搅拌摩擦加工IF钢的组织性能

对3 mm厚的DC04冷轧IF钢板进行搅拌摩擦加工,研究加工区域的微观组织与力学性能. 在旋转速度为950 r· min-1 ,加工速度为60 mm·min-1时,采用加工后强制冷却技术可获得光滑平整且没有缺陷的加工表面. 搅拌摩擦加工后组织显著细化,加工中心的平均显微硬度约为HV 135. 6,是母材硬度的1. 4倍,表面细晶层硬度最高可达到HV 312. 8,细晶层和过渡层的抗拉强度分别比母材的抗拉强度提高50. 9%和47. 6%,加工前后试样的拉伸断口均呈微孔聚合韧性断裂特征. 细晶强化对材料抗拉强度的提高起主要作用.     

Improvement of microstructure and corrosion properties of friction stir welded AA5754 by adding Zn interlayer

This study investigated the effect of Zn foil layers on the microstructure and corrosion characteristics of friction stir welded aluminum alloy 5754. Samples of various joints were prepared by applying different rotational and welding speeds, and their microstructures were evaluated via a metallographic technique and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy elemental analysis. The anticorrosion behavior of joints in the absence and presence of a Zn interlayer was studied by cyclic potentiodynamic polarization test in 3.5wt% NaCl aqueous solution, and sound welds were obtained in the presence of the Zn interlayer foil. The results revealed that the joint made at a rotational speed of 800 r/min and traveling speed of 15 mm/min achieved a chemical composition identical to that of aluminum alloy 7xxx series, and as such, it showed the best resistance to corrosion.     

A comparative study between friction stir processing and friction stir vibration processing to develop magnesium surface nanocomposites

Friction stir processing(FSP) can be used to improve surface composites. In this study, a modified method of FSP called friction stir vibration processing(FSVP) was applied to develop a surface composite on AZ91 magnesium alloy. In this technique, the workpiece is vibrated normal to the processing direction. The results illustrated that compared with the FSP method, the FSVP caused a better homogeneous distribution of SiC particles in the microstructure. The results also showed that matrix grains of friction stir vibration processed(FSV-processed) samples((26.43 ± 2.00) μm) were finer than those of friction stir processed(FS-processed) specimens((39.43 ± 2.00) μm). The results indicated that the ultimate tensile strength(UTS) of FSV-processed specimens(361.82 MPa) was higher than that of FS-processed specimens(324.97 MPa). The higher plastic strain in the material during FSVP, due to workpiece vibration, resulted in higher dynamic recrystallization,and consequently, finer grains were developed. The elongation and formability index of the FSV-processed specimen(16.88% and 6107.52 MPa·%, respectively) were higher than those of the FS-processed sample(15.24% and 4952.54 MPa·%, respectively). Moreover, the effects of FSVP were also found to intensify as the vibration frequency increased.     

Mechanical properties and characteristics of nanometer-sized precipitates in hot-rolled low-carbon ferritic steel

The microstructures and properties of hot-rolled low-carbon ferritic steel have been investigated by optical microscopy, field-emission scanning electron microscopy, transmission electron microscopy, and tensile tests after isothermal transformation from 600℃ to 700℃ for 60 min. It is found that the strength of the steel decreases with the increment of isothermal temperature, whereas the hole expansion ratio and the fraction of high-angle grain boundaries increase. A large amount of nanometer-sized carbides were homogeneously distributed throughout the material, and fine (Ti, Mo)C precipitates have a significant precipitation strengthening effect on the ferrite phase because of their high density. The nanometer-sized carbides have a lattice parameter of 0.411–0.431 nm. After isothermal transformation at 650℃ for 60 min, the ferrite phase can be strengthened above 300 MPa by precipitation strengthening according to the Ashby-Orowan mechanism.     

CSP工艺生产低碳高强度汽车板力学性能特征及强化机理

研究了珠钢电炉CSP工艺生产低碳高强度汽车梁用钢板ZJ510L生产工艺、组织演变、强化机理与组织性能之间的关系.通过光学显微镜、透射电镜和力学性能实验研究表明:ZJ510L显微组织随着轧制道次和冷却速度的增加而细化,最终铁素体晶粒尺寸约为5～6μm;析出的第二相粒子主要为A12O3,MnS和AlN以及大量的碳化物,尺寸大多在20～150nm之间;成品板强度和延伸率较高,并具有良好的成形性能和低温冲击韧性.细晶强化是ZJ510L钢板的主要强化方式.     

