STUDY ON THE STABILITY OF T＇ PHASE IN THE Al-Zn-Cu TERNARY SYSTEM

The phase constitutes and phase compositions in the eight alloys designed with different compositions of Al-Zn-Cu system have been determined after the homogenous treatment and then equilibrium cooling to 20~C by use of optical microscope, electron probe microanalysis and X-ray diffraction. It has been found that there existed the T‘phase in the seven alloys. Consequently, it was testified that the T‘ phase was stable at room temperature. At the same time, the phase relationship was not locally right for the isothermal section of 20℃ of Al-Zn-Cu system of the ASM published in 1997.     

ISOTHERMAL SECTION OF Mg-Zn-La SYSTEM IN Mg RICH CORNER AT 350℃

Alloys of Mg-Zn-La system in Mg rich corner at 350?C have been prepared in this study. Scanning electron microscopy (SEM), electron probe microanalysis with energy dispersive X-ray spectroscopy (EPMA-EDS), and X-ray diffraction (XRD) have been used to identify the phase equilibrium and the composition of each phase in the alloys. As a result, the isothermal section of Mg-Zn-La system in Mg rich corner at 350℃ has been determined. The result shows that, in addition to some binary phases, there exists a li...     

PHASE DIAGRAM OF Nd-Fe-B TERNARY SYSTEM——I.Isothermal Section at Room Temperature

The microstructures of both as-cast and homogenized Nd-Fe-B ternary alloys have beenstudied. The stable phase regions existing in Nd-Fe-B ternary system at room temperaturehave been established by the microzone composition analysis and the phase identification.Based on the obtained results, an isothermal section of Nd-Fe-B ternary system at roomtemperature was drawn.     

Review on ω Phase in Body-Centered Cubic Metals and Alloys

An to phase with a primitive hexagonal crystal structure has been found to be a common metastable phase in body-centered cubic(bcc) metals and alloys.In general,to phase precipitates out as a high density of nanoscale particles and can obviously strengthen the alloys;however,coarsening of the co particles significantly reduces the alloy ductility.The co phase has coherent interfacial structure with its bcc matrix phase,and its lattice parameters are a_ω =2~(1/2)×a_(bcc) and C_ω= 3~(1/2)/2 ×a_(bcc).The common {112}(11 l)-type twinning in bcc metals and alloys can be treated as the product of theω→ bcc phase transition,also known as the ω-lattice mechanism.The ω phase's behavior in metastable β-type Ti alloys will be briefly reviewed first since the ω phase was first found in the alloy system,and then the existence of the ω phase in carbon steels will be discussed.Carbon plays a crucial role in promoting the ω formation in steel,and the ω phase can form a solid solution with various carbon contents.Hence,the martensitic substructure can be treated as an α-Fe matrix embedded with a high density of nanoscale ω-Fe particles enriched with carbon.The recognition of the ω phase in steel is expected to advance the understanding of the relationship between the microstructure and mechanical properties in bcc steels,as well as the behavior of martensitic transformations,twinning formation,and martensitic substructure.     

Enthalpy of formation of quasicrystalline phase and ternary solid solutions in the Al-Fe-Cu system

1. Introduction A novel intermetallic-phase quasicrystal was discovered in 1984. At first, the quasicrystalline phase was observed in rapidly quenched alloys of the Al-Mn system [1]. Till date quasicrystalline phases have been obtained in more than 100 systems; mainly Al, Cu, Ti, and Zr-based systems. The pecu- liarity of the quasicrystalline phases is that the exis- tence of symmetry axes for the fifth and tenth orders are forbidden by classic crystallography. The quasi- crystalline phases…     

Isothermal section of Mg-Zn-La system in Mg-rich comer at 400℃

Alloys with different compositions in Mg-rich corner of Mg-Zn-La system at 400 ℃were prepared, the phase equilibrium in the Mg-rich corner of Mg-Zn-La system was determined by scanning electron microscopy（SEM）, electron probe microanalysis based on energy dispersive X-ray spectroscopy （EPMA-EDS） and X-ray diffraction（XRD）, and the isothermal section at 400℃ was established. The results show that there exists a ternary compound （T-phase） with a constant La content and changable Mg/Zn contents in the Mg-Zn-La system. The mole fraction of La in T-phase is about 8%, and that of Zn is from 16% to 43%, There exist a two-phase equilibrium which consists of T-phase plus hcp-Mg and a three-phase equilibrium which is composed of T-phase, hcp-Mg and a liquid phase （L-phase） at 400℃. The L-phase consists of 70% Mg, 30% Zn and is free of La.     

PHASE BOUNDARY OF α_2 PRECIPITATION IN Ti-Al-La TERNARY SYSTEM

The phase boundary,of α_2 precipitation at 600℃ in Ti-AI-La ternary system has been de-termined by TEM examination,which shows three kinds of phase regions,namely thesingle α phase region,the transitional phase region where there is superlattice reflection butno α_2 precipitation,and the α+α_2 region.A point of maximum aluminium content was foundto exist on the α/(α+α_2)boundary and the track of the boundary was explained in terms ofthe internal oxidation of lanthanum and the electron concentration rule for α_2 formation.     

