High Temperature Precipitation Hardening and Recrystallization of Al-Zr-Yb-Cr Alloys

采用透射电镜研究了Al-Zr-Yb-Cr合金中析出的弥散相的形态、结构和成分,采用硬度和金相观察对比了弥散相在500 ℃的析出硬化作用及其稳定性,以及对合金再结晶的抑制作用。结果表明：Al-Zr-Yb-Cr合金经500 ℃均匀化处理后析出了大量共格的、L12结构 (Al, Cr)3(Zr, Yb) 弥散相,弥散相均匀化处理400 h仍保持共格态,粒径维持在15~ 25 nm。其高温析出硬化及抑制铝基体再结晶作用优于Al3Zr和Al3(Zr,Yb)弥散相。     

Initial stage of crystalline rubrene thin film growth on mica (0 0 1)

We have studied the morphology and the spatially resolved photoluminescence of rubrene thin films at the early stage of crystallization. The initial growth proceeds via the formation of a wetting layer and the nucleation of islands with an amorphous structure. Crystallization starts when the amorphous islands coalesce and needle like crystalline fibers are formed in the gap between islands. The crystalline fibers then grow on top and in between the original amorphous islands leading to an "open network" of islands. The latter acts as the basis for the growth of semi-crystalline spherulites.     

Influence of Al Addition on Oxidation Behavior of Cu–Ni–Cr Alloys at 973–1073 K in 1.01 × 10<Superscript>2</Superscript> kPa Pure Oxygen

The oxidation behavior of Cu–20Ni–15Cr–2.5Al and Cu–20Ni–20Cr–2.5Al alloys was studied at 973–1073 K in 1.01 × 10² kPa pure oxygen. The oxidation kinetics exhibited large deviations from the parabolic rate law and were comprised of three or four quasi-parabolic stages. Oxidation rates of the present alloys were much lower than those previously reported for a Cu–20Ni–20Cr alloy. Cu–20Ni–15Cr–2.5Al alloy formed a continuous scale of chromia in contact with the alloy, while at other locations, the scale formed deep protrusions into alloy along β phases. Cu–20Ni–20Cr–2.5Al alloy formed a continuous scale of chromia with a small quantity of light and unoxidized precipitates of α phase, especially at 1073 K. There was a thin layer depleted in Cr beneath the continuous scales of chromia. The addition of 2.5 at.% Al to Cu–Ni–Cr alloy made the diffusion of reactive component Cr become much faster and facilitated the formation of a continuous external scale of chromia for a lower Cr content.     

Comparison of a Directionally Solidified TiAl Alloy by Φ15 mm Cylindrical and 29 × 6 mm Plate Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Molds

To begin a preliminary exploration on the effect of shape, the effect of a novel shaped 29 × 6 mm plate mold on the microstructure and mechanical properties of directionally solidified (DS) Ti-45Al-2Cr-2Nb was investigated. For comparison, Φ15 mm cylindrical molds with an equivalent cross-sectional area were used. Experimental results show that the typical microstructures of the DS region in all samples consist of regular well aligned α ₂/γ lamellar structure, B2 phase and Y₂O₃ particles. Due to the lower strength of flow generated by the shape factor of the mold, the plate sample has coarser lamellae and more B2 phase, but fewer Y₂O₃ particles. Additionally, the room temperature (RT) fracture toughness and tensile properties of the plate sample are improved.     

Effect of Heat Treatments on Microstructures and Tensile Properties of Cu–3 wt%Ag–0.5 wt%Zr Alloy

The microstructures and tensile properties of Cu–3 wt%Ag–0.5 wt%Zr alloy sheets under different aging treatments are investigated in this research. As one kind of precipitate, Ag nanoparticles with coherent orientation relationship with matrix precipitate. However, after the peak-age point, most of Ag nanoparticles grow into short rod shape with the interface translating to semi-coherent, which leads to the lower strength of over-aging sample. The yield strength is estimated by considering solid solute, grain boundary and precipitation strengthening mechanisms. The result shows that the Ag precipitates provide the main strengthening role. Then a constitutive equation representing the evolution of dislocation density with plastic strain is built by considering work-hardening behavior coming from shearable and non-shearable precipitates which is mainly the particles containing Zr. The flow stress contributed by shearable particle hardening is higher than that of non-shearable one. Due to the coarsening of grain boundary precipitates and low rate of damage accumulation of these non-shearable particles, the micro-cracks nucleate easily at grain boundary which leads to intergranular fracture.     

