3D ATOM PROBE CHARACTERIZATION OF ALLOYING ELEMENTS PARTITIONING IN CEMENTITE OF A Nb-V MICROALLOYED STEEL

将Nb-V微合金钢在1200 ℃固溶0.5 h后淬火, 然后在450 ℃回火4 h, 结合扫描电子显微镜(SEM)和透射电子显微镜(TEM), 用三维原子探针(3DAP)研究渗碳体内部和渗碳体/基体界面处的元素分布和成分变化. 结果显示, 淬火样品中C原子由于自回火而出现轻微偏聚, 其它合金原子V,Nb, Si, Mn, Mo和Al等分布均匀. 450 ℃回火4 h样品中出现C原子偏聚区, 在该区域内, Mn含量较高, Mo和V轻微偏聚, Si和Al很少, 对应渗碳体析出, Si富集在渗碳体/基体界面处; 另外, 观察到C和V明显偏聚的单原子面, 周围富集Si和Mn, 对应合金碳化物析出初期形成的G.P.区, 成分主要为V4C3.     

Nb-V微合金钢中渗碳体周围元素分布的三维原子探针表征

将Nb-V微合金钢在1200℃同溶0.5 h后淬火,然后在450℃回火4 h,结合扫描电子显微镜(SEM)和透射电子显微镜(TEM),用三维原子探针(3DAP)研究渗碳体内部和渗碳体/基体界面处的元素分布和成分变化.结果显示,淬火样品中C原子由于自回火而出现轻微偏聚,其它合金原子V,Nb,Si,Mn,Mo和Al等分布均匀.450℃回火4 h样品中出现C原子偏聚区,在该区域内,Mn含量较高,Mo和V轻微偏聚,Si和Al很少,对应渗碳体析出,Si富集在渗碳体/基体界面处;另外,观察到C和V明显偏聚的单原子面,周围富集Si和Mn,对应合金碳化物析出初期形成的G.P.区,成分主要为V4C3.     

回火马氏体中合金碳化物的3D原子探针表征Ⅲ.粗化

Nb-V微合金钢在1200℃固溶0.5 h后淬火,在650℃回火4 h,利用SEM和HRTEM观察显微组织,合金碳化物的形貌特征和精细结构,用三维原子探针(3DAP)研究合金碳化物中元素分布规律.结果表明,淬火微合金钢在650℃回火4 h后,马氏体板条内位错和板条界面因回复而消失,粗化的合金碳化物分布在原马氏体板条界面和板条内部.同时,伴随着合金元素的再分配,早期析出的圆盘状碳化物沿厚度方向生长,出现一个与基体(M_(bcc))和原碳化物(P_(inner))成半共格关系的新生过渡相(P_(outer)).非碳化物形成元素Si和Al主要分布在碳化物/基体界面处;V和Mn主要分布在碳化物内层,而Mo和Nb分布在整个碳化物区域.粗化的碳化物是一种具有核心和外壳结构的合金碳化物,内层主要是V-Mn-Mo-Nb的碳化物,而外层主要是Mo-Nb的碳化物.     

铁素体耐热不锈钢0.1C-18Cr-1Al-1Si铸造合金析出相研究

采用相图计算、透射电子显微镜分析等手段,研究了铁素体耐热不锈钢0.1C-18Cr-1Al-1Si铸造合金析出相种类、析出规律和形貌。结果表明:0.1C-18Cr-1Al-1Si在平衡状态下平衡相由铁素体相、α-Cr相、AlN相、M_7C_3相、M_(23)C_6相等组成;随着温度降低,M_(23)C_6相中C含量先升高后降低,Fe含量逐渐降低,Cr含量逐渐升高;M_(23)C_6相具有复杂面心结构,M_7C_3晶体结构为正交结构;AlN为密排六方结构,密排面为(0001),密排面的面间距d=0.476 nm。     

