TiAl基合金的辉光离子渗氮试验

研究了TiAl基合金的辉光离子渗氮。渗氮气氛为NH3,渗氮温度分别为850℃、900℃、950℃,渗氮时间分别采用2h到12h不等。结果表明:TiAl基合金经辉光离子渗氮后,在表面形成由氮化物层和过渡层组成的氮化层,氮化层形成速度明显快于高温气体渗氮。采用NH3气氛、900℃×9h工艺参数时,渗层厚度可达12μm,渗层的显微硬度值可达1097HV0.1。     

在密封箱式炉中的短时气体渗氮

用密封箱式炉进行短时渗氮 ,只通入氨气和氮气 ,炉气中无任何含碳气体 ,可以彻底消除HCN对环境的污染。经 560℃× 3h短时渗氮后 ,在钢的表面形成大约 ( 1 2～ 2 5) μm的化合物层。 2 0Cr钢、2 0CrMnTi、45钢和SCM 41 5钢短时渗氮后的表面硬度及渗层硬度分布都和同一设备中气体氮碳共渗的结果相同 ,除了低碳钢之外 ,用短时渗氮替代氮碳共渗是值得推广的。     

微量钛对离子渗氮渗层特性及性能的影响

为调控离子渗氮渗层特性,获得少脆性化合物层、厚韧性扩散层的渗氮层,提高离子渗氮渗层抗冲击性和重载下的耐磨性,对 42CrMo 钢进行了添加微量钛的创新离子渗氮处理。 利用光学显微镜、SEM、XRD 和显微硬度计对渗层的截面显微组织、表面形貌和成分、物相和截面硬度进行了测试和分析。 结果表明:添加微量钛离子渗氮可显著改善渗层特性,获得少化合物层的高硬高韧渗氮层,同时显著提高离子渗氮效率。 在 540 ℃ ×4 h 工艺条件下,添加微量钛可使离子渗氮有效硬化层厚度显著增加,由常规离子渗氮的 225 μm 增加到 380 μm,即渗氮效率提高近 70%;有效硬化层厚度提高的情况下,化合物层厚度反而减薄,由常规离子渗氮的 19 μm 降低到 10 μm,即化合物层厚度降低了约 50%;渗层中化合物层与有效硬化层之比值由常规离子渗氮的 8. 5%降低到 2. 6%。 同时添加微量钛离子渗氮渗层中形成了高硬度强化相 TiN,使渗层表面硬度由 703 HV0. 05 提高至 895 HV0. 05 。 添加微量钛离子渗氮获得了薄化合物层、高硬高韧、厚有效硬化层的优良渗氮层特性,该渗层特性对改善离子渗氮零部件抗冲击性和重载下的耐磨性具有重要研究和应用价值。     

超声波冷锻对Cr12MoV钢渗氮组织与性能的影响

为优化渗氮工艺,提高渗氮层的厚度与硬度,提出用超声波冷锻技术(Ultrasonic cold forging technology,UCFT)对Cr12MoV模具钢进行表面纳米化预处理,并在450℃和520℃两个温度条件下离子渗氮.采用扫描电镜、金相显微镜、白光形貌仪、X射线衍射仪和维氏显微硬度计对样品的微观组织结构和性能进行表征.结果表明:UCFT是一种能与离子渗氮有效复合的预处理工艺,经UCFT表面纳米化预处理后,Cr12MoV模具钢表面形成表面硬度约520 HV,厚度为350 μm的塑性变形影响层;经UCFT表面纳米化预处理后和离子渗氮复合处理后,渗氮层厚度与硬度与原始样品直接渗氮相比有显著提高;UCFT预处理后在520℃离子渗氮4h,材料表面硬度可高达1350 HV,复合改性层厚度也可增至约400 μm.     

退氮处理对SDHS2模具钢渗氮层组织与性能的影响

采用光学显微镜和显微硬度仪对比研究了离子渗氮的SDHS2模具钢退氮处理前后渗氮层的组织和性能。结果表明:通过离子渗氮处理得到的渗层深度约230μm,渗层表面硬度达1 000 HV0. 3以上,渗层组织致密,与基体结合良好;分别经530和550℃退氮处理8、12、16 h后,渗氮层的硬度均大幅度降低。但随着渗氮时间的延长,渗层硬度随之提高;退氮温度的升高也会导致基体硬度的大幅度下降。综合比较得出,SDHS2模具钢退氮处理的最佳工艺为:退氮温度530℃、退氮时间8 h。在保证基体硬度满足要求的条件下,退氮处理可使表面硬度由处理前的1 000 HV0. 3以上降低至780 HV0. 3左右。     

离子渗氮工艺参数对4Cr5MoSiV钢表层组织与性能的影响

目的 研究离子渗氮的温度及时间对4Cr5MoSiV钢渗氮层组织、表面硬度及耐磨性的影响,获得提高硬度、耐磨性的最优工艺参数。方法 对4Cr5MoSiV钢表面进行离子渗氮处理,渗氮温度分别为450、480、510、540 ℃,保温时间分别为5、10、15、20 h。利用维氏显微硬度仪测量渗层深度及表面硬度;利用X射线衍射仪分析渗层物相组成;利用摩擦磨损试验机评价试样耐磨性;通过扫描电镜观察表面磨痕区域。结果 离子渗氮渗层表面的物相主要为γ''-Fe4N相和ε-Fe2~3N相。在实验范围内,随着温度的升高或时间的增加,材料渗层深度、表面硬度增加,磨损率减少,但当温度过高或时间过长时,表面硬度下降,磨损率增加。在480 ℃的条件下进行20 h离子渗氮的材料,表面具有最好的摩擦学性能,表面硬度为1147 HV0.2,磨损率为2.13×10-5 mm3/(N?m),渗氮层深0.24 mm,化合物层深14.05 μm,摩擦系数为0.45,磨损状态为磨粒磨损。结论 离子渗氮是适合于变截面弹簧的表面强化方式,可以在材料表面形成具有一定厚度、均匀分布的渗氮层组织,显著提升表面硬度和耐磨性,降低摩擦系数。     