Improvement in the mechanical properties of Al/SiC nanocomposites fabricated by severe plastic deformation and friction stir processing

Severely deformed aluminum sheets were processed by friction stir processing (FSP) with SiC nanoparticles under different conditions to improve the mechanical properties of both the stir zone and the heat affected zone (HAZ). In the case of using a simple probe and the same rotational direction (RD) of the FSP tool between passes, at least three FSP passes were required to obtain the appropriate distribution of nanoparticles. However, after three FSP passes, fracture occurred outward from the stir zone during transverse tensile tests; thus, the strength of the specimen was significantly lower than that of the severely deformed base material because of the softening phenomenon in the HAZ. To improve the mechanical properties of the HAZ, we investigated the possibility of achieving an appropriate distribution of nanoparticles using fewer FSP passes. The results indicated that using the threaded probe and changing the RD of the FSP tool between the passes effectively shattered the clusters of nanoparticles and led to an acceptable distribution of SiC nanoparticles after two FSP passes. In these cases, fracture occurred at the HAZ with higher strength compared to the specimen processed using three FSP passes with the same RD between the passes and with the simple probe. The fracture behaviors of the processed specimens are discussed in detail.     

低碳贝氏体钢在薄液膜下的初期腐蚀

用质量分数3.5%的NaCl溶液作为腐蚀液,滴于低碳铁素体钢、09CuPCrNi钢和低碳贝氏体钢的表面并形成薄液膜,用金相显微镜观测薄液膜下三种钢的初期腐蚀.低碳铁素体钢和09CuPCrNi钢均出现了明显的晶界择优腐蚀,而低碳贝氏体钢没有出现明显的晶界择优腐蚀.钢基体的电化学阻抗谱和极化曲线测量结果显示低碳贝氏体钢具有最高极化电阻和最小腐蚀电流,表明细晶组织的低碳贝氏体钢的初期腐蚀速率低于其他两种钢.     

E690海洋平台用钢力学性能和海洋大气腐蚀行为

以传统的E36海洋平台钢为对比钢,研究三种E690海洋平台钢的组织和力学性能,以及模拟海洋大气环境下的腐蚀行为.通过失重法测得实验钢在不同腐蚀时间下的腐蚀速率,利用扫描电镜和X射线衍射仪观察并测定了锈层的形貌特征和相组成,采用电子背散射衍射技术对实验钢的晶界类型进行分析.结果表明:以贝氏体组织为特征的E690海洋平台钢具有优异的力学性能,-40℃的冲击值超过了200J;晶界类型主要为3°～15°的亚晶界和大于50°的大角度晶界;E690海洋平台钢周浸16 d后的锈层致密且腐蚀速率已趋于稳定,最低腐蚀速率为0.84 mm.a-1,远低于组织为铁素体+珠光体钢的1.4 mm.a-1,实验钢的锈层主要由Fe3O4、α-FeOOH、β-FeOOH及γ-FeOOH四种晶态相和非晶无定形物组成.通过分析得出,热处理工艺和组织构成对材料的初期腐蚀行为有重要影响,而化学成分和锈层自身的致密性对材料后期腐蚀行为起决定作用.     

多道次摩擦搅拌处理和镁添加对Al 1050合金的微观结构和拉伸性能的影响

研究了多道次搅拌摩擦加工 (FSP) 和镁粉添加对 Al 1050 合金不同微观结构部分的影响,包括搅拌区 (SZ)、热影响区 (HAZ) 和热机械影响区 (TMAZ)等。对微观结构分析结果表明,随着 FSP 道次的增加,非复合样品和复合样品中 SZ 的晶粒尺寸减小,而非复合样品中 TMAZ 和 HAZ 的晶粒尺寸增加。此外,镁粉的加入导致了大程度的晶粒细化,增加 FSP 道次的数量导致原位复合样品中 Al–Mg 金属间化合物的分布更均匀。拉伸试验结果表明,与母材和复合材料样品相比,经过四道 FSP 的非复合材料样品表现出更高的伸长率和韧性断裂。然而,与母材和非复合样品相比,该样品表现出脆性断裂和更高的拉伸强度。与经过 FSP 的母材和非复合材料样品相比,复合材料样品的制造显着提高了硬度。     

