Γ2 Phase Research Articles

Liquid-State Interfacial Reactions of Sn-Zn/Co Couples at 250°C

This study examined the interfacial reactions between liquid Sn-Zn alloys and Co substrates at 250°C with different Zn compositions from 1 wt.% to 9 wt.%. The reaction phases formed at the interface were significantly affected by the Zn content. One irregular reaction phase, γ2-CoZn13, was observed in the Sn-9 wt.%Zn/Co reaction. Decreasing to 7 wt.% Zn, the interfacial product changed to the γ1 phase. After a longer reaction time, a new ternary compound with composition Sn-20.2 at.%Zn-31.4 at.%Co, the T phase, was formed between the γ1 phase and Co substrate. Only one very thin and continuous T phase layer was found, and it was stable at the Sn-4 wt.%Zn/Co interface, even after 120 h reaction. However, the Sn-3 wt.%Zn/Co couples revealed significant microstructural evolution in both the T and CoSn3 layers. Moreover, the dominant phase became CoSn3 as the Zn content decreased below 2 wt.%. Based on these interfacial results, a predicted Sn-Zn-Co phase diagram (less than 30 at.% Co) at 250°C is proposed. The corresponding reaction paths of these couples are illustrated on the phase diagram.

Structurally inhomogeneous fct-martensite in alloys based on the Mn – Cu system: structure, strain mechanism and strength characteristics

The conditions of occurrence of high-temperature fcc →fct martensitic transformation in alloys of the Mn – Cu system containing two isomorphic nanocrystalline γ1 and γ2 phases with high and low manganese content, respectively, are considered. The structure formed as a result is studied. The mechanisms of straining of the inhomogeneous fct-martensite and the factors determining its strength properties are determined.

Influence of heat treatment on microstructure and passivity of Cu–30Zn–1Sn alloy in buffer solution containing chloride ions

Tin as an alloying element is of great interest in brasses for dezincification impediment. In this paper, Cu–30Zn–1Sn alloy was submitted to three different heat treatments, viz. A (heating up to 800 °C for 20 h, held at 200 °C for 20 h in salt bath and air cooled), B (heating up to 800 °C for 20 h and water quenched) and C (heating up to 600 °C for 20 h and water quenched). The influence of heat treatment on microstructure was evaluated by OM and SEM–EDS analysis. The corrosion resistance in buffer solution (pH 9), H3BO3/Na2B4O7 ·10H2O, with various concentrations of chloride ions was evaluated by potentiodynamic polarization curves and compared with multi-component Pourbaix diagrams. A correlation between the heat treatment, microstructure and passivity of the heat treated samples was observed. The results indicated that all heat treatment procedures led to formation of α, and γ-Sn-rich phases as microstructure constituents with a small fraction of β′ phase in A. Sn-rich phase appears in grain boundaries and its morphology was slightly changed due to heat treatment. Beneficial influence of low concentration chloride ions on passivity was associated with the formation of copper oxides/hydroxide and chloride complexes. Deterioration was observed at concentrations higher than 0·05 M NaCl due to accelerated dissolution of copper by formation of CuCl\(_{2}^{-}\). As a result of dezincification process, preferential corrosion attack and copper redeposition on α phase (matrix) were observed. However, Sn-rich (γ1) phase in grain boundaries was not attacked due to SnO2 formation. In buffer solution, the higher passivity current density in A was related to the presence of small amount of β′ phase. On the other hand, in 1 M NaCl, lower critical current density for passivation in B and A (about two times lower than C) was attributed to the grain size effect.

Influence of heat treatment on the precipitation of γ1 phase in high Nb containing TiAl-based intermetallic alloys

A new intermetallic compound γ1 (Ti4Nb3Al9) phase can be observed with the increasment of Nb content in the Ti-Al-Nb ternary system. This work deals with the influence of heat treatment on the precipitation of γ1 phase in high Nb containing TiAl-based intermetallic alloys. The experiment results showed that 1400°C was acceptable as the homogenization temperature for the super-high Nb containing TiAl-based alloys. The new γ1 phase precipitated from the γ phase matrix during the following furnace cooling process. TEM and XRD tests were applied to identify γ1 phase. The experimental results revealed that γ1 phase could precipitate from the Ti-48Al-10Nb alloy after exposure at 1200°C for 100-240h.

