合金元素在fcc-Fe/NbX(X=C,N)界面的偏析及影响

基于密度泛函理论(DFT)第一性原理方法,研究了Si、Ni、Mn、Cr、Mo在fcc-Fe/NbX (X=C, N)界面的偏析行为,并分析了合金元素偏析对界面体系的影响。结果表明,fcc-Fe/NbN界面结合强度相较于fcc-Fe/NbC界面结合强度略有提升;Si稳定存在于Fe基体中,Ni、Mn在界面有轻微偏析倾向,Cr、Mo在界面和NbX (X=C,N)内均存在偏析,其中,Mo向界面偏析倾向更大;Cr、Mo偏析在fcc-Fe/NbC界面一定程度上降低了界面的结合能力,但体系稳定性有所提升,Cr、Mo偏析在fcc-Fe/NbN界面一定程度上提高了界面的结合能力,但Mo使得体系稳定性下降。     

镍基合金焊丝GTAW熔敷金属凝固偏析行为

采用OM,SEM,EDS,EPMA等分析手段对试制的镍基合金焊丝GTAW熔敷金属开展了凝固偏析行为研究.结果表明,熔敷金属中主要包括γ相、（Nb,Ti） C碳化物、Laves相等,金相组织主要为柱状晶,在枝晶间存在宽度约为5~10 μm的偏析区域;按照Scheil公式对EPMA分析结果进行了偏析系数计算,估算的Nb,Mo,Ni,Cr,Fe偏析系数分别为k_Nb=0.23,k_Mo=0.68,k_Ni=1.07,k_Cr=1.05,k_Fe=1.23,在结晶过程中Nb,Mo更倾向于分配在残余液相,Nb的偏析倾向最大,Mo次之,Fe更倾向于分配在固相中,Ni,Cr基本为固液平均分配.文中试验用镍基合金焊丝GTAW熔敷金属凝固结晶路径为L→L+γ→L+γ+MC→L+γ+MC+Laves相→γ+MC+Laves相.     

微合金钢中Mo对α-Fe/NbC界面影响的第一性原理研究

利用基于密度泛函理论的第一性原理方法,研究了钼元素掺杂前后α-Fe/NbC界面的黏附功、界面能、电子结构和成键特征等性质。考虑了2种不同原子的终端界面,并分析了6种Mo原子置换位置对α-Fe/NbC界面结构的影响。结果表明:C终端界面结构的稳定性比Nb终端界面的稳定性更强,而Mo原子进入界面NbC侧置换Nb原子形成的α-Fe/(Nb,Mo) C界面则表现出比未掺杂界面更好的稳定性。因此,Mo对NbC在铁素体中的形核有一定的促进作用。另外,6种界面的差分电荷密度、态密度和Milliken布居分析也解释了Mo能强化α-Fe/NbC界面的原因。     

Al、Cr和Nb在Mo(111)/MoSi2(110)界面的元素效应

运用第一性原理平面波赝势方法计算了Mo(111)/MoSi2(110)的界面结构,并通过元素界面偏析能的计算确定了Al、Cr和Nb在Mo(111)/Mo Si2(110)的偏析位置,结合脱粘功和差分电荷密度揭示了Al、Cr和Nb对Mo/Mo Si2界面结合强度的影响。结果表明:Si顶位型配位方式的界面能最小,最为稳定,在Mo(111)/MoSi2(110)界面结构中倾向于以Si顶位型配位方式结合,其界面分离面在近界面Mo Si2(110)一侧的亚界面层。Nb对界面结合不利,Cr可适当提高界面结合强度,而Al对界面强度的影响取决于其界面覆盖度。究其原因是由于Nb在界面偏析形成的Nb—Si键相比于Mo—Si键有明显减弱,Cr形成的Cr—Si键略有增强,而Al的界面覆盖度对形成的Mo—Al键强弱影响较大。     