Equilibrium Phase Diagram of the Ternary 2-Nitrobenzoic acid-3-Nitrobenzoic Acid-Acetone System at 283.15 K and 313.15 K

In this investigation, the mutual solubilities for ternary 2-nitrobenzoic acid-3-nitrobenzoic acid-acetone system were measured at 283.15 K and 313.15 K, respectively. Two partial isothermal phase diagrams of the system were constructed on the basis of the measured solubilities, one at 283.15 K and the other at 313.15 K. The phase diagrams of the ternary system are similar at the different temperature. Two solid phases were formed and confirmed by the Schreinemaker’s wet residue method, and the two were identified as 2-nitrobenzoic acid and 3-nitrobenzoic acid. The crystallization regions of 2-nitrobenzoic acid and 3-nitrobenzoic acid increase as the temperature decreases.

Isothermal Section of Er-Ag-Sn System at 873 K

The isothermal section of the Er-Ag-Sn system at 873 K was constructed with the use of scanning electron microscopy, energy-dispersive x-ray microanalysis and x-ray powder diffraction. Two ternary compounds were confirmed at this temperature: ErAgSn (LiGaGe structure type, P6₃mc, Z = 2, a = 4.6595(2) Å, c = 7.2872(3) Å) and non-stoichiometric phase ErAg_1?xSn_2+x (Cu₃Au structure type, Pm-3m, Z = 1). For the last one homogeneity range was established (0.08 < x < 0.24) and lattice parameters were determined (a = 4.5007(4), 4.5040(2), 4.5107(1), 4.5412(1) Å for the compositions Er_25.4Ag_23.4Sn_51.2, Er_25.7Ag_23.0Sn_51.3, Er_25.7Ag_21.7Sn_52.6, Er_25.2Ag_18.6Sn_56.2 (at.%) respectively). Melting point of the phase Er_25.7Ag_21.7Sn_52.6 (at.%) was determined to be 1199 K by differential thermal analysis.     

Effect of Zn Additions on the Oxidation of Cu–2 at.% Al and Cu–4 at.% Al Alloys in 1 atm O2 at 800 °C

Four ternary Cu–Zn–Al alloys containing 5 or 10 at.% Zn and 2 or 4 at.% Al plus an alloy containing 2 at.% Al and 15 at.% Zn have been oxidized at 800 °C in 1 atm O₂, and their behavior has been compared with that of the corresponding binary Cu–Zn and Cu–Al alloys. For the alloy containing 4 at.% Al, which is already able to form external alumina scales, the addition of Zn is only effective in reducing the mass gain during the fast, initial-oxidation stage. Conversely, the addition of 15 at.% Zn to Cu–2Al is able to prevent the formation of external scales containing mixtures of the Cu and Al oxides, resulting in the formation of external alumina scales after an initial stage of faster rate, producing a limited third-element effect. Finally, the addition of Al to both Cu–5Zn and Cu–10Zn is able to prevent the internal oxidation of Zn, producing a kind of reversed third-element effect. Possible mechanisms for these effects are examined on the basis of general treatments concerning the scaling behavior of ternary alloys.     

Experimental Investigation of the Al-Fe-Nd System at 773 K

The phase diagram of Al-Fe-Nd is helpful for development of the magnetic and amorphous materials based on this system. The entire isothermal section of Al-Fe-Nd at 773 K was determined by means of x-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive analysis (EDX) and optical microscopy (OM). The existences of 12 binary compounds of the Al-Fe, Al-Nd and Fe-Nd systems were confirmed, and binary phases Al₂Nd and Fe₁₇Nd₂ demonstrated appreciable ternary solubility. The ternary compounds: τ₁-Al₁₀Fe₂Nd, τ₂-Al_8+x Fe_4?x Nd (0 < x < 0.7) and λ-Nd₃₀Fe_62?x Al_8+x (0 < x < 17) were confirmed in the present work. The isothermal section consists of 18 single-phase regions, 36 two-phase regions and 19 three-phase regions.     

