Primary Precipitation Phase Research Articles

Influence of precipitation on the intergranular corrosion sensitivity of aged Alloy 31 using a modified electrochemical potentiokinetic reactivation method

The influence of precipitation on the intergranular corrosion sensitivity of Alloy 31 aged at 950 ℃ for 0–96 h was investigated by microstructure analysis and the modified double loop electrochemical potentiokinetic reactivation method. The results reveal that the kinetics of the primary precipitated sigma phase agree with the Yamamoto equation. The degree of sensitization increases rapidly to 4 h, then decreases to 8 h with self-healing, but no further self-healing occurs after that. The degree of sensitisation depends on the Cr and Mo-depletion zone neighbouring the precipitated sigma phase.

Tunable and attractive magnetic properties of FeBPSiCu alloys

Novel Fe76-xB10P5Si9Cux (x = 0, 0.5, 1 and 1.5 at.%) amorphous alloys with low Fe content were successfully synthesized with aim of investigating the crystallization behaviors and magnetic properties. Thermodynamic behavior revealed that Cu substitution triggered the transition of primary precipitation phase from Fe23B6 to α-Fe, which favored the high saturation magnetic flux density (Bs) of alloys after annealing. Through adjustment of Fe/Cu ratio, the Fe75B10P5Si9Cu1 alloy exhibited the attractive and tunable magnetic properties, i.e. the high effective permeability (μe) of 25000 and low coercivity (Hc) of 1.3 A/m in amorphous state as well as the high Bs of 1.62 T and μe of 18000 in crystallization state. The high Bs could be attributed to the uniform refined composite microstructure, whereas the excellent magnetic softness characterized by magnetic domain patterns was determined by magnetic anisotropy induced via different atomic structures. Such tunable performance can promise alloy a potential soft-magnetic material to meet the requirement of most electric devices.

Formation of Metastable Aluminides in Al–Sc–Ti (Zr, Hf) Cast Alloys

The effect of the ternary alloys composition and overheating of their melts (at 100–370 K above the liquidus temperature) on the morphology and composition of aluminides in the Al–Sc–Ti, Al–Sc–Zr, Al–Sc–Hf systems were investigated. It was shown that during the crystallization of these melts under certain conditions, the primary precipitated phase are the complex aluminides Al3(ScxZr1−x), Al3(ScxTi1−x), Al3(ScxHf1−x) having a metastable cubic lattice with L12 structure, which matches the α-Al structural type. The variety of growth forms of aluminides is explained by a combination of a number of factors: the magnitude of overheating of the melt, the difference in the diffusion coefficients of transition metals, and the local concentration of transition metals in the respective growth zones.

Influence of Ag replacement on the formation and heating-induced phase decomposition of Zr65Al7.5Co27.5-xAgx (x=5 to 20 at%) glassy alloys

A glass-type alloy with glass transition (GT) and supercooled liquid region was formed at a limited Ag/Co content ratio around 1.2 in melt-spun Zr65Al7.5Co27.5-xAgx (x = 5–20 at%) alloys. This alloy crystallized through two-stage exothermic reactions where an icosahedral (I) phase appears as a primary precipitation phase, followed by the second-stage reaction from glass + I-phase to four crystalline phases. The I-phase has a spherical morphology and its size is about 8 nm. The Zr65Al7.5Co17.5Ag10 alloy without GT keeps a glass-like structure even after heating for 3.6 ks at 750 K above the first exothermic peak, indicating the formation of a cluster-like glassy phase. The Zr65Al7.5Co17.5Ag10 alloy rod keeps a glassy phase in the diameter up to 1.7 mm, though the rod does not show the first-stage exothermic reaction. These features are the same as those for the annealed ribbons, indicating that a clustered glassy phase is also formed for the bulk alloy. This alloy satisfies with the formation criterion of the clustered glassy phase, i.e., large atomic size mismatch and positive heat of mixing for solute elements. The high stability of glassy phase leading to the formation of the clustered glassy phase is due to the resistance to atomic rearrangement of unlike Co and Ag elements. The Zr65Al7.5Co12.5Ag15 alloy exhibits the lowest decomposition temperature (Tx) and the highest hardness, being opposite to the previous relation for hardness to increase with increasing Tx. The relationship between GT and I-phase precipitation suggests that the GT is attributed to the development of I-like medium-range ordered structure.

