Tempering Behavior of M50 Steel with Different Austenite Proportion Induced by High Current Pulsed Electron Beam

M50 steel was irradiated by high current pulsed electron beam(HCPEB)with different pulses.The subsequent tempering was carried out between 500 and 625℃.Microstructure evolution was analyzed by scanning electron microscopy and X-ray diffraction.It is found that the HCPEB treatment could constrain martainsite transformation in the surface layer of the samples.Tempered behavior of HCPEB remelted layer strongly depends on the proportion of retained austenite.Austenite saturated more carbon and metallic elements depict higher tempering stability.During tempered process,carbides precipitates among the grain and phase boundaries.The decreased solution of the elements promotes the retained austenite into martensite.     

强流脉冲电子束表面改性FeCrAl涂层的显微组织及耐高温腐蚀性能研究

目的改善FeCrAl涂层表面组织,提高其耐高温盐溶液腐蚀性能。方法用电弧喷涂方法在45碳钢表面制备FeCrAl(Cr 25.5%,Al 5.5%,Fe余量)涂层。用强流脉冲电子束(HCPEB)对FeCrAl涂层进行表面改性处理,工作参数为:脉冲宽度200μs,能量密度分别为20、25、30、40 J/cm^2。处理脉冲次数均为1次。通过金相显微镜和扫描电子显微镜对改性层形貌进行分析,通过电子探针方法测量改性前后涂层中Fe、Cr、Al和O元素的分布变化,利用X射线衍射分析对比改性层的相成分组成。在温度650℃下,以Na2SO4+K2SO4饱和盐溶液为腐蚀介质,测试FeCrAl涂层的高温腐蚀性能,并对腐蚀表面形貌进行分析。结果HCPEB处理FeCrAl涂层发生表层重熔,原始粗糙疏松的涂层组织变得光滑致密,表面出现分离的球冠状凸起,凸起内部由排列紧密的Fe-Cr柱状晶组成,Al元素向凸起结构的表面和周围凹陷处聚集。随HCPEB处理能量密度增大,凸起结构尺寸增加,涂层表面的Fe2O3相消失,α-Al2O3相含量增多。经120h高温腐蚀后,原始涂层腐蚀增重63.8 mg/cm^2,HCPEB能量密度20 J/cm^2处理的样品腐蚀增重51 mg/cm^2。结论使用HCPEB在脉冲宽度200μs和能量密度20 J/cm^2下处理FeCrAl涂层后,其高温腐蚀增重较原始涂层减少20%,而使用过高的HCPEB能量密度处理会导致FeCrAl涂层表面结构和耐高温腐蚀性能变差。     

强流脉冲电子束辐照YG8硬质合金的组织与性能

采用强流脉冲电子束(HCPEB)表面改性技术对YG8硬质合金表面进行辐照处理试验。利用金相显微镜、X射线衍射仪和扫描电镜对处理样品的表层组织进行分析,测量改性样品的显微硬度和摩擦磨损性能指标。结果表明,强流脉冲电子束处理使YG8样品表层重熔平整,WC颗粒形状圆整并与粘结剂Co基体发生溶解扩散,表层显微硬度增加到3523.6 HK,耐磨性提高约19%。     

Effect of high current pulsed electron beam treatment on surface microstructure and wear and corrosion resistance of an AZ91HP magnesium alloy

This paper reports an analysis of the microstructure and property modifications on a commercial Mg alloy AZ91HP treated by using High Current Pulsed Electron Beam (HCPEB). It is shown that, a thin layer consisting of nanograined MgO formed on the top surface after HCPEB (electron energy ∼ 30 keV, pulse duration 1 μs, energy density ∼ 3 J/cm²) treatment, below which is a melted layer with depth of about 8-10 μm. The heat affected zone (HAZ) underneath the melted layer and stress wave affected zone contains many stress induced deformation marks. Meantime, a nearly complete dissolution of the intermetallic phase Mg₁₇Al₁₂ in the melted layer is observed, leading to the formation of a super-saturated solid solution on the surface. This is due to the solute trapping effect occurred during the fast solidification process. As a result, the wear and corrosion resistance of the alloy were significantly improved as shown by sliding friction, wear and immersion tests.     

Effect of carbon content on the microstructure and mechanical properties of Mo2FeB2 based cermets

Four series of Mo₂FeB₂ based cermets with different carbon contents were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The transverse rupture strength (TRS), hardness (HRA) and fracture toughness (K_IC) were also measured. The free carbon present in the green compact significantly decreased the grain size; however, a high carbon content resulted in the formation of graphite phase and Fe₃C phase. An increasing carbon content promoted the dissolution of Mo in the binder phase. In addition, the binder phase varied from ferrite to martensite with increasing carbon content. The highest hardness was found for the cermets with 0.5 wt.% carbon addition, whereas the cermets without carbon addition exhibited the maximum TRS and fracture toughness.     

