Variable precipitation behaviors of Laves phases in an ultralight Mg-Li-Zn alloy

Precipitation habits plays a decisive role in strengthening materials,especially for Mg alloys the non-basal plane precipitation is necessary but very limited.Generally,the precipitates would nucleate and grow up in a specific habit plane owing to the constraint of free-energy minimization of the system.Herein,in an aged ultralight Mg-Li-Zn alloy,we confirmed that the precipitates dominated by C15 Laves structure could form in a variety of habit planes,to generate three forms of strengthening-phases,i.e.,precipitate-rod,precipitate-lath,and precipitate-plate.Among which,the precipitate-plates are on basal plane as usually but precipitate-rods/laths are on non-basal plane,and such non-basal precipitates would transform into the basal(Mg,Li)Zn_(2)Laves structure with prolonged aging.These findings are interesting to understand the precipitation behaviors of multi-domain Laves structures in hexagonal close-packed crystals,and expected to provide a guidance for designing ultralight high-strength Mg-Li based alloys via precipitation hardening on the non-basal planes.

Introduction of a New Method for Regulating Laves Phases in Inconel 718 Superalloy during a Laser-Repairing Process

The morphology,size,and distribution of Laves phases have important influences on the mechanical properties of laser-repaired Inconel 718(IN718)superalloy.Due to the deterioration of the substrate zone,the Laves phase in the laser cladding zone of IN718 superalloy cannot be optimized by a hightemperature solution treatment.In this study,an in situ laser heat-treatment method was proposed to regulate the morphology and size of the Laves phase in the laser cladding zone of IN718 superalloy without impacting the substrate zone.In the in situ laser heat-treatment process,a laser was used to heat previously deposited layers with optimized manufacturing parameters.A thermocouple and an infrared camera were used to analyze thermal cycles and real-time temperature fields,respectively.Microstructures and micro-segregations were observed by optical microscopy,scanning electron microscopy,and electron probe microanalysis.It was found that the in situ laser heat treatment effectively changed the morphology and size of the Laves phase,which was transformed from a continuous striplike shape to a discrete granular shape.The effective temperature range and duration were the two main factors influencing the Laves phase during the in situ laser heat-treatment process.The effective temperature range was determined by the laser linear energy density,and the peak temperature increased with the increase of the linear energy density.In addition,the temperature amplitude could be reduced by simultaneously increasing the laser power and the scanning velocity.Finally,a flow diagram was developed based on the in situ laser heat-treatment process,and the deposition of a single-walled sample with fine and granular Laves phases was detected.

Transformation of Laves phases and its effect on the mechanical properties of TIG welded Mg-Al-Ca-Mn alloys

The effects of Al content and Ca/Al mass ratio on the microstructure and mechanical properties of tungsten inert gas(TIG)welded Mg-2Ca-x Al-0.5Mn(x=0,1,5)alloy joints were studied in present work.Results showed that increasing Al content was effective in reducing the dendrite spacing at the fusion zone(FZ)edge.The Laves phases in the FZ and the heat-affected zone(HAZ)can be changed from Mg_(2)Ca to(Mg,Al)_(2)Ca with the decrease of Ca/Al ratio,and the(Mg,Al)_(2)Ca could be further transformed to Al_(2)Ca under welding thermal cycle.Furthermore,dynamic dissolution and precipitation of Laves phases and Al_(8)Mn_(5)phases occurred in the HAZ,resulting in a gradient microstructure and hardness peak in this area.The tensile properties of the joints were significantly improved with the increase of Al content,which was mainly due to the modification of Laves phases.

