氩氮混合保护TIG焊在紫铜厚大件上的应用

我公司产品中有一种材料为Ｔ2的紫铜零件 ,见图1,设计要求将 5ｍｍ厚封水紫铜板与主体焊接。公司只有一台大功率ＴＩＧ焊机 ,开始时采用纯氩保护ＴＩＧ焊 ,需先用氧乙炔火焰将工件预热到 60 0℃左右。一个工件预热约需 4 0ｍｉｎ ,焊接过程中随着温度的降低 ,极易产生缺陷 ,水压试验经常出现渗漏。为了能提高效率 ,降低成本 ,并改善焊接质量 ,我们尝试无预热状态下用氩氮混合保护ＴＩＧ焊方法进行焊接。图 1　水冷夹头1　试验方案1.1　试验依据图 2是非熔化极在氩、氮、氦三种气体保护下焊接铜时的电弧静特性。在相同的电流和弧长下 ,氮弧的…     

Modelling the effect of graphite morphology on the modulus of elasticity in cast irons

Abstract

Nine grades of pearlitic cast iron containing different graphite morphologies (from flake, compacted and spheroidal) have been studied. The parameters investigated include the graphite aspect ratio, nodularity, graphite size and modulus of elasticity. These parameters have been correlated and compared with different existing bound and model equations. It has been found that the modulus of elasticity of the graphite phase increases as the aspect ratio and nodularity of the graphite increases, i.e.flake graphite gives a lower modulus of elasticity than spheroidal graphite. The experimental values of the modulus of elasticity show good agreement to bound and model equations, although flake graphite cast irons show higher deviation from the modelled values. An equation for the correlation between the graphite modulus of elasticity and the nodularity is presented. Introducing this linear correlation into an existing model for the determination of the effective modulus of elasticity gives a continuous function, including all grades of cast irons, with a very good agreement with experimental values. The modulus of elasticity of cast irons can be accurately predicted from both bound and especially model equations, using the aspect ratio and nodularity of the contained graphite particles. The fit is improved by using a modulus of elasticity of the graphite phase that is based on the graphite morphology, considering that the modulus of elasticity of the graphite is different in the basal and prismatic planes.     

Comparison of plasma-sprayed coatings produced in argon or nitrogen atmosphere

When spraying is conducted at ambient atmosphere, the entrainment of air cools the plasma jet and affects its expansion. It can also cause oxidation or chemical decomposition of the sprayed materials. Inert plasma spraying (IPS), generally conducted in an argon atmosphere, prevents these phenomena. However, the main drawbacks of IPS in comparison with air plasma spraying are the capital and operating costs. This paper presents a study in which nitrogen is used as a substitute for conventional argon atmosphere, thus reducing costs by 25 to 30%. Titanium carbide and niobium powders were sprayed in both argon and nitrogen atmospheres. Cryogenic cooling of the substrate was used during the spray process. This helps to maintain a low temperature in the chamber, produce thick coatings, and allows the use of substrate materials that are sensitive to heat. The velocity, temperature, and composition fields of the argon-hydrogen plasma jet flowing in argon or nitrogen at atmospheric pressure are compared from numerical simulation. The adhesion, roughness, and microstructure of the niobium and TiC coatings produced in both atmospheres are discussed as well as their nitrogen content.     

Corrosion behaviour of nitrogen implanted titanium in simulated body fluid

Abstract

Titanium is one of the most important materials for medical applications, as a result of its uniquely high biocompatibility. The effect of nitrogen implantation on the biocompatibility and the corrosion resistance of cp titanium are reported. Grazing incidence X-ray diffraction studies showed that implantation formed a δ-TiN_x phase. Electrochemical tests in HBSS showed an optimal decrease in corrosion current density for specimens implanted with 3 × 10¹⁷ ions cm^-2 at 25 keV, compared with unimplanted titanium. Following implantation and immersion in a commercial physiological solution, phases are precipitated which are rich in calcium and phosphorus, and these hydroxyapatite precursors indicate that this implantation regime confers optimal properties of corrosion resistance and biocompatibility.     

An investigation of dynamical metal transfer in GMAW—Effects of argon shielding gas

The unbalance radial electromagnetic force was firstly obtained by measuring the real-time input electrical impedance of GMAW. This force acts as an attaching force because it pushes the droplet aside of the welding wire and sticks on the tip of welding wire as result of surface tension force. In spray transfer mode, lower unbalance radial electromagnetic force was observed when argon shielding gas was used. The finding presented in this paper is contrary to the literature which reported that higher electromagnetic force is desirable for faster transfer rate of droplets in spray transfer mode.     

