离子渗氮温度对Fe-C-Cr-Ni-Mn-V沉淀硬化型奥氏体不锈钢渗层组织和性能的影响

采用离子渗氮工艺对一种Fe-C-Cr-Ni-Mn-V沉淀硬化型奥氏体不锈钢进行表面改性处理。利用光学显微镜(OM)、X射线衍射(XRD)、电子探针显微分析仪(EPMA)和维氏硬度计对不同离子渗氮温度下渗层的组织和性能进行了研究。结果表明,Fe-C-Cr-Ni-Mn-V沉淀硬化型奥氏体不锈钢经430~520 ℃离子渗氮处理10 h后,试样表面均形成一层厚度均匀的渗氮层,表面硬度显著增大。随着离子渗氮温度的升高,渗层厚度增大,520 ℃渗氮时渗层厚度达到78 μm。当渗氮温度为430 ℃时,渗层表面主要由γ_N+CrN+γ′-Fe₄N相组成;当渗氮温度升高至520 ℃时,渗层表面主要由γ′-Fe₄N+CrN+ε-Fe_2-3N相组成。在3种渗氮温度下,渗层中均有CrN析出,导致渗层耐蚀性低于基体组织。     

304奥氏体不锈钢低气压离子渗氮组织与性能研究

在400℃、低气压下对304奥氏体不锈钢进行低温低压离子渗氮处理。采用扫描电镜、显微硬度计及万能摩擦试验机对表面改性后的304奥氏体不锈钢渗层组织、硬度及耐磨性进行了测试和分析。结果表明:304奥氏体不锈钢低温低气压渗氮形成了明显的白亮层;低气压对304奥氏体不锈钢离子渗氮具有良好的催渗效果,即渗层厚度随气压的减小而增加,在100 Pa条件下,渗层厚度达到最大值51.7μm;渗氮后试样表面硬度达到最大值1100 HV0.01;低温低气压离子渗氮能够提高304奥氏体不锈钢耐磨性,80 Pa和100 Pa是提高304奥氏体不锈钢耐磨性的最佳气压。     

AISI 300系列奥氏体不锈钢渗氮层组织和性能研究

目的 在AISI 300系列奥氏体不锈钢表面制备单一S相渗氮层,提高该系列不锈钢渗氮层的硬度、抗磨损性能,对比揭示渗氮前后不锈钢的磨损机制。方法 采用低温辉光等离子渗氮技术(LTPNT)在AISI 300系列奥氏体不锈钢表面制备渗氮层。利用光学显微镜(OM)、扫描电子显微镜(SEM)、电子探针(EPMA)、X射线衍射仪(XRD)分析渗氮层的截面形貌、元素分布和物相组成;通过比磨损率和磨痕形貌分析渗氮层的摩擦学性能;利用电化学实验考察渗氮前后3种不锈钢的耐蚀性。结果 AISI 300系列奥氏体不锈钢经380 ℃、12 h处理后,其表面获得了厚度为15 μm左右、与基体致密结合、组织成分均匀的渗氮层;渗氮层的相结构主要为S相,无CrN相析出;经渗氮后,该系列不锈钢表面硬度均为1 100HV左右,较基体硬度提高了5倍左右;不锈钢基体的磨损机理为黏着和磨粒磨损,经渗氮后转变为氧化磨损和微切削;渗氮层的比磨损率约为不锈钢基体的1/20,抗磨损的能力得到显著提升;在25 ℃环境温度下渗氮后,304L、316L和321的自腐蚀电位下降,腐蚀电流密度增加,腐蚀速率加快,耐腐蚀性能稍有降低。通过对比腐蚀形貌发现,渗氮层仍具有一定的耐蚀性能。结论 通过LTPNT可以获得高硬度、组织均匀致密、结合强度高的渗氮层,渗氮层中S相的存在可以显著提高AISI 300系列奥氏体不锈钢的表面硬度、抗磨损能力,降低其摩擦因数和比磨损率,对延长不锈钢的服役寿命有着积极的作用。     

304奥氏体不锈钢低温盐浴渗氮处理

采用430℃低温盐浴对304奥氏体不锈钢进行渗氮处理,研究了渗氮时间对渗氮层组织和性能的影响。利用XRD衍射仪、光学显微镜、表面显微硬度计和带能谱仪(EDS)的扫描电镜(SEM)分别分析渗氮层的相组成、厚度、表面硬度和显微组织。结果表明:304奥氏体不锈钢在430℃渗氮不同时间后,渗氮层厚度和表面硬度都随着时间的延长而增加。渗氮时间为1 h时,渗氮层仅为单一的S相,随着渗氮时间的增加,渗氮8 h时开始有少量CrN生成,渗氮16 h时,渗氮层由大量CrN+S相两相混合。用电化学极化的方法评价耐蚀性能的结果表明:盐浴渗氮处理后耐Cl-点蚀性能得到了一定的改善,在430℃渗氮4 h,其耐蚀性能是最好的,优于没经过渗氮的试样,而在所有的渗氮试样中,渗氮8 h、16 h的试样耐点蚀性能较差。     