Understanding the bottom buildup in an electric copper smelting furnace by thermodynamic calculations

ABSTRACTThermodynamic calculations were used to investigate the liquidus temperature of the slag and the possible influence on the buildup formation in an electric copper smelting furnace. The impact of parameters such as Fe/SiO2 ratio, partial pressure of oxygen and the content of the oxides ZnO, Al2O3 and Cr2O3 in the slag were investigated with respect to the liquidus temperature of the slag. Results show that the chromium content in the slag has the greatest impact on the liquidus temperature and on the formation of solid particles. The characterisation of the buildup done earlier showed that spinel phases were among the dominating phases. This is supported by the thermodynamic calculations in the present paper, where the chromite solid solution was found to be the primary precipitation phase.

Enhancement of plasticity in Zr-Cu-Ni-Al-Ti bulk metallic glass by heterogeneous microstructure

Icosahedral phase was found as a primary precipitated phase in the Zr70−xCu12.5Ni10Al7.5Tix (x=0–8) BMGs with two or three steps of crystallization process. Remarkable plasticity was realized in a wide range of alloy composition. The enhanced plasticity is attributed to the presence of icosahedral medium-range order clusters and the local heterogeneous distribution of free volume.

Influence of Ag replacement on supercooled liquid region and icosahedral phase precipitation of Zr65Al7.5Ni10Cu17.5-xAgx (x = 0–17.5 at%) glassy alloys

The glass transition phenomenon for Zr65Al7.5Ni10Cu17.5-xAgx (x = 5–17.5 at%) glassy alloys was observed in the Ag content range below about 15% and the icosahedral phase precipitated as the heating-induced primary phase in the limited Ag content range. In the higher Ag content range where glass transition is not clearly observed, the primary precipitation phase changed to mixed phases of tetragonal Zr3Ag + tetragonal Zr2Ni + hexagonal Zr4Al3. The good correspondence between the appearance of glass transition and the icosahedral phase precipitation was recognized in the multicomponent glassy alloys containing the immiscible type atomic pairs of Ni-Ag and Cu-Ag. Although neither glass transition nor supercooled liquid region is observed for Zr65Al7.5Ni10Ag17.5 and no icosahedral phase is formed, a modified Zr65Al7.5Ni17.5Ag10 alloy with higher Ni/Ag content ratio exhibits glass transition and supercooled liquid region and the primary precipitates also changes to an icosahedral phase. The good correspondence can be interpreted on the basis of the previous knowledge that the appearance of glass transition and supercooled liquid state originates from icosahedral-like medium range ordered atomic configurations. Besides, the 6%Ag-containing alloy keeps high glass-forming ability which is high enough to form a bulk glassy alloy rod of 6 mm by suction casting. The close correlation between the appearance of glass transition phenomenon and the primary precipitation of icosahedral phase is expected to provide a useful knowledge on the role of icosahedral-like atomic configuration in the achievement of bulk glass-forming ability through the stabilization of supercooled liquid.

Effect of Aging Treatment on the Precipitation Behavior and Mechanical Properties of Mg-9Gd-3Y-1.5Zn-0.5Zr Alloy

Aging heat treatments of an extruded Mg-9Gd-3Y-1.5Zn-0.5Zr (wt.%) alloy at 200, 225, and 250 °C for various times were studied. The results show that dynamic recrystallization (DRX) occurred during the extrusion process and the alloy exhibited a significant aging hardening response at temperatures ranging from 200 to 225 °C. The precipitation sequence of the alloy at 225 °C was supersaturated solid solution (SSSS) → β″ (D019, Mg3RE) → β′ (bco, Mg15RE3), where the β′ phase was the primary precipitated phase. A large amount of discontinuous lamellar-shaped 14H-structure long period stacking ordered (LPSO) phase was also observed in the α-Mg matrix before and after aging treatments. Owing to the combined strengthening effect of fine DRXed grains, β′ nanoparticles, and widespread LPSO phases, the ultimate tensile strength and tensile yield strength of the peak-aged extruded alloy reached 409 and 303 MPa, respectively. The elongation in this circumstance was ~7.1%, which was slightly lower than that of the alloy before aging treatment.

Proterozoic microbial mats and their constraints on environments of silicification.