The precipitation processes of the γ1 phase in Ti–53Al–18Nb alloys

The microstructures of high-Nb-containing TiAl alloys with a nominal composition of Ti–53Al–18Nb (at.%) having a γ 1 + γ phase region were studied. The range of Al and Nb content in which the γ 1 phase is able to precipitate has been determined. High Al content and high Nb content favor the precipitation of the γ 1 phase in the γ matrix. The distribution and morphology of the γ 1 phase in the γ matrix were also studied.

Effect of γ2 phase evolution on mechanical properties of continuous columnar-grained Cu–Al–Ni alloy

Effect of γ2 phase evolution on mechanical properties of Cu–14%Al–3.8%Ni (mass fraction) alloy wires fabricated by continuous unidirectional solidification technology was investigated before and after heat treated at 700–780 °C. Mechanism for the improvement of mechanical properties of the alloy was analyzed. It was found that the alloy retained continuous columnar grains after heat treatment. With the heat treatment temperatures increasing from 700 °C to 770 °C, the coarse dendrite γ2 phase evolved into the fine polygonal, ellipsoidal and spherical particles in the grains, while the long-banding, discontinuous block and ellipsoidal particles at the grain boundaries. The average size of the γ2 phase decreased from 20 μm before heat treatment down to 2 μm, and its amount reduced from 50.0% down to 0.8%. The γ2 phase was full dissolution at 780 °C. The tensile strength of the alloy treated at 700–780 °C ranged from 577 MPa to 710 MPa. The elongation of the alloy ranged from 7.5% to 23.8% and had a peak value at 760 °C. Excellent balance between strength and elongation could be obtained when the spherical γ2 phase was distributed throughout the alloy with the size smaller than 5 μm and the amount in the range of 11.4–16.6%. The nano-hardness and elastic modulus of the γ2 phase decreased gradually with the reduction of the amount, leading to the improvement of mechanical properties.

Effects of solidification parameters on microstructure and mechanical properties of continuous columnar-grained Cu–Al–Ni alloy

AbstractEffects of melt temperature and casting speed on microstructure and mechanical properties of Cu-14%Al-3.8%Ni (mass fraction) alloy wires fabricated by continuous unidirectional solidification technology were investigated. It was found that the average size of columnar grain in the alloy decreased and grain boundary turned clear and straight with increasing the casting speed at a given melt temperature. When the melt temperature was up to 1 280 °C, the β1 phase gradually transformed into lozenged and lanciform γ1' martensite, as well as parallel-sided plate β1' martensite. The alloy with numerous coarsely dendritic γ2 phase has poor mechanical properties due to the difficulty of stress-induced martensitic transformation. When the amount of the γ2 phase reduced and the coarse dendrite γ2 phase evolved into the fine square particles, the elongation of the alloy increased gradually with a decrease in tensile strength. Meanwhile, the plasticity of the alloy could also be improved by increasing the amount and size of martensites, particularly the lanciform γ1' martensite. When the alloy was almost composed of coarse lanciform γ1' martensite, the tensile strength and elongation of the alloy could be up to 772 MPa and 18.9%, respectively, and the tensile curve consisted of three transformation platforms.

Cu-8.6wt%Al 삽입금속을 사용한 페라이트계 스테인리스강의 아크 브레이징 접합부의 미세조직과 인장성질

Microstructures and tensile properties in arc brazed joints of ferritic stainless steel, 429EM using Cu-8.6%Al insert metal was investigated as function of brazing current. The brazing speed was fixed at 800mm/min and brazing current varied in the range of 80A to 120A. The initial phase of filler metal was Cu single phase. However, the insert metal structures of brazed joints was composed of Cu matrix and intermetallic compound such as γ1(Al4Cu9), and flower-shape Fe-Cr. The fraction of γ1(Al4Cu9) phase was similar with 80A and 100A brazing currents while that of brazed with 120A was decreased. On the other hand, the fraction of Fe-Cr phase increased with increasing of the brazing current. A reaction layer at the base metal/insert metal interface was observed and this reaction layer was thickened with increasing of the brazing current. In the brazed joints with the current lower than 100A, crack was grew up along the interface which was perpendicular to the tensile stress, and then, passed through the insert metal in the final stage of fracture. As the brazing current increased to 120A, fracture occurred at the base metal.

