CO浓度对316L不锈钢准平衡气体渗碳的影响

采用准平衡气体渗碳工艺,在不同CO浓度的CO/H2/N2混合气体条件下制备了表面强化层,研究CO浓度对316L奥氏体不锈钢渗碳层的微观结构、碳浓度分布、表面纳米硬度和残余应力的影响。结果表明,准平衡气体渗碳层为单一的扩张奥氏体相;当CO浓度小于30%时,渗碳层厚度、表面纳米硬度和压缩残余应力均随CO浓度的提高而提高,当CO浓度高于35%时,渗碳气体碳活度降低,渗碳表面强化效果降低;经470℃条件下准平衡渗碳20 h后,316L不锈钢渗碳层厚度最高可达30μm,表面碳浓度增加至2.6 mass%,导致表面纳米硬度从3 GPa增加至9 GPa,并产生1300 MPa以上的压缩残余应力。     

低温气体渗碳对304L奥氏体不锈钢抗氢性能的影响

对304L奥氏体不锈钢进行低温(470℃)气体渗碳,采用光学显微镜(OM),电子探针显微分析仪(EPMA)以及X射线应力分析仪(IXRD)研究了304L奥氏体不锈钢低温气体渗碳强化层的厚度、碳含量及残余应力分布。通过电化学充氢实验,结合X射线相结构分析(XRD),慢应变单轴拉伸试验,扫描电镜(SEM)观察以及氢含量检测等方法分析低温气体表面渗碳对304L不锈钢抗氢脆性能的影响。研究表明:304L不锈钢经30 h低温气体表面渗碳处理后,形成了约22μm的渗碳层,渗碳层中碳含量和残余应力在表面最高,分别为2%(质量分数)及-1.47 GPa,并沿深度方向梯度减小;低温气体表面渗碳大幅度提高304L不锈钢表面的稳定性,在充氢过程中不产生马氏体相变,从而提高其抗氢性能。此外,渗碳层中的压缩残余应力对抑制H扩散,也起到了积极的作用。     

表面形貌对316L奥氏体不锈钢低温气体渗碳的影响

利用金相显微镜、显微硬度计和残余应力分析仪研究了4个具有不同表面形貌的316L奥氏体不锈钢经低温气体渗碳处理后的渗碳层微观形貌、硬度和残余应力。结果表明:渗碳后各试样表面均形成一层高硬度、高残余压应力的渗碳层,表面强化效果显著。表面形貌对316L奥氏体不锈钢低温气体渗碳有一定影响。随着试样表面粗糙度的下降,渗碳处理后的硬度、残余应力和渗碳层厚度均降低,表面强化效果下降,并最终趋于稳定。     

快速冷却对304奥氏体不锈钢低温气体渗碳强化的影响

利用光学显微镜、X射线衍射仪、电子探针X射线微区分析仪、显微硬度计和残余应力分析仪研究了不同冷却速度下304奥氏体不锈钢低温气体渗碳后的性能。结果表明:渗碳后各试样表面均形成一层高硬度、高残余压应力的扩张奥氏体层,表面强化效果显著。经不同冷却速度处理后,试样表面的显微形貌、物相组成、碳浓度分布、硬度和残余应力均无明显差异,说明快速冷却对304奥氏体不锈钢低温气体渗碳强化并无影响。     

316L奥氏体不锈钢低温气体渗碳后的表面特性

提出了一种新型的奥氏体不锈钢低温气体渗碳工艺,采用该工艺对316L奥氏体不锈钢进行不同时间的渗碳处理,并对渗碳后不锈钢的表面特性进行了分析和探讨。结果表明,渗碳后试样表面晶格发生膨胀,形成了15~35 μm的扩张奥氏体层,该层具有高残余压应力、高硬度、高含碳量及良好的韧性,且层中无碳化铬析出,说明该工艺兼顾了奥氏体不锈钢的表面强化与抗腐蚀性能;同时,渗碳时间对表面的强化效果影响显著,表面残余应力、硬度及碳含量等随渗碳时间延长均增加。     

渗碳气氛对奥氏体不锈钢低温离子渗碳的影响

奥氏体不锈钢低温离子渗碳处理是一种能在不降低耐蚀性能的前提下显著提高其表面硬度的有效方法。本文研究了奥氏体不锈钢低温离子渗碳气体比例及炉内压强对渗碳层硬度及厚度的影响。试验结果表明,炉内气体比例及压强对渗碳层硬度及厚度都有较大的影响。当氢气与甲烷比例为(20~30):1、气体压强为400 Pa时,渗碳层的硬度最高,硬化层最厚。     

奥氏体不锈钢低温超饱和渗碳实验及热动力学模拟研究

采用OM,EPMA,XRD和IXRD等手段,研究了低温超饱和渗碳(low temperature colossal carburization,LTCC)工艺中CO气体浓度对316L不锈钢表面渗碳层的微观组织、C浓度分布、表面相结构以及残余应力的影响.基于热动力学理论建立了LTCC传质和扩散模型,利用DICTRA软件计算了渗碳层的C浓度和活度分布,并与实验结果进行比较.结果表明,经LTCC工艺处理后的316L不锈钢表面会形成高硬度的S相,并产生压缩残余应力.另外,增加渗碳工艺中CO浓度可以显著提高不锈钢表面渗碳层中的C浓度,进而提高其硬度和压缩残余应力.在C浓度较低时,计算的C浓度和活度分布与实验结果吻合很好,当C浓度较高时,由于陷阱阵点的减少以及较大压缩残余应力的作用导致计算结果偏低.     

