Effect of pre-annealing on thermal stability of amorphous Zr-Cu-Ni alloy

The influence of pre-annealing on thermal stability of the amorphous Zr70Cu20Ni10 alloy was reported by em-ploying the differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM) tech-niques. It has been observed that the supercooled liquid region decreases with increasing the annealing time under isothe-mal conditions, indicating that the thermal stability of the amorphous Zr70Cu20Ni10 alloy decreases gradually. HRTEM ob-servations reveal that there exist some ordered atomic clusters in the amorphous matrix at the relaxation stage. These or-dered atomic clusters can be regarded as precursors for the precipitation of the crystalline phases in the subsequent crystal-lization process. The reasons resulting in the decrease in thermal stability of the amorphous Zr70Cu20Ni10 alloy with anneal-ing time are discussed through the Gaussian decomposition for the radial distribution function of the amorphous Zr70Cu20Ni10 alloy.     

Crystallization of amorphous Zr70Cu30—xNix alloys

X－ray diffraction (XRD)and differential scanning calorimetry(DSC) were employed to investigate the influence of Ni content on the crystallization of amorphous Zr70Cu30-xNix(atom fration in%) alloys,Experimental results show that with the Ni content increasing the activation energies for crystallization of amorphous Zr70Cu30-xNix alloys increase correspondingly,indicating that the thermal stability is greatly improved.All the DSC traces of amorphous Zr70Cu30-xNix alloys exhibit two exothermic peaks,suggesting that the crystallization process via a double-stage ticles,while the second one corresponds to the precipitaion of nano-scale Zr2Ni phase and crystallization of residual amporphous phase,The mechanism on the crystallization of amorphous Zr70Cu30-xNix alloys was discussed.     

Crystallization behavior in severely cold-drawn Ti50Ni47Fe3 wire

The microstructures and crystallization behavior of Ti–47 at% Ni–3 at% Fe shape memory alloy wire under the condition of severe cold drawing at room temperature and different post-deformation annealing processes were intensively investigated using transmission electron microscope(TEM) and differential scanning calorimetry(DSC). It is indicated that the amorphous phase is dominant in the Ti50Ni47Fe3 wire after the cold drawing of 78 % areal reduction. The critical temperature for recrystalization is determined at about 300 °C. The average grain size grows from 7 up to 125 nm when annealing temperature rises from300 to 500 °C. Post-deformation annealing process exerts significant influence on the crystallization temperature which climbs up with the increase of annealing temperature.     

Effect of preannealing on crystallization process of amorphous Sm5Fe80Cu1Si5B3C2.5Zr3.5 alloy

In the view of crystallization activation energy of amorphous alloy,the mechanism of coarse grain in annealed Sm5Fe80Cu1Si5B3C2.5ZR3.5 amorphous alloy was analyzed.It reveals the e4ffect of preannealing on the process crystallization.The results show that preannealing can be used to change the crystallization behavior of the α-Fe phase in the Sm5Fe80Cu1Si5B3C2.5Zr3.5 amorphous alloy,whick is helpful for forming α-Fe phase grains;and it is not large for Sm2Fe17Cx phase.     

Formation and crystallization of Zr-Ni-Ti metallic glass

The metallic Zr65 Ni25 Ti10 (mole fraction, ％) glass has been fabricated by a single roller melt-spinning method. The glass forming ability(GFA) and thermal stability of the Zr65 Ni25 Ti10 melt-spun ribbons were investigated by using X-ray diffraction(XRD) and differential scanning calorimetry(DSC) in the mode of continuous heating. It is shown that the reduced glass transition temperature (Trg) is 0. 506 and the supercooled liquid region (△Tx) is 30 K. Two exothermic peaks were observed in the DSC curves of the as-quenched ribbon, which indicates that the crystallization process undergoes two different stages. The phase transformation during the isothermal annealing was investigated by X-ray diffraction(XRD) and transmission electronic microscope(TEM). It is observed that the metastable FCC Zr2 Ni(Fd3m, a= 12.27 A) precipitated while annealing in the suppercooled region(615 K) and the stable BCT Zr2Ni(I4/mcm, a= 6.499 A, c= 5.270 A) precipitated while annealing at higher temperature(673 K or 723 K). The crystallines are on nanoscale, with grain size of 15-30 nm. The reason for the precipitation of the different structural Zr2 Ni from the glassy matrix under different annealing conditions was discussed based on the concept of multi-component chemical short range order(MCSRO).     

