X65管线钢对接接头的疲劳性能

试验表明 ,焊接结构的疲劳裂纹主要起源于接头焊趾处 ,因此合理地处理焊接接头焊趾可改善其疲劳性能。超声冲击处理是一种通过改变焊趾区几何形状、消除焊趾缺陷以及调整焊趾区残余应力场来改善焊接接头及结构疲劳强度的有效方法。利用自行研制的超声冲击装置对X6 5钢焊接对接管接头实施了处理 ,然后进行了焊态、超声冲击处理态及母材的疲劳对比试验。结果表明 ,X6 5钢焊接对接管接头焊态疲劳强度△σ(2× 10 6)为 2 19MPa ;母材的疲劳强度△σ(2× 10 6)为 338MPa;超声冲击处理后接头的疲劳强度△σ(2× 10 6)为 30 2MPa。     

超声冲击改善MB8镁合金焊接接头超高周疲劳性能机理探究

通过超声疲劳试验探究超声冲击对MB8镁合金焊接接头超高周疲劳性能的影响。同时,从应力集中、残余应力、晶粒细化等三个因素来探究超声冲击改善MB8镁合金焊接接头超高周疲劳性能的机理。结果表明：在1.0×108寿命下,焊态试样疲劳强度为31.62MPa,冲击态试样疲劳强度为39.81MPa,冲击态试样疲劳强度相较于焊态提高了26%。这说明超声冲击可以明显提高MB8镁合金焊接接头超高周疲劳性能。焊态试样焊趾处应力集中系数Kt1=1.95,冲击态试样焊趾处应力集中系数Kt2=1.67,应力集中系数降低了14.4%,所以超声冲击可以降低焊趾处的应力集中程度。超声冲击后试样焊趾处的应力由残余拉应力转变成残余压应力。超声冲击细化焊趾表面晶粒改善MB8镁合金焊接接头的超高周疲劳性能。     

超声冲击改善MB8镁合金焊接接头超高周疲劳性能的机理

通过超声疲劳试验探究超声冲击对MB8镁合金焊接接头超高周疲劳性能的影响。同时,从应力集中、残余应力、晶粒细化等3个因素来探究超声冲击改善MB8镁合金焊接接头超高周疲劳性能的机理。结果表明:在1.0×108疲劳寿命下,焊态试样疲劳强度为31.62 MPa,冲击态试样疲劳强度为39.81 MPa,冲击态试样疲劳强度相较于焊态提高了26%。这说明超声冲击可以明显提高MB8镁合金焊接接头超高周疲劳性能。焊态试样焊趾处应力集中系数K_(t1)=1.95,冲击态试样焊趾处应力集中系数K_(t2)=1.67,应力集中系数降低了14.4%,所以超声冲击可以降低焊趾处的应力集中程度。超声冲击后试样焊趾处的应力由残余拉应力转变成残余压应力。超声冲击细化了焊趾表面晶粒从而改善了MB8镁合金焊接接头的超高周疲劳性能。     

超声冲击对MB8镁合金对接接头疲劳性能的影响

采用HJ-Ⅲ型超声冲击设备对MB8镁合金对接接头焊趾区域进行冲击处理.利用EHF-EM200K2-070-1A电液伺服疲劳试验机对超声冲击前后的MB8镁合金对接接头进行疲劳对比试验.采用光学显微镜和高分辨率的透射电镜对超声冲击后的MB8镁合金对接接头的表层组织进行了分析.结果表明,在试验循环基数为2×106周次的条件下,超声冲击态接头的疲劳强度为52.8 MPa,比焊态试样的疲劳强度提高了37.5%,在同等应力水平下,接头的疲劳寿命提高了58～65倍.超声冲击后,焊趾处的应力集中程度降低,焊址及附近区域发生明显塑性变形,变形层厚度大约为70 μm,并在焊趾表面获得了纳米晶组织,同时把焊接残余拉应力转变为压缩应力.超声冲击可以大幅度地提高MB8镁合金焊接接头的疲劳寿命.     

