Limitation of the Johnson-Mehl-Avrami equation for the kinetic analysis of crystallization in a Ti-based amorphous alloy

The primary crystallization of the Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ amorphous alloy was studied by isochronal differential scanning calorimetry (DSC). The activation energy was determined by the Kissinger-Akahira-Sunose method. Trying to analyze the crystallization kinetics of the Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ amorphous alloy by two different methods, it was found that the crystallization kinetics did not obey the Johnson-Mehl-Avrami equation. A modified method in consideration of the impingement effect was proposed to perform kinetic analysis of the isochronal crystallization of this alloy. The kinetic parameters were then obtained by the linear fitting method based on the modified kinetic equation. The results show that the isochronal crystallization kinetics of the amorphous Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ alloy is heating rate dependent, and the discrepancy between the Johnson-Mehl-Avrami method and the modified method increases with the increase of heating rate.     

Effect of Dy substitution on the microstructure and magnetic properties of nanograin Nd-Fe-B single-phase alloys

Nanocrystalline single-phase alloys with the nominal compositions (at%) of Nd_12.3-xDy_xFe_79.7Zr_0.8Nb_0.8Cu_0.4B_6.0 (x=0, 0.5, 1.5, and 2.5) were prepared by melt-spinning and subsequent annealing. X-ray diffraction analysis shows that the as-spun ribbons were mainly composed of the amorphous phase. A slight content of Dy stabilizes the amorphous phase during annealing treatment. The grain size becomes smaller and the coercivity of the annealed ribbon is gradually improved with the increase of Dy content. Excessive Dy is harmful to the remanence. It is found that no intergranular phase exists between the grains by high-resolution transmission electron microscopy, and the grain boundaries are crystallographically coherent in the optimally annealed sample. The optimum magnetic properties of remanence (J_r=1.09 T), coercivity (H_ci=1048 kA/m), and maximum magnetic energy product ((BH)_m=169.5 kJ/m3) are obtained from the x=0.5 ribbon in a post heat-treated state (700℃, 10 min).     

Transitions of amorphouscrystalline-amorphous in bulk metallic glass under HP and HT

In-situ SR-XRD measurements revealed that the crystallization process in Zr₄₁.2Ti₁₃.8Cu_12.5Ni₁₀Be_22.5 bulk metallic glass is significantly different from that in traditional glasses. Subsequent heating at 10 GPa converts the sample from amorphous phase into the metastable fcc phase and then leads to the fcc phase back to the amorphous phase, indicating that there exists ‘reversible’ phase transition phenomena in the material under high pressure and high temperature.     

Fabrication of bulk glassy Zr41Ti14Ni8Cu12.5Be22.5Fe2 alloy by water quenching

A glassy Zr₄₁Ti₁₄Ni₈Cu_12.5Be_22.5Fe₂ rod with a diameter of 9 mm was successfully produced by water quenching. The effects of iron addition on thermal stability and hardness of Zr₄₁Ti₁₄Ni₈Cu_12.5Be_22.5Fe₂ bulk amorphous alloy were investigated by XR D, DSC and microhardness test. It is found that the full annealing would enhance the strength of the alloy significantly. The cause of the increase in hardness was analyzed and the formation mechanisms of the bulk amorphous alloy are discussed.     

Mechanism of Ag and Al on improving the glass forming ability of CuZr-based alloys

By a mean field theoretical computation, the equilibrium distributions of additional Ag and Al in the crystalline phase of CuZr-based alloys were determined to occupy the two sublattices of the B2 structure randomly. With the molecular dynamics technique, the effects of Ag and Al on the enthalpy difference (ΔH) between the supercooled melt and the crystalline phase were evaluated. The improved glass forming ability of Cu₄₅Zr₄₅Al₁₀and Cu₄₅Zr₄₅Ag₁₀ can be attributed to their remarkably smaller ΔH than that of CuZr. The calculated diffusion coefficients are more sensitive to the atomic weight of the component atoms than to their interaction strength. As the component atom with the largest mass, the additional Ag increases the viscosity of the supercooled melt significantly and the experimentally stronger glass formation ability of Cu₄₅Zr₄₅Ag₁₀ than Cu₄₅Zr₄₅Al₁₀ can be well understood.     