新型电磁搅拌用无磁钢

目前无磁辊的原设计材质是X5 NiCrTi26-15(西马克),属于德国牌号.国产牌号为GH2132,0 Cr15 Ni25 Ti2 MoAlVB.该成分的主要特点添加大量的稳定奥氏体化的元素Ni,来获得单相的奥氏体钢,使其具有低的磁导率. 本课题成分设计的目的是降低成本,同时获得要求的性能,如足够低的磁导率、较高的屈服强度和抗拉强度、合适的伸长率.要获得无磁钢,必须获得单相奥氏体.在此基础上,保证强度和合适的伸长率.稳定奥氏体的元素有Ni、Co、Mn、C、N等,不稳定奥氏体的元素有Ti、V、Mo、W、Cr、B、Nb等.非碳化物形成元素:Ni、Co、Al、Cu、Si、P、S等;碳化物形成元素有Ti、V、Cr、Mn、Fe、Nb、Mo、W等.在设计成分时,考虑用较便宜的奥氏体化元素如Mn、N等来降低或者替代Ni.当含Mn元素较高,奥氏体钢易发生形变诱导硬化,使其具有高的强度和韧性.另一方面,降低不稳定奥氏体化的元素,如Cr等.     

基于原位拉伸的ERNiCrFe-13焊丝熔敷金属断裂机制分析

针对ERNiCrFe-13焊丝熔敷金属拉伸过程中的微观组织演变规律和微裂纹的萌生扩展机制，采用SEM原位拉伸结合扫描电子显微镜(scanning electron microscope,SEM)观察和能谱(energy dispersive spectrometer,EDS)分析对熔敷金属组织及断裂行为等进行分析.结果表明，ERNiCrFe-13焊丝熔敷金属组织主要由柱状晶γ相(NiCrFe固溶体)、枝晶间富Nb和Mo元素的Laves相(Cr,Fe,Ni)₂(Nb,Mo)、MC碳化物与共晶组织组成，Laves相的形成主要与凝固过程中Nb和Mo元素的偏析有关，且具有尺寸效应，水平方向Laves相尺寸大于4μm易发生开裂，断裂机制为枝晶间析出相在切应力作用下本体断裂萌生微裂纹，在轴向拉应力的作用下进一步沿晶界扩展连通至断裂失效，断口呈韧性断裂，碳化物偏析(NbC、TiC)和大尺寸Laves相是晶界裂纹产生的主要原因.     

GH742y合金凝固偏析行为

采用组织分析和差热分析相结合的方法系统研究GH742y合金的凝固偏析行为和铸态组织形成规律。GH742y合金枝晶偏析严重,组织析出复杂:Cr、Co、W、V和Al偏析于枝晶干,而Nb、Ti和Mo等元素在枝晶间的富集导致一次和二次γ′相、(γ γ′)共晶、MC碳化物、M6C碳化物、Laves相和δ相的析出;稀土元素La和Ce的偏析导致Ni5Ce相和富氧硫稀土相的枝晶间析出。相分计算表明,严重的元素偏析以及大量富Nb和Ti相的析出是σ相和μ相等有害TCP相析出的主要原因。GH742y合金的凝固顺序为:γ基体、MC碳化物、一次γ′相、(γ γ′)共晶、Laves相、Ni5Ce相和M6C碳化物。     

基于数字图像处理对NbC/Ni_3Si基复合涂层的定量分析

通过对激光熔覆技术在镍基高温合金GH864表面制备NbC增强Ni3Si复合涂层。提出一种对激光熔覆金相组织定量分析的数字图像处理方法,对涂层显微组织进行定向金相研究。以Matlab软件为基础,采用数字图像处理中的灰度处理、平滑滤波、边缘锐化处理、阈值分割、边缘检测等对金相图进行处理,利用ImageJ软件为工具,计算出在添加不同含量的[Nb+C]状态下,NbC/Ni3Si复合涂层中增强相NbC所占比例。结果表明,该数字图像处理方法可实现对激光熔覆显微组织的金相图片的处理和定量分析,在NbC/Ni3Si基复合涂层的显微组织中,添加8%的[Nb+C]时NbC占3.193%,15%的[Nb+C]时NbC占5.350%,20%的[Nb+C]时NbC占5.857%。     

合金钢中合金元素的存在形式

合金钢中可添加的合金元素种类很多,常用的有Si、Mn、Cr、Ni、Al、B、Mo、W、V、Ti、Nb、Cu、Co、等。它们都可以固溶在δ固溶体、奥氏体和铁素体中。Mn、Cr、W、Mo、V、Ti、Nb等还可以固溶在渗碳体中,其分子式用（Fe,M）3C表达。     

