氧化物弥散强化材料的搅拌摩擦焊分析

为了探索搅拌摩擦焊技术应用于氧化物弥散强化材料的可焊接性及其基本特点,文中对厚度为4 mm的氧化物弥散强化铜合金进行了焊接试验,并对焊接接头的宏观形貌、微观组织、显微维氏硬度进行了分析. 发现焊接接头横截面由搅拌区、热力影响区、热影响区和母材区4部分组成. 前进侧热影响区与热力影响区形成明显的分界线,后退侧则相对模糊. 搅拌区的组织为细小的等轴晶粒,出现了洋葱环和L线,热力影响区晶粒沿一定方向发生形变,热影响区组织粗化. 沿焊缝横截面的显微维氏硬度呈V形分布,其中搅拌区硬度值最低.     

2219铝合金搅拌摩擦焊接头晶间腐蚀分析

采用晶间腐蚀试验研究了2219铝合金搅拌摩擦焊接头的晶间腐蚀行为,结合接头显微组织、微观硬度、腐蚀形貌及腐蚀深度,分析母材与焊核区的差异,并对接头晶间腐蚀机理进行了初步的探讨.结果表明,焊核区为细小的等轴晶组织,且接头上表面焊核区的晶粒要大于下表面焊核区的晶粒;母材区硬度最高,下表面焊核区硬度最低;焊核区的耐蚀性优于母材,且上表面焊核区耐蚀性优于下表面焊核区,母材最大腐蚀深度为145.9 μm,上表面焊核区及下表面焊核区最大腐蚀深度为46.3 μm和84.1 μm.     

Investigation of the growth and stability of (1 0 0)[0 0 1] NiO films grown by thermal oxidation of textured (1 0 0)[0 0 1] Ni tapes for coated conductor applications during oxygen exposure from 700 to 1400 °C

Thin (<1 μm) transparent epitaxial NiO films were grown on oxide-free (1 0 0)[1 0 0] Ni tapes by thermal oxidation at about 1250 °C in air. The growth of this oxide layer successfully suppressed the secondary recrystallization of pure Ni tapes, normally observed at these temperatures. A dense NiO <1 0 0> nucleation rather than competitive grain growth controls the texture in this case. Nevertheless, the removal of the native oxide layer is crucial. Further oxidation of these templates in the temperature range from 800 to 1400 °C produced single crystal-like NiO films with a thickness up to ~70 μm and an improved cube texture. Comparison with the literature data indicates that volume diffusion of Ni contributes predominantly to the NiO growth over the whole temperature range. These NiO films can act as a good oxidation barrier at lower temperatures (~800 °C) for coated conductor applications.     

The Influence of Oxidizing Medium on Structure,Mechanical Properties,and Breakage Pattern of Oxide Films of Zr—1% Nb Alloy under Conditions Simulating Oxidizing Media of WWER and PWR Reactors

This article investigates into the structure, phase composition, mechanical properties, and breakage pattern of oxide films formed on the surface of Zr—1% Nb alloy after corrosion tests in autoclave in water, steam, and water with lithium. Oxidation in water with lithium promotes formation of oxide films with a thickness of more than 100 μm, and, after oxidation in water or steam, the thickness is 5–15 μm. Upon oxidation in water, oxide films are generated with laminar structure: in the substrate, the grains are extended with the thickness of ~80 nm, near film surface the grains are equiaxial with the diameter of ~30 nm. After holding of the specimens in steam the oxide films are comprised mainly extended grains with the thickness of ~95 nm with a minor amount of equiaxial grains, 10%, with a diameter of ~30 nm, after oxidation in water with lithium the mixture of equiaxial and weakly extended nanograins is observed in the film structure. Upon loading of specimens with the structure of equiaxial and weakly extended grains the oxide films are broken due to generation of transversal cracks propagating to basic metal. The oxide films with laminar structure oxidized in water are broken due to exfoliation along the interface between the layers of extended and equiaxial grains. Breakage of films with the structure of equiaxial and weakly extended grains starts at the stage of elastic deformation at a stress of 300 MPa. The highest breakage stresses of 1150 MPa are characteristic for alloy specimens oxidized in steam. Breakage of films with laminar structure after oxidation in water occurs at average stresses of 798 MPa. The cohesive/adhesive strengths of films oxidized in water and steam are nearly the same. In thick alloys, oxide films oxidized in water with lithium, substrate does not open even at loading of 100 N. According to data of Raman spectroscopy, oxide film is mainly comprised of monoclinic phase of zirconium oxide; however, after oxidation in steam at the metal—film interface, a barrier layer of tetragonal phase of zirconium dioxide has been detected that prevents accelerated oxidation.     