不锈钢低温渗氮/渗碳S相渗层技术的研究进展

奥氏体不锈钢通过低温渗氮/渗碳,获得含氮/碳固溶饱和的扩散层,即S相渗层,不仅提高了不锈钢表面硬度,而且还提高了不锈钢的耐蚀性。本文综述了不锈钢S相渗层研究与应用技术的最新研究进展,分析了低温离子渗氮/渗碳、气体低温渗氮/渗碳、高温渗氮固溶淬火及离子注入渗氮技术的工艺特点。讨论了S相渗层的力学性能和耐蚀性能,分析了国内S相低温渗层技术工业应用存在的问题,展望了S相技术的发展前景。     

AISI 316L奥氏体不锈钢低温离子-气体渗碳工艺优化

目的将低温离子-气体乙炔渗碳应用于AISI 316L奥氏体不锈钢表面硬化处理,同时探讨其硬化处理的最优工艺参数及优化效果。方法采用离子轰击去除不锈钢表面钝化膜并活化其表面,再进行低温气体乙炔渗碳,实验过程使用脉冲式供气循环处理方式。进行温度梯度实验,寻找渗碳处理的临界温度。并采用正交试验法设计3因素3水平共9组实验,分析气体比例、离子轰击时间、保温压强3个因素对渗碳层硬度和厚度产生的影响,以期得到不锈钢低温离子-气体乙炔渗碳优化工艺。通过对经过最优化工艺处理过后的不锈钢硬化层组织、成分、厚度、硬度、耐磨性、耐蚀性能的研究分析,验证此工艺对AISI 316L奥氏体不锈钢硬化处理的适用性。结果处理温度为540℃时渗碳层有碳的铬化物析出;离子轰击时间对渗碳层硬度影响最大,保温压强对硬化层厚度影响最明显。在硬化处理温度为520℃,V(H2)∶V(C2H2)=1∶1,渗碳压强为-0.02 MPa,离子轰击时间为20 min时,316L奥氏体不锈钢离子-气体乙炔渗碳效果最优。经优化工艺处理后不锈钢硬化层厚度达到30μm左右,表面硬度达到838HV0.05,耐蚀性和耐磨性能等都显著提高。结论低温离子-气体乙炔渗碳硬化处理适用于AISI 316L奥氏体不锈钢,其处理最合适温度为520℃。经优化工艺处理后的不锈钢具有较高的硬度、厚度,良好的硬度梯度,高耐蚀性能及高耐磨性能。     

316奥氏体不锈钢低温气体渗碳层组织与强化性能

采用自主研发的低温气体渗碳技术对AISI316奥氏体不锈钢进行处理,目的是增强耐磨性且不损害其耐蚀性。对低温气体渗碳层显微组织、硬度梯度、耐蚀性和耐磨性进行分析。结果表明:低温气体渗碳层硬度梯度变化与其组织和碳浓度有一定关系,随渗碳层深度的不同表现出不同的组织和性能。低温气体渗碳处理前后AISI316奥氏体不锈钢的磨损机制由粘着磨损转变成磨粒磨损,S相是提高耐磨性的主要因素,470℃时表现出较好的耐磨性,其耐蚀性基本保持不变。     

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.     

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 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.     

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.     

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.     

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.     

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.     

白藜芦醇对急性脊髓损伤早期脂质过氧化反应和活性氧水平的抑制作用

目的: 探讨脊髓损伤后使用白藜芦醇(resveratrol,Res) 对脊髓损伤(SCI) 早期脂质过氧化反应和活性氧水平的抑制作用。方法: 采用重物下落撞击法制备成年大鼠的SCI 模型, 于损伤后即刻腹腔注射给予Res 50, 100 mg·kg^-1 和甲基强的松龙(MPSS)100mg·kg^-1, 测定SCI 后1, 24, 48 h 时Res 组受损脊髓组织超氧化物歧化酶(SOD) 和脂质过氧化反应产物丙二醛(MDA) 及活性氧(ROS) 水平, 并与MPSS 组进行疗效对比。结果: Res 50mg·kg^-1与100 mg·kg^-1均能够显著提高SCI 后损伤部位SOD 水平和抑制MDA 产生(P<0.01), 以48 h 为最明显;显著降低ROS 水平(P<0.01), 也以48 h 最大, 抑制率大于40 %;且有明显剂量依赖性, 作用与MPSS 相当或更优。结论: Res 可以有效抑制脊髓损伤后早期受损局部脂质过氧化反应和活性氧水平, 对脊髓损伤有潜在的保护与治疗作用。     

抗中性粒细胞胞质抗体相关性小血管炎的机制与治疗进展

血管炎是一类可引起血管非特异性炎症和坏死的自身免疫性疾病。按血管受累的大小分类,包括了小血管炎、中等血管炎及大血管炎。抗中性粒细胞胞质抗体（ANCA）相关性小血管炎（AAV）属于小血管炎的范畴,主要包含了肉芽肿性多血管炎（GPA）,显微镜下多血管炎（MPA）和嗜酸肉芽肿性多血管炎（EGPA）。它们可累及全身不同脏器,活动期异常凶险,治疗不及时可致高死亡率。本文简要综述AAV的发病机制及治疗进展。