STUDY ON THE SHOCK WAVE CRYSTALLIZATION OF AMORPHOUS ALLOYS BY DSC

Shock wave and annealing crystallization of amorphous alloys FeSiB, FeMoSiB and FeCuNbSiB were studied by isothermal and non-isothermal DSC technique. It was found that the shock wave crystallization is very perfect, the fraction crystallized is very close to 100%, though the period of crystallization is very short, only about 10-4-10-6s. Their produced phases differ from the parent phase in structure and composition. The high velocity of the transformation is very difficult to explain by the diffusion theory of solid state phase transition.     

Deformation of Zr41Ti14 Cu12. 5Ni10Be22.5 bulk amorphous alloy under isobaric pressure in super-cooled liquid region

The curve of crystallization transition during continuous heating for the Zr41Ti14 Cu12. 5Ni10Be22.5 bulk amorphous alloy was measured by means of dilatation(Fully automatic transformation recording/measuring instrument) and X-ray diffraction(XRD) method. The deformation behavior of the alloy at various heating rates in the supercooled liquid region was studied. The results show that the glass transition temperature of the alloy increases slightly and the supercooled liquid region(SLR) increases significantly with increasing heating rate. The deformation amount under isobaric pressure of 1 N for the alloy in the SLR increases with increasing heating rate. As the heating rate of the alloy increases from 5 to 100℃/rain, the amount of deformation of the alloy increases from 8.3% to 45%     

Effect of post annealing on phase transformation of Ni-Mn-Ga ferromagnetic shape memory alloy particles prepared by ball milling

The effect of post annealing on the phase transformation of Ni52Mn24Ga24 ferromagnetic shape memory alloy particles prepared by ball milling was studied. Ni52Mn24Ga24 alloy particles at micron scale were prepared successfully by ball milling the crushed bulk alloy. SEM observation reveals that the shape of the as-milled particle is regular polygon and a lot of cracks can be seen at the surface of the particles. For as-milled particles, the widening of characteristic peak can be found in the XRD pattern, and no transformation characterization can be detected by DSC. Post annealing at the elevated temperature will recover the transformation behavior of milled particles to the same level as that of bulk sample. It is shown that with increasing annealing temperature above 400 ℃, Ms decreases and As increases, while the magnetic transition temperature keeps constant. XRD results indicate that the change of grain size of the particles results in such an effect of post annealing.     

Crystallization Behavior and Magnetic Properties of （Fe0.6Co0.4）86Hf7B6Cu1 Alloy

(Fe0.6Co0.4)86HfTB6Cu1 nanocrystalline alloy obtained in isothermal annealing process from amorphous precursor was investigated as candidate of soft magnetic materials for high temperature applications. Co substitution for Fe can enhance the curie temperature of amorphous alloy (Tc = 630℃) and improve the magnetization of nanocrystalline alloy at high temperature ( ≈ 1.56T at 550℃). After annealing amorphous precursor at 550℃ for 1 hour, the optimum nanocrystalline alloy can be obtained which shows the local minimum coercivity ( ≈ 16 A/m). The coercivity increases with the increase of annealing temperature corresponding to the formation of ferromagnetic phase in the secondary crystallization. Furthermore, additions of Hf and B elements reduce the melting temperature of the alloy studied comparing with the Fe-Co binary alloy.     

Microstructure and thermal expansion of copper-based amorphous alloys during structural relaxation

(Cu43Zr48Al9)98Y2 amorphous alloy bar was prepared by the arc melting copper mold absorption casting method,and then,the amorphous alloy was annealed at different temperatures for different times.The influence of heating rate on thermal expansion and thermal stability was studied by thermomechanical analysis(TMA),and the microstructure evolution of the amorphous alloy during structural relaxation and crystallization was studied by XRD and TEM.Results show that the structural evolution behavior of the(Cu43Zr48Al9)98Y2 amorphous alloy can be divided into five different stages(structural relaxation preparation stage,structural relaxation stage,first crystallization stage,second crystallization stage,and grain growth stage).When the heating rate is 20 K/min,the amorphous alloy has the smallest thermal expansion coefficient and the best thermal stability.The width of the supercooled liquid region is 66.42 K.Samples with different relaxation states were prepared by annealing at the heating rate of 20 K/min.The structural evolution of amorphous alloys with different relaxation states is as follows:amorphous→CuZr2+AlCu2Zr7→CuZr2+AlCu2Zr7+CuZr(B2)+CuZr(M)+Cu10Zr7→CuZr2+AlCu2Zr7+CuZr(B2)+CuZr(M).After annealing at 706 K and 726 K(in the supercooled liquid region)for 1.5 h,the amorphous-nanocrystalline composites were obtained.When the annealing temperature is 706 K,the crystallization process of the sample is as follows:amorphous→Cu10Zr7→Cu10Zr7+CuZr,and for the sample at 726 K,it is as follows:amorphous→CuZr2+AlCu2Zr7+Cu10Zr7→Cu10Zr7+CuZr2→CuZr2+CuZr(B2)+Cu10Zr7.     