Effect of carbon content on the microstructure and mechanical properties of Mo2FeB2 based cermets

Four series of Mo₂FeB₂ based cermets with different carbon contents were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The transverse rupture strength (TRS), hardness (HRA) and fracture toughness (K_IC) were also measured. The free carbon present in the green compact significantly decreased the grain size; however, a high carbon content resulted in the formation of graphite phase and Fe₃C phase. An increasing carbon content promoted the dissolution of Mo in the binder phase. In addition, the binder phase varied from ferrite to martensite with increasing carbon content. The highest hardness was found for the cermets with 0.5 wt.% carbon addition, whereas the cermets without carbon addition exhibited the maximum TRS and fracture toughness.     

Microstructural evolution and sintering kinetics during spark plasma sintering of Fe and Al blended powder

The reaction diffusion between Fe and Al during spark plasma sintering (SPS) was studied. Microstructural evolution was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the sintering kinetics was disclosed. The main interphase of the SPS sample was Fe₂Al₅ at 773–873 K. Ball-milling enabled a large number of lattice defects and grain boundaries thus the reaction kinetics was accelerated, although the direct current can also promote those defects. After milling, the phase transformation kinetics was improved from 0.207 before mill to 4.56×10^?3. Besides, this work provided more details for the generation of Joule heating. The resistance offered to the electric path was considered to be the source of Joule heating, and particularly the resistance offered by the different contact interfaces of die, punch, graphite foil and the sample played a leading role for the generation of Joule heating during spark plasma sintering.     

Mg元素对强流脉冲电子束改性后Al-20Si合金表面微观组织及性能的影响

目的通过添加Mg元素改善Al-20Si合金的组织,提升其表面力学性能。方法运用场发射扫描电镜(FESEM)、显微硬度计及多功能材料表面性能试验仪等一系列检测手段,考察Mg元素对强流脉冲电子束改性Al-20Si合金表面效果的影响,及合金表面微观组织和表面力学性能的变化。结果 Mg元素能与硅相形成更细小的Mg_2Si相来细化初生硅相,同时可改善强流脉冲电子束处理后铝硅合金表面产生的微裂纹。材料表面经强流脉冲电子束改性后,所有的衍射峰发生了宽化及偏移。两组合金铝基体的显微硬度随着脉冲数的增加而逐渐递增,Al-20Si合金铝基体的显微硬度由745.5MPa增加到2170.7MPa,Al-20Si-5Mg合金的铝基体显微硬度由1061.3 MPa增加到2403.6 MPa,Mg元素的添加可提高Al-20Si合金的硬度。另外,通过往复摩擦试验发现,Mg元素及强流脉冲电子束都能提高材料的耐磨性。结论 Mg元素能改善强流脉冲电子束处理后Al-20Si合金表面的微观组织,添加Mg元素后,Al-20Si合金表面的力学性能得到提高。     

Effect of ambient air pressure on the oxidation kinetics of Fe-6 at.% Si alloy

Surface oxidation of Fe-6 at.% Si alloy was investigated during annealing in ambient air of various pressures with simultaneous isothermal resistivity registrations. Measurements have been done in the temperature range 500-540 °C. Chemical and phase compositions of the samples were analyzed using X-ray photoelectron spectroscopy, conversion electron Mössbauer spectroscopy (CEMS), transmission Mössbauer spectroscopy (TMS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Phase analysis showed that during isothermal resistivity measurement in a low pressure air 100 mbar a protective film of hematite α-Fe₂O₃ was formed on the surface of FeSi substrate. By decreasing pressure to 10⁻² mbar the time dependence of the resistivity exhibits an increase due to the transformation of hematite to magnetite Fe₃O₄. The activation energy for this transformation is 115 ± 5 kJ/mol. By regressive increasing the pressure back from 10⁻² to 100 mbar a non-protective oxide scale of hematite + magnetite was formed. The results were interpreted in the light of the iron-oxygen phase diagram.     

Investigations of the Failure in Boilers Economizer Tubes Used in Power Plants

In this study, failure of a high pressure economizer tube of a boiler used in gas-Mazut combined cycle power plants was studied. Failure analysis of the tube was accomplished by taking into account visual inspection, thickness measurement, and hardness testing as well as microstructural observations using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). Optical microscopy images indicate that there is no phase transformation during service, and ferrite-pearlite remained. The results of XRD also revealed Iron sulfate (FeSO₄) and Iron hydroxide sulfate (FeOH(SO₄)) phases formed on the steel surface. A considerable amount of Sulfur was also detected on the outer surface of the tube by EDS analysis. Dew-point corrosion was found to be the principal reason for the failure of the examined tube while it has been left out-of-service.     