高钨K416B镍基合金蠕变期间细小碳化物析出行为及热力学分析（英文）

通过蠕变测试和组织形貌观察,研究K416B合金中细小碳化物的析出行为。结果表明:在高温蠕变期间,纳米级M6C碳化物沿基体内和γ/γ′界面不连续析出,其中,随着蠕变进行,细小M6C碳化物析出数量逐渐增多,且粒状M6C相自γ基体析出的共格界面为{100}和{111}晶面。热力学分析表明:在蠕变过程中,合金在轴向拉伸应力下变形时,元素C在基体中的溶解度减小,并在应力集中处偏聚,与W、Co等碳化物形成元素结合,促使细小M6C碳化物从γ基体中析出。     

升温过程中Nb和Nb-Mo微合金化钢中碳化物的析出行为研究

利用Gleeble热模拟实验机、Vickers硬度计、SEM,HRTEM及DSC研究了淬火态含Nb和Nb-Mo微合金钢在升温过程中碳化物的析出行为.利用经典形核长大理论及Avrami方程对淬火态钢中MC型碳化物的析出动力学进行了计算.结果表明,含Nb和Nb-Mo微合金钢淬火后以20℃/min的速率加热至不同温度水冷,在300和700℃,由于e-碳化物和MC型碳化物析出而出现了硬度峰值.MC型碳化物在650℃左右析出,由于析出强化而硬度上升,与理论计算得到的MC型碳化物的析出鼻子点温度约650℃的结果相一致.Mo进入Nb C中降低了Nb C与铁素体基体的错配度,从而减小了析出相与铁素体基体间的界面能,使得(Nb,Mo)C析出动力学加快,所以Nb-Mo钢中析出相粒子分布更为密集,尺寸更为细小,具有较高的析出强化作用.     

高钨高速钢中碳化物结构及界面特征

采用铸造法制备了含钨10%的高钨高速钢,利用XRD、SEM、HRTEM、EDAX研究了高钨高速钢中碳化物的类型、成分、结构及其界面晶体学特征。结果表明:高钨高速钢中的碳化物有两种,一种是凝固过程中析出的鱼骨状共晶碳化物,别一种为回火过程中析出的颗粒状二次碳化物,二者均为面立方晶体结构的M_6C。共晶M_6C的分子式可表达为(Fe_(0.55)W_(0.30)Cr_(0.08)Mo_(0.07))_6C,二次M_6C中的合金元素含量与之基本相同。共晶M_6C型碳化物与基体间存在晶体学关系,在铸态组织中,M_6C的(111)晶面平行于铁素体(110)晶面,即M_6C(111)//α-Fe(110),而高速钢回火后,基体组织转变成马氏体(M)与残留奥氏体,界面的晶体学位向关系变为:M_6C(111)//M(020)。二次M_6C型碳化物与马氏体界面为良好的冶金结合,M_6C的(133)晶面与马氏体的(101)晶面夹角约为140°。部分二次M_6C可以依附于共晶M_6C析出,二者的(202)晶面共格。     

5Cr8Mo2SiV钢淬火和回火过程中碳化物的析出

对球化退火后的5Cr8Mo2Si V刃具钢进行淬火和回火工艺的探究,用SEM和EDS对淬、回火后的显微形貌进行分析,用碳化物电解萃取和XRD分析等研究了5Cr8Mo2Si V刃具钢淬、回火过程中碳化物的析出行为,并用Jmat-Pro模拟回火过程中碳化物析出相的变化。结果表明:5Cr8Mo2Si V钢退火试样在1100℃淬火+520℃回火时有明显的二次硬化现象,球化退火组织中存在VC、Cr_(23)C_6、Cr_7C_3、Fe_3C、Si C和Mo_6C类碳化物。Mo_6C、Si C、Fe_3C、Cr_7C_3和Cr_(23)C_6型碳化物随着淬火温度升高依次溶入马氏体基体,最终只有VC分布在基体上。Mo_2C、VC、Cr_7C_3和Cr_(23)C_6型碳化物在回火过程中从马氏体中析出,且Mo_2C和VC型碳化物在520℃回火析出量出现峰值。结合Jmat-Pro模拟结果发现,5Cr Mo2Si V钢的二次硬化现象是残留奥氏体二次淬火和Mo_2C粒子的第二相强化共同导致,且Mo_2C粒子第二相强化效应符合位错切过机制。     

