of these organic phases imposes local conditions which allow the transformation of VO₂⁺ and VO₂SO₄⁻ into polyvanadates, but also modify the chemical shifts compared to the ones observed in bulk aqueous solutions for mononuclear and polynuclear vanadium (V) species.     

Textural Evolution During Dynamic Recovery and Static Recrystallization of Molybdenum

In the current investigation, sintered molybdenum specimens with random textures were deformed in compression in a deformation dilatometer over a range of temperatures from 0.44T _M [K] to 0.61T _M [K] and true strains between ???=?0.3 and 0.92. Subsequent annealing treatments were carried out in the dilatometer in order to study static recrystallization phenomena. Electron backscatter diffraction scans of deformed and recrystallized specimens revealed that the microstructure after hot deformation is a recovered structure with two remarkably strong orientation components, ??111?? parallel to the loading direction exhibiting a high Taylor factor and ??100?? parallel to the loading direction with a low one. The fraction of the first component increases with lowering the deformation temperature, while static recrystallization leads to a higher fraction of the second component. The late-stage recrystallization behavior is sluggish due to a high amount of recovery. The results are discussed employing models for textural evolution in body-centered cubic (bcc) metals on the one hand and recrystallization of high-stacking-fault energy materials on the other.     

Preparation of materials in the system Al2O3 (with additions)-TiB2 and study of their electrical resistance

Materials in the system AI₂O₃ (with additions of ZrO₂, SiO₂, CeO₂, Si₃N₄, AIN)-TiB, containing titanium boride concentrations up to 70 wt. % were prepared by sintering in carbon monoxide (T = 1873 K, t = 3 h). The relative density of these materials did not exceed 69% of theoretical, with a minimum at approximately 38% TiB₂ on the density vs. composition curve. The specific electrical resistance of the materials decreased from 3.410⁹ to 82 Ω cm with increasing titanium boride concentration. An abrupt decrease in electrical resistance occurred in the range 20-30% titanium boride.     

Hydrophilic and photocatalytic performances of lanthanum doped titanium dioxide thin films

Pure and La-doped TiO2 thin films were prepared on glass by sol-gel method using tetrabutyl titanate as Ti precursors. Their chemical composition, structure and properties were characterized by X-ray d...     

Phase and Formation/Dissolution of Precipitates in Biomedical Co-Cr-Mo Alloys with Nitrogen Addition

The precipitates in as-cast and heat-treated biomedical Co-28Cr-6Mo-(0 to 0.35)C-(0.15 to 0.25)N alloys (mass pct) were investigated. Heat treatment was carried out at temperatures of 1473?K to 1573?K (1200???C to 1300???C) for holding periods of 0 to 43.2?ks. In the as-cast and heat-treated Co-Cr-Mo-N alloys, no precipitates were detected; nitrogen effectively inhibited the formation of the ??-phase and stabilized the face-centered cubic (fcc) metallic ??-phase. The precipitates observed in the as-cast and heat-treated Co-Cr-Mo-C-N alloys were of the M₂₃X₆ type, M₂X type, ??-phase (M₂T₃X type with a ??-Mn structure), and ??-phase (M₆X-M₁₂X type). Complete precipitate dissolution was detected in the alloys with carbon contents of less than 0.3 mass pct regardless of the nitrogen content. The main precipitates were of the M₂X and M₂₃X₆ types after heat treatment for 1.8 to 43.2?ks. The ??-phase precipitate was detected in the early stage of heat treatment at high temperatures. The formation of the M₂X-type precipitate was enhanced by the addition of nitrogen, although the constitution of the precipitates depended on the balance between the nitrogen and carbon contents and the heat-treatment conditions.     