Superconducting properties of the C15-type Laves phase ZrIr_(2) with an Ir-based kagome lattice

We report systematic studies on superconducting properties of the Laves phase superconductor ZrIr_(2).It crystallizes in a C15-type(cubic MgCu_(2)-type,space group Fd3m)structure in which the Ir atoms form a kagome lattice,with cell parameters a=b=c=7.3596(1)?.Resistivity and magnetic susceptibility measurements indicate that ZrIr_(2) is a type-Ⅱsuperconductor with a transition temperature of 4.0 K.The estimated lower and upper critical fields are 12.8 mT and 4.78 T,respectively.Heat capacity measurements confirm the bulk superconductivity in ZrIr_(2).ZrIr_(2) is found to possibly host strong-coupled s-wave superconductivity with the normalized specific heat change△C_(e)/γT_(c)~1.86 and the coupling strength△_(0)/k_BT_(c)~1.92.First-principles calculations suggest that ZrIr_(2) has three-dimensional Fermi surfaces with simple topologies,and the states at Fermi level mainly originate from the Ir-5d and Zr-4d orbitals.Similar to SrIr_(2) and ThIr_(2),spin–orbit coupling has dramatic influences on the band structure in ZrIr_(2).

Effects of temperature and point defects on the stability of C15 Laves phase in iron:A molecular dynamics investigation

Molecular dynamics simulations are used to investigate the stabilities of C15 Laves phase structures subjected to temperature and point defects. The simulations based on different empirical potentials show that the bulk perfect C15 Laves phase appears to be stable under a critical temperature in a range from 350 K to 450 K, beyond which it becomes disordered and experiences an abrupt decrement of elastic modulus. In the presence of both vacancy and self-interstitial, the bulk C15 Laves phase becomes unstable at room temperature and prefers to transform into an imperfect body centered cubic（BCC）structure containing free vacancies or vacancy clusters. When a C15 cluster is embedded in BCC iron, the annihilation of interstitials occurs due to the presence of the vacancy, while it exhibits a phase transformation into a（1/2） 111 dislocation loop due to the presence of the self-interstitial.

Synthesis of Iron-Based Laves Phase Containing Praseodymium Magnetostrictive Materials

The synthesis and magnetostriction of PrxTb1-x.Fe2, PrxTb1-x Fe2BO2 and PrxTb1-x（Fe0.6Co0.4）2 alloys were investigated in this study. The addition of boron or cobalt atom in PrxTb1-xFe2 could effectively prevent the formation of non-cubic phases, and Pr concentration limit was successfully increased from 0.2 to 0.4. X-ray step scanning for the PrxTb1-xFe2BO2 and PrxTb1-x（Fe0.6Co0.4）2 alloys showed that PrFe2 possessed a large spontaneous magnetostriction λ1111.

Kink-band formation in directionally solidified Mg/Mg_(2)Yb and Mg/Mg_(2)Ca eutectic alloys with Mg/Laves-phase lamellar microstructure

For the development of high-strength Mg alloys,active use of Laves phases such as C14-type Mg_(2)Yb and Mg_(2)Ca is strongly expected.However,the brittleness of the Laves phases is the biggest obstacle to it.We first found that kink-band formation can be induced in directionally solidified Mg/Mg_(2)Yb and Mg/Mg_(2)Ca eutectic lamellar alloys when a stress is applied parallel to the lamellar interface,leading to a high yield stress accompanied with ductility.That is,microstructural control can induce a new deformation mode that is not activated in the constituent phases,thereby inducing ductility.It was clarified that the geometric relationship between the operative slip plane in the constituent phases and the lamellar interface,and the microstructural features that provide kink-band nucleation sites are important factors for controlling kink-band formation.The obtained results show a possibility to open the new door for the development of novel high-strength structural material using the kink bands.

Vacuum Electromagnetic Levitation Melting and Undercooling of Peritectic Terfenol-D

For the first time, the undercooling of a magnetostrictive material a near peritectic Tb 0.27 Dy 0.73 Fe 1.90 alloy was realized by vacuum electromagnetic levitation melting and 60 K undercooling was obtained. There is one recalescence behavior during solidification of the undercooled melt,which can attribute to the priority precipitation of REFe 2 phase instead of REFe 3 phase, due to preferential nucleation and higher crystal growth rate of REFe 2 phase and the suppression of peritectic reaction. According to the crystal structural characteristics of REFe 2 and REFe 3, REFe 2 is a Laves phase intermetallics with MgCu 2 type structure, which has similar polytetrahedral structure with short range ordered structure in undercooled melt and has lower potential barrier for nucleation than that of REFe 3,which lead to the preferential nucleation of REFe 2 phase directly from the undercooled melt. Also, the similarity of structures between REFe 2 phase and undercooled melt leads to higher crystal growth rate of REFe 2 phase than that of REFe 3.