超声冲击对SMA490BW钢焊接接头超高周疲劳性能的影响

采用超声冲击工艺对转向架用SMA490BW钢对接接头焊趾表面进行冲击处理,研究了超声冲击对接头超高周疲劳性能的影响。借助金相显微镜、SEM和TEM研究了冲击层金相组织、冲击前后焊趾处的形貌及表层金属晶粒细化程度。运用有限元软件计算焊接接头的应力分布,采用X射线应力仪对冲击前后焊趾表层的应力进行了测量和分析。结果表明,在5×10~6循环周次下,冲击态接头和焊态接头的疲劳强度分别为206 MPa和153 MPa,经冲击处理后疲劳强度提高了34.6%。在1×10~8循环周次下,冲击态接头的疲劳强度为195 MPa,与焊态接头的141 MPa相比提高了38.3%。在240 MPa的应力水平下,焊接接头经超声冲击处理后的疲劳寿命提高了7倍。经冲击处理的焊趾部位的应力集中系数下降了19.1%,其表面的残余拉应力得到消除,并转变为有益的残余压缩应力,焊趾表层组织得到明显细化,这3个方面均对提高焊接接头疲劳性能起到了积极贡献。     

承载超声冲击提高TC4钛合金焊接接头的疲劳性能

利用自行研制的HJ-II型超声冲击处理装置对钛合金十字接头焊趾处进行了处理,并对接头的疲劳性能进行了研究.结果表明,在应力比R=0.5加载条件下,非承载超声冲击处理的TC4钛合金焊接接头较原始焊态的疲劳强度提高了约73.5%,寿命延长了12~17倍左右,承载超声冲击处理的TC4钛合金焊接接头较原始焊态的疲劳强度提高了148.1%,寿命延长了23~26倍左右.同时,从超声冲击前后应力集中系数的改变、焊接接头残余应力的改变、接头焊趾区表层塑性变形及硬度的变化等几个方面阐述了超声冲击提高焊接接头疲劳性能的机理,特别是承载超声冲击提高TC4钛合金焊接接头疲劳性能的原因.     

超声冲击对金属焊接接头组织及性能影响的研究现状

用超声冲击法处理金属焊接接头后,可获得具有一定厚度的塑性变形层,晶粒明显得到细化,某些晶粒尺寸甚至可达纳米量级。超声冲击还能提高金属焊接接头的显微硬度、抗拉强度和疲劳强度等性能,此外超声冲击可引入对提高疲劳强度有利的残余压应力及改善焊趾处的应力等。超声冲击法在金属焊接接头的焊后强化处理及相关领域方面的应用愈来愈广泛,具有很大的发展潜力。     

超声冲击对SMA490BW耐候钢十字焊接接头疲劳性能的影响

采用HJ2-Ⅲ型超声冲击枪对SMA490BW耐候钢十字焊接接头焊趾表面进行超声冲击处理。利用EHF-EM200K2-070-1A疲劳试验机对SMA490BW钢焊态和超声冲击态十字接头试样进行疲劳试验,利用显微硬度计测试焊缝处的力学性能,采用高分辨透射电镜对冲击后的十字接头焊趾区域表面微观组织进行分析。结果表明:焊态、超声冲击态十字接头的条件疲劳极限(2×10~6)分别为165.96、219.28 MPa,超声冲击处理态十字接头的疲劳强度提高了32.13%。经超声冲击处理后焊趾处的显微硬度得到提高,超声冲击处理前后焊趾区的平均硬度为203、228 HV,超声冲击处理后焊趾区的硬度提高了12.3%。焊趾表层的晶粒在超声冲击处理后得到细化,大多数晶粒的尺度在250 nm左右,有少量的晶粒尺度达到纳米级别。     

TCS不锈钢接头超声冲击处理疲劳对比试验研究

日益繁忙的交通运输对车辆承受动载能力的要求越来越高,车辆的疲劳强度及提高和改善焊接接头疲劳强度越来越受到重视.对TCS铁素体不锈钢焊接接头进行了原始焊态与超声冲击处理十字焊接接头疲劳性能的对比试验,对恒幅载荷作用下超声冲击处理焊接接头的疲劳行为进行了研究.试验结果表明:超声冲击处理态试件与原始焊态试件相比,疲劳强度提高了60%左右.     

铁路快捷货车焊接转向架典型接头疲劳性能研究与应用

采用三点弯曲疲劳试验和断口微观分析等方法对焊态(不做工艺处理)和焊后经不同处理的快捷货车焊接转向架的典型焊接接头疲劳性能进行研究。研究结果表明:全熔透T型接头焊态的疲劳强度为146.25 MPa,焊趾经打磨处理后接头的疲劳强度为165.75 MPa,焊趾经喷丸处理后接头的疲劳强度为180.45 MPa,焊趾经打磨+喷丸处理后接头的疲劳强度为203.75 MPa。通过焊后对焊趾进行打磨、喷丸以及打磨+喷丸处理,可有效改善接头焊趾部位的应力集中,并使焊趾处表面拉应力变为压应力,显著提高T型全熔透焊接接头的疲劳强度。     

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。