Effect of melt holding on morphological evolution and sedimentation behavior of iron-rich intermetallic phases in Al-Si-Fe-Mn-Mg alloy

The effect of the melt holding temperature on the morphological evolution and sedimentation behavior of iron-rich intermetallics in Al-7.0 Si-1.0 Fe-1.2 Mn-0.25 Mg alloy was investigated using an optical microscope,scanning electron microscope and differential thermal analyzer.The results show that as the holding temperature decreases,the morphologies of the primary iron-rich phase in matrix change from star-like to polygonal,and the number of the primary phases gradually decreases and disappears at 615°C.Finally,the Chinese script phases with small size,high compact and uniform distribution are obtained.In contrast,the primary iron-rich phases in slag transform into a coarser polygonal shape with lower roundness,and some of them have hollow structures.Furthermore,the area fraction of intermetallics and Fe content in the matrix decrease gradually due to the formation and growth of sludge and subsequent natural sedimentation during melt holding.With the decrease of holding temperature,the main factors hindering the settlement of the primary phases are morphology,size,and density in turn.

Microstructural characteristics of intermetallic phases in spray-deposition Al-8.5Fe-1.3V-1.7Si alloy

Analysis electron microtechnique (AEM) and high resolution electron microtechnique (HREM) studies were conducted on a spray deposition Al 8.5Fe 1.3V 1.7Si(mass fraction, %) alloy to determine the characteristics of the intermetallic phases. The results show that the striking characteristics of the microstructures in as deposited and as extruded alloys indicate the presence of a large amounts of homogeneously distributed fine particles and a few coarse particles, while small amount of eutectics consisted of α (Al) and α AlFeSi are found in local zone in as deposited alloy. The fine particle is identified to be bcc α AlFeSi phase, and the coarse particles are monoclinic α Al 13 Fe 4 equilibrium phase, bcc α AlFeSi phase and newly found hexagonal h AlFeSi metastable phase. In α Al 13 Fe 4 , stacking faults on (100) and (001) plane and microtwin on (100) twinning plane are frequently observed. The extra reflection spots in α AlFeSi reflection pattern can be induced by α AlFeSi superstructure. The hexagonal metastable phase transforms to bcc phase, and the compositions of two phases are very similar. A close crystallographic orientation relationship between hexagonal and bcc phases are determined, and HREM image shows that the interface between them is coherent. [

Multiplex intermetallic phases in a gravity die-cast Mg-6.0Zn-1.5Nd-0.5Zr(wt%) alloy

Components and crystal structures of the intermetallic phases in a gravity die-cast Mg-6.0Zn-1.5Nd-0.5Zr(wt%)alloy were investigated using transmission electron microscopy.The results indicate that this alloy has multiple intermetallic phases and various inner faults.Totally,six eutectoid intermetallic phases,namely W(Mg Nd Zn_(3)),T(Mg_(39)Zn_(55)Nd_(6)),(Mg,Zr)Zn_(2),Z(Mg_(28)Zn_(65)Nd_(7)),H_(2)(Mg_(15)Zn_(70)Nd_(15)),and H1(Mg_(24)Zn_(64)Nd_(11)),were simultaneously observed at grain boundaries,and six precipitates(Z,Mg_(7)Zn_(3),T,Mg_(4)Zn_(7),β_(1)-Mg Zn_(2) and β_(2)-Mg Zn_(2))were found inα-Mg grains.Furthermore,faults like sub-grain boundaries,orientation domains(coherent with the same matching plane but with different orientations),stacking faults and twins were observed in the eutectoid intermetallic phases.Finally,some new orientation relationships between the known intermetallic phases were revealed.This paper can provide new insight into alloy design for Mg-Zn-RE(RE:rare earth)based alloys.

Study on the formation of intermetallic phases in the new type of Zn-Mg coatings on steel sheets

Zn-Mg alloy coatings were obtained by physical vapor deposition （PVD） on electroplated steel sheets. Study on the formation of intermetallic phases in the coatings was conducted through the use of X-ray diffraction （XRD） ,scanning electron microscope （SEM） and glow discharge optical emission spectrometry （GDOES）. It is found that MgZn2 is the main Zn-Mg alloy phase formed after heat treatment. The formation of Mg-Zn intermetallic phases is controlled not only by thermodynamics, but also by kinetics. MgZn2 has different morphologies, such as laminar structure,porous structure and floc-like structure,which are mainly determined by the annealing temperature. Obvious diffusion of Mg starts at 350 ℃, and the diffusion of iron increases significantly when the temperature is elevated to 380℃.