三维原子探针对回火铌钒微合金钢中析出物的研究

将Nb-V微合金钢在1200℃固溶0.5h后淬火,分别在500℃和600℃回火4h,用三维原子探针(3DAP)研究析出物的特征.结果显示,固溶后Ⅴ、Nb完全溶入基体;500℃回火后,基体中析出大量的C-Ⅴ-Nb细小粒子,Mo出现偏聚;600℃回火后,析出粒子数量减少,尺寸增大,C、Ⅴ、Nb和Mo的含量均增加,形成具有一定化学比的复合碳化物(Mo,Ⅴ,Nb)C.     

回火马氏体中合金碳化物的3D原子探针表征Ⅰ.形核

Nb-V微合金钢在1200℃固溶0.5 h后淬火,在450℃回火不同时间,用三维原子探针(3DAP)研究了回火过程中合金碳化物的形核规律.结果显示,淬火态Nb-V微合金钢在450℃回火时合金碳化物处于形核阶段,合金元素可通过动态再分配,实现渗碳体到合金碳化物的原位转变,或者在位错等缺陷处直接与C结合,完成合金碳化物的单独成核长大,或者偏聚在残余奥氏体/基体和未溶的AlN粒子/基体界面处,实现合金碳化物的异质形核长大.     

Influence of metal ions on the formation of artificial zinc rusts

The artificial rust particles were prepared from ZnCl₂ solutions dissolving Al(III), Fe(III), Fe(II), Ni(II), Co(II) and Mg(II) at different atomic ratios from 0 to 0.3 in metal/Zn. With increasing metal/Zn the crystal phases of the products turned following as ZnO → a mixture of ZnO and Zn₅(OH)₈Cl₂ · H₂O (ZHC) → ZHC. Al(III) most facilitated the formation of ZHC but Mg(II) and Fe(III) produced no ZHC. The morphology of the formed particles varied following as agglomerate → fine → rod → sheet → irregular with the increase of metal/Zn. The sheet and irregularly shaped particles were identified as ZHC and the other particles as ZnO.     

Effect of dislocation density on the low temperature aging behavior of an ultra low carbon bake hardening steel

Strain aging was studied in an ultra low carbon (ULC) steel with a total carbon content of 20 ppm (wt.%) in order to identify the process stages and mechanism of bake hardening in this type of steel. The effects of dislocation density, varied by means of uniaxial tensile prestraining (1–10%) on the aging kinetics were investigated within an aging temperature range of 50–170°C. The aging was evaluated by means of strength measurements and the determination of interstitial carbon content after aging using a piezoelectric composite oscillator operating at 40 kHz. The interaction between interstitial carbon and dislocations was examined through amplitude dependent internal friction measurements. The influence of dislocation density on the aging behavior have been discussed with reference to the kinetics and mechanism of the aging process.     

A corrosion study of the main constituent phases of AZ91 magnesium alloys

The different constituents of an AZ91 alloy (α,β, and MnAl phases) were synthesized and their corrosion resistance was studied by electrochemistry in ASTM D1384 water, pH 8.3. The pure phases were characterised through the corrosion potential, the polarisation resistance, and polarisation curves, then systematically coupled to assess the galvanic corrosion occurring in the AZ91 alloy. The aluminium content of the oxide film was obtained by X-ray photoelectron spectroscopy measurements. The corrosion rate of the α solid solution alloys depends closely on their Al content. Aluminium enhances the corrosion resistance of the α-phase through the formation of an Al enriched superficial layer. The β-phase is 150 mV nobler than the α-phase, but their corrosion rates are similar. The galvanic currents are low (below 20 μA cm⁻²) whatever the implemented couples and close to the corrosion current previously measured for the AZ91 alloys.     