Microstructure and martensitic transformation behavior of Ni56-xMn25FexGa19 shape memory alloys简

Microstructure, martensitic transformation behavior, mechanical and shape memory properties of Ni56-x Mn25 Fex Ga19(x = 0, 2, 4, 6, 8) shape memory alloys were investigated using optical microscopy(OM), X-ray diffraction analysis(XRD), differential scanning calorimeter(DSC), and compressive test. It is found that these alloys are composed of single non-modulated martensite phase with tetragonal structure at room temperature, which means substituting Fe for Ni in Ni56 Mn25 Ga19 alloy has no effect on phase structure. These alloys all exhibit a thermoelastic martensitic transformation between the cubic parent phase and the tetragonal martensite phase. With the increase of Fe content, the martensitic transformation peak temperature(Mp) decreases from 356 °C for x = 0 to 20 °C for x = 8, which is contributed to the depressed electron concentration and tetragonality of martensite. Fe addition remarkably reduces the transformation hysteresis of Ni–Mn–Ga alloys. Substituting Fe for Ni in Ni56 Mn25 Ga19 alloy can decrease the strength of the alloys and almost has no influence on the ductility and shape memory property.     

Amorphous in a Zr-IQC-DQC pseudo-ternary alloy system

A pseudo-ternary alloy system was constructed by combining an icosahedral quasicrystal (IQC), a decagonal quasicrystal(DQC), and Zr into one alloy system. Different proportions of Zr were added to pseudo-binary alloy IQC80DQC20 (mass fraction in %). Structural evolution in these alloys was discussed. An amorphous alloy composition was found in this system and a melt-spinning amorphous alloy was produced in this composition. Through DSC analysis, the amorphous alloy exhibits high glass forming ability comparable to that of the Inoue Zr65Al75Cu17.5Ni10 amorphous alloy.     

Direct electroless Ni-P plating on AZ91D magnesium alloy

An electroless Ni-P plating treatment was applied on AZ91D magnesium alloy to improve its corrosion resistance. Optimum pretreatment conditions and optimum bath of electroless nickel plating for magnesium alloy were found through many experiments. In order to avoid bother of pre-plating medium layer, a set of procedure of direct electroless Ni-P under the acid condition was investigated. The properties of the coating with 10% phosphorus were investigated. The results show that a coating with high hardness, low porosity and good adhesive strength is obtained. X-ray diffraction patterns show that the structure of the coating is an amorphous phase. After annealing at 400 ℃, the amorphous phase of Ni-P is transformed to crystalline phases, and some intermetallics as Ni3P and Ni5P2 are deposited from Ni -P solid solution along with an enhancing hardness from Hv 450 to Hv 910.     

TRANSFORMATION BEHAVIOR OF Ti50-x/2Ni50-x/2Cux ALLOYS

1.IntroductionIt is known that transformation behavior of Ti50Ni50-xCux shape memory alloys depends on the Cucontent[1-3].When the substitution of Cu for Ni is less than5at.%,the alloy transforms similar to that ofthe equiatomic Ti-Ni alloy,i.e.,from cubic(B2)to monoclinic(B19′).When the substitution of Cureaches10at.%,the alloy transforms in two stages,i.e.,from cubic(B2)to orthorhombic(B19),and thenfrom orthorhombic to monoclinic(B19′).By further substitution exceeding20at.%,the allo…     

Aging-induced two-stage reverse martensitic transformation behavior in Co_（46）Ni_（27）Ga_（27） high-temperature shape memory alloy

The effect of austenite aging at 823 K on the microstructures and martensitic transformation behavior of Co 46 Ni 27 Ga 27 alloy has been investigated using optical microscopy (OM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and differential scanning calorimeter (DSC). The microstructure observation results show that the unaged Co 46 Ni 27 Ga 27 alloy is composed of the tetragonal nonmodulated martensite phase and face-centered cubic γ phase. It is found that a new nanosized fcc phase precipitates in the process of austenite aging, leading to the formation of metastable age-affected martensite around the precipitates with composition inhomogeneity. Two-stage reverse martensitic transformation occurs in the samples aged for 2 and 24 h due to the composition difference between the age-affected martensite and the original martensite. For the Co 46 Ni 27 Ga 27 alloy aged for 120 h, no reverse transformation can be detected due to the disappearance of the metastable age-affected martensite and the small latent heat of the original martensite. The martensitic transformation temperatures of the Co 46 Ni 27 Ga 27 alloy decrease with an increase in aging time.     