Isothermal Section of Al-Si-Ce Ternary System at 1073 K

The phase equilibria in the Al-Si-Ce ternary system at 1073 K is investigated by means of x-ray diffraction and scanning electron microscope coupled with energy dispersive spectroscopy. There exist 12 three-phase regions exist in this system and one can be deduced. One ternary compound T (Ce(Al _x Si_1?x )₂) found in the isothermal section at 1073 K has the LaPtSi structure with a lattice parameter a = 0.4242 nm which composition span ranges from 32.1-47.8 at.%Al, 17.9-33.7 at.% Si, 33.4-34.0 at.% Ce. The maximum solubility of Al (in at.%) in CeSi_2?α, CeSi, Ce₅Si₄, Ce₃Si₂ and Ce₅Si₃ at 1073 K is 29.3, 23.8, 2.8, 13.6 and 6.5 respectively, and the maximum solubility of Si (in at.%) in Al₄Ce, Al₃Ce, Al₂Ce and AlCe at 1073 K is 1.4, 1.7, 1.8 and 2.1 respectively.     

Experimental Investigation of the Al-Fe-Gd System at 773 K

The phase equilibrium of the Al-Fe-Gd plays an important role of development of bulk amorphous alloys and magnetocaloric materials. The entire isothermal section of the phase diagram for Al-Fe-Gd ternary system at 773 K has been investigated by means of x-ray powder diffraction, scanning electron microscopy with energy dispersive analysis, and optical microscopy. The existences of 13 binary compounds for the Al-Fe, Al-Gd, and Fe-Gd binary systems were confirmed. The binary phases, i.e., Al₂Gd, Fe₂Gd, and α-Fe₁₇Gd₂ present appreciable ternary solubility. Three ternary compounds: τ₁-Al₁₀Fe₂Gd, τ₂-Al_8+x Fe_4-x Gd (0 ≤ x ≤ 2), and λ-Al_2?x Fe _x Gd (0.951 ≤ x ≤ 1.245) were determined. The isothermal section consists of 19 single-phase regions, 40 binary-phase regions, and 20 ternary-phase regions.     

Phase Equilibria of the Al-Mo-Dy Ternary System at 873 K

The phase relationship in the Al-Mo-Dy ternary system at 873 K has been investigated mainly by means of x-ray powder diffraction and scanning electron microscopy. The existences of ten binary compounds (i.e. AlMo₃, Al₈Mo₃, Al₄Mo, Al₅Mo, Al₁₂Mo, AlDy₂, Al₂Dy₃, AlDy, Al₂Dy and Al₃Dy) and one ternary compound (Al₄₃Mo₄Dy₆) have been confirmed. A new ternary compound Al₄Mo₂Dy (with a similar structure of the reported Al₄Mo₂Er) was found in the system. The 873 K phase diagram of this system consists of 15 single-phase regions, 29 two-phase regions and 15 three-phase regions. The maximum solid solubility of Al in AlMo₃ and Al₈Mo₃ is about 6 and 5 at.%, respectively.     

Nickel release rate of 18 KW gold alloy for ornaments

Nickel is widely used as a bleaching element in white gold alloys, but it is a potential allergen. In this paper, a popular 18 KW gold alloy, often called "safe nickel," was chosen as the experimental material; its nickel release rates under six different processing conditions were evaluated according to the EN1811 standard. The results reveal that both the surface processing method and heat treatment technology significantly affect the nickel release rate. A coarse surface releases more nickel ions than a smooth surface. The sample normalized at 700℃ in the single region has a lower nickel release rate than the one treated at 550℃ in the two-phase phase region, while high temperature normalizing at 800℃ will accelerate it. All the measured nickel release rates of the experimental material under various processing conditions exceed the permitted threshold value in the Nickel Directive, which indicates that there exists the potential risk of nickelinduced allergy when it is used to make jewelries, especially for piercing types.     

Experimental and Thermodynamic Exploration of the High-Temperature Microstructures of Co-30 wt.% Cr- (2.5-5.0 wt.%) C Alloys

Cobalt alloyed with high contents in Cr and C potentially may lead to hard alloys candidate for high temperature applications involving reduced wear degradations. The Co-30wt.%Cr-xC system was explored from x = 2.5 to 5 wt.% by both experiments and thermodynamic calculations. The stable microstructures at 1000, 1100 and 1200 °C and the temperatures of solidus and liquidus were of interest. When the carbon content is between 2.5 and 3.5 the alloys display (hypo-)eutectic microstructures composed of FCC Co-based matrix and M₇C₃ carbides. Between 4 and 5 wt.%C, the microstructures contain coarse pro-eutectic M₇C₃ carbides, leading to a total volume fraction of M₇C₃ close to 50% or higher. The C-richest alloys also contain graphite, instead cementite as predicted by calculations. A better agreement between experiments and calculations about microstructures and solidus temperature can be obtained by forbidding cementite in the calculation conditions. The obtained hardness level is about 650 Hv but decreases when the heat-treatment temperature increases.     

