Effect of Electroplating Parameters on Microstructure of Nanocrystalline Nickel Coatings

In order to achieve the optimum conditions for electroplating nanocrystalline nickel coating from Watts-type bath, the effect of some process parameters namely, bath temperature, current density, and saccharin addition on grain size and texture coefficient (TC= I(200)/I(111)) of the deposits were investigated by X-ray diffraction (XRD). The results showed that in a bath containing 5 g/L saccharin, by increasing the bath temperature from 45°C to 55°C, the grain size decreased, whereas further increase of bat...     

Effect of Nickel on the Microstructures of Coating in Hot-Dipped Aluminide Steel

Hot-dipping aluminizing of 45 steel was carried out in molten Al baths containing 0.0, 1.0, 3.0, and 5.0 wt.% Ni at 710°C for 10, 120, 300, and 600 s. The coatings were analyzed by x-ray diffraction (XRD) and scanning electron microscope (SEM) equipped with energy-dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD). The coating hot-dipped in the Al-5Ni bath consisted of an outer Al-Ni topcoat (α-Al, θ-Al₃Fe, Al₃Ni, τ₁-Al₉FeNi), minor τ₁-Al₉FeNi, minor θ-Al₃Fe, and major η-Al₅Fe₂ layers, respectively, while no τ₁-Al₉FeNi layer was identified in the coating hot-dipped in the Al-1Ni and Al-3Ni bath. Diffusion path model was introduced to explain this phenomenon. Ni as an alloying element added into Al bath decreased the growth rate of η-Al₅Fe₂ layer. The average thickness of η-Al₅Fe₂ layer followed the parabolic law in hot-dipping in the Al-5Ni bath. Also, η-Al₅Fe₂ had the largest growth rate among the intermetallic layers.     

HP40Nb钢热浸镀Al-Si高温氧化行为及组织研究

为提高高温抗氧化性能,对HP40Nb钢进行了热浸镀Al-10%(质量分数)Si,并进行不同温度扩散处理,研究了不同扩散处理试样在1000℃条件下的高温氧化行为,通过SEM,EDS和XRD分析了经不同扩散处理后的渗层在高温氧化过程中的组织结构变化.结果表明:经800℃/4h扩散处理,渗层由内层(NiAl+ Cr3 Si)...     

Effects of Forging and Heat Treatments on the Microstructure and Oxidation Behavior of 316LN Stainless Steel in High Temperature Water

Microstructure of 316 LN stainless steel(ss),including the as-received material and samples processed by solution anneal treatment and stress relief treatment after forging,was characterized by Vickers hardness(HV) testing and electron back scattering diffraction(EBSD).The oxide film formed on samples after immersion in borated and lithiated water at 583.15 K was investigated by scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS).Results showed that the grain size of samples was largely reduced after forging.Higher fraction of coincidence site lattice(CSL) boundaries and lower residual strain were observed in samples with either solution anneal treatment or stress relief treatment.The proportion of CSL boundaries was largely enhanced by solution anneal treatment after forging,due to the recrystallization occurring during solution anneal treatment.The oxide film grown on 316 LNss with solution anneal treatment after forging exhibited more strong protectiveness,as compared to the oxide film grown on samples with stress relief treatment after forging and the oxide film grown on asreceived samples without forging.The mechanisms of oxidation were then discussed.     

AISI 316L不锈钢表面沉积Ti掺杂金刚石薄膜及其性能

为了进一步评价医用材料AISI 316L不锈钢表面沉积掺杂Ti类金刚石薄膜的应用性能,采用离子束辅助沉积技术在AISI 316L不锈钢表面沉积了掺杂Ti类金刚石(DLC-Ti)薄膜.分别利用X射线衍射仪、扫描电子显微镜、摩擦磨损试验机、电化学工作站及纳米压痕仪对DLC-Ti薄膜的晶体结构,表面与截面形貌,摩擦磨损性能,电化学性能,硬度和弹性模量进行了表征.结果表明:DLC-Ti薄膜的摩擦系数超低(0.017～0.029)且未出现磨损,自腐蚀电位和点蚀电位相对于基体向正电位方向移动.DLC-Ti薄膜综合性能较好,在整形外科及刀具等应用方面具有很好的前景.     

