TC4钛合金不同气源激光渗氮行为

在用矩形光斑高功率半导体激光器,在纯氮气和氮氩混合两种不同方式下,通过不同气流量和氮氩混合对Ti-6Al-4V进行表面渗氮,研究气体流量、氮氩混气比对渗氮熔池形态及渗氮组织和力学性能的影响。采用SEM、EDS以及XRD对渗氮层的显微组织、微区成分及相组成进行研究。结果表明:采用纯氮渗氮时,在15 L/min气流量下获得均匀渗氮层,继续增大气流量渗氮熔池流动紊乱,出现贯穿裂纹,且渗氮深度和硬度并未随气流量增加;采用不同氮氩混气比渗氮时,渗氮层的表层硬度均较相同条件下纯氮气渗氮层的有所降低,且渗氮层裂纹倾向减弱,渗氮层组织由表至里在200~800μm内按层深依次存在TiN0.88、TiN0.61、TiN0.3三种稳定相;分别采用纯氮气和不同氮氩混气比渗氮时,渗氮层组织沿层深分布依次均为粗短树枝晶、等轴晶、细长树枝晶、针状晶。     

渗氮压力对TA2工业纯钛渗层特性的影响

采用低压脉冲渗氮对TA2工业纯钛进行表面强化,研究了渗氮压力对TA2工业纯钛渗层特性的影响。结果表明:随着渗氮压力的升高,TA2工业纯钛表面TiO_2相逐渐减少,氮含量随之增加,扩散难度也逐渐增大。当渗氮压力为-25 kPa时,工业纯钛表现出最佳的表面硬度和最深的有效硬化层。低压脉冲渗氮后其耐蚀性大幅度提高,且随着压力的降低,合金的耐蚀性逐渐提高。     

空心阴极放电复合稀土氧化物对Ti6Al4V合金离子渗氮组织及性能的影响

目的 改善Ti6Al4V合金的耐磨和耐蚀性能,探究辅助渗氮手段的引入对Ti6Al4V合金离子渗氮组织和性能的影响。方法 利用空心阴极放电(Hollow Cathode Discharge,HCD)及稀土氧化物(Y2O3纳米颗粒)辅助在720 ℃对Ti6Al4V合金进行4 h离子渗氮处理。通过光学显微镜、扫描电子显微镜、X射线衍射仪、显微硬度测试仪、往复式摩擦磨损实验仪以及电化学工作站,对比研究常规离子渗氮、HCD辅助离子渗氮以及HCD复合稀土氧化物辅助离子渗氮3种条件下Ti6Al4V合金的渗氮组织和性能。结果 HCD复合稀土氧化物辅助离子渗氮条件下,Ti6Al4V合金表面生成约126 μm厚的渗氮层,分别是常规离子渗氮条件和HCD辅助离子渗氮条件的3.1、2.4倍。化合物层中,TiN含量显著增加,渗氮层表面硬度达到1 067.9HV0.05。渗氮层整体硬度明显提高,且硬度梯度降低。Ti6Al4V合金的摩擦系数从常规离子渗氮时的0.4降至0.2。同时,TiN含量的提高,使Ti6Al4V合金在3.5% NaCl溶液中的自腐蚀电流降低,极化电阻增大,耐蚀性能得到改善。结论 HCD复合Y2O3辅助可显著提高氮势,促进氮向Ti6Al4V合金内快速扩散,提高合金的硬度,改善合金的耐磨性能和耐蚀性能。     

奥氏体不锈钢VOD冶炼过程中氮行为的研究

建立了VOD精炼过程中氮行为的动力学模型,并进行了316L不锈钢控氮的实验室的热模拟试验。实验结果表明:钢中氮溶解度随氮分压的增大而增大,随温度降低而增大。渗氮速率随吹氮流量、氮分压增加而增大;初始氮含量越大,渗氮速率越小;温度对于渗氮速率影响较小。钢中氮含量随吹氩时间、吹氩流量增加而降低;吹氩流量越大,脱氮速率越大。     