Influence of magnetically constricted arc traverse speed (MCATS) on tensile properties and microstructural characteristics of welded Inconel 718 alloy sheets

The magnetically constricted arc technique was implemented to mitigate the heat input related metallurgical problems in Gas Tungsten Arc Welding(GTAW)of Inconel 718 alloy particularly Nb segregation and subsequent laves phase evolution in fusion zone.This paper reports the direct effect of magnetically constricted arc traverse speed(MCATS)on bead profile,tensile properties and microstructural evolution of Inconel 718 alloy sheets joined by Gas Tungsten Constricted Arc Welding(GTCAW)process.The mechanism amenable for the microstructural modification and corresponding influence on the tensile properties of joints is investigated both in qualitative and quantitative manner related to the mechanics of arc constriction and pulsing.It is correlated to the solidification conditions during welding.The relationship between MCATS and Arc Constriction Current(ACC)was derived.Its interaction effect on the magnetic arc constriction and joint performance was analysed.Results showed that the joints fabricated using CATS of 70 mm/min exhibited superior tensile properties(98.39% of base metal strength with 31.50% elongation).It is attributed to the grain refinement in fusion zone microstructure leading to the evolution of finer,discrete laves phase in interdendritic areas.

Bulk glass formation in ternary Cu-Zr-Ti system

The formation of bulk metallic glasses (BMGs) in ternary Cu-Zr-Ti system was investigated by a copper mold casting method. The nature of the amorphous phase was verified by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). It was demonstrated that the BMGs could be formed in a broad composition range in this system. Cu50Zr42.5Ti7.5, Cu60Zr27.5Ti12.5, Cu60Zr30Ti10 and Cu60Zr32.5Ti7.5 alloys exhibit strong glass-forming ability (GFA), and fully glassy rods of 5 mm in diameter can be obtained. In the center region of the ternary diagram, however, the GFA of the alloys was degraded due to the presence of Laves phase. The degradation of the GFA results from easy nucleation of the Laves phase in the undercooled liquid.

Effect of Mn on the Magnetostriction and Magnetic Properties in Zr_(0.1)Tb_(0.9)(Fe_(1-x)Mn_x)_2 and Y_(0.1)Tb_(0.9)(Fe_(1-x)Mn_x)_2

Effect of Mn substitution for Fe in cubic Laves Zr_(0.1)Tb_(0.9)(Fe_(1-x)Mn_x)_2 and Y_(0.1)Tb_(0.9)(Fe_(1-x)Mn_x)_2 com- pounds is presented.Similar results in both systems are obtained: The structure and the magnetism of TbFe_2 are both influenced slightly by a small amount of Y or Zr substitution for Tb;With increasing x value,the lattice constant increases monotonously;the Curie temperature decreases linearly;while saturation magnetization increases linearly.For the small amount of Mn substitution for Fe in both systems,magnetostriction is significantly larger than that in the pure iron alloys.The largest magnetostriction of|γ_‖-|γ_|=2200×10^(-6) at magnetic field of 2×10~7/4π A/mis obtained for Y_(0.1)Tb_(0.9)(Fe_(0.95)Mn_(0.05)_2.