Sintering of titanium in argon and vacuum: Pore evolution and mechanical properties

Reducing porosity can help to improve the mechanical properties of an as-sintered material. An alternative is, however, to tailor the size, distribution and morphology of the residual pores without having to further reduce porosity. This study investigates the sintering of commercially pure titanium (CP Ti) in a flowing argon (Ar) atmosphere and compares the results with sintering in a vacuum of 10⁻² Pa. The CP Ti sintered in Ar at 1300 °C for 2–3 h exhibited a marginally lower density but clearly better tensile ductility than Ti sintered in vacuum. The sensitivity of tensile ductility to residual pores was analyzed. Samples sintered in Ar exhibited much lower sensitivity than those sintered in vacuum. The superior ductility arises from the beneficial effect of sintering in Ar, which resulted in a greater number of but smaller residual pores with lower pore aspect ratios and finer matrix grains due to the grain-growth inhibiting role of the residual pores. The reason is attributed to the entrapped Ar in the closed pores during sintering, which is insoluble in Ti at the sintering temperature. The ever-increasing internal pore pressure prevents further pore shrinkage after reaching a critical size. The final pore size range is predicted and compared with experimental observations. Sintering of titanium in Ar is advantageous over sintering in vacuum in terms of both pore size distribution and pore morphology within a reasonable isothermal sintering period (e.g., 3 h at 1300 °C). Therefore, it can be more attractive for non-fatigue critical applications than sintering in vacuum.     

Wear and corrosion properties of plasma-based low-energy nitrogen ion implanted titanium

Plasma-based low-energy nitrogen ion implantation, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition, has emerged as a low-temperature surface engineering technique for metal and alloy. In this paper, the pure metal Ti samples have been modified by the plasma source ion nitriding process at a process temperature of 700 °C for a processing time of 4 h. The nitrided Ti surfaces were constructed of a continuous and dense Ti₂N compound layer about 2 μm thick and a 7-8 μm diffused layer. During tribological test on a ball on disk tribometer against the Si₃N₄ ceramic counterface, a low friction coefficient of about 0.3 and the faint wear volume were obtained for the nitrided Ti samples. The cyclic polarization curves of the nitrided Ti samples in 3.5% and 6.0% NaCl solutions showed that the improved pitting corrosion resistance with an increase of corrosion potential and a decrease of passive current, compared with that of the unnitrided Ti sample. The plasma source ion nitriding of the Ti samples provided the engineering surfaces for the functional applications with the combined improvement in wear and corrosion resistance.     

Changes in moduli of elasticity and a new equation of fatigue lifetime

Cyclic dependences of the defect of the modulus of elasticity and the fatigue endurance of copper specimens, carbon steels, and titanium and aluminum alloys are studied. An equation describing fatigue lifetime with allowance for the conditions of preliminary excitation of vibrations up to a stationary loading mode is suggested. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 8–12, May, 1998.     

The effects of implanted nitrogen ions on the magnetic properties of Mn-implanted GaN

The effects of implanted N ions on the magnetic properties of Mn-implanted GaN were studied. The ferromagnetic signal increased when N ions were implanted into GaN prior to the implantation of Mn ions and annealed at 900°C. Synchrotron radiation photoemission spectroscopy revealed that the Ga−Mn magnetic phases contributing to ferromagnetic properties increased. Mn−N binary phases such as Mn₆N₂₅₈ and Mn₃N₂ decreased and sheet resistivity significantly increased, indicating a reduction of N-vacancies. Consequently, it is suggested that the enhancement of the ferromagnetic properties in (Mn+N)-implanted GaN originated from the decrease of N-vacancies and the increase of Ga−Mn magnetic phases.     

紫铜带材性能与杯形件制耳的关系

通过对紫铜带材的性能与拉深试验,分析、介绍了材料的性能与各向异性对拉深杯形件制耳的影响,以及消除制耳的一般方法。     

Machining and mechanical engraving of copper thermal-sprayed coatings

Copper rolls and copper thermal spray coated rolls are being used throughout the printing industry. Copper is the material of choice for printing rolls that are subsequently machined, mechanically engraved, and hard chrome plated. However, there are several limitations associated with the application of copper thermal spray coatings, especially onto copper substrates at thicknesses greater than 0.015 in. This article presents thermal spray techniques that will improve the coating quality of copper coatings. These techniques reduce the oxide content, lower the porosity level, and produce a coating with a more desirable hardness range that allows for improved machining and easier mechanical engraving of copper coatings.     

Liquid phase surface alloying of CP-titanium with aluminum in an atmosphere of argon and nitrogen

In the present work, surface alloying of CP-titanium with different mixtures of titanium and aluminum powders in a gas mixture of 20% argon and 80% nitrogen was carried out using tungsten inert gas (TIG) process. The microstructures of the alloyed layers were investigated by optical microscope (OM), scanning electron microscope (SEM), and the phases formed were studied by X-ray diffraction analysis. The hardness of these layers was also evaluated using a microhardness machine. The results showed that the surface hardness was significantly enhanced from 175 HV_0.1 for the untreated substrate to more than 1000 HV_0.1 for the alloyed layers, due to the formation of Ti₃Al₂N₂ as well as Ti₃Al and TiN in the modified layers. It was also noticed that the alloyed layers exhibited better wear resistance as compared with the untreated substrate.     

镀银铜箔平行微隙电阻焊接头组织与性能

研究了0.1 mm厚镀银铜箔与纯铜箔平行微隙电阻焊接头的微观组织和力学性能,分析了不同参数对接头力学性能的影响,利用扫描电子显微镜对典型接头界面处的微观组织特征进行了分析. 结果表明,焊点连接面处组织致密;连接面由富银相和富铜相组成的两相区和只有富铜相的单相区组成,焊接温度达到了银的熔点,其连接机理与钎焊类似;试验所用参数范围内,焊点的最大剪切抗力达到了59 N,焊接功率和焊接时间对焊点性能的影响较大,而电极压力的影响较小.