激光熔覆(Ni60+NbC)+h-BN@Cu涂层组织与性能研究

目的 通过添加铜包覆六方氮化硼(h-BN@Cu)粉末,改善激光熔覆Ni基NbC涂层的性能。方法 采用激光熔覆技术,使用添加不同质量分数铜包覆六方氮化硼的镍基碳化铌复合粉末,在45钢基体表面沉积镍基复合涂层。利用扫描电子显微镜(SEM)和X射线衍射(XRD)设备,研究h-BN@Cu对Ni60/NbC的激光熔覆镍基复合涂层微观结构的影响,利用显微硬度计和布鲁克UMT-2摩擦磨损试验机及白光干涉模块,测量熔覆层的显微硬度、摩擦磨损系数和磨痕宽度。结果 熔覆层中的主相为Ni-Cr-Fe,除此之外还存在FeNi3、CrB、M7C3、NbC、M23C6、Cr2Nb等多种相。研究发现,添加的润滑相h-BN@Cu与硬质相NbC会发生部分分解,Nb原子和B原子进入熔池,与熔池中的Cr原子反应,生成CrB、Cr2Nb等,这些金属间化合物具有硬度高、耐磨性好等特点。当h-BN@Cu的质量分数为10%时,熔覆层的显微硬度为650HV1.0,摩擦系数为0.4,磨痕宽度为0.406 mm。结论 相比于不添加h-BN@Cu的Ni60/NbC熔覆层,添加h-BN@Cu的Ni60/NbC熔覆层的平均硬度略微下降,但熔覆层硬质相分布更加均匀,此时硬度仍为45钢基体硬度的3.1倍,摩擦系数降低约27%,磨痕宽度减小约21%。     

Grain and phase boundary segregation in WC-Co with TiC, ZrC, NbC or TaC additions

The microstructure of interfaces in WC-Co based cemented carbides with TiC, ZrC, NbC or TaC additions was analysed using energy dispersive X-ray analysis in a transmission electron microscope and using atom probe tomography. Segregation to WC/WC grain boundaries and WC/(M,W)C phase boundaries corresponding to between 0.4 and 1.2 atomic layers of close packed monolayers of Co was observed in all the materials. In addition to Co, Ti, Zr and Nb, but not Ta, segregate to the WC/WC grain boundaries. Segregation was also observed for B, P, Fe and Cr, but not Ni, to the boundaries. These are impurities that originate from the material production. Segregation of Ti, Zr, Nb and Ta to WC/binder phase boundaries was observed. If formation of a MC phase at the interface is assumed, the segregation corresponded to a thickness less than a monolayer.     

Effects of ternary additions on the microstructure and thermal stability of directionally-solidified MoSi2/Mo5Si3 eutectic composites

Effects of ternary additions on the microstructure and thermal stability of directionally-solidified MoSi₂/Mo₅Si₃ eutectic composites have been studied for twelve different elements (Ti, V, Cr, Fe, Co, Ni, Nb, Ta, W, Ir, B and C) paying special attention to the variation of lattice misfits and interface segregation behavior with ternary additions. Among six elements (type-1: Ti, V, Cr, Nb, Ta and W) with a relatively high solubility in MoSi₂ and Mo₅Si₃, Ta and W are found to be beneficial to microstructure refinement. All other six ternary elements (type-2: Fe, Co, Ni, Ir, B and C) with a negligibly low solubility in MoSi₂ and Mo₅Si₃ exhibit a strong tendency to segregate on MoSi₂/Mo₅Si₃ interfaces, resulting in both microstructure refinement and the modification of the interface morphology.     

Effects of alloy elements on microstructure and crack resistance of Fe-C-Cr weld surfacing layer

0　IntroductionFe C Crsurfacingalloysarewidelyusedinindustries ,mainlyduetotheirhighwearresistance .Underconditionsofabrasiveenvironments,theeffectofcompositionandmi crostructureontheabrasionresistancehasbeenextensivelystudied[1～4 ] .TheauthorsalsoevaluatederosionresistanceofFe C Crweldsurfacinglayersbecausealargenumberofma chinecomponentssufferedfromsevereerosion ,suchasper cussiveplate ,rotorbladeandexhaustpipe ,etc .However,thelowcrackresistanceofFe C Crweldsurfacinglayershasbecomethei…     

Cold cracking studies on low alloy steel weldments: effect of filler metal composition