Effect of Ti content on the hydrogen storage properties of Zr_(1-x)Ti_xMn_2Ce_(0.015) alloys

The effect of Ti content on the hydrogen storage properties of Zr1-xTixMn2 Ce0.015（x = 0,0.2,0.3,0.5） alloys was studied by X-ray diffraction,scanning electron microscopy and pressure-composition（p-c） isotherm measurement.All of the alloys mainly consist of C14-type Laves and CeO2 phases.As the Ti content increases,the lattice parameters of the Laves phase decrease and the unit cell shrinks anisotropically,the total hydrogen absorption capacity decreases but the reversible hydrogen desorption capacity of the alloys increases,and the equilibrium pressure of the alloys increases but the plateau becomes sloping.The changes of hydrogen storage properties of Zr1-xTixMn2 Ce0.015 alloys are related to the differences in both atomic radius and hydrogen affinity between Ti and Zr elements.

EFFECT OF W ON MECHANICAL PROPERTIES OF 12%Cr HEAT-RESISTANT STEEL

The effect of W on mechanical properties of 12% Cr-W-V-Nb heat resistant steel at high temperatures and room temperature is reported.The experimental results indicated that if the W content was about 2.2—3.0 wt-%,there was no obviously change of R.T.tensile strength, but impact toughness decreased with the rise of W content.On the other hand,the increase of W content enhanced the short time stress rupture strength,but did not for the long time one. The increase of W have two effects on the precipitation behavior,promoting Laves formation of type Fe_2W,increasing the precipitated phase amount and speeding up the coarsening pro- cess of precipitated phase at high temperatures.The effect of W on the mechanical properties is closely associated with precipitation behaviors.When the rupture life is short,there has no enough time to coarsen the precipitated phases,so the increase of precipitated phases results in strengthening effect,i.e.the W increases the high temperature strength.After prolonged expo- sure,the evident coarsening took plaee,that decreased the effect of precipitation.

Preparation and Magnetostriction of Tb_(0.22)Dy_(0.48)Ho_(0.35)Fe_2 Alloys

Tb0.22Dy0.48Ho0.35Fe2 quaternary alloys are prepared by melting-top casting-annealing process. X-ray diffraction reveals that the alloy is single phase polycrystalline alloy with MgCu2 type cubic Laves phase structure, and (511) preferred orientation occurs in its. The magnetostriction measurements are carried out at room temperature using standard strain gauge technique in magnetic fields up to 400 kA·m-1. The results show that when the magnetic field, H, is 90 kA·m-1, the magnetostriction, λ, of Tb0.22Dy0.48Ho0.35Fe2 quaternary alloys is 260×10-6, and when the H is 210 kA·m-1, the λ is 438×10-6. When the H is 400 kA·m-1, the λ is up to the saturation value, 538×10-6. As compared with TbDyFe ternary alloys, the λ of the quaternary alloy is significantly higher when the H is less than or equal to 210 kA·m-1. When the H is 120 kA·m-1, the λ of the alloy is 333×10-6, 70×10-6 more than the ternary alloy. Research results and mechanism are discussed.

Structure, Magnetic Properties and Magnetostriction of Pr_xTb_(1-x)(Fe_(0.6)Co_(0.4))_(1.9) Alloys

The structure, magnetic properties and magnetostriction of PrxTb1-x(Fe0.6Co0.4)1.9 alloys were investigated. It was found that PrxTb1-x(Fe0.6Co0.4)1.9 alloys with x<0.4 were composed of single cubic Laves phase, while a mass of PuNi3-type phase appeared when the Pr concentration was higher than 0.4. The magnetization measurement showed that there were two different magnetic phases in Pr0.2Tb0.8(Fe0.6Co0.4)1.9 alloys. The saturation magnetostriction of Pr0.2Tb0.8(Fe0.6Co0.4)1.9 alloys at 900 kA·m-1 is 1765×10-6, which was higher than that of Tb0.27Dy0.73Fe2(1600×10-6). The spontaneous magnetostriction λ111 showed a maximum value at x=0.3.