Effect of proton irradiation on structure relaxation of Zr<Subscript>41.5</Subscript>Ti<Subscript>14.9</Subscript>Cu<Subscript>12.6</Subscript>Ni<Subscript>10.5</Subscript>Be<Subscript>20.4</Subscript> bulk metallic glass

Effects of proton irradiation on structure re-laxation of Zr_(41.5)Ti_(14.9)Cu_(12.6)Ni_(10.5)Be_(20.4) bulk metallic glass areinvestigated by means of X-ray diffraction, differential scan-ning calorimetric and electronic resistance measurements.The results show that, at 203 K, the structure ofZr_(41.5)Ti_(14.9)Cu_(12.6)Ni_(10.5)Be_(20.4) bulk metal glass is relaxed obvi-ously by proton irradiation with the energy and the dosebeing of 160 keV and 1.65×10~(16) ions/cm~2, respectively. How-ever, Zr_(41 .5)Ti_(14.9)Cu_(12.6)Ni_(10.5)Be_(20.4) bulk metallic glass becomesmore steady amorphous state under two conditions, one isthat the energy and the dose are 160 keV and 1.1×10~(15)ions/cm~2, respectively. Another is that the energy and thedose are 120 keV and 6.5×10~(15) ions/cm~2, respectively.     

A Ti–Zr–Cu–Ni–Co–Fe–Al–Sn amorphous filler metal for improving the strength of Ti–6Al–4V alloy brazing joint

Ti_(50)Zr_(27)Cu_8Ni_4Co_3Fe_2Al_3Sn_3(at%) amorphous filler metal with low Cu and Ni contents in a melt-spun ribbon form was developed for improving mechanical properties of Ti–6Al–4V alloy brazing joint through decreasing brittle intermetallics in the braze zone. Investigation on the crystallization behavior of the multicomponent Ti–Zr–Cu–Ni–Co–Fe–Al–Sn amorphous alloy indicates the high stability of the supercooled liquid against crystallization that favors the formation of amorphous structure. The Ti–6Al–4V joint brazed with this Ti-based amorphous filler metal with low total content of Cu and Ni at 1203K for 900s mainly consists of α-Ti, β-Ti,minor Ti–Zr-rich phase and only a small amount of Ti_3Cu intermetallics, leading to the high shear strength of the joint of about 460 MPa. Multicomponent composition design of amorphous alloys is an effective way of tailoring filler metals for improving the joint strength.     

机械合金法制备高生物相容性镁基非晶合金粉末

选择具有高生物相容性的Mg₆₅Zn₃₀Ca₃Si_1.766Zr_0.234合金体系作为研究对象,从原料单质粉末开始,采用雾化制粉、球磨制得该合金的非晶粉末,再通过X射线衍射（XRD）、差示扫描量热法（DSC）、电化学测试等手段,研究了球磨所制得粉末的非晶程度、非晶合金的热力学性能以及该体系镁基非晶合金的耐腐蚀性能.研究表明,经过80 h以上的球磨,可以使该体系下的镁基合金完全转变为非晶态,并且其耐腐蚀性能在相同情况下较ZK61晶态合金更为良好.     

The enhanced corrosion resistance of UMAO coatings on Mg by silane treatment

The surface silanization was carried out on ultrasonic micro-arc oxidation(UMAO) coatings on pure magnesium using KH550 as silane coupling agent(SCA). The surface morphology, chemical bonds and corrosion resistance of the silane films were investigated by scanning electron microscope(SEM), Fourier transform infrared spectroscopy(FTIR) and electrochemical workstation, respectively. The results showed that hybrid coatings were successfully prepared on pure magnesium by UMAO-Na OH(1 mol/L, 2 mol/L, 3 mol/L)-SCA processing. The organic films with Si–O–Mg bonds are helpful for the reduction of the pores in UMAO coatings. The pores decreased with increasing Na OH concentration. Compared with single UMAO treatment, the corrosion potentials(Ecorr) of magnesium plates with UMAO-Na OH(1 mol/L,2 mol/L, 3 mol/L)-SCA treatment increased by 29 m V, 53 m V and 75 m V, respectively, meanwhile the corrosion current density(Icorr) reduced one to two orders of magnitude. It indicated that the corrosion resistance of the coatings was improved by silane treatment.     

Effects of annealing temperature on the microstructure and hardness of TiAlSiN hard coatings

TiAlSiN hard coatings were synthesized on high-speed steel using an arc ion enhanced magnetic sputtering hybrid system.The microstructure and hardness of the coatings at different annealing temperatures were explored by means of XRD,TEM,EDAX and Vickers indentation.The as-deposited TiAlSiN coatings were confirmed to be amorphous due to high depositing rate and low deposition temperature during the film growth.The transformation from amorphous to nanocomposites of nano-crystallites and amorphousness were observed after the annealing treatment,the microstructure of TiAlSiN coatings annealed at 800°C and 1000°C were consisted of crystalline hcp-AlN,fcc-TiN and amorphous phase,however,the coatings were only consisted of fcc-TiN and amorphous phase when annealing at 1100°C and 1200°C.Meanwhile,the formation of Al2O3 was detected on the coating surface after annealing at 1200°C and it indicated the excellent oxidation resistance of the TiAlSiN coatings under the present experimental conditions.Furthermore,the average grain size of the TiAlSiN coatings after high temperature annealing even at 1200°C was less than 30 nm and the size increased with the increasing temperature.However,the hardness of the so-deposited coatings with HV0.2N=3300 dramatically decreased with the increase of temperature and reached nearly to the hardness of TiN coatings with HV0.2N=2300.     