Morphologies of intermetallic compound phases in Sn-Cu and Sn-Co peritectic alloys during directional solidification

The morphologies of intermetallic phases(IMCs)during directional solidification of the Sn-Cu(L+Cu_(3)Sn→Cu_(6)Sn_(5))and Sn-Co(L+CoSn→CoSn_(2))peritectic systems were analyzed.The primary Cu_(3)Sn and peritectic Cu_(6)Sn_(5)phases in Sn-Cu alloy are IMCs whose solubility ranges are narrow,while both the primary CoSn and peritectic CoSn_(2)phases in Sn-Co alloy are IMCs whose solubility ranges are nil in equilibrium condition.The experimental results before acid corrosion shows that the dendritic morphology of both the Cu_(6)Sn_(5)and CoSn_(2)phases can be observed.The investigation on the local dendritic morphology after deep acid corrosion shows that these dendrites are composed of small sub-structures with faceted feature.Faceted growth of the primary Cu_(3)Sn and CoSn phases is also confirmed,and a faceted to non-faceted transition in their morphologies is observed with increasing growth velocities.Further analysis shows that the dendritic morphology is formed in the solidified phases whose solubility range is larger during peritectic solidification.

Evolution of intermetallic phases of Al-Zn-Mg-Cu alloy during heat treatment

Al-Zn-Mg-Cu alloy is a favorable choice for aerospace applications requiring good combination of strength and toughness, which is greatly influenced by the coarse intermetallic particles. The evolution of intermetallic particles in an Al-Zn-Mg-Cu alloy during heat treatment was studied by field emission gun scanning electron microscopy (FEG-SEM) and X-ray diffractometry(XRD). The results show that there are lamellar eutectic structure (α(Al)+Mg(Zn,Al,Cu)2) and Al7Cu2Fe particles in the solidified structure. The Al7Cu2Fe particles are embedded in the eutectic structure. The content of eutectic structure decreases with the increase of holding time and disappears after 24 h. The size and morphology of Al7Cu2Fe particles exhibit no change during the heat treatment. It is found that the Al2CuMg phase is formed during the treatment at 460℃. A transformation process from the primary eutectic phase Mg(Zn,Al,Cu)2 to Al2CuMg is observed, and the transformation mechanism and kinetics are analyzed. The Al2CuMg constituents form in the primary Mg(Zn,Al,Cu)2 phase, and grow along the eutectic microstructure.

Intermetallic phase evolution of 5059 aluminum alloy during homogenization

Intermetallic phase evolution of 5059 aluminum alloy during homogenization was investigated by means of optical microscopy （OM）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, energy dispersive spectrometry （EDS）, differential scanning calorimetry （DSC） and X-ray diffraction analysis （XRD）. The results show that severe dendritic segregation exists in as-cast alloy. The dissolvable intermetallic phases in as-cast alloy consist of Zn-and Cu-rich non-equilibriumβ（Al3Mg2） phase, Fe-rich eutectic Al6Mn phase and equilibrium Mg2Si phase. During the homogenization, Zn- and Cu-rich non-equilibrium β （Al3Mg2） phase, Fe-rich eutectic Al6Mn phase and equilibrium Mg2Si gradually dissolve into matrix. Fine dispersed β（Al3Mg2） particles and rod-shaped Al6Mn particles form in the Al matrix after homogenization. The proper homogenization processing is at 450 °C for 24 h, which is consistent with the results of homogenizing kinetic analysis.