Effects of Boron on Pr_ (0.1)Ce_ (0.6)Tb_ (0.3)Fe_ ( 1.9) Compound

The structure, Curie temperature and magnetostriction of Pr_ 0.1Ce_ 0.6Tb_ 0.3Fe_ 1.9-xB_x compounds were investigated by means of X-ray diffraction using a Vibrating sample magnetometer and a standard strain technique. All the samples show entire MgCu_2-type laves phase structure. The lattice parameter decreases slightly when x≤0.1, and decreases rapidly when x>0.1 with increasing B content. Curie temperature exhibits a peak at x=0.1. The substitution of B for Fe causes the decrease of magnetostriction at room temperature.

Magnetic properties and magnetostriction of PrxNd_(1-x)Fe_(1.9)(0≤x≤1.0) alloys at low temperature

The crystal structure,magnetic and magnetostrictive properties of high-pressure synthesized Prx Nd1-xFe1.9（0≤x≤1.0） alloys were studied.The alloys exhibit single cubic Laves phase with MgCu 2-type structure.The initial magnetization curve reveals that Pr0.2Nd0.8Fe1.9 has a minimum magnetocrystalline anisotropy at 5 K.The magnetostriction curve at 5 K shows that Pr0.2Nd0.8Fe1.9 has a very good low-field magnetostrictive property,and the magnetostriction of the PrxNd1-xFe1.9 alloy in high magnetic field is attributable mainly to Pr.The temperature dependence of the magnetostriction（λ ｜｜） at the field of 5 kOe shows that the substitution of Nd reduces the K 1 remarkably,and the values of λ｜｜ of Pr0.2Nd0.8Fe1.9 and Pr0.8Nd0.2Fe1.9 alloys are nearly five times larger than that of the PrFe 1.9 alloy below 50 K;the λ｜｜ of Pr0.8Nd0.2Fe1.9 reaches up to 1082 ppm at 100 K,which makes it a potential candidate for application in this temperature range.

Hybrid DFT study of structural,electronic,magnetic and elastic properties of laves phase binary intermetallics RFe_(2)(R=La,Ce,Pr and Nd)

Hybrid density functional theory was used to investigate the structural,electronic,magnetic and elastic properties of the Laves phase binary intermetallics RFe_(2)(R=La,Ce,Pr and Nd) in C_(15) crystal structure.The calculated lattice constants of these materials are found in good agreement with the experiments.The band structures and density of states distribution confirm the metallic nature of all these intermetallics.The optimized energies in different magnetic phases and magnetic susceptibilities by postDFT treatments confirm that all the understudy compounds are ferromagnetic in nature.Elastic parameters were calculated from the cubic elastic coefficients C_(11),C_(12) and C_(44).The elastic properties reveal that these intermetallics are incompressible,ductile,elastically anisotropic and mechanically stable.Based on the metallic nature and ferromagnetic properties,it is expected that these intermetallics are suitable materials for spintronic technology.

Effect of cerium on microstructure,eutectic carbides and Laves phase in electroslag remelted 15Cr-22Ni-1Nb austenitic heat-resistant steel

The dendrites,eutectic carbides,Laves phase and microsegregation of alloying element in electroslag remelted 15Cr-22Ni-1Nb austenitic heat-resistant steel with varying cerium contents were studied.The liquidus and solidus temperatures of the steel were determined to reveal the effect of cerium on solidification temperature interval and local solidification time of the steel.The secondary dendrite arm spacing decreases from 57.10 to 40.18μm with increasing the cerium content from 0 to 0.0630 wt.%.The eutectic NbC and Laves phase in as-cast ingots exhibit blocky and honeycomb morphology,respectively.The area fractions and sizes of eutectic NbC and Laves phase in as-cast ingots decrease with the increase in cerium content.The atomic percentage of Laves phase-forming element(Ni,Nb,Cr,Mo and Si)decreases with the increase in cerium content of the steel.The microsegregation of Mo,Ni,Si,Cr and Nb decreases with increasing the cerium content,which is favorable to reducing both the amount and sizes of eutectic NbC and Laves phase in as-cast ingots.The solidification temperature interval and local solidification time of the steel decrease as the cerium content is increased from 0 to 0.0630 wt.%,which inhibits the growth of dendrites,eutectic NbC and Laves phase.