A novel approach to boriding of TZM by spark plasma sintering method

Boriding can be candidate method to increase mechanical properties and oxidation resistance of molybdenum based alloys. Rapid oxidation of TZM at elevated temperature and low wear resistance are considered to be main drawbacks for possible applications. In this study molybdenum boride layer was formed on the surface of TZM by spark plasma sintering (SPS) method. Pre-mixed TZM was used as a raw material in powder form. Both sintering and boriding process were performed in a single step at constant temperature of 1420 °C in various pressures (40–60 MPa) and holding times (5–15 min) under vacuum. The effects of molybdenum boride layer on density, hardness and oxidation behavior were investigated. Thickness, microstructure and hardness of Mo-B based protective layer showed a variety with different process parameters. The boride layer thickness was reached to approximately 200 μm by increasing pressure and holding time. Formation of this layer provided a decrease in mass loss about 73.4% during oxidation test at 1000 °C for 60 min. The maximum surface hardness value was obtained as 21.4 GPa while hardness of base metal was 2.3 GPa.     

Effect of the welding thermal cycles on the structural changes in the heat affected zone and on its properties in joints welded in low‐alloy steels

Summary

Pure tungsten (W) was friction welded to oxygen free copper (Cu) with an intermediate layer to improve the weldability of W to Cu. W and Cu rods were 25 mm in diameter. The intermediate layer consisted of Nb foils of 7, 10, 15 and 25 μm thickness. A strartfied mixed layer which was composed of finer Nb particles was formed in Cu at the weld. The thickness of the mixed layer became smaller with a decrease in Nb thickness by being expelled through the flash of the Cu side. A microstructure without a mixed layer was observed at the weld for a joint with 7 μm thick Nb. The joint with 7 μm thick Nb fractured in the Cu base metal in a tensile test, while all joints except that with 7 μm thick Nb fractured at the weld or on the W side next to the weld. Bond strength of joints with 7 μm thick Nb could be improved markedly, compared with that of joints without an intermediate layer. Oxygen was detected at the weld by line analysis with EPMA regardless of Nb thickness. However, because the joint with 7 μm thick Nb fractured in the Cu base metal in a tensile test, it suggests that the effect of oxidation at the weld on the bond strength of joints was very small.     

7075铝合金搅拌摩擦焊接头沉淀相析出行为

利用搅拌摩擦焊(friction stir welding,FSW)技术对厚度为6 mm的7075铝合金进行平板对焊,使用金相显微镜、显微维氏硬度仪对7075铝合金FSW接头进行微观组织观察和显微维氏硬度测试,使用X射线衍射仪(X-ray diffraction,XRD)对合金进行物相分析,使用透射电镜(transmission electron microscopy,TEM)对接头焊核区(welding nugget zone,WNZ)、热机影响区(thermal-mechanically affected zone,TMAZ)、热影响区(heat affected zone,HAZ)及母材(base metal,BM)中的沉淀相分布、形貌等进行观察,并对沉淀相的晶格条纹间距进行计算。研究结果表明,7075铝合金FSW接头的组织及显微维氏硬度分布极其不均匀;接头中沉淀相主要有棒状MgZn_2和椭圆状AlCuMg两种,沉淀相种类与形状不同,强化效果不同,AlCuMg强化效果好于MgZn_2;WNZ中沉淀相主要是AlCuMg,加之细晶强化,显微维氏硬度较高;相比WNZ,TMAZ中沉淀相AlCuMg数量少,MgZn_2相对增多,强化效果相对减弱,导致显微维氏硬度降低;HAZ中的MgZn_2相对更多,加工硬化和细晶强化效果减弱,HAZ与TMAZ交界处显微维氏硬度达到接头的最低值。     