High-temperature frictional wear behavior of MCrAlY-based coatings deposited by atmosphere plasma spraying

Al₂O₃-Cr₂O₃/NiCoCrAlYTa coatings were prepared via atmosphere plasma spraying (APS). The microstructure and phase composition of the coatings were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser confocal scanning microscopy (LSCM), and transmission electron microscopy (TEM). The dry frictional wear behavior of the coatings at 500℃ in static air was investigated and compared with that of 0Cr25Ni20 steel. The results show that the coatings comprise the slatted layers of oxide phases, unmelted particles, and pores. The hot abrasive resistance of the coatings is enhanced compared to that of 0Cr25Ni20, and their mass loss is approximately one-fifteenth that of 0Cr25Ni20 steel. The main wear failure mechanisms of the coatings are abrasive wear, fatigue wear, and adhesive wear.     

Influence of pulsing current on the glass transition and crystallizing kinetics of a Zr base bulk amorphous alloy

Based on the thermal analysis, the influence of pulsing current on the glass transition and crystallizing kinetics of Zr41.3Ti14.2CU12.8Ni10.3Be21.4 bulk amorphous alloy has been studied. The obtained results show that after the Zr41.3Ti14.2CU12.8Ni10.3Be21.4 bulk amorphous alloy was pretreated by high-density pulsing current at low temperature, its glass transition temperature Tg, the initial crystallizing temperature Tx and the corresponding exothermic peak of crystallization Tpi were reduced. But the temperature range of supercooled liquid △T=Tx-Tg is almost the same. The calculated results with Kissinger equation show that the activation energy of glass transition of the alloy pretreated is reduced significantly, while the activation energy of crystallization is basically unchanged. The influence of pulsing current on the glass transition and crystallization of theZr41.3Ti14.2CU12.8Ni10.3Be21.4 bulk amorphous alloy is believed to be related with the structure relaxation of the glass caused by the current.     

Thermal damage and ablation behavior of plasma sprayed Ba2SmTaO6 coatings irradiated by high power continuous laser

Ba₂SmTaO₆ laser protection coatings of ≈200 μm thickness were deposited onto stainless steel surfaces by air plasma spraying, and the laser irradiation resistance of the coatings was investigated. For laser irradiation with a laser power density less than 1000 W/cm², the coatings kept intact. For a laser power density exceeding 1500 W/cm², the Ba₂SmTaO₆ coatings underwent recrystallization, grain growth occurred, and certain spray...     

Surface modification of Ti-45Al-8.5 Nb alloys by microarc oxidation to improve high-temperature oxidation resistance

Microarc oxidation(MAO)electrolysis plasma deposition was used to prepare Al_2O_3coatings on Ti-45Al-8.5 Nb alloys to improve high temperature oxidation resistance.The surface and cross-section morphologies before and after high-temperature oxidation,the chemical composition,and the phase identification of the coatings were investigated by scanning electron microscopy(SEM),electron probe microanalyses(EPMA),and X-ray diffraction(XRD).The results show that Al_2O_3coatings with a thickness of approximately 8μm can be obtained on the Ti-45Al-8.5 Nb alloys by MAO for 600 s.The samples with the Al_2O_3coatings exhibited better high-temperature oxidation resistance.A minimal weight gain of only 0.396 g/m~2after 100 h oxidation at 900°C was observed for the coatings formed with a deposition voltage of 400 V and using a duty cycle of 3%.The deposition mechanism of the Al_2O_3coatings and the effect of the MAO parameters are also described.     

Formation mechanism of an aluminium-based chemical conversion coating on AZ91D magnesium alloy

An environmentally clean aluminium-based conversion coating on AZ91D magnesium alloy was studied in aluminium nitrate solutions. The morphology, composition, structure, and formation mechanism of the coating were investigated in detail using scanning electron microscopy/energy dispersion spectrometry, X-ray diffraction, transmission electron microscopy, and electrochemical corrosion tests. The results show that the conversion coating is composed of magnesium, aluminium, and oxygen, and shows an amorphous structure. In the initial stage of coating formation, the grain-like nucleus is composed of Al₁₀O₁₅·xH₂O, (Al₂O₃)_5.333, Al₂O₃, AlO(OH), MgAl₂O₄, (Mg_0.88Al_0.12)(Al_0.94Mg_0.06)₂O₄, and (Mg_0.68Al_0.32)(Al_0.84Mg_0.16)₂O₄. The conversion coating formed in the 0.01 mol/L aluminium nitrate solution for 15 min can improve the corrosion resistance of the magnesium alloy greatly. The discussion reveals that the possible formation mechanism for the aluminium-based conversion coating is the reduction reaction on micro-cathodic sites due to the electrochemically heterogeneous magnesium alloy substrate.     