Physicochemical aspects of technology of the Al2O3-Al layered cermet obtained using reaction sintering

Certain features of the technology of the Al₂O₃-Al layered cermet obtained by the reaction sintering (RS) in air of powdered billets that were fabricated by pressing the charge from the PAP-2 plateletshaped aluminum powder. The RS process was activated by the introduction of a dry residue of liquid glass (DRLG) into the charge (C = 3?C28%). According to the data of the X-ray phase analysis, the sintered material contains (vol %): Al (61?C82), ??-Al₂O₃ (8?C25), Na₂Si₂O₅ (2?C15), and Si (1?C14). Oxide phases and silicon are nanodimensional morphological objects (13?C100 ??m) in the layered aluminum host. The cermet density is 2.1?C2.45 g/cm³, tensile strength is 45?C90 MPa, and the ultimate bending strength is 320 MPa. The activation of RS by a small DRGL additive (3%) retains the layered cermet structure. It is leveled at a considerable increase in the RS time (up to 600 min) or C (up to 28%) because of recrystallization and involves plateletshaped aluminum particles in the chemical interaction.     

Dendrite growth directions in aluminum-zinc alloys

The dendrite growth directions in fcc aluminum-zinc alloys have been measured by electron backscattered diffraction (EBSD) as a function of the zinc concentration,c _o . In specimens produced by directional or Bridgman solidification, 〈100〉 dendrites were observed up to 25 wt pct Zn, whereas, above 60 wt pct, the dendrite growth direction was clearly 〈110〉. In between these two concentrations, the angle, φ(c _o ), between 〈100〉 and the 〈hk0〉 dendrite growth direction, varied continuously between 0 and 45 deg asc _o increased. Following an analysis of growth directions suggested by Karma but restricted to two dimensions in a (001) plane,^[1] this angle was fitted with a function ¼ arcos (?η₄/4η₈), where η₄(c _o ) cos (4φ) and η₈(c _o ) cos (8φ) are the first two contributions to the solid-liquid interfacial stiffness anisotropy in a (001) plane. This analysis also gives a qualitative explanation to textured seaweed structures observed aroundc _o ≈ 25 and 60 wt pct. These findings are discussed in light of recent measurements of the weak interfacial solid-liquid energy anisotropy of aluminum^[2,3] and of dendrite growth directions in hcp Zn-Al alloys.^[4]     

The Sintering, Sintered Microstructure and Mechanical Properties of Ti-Fe-Si Alloys

A systematic study has been conducted of the sintering, sintered microstructure and tensile properties of a range of lower cost Ti-Fe-Si alloys, including Ti-3Fe-(0-4)Si, Ti-(3-6)Fe-0.5Si, and Ti-(3-6)Fe-1Si (in wt pct throughout). Small additions of Si (??1?pct) noticeably improve the as-sintered tensile properties of Ti-3Fe alloy, including the ductility, with fine titanium silicides (Ti₅Si₃) being dispersed in both the ?? and ?? phases. Conversely, additions of ?>1?pct Si produce coarse and/or networked Ti₅Si₃ silicides along the grain boundaries leading to predominantly intergranular fracture and, hence, poor ductility, although the tensile strength continues to increase because of the reinforcement by Ti₅Si₃. Increasing the Fe content in the Ti-xFe-0.5/1.0Si alloys above 3?pct markedly increases the average grain size and changes the morphology of the ??-phase phase to much thinner and more acicular laths. Consequently, the ductility drops to <1?pct. Si reacts exothermically with Fe to form Fe-Si compounds prior to the complete diffusion of the Fe into the Ti matrix during heating. The heat thus released in conjunction with the continuous external heat input melts the silicides leading to transient liquid formation, which improves the densification during heating. No Ti-TiFe eutectoid was observed in the as-sintered Ti-Fe-Si alloys. The optimum PM Ti-Fe-Si compositions are determined to be Ti-3Fe-(0.5-1.0)Si.     