离子氮铝共渗方法及对42CrMo钢组织性能的影响

目的 研发离子氮铝共渗试验方法,达到不影响42CrMo钢基体组织性能前提下,显著提高试样表面硬度和耐磨性效果。方法 采用电解法在42CrMo钢表面沉积氢氧化铝膜,再在520 ℃/4 h工艺下进行离子氮铝共渗处理,并在相同工艺参数条件与传统离子渗氮进行对比。用光学显微镜、维氏显微硬度计、摩擦磨损测试机、X射线衍射仪及SEM对截面显微组织、截面硬度、耐磨性及物相等进行了测试和分析。结果 获得了离子氮铝共渗试验方法,在520 ℃/4 h相同工艺参数下,离子氮铝共渗形成的化合物层和有效硬化层厚度比常规离子渗氮显著增加,其中,化合物层厚度由17.24 μm增加到52.13 μm,有效扩散层从175 μm增加到1 050 μm,相当于等离子处理效率提升6倍;同时,渗层形成了AlN及FexAl强化相,大幅度提高了渗层的硬度及耐磨性能。表面硬度由750HV0.025提高到1 250HV0.025,摩擦因数由常规离子渗氮0.52下降到0.29,磨损率由常规离子渗氮3.22×10^?5 g/(m.N)下降到1.21×10^?5 g/(m.N),磨痕明显减轻。结论 采用电解硝酸铝生成氢氧化铝沉淀附着在工件表面作为预处理,获得了离子氮铝共渗试验方法,与常规离子渗氮相比,离子氮铝共渗形成了多层次渗层结构,大幅度提高常规离子处理效率、表面硬度及耐磨性。     

钛合金真空离子渗氮组织及耐磨性能

采用真空离子渗氮设备开展了TC4及TA7钛合金真空离子渗氮工艺试验,采用SEM、XRD等分析了渗层组织,测量了渗氮层显微硬度及渗氮深度,测试了渗氮层的耐磨性能。结果表明,钛合金离子渗氮可形成化合物层+扩散层的典型渗氮层,总渗氮深度可达100 μm以上,渗氮层表面硬度达1200 HV0.1以上。TC4钛合金850 ℃渗氮16 h后,耐磨性能与基体相比显著提高。     

304不锈钢喷砂助低温渗铝工艺

采用喷砂技术对304不锈钢板表面进行处理,并对喷砂处理后的试样进行热处理和低温固体粉末包埋渗铝处理,分析讨论了喷砂助低温渗铝的最佳工艺参数。结果表明：表面经喷砂处理后,试样表层形成厚约250 μm的变形区,同时表面发生了马氏体相变,硬度明显提高。喷砂试样经400～600 ℃热处理后,变形层组织仍为马氏体相,硬度有所下降,变形层具有热稳定性。表面喷砂处理可以降低渗铝温度,提高渗铝速度。最佳渗铝工艺为经过优化喷砂工艺处理后在530 ℃渗铝3 h随炉冷却,试样表面可形成约50 μm的渗层,渗层主要由金属间化合物FeAl2构成,表面硬度可达640 HV0.2。     

钛催渗低温离子渗氮对304不锈钢组织性能的影响

目的 在保障304奥氏体不锈钢良好耐蚀性前提下,研发显著改善表层硬度及耐磨性的低温高效离子渗氮技术。方法 低温离子渗氮时,在试样周围均匀放置微量海绵钛,研发304奥氏体不锈钢创新钛催渗低温离子渗氮技术。采用光学显微镜、扫描电子显微镜、能谱分析仪、X射线粉末衍射仪、显微维氏硬度计、摩擦磨损测试仪,以及电化学工作站等设备分别对试样截面显微组织、物相及成分、截面显微硬度、渗层耐磨性能、耐蚀性能等渗层组织性能进行测试与分析。结果 304奥氏体不锈钢在420 ℃/4 h钛催渗离子渗氮处理后,不仅保持了良好耐蚀性,且渗层耐蚀性比常规低温离子渗氮略有提升,同时,表面硬度与耐磨性大幅提高,表面硬度由常规离子渗氮的978HV0.025提升至1350HV0.025。磨损率由20.9 μg/(N.m)降低至7.4 μg/(N.m),下降了约2/3。特别有价值的是,钛催渗低温离子渗氮效率比传统离子渗氮显著提升,渗氮层厚度由常规离子渗氮的11.37 μm增厚到48.32 μm,即渗氮效率提高到常规离子渗氮的4倍以上。结论 本研究研发的钛催渗低温离子渗氮技术在保障304奥氏体不锈钢优良耐蚀性的同时,能够大幅度提升不锈钢表面硬度及耐磨性能,且具有显著的催渗效果。     

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。