Copper Corrosion Under Non-uniform Magnetic Field in 0.5 M Hydrochloric Acid

The influence of a magnetic field on the electrochemical reactions taking place at the surface of a copper electrode immersed in a 0.5 M HCl solution at room temperature has been studied. The symmetry axis of the magnetic field was lined up in the same direction of the ion flow to minimize the Lorentz forces. Measurements of potentiodynamic polarization curves, electrochemical impedance spectroscopy and electrochemical noise allow concluding that the magnetic field significantly affects the cathodic reactions, with corrosion rates increasing under the presence of oxygen in acid media and decreasing when oxygen is eliminated.     

Experimental Investigation on Phase Equilibria of Al-Fe-Y System at 773 K

The phase diagram determination of Al-Fe-Y is helpful for development of magnetic and amorphous materials. The entire isothermal section of Al-Fe-Y at 773 K has been determined by means of x-ray powder diffraction, scanning electron microscopy with energy dispersive analysis and optical microscopy. The existences of 14 binary compounds in the Al-Fe, Al-Y and Fe-Y binary systems were confirmed. The binary phases Al₂Y, Fe₂Y, Al₂Y₃, Fe₂₃Y₆ and Fe₁₇Y₂ in this study present appreciable ternary solubility: Fe_17?x Al _x Y₂ (0 ≤ x ≤ 8.5), Y(Fe_1?x Al _x )₂ (0 ≤ x ≤ 1), Al₂(Fe _x Y_1?x )₃ (0 ≤ x ≤ 0.3), and (Fe,Al)₂₃Y₆ with Al up to 22 at.%. The ternary compounds: τ₁-Al₁₀Fe₂Y, τ₂-Al_8?x Fe_4+x Y (0 ≤ x ≤ 2) were confirmed. The isothermal section consists of 19 single-phase regions, 33 two-phase regions and 17 three-phase regions.     

Cementite Dissolution Kinetics of High Carbon Chromium Steel During Intercritical Austenitization

The cementite dissolution behavior of a hypereutectoid high carbon chromium bearing steel has been studied using the theory of local equilibrium assumption at interface. The dissolution mode was established and the process was calculated using DICTRA software. Heat treatment was performed on DIL 805 formastor, and microstructure was observed by ZEISS-SUPRA-55 SEM. Fraction and size of cementite particles were counted by ImageJ software. The results indicate that dissolution rate of cementite is fast in the beginning and then becomes slowly when holding at 840, 860 and 880 °C respectively. The simulation results are in good agreement with statistical results of SEM graphs. The fast dissolution stage is controlled by diffusion of C atoms, and the subsequent sluggish stage is governed by diffusion of Cr. Microscopically, dissolution of cementite depends upon the temporary destruction and instant recovery of local equilibrium at austenite/cementite interface. Diffusion rate of carbon is high, leading to the rapid distribution between cementite and austenite. C content in austenite increases significantly with the holding time, while little change happens to Cr content. The increase of Cr content in cementite obviously enhances its stability and reduces subsequent dissolution rate.     

Microstructure and Softening of Laser-Welded 960 MPa Grade High Strength Steel Joints

The microstructural evolution of laser-welded 960 MPa grade high strength steel joints and its effect on softening behavior of heat affected zone (HAZ) were investigated in this paper. The results show that microstructure of HAZ and fusion zone (FZ) is composed of lath martensite and bainitic ferrite. The microstructure of mixed grained zone presents strip-like characteristics and small block martensite distributes along the grain boundary. The grain size near the fusion line is about 25 μm, and the grain size in the fine grain zone is less than 5 μm. Microhardness of HAZ and FZ is lower than base metal. The soft zone locates in transitional region between tempering zone and mixed grained zone due to the interaction of the martensite tempering and the recovery and recrystallization of the rolled microstructure. Microhardness of soft zone is 310 HV and drops 18% compared to base material. Welding heat input has a remarkable effect on the width of soft zone and microhardness. The tensile properties of weld joints are closely related to the softening behavior of HAZ.