Filamentous carbon formation caused by catalytic metal particles from iron oxide

The thermodynamic equilibrium between metallic iron, iron oxides, iron carbides and an hydrocarbon/hydrogen mixture was calculated at 600°C. On the basis of the metastable Fe‐C‐O phase diagram, both metallic iron and iron oxides can be directly converted into carbides in reducing and carburizing atmosphere. Thermogravimetric (ATG) measurements have been performed in iC₄H₁₀‐H₂‐Ar atmosphere at 600°C on reduced and pre‐oxidised iron samples. The kinetic of coke formation was studied on both surface states by sequential exposure experiments. The initial stages of the transformation were characterised by scanning electron microscopy (SEM) observations and X‐ray diffraction (XRD) analysis. On a reduced surface, the results are consistent with the mechanism currently proposed to explain catalytic coke formation. Cementite (Fe₃C) is formed on the iron surface after carbon supersaturation (a_c > 1). The graphite deposition on its surface (a_c = 1) induces its decomposition. Iron atoms from cementite diffuse through the graphite and agglomerate to small particles that act as catalysts for further carbon deposition. A new mechanism of catalytic particle formation is proposed when an oxide scale initially covers the iron surface. In the carburizing and reducing atmosphere, magnetite (Fe₃O₄) can be directly converted into cementite (Fe₃C). XPS analysis confirm that, in this process, metallic iron is not an intermediary specie of the oxide/carbide reaction. At the same time, graphite deposition occurs at the metal/oxide interface through the cracks present in the oxide scale. Iron carbide in contact with graphite is partially decomposed and acts as catalyst for graphitic filaments growth.     

Influence of Chemical Composition and Melting Process on Hot Rolling of NiTiHf Shape Memory Alloy

NiTiHf high-temperature shape memory alloy ingots with transformation temperatures above 100 °C were produced by vacuum induction melting (VIM) and vacuum arc melting (VAM). The effects of melting process and compositional changes were investigated on hot rolling of cast samples. The amount of (Ti,Hf)₂Ni second phase which was formed during solidification and the (Ti,Hf)C formed due to graphite crucible using in VIM have significantly affected the microstructure of the cast sample due to poor coherency, which affected the hot-rolling behavior. Optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy were used to inspect the observed cracks in the microstructure after the hot-rolling process. The results displayed that the formation of (Ti,Hf)C and the existence of (Ti,Hf)₂Ni second phase had harmful effects on the workability of the cast specimen due to the feeble coherency of (Ti,Hf)C and (Ti,Hf)₂ Ni with the matrix, which caused a failure in the hot-rolled specimen. The Ni₅₀Ti₄₀Hf₁₀ alloy produced by VAM shows better workability in hot rolling due to lower amount of (Ti,Hf)₂Ni, (Ti,Hf)C phases.     

Diamond-like carbon thin films produced by femtosecond pulsed laser deposition of fullerite

Diamond-like carbon films have been deposited from a fullerite target by ultra-short pulsed laser deposition technique. The results indicate that the films morphology and structure, determined by scanning electron microscopy, atomic force microscopy and energy dispersive X-ray diffraction, depend strongly on the substrate temperature. X-ray photoelectron, X-ray Auger electron, Raman and surface enhanced Raman scattering spectra indicate that the fs-DLC films composition involves a mixed sp, sp² and sp³ carbon network consisting of aromatic rings and sp³ diamond-like structures linked by chains of different lengths and composition. The films deposited at room temperature, presenting the higher content of sp³ carbon (48%), also contain C₆₀ crystalline phase and show a very high hardness of 49 GPa.     

Phase transformation behavior of Al9(Mn,Ni)2 eutectic phase during heat treatment at 600 °C in Al-4Ni-2Mn alloy

The morphology evolution and phase transformation of Al₉(Mn,Ni)₂ eutectic phase in an Al-4Ni-2Mn alloy during heat treatment at 600 °C were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results show that nearly all of the eutectic fibers change into prolate ellipsoid and spherical particles in the process of heat treatment, and Ostwald ripening phenomenon occurs in the eutectic region with the increase of the heat treatment time. Besides, a phase transformation from Al₉(Mn,Ni)₂ to O-phase is confirmed. The morphologies of the transformed particles indicate that the O-phase preferentially nucleates on the specific crystal plane of the Al₉(Mn,Ni)₂ eutectic phase and grows in a certain direction. During the phase transformation, the (010)[001] slip system in O-phase is activated, and the resultant slip traces appear on the surface of some O-phase particles.     