Phase equilibria in the Mg-rich corner of the Mg-Zn-La system at 350℃

The phase equilibria in the Mg-rich comer of the Mg-Zn-La system at 350℃ have been investigated by scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. It has been shown that the linear compound （Mg,Zn）17La2 existed in the Mg-Zn-La system at 350℃. The linear cornpound （so-called Tphase） was with the C-centred orthorhombic crystal structure induced by the solution of significant quantities of the third element. The three-phase region α（Mg） ＋ MgZn（La） ＋ T and the two-phase region composed of the α（Mg） and the linear-compound T phase existed in the Mg-rich comer of the Mg-Zn-La system at 350℃.     

ISOTHERMAL SECTION OF Mg-Zn-La SYSTEM IN Mg RICH CORNER AT 350℃

Alloys of Mg-Zn-La system in Mg rich corner at 350℃ have been prepared in this study. Scanning electron microscopy （SEM）, electron probe microanalysis with energy dispersive X-ray spectroscopy （EPMA-EDS）, and X-ray diffraction （XRD） have been used to identify the phase equilibrium and the composition of each phase in the alloys. As a result, the isothermal section of Mg-Zn-La system in Mg rich corner at 350℃ has been determined. The result shows that, in addition to some binary phases, there exists a linear ternary compound called T-phase in Mg-Zn-La system at 350℃, in which the La content is about 8 at. pct ±0.4 at. pct and the Zn content is 8 at. pct- 48 at. pct. The T-phase has a C-centered orthorhombic crystal structure, and the lattice parameters are a=0.965-1.020 nm, b=1.121 1.142 nm, c=0.950-0.977 nm.     

Tensile Properties of Cast Alloy IN625 in Relation to δ Phase Precipitation

The relationship between the tensile properties and S(delta) phase precipitation in cast alloy IN625 was investigated in this paper. Although the influences of δ phase on the mechanical properties have been pointed out in our previous work, the relationship is still not directly determined due to the coexistence of γ"(gamma double prime) and δ precipitates. In order to exclude the effect from γ" phase, various fractions of δ precipitates with few γ" precipitates were obtained by a set of experimental alloys aging at 750 ℃, and tensile tests were conducted in parallel. The results showed that both yield strength and ultimate tensile strength increased nearly in linear with increasing δ phase fraction, while the elongation was relatively and limitedly affected by δ precipitation when the area fraction of δ phase was above 10%.     

METASTABLE R-PHASE IN Fe-Cr-Mo AND Fe-Cr-W ALLOYS

The precipitation behaviour of Fe-Cr-Mo and Fe-Cr-W alloys during aging has been ex- perimentally studied.It was found that in the early stage of aging,a metastable R phase pre- cipitated in both alloys,it was transformed into stable μ-phase,Laves-phase,X-phase or σ-phase in the later stages.The crystallographic structure of metastable R-phase is rhombohedral with lattice parameters of a=0.9075 nm and α=74.45°.The chemical compo- sition of R-phase is Fe-(27.5—34.9)Mo-(0—25.5)Cr and Fe-(28.9—33.0)W-(9.36— 21.0)Cr in at.-% in Fe-Cr-Mo and Fe-Cr-W system,respectively.     

PRECIPITATION OF TiC IN METASTABLE β-Ti ALLOY

In order to clarify that the IFP and the “Type 2”α phase are also arising from TiC,ametastable β-Ti alloy was selected for investigation in this work.The results showed that af-ter heating the alloy just below the α+β→β transus temperature and quenching,the TiC lay-er existed at the α/β interface.The morphology of TiC is similar to that of the IFP arisingfrom TiH_2 in the α-β two-phase alloys.The IFP TiC also provided an easy crack path orthe crack initiation sites.The fracture is also identical to that caused by IFP TiH_2.The arceddiffractions(characteristic of “Type 2”α)were found in the selected area diffraction pat-terns of some specimens which had been isothermally aged after solid solution treatment.Theparticles which bring on the arced diffractions may be TiC on the basis of structure and lat-tice parameter analysis,not the so called “Type 2”α phase.     

Microalloying Effect of Sn on Phase Transformation During Heat Treatment in Mg–Y–Zn–Zr Alloys

The microstructure and mechanical properties of the as-cast and heat-treated Mg-4.6 Y-2.5 Zn-0.6 Zr-x Sn(x = 0, 0.2 and0.5 wt%) alloys were investigated in this work. The results showed that the eutectics have been refined with 0.2% Sn addition and it has no effect on the phase category of the alloys. However, Sn3 Y5 phase was found in 0.5% Sn-added alloy.After heat treatment at 520 °C, the transformation of the long-period stacking ordered(LPSO) phase takes place in the Mg-Y-Zn-Zr alloy, but the transition is not completed in the alloys containing Sn. In addition, during the heat treatment, the mechanical properties of Sn-free alloys are significantly improved, and the strength of alloys containing Sn does not change much. Through observation and analysis of the microstructure and mechanical properties, it is found that Sn addition hinders the process of a0-Mg ? a-Mg ? 14 H and the process is the key to the transition of 18 H-LPSO to 14 H-LPSO.     