On the Influence of Non-Protective CuO on High-Temperature Oxidation of Cu-Rich Cu-Ni Based Alloys

A number of copper-rich Cu-Ni alloys wereoxidized from 750 to 1000^°C at differentoxygen pressures. The oxide scales formed consist of anouter copper oxide layer and an inner porous layer where internal oxide-derived NiO particles aredispersed in a copper oxide matrix. The copper oxide maybe both single-phase CuO and a two-phase(CuO+Cu₂O). At the lower part of thetemperature range, the oxidation kinetics and oxidemorphology depend strongly upon the formation of CuO.The CuO layer is nonprotective and further oxidation ofCu₂O, forming CuO, therefore changes the oxidation from being approximately parabolic tohaving a breakaway-like behavior. The relative thicknessof nonprotective CuO increases with increasing NiO andreflects that the solid-state flux of copper across the Cu₂O decreases due to abarrier effect of the NiO particles and porosity in theoxide and NiO particles in the alloy. The beneficialeffect of Ni in reducing the oxidation rate is lost due to the extensive formation ofnonprotective CuO.     

致密SiC涂层在水蒸气及与空气混合气氛中的氧化行为

本实验主要针对在球形燃料元件基体石墨样品上用流化床化学气相沉积工艺所制备的致密SiC抗氧化涂层,于1400℃下,对其在水蒸气及与空气混合气氛中的氧化行为进行研究与机理分析。结果表明,气氛对氧化层厚度有显著影响。单一水蒸气情况下,所得氧化层的厚度均比混合气氛的氧化层厚度薄。单一水蒸气氧化后的样品比混合气氛氧化的样品具有更平整的表面、更轻微的点状开裂和更小的线性裂纹。致密SiC涂层氧化均发生在表面,没有破坏致密层的结构。氧化机理分析表明,致密SiC涂层的表面形貌变化、裂纹的产生以及厚度变化等均与氧化竞争反应和氧化中间产物有关。致密SiC涂层在空气和水蒸气等不同环境的氧化过程中,均能在表面形成一定厚度的SiO2自愈合层,且10 h的氧化后,涂层的氧化深度仅在表层的3.5μm以内,没有破坏致密层结构。     

搅拌针转速对厚板镁合金SSFSW焊缝组织及性能的影响

对9 mm厚板AZ31B镁合金进行静止轴肩搅拌摩擦焊(stationary shoulder friction stir welding,SSFSW)工艺试验,探讨搅拌针转速(500～1 000 r/min)对焊缝组织及力学性能的影响规律.结果表明,在给定焊接速度80 mm/min下,搅拌针转速在600～800 r/min范围可获得表面光滑、无内部缺陷的对接焊缝,当转速为1 000 r/min时焊缝表面出现不连续凹坑但内部仍无缺陷.随着转速增加,晶粒尺寸由(11.11±1.68)μm增加到(18.95±1.83)μm;在700 r/min时焊核区晶粒尺寸沿板厚差异最小.焊缝中间硬度分布具有不均匀性且随转速增加而减小,最大差异为10.97 HV,最低硬度47 HV位于前进侧的热力影响区与焊核区界面处.在700 r/min下接头力学性能最佳,强度系数为90.2%、对应断后伸长率为母材69.3%.随着转速增加,断裂模式由韧-脆混合断裂转变为剪切-韧性混合断裂.     

The relationship between the corrosion resistance and impurity content of aluminium oxide layers

In the last few years there has been an increased production and application of aluminium foil of under 20 μm thickness all over the world. Household foil is often stored in a wet environment, where the surface is only protected against corrosion by an aluminium oxide layer produced during manufacturing. In this study it has been shown that the aluminium-water vapour reaction is greatly affected by the composition and structure of the amorphous oxide layer on the surface and this depends on the composition of base metal and on the annealing of the foil. The incubation period of aluminium hydroxide nucleation is shortened and its growth rate accelerated by alkali and alkaline earth metal cations incorporated in the oxide layer. In particular the corrosion resistance is decreased by the presence of alkali (Li) and alkaline earth metal (Mg) cations in the oxide layers.     