高速钢M2强流脉冲电子束表面改性研究

为了改善高速钢M2的表面强度和耐蚀性能,利用强流脉冲电子束（HCPEB）对高速钢M2进行了表面改性处理,辐照次数分别为1,3,5,7,9次。采用扫描电子显微镜、显微硬度计、能谱仪和盐雾腐蚀试验机测试辐照前后试样表面形貌、硬度、元素分布和耐蚀性能,并分析变化规律。结果表明：强流脉,中电子束辐照处理使高速钢表面极速加热又快速冷却,产生表面淬火作用,导致碳化物溶解,马氏体溶碳量增大,试样表面的显微硬度提高,出现表面光滑化,表面层晶粒细化,改善了耐腐蚀性能。     

Hot corrosion behavior of MCrAlY coatings on IN738LC

The hot corrosion behavior of CoNiCrAlY coatings deposited on IN738LC super alloy using low pressure plasma spray (LPPS) was investigated using samples immersed in a solution of Na₂SO₄-10 wt.% NaCl and dried as to be covered with a 2.5 mg/cm² costing. Specimens were heat-treated in furnace at 850 °C and after 24 h in the furnace were accurately weighed. Microstructural characterizations were carried out by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) indicated interactions within microstructure of the coating with clearly diminished thickness of MCrAlY coating. Phase transformation and β-NiAl phase depletion in the MCrAlY coatings were shown to be directly related to the thermal cycles experienced by the samples and revealed outward diffusion of Al in the coating and the inward migration of Ni toward the coating causing β → γ′ phase transformation as the main cause of instability of the β-NiAl.     

Effect of Graphite Addition on Structure and Properties of Ti(CN) Coatings Deposited by Reactive Plasma Spraying

Ti(CN) coatings with graphite addition ranging from 0 to 50 wt.% were prepared using reactive plasma spraying technology and their microstructure, mechanical, and tribological properties were investigated using scanning and transmission electron microscopy, x-ray diffraction analysis, x-ray photoelectron spectroscopy, Vickers microhardness testing, and block-on-ring wear testing. The results showed that graphite addition resulted in crystallite size refinement and an increase in the amount of amorphous phase. The Ti(CN) coatings consisted of a mixture of Ti(CN), graphite, CN _x , and amorphous phases. The hardness first increased then decreased as the graphite content was increased, with a maximum of 1450 HV_0.2 for 30 wt.% graphite addition. The fracture toughness decreased from 4.38 MPa m^1/2 to 2.76 MPa m^1/2 with increasing graphite content. The friction coefficient decreased due to unreacted graphite embedded in the matrix. Also, the wear rate first decreased then increased, with a minimum value of 2.65 × 10^?6 mm³ N^?1 m^?1 for 30 wt.% graphite addition. The wear mechanisms of the Ti(CN) coatings included abrasive, adhesive, and oxidation wear.     

Microstructural and phase evolution of spark plasma sintering of graphitized Ti (C0.9N0.1) composites

Graphite addition on the particle grain sizes, multiple phases and the ultrafine Ti (C_0.9, N_0.1) composite produced by means of spark plasma sintering (SPS) was examined by means of X-ray diffractometer (XRD), and scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS). From the results analysed, the presence of graphite increased the porosity of sintered Ti (C_0.9, N_0.1) cermet and thereby crippled the sinterability of Ti (C_0.9, N_0.1). Significantly, graphite additions had an influence on particle size, morphology, microstructure and phases of ultrafine Ti (C_0.9, N_0.1) by inhibiting the dissolution of titanium carbonitride, outer rims phases and the inner rim formation, thereby causing grain growth reduction. Because of depressed dissolution and solution precipitate, graphite phase evolution in the composite has reduced. Furthermore, the presence of graphite improved the micro indentation hardness of Ti (C_0.9, N_0.1) composite and sintered relative density of the cermets.     

Luminescence of complex ion WO12 in Dy doped nanocrystal Gd6WO12 phosphor

Nanocrystal Gd₆WO₁₂ phosphor doped with Dy³⁺ was prepared by a co-precipitation method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and selected area electron diffraction (SAED) were used to characterize the structure and morphology of the resultant phosphor. It was found that the phosphor exists in tetragonal phase and the phosphor particles show sphere-like shape with an average size of 31 nm. In aid of excitation and emission spectra, the energy levels of the complex ion WO₁₂¹⁸⁻ were confirmed, and that the possible luminescent mechanisms for various wavelengths excitation were analyzed. The cross relaxation and energy transfer between complex ion and Dy³⁺ were discussed. The dependence of luminescent intensity and color coordinates on the excitation wavelength was also investigated.