Effects of aging on the microstructure of a Cu-Al-Ni-Mn shape memory alloy

The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy (SMA) was studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometer, and differential scanning calorimeter (DSC). Experimental results show that bainite, γ2, and α phase precipitates occur with the aging effect in the alloy. After aging at 300dgC, the bainitic precipitates appear at the early stages of aging, while the precipitates of γ2 phase are observed for a longer aging time. When the aging temperature increases, the bainite gradually evolves into γ2 phase and equilibrium α phase (bcc) precipitates from the remaining parent phase. Thus, the bainite, γ2, and α phases appear, while the martensite phase disappears progressively in the alloy. The bainitic precipitates decrease the reverse transformation temperature while the γ2 phase precipitates increase these temperatures with a decrease of solute content in the retained parent phase. On the other hand, these precipitations cause an increasing in hardness of the alloy.

Chemical, physical and morphological characterization of ZnNi films electrodeposited on 1010 steel substrate from acid baths containing polyalcohol

ZnNi alloy electrodeposition on a 1010 steel electrode in boric-acid baths containing sorbitol, mannitol or glycerol was investigated by cyclic voltammetry. Electrodeposits obtained galvanostatically were characterized by SEM, EDS and XRD. It was found that in baths containing sorbitol or mannitol, the deposition current density (jd) was reduced, but in none of the baths was the initial deposition potential affected. SEM images of deposits revealed that the boric-sorbitol and boric-mannitol complexes refine the grain, even at high jd. XRD patterns of the ZnNi deposits produced at jd=50mAcm−2, in ZnNi1 bath and in ZnNi1 bath contained sorbitol or mannitol, indicated that the films were formed mainly of Zn and γ1 phases. To ZnNi2 baths contained glycerol the films were formed of γ and γ1 phases. The Ni content in the deposits produced in the bath without polyalcohol or containing glycerol increased from ~5 to 19wt.% with increasing jd. With sorbitol or mannitol, there was a smaller rise from ~7 to 10wt.% Ni. Thus, ZnNi deposits providing sacrificial protection can be obtained in baths with or without polyalcohol. The linear polarization method showed that ZnNi alloy deposited from baths contained polyalcohol have greate Rp.

Study on Friction and Wear Properties of Plasma and Laser Coatings of Aluminium Bronze Powder

Cu-14Al-X alloys was made into powder and then the powder was coated onto the surface of AISI 1045 steel respectively via plasma spraying and laser cladding technologies. Microstructure and phases of the coating were investigated by EPMA, XRD, SEM et al. Friction and wear properties of the two coatings were tested by RFT- friction and wear testing machine. The results indicates that the two coatings all consists of β′, α, K and γ2 phases and the structure of laser cladding is more evenly distributed. Under the condition of boundary lubrication, abrasion mechanism of laser coating remains abrasive grain abrasion. There is also adhesion abrasion under the condition of high load. While abrasion mechanism of plasma coating is slight abrasive grain abrasion and adhesion abrasion under low load. With the load increasing, adhesion abrasion intensifies. In a word, microstructure of laser coating is more even and compact.