Effect of cooling conditions on corrosion resistance of friction stir welded 2219-T62 aluminum alloy thick plate joint

Friction stir welding (FSW) with water cooling and air cooling was used to weld 2219-T62 aluminum alloy joints with a thickness of 20 mm. The effect of cooling conditions on the corrosion resistance of joints in 3.5% NaCl solution was investigated using the open circuit potential (OCP), the potentiodynamic polarization, and the corrosion morphology after immersing for different time. And the precipitates distribution was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that the weld nugget zone (WNZ) owning positive potential, lower corrosion current density and fine and uniform precipitates, is much more difficult to corrode than the heat affected zone (HAZ) and the base metal (BM). Compared with air-cooled joint, the water-cooled joint has better corrosion resistance. In addition, the results of microstructure observation show that the potential, distribution and size of second phase particles determine the corrosion resistance of FSW AA2219 alloy joints in chlorine-contained solution.     

钛/铝/镁爆炸焊复合板波形界面及力学性能

文中提出以薄的铝合金板作为过渡层,采用爆炸焊接技术成功制备钛/铝/镁层状复合材料. 对钛/铝接合界面、铝/镁接合界面及钛/铝/镁爆炸复合板的整体力学性能进行了分析研究. OM和SEM试验结果表明,钛/铝接合界面和铝/镁接合界面均为波状接合界面,在铝/镁界面出现了局部熔化区;钛/铝接合界面为小尺寸波(λ=160 μm,h=26 μm),铝/镁接合界面为大尺寸波(λ=1 740 μm,h=406 μm);拉-剪试验表明,复合板沿着铝/镁接合界面断裂;弯曲性能测试表明,钛板一侧受拉时复合板弯曲强度和塑性均优于镁合金板一侧受拉,断裂始于铝/镁接合界面,最终从镁合金板一侧剪切断裂失效.     

自钝化W-Cr-Y合金层的制备及其抗氧化性能

为防止或缓解钨氧化,用双辉等离子体表面冶金技术在纯钨基材表面制备了W-Cr-Y自钝化合金层。采用扫描电镜(SEM)和X射线衍射仪(XRD)对合金层的组织和相结构进行了分析,并在模拟发生核聚变发电站冷却失效事故时的高温大气环境下对合金层的抗氧化性能进行了研究。结果表明,制备温度为800、900、1000和1100℃时,均成功地在纯钨表面形成了由W(Cr, Y)固溶体构成的厚度超过20μm的W-Cr-Y合金层。制备温度为1000℃时合金层厚度达到了35μm,表面光滑致密,合金层与纯钨基体呈现良好、无缺陷的冶金结合。制备温度较低(800℃和900℃)时,合金层在1000℃氧化10 h后的表面未形成连续的自钝化合金层,抗氧化性能较差。制备温度较高(1000℃和1100℃)时,合金层在氧化后形成了致密平整的氧化层,且制备温度为1000℃时合金层氧化后的质量增加最小,抗氧化效果最优。     

Producing and investigating oxide coatings containing manganese and nickel compounds on titanium from electrolyte suspensions

Elemental and phase compositions, as well as the surface structure of oxide coatings formed on titanium by plasma-electrolytic oxidation in aqueous electrolyte suspensions containing dispersed MnO₂, NiO, and Mn₂O₃ particles with sizes of 5–10 μm, are determined. The coatings are investigated using X-ray spectral analysis, X-ray photoelectron spectroscopy, and X-ray phase analysis, as well as electron and atomic force microscopy. The amount of transient metals contained in the surface layer of the coatings is found to be determined by the concentration of oxide particles added to the solution, their nature, and the nature of the base solution. The relations discovered can be used when carrying out a directional formation of coatings containing the necessary oxide systems, including their mixtures with particular component ratios.     