超高强度抽油杆用非调质贝氏体钢摩擦焊接头的力学性能

以材料型超高强度抽油杆用钢 FG- 2 0为对象 ,研究了抽油杆接头力学性能与摩擦焊工艺参数之间的关系 .研究结果表明 :( 1 ) FG- 2 0钢摩擦焊焊接接头的抗拉强度稳定 ,且略高于母材 .但焊接接头的冲击韧性比母材下降 5 0 %或以上 .( 2 )通过提高顶锻压力 ,增加顶锻变形量 ,减小工进过度和轴向温度梯度 ,可明显提高 FG- 2 0钢摩擦焊焊接接头的力学性能指标及其稳定性 .( 3)在试验温度范围内 ,随回火温度的提高 ,抗拉强度下降 ;断面收缩率、延伸率和冷弯角提高 .( 4 )采用表 4中序号 9焊接工艺的接头的力学性能可满足 SY/T62 72 - 1 997标准对超高强度材料型抽油杆力学性能的要求     

磁控溅射GeSbTe相变薄膜黏附与摩擦特性

室温下通过调整磁控溅射时间制备了不同厚度的GeSbTe薄膜.利用原子力显微镜和台阶仪观察薄膜的表面形貌,测量薄膜厚度,并借助TriboIndenter纳米力学测试系统,分析探讨了薄膜的黏附和摩擦特性.研究结果表明:随着溅射时间的增加,薄膜表面粗糙度减小,厚度增加,同时表面质量提高;探针直径、相对湿度、薄膜表面质量以及探针载荷等因素对薄膜的黏附和摩擦特性均有重要影响;在满足存储要求的前提下,通过减小探针直径、降低相对湿度能够有效降低黏附力和摩擦力;而提高薄膜表面质量,为探针施加合适的载荷,有助于改善探针与薄膜表面之间的摩擦特性.     

钢/铝回填式搅拌摩擦点焊接头界面形貌和组织研究

采用回填式搅拌摩擦点焊实现了钢和铝合金板的连接。利用光学显微镜、扫描电子显微镜和电子探针X射线显微分析仪等设备观察了钢/铝点焊接头的界面形貌,并分析了钢/铝点焊接头的力学性能与界面形貌的关联机制。结果显示,钢/铝点焊接头的断裂类型为钮扣断裂,力学性能较好。钢/铝点焊接头结合良好,未见明显的焊接缺陷。在钢/铝点焊接头界面处可以观察到钩状结构和漩涡结构,这些结构提供机械互锁效果,有利于母材的结合。钢/铝点焊接头界面处形成了主要元素为Al、Fe和Si的金属间化合物层。有效的冶金结合和机械结合是钢/铝点焊接头性能良好的主要原因。     

冷却条件对2519A铝合金搅拌摩擦焊焊缝性能的影响

采用搅拌摩擦焊焊接厚度为2.75 mm的2519A铝合金板材。分别研究在空气和水流中冷却对焊接性能和焊缝组织的影响。实验结果表明:在旋转速度为2 700 r/min,焊接速度为60 mm/min条件下,水冷焊接得到美观并无明显缺陷的接头,提高了接头强度,抗拉强度达到340 MPa;在水冷条件下,热影响区的范围变窄,热影响区平均硬度提高,焊核区晶粒粒度比空冷条件下的更加小,硬度几乎呈直线分布;而在空冷条件下,焊核区硬度呈先上升后下降趋势,变化明显,水冷焊核区平均硬度低于空冷条件下平均硬度,这是因为空冷焊接能够提高固溶度并促进随后的时效发生。     

Q125级ERW用石油套管钢力学性能及CO2腐蚀行为

设计研发一种低碳的Q125级ERW用石油套管用钢。运用SEM和TEM分析实验钢的强化机制,并采用高温高压反应釜对实验钢的CO2腐蚀行为进行研究。实验结果表明:实验钢的晶粒粒径10～15μm,晶区的长度约为2μm,马氏体板条束宽度约150 nm,这些均为实验钢具有较好的强韧性配合提供条件;直径约为50 nm的圆形(Nb,Ti)(C,N)析出物,通过钉扎晶界阻止γ晶粒的粗化过程,可有效阻止奥氏体晶粒的长大;直径约20 nm的椭圆形(Nb,Ti)C以及纳米级圆形NbC析出物,可起到钉扎位错的作用,阻止位错移动,可很大程度地提高强度;实验钢腐蚀速率随着温度的增加先增大后减小,在90℃时平均腐蚀速率和点蚀速率均达到最大值;在60℃时,点蚀速率与平均腐蚀速率相差程度最大。     

紫铜的搅拌摩擦焊工艺与接头性能分析

搅拌摩擦焊是一种新型固相塑性连接方法,它的出现为铜的焊接提供了一种新的工艺.对紫铜的搅拌摩擦焊工艺进行了研究,通过工艺试验,对其焊缝成形、接头组织形态及其力学性能进行了分析.研究结果表明,搅拌摩擦焊接紫铜时应选用搅拌头旋转速度在400~700 r/min,焊接速度为35~60 mm/min;从显微组织角度,由于接头主要发生了动态再结晶,焊接接头没有热力影响区,而是三个区,即焊核区、热影响区、母材区.研究还发现用搅拌摩擦焊得到的铜接头出现了明显的软化现象,接头的机械性能比母材低,但比熔化焊得到的接头性能要高,其平均抗拉强度可达到母材的80%.     