RECRYSTALLIZATION OF A NICKEL-BASE SINGLE CRYSTAL SUPERALLOY UNDER COMPRESSION

Recrystallization behavior of a nickel-base single crystal superalloy cold-deformed by compression has been investigated. The effects of plastic strain, annealing temperature and annealing time have been studied, and recrystallization diagram has been obtained. It has been found that a very strong dependence upon temperature is evident. For the single crystal superalloy with 4.5% strain, full recrystallization has been observed when annealing at 1300°C for 1h, surface recrystallization at 1250°C for 1h, cellular recrystallization at 1150°C for 1h and no recrystallization at 1100° for 1h. With the drop of temperature, the volume fraction of γ′ phase increases, which incrementally restricts recrystallized boundary migration. With the increasing of annealing time or strain, the sensitivity of recrystallization increases. Recrystallization tendency of standard- heat-treated superalloy is weaker than that of as-cast single crystal superalloy, because standard heat treatment reduces the microsegregation, lowers the eutectic amount and forms homogeneous γ1 phase distribution, which decrease preferential nucleation site of recrystallized grain and increase the resistance of boundary migration of recrystallization.

High-Temperature Transformation Processes in Cu-13.4Al-5Ni Shape Memory Alloy Single Crystals

Cu-13.4Al-5Ni alloy single crystals were investigated after performing the corresponding heat treatments to reveal the formation of equilibrium α and γ2 phases and to examine transformation processes occurring in the alloy during heating-cooling cycles between room temperature and 970 K. Transformation processes were examined using heat flux DSC, structure examinations were performed using optical microscope and SEM devices, and phase identifications were carried out by XRD method. Identification of the equilibrium α phase using XRD method was not possible on the single crystal samples. According to the results, the equilibrium phases (α and γ2) form only after long-term heat treatments. Because of that, aging processes do not affect the thermoelastic martensitic transformation of the CuAlNi alloy. This phenomenon is probably caused by the high Ni content that decreases the diffusion rate in CuAlNi alloys.

Optimization of Galvannealing Parameters through Numerical Modeling of Galvannealing Process

In the galvannealing process, a galvanized sheet is subjected to an annealing treatment to transform the zinc-coated steel sheet to iron-zinc alloy-coated steel. In the present work, the galvannealing process has been treated as a binary multiphase diffusional phase transformation reaction, and a rigorous mathematical model has been developed to simulate the galvannealing process. The results obtained by the model have been compared with experimental as well as plant data, and the results have been found to be in good agreement. The model prediction shows that the excessive growth of undesirable Γ and Γ1 phases takes place when the iron content in the coating exceeds around 11 pct during galvannealing. It has also been observed that decreasing the line speed to obtain the desired iron content in the coating leads to excessive growth of the undesirable Γ and Γ1 phases. It has been concluded that the developed mathematical model can be used to optimize the galvannealing parameters.

Phase equilibria in the system Tl2Te-SnTe-TlBiTe2

The phase equilibria in the system Tl2Te-SnTe-TiBiTe2 (A) have been studied using differential thermal analysis, x-ray diffraction, and microhardness measurements. We have constructed the T-x phase diagrams along the SnTe-TlBiTe2, SnTe-Tl9BiTe6, and Tl4SnTe3-TlBiTe2 joins, the 600-and 800-K sections of the phase diagram of system A, and its liquidus diagram. The results demonstrate that the system contains broad ranges of Tl5Te3-structured and SnTe-based solid solutions (δ and γ1 phases, respectively). There are also relatively small fields of the Tl2Te-based phase (α) and low-and high-temperature TlBiTe2-based solid solutions (γ2 and γ′2). The liquidus surface of system A comprises the primary crystallization fields of the δ, γ1, and γ′2 phases. The liquidus of the α phase is degenerate. The ternary eutectic between the δ, γ1, and γ′2 phases melts at 755 K.

Interfacial reaction between solid nickel and liquid zinc

Interfacial reactions between solid nickel and liquid zinc at 450–650 °C for 30–600 s were studied. The morphology and growth behavior of intermetallic compound layers at the interface between solid nickel and liquid zinc were observed and analyzed by SEM and EDS. The results show that γ and δ phases are formed at 450 °C at the Ni/Zn interface, and at 550 °C and 650 °C only γphase is formed at the interface and some δ phase particles will be participated during solidification on the surface of γ phase layer. The δ1 phase is absent under experimental conditions. Many cracks occur in the layers due to the difference in thermal expansion coefficients of these phases. It is found that the kinetics of the intermetallic compounds growth follows a parabolic law of time, as controlled by the diffusion mechanism. The apparent activation energies are 113.9 kJ/mol for the growth of γ phase and 125.87 kJ/mol for γ1 phase, respectively.