An investigation of the effect of the electrolyte composition on the consumption of fired anodes during electrolytic aluminum production

The effect of adding CaF₂, AlF₃, and KF into electrolyte on the consumption of fired anode during aluminum electrolysis is investigated. The CaF₂ content varied from 5 to 10 wt % in the electrolyte of the industrial composition. Correspondingly, the concentration of AlF₃ and KF varied from 4 to 10 and from 0 to 4.7 wt % in the modified electrolytes. Based on the procedure used, the total consumption of carbon and the amount of carbon transported into the gas phase (m _g) and foam (m _f) were determined. Electrolysis duration was 12 h, the distance between the poles was 40 mm, the temperature was 960°C, and the current density was 0.85 and 1.2 A/cm². It is established that adding CaF₂ and AlF₃ increases the consumption of anode, while adding KF decreases it. For CaF₂, ?m _f/?[CaF₂] is larger than ?m _g/?[CaF₂], 15.4 and 6.6 kg/(t_Al wt %) CaF₂, respectively. For AlF₃, ?m _f/?[AlF₃] is also larger than ?m _g/?[AlF₃] and equals 6.8 and 4.2 kg/(t_Al wt %) AlF₃. For KF, ?m _f/?[KF] is smaller than ?m _g/?[KF], being ?11.3 and ?8.1 kg/(t_Al wt %) KF.     

Modification of eutectic silicon andβ-Al5FeSi phases in as-cast ADC12 alloys by using samarium addition

The effects of Sm additions (0, 0.5 wt.%, 1.0 wt.%and 1.5 wt.%) on the eutectic Si and β-Al5FeSi phases of ADC12 as-cast alloys were studied by optical microscopy (OM), scanning electron microscopy (SE...     

Anodic behavior of the NiO-Fe2O3-Cr2O3-Cu composite during the low-temperature electrolysis of aluminum

In order to fabricate oxide-metallic composites with the composition 25.3NiO-41.2Fe₂O₃-13.5Cr₂O₃-20.0Cu (wt %), the temperature and duration of sintering (1350°C, 30 min) that ensure the formation of the solid solution of chromium oxide in nickel ferrite have been determined. This material is tested as an anode for the electrolysis of the low-temperature solution with the composition 12.0NaF-36.8KF-51.2AlF₃ (wt %), which was saturated with Al₂O₃ (t = 800°C). The amount of gaseous oxygen evolved on the anode was measured. It is shown that the main reaction on an anode at current density i = 0.015–1.0 A cm^?2 is the oxidation of oxygen-containing anions from a melt with the formation of gaseous O₂ and a substantial increase in the oxidation rate of the composite anode is observed at i > 1.0 A cm^?2. The voltage across the electrolyzer (4.5 ± 0.5 V) and the anodic potential (2.43 ± 0.2 relative to the Al reference electrode) during a prolonged experiment (for 89 h, i = 0.4 A cm^?2) indicate a stable and acceptable electrical conductivity of the material, while the dissolution rate, which was calculated by the weight loss (0.6 kg/yr) and volume loss (0.7 cm/yr), satisfy the requirements to inert anodes.     

Microstructure evolutions of Mg-8Gd-2Er （wt.%） alloy during isothermal ageing at 200 ℃

The precipitation of the Mg-8Gd-2Er(wt.%) alloy at 200 oC was investigated by transmission electron microscopy(TEM) and X-ray diffraction(XRD).The precipitation sequence was described as supersaturated solid solution(S.S.S.S.,cph)→β’’(D019)→β’(bco)→β-phase(fcc),which was different from previously reported four stages sequence:(S.S.S.S.,cph)→β’’(D019)→β’(bco)→β1(fcc)→β-phase(fcc).The morphologies and crystal structures of both β’’ and β’ precipitates in the alloy were studied in the present investigation.The orientation re-lationship between the precipitate phases and the α-matrix was observed.The ultimate tensile strength(UTS) and tensile yield strength(TYS) of the as-cast alloy were 189 and 110 MPa,respectively,and the UTS and the YTS were improved greatly after ageing treatment.The values of UTS and YTS after peak ageing process were 308 and 246 MPa,respectively.The improved mechanical properties were mainly ascribed to the formation of β’ phase.The age hardening response decreased with increasing ageing time because the β’ phase got coarse as ageing time increased.