Phase stability,elastic properties and electronic structures of Mg-Y intermetallics from first-principles calculations

The phase stability,elastic properties and electronic structures of three typical Mg-Y intermetallics including Mg_(24)Y_(5),Mg_(2)Y and MgY are systematically investigated using first-principles calculations based on density functional theory.The optimized structural parameters including lattice constants and atomic coordinates are in good agreement with experimental values.The calculated cohesive energies and formation enthalpies show that either phase stability or alloying ability of the three intermetallics is gradually enhanced with increasing Y content.The single-crystal elastic constants C_(ij) of Mg-Y intermetallics are also calculated,and the bulk modulus B,shear modulus G,Young's modulus E,Poisson ratio v and anisotropy factor A of polycrystalline materials are derived.It is suggested that the resistances to volume and shear deformation as well as the stiffness of the three intermetallics are raised with increasing Y content.Besides,these intermetallics all exhibit ductile characteristics,and they are isotropic in compression but anisotropic to a certain degree in shear and stiffness.Comparatively,Mg_(24)Y_(5) presents a relatively higher ductility,while MgY has a relatively stronger anisotropy in shear and stiffness.Further analysis of electronic structures indicates that the phase stability of Mg-Y intermetallics is closely related with their bonding electrons numbers below Fermi level.Namely,the more bonding electrons number below Fermi level corresponds to the higher structural stability of Mg-Y intermetallics.

Intermetallics and phase transformations of the Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cr alloy

Intermetallics and phase transformations of the zirconium-based alloy, Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cr, were investigated by conventional X-ray diffraction （XRD）, differential scanning calorimetry （DSC）, and dilation measurement. Three types of precipitates, namely, （ZrNb）2Fe, Zr（CrFe）2, and Zr3Fe, were detected by XRD. The cubic Ti2Ni-type （ZrNb）2Fe was found to be the main precipitate in the alloy, and it was proposed to dissolve at 861℃, whereas Zr3Fe dissolved at 780℃ and Zr（CrFe）2 at 814℃. No precipitates were observed at a temperature higher than 900℃. The transformation-start temperature of α-Zr → β-Zr was reconfirmed to be 780℃, and the end temperature of α-Zr →βZr was determined to be 955℃. The dilation result also revealed that the martensitic transformation-start temperature, Ms, and the finish temperature, Mf, of this alloy were 741℃ and 645℃, respectively.

Structure of the Intermetallic Compound Ni_3Al Synthesized under Compression of the Powder Mixture of Pure Elements Part Ⅰ: Phase Composition and Microstructure of Main Phase

It was shown by TEM and X-ray analysis that there are four types of grains of the main Ni3Al phase in the structure of the intermetallic obtained by the self-propagation high temperature method (SHS). Every type of grains has its own domain and dislocation structure. There are mono- and polydomains with and without dislocations. The grains of the main phase of monoand polydomains without dislocations and polydomains with dislocations were formed by diffusion in the solid phase. In these conditions NiAl3 phase is located on the grain boundary of the main phase. The Ni2Al3 phase is located at the triple joints of the main phase.

Intermetallic Getters Reactants for Vacuum Applications

The present work continues a series of publications devoted to the study of the sorption properties of reactive alloys based on IIA metals and the development of advanced getter materials for gas and vacuum technologies. This publication attempts to answer the current challenges in the field of gas sorption associated with the emergence of new vacuum products such as vacuum insulated glasses, electronic systems, cryogenic devices, etc. An analysis of the problems that arise here, as well as the results of sorption measurements, carried out with the participation of intermetallic phases of the composition CaLi2 and Ca0.33Li0.48Mg0.19, show that the best getter support for these new hermetically sealed products can be provided by intermetallic compounds formed in systems Li-IIA metals. Intermetallic phases of this family are easy to manufacture and demonstrate outstanding service characteristics: their specific sorption capacity is recorded high, exceeding traditional gas sorbents in this respect by at least an order of magnitude;the kinetics of gas capturing is set at the stage of alloy production, i.e., is adjustable;the temporary resistance of these phases to atmospheric gases allows to install the getter at its workplace in air, without further thermal activation. The sorption superiority of reactive intermetallics is explained by their special sorption mechanism: the gas/metal interaction is formed here as a combination of two processes, continuous growth of reaction products on a metallic surface and corrosion decay of brittle intermetallic phase under mechanical forces, which feeds the chemical reaction with a fresh surface. The advantages of sorption processes of this new type are undoubted and significant: compared with the conventional sorbents, an intermetallic getter reactant solves two important problems;it reduces production costs and increases the sorption yield.