Applicability of Johnson-Mehl-Avrami model to crystallization kinetics of Zr60Al15Ni25 bulk amorphous alloy

The applicability of Johnson-Mehl-Avrami（JMA） model to the crystallization kinetics of Zr60Al15Ni25 bulk amorphous alloy is investigated by differential scanning calorimetry（DSC） under isochronal and isothermal conditions. A criterion Xm, at which a defined function z（x） exhibits the maximum value, is introduced to check the validity of JMA model to the kinetics analysis. The value Of Xm has a constant of 0.632 for JMA model. It is found that the values Of Xm at different isothermal annealing temperatures （743,748, 753 and 758 K） are almost near 0.632, which indicates that the isothermal crystallization kinetics can be modeled by JMA equation. However, the values Of Xm at different heating rates （10, 20, 30 and 40 K/min） are about 0.52, implying that JMA model is not valid to the isochronal crystallization kinetics. The reason why the JMA model is not valid to the isochronal crystallization kinetics is discussed.     

Structural transition of Ni-Mn-Ga ferromagnetic shape memory alloy particles prepared by ball milling

The size, crystal structure and phase transformation of Ni49.8Mn28.sGa21.7 alloy particles prepared by planetary ball milling （PBM） and vibration ball milling （VBM） were investigated by SEM, XRD and DSC. The results show that the particles milled by PBM for 4 h exhibit irregular polyhedron, with the size distribution between 5 pm and 40 pm. These particles present disordered fct structure with no phase transformation behaviour. When annealed at 600℃ for 1 h, the crystal structure of the particles evolves from disordered fct to Heusler completely. The particles milled by VBM for 4 h exhibit flaky shape, with the size distribution from 3 μm to 30μm. The particles present disordered fcc structure with no phase transformation behaviour. However the crystal structure of these particles doesn＇t transform from disordered fcc to Heusler completely aider annealing at 600 ℃ for 1 h, for the severe lattice distortion induced in the VBM process is not eliminated entirely.     

Transient liquid-phase bonding of superalloy K465 using a Ni-Cr-Fe-B-Si amorphous interlayer alloy

A kind of Ni-Cr-Fe-B-Si system amorphous alloy was used as interlayer in transient liquid-phase bonding(TLP bonding) of polycrystalline superalloy K465.The bonding behavior,microstructure feature and the tensile properties of the joints were investigated.There are B-rich phase and Si-rich phase formed in the center of the seam after bonding at 1210℃ for 30 min.The isothermal solidification is complete after bonding at 1210℃ for 4 h.The relationship of the average width of the remnant eutectic zone and bonding time at 1210℃ is nonlinear.The tensile strength of the bonded joint at room temperature and 900℃ is comparable to that of K465 alloy.     

Effects of Zr on crystallization kinetics of Pr—Fe—B amorphous alloys

The effects of Zr on crystallization kinetics of Pr-Fe-B amorphous alloys have been investigated by DTA and XRD methods.It was found that for Pr8Fe86-xZrxB6(x=0,1,2)amorphous alloys,the final crystallized mixture is α-Fe and Pr2Fe14B,and the metastable Pr2Fe23B3 phase occurs during crystallization of Pr8Fe86B6 amorphous alloy,not during crystallization of Pr8Fe86-xZrxB6(x=1,2)amorphous alloys,By analyzing the activation energy of crystallization,the formation of an α-Fe/Pr2Fe14B composite microstructure with a coarse grain size in annealed Pr8Fe86B6 alloy,is attributed to a difficult nucleation and an easy growth for both the α-Fe and Pr2Fe14B in the alloy.The addition of Zr can be used to change the crystallization behavior of the α-Fe phase in Pr-Fe-B amorphous alloy,which is helpful to reduce the grain size for the α-Fe phase.     

Crystallization kinetic characteristics of oxygen-induced/-phase and Zr2Cu phase in Zr65Cu27.5A17.5 glassy alloy

Based on the construction of TTT diagrams by isothermal DSC measurements, the thermal stabilities of Zr65Cu27.5A17.5 glassy alloys containing 0.68% and 0.06% [O] （molar fraction） were compared. The changing tendencies of the thermal stabilities reflected in the TTT-diagrams were validated by XRD analyses and TEM observations. The crystallization kinetic characteristics of oxygen-induced I-phase and Zr2Cu phase in Zr65Cu27.sm17.5 glassy alloy were discussed. It is found that oxygen promotes the precipitation of I-phase and retards the formation of Zr2Cu phase. If the pre-crystallization event for oxygen-induced I-phase is permitted and the main-crystallization event for Zr2Cu phase is taken as the thermal stability criterion, the alloy with higher oxygen content has longer onset time for crystallization within a rather large supercooling temperature range. The possibility for the preparation of Zr65Cu27.sm17.5 glassy alloy-based composite containing oxygen-induced I-phase was also forecasted.