Microstructure and Fracture Behavior of 316L Austenitic Stainless Steel Produced by Selective Laser Melting

Selective laser melting is an additive manufacturing method based on local melting of a metal powder bed by a high power laser beam. Fast laser scans are responsible for severe thermal gradients and high cooling rates which produce complex hydrodynamic fluid flow. These phenomena affect crystal growth and orientation and are believed to be the cause of material spattering and microstructural defects, e.g.pores and incompletely melted particles. In this work, the microstructure and texture of 316 L bars built along two different orientations and the effect of different distribution of defects on their mechanical response and failure mechanisms were investigated. Partially molten powder particles are believed to be responsible for the scattering in elongation to failure, reduced strength, and premature failure of vertical samples.     

High temperature oxidation of Ni–W coatings electroplated on steel

The high-temperature oxidation of Ni–16 at.% W coating electroplated on the steel substrate was studied at 700 and 800 °C in air. Before oxidation, the coating consisted of supersaturated, nanocrystalline Ni grains. During oxidation, oxygen diffused inward, Ni and the substrate elements such as Fe and Cr diffused outward. The outer NiO layer was not pure but had some dissolved ions of W⁶⁺ and Fe³⁺. Some Fe³⁺ ions were dissolved in the inner (NiO+NiWO₄) mixed layer, below which (W, Fe)-supersaturated, unoxidized Ni grains existed. Below these grains, tiny Ni–W–Fe precipitates, which were formed by the outward diffusion of Fe from the substrate, were surrounded by unoxidized (Fe-enriched, Cr-containing) Ni grains. Detailed oxidation mechanism of Ni–16 at.% W coating is proposed.     

Experimental and Simulative Failure Analysis of AISI 316L Stainless Steel Screw Shaft

This paper presents a study on failure analysis of a screw shaft in a pure terephthalic acid screw conveyor after about 6-year operation. A series of characterization analysis were performed by careful visual observation, mechanical properties tests, chemical content examination, microstructural analysis and microchemical analysis of nonmetallic inclusions. Furthermore, the outer surface topography of the shaft at the fracture position was measured by three-dimensional scanning method. Finite element method considering surface topography was also employed to define the evolution of critical region. Results reveal that the serious stress concentration resulted from structure discontinuity including small radius at the transition and surface roughness was the main reason leading to the crack initiated and propagated, and the latter one was proved to be the biggest driving. To prevent the failure, better controls of surface state and structure size were strongly recommended.     

316L不锈钢焊接接头高温低周期疲劳显微结构变化和断裂特征

本研究对316L奥氏体不锈钢母材和焊缝分别进行高温低周疲劳试验,对试样的微观结构和裂纹扩展形貌进行观察,分析母材和焊缝在高温低周疲劳循环应力响应下的位错结构和损伤机制。结果表明,316L奥氏体不锈钢母材在试验过程中由于位错增殖和位错湮灭导致发生循环硬化和循环稳定,在焊缝中由于位错湮灭导致发生循环软化。母材和焊缝在连续低周疲劳试验中裂纹主要以穿晶方式扩展,焊接接头处孔洞的连接是最终导致焊接接头疲劳断裂的主要机制。     

表面纳米化对316L不锈钢抗点蚀性能的影响

分别对未表面纳米化、表面纳米化和表面纳米化后退火处理的316L不锈钢的样品进行点蚀试验,在3.5%NaCl水溶液中分别测出它们的极化曲线.结果表明,316L不锈钢表面纳米化后抗点蚀性能下降;表面纳米化后经退火处理的316L不锈钢随退火温度的升高和退火时间的延长抗点蚀性能会重新恢复.     