Site occupations and ordering behaviour of O phase in Ti_2AlNb-based intermetallics

The site occupations of the alloying elements of O phase in Ti 2AlNb based intermetallics are clarified. The ordering behaviours of the O phase in Ti y Al z Nb( y ≥ 25%, mole fraction) orthorhombic alloys are also investigated with a Bragg Williams model. In the temperature range where the O phases exist, the order parameters change with the alloy composition and temperature continuously, and the first order transition character is very "

Atomistic Simulation of Phase Transformation and Fracture in Ordered Intermetallics

A review of computer simulations carried out at our Center for Materials Simulation applied to stud- ying the different atomistic processes of fracture and displacive (martensitic) transformations is pres- ented.Since these processes can happen extremely rapidly and involve only a small number of atoms initially,they are ideally suited for molecular dynamics type simulations which can currently only span times of the order of one nanosecond and involve at most a million atoms.A method is also presented for simulating much larger samples for much longer times through the use of the Monte-Carlo technique combined with a Ginzburg-Landau free energy functional,where the rele- vant material parameters are determined from molecular dynamics runs on the same alloy system.A summary of studies on fracture simulations in the ordered intermetallics NiAI and RuAl is given,as well as a discussion of the observation and analysis of the heterogeneous nucleation of the martensitic transformation in NiAI which shows localized soft mode phenomena.It is concluded that computer simulations,whether of the atomistic molecular dynamics type or of the larger scale Monte-Carlo variety,are rapidly becoming of greater and greater use in understanding the properties of solids under a wide rancle of temperature and stress conditions.

Microstructure of the Ductile Phase in Intermetallic Compound Ni_(50)Al_(20)Fe_(30)

The microstructure of the single hot extruded and annealed Ni50Al20Fe30Y0.003 intermetallic compound alloys has been examined by means of high resolution electron microscopy (HREM). In these extruded and annealed alloys. the ductile phase is of a mixture of the disordered fcc γ matrix and or dered γ' precipitates. This fact well interprets the reason why the degree of annealing treatment can influence the strength and ductility of these alloys. The HREM observation revealed directly that there was some strain concentration at γ'-γ interfaces, due to the presence of more iron atoms in these two phases. The fixed orientation relationship between the γ phase and γ' precipitates was identified to be {001}γ||{00 }γ' and <100 >γ|| < 100 > γ'

Effect of Fe and Mo additions on microstructure and mechanical properties of TiAl intermetallics

The ductility of TiAl intermetallics can be improved through stabilizing the ductile β phase.New β-stabilized Ti-45Al-xFe-yMo（x,y=1,2,3,4） alloys were designed through adding the β stabilizing elements Fe and Mo.The microstructural evolution and deformation behavior of the Ti-45Al-xFe-yMo alloys were investigated.The results show that the amount of β（B2） phase is increased with the increase of alloying elements.Mo shows a higher capability for stabilizing the β phase than Fe.In the optimized Ti-45Al-3Fe-2Mo alloy,the grains are significantly refined to about 12 μm,and this alloy shows a very good hot ductility at the elevated temperature.

Review of magnetic properties and magnetocaloric effect in the intermetallic compounds of rare earth with low boiling point metals

The magnetocaloric effect （MCE） in many rare earth （RE） based intermetallic compounds has been extensively in- vestigated during the last two decades, not only due to their potential applications for magnetic refrigeration but also for better understanding of the fundamental problems of the materials. This paper reviews our recent progress on studying the magnetic properties and MCE in some binary or ternary intermetallic compounds of RE with low boiling point metal（s） （Zn, Mg, and Cd）. Some of them exhibit promising MCE properties, which make them attractive for low temperature magnetic refrigeration. Characteristics of the magnetic transition, origin of large MCE, as well as the potential application of these compounds are thoroughly discussed. Additionally, a brief review of the magnetic and magnetocaloric properties in the quaternary rare earth nickel boroncarbides RENi2B2C superconductors is also presented.