The occurrence of microfossiliferous, early diagenetic chert in Proterozoic successions is broadly restricted to peritidal marine environments. Such coastal environments are amongst the most environmentally variable of marine environments, experiencing both enhanced evaporation and potential influx of terrestrial freshwaters. To better understand potential conditions under which silicification occurs, we focus on microfossiliferous early diagenetic chert from the Mesoproterozoic Bylot Supergroup, northern Baffin Island. Spectacular preservation of silicified microbial mats, their associated mineral phases, and the petrographic fabrics of the chert itself require that silicification occurred at the sediment-water interface, penecontemporaneously with mat growth. In some cases, silica is the primary precipitated mineral phase and is not associated with replacement of precursor mineral phases. In other cases, silica deposition includes the mimetic replacement of carbonate, gypsum, and halite mineral phases. These petrographic constraints suggest that silicification potentially occurred under a range of fluid chemistries associated with environmental variability in nearshore peritidal environments. Here we provide the first direct thermodynamic modeling of hypothetical Proterozoic seawater solutions, seawater-derived brines, and mixed seawater-freshwater solutions, and demonstrate that peritidal environments are capable of providing a wide range of fluid chemistries under which early diagenetic silica can both precipitate and replace primary mineralogical phases. Despite the thermodynamic potential for silica deposition under a wide range of fluid compositions, chert is not ubiquitous in Proterozoic nearshore environments, suggesting that the kinetics of silica polymerization exert a primary control over deposition.

High formability of glass plus fcc-Al phases in rapidly solidified Al-based multicomponent alloy

A multicomponent Al84Y9Ni4Co1.5Fe0.5Pd1 alloy was found to keep a mixed glassy + Al phases in the relatively large ribbon thickness range up to about 200 μm for the melt-spun ribbon and in the diameter range up to about 1100 μm for the wedge-shaped cone rod prepared by injection copper mold casting. The glassy phase in the Al-based alloy has a unique crystallization process of glass transition, followed by supercooled liquid region, fcc-Al + glass, and then Al + Al3Y + Al9 (Co, Fe)2 + unknown phase. It is also noticed that the primary precipitation phase from supercooled liquid is composed of an Al phase instead of coexistent Al + compound phases, being different from the crystallization mode from supercooled liquid for ordinary Al-based glassy alloys. In addition, it is noticed that the mixed Al and glassy phases are extended in a wide heating temperature range of 588–703 K, which is favorable for the development of high-strength nanostructure Al-based bulk alloys obtained by warm extrusion of mixed Al + amorphous phases. The Vickers hardness is about 415 for the glassy phase and increases significantly to about 580 for the mixed Al and glassy phases. The knowledge of forming Al + glassy phases with high hardness in the wide solidification and annealing conditions through high stability up to complete crystallization for the multicomponent alloy is promising for future development of a high-strength Al-based bulk alloy.

Thermal stability, crystallization and soft magnetic properties of Fe-P-C-based glassy alloys

Thermal stability, crystallization and magnetic properties of Fe80P11C9, Fe80P9B2C9, and Fe77Al3P9B2C9 glassy alloys were investigated. The relationships of glass-forming ability (GFA) with thermal properties and crystallization, magnetic properties with crystallization were also discussed. The variation trend of GFA for these glassy alloys is in agreement with the reduced glass transition temperature. The annealing experiment shows that the primary precipitation phase both for the Fe80P11C9 and Fe80P9B2C9 glassy alloys is α-Fe, and the addition of small amounts of Al is effective for suppression of the formation of α-Fe phase, resulting in the extension of supercooled liquid region and significant enhancement of GFA. The activation energy for primary crystallization calculated by Kissinger's equation indicates the addition of B in Fe–P–C alloy or Al in Fe–P–B–C alloy makes nucleation more difficult, which is responsible for the enhancement of GFA. In addition, it was found that the crystallized Fe80P9B2C9 specimen with ultrafine α-Fe grains exhibits high saturation magnetic polarization of up to 1.60T and low coercive force of about 3.0A/m.

Separation of Metal Impurities from Metallurgical Grade Silicon via CaO-SiO2-CaF2 Slag Treatment Followed by Leaching with Hydrochloric Acid

The separation of metal impurities from metallurgical grade silicon by a combination of slag treatment and acid leaching was investigated. Based on a detailed analysis of microstructure evolution in metallurgical grade silicon, the primary precipitated phase in silicon was tended to form Si-Ca system intermetallics after CaO-SiO2-CaF2 slag treatment. Moreover, the extraction efficiency of metal impurities from silicon with slag treatment was higher than that without slag treatment in the leaching process. Some parameters such as acid concentration, temperature, particle size, stirring speed and leaching time were also discussed. The extraction of impurities Fe, Al and Ca increased with increasing acid concentration, leaching time and decreasing particle size. Besides, the leaching kinetics of these metal impurities was confirmed to be controlled by chemical reaction with the application of cracking shrinking model.