Abstract

The resistance to hydrogen cracking of Cr - Mo, Ni - Cr - Mo and Si - Mn steels which are employed in armoured vehicle construction was evaluated under implant test conditions. Austenitic stainless steel filler (AWS E312), which is reported to be resistant to hydrogen assisted cracking, was used to study the cracking tendency of all the three steels. Four other fillers, namely a nickel based filler (ENiCrFe-3), a low carbon, low alloy steel, a mild steel (AWS E6013) and a matching filler for Cr - Mo, were employed to evaluate their relative cracking tendency. Cr - Mo and Ni - Cr - Mo steels exhibited high cracking tendency while Si - Mn steel was resistant to cracking with the E312 filler. Cr - Mo steel was resistant to cracking with the nickel based filler, the low carbon, low alloy steel and the matching filler. The observed cracking tendency of the steels is linked to a susceptible interface/fusion boundary microstructure.     

17CrNiMo6齿轮钢的组织均匀化

以17CrNiMo6齿轮钢为研究对象,通过对其锻态试样进行不同温度和不同时间的退火处理,采用光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)组织分析手段和Origin数据处理软件,对其带状组织形成原因以及均匀化行为进行了研究与定量分析。结果表明,C、Cr、Ni、Mn和Mo元素在珠光体+贝氏体区域的富集是17CrNiMo6齿轮钢带状组织产生的根本原因,当加热温度为1100 ℃、保温时间为11 h和加热温度为1250 ℃、保温时间为2 h以上时,带状组织已消除,但合金元素不均匀程度仍较高。当加热温度为1250 ℃、保温时间为4 h时,C、Cr、Mn、Ni、P、S、Mo的偏析系数K分别为1.02、0.98、1.02、1.02、1.01、0.98、0.98,元素分布也达到均匀。     

The effect of various ternary additives on the oxidation behavior of TiAl in high-temperature air

Twenty-four ternary element additions were made to a binary TiAl alloy (Ti–34.5 wt.% Al), and the oxidation behavior was studied. As a result of the oxidation tests in air at 1173 K for 360 ks, ternary elements were classified into three groups according to their effects, namely, (a) detrimental; V, Cr, Mn, Pd, Pt, Cu; (b) neutral; Y, Zr, Hf, Ta, Fe, Co, Ni, Ag, Au, Sn, O; (c) beneficial; Nb, Mo, W, Si, Al, C, B. This classification was valid for Cr, Mn, Mo, and W under several other temperature and time conditions. The influence of the additions was very significant, the difference in the weight gain between the best and the worst alloys being approximately two orders of magnitude. As a result of detailed examinations, it was confirmed that Cr and Mn additions caused linear-oxidation behavior from the outset at 1173 K, virtually no Al₂O₃ barrier being formed. This is probably due to the doping of those elements in TiO₂. The beneficial elements, such as Mo, Nb, W, resulted in protectiveoxidation behavior. The characteristic features of the scale on those alloys were the presence of a continuous Al₂O₃ layer as the second layer from the outer surface and the relatively massive precipitation of Al₂O₃ in the vicinity of the scale-metal interface. Also, these alloys did not show any evidence of internal oxidation. The scale types and the proposed mechanism for the innerscale formation are described.     

High Temperature Corrosion of Cast Alloys in Exhaust Environments. II—Cast Stainless Steels

This paper describes in detail the oxidation of two cast stainless steels in synthetic diesel and gasoline exhaust gases. One alloy was ferritic (Fe18Cr1.4Nb2.1Mn0.32C) and one austenitic (Fe20Cr9Ni1.9Nb2.7W0.47C). Polished sections were exposed, mostly for 50 h, at temperatures between 650 and 1,050 °C. The oxidation product was characterized by means of SEM/EDX, AES, and XRD. Inter-dendritic non-Cr carbides initiated thick oxides. The ferritic steel formed a rather thin and adherent oxide scale at all temperatures. It consisted of (Mn, Cr) oxide on top of Cr₂O₃ and, starting at 850 °C, a thin silica film at the metal–oxide interface. Chromium depletion triggered dissolution of carbides providing Cr to the oxide. Water vapor did not accelerate the attack since the outer (Mn, Cr) spinel oxide reduced the Cr evaporation. The austenitic grade was very sensitive to water vapor. Chromium segregation directed pitting to the dendrites up to 950 °C whereas uniform catastrophic oxidation occurred at 1,050 °C.