Effect of Cr on Microstructure and Fracture Toughness of Nb-20Ti-16Si-xCr Alloys

The present paper reported the phase stability and microstructures evolution of Nb-20Ti-16Si-xCr (x = 0～20at.%) in-situ composites as function of Cr addition. It was suggested that with the addition of Cr less than 7%, the silicide phase in as-cast Nb-20Ti-16Si alloy was Nb3Si. The silicides changed to be α-Nb5Si3 by the addition of Cr above 7%. It was found that annealing of 1300 ℃ for 100 h could result in the decomposition of Nb3Si to NbSS and α-Nb5Si3 in Cr containing Nb-20Ti-16Si based alloys by means ...     

Mechanical and Electrical Properties of the. Ternary Ag-Sb-Zn System

This paper presents comparative review of experimental and thermodynamic assessment of ternary Ag-Sb-Zn system.Isothermal section of the Ag-Sb-Zn system at 300 ℃ has been calculated by CALPHAD method using thermodynamic parameters from literature.Microstructural analysis of a number of alloys was carried out by scanning electron microscopy and optical microscopy,whereas chemical composition of observed phases was analyzed using energydispersive X-ray spectroscopy.Hardness of selected alloys from four vertical sections was determined using Brinell hardness test and additionally by micro Vickers hardness test.Electrical conductivity of a number of alloys in the ternary Ag-Sb-Zn system was experimentally determined.Good overall agreement between experimental and calculated values was obtained.     

Influence of Si content and heat treatment on microstructure of Al-Fe-Si alloys

The effect of Si addition and heat treatment on the Al-5wt.%Fe al oy has been investigated by OM, SEM-EDS and XRD. The results show that the Si plays a significant role in refining the primary Al3Fe phase. It was found that the addition of 3.0wt.% Si made the al oy present the finest and wel -distributed primary Al3Fe phase, but the Al3Fe phase almost disappeared when 5wt.% Si was added. With further increase in the Si content, some Fe-rich phases appeared in the inter-grains and coarsened. In addition, the heat treatments exert a significant impact on the microstructural evolution of the Al-5wt.%Fe-5wt.%Si al oy. After heat treatment for 28 hours at 590 oC, the coarse platelet or blocky Fe-rich phase in Al-5wt.%Fe-5wt.%Si al oys was granulated; the phase transformation from metastable platelet Al3FeSi and blocky Al8Fe2Si to stable Al5FeSi had occurred. With the extension of heat treatment, the Si phase coarsened gradual y.     

MICROSTRUCTURE OF Mg-Zn-Zr-Y ALLOYS

In the as-cast Mg-Zn-Zr-Y alloys.the quasierystal phases show massive and eutectoidplate morphologies.The selected area diffraction(SAD)revealed that a large part of the quasicrystals are face-centered icosahedral(FCI),while a small amout of the quasierystals belong to the simple icosahedral(SI)phase.It was found that in homogenized alloys,a part of the grain boundry phases was dissolved,and small massive W-phase and lath-shape MgZn_2 phase dispersedly precipitate in the grains.The transformation of the quasicrystals relates to the temperature.After homogenizing at 360℃,the quasicrystals still present,while after homogenizing at 400℃,the quasicrystals transformed into a new C-typeorthorhombic phase with a=0.975nm,b=1.137nm and c=0.935nm.     

TEM STUDIES OF THE W PHASE AND ITS ORDERED W'PHASE IN RARE EARTH Mg ALLOYS

By means of transmission electron microscopy(TEM),the W phase and its ordered W'phase in as-cast Mg-Zn-Zr-Y system alloys were studied.The W phase,which distributes alongthe grain boundaries in the form of a lamellar eutectoid with Mg,is of FCC structure with α=0.865 nm.The W'phase,which is an ordered structure of the W phase with α=2.055 nm,was found in the alloy with lower Y content.The W and W'phases have a simple orientationrelationship of(100)_W//(100)_(W'),(010)_W//(010)_(W'),and(001)_W//(001)_W;but they do nothave an orientation relationship with the α-Mg matrix.The results of convergent electroncliffractions(CBD)on these phases show that their point group is m3m and that the space group isFm3m.     

EFFECT OF NANOCRYSTALLIZATION ON THE SCALING OF NiAl AT 1000℃ IN AIR

The oxidation behavior of a magnetron sputtered nanocrystalline NiAl coating was investigated at 1000℃ in air. Comparing with cast NiAl and NiAl-0.1at.%Y alloys reveals influences of nanocrystallization as well as yttrium addition on the oxidation behavior of NiAl. Results show that a phase transformation from metastable θ-Al2O3 to stable a-Al2O3 occurred in scales, which was accelerated by the microcrystallization and retarded by the addition of Y. The addition of Y as well as the nanocrystallization reduced the void formation at the interface between the scale and the substrate.     

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…