Effect of Cu and Nb additions on crystallization kinetics of Fe80P13C7 bulk metallic glasses

Abstract The crystallization kinetics of Fe80−x−yP13C7CuxNby (x, y = 0, 0.6 at.%) bulk metallic glasses (BMGs) for the first crystallization peak is investigated to understand the crystallization mechanism. The effects of a minor Cu and Nb addition on the glass forming ability (GFA), thermal stability, apparent activation energy and crystallization kinetics of Fe80P13C7 BMG have been studied. Nb addition can enhance the GFA and thermal stability but it is opposite to Cu addition. The apparent activation energy decreases with Cu addition but increases with Nb addition. The local Avrami exponent indicates the primary crystalline phase without Cu addition, i.e. Fe3(P,C), is a low-dimensional growth of pre-existing nuclei. With Cu addition, the primary crystalline phase is α-Fe, which is a high-dimensional growth with an increasing nucleation rate. Nb addition suppresses the growth rate of the primary precipitated phase, resulting in a higher-dimensional growth.

Microstructural Characterization in Metallurgical Grade Silicon after Treatment by CaO-SiO<sub>2</sub> and Na<sub>2</sub>O-SiO<sub>2</sub> Slags

The microstructure and impurities distribution in metallurgical grade silicon with treated by CaO-SiO2 and Na2O-SiO2 slags were investigated. An exhaustive analysis of the transformation of precipitated phase at grain boundaries has been carried out. Prior to slag treatment, Si-Fe system intermetallic was the primary precipitated phase in metalllurgical grade silicon. After treated by CaO-SiO2 slag, Si-Ca system intermetallic became the main precipitated phase, such as Si-Ca, Si-Ca-Ti, Si-Ca-Al and Si-Fe-Ca. But Na2O-SiO2 slag had another result on refining metallurgical grade silicon; only Si-Fe-Ti phase was generated in precipitated phase and the low level of sodium in treated silicon was obtained.

Primary precipitation phase with β-Mn structure in FeSiBP base multicomponent metallic glasses

Abstract Rapidly quenched amorphous soft magnetic FeSiPB alloys were studied at the initial stages of devitrification by means of transmission electron microscopy and X-ray diffraction. Metastable π-phase with the β-Mn type structure is formed as a primary phase in alloys with 8–9 at.%B, 7–10%Si, 3–5%P. Transition from amorphous to π-phase proceeds via nearly polymorphous transformation, composition of the phase is close to that of amorphous matrix, it contains metalloid atoms at interstitial positions. Small alloying additions are prone to change the type of the primary phase to α-Mn type and related structures.

Thermal stability and crystallization behavior of (Fe0.75 − xDyxB0.2Si0.05)96Nb4 (x = 0–0.07) bulk metallic glasses

Effects of Dy addition on the glass-forming ability (GFA), thermal stability, and crystallization behavior in (Fe0.75−xDyxB0.2Si0.05)96Nb4 (x=0–0.07) bulk metallic glasses (BMGs) were investigated. The thermal stability of the supercooled liquid was greatly improved by alloying with a small amount of Dy. The largest supercooled liquid region of 100K was achieved for the x=0.04 alloy, leading to the best GFA with a diameter of 4mm. The activation energy for the first crystallization peak increased with the addition of Dy. However, adding more Dy may also increase the frequency factor and change the primary precipitation phase from Fe23B6 phase into DyFe11Si and DyFe3 phases, decreasing the thermal stability of the supercooled liquid. The possible relation between GFA and thermal stability, as well as crystallization behavior is discussed.

Formation, Thermal Stability and Mechanical Properties of Bulk Glassy Alloys with a Diameter of 20 mm in Zr-(Ti,Nb)-Al-Ni-Cu System