搅拌摩擦焊机控制器的研制

搅拌摩擦焊机控制器的研制是研究FSW技术的关键之一.针对不同材料、不同规格工件时,必须使用不同的规范进行焊接,并且能在一定范围内调节摩擦功率,这也是该焊机所必须具备的性能.论述了以电流限值作为力矩自适应调节的方法,以变频调速技术为基础的主轴转速调节手段,从而保证了摩擦头在较大转速范围内改变且运行稳定,满足了不同板厚时的热量需求.同时利用MCGS软件实现了对焊接参数的控制、读取和显示.实际运行表明,该焊机控制器完全满足了设计要求.     

R.F.溅射Ba0.5Sr0.5TiO3薄膜及其光学特性研究

用R．F．磁控溅射法在石英衬底上沉积Ba0.65Sr0.35TiO3薄膜,应用XRD与SEM表征了BST薄膜的晶化行为及其表面形貌．在550℃衬底温度下沉积的薄膜,其表面光滑、晶粒大小分布均匀．应用双光束分光光度计,在200～900nm的波长范围测量了薄膜的透射光谱,并根据“包络法”理论计算薄膜的折射指数．结果表明,随着辐射波长从650nm减小到480nm,薄膜的折射率从2．04增加到2．15;随着波长进一步降低,折射率急速上升,到420nm时,折射率升至2．40,显示出典型的电子带间跃迁的色散曲线．由“包络法”和Tauc关系确定BST薄膜的光学能隙约为3．66eV．     

羟基磷灰石/氟金云母复合的生物玻璃陶瓷的力学性能

通过粉末冶金方法制备羟基磷灰石玻璃/氟金云母生物医用玻璃陶瓷材料.利用力学性能检测、显微观察和相成分分析等手段,研究烧结温度以及玻璃相含量对材料抗弯强度、断裂韧性和硬度等力学性能的影响.结果表明:随着烧结温度的升高,材料的致密度不断提高,力学性能也得到改善,对于含80%氟金云母的玻璃陶瓷而言,抗弯强度从1000℃的55.1 MPa,提高到1100℃的120.1 MPa.随着玻璃陶瓷中氟金云母的增加,材料的抗弯强度、弹性模量、断裂韧性都有所提高.当氟金云母的含量达到80%时,得到的玻璃陶瓷复合材料的力学性能最佳.组分对HA/FG生物医用玻璃陶瓷力学性能的影响主要归因于其对材料致密度、相组成和结晶度的作用.     

Effect of austempering time on microstructure and properties of a low-carbon bainite steel

The effect of austempering time after the bainitic transformation on the microstructure and property in a low-carbon bainite steel was investigated by metallography and dilatometry. The results showed that by prolonging the austempering time after the bainite transformation, the amount of large-size martensite/austenite islands decreased, but no significant change of the amount and morphology of bainite were observed. In addition, more austenite with a high carbon content was retained by prolonging the holding time at the bainite transformation temperature.Moreover, with a longer holding time, the elongation was improved at the expense of a small decrease in tensile strength. Finally, the Avrami equation B_(RF) = 1-exp(-0.0499 × t~(0.7616)) for bainite reaction at 350°C was obtained for the tested steel. The work provided a reference for tailoring the properties of low-carbon steels.     

摩擦条件对钢质摩擦材料第三体及磨损的影响

摩擦条件对摩擦材料表面第三体的连续性产生重要影响,进而影响材料的摩擦磨损性能.选用两种轨道车辆用低合金制动盘材料与铜基粉末冶金材料为配对摩擦副,在不同速度、压力条件下进行摩擦试验,观察第三体的形成过程中,表面形貌的变化规律及磨损机理.结果表明:在特定的摩擦条件下,第三体的显微硬度可达800~900HV,远高于基体材料的硬度;连续、致密的第三体,使材料具有最低的磨损率;当摩擦转速和压力过低时,磨粒磨损为主要磨损形式,当摩擦转速和压力过高时,黏着磨损将成为主导;在第三体的形成破坏过程中,摩擦速度、压力过低或过高均可能使第三体的破坏速度大于形成速度,使材料的磨损率增大.