TA2钛材的激光相变硬化复合低温气体渗氮工艺

为了提高TA2钛合金的耐磨性和耐蚀性,采用激光相变硬化-气体渗氮工艺对TA2钛进行表面改性。利用体视光学显微镜、透射电镜和X射线衍射仪对TA2激光相变硬化-气体渗氮层进行表面形貌、微观组织和相组成分析;利用显微硬度计对两种复合改性层的显微硬度进行测试。结果表明:TA2钛表面经激光相变硬化后,可实现430℃低温渗氮。此条件下晶粒得到细化,亚结构和缺陷密度的增加有利于氮元素和晶内扩散,相变组织与氮势梯度具有良好的对应关系。通过改善渗层的组织结构和化学成分分布状态,获得了性能优良的TA2钛表面硬化层。     

钛合金激光渗氮层的组织与性能研究

对Ti-6AI-4V合金在氮和氩的混合气体中通过激光加热形成的渗氮层进行了研究。结果表明，渗氮层由a和TiN两相组成。靠近表层的粗树枝状组织为胞状纳米晶的TiN相，熔区内的显微硬度在500HV～800HV范围内呈阶梯状变化。     

2Cr13钢440℃等离子体渗氮

对2Cr13钢进行了440℃等离子体渗氮,利用金相显微镜(OM)、分析天平、X射线衍射仪(XRD)、显微硬度计和电化学工作站等仪器,对渗氮层的显微结构、增重、相组成、硬度分布和耐腐蚀性能进行了测试。结果表明:2Cr13钢在440℃氮氢比为1∶3条件下渗氮4 h、8 h和16 h后,渗氮层厚度逐渐增加,最厚为58.9μm;渗氮层质量随时间的增加而增大,增重最高为1.57×10~(-3)g/cm~2;渗氮层显微硬度显著增高,最大为1170.0 HV0.05;渗氮层表面由ε-Fe_3N和γ'-Fe_4N组成;渗氮层表面极化曲线出现钝化区,腐蚀速率显著下降,耐蚀性显著提高。     

Ti6Al4V无氢离子渗氮摩擦学性能的研究

以N2和Ar的混合气为气源，在Ti6Al4V表面离子渗氮形成渗氮层。对渗层的相结构、表面粗糙度、显微硬度及与基体的结合强度等进行了测试分析，并用球-盘滑动磨损试验机对渗层的摩擦学性能进行了研究。结果表明：在N2／Ar=1：1，900℃的渗氮条件下，渗氮层主要由化合物Ti2N，TiN和氮在α-Ti中的固溶体α相等相组成；渗氮后试样的表面粗糙度增大；渗氮层的硬度较基材Ti6Al4V有很大提高，且与基体间有较好的结合强度；在球-盘滑动磨损试验中，渗氮层无减摩效果，但其耐磨性较基材Ti6Al4V大大增强。     

4Cr14Ni14W2Mo钢离子渗氮层剥落的研究

研究了经不同加热温度锻造、固溶和７５０℃时效后钢的晶粒度、孪晶、碳化物的分布及纯氨和氨加氩做介质离子渗氮后渗层组织、相组成、应力状态、氮碳浓度分布、剥落坑形貌。分析表明：纯氨离子渗氮后表面层的碳向里扩散，并出现一峰值：氨加氩渗氮降低了渗层中氮浓度，从而降低了渗层中的应力，这是消除该钢渗氮层剥落的有效途径。     

低压真空渗氮处理TC4钛合金的腐蚀性能研究

采用低压真空渗氮的方法在Ti6A14V钛合金表面制备渗氮层,通过金相观察、X射线衍射、失重法及电化学测试对渗氮层组织成分及腐蚀性能进行了研究。结果表明,通过低压真空渗氮方法在钛合金表面形成了均匀致密的渗氮层,其主要由TiN、Ti2N及TiAlN等硬质相膜层组成。在100 mL/L HF+200 mL/L HNO3混合体系中进行加速腐蚀后膜层表面基本保持完好,其腐蚀速率是基体腐蚀速率的1/163,自腐蚀电位由基体的-0.762 5 V提高到-0.449 8 V,腐蚀电流降低两个数量级。     

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。