Bulk glassy alloy rods with a diameter of 20 mm were produced for Zr61Ti2Nb2Al7:5Ni10Cu17:5 and Zr60Ti2Nb2Al7:5Ni10Cu18:5 by a tilt casting method. The replacement of Zr by a small amount of Ti and Nb caused a distinct increase in the maximum diameter from 16 mm for Zr65Al7:5Ni10Cu17:5 to 20 mm, accompanying the decrease in liquidus temperature and the increase in reduced glass transition temperature. The primary precipitation phase from supercooled liquid also shows a distinct change, i.e., from coexistent Zr2Cu, Zr2Ni and Zr6NiAl2 phases for the 65%Zr alloy to an icosahedral phase for the 61%Zr and 60%Zr alloys. These results allow us to presume that the enhancement of the glassforming ability is due to an increase in the stability of supercooled liquid against crystallization caused by the development of icosahedral shortrange ordered atomic configurations. The 60%Zr specimens taken from the central and near-surface regions in the transverse cross section at the site which is 15 mm away from the bottom surface of the cast glassy rod with a diameter of 20 mm exhibit good mechanical properties under a compressive deformation mode, i.e., Young’s modulus of 81 GPa, large elastic strain of 0.02, high yield strength of 1610 MPa and distinct plastic strain of 0.012. Besides, a number of shear bands are observed along the maximum shear stress plane on the peripheral surface near the final fracture site. The finding of producing the large scale Zr-based bulk glassy alloys exhibiting reliable mechanical properties is encouraging for future advancement of bulk glassy alloys as a new type of functional material. [doi:10.2320/matertrans.MER2008179]

Effects of additional element on the glass forming ability and corrosion resistance of bulk Zr-based amorphous alloys

By using the real-place recursion method， bulk Zr-based amorphous alloys with effects of additional element Nb，Ta，Y，La on the glass forming ability and corrosion resistance were studied. The atomic structure model of primary precipitation phase Zr2Ni in Zr-based amorphous alloys were constructed by computer programming. The icosahedron cluster in Zr-based amorphous alloys was simulated by using the icosahedral cluster in Zr2Ni primary precipitation phase. The local density of states (LDOS) curves of Zr，Ni (before substitution) and alloying elements (after substitution) at the center or the corner of icosahedron cluster， the total bond order integral between the centered Ni atom and it's nearest neighbor (Zr，Nb，Ta，Y，La) in the icosahedron cluster， and the Fermi energy levels of the icosahedron cluster (before and after alloying elements' substitution) were calculated. The LDOS calculation results showed that the Cu atom occupies the center site of the icosahedral cluster， Nb， Ta， Y， La atoms occupy the site of Zr atom at the corner in Ni-Zr icosahedral clusters. The bond order integer calculation results suggest that Y increases the glass forming ability (GFA) of Zr-base amorphous alloys， Nb and Ta decreased the GFA， and La has little influence on the GFA. The calculated Fermi energy levels suggest that Nb， Y， La make Zr-based amorphous alloys easy to be passivated and improve the Zr-based amorphous alloys corrosion resistance. Ta has little influence on the corrosion resistance of the alloys. Therefore， Y and La are most effective on improving the GFA and corrosion resistance of Zr-based amorphous alloys. By addition of small amounts of Y and La， new bulk amorphous alloys with good corrosion resistance can be prepared.

Crystallization kinetics of an amorphous Zr70Cu20Ni10alloy

Differential scanning calorimetry and transmission electron microscopy (TEM) were employed to investigate the crystallization kinetics of an amorphous Zr70Cu20Ni10 alloy. It has been found that the crystallization process is mainly controlled by three-dimensional nucleation and growth with an increasing nucleation rate. The activation energy for crystallization is approximately 388 kJ/mol. TEM observations confirmed that the primary precipitation phase during the isothermal crystallization process is the Zr2Ni phase, which can be partly attributed to the stronger binding nature between Zr and Ni atoms than that between Zr and Cu atoms.

Stability and Icosahedral Transformation of Supercooled Liquid in Metal-Metal type Bulk Glassy Alloys

ABSTRACTThe glassy structure and the primary precipitation phase from supercooled liquid were examined in metal-metal type Zr-, Hf- and Cu-based alloy systems by various advanced analytical techniques. The icosahedral phase precipitates as the primary phase from supercooled liquid for all the metal-metal type glassy alloys examined in the present study. The icosahedral phase has a rhombic triacontahedra type for the Zr-Al-Ni-Cu-NM (NM=Ag, Pd, Au, Pt), Zr-Cu-NM, Hf-Al-Ni-Cu-NM, Cu-Zr-Ti-Pd and Cu-Hf-Ti alloys. In addition, the short-range atomic configurations in their glassy alloys have the features of highly dense packed atomic configuration, new local atomic configurations and long-range homogeneity with attractive interaction. It is therefore concluded that the high glass-forming ability of the metal-metal type alloys is due to the self-formation of the unique glassy structure with the above-described three features which are consistent with the formation of short-range icosahedral atomic configuration.