Effects of crystallization on corrosion behaviours of a Ni-based bulk metallic glass

The effects of microstructure change on the corrosion behaviours of Ni₅₅Nb₂₀Ti₁₀Zr₈Co₇ bulk glass-forming alloy were investigated in 1 mol/L HCl and 0.5 mol/L H₂SO₄ solutions. Different microstructures of the Ni-based alloy were achieved by annealing the bulk glassy rod prepared by copper mould casting. The microstructure, grain size, grain distribution, and phase composition were characterized. Electrochemical behaviours of the Ni-based alloy were revealed by static immersion and anodic potentiodynamic polarization tests. It is indicated that the corrosion behaviours of the Ni-based bulk glass-forming alloy are related to its microstructures, while the fully crystallized alloy exhibits a relatively lower corrosion resistance than those of the amorphous states.     

Glass-forming ability,microhardness, corrosion resistance,and dealloying treatment of Mg60-xCu40Ndx alloy ribbons

The influence of Nd addition on the glass-forming ability (GFA), microhardness, and corrosion resistance of Mg_60-xCu₄₀Nd_x (x=5, 10, 15, 20, and 25, at%) alloys were investigated by differential scanning calorimetry, Vickers-type hardness tests, and electrochemical methods. The results suggest that the GFA and microhardness of the amorphous alloys increase until the Nd content reaches 20at%. The corrosion potential and corrosion current density obtained from the Tafel curves indicate that the Mg₃₅Cu₄₀Nd₂₅ ternary alloy exhibits the best corrosion resistance among the investigated alloys. Notably, nanoporous copper (NPC) was synthesized through a single-step dealloying of Mg_60-xCu₄₀Nd_x (x=5, 10, 15, 20, and 25) ternary alloys in 0.04 mol·L-1 H₂SO₄ solution under free corrosion conditions. The influence of dealloying process parameters, such as dealloying time and temperature, on the microstructure of the ribbons was also studied using the surface diffusivity theory. The formation mechanism of dealloyed samples with a multilayered structure was also discussed.     

Eutectic reaction and cored dendritic morphology in yttrium doped Zr-based amorphous alloys

The microalloying effect of yttrium on the crystallization behaviors of (Zr_0.525Al_0.10Ti_0.05Cu_0.179Ni_0.146)_100-x Y_x, and (Zr_0.55Al_0.15-Ni_0.10Cu_0.20)_100-x Y_x (x=0, 0.4, and 1, thus the two alloy systems were denoted as Zr52.5, Zr52.5Y0.4, Zr52.5Y1, and Zr55, Zr55Y0.4, Zr55Y1, respectively) was studied. Transmission electron microscopy (TEM) results suggested that the crystalline phases were different in the two Zr-based alloys and with different yttrium contents. ZrNi-phase and Al₃Zr₅ phase precipitations can be well explained by the mechanisms of nucleation and growth. Al₃Zr₅ phase is mainly formed by a peritectic-like reaction, while ZrNi-phase by a eutectic reaction. The contents of elements Y, Al, and Ti may dominate the reaction types. The orientation relationship between Y₂O₃ particles and Al₃Zr₅ phase is also discussed.     

激光熔覆AlCoCrFeNiTi0.5合金涂层制备及其组织性能

采用激光熔覆方法制备AlCoCrFeNiTi0.5高熵合金涂层,研究了激光工艺参数对涂层成形及组织性能的影响。结果表明：激光功率为3.5 kW,扫描速度为300 mm/min,光斑直径5 mm时,单道熔覆涂层表面成形性最好。熔覆层主要为BCC结构固溶体,并且有Al80Cr13Co7和Al95Fe4Cr复杂相析出,涂层平均硬度已达到989 Hv。     

外镀铜层玻璃包裹丝的巨磁阻抗效应

首先利用高频感应加热熔融拉丝法制备了Fe_(73.0)Cu_(1.0)Nb_(2.0)Si_(13.5)B_(9.0)玻璃包裹非晶丝;然后在氮气保护下480～650℃之间退火0.5 h;最后利用化学镀方法在570℃退火的玻璃包裹丝上沉积了一层铜,构成复合结构丝.利用扫描电镜测量了材料的几何尺寸,研究了玻璃包裹丝退火前后及复合结构丝的巨磁阻抗效应.结果表明,材料的软磁特性改善提高了材料的磁阻抗比,铜层与磁性层之间的电磁相互作用也影响磁阻抗比.