Effect of solution heat treatment on galvanic coupling between intermetallics and matrix in AA7075-T6

Susceptibility to localised corrosion is strongly affected by heat treatments performed on Al-Zn-Cu-Mg alloys. In order to study how galvanic coupling between intermetallics and matrix is affected by solution heat treatment, AA7075-T6 and solution heat treated AA7075 have been characterised by means of scanning electron microscopy and scanning Kelvin probe force microscopy. Solution heat treatment strongly increased the Volta potential difference between the intermetallics and the surrounding matrix showing a strong increase in galvanic coupling. This is explained by Zn and Mg enrichment of the matrix caused by dissolution of strengthening particles during solution heat treatment.     

硬质合金Hc、Com、D、HV_3的初步探讨

通过研究硬质合金的矫顽磁力、钴磁、密度和硬度,阐述了这些性能之间的相互关系,以及影响这些性能的主要原因,说明了其对生产实践中质量控制的重要意义。     

Characterizing corrosion behavior under atmospheric conditions using electrochemical techniques

AC and DC electrochemical experiments were performed as a function of humidity and contaminant concentration in an effort to identify the range of atmospheric environments where corrosion processes could be detected and possibly quantified. AC measurements exhibited two time constants at 25% relative humidity (RH), possibly indicating the ability to resolve both electrolyte resistance and interfacial impedance. Galvanic current measurements were sensitive to the presence of Cl_2(g) at 30% RH and electrochemical transients were detected at both 30% and 50% RH levels, also indicating sensitivity to interfacial processes. Higher humidity levels allowed better quantification due to decreasing electrolyte and interfacial impedances.     

Electrochemical behaviour of amorphous and nanoquasicrystalline Zr-Pd and Zr-Pt alloys in different environments

The corrosion behaviour of melt spun amorphous and nanoquasicrystalline Zr₇₀Pd₃₀ and Zr₈₀Pt₂₀ alloy ribbons has been investigated using potentiodynamic polarization study in NaCl, H₂SO₄ and NaOH solutions at different concentrations. The amorphous and nanoquasicrystalline alloys show better corrosion resistance than Zr in all the solutions studied. Both the alloys are susceptible to chloride attack and pitting has been observed. Complete passivation has been observed in H₂SO₄, while gradual break down of passivating layer occurs in NaOH. In general, nanoquasicrystalline state in both the alloys shows better corrosion resistance than amorphous state in all the solutions studied.     

A study on the deactivation of an IrO2–Ta2O5 coated titanium anode

The deactivation of an IrO₂–Ta₂O₅ coated titanium anode was studied during an accelerated life test at 2 A cm⁻² in 1 mol dm⁻³ H₂SO₄ solution using CV, EIS, SEM and EDX. The changes of voltammetric charge, double layer capacitance, oxide film resistance and charge transfer resistance of oxygen evolution with time during the electrolysis were monitored. The morphology and surface composition of the oxide anode before and after electrolysis test were analysed. A comprehensive process of deactivation of the oxide anode was proposed based on the test results and analysis.     

加速发展我国的快速成形技术

介绍了第二届北京国际快速成形及制造会议概况，分析了快速成形（RP）技术的发展趋势，指出RP技术研究领域的重大进展及学科发展的主攻方向是：由RP向快速制造（RM）发展，由RP向快速模具（RT）发展，RP技术在生物医学领域的应用。     

Corrosion behaviour of powder metallurgical and cast Al-Zn-Mg base alloys

The behaviour of Al-Zn-Mg base alloys produced by powder metallurgy and casting has been studied using potentiodynamic polarisation in 0.3% and 3% NaCl solutions. The influence of alloy production route on microstructure has been examined by scanning electron microscopy, Auger electron spectroscopy and secondary ion mass spectrometry. An improvement in performance of powder metallurgy (PM) materials, compared with the cast alloy, was evident in solutions of low chloride concentration; less striking differences were revealed in high chloride concentration. Both powder metallurgy and cast alloys show two main types of precipitates, which were identified as Zn-Mg and Zr-Sc base intermetallic phases. The microstructure of the PM alloys is refined compared with the cast material, which assists understanding of the corrosion performance. The corrosion process commences with dissolution of the Zn-Mg base phases, with the relatively coarse phases present in the cast alloy showing ready development of corrosion.