AISI 316L奥氏体不锈钢空心阴极放电离子源渗氮技术

采用双层圆筒不锈钢板组成空心阴极电极结构,作为奥氏体不锈钢渗氮的等离子体源。对AISI 316L奥氏体不锈钢分别进行常规直流离子渗氮和空心阴极等离子体源渗氮处理试验。氮化温度均为450℃,氮化时间为4h。采用X射线衍射仪、金相显微镜、粗糙度仪、显微硬度仪、电化学工作站和摩擦磨损试验机等分析表征氮化试样。结果表明:空心阴极等离子体源渗氮能够有效处理AISI 316L奥氏体不锈钢,可在表面制备5μm厚的γN相氮化层。与传统离子渗氮相比,氮化表面硬度均一,粗糙度较低,特别是边缘效应明显降低。γN相氮化层的耐蚀性能优异,且减摩效果较好。     

1Cr18Ni9Ti奥氏体不锈钢的真空固溶渗氮处理

为了提高表面硬度和耐磨性,对1Cr18Ni9Ti不锈钢进行真空固溶渗氮处理。采用金相显微镜,X射线衍射仪、显微硬度计和耐磨试验机分析了渗氮层的组织与性能。结果表明,1Cr18Ni9Ti不锈钢经1 050℃真空固溶渗氮8 h后,获得了由γ′-Fe4N、CrN及含氮奥氏体组成的渗氮层;渗氮层组织致密,表面硬度为900~950 HV,有效渗层深度200μm以上;合金耐磨性得到改善,磨损失重仅为基体合金的1/26。     

气压对304奥氏体不锈钢低温离子渗氮组织与性能影响

在400℃、8 h、不同气压(80~400 Pa)条件下对304奥氏体不锈钢进行离子渗氮处理。采用扫描电镜(SEM)、X射线衍射仪、显微硬度计及万能摩擦试验机对表面改性后的304奥氏体不锈钢渗层组织、相结构、渗层硬度以及耐磨性进行了测试和分析。结果表明,400℃离子渗氮处理后304奥氏体不锈钢形成了明显的白亮层,即单相S相层;低压对304奥氏体不锈钢离子氮化具有良好的催渗效果,即渗层厚度随气压的减小而增加,在100 Pa条件下,渗层厚度达到最大值51.7μm;渗氮后试样表面硬度达到最大值1100 HV0.01;低温低压离子渗氮能够提高304奥氏体不锈钢耐磨性,80 Pa和100 Pa是提高304奥氏体不锈钢耐磨性的最佳气压。     

氢氮比对奥氏体不锈钢低温离子渗氮性能的影响

采用空心阴极离子源辅助,研究了低温(400℃)低压(2 Pa)下工作气体中氢气含量(氮氢比)对316L不锈钢离子渗氮层的组织形貌和性能影响。采用显微硬度计、球-盘滑动摩擦磨损仪、电化学工作站等仪器研究了渗氮处理对奥氏体不锈钢力学性能和电化学腐蚀性能的影响。结果表明:工作气体中随着氢气含量的增加,渗氮层深度、表面硬度等单调地降低;随着工作气体中氮气含量的增加,渗氮层组成相γN的晶格参数单调增加,晶粒膨胀程度增加,表面滑移带密度随之增加。通过离子源辅助,低温低压离子渗氮可有效地使316L不锈钢渗氮层表面硬度超过1100 HV,且在3.5%NaCl溶液中腐蚀电流密度比316L奥氏体不锈钢基体降低1倍。     

304奥氏体不锈钢固溶渗氮的研究

在氮气中对304奥氏体不锈钢进行固溶渗氮，用电子探针测定了渗氮层的氮浓度分布，用扫描电子显微镜观察了渗氮层的金相组织。结果表明，固溶渗氮可以使304奥氏体不锈钢获得高氮奥氏体层；表面氮浓度随渗氮温度的升高和氮气压力的增大而增加，渗氮层深度随渗氮温度的升高和保温时间的延长而增加；渗氮后空冷和水冷时氮为固溶状态，炉冷时会析出氮化物。     

复合表面处理改善304不锈钢的微观结构和耐磨性

目的 提高奥氏体不锈钢的耐磨性.方法 采用电镀法在304奥氏体不锈钢表面进行镍涂层预处理,然后在450℃及以下,于流动的高纯度NH3中进行气体渗氮,获得复合表面处理试样.使用扫描电子显微镜、X射线衍射仪和显微硬度仪,研究了渗氮层的组织、相组成和显微硬度.使用球盘式摩擦磨损试验机,选用硬度相差很大的两种材料GCr15和Si3N4作为摩擦副,对其耐磨性进行了探讨.结果 在400℃时,复合表面处理试样的基底表面生成约6.34μm厚的连续渗氮层,而单一渗氮试样表面没有渗氮层形成,而且450℃复合表面处理试样的渗氮层厚度为24.26μm,约是单一渗氮处理试样的7.85倍.400℃复合表面处理试样的渗氮层主要由γN-Fe组成.450℃复合表面处理试样的渗氮层主要由γN-Fe和少量铬的氮化物组成.400℃和450℃复合表面处理试样的最大硬度分别为780HV0.05和1450HV0.05,分别是原材料的3.3和6.2倍.与原材料相比,以GCr15作摩擦副时,400℃和450℃复合表面处理试样的磨损量分别下降了约75.7％和89.4％;以Si3N4作摩擦副时,400℃和450℃复合表面处理试样的磨损量分别下降了约82.5％和88％.结论 镍涂层预处理有利于提高气体渗氮效率.复合表面处理明显提高了材料的渗氮层厚度、硬度及耐磨性.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。