Control of Silicon Reactivity in General Galvanizing

In general galvanizing Si dissolved from steels destabilizes the Γ and Γ1 phases in the alloy layer of the coating. It also alters the morphology of ζ crystallites in the alloy layer thereby exposing the δ layer to the melt. The incompatibility of the liquid phase and the δ phase cause the latter to disintegrate. These changes result in an excessive steel reactivity in general galvanizing. This reactivity can be easily controlled by alloying the Zn bath with metals, such as Ni, if the Si content of the steel does not exceed 0.20%. To combat a fully developed reactivity problem, one has to stabilize the Γ and δ sublayers in the coating. Alloying the bath with suitable metals can generate new equilibrium states to allow the co-existence of the liquid phase and the δ phase thereby preventing its disintegration; the Γ and Γ1 phases can be stabilized through solid solution of the alloying elements in these phases. The introduction of Al to general galvanizing baths generates new equilibrium states thereby ushering a total new approach to Si reactivity control.

Corrosion Fatigue of High-Copper Dental Amalgams

Abstract Given its remarkable properties, dental amalgam is still a favorable dental material. These alloys are produced in different varieties of chemical compositions and morphologies, such as lath-cut and spherical. However, the best mechanical and clinical properties have been observed in high-copper, non-zinc amalgams with disperse spherical particles. This is due to the absence of a weak γ2 phase in the microstructure. In the present work, fatigue behavior of three high-copper amalgams in air, physiological serum, and acetic acid (CH3COOH) environments under the loading frequency of 10 Hz have been investigated. Two of the amalgams are in the form of lath-cut and the other one is in the form of spherical particles. Results showed that the fatigue strength of spherical particle amalgams is more than that of lath-cut amalgams. Maximum and minimum fatigue strength were observed in acetic acid and physiological serum solutions, respectively. It seems that high fatigue strength of these amalgams in an ac...

Microstructural Evolution in CuAlNi Alloy with Ageing

This research has been performed to investigate the effect of ageing onto the grain refinement of 82wt%Cu-13.5wt%Al-4.5wt%Ni-0.1wt% misch metal alloy with ageing temperature and time. The variation of transformation temperature with ageing has been found to be heavily dependent on ageing time and temperature. In the second reversed transformation cycle, the temperature of Ms point decreases with ageing time at 300, but no variation at 100. The temperature of As point increases with ageing time at both temperatures. After the second reversed transformation cycle, the transformation temperature does not show any significant changes in martensitic phase with ageing, the temperature of Ms point being the same afterwards. Parent phase after ageing appears to show M18R and N2H martensitic phases depending on the ageing time and temperature. It is also found that α and γ2 phases are formed only at the condition of 300 and 24h.

Effect of Aging and Microstructure on Mechanical Rolling CuAlNi Shape Memory Alloy

CuAlNi shape memory alloy with Cu-13.5Al-4.5Ni(wt%) composition was prepared by cross-rolling method and the aging effect, phase transformation characteristics, microstructural variation were investigated. Transformation temperature was greatly increased in aged specimens at 250°C. Transformation temperature was not changed after the second reversed transformation, and Ms point was same in most specimens with third reversed transformation cycle. The variation of Ms point was not seen with aging at 100°C, but it was decreased with aging at 250°C. Transformation temperatures appear to be constant, to an measurable extent, in specimens prepared by both hotrolling and cross-rolling at 900°C. Plate shaped-specimen with the thickness of about 1mm was prepared by cross-rolling treatment at 350°C. The transformation temperatures did not change after the second transformation-reverse transformation cycling, and specially transformation start temperature was the same in most specimens experiencing third thermal cycle and thereafter. Undesirable tweed-like structure was observed in 250°C-aged specimen after a cross-rolling at 350°C. On aging the specimen prepared by cross-rolling, G.P zone was formed easier than that of γ2 phase. This phase was transformed to plate-like θ phase during aging.