P92钢焊接接头的高温抗氧化性研究

P92钢因优异的综合性能逐渐成为超超临界机组过热器、再热器等零部件的理想用钢,材料经焊接后,焊接接头在服役温度中的高温抗氧化性直接影响零部件的使用寿命。利用增重法研究P92钢焊接接头在650℃高温空气介质中的氧化动力学,采用OM、SEM观察和分析氧化层表面及截面形貌,利用XRD分析氧化物物相。结果表明:在一定温度下,P92钢焊接接头各区域氧化速率均是先增加后降低,然后趋于稳定值,符合抛物线规律;在650℃空气介质中氧化132 h后,焊接接头中距焊缝3 mm热影响区A部位、焊缝、母材各区域氧化层的厚度分别为45μm,30μm,27μm;焊接接头氧化后表面的主要氧化产物为Fe_2O_3。     

铝合金FSW拼焊板塑性变形规律研究

铝合金搅拌摩擦焊拼焊板焊缝各区力学性能的差异导致拼焊板成形时严重的不均匀性,降低了拼焊板的成形性能,极大地限制了铝合金拼焊板的应用。以2024铝合金搅拌摩擦焊拼焊板为研究对象,通过实验和有限元模拟系统研究接头力学性能失配对铝合金拼焊板塑性成形性能的影响规律和机理。对铝合金搅拌摩擦焊接头进行金相检验和硬度测试,根据接头组织及硬度分布特征,将搅拌摩擦焊接头划分为焊核区、热机影响区、热影响区以及母材区4个部分,以此建立搅拌摩擦焊接头的有限元模型,并对接头变形过程中的约束与协调变形规律进行分析。接头变形时拉伸应力在屈服应力最小的区域最低,在屈服应力较大的区域相应升高,且在接头中存在失配比交界处都会发生突变。从形变能的角度分析,这主要是由于力学性能失配而导致变形不协调及相互约束,表现在接头拉伸性能上就是屈服强度及屈服位置、抗拉强度、延伸率随接头各区失配比组合的差异。     

Spallation Behavior of Thermally Grown Nickel Oxide on Nickel

Thermally grown oxide scales are often under compressive residual stresses, especially upon cooling, which can lead to spontaneous spallation and a loss of their protectiveness. This study uses nickel oxide formed on different purity of nickel as an example to investigate the spallation process. Samples oxidized after different times between 800 and 1100 °C were observed during cooling. The oxide scale buckled and spalled after reaching a critical thickness that depended on oxidation temperatures, substrate thickness, and metal purity. The observed buckling was only a secondary process that followed scale delamination under local tensile stresses at sample edges or corners. When the delamination eventually extended over a large enough area on the face of the specimen, the scale above it buckled, driven by the residual compressive stress in the oxide. Growth of the buckles took place by crack extension along regions of high pore densities in the oxide scale. The development of pores in the oxide layer, which depended strongly on substrate impurity levels, was found to be the most important factor controlling failures of the NiO scales. Sulfur segregated on pore surfaces, whereas TEM studies showed no S at NiO/Ni interfaces.     

Friction stir welding of 304 stainless steel using Ir based alloy tool

Abstract

In order to investigate the durability of an Ir based alloy tool, friction stir welding (FSW) of 304 stainless steel plates was performed under various welding conditions, and the mechanical properties of the joints were measured. Defect free joints are possible under certain conditions, and the mechanical properties of the joints are the same as the base material. When the rotation pitch is ～0·3, the degree of wear of the Ir based alloy tool with 1·4 mm probe height, which was used for the FSW of a 304 stainless steel plate with 2 mm thickness, was less than or equal to that of the polycrystalline cubic boron nitride tool with 2 mm probe height, which was used for the FSW of a 304 stainless steel plate with 9 mm thickness. The result of the tool life test in this study showed that the Ir based alloy tool enabled the FSW of 304 stainless steel over a 75 m length.     

厚板铝合金FSW和MIG焊接接头疲劳性能

对厚度10 mm的6082-T6铝合金搅拌摩擦焊(FSW)和MIG焊接接头的疲劳强度进行了试验研究,并与6082-T6母材疲劳性能进行了对比分析.结果表明,6082-T6母材的疲劳S-N曲线最高、MIG焊接接头S-N曲线度最低,而FSW接头的疲劳S-N曲线近似位于两者之间;在高应力区FSW疲劳强度低于MIG焊接接头、而在低应力区高于MIG焊接接头.大部分FSW试样疲劳裂纹启始于焊缝根部的"弱连接"缺陷,采用机械加工去掉1.4 mm厚度焊缝根部材料后,FSW疲劳强度明显提高并接近母材数据.厚板6082-T6铝合金FSW焊缝根部质量控制是影响疲劳性能的关键因素.