Characterization of Phases in an As-cast Copper-Manganese-Aluminum Alloy

Copper-manganese-aluminum （CMA） alloys, containing small additions of Fe, Ni, and Si, exhibit good strength and remarkable corrosion resistance against sea water. The alloys are used in as-cast condition, and their microstructure can show wide variations. The morphology, crystallography and composition of the phases presented in an as-cast （CMA） alloy of nominal composition Cu-14%Mn-8%Al-3%Fe-2%Ni were investigated using optical, electron optical, and microprobe analytical techniques. The as-cast microstructure consisted of the grains of fcc α and bcc β-phases alongwith intermetallic precipitates of various morphologies. The room temperature microstructure exhibited four different types of precipitates inside the α-grains： the ＇large＇ dendritic-shaped particles and the cuboid-shaped precipitates, which were rich in Fe and Mn and had an fcc structure, while the ＇small＇ dendritic-shaped particles and the globular precipitates were based on FeaAI and had DO3 structure. These four different morphologies of intermetallic precipitates exhibited discrete orientation-relationships with the α-matrix. The β-grains only contained very small cuboid shaped precipitates, which could only be resolved through transmission electron microscopy. These precipitates were found to be based on Fe3Al and had the DO3 structure.

Fabrication of porous Fe Al-based intermetallics via thermal explosion

Porous FeAl-based intermetallics were fabricated by thermal explosion（TE） from Fe and Al powders. The effects of sintering temperature on phase constitution, pore structure and oxidation resistance of porous Fe-Al intermetallics were systematically investigated. Porous Fe-Al materials with high open porosity（65%） are synthesized via a low-energy consumption method of TE at a temperature of 636 ℃ and FeAl intermetallic is evolved as dominant phase in sintered materials at 1000 ℃. The porous materials are composed of interconnected skeleton, large pores among skeleton and small pores in the interior of skeleton. The interstitial pores in green powder compacts are the important source of large pores of porous Fe-Al intermetallics, and the in-situ pores from the melting and flowing of aluminum powders are also significant to the formation of large pores. Small pores are from the precipitation of Fe-Al intermetallics particles. In addition, the porous specimens exhibit high resistance to oxidation at 650 ℃ in air.

INTERMETALLIC ALLOYS AND COMPOSITES FOR THE 21ST CENTURY: A BASIC ENERGY SCIENCES PROGRAM OF THE U. S. DEPARTMENT OF ENERGY

Progress has been made in intermetallic alloys over the past decade and a half, but intermetallics remain a relatively unexplored class of materials for energy applications. Hence, they offer considerable opportunities both for scientific research on fundamental structural property processing relationships and for technological development. The Department of Energy supports a program of scientific research on intermetallic alloys such as the nickel and iron aluminides and is establishing new research efforts in silicides and Laves phases through the program of the Division of Materials Sciences, of the Office of Basic Energy Sciences. Areas of research include theory and materials simulation, microalloying, high resolution sudies of structure and composition, mechanical properties, point defects and dislocation mechanics, phase transformations, and processing. Research is conducted through programs at the Department of Energy National Laboratories and through grants to academic and industrial researchers.Research results from Division of Materials Sciences programs have provided the basis and transportation. In addition, a cooperative effort between research groups has been established as a project on intermetallic materials under the Center of Excellence in Synthesis and Processing of Advanced Materials.

Electrochemical extraction and the analysis of inter-metallic phases and nitrides in tempered duplex stainless steels

During aging at a temperature ranging from 650 -950 ℃,the ferric matrix in duplex stainless steels undergoes various decomposition processes which could form the precipitates of the Sigma （σ） and Chi （X） phases, as well as nitrides. It is well known that these precipitates lead to a reduction in creep ductility and adversely affect toughness and corrosion properties of steel. This experiment carded out qualitative and quantitative analyses of intermetallic phases and nitrides and established an analytical procedure, including specimen preparation, the choosing of the electrolyte and electrolytic systems,electrolytic isolation,wet chemical separation, and physical and chemical analysis, etc. The residues were collected by ultrasonic cleaning and filtration after galvanostatic electrolysis. Dynamic laser scattering sizer （DLS- sizer） ,scanning electron microscope （SEM） and transmission electron microscope （TEM） were used to examine their structure,modality and size. Qualitative and quantitative analyses were performed by using X-ray diffraction （XRD）, oxygen-nitrogen analyzer and wet chemical analysis. Furthermore, there is a discussion on the effect of isothermal treatment on precipitation that occurs at different temperatures for different periods of time.