钎缝间隙对316L不锈钢真空钎焊接头组织的影响

采用镍基钎料BNi2+40%BNi5对316L不锈钢进行真空钎焊。主要通过光学显微镜、电子探针显微分析仪、硬度计等研究了3种钎缝间隙下钎焊接头的显微组织、钎缝成分分布以及钎缝显微硬度。结果表明316L不锈钢的钎焊接头主要由固溶体、共晶组织及网状化合物组成,硼、硅是导致化合物相产生的主要合金元素;随着钎缝间隙的减小,钎焊接头中金属间化合物相的含量逐渐减小,当钎缝间隙为30μm时,接头组织基本为固溶体。     

Development and Oxidation Behavior of Al-Cu-Fe Quasicrystalline Coating on Ti Alloy

An oxidation resistant Al-Cu-Fe quasicrystalline coating was fabricated on substrate of Ti alloy by low pressure plasma spraying (LPPS) method. As-sprayed Al-Cu-Fe coating has a rapidly solidified lamellar microstructure consisting of quasicrystalline phase and crystalline phase. The formation of quasicrystalline coating is related to the annealing. The results from the ox!dat!on experiments showed that Al-Cu-Fe quasicrystalline coating improved the oxidation resistance of Ti-base alloys. During the oxidation period there is no evident spallation of the coating from the substrate. Oxide formed on the surface of Al-Cu-Fe quasicrystalline coating after oxidation consisted of Al2O3. Oxidation occurs Ieading to a change of concentration and phase transformation in the coating surface. Selective oxidation of AI transforms the quasicrystalline phase into the phase.     

316L不锈钢焊缝的点蚀行为

采用数显恒温水浴锅HH-4静态模拟点腐蚀的试验方法,研究316L奥氏体不锈钢焊缝在不同Cl^-浓度和温度下的三氯化铁溶液中点腐蚀行为,探讨不同的Cl^-浓度和温度变化对焊缝耐蚀性能的影响。结果表明：在三氯化铁溶液中,Cl^-浓度增加、温度升高,316L奥氏体不锈钢焊缝的耐点蚀性能下降,腐蚀速率增加,腐蚀后的表面形貌为不均匀点腐蚀。     

Microstructure and Corrosion Resistance of Dissimilar Weld-Joints between Duplex Stainless Steel 2205 and Austenitic Stainless Steel 316L

The microstructure and corrosion resistance of dissimilar weld-joints between stainless steel SAF 2205 and stainless steel AISI 316 L were investigated. Welding was accomplished by different types of welding wires AWS ER 347, AWS ER 316 L and AWS ER 309 L. To verify soundness of welded samples, nondestructive tests were performed. Metallographic samples were prepared from cross-section areas of weldjoints to investigate microstructure of different regions of weld-joints by optical microscopy and scanning electron microscopy. Corrosion resistance of weld-joints was evaluated in NaCl solution by potentiodynamic polarization and electrochemical impedance techniques. In the weld metal AWS ER 347, the brittle sigma phase was created, resulting in the decrease of weld-joint corrosion resistance. According to the results of metallurgical investigations and corrosion tests, welding wire AWS ER 309 L was suitable for welding duplex stainless steel(SAF 2205) to austenitic stainless steel(AISI 316L) by gas tungsten arc welding(GTAW)process.     

扩散工艺对渗铝钢循环氧化和剥落性能的影响机理研究

通过不同扩散工艺实验,研究了热浸渗铝钢的抗氧化和剥落性能及其机理.结果表明,随扩散温度升高和时间延长,扩散层的空洞不断增加,次外层和过渡层之间空洞逐步聚集连接成波浪线状空洞带.在高温氧化期间,空洞带又连接成平行于表面的线状裂纹,其内部产生了内氧化.因此,渗铝钢的抗循环氧化和剥落性能不仅与扩散层组织和表面的氧化速度有关,而且与扩散层的空洞和内氧化有关.最佳的扩散工艺参数是900℃×2h.     

AISI 316奥氏体不锈钢等离子体源渗氮及其耐磨抗蚀性能

目前,对AISI 316奥氏体不锈钢单一面心结构γΝ相改性层耐磨抗蚀性能的报道差异较大,有些甚至相互矛盾。采用等离子体源渗氮技术,于450℃,6 h改性AISI 316奥氏体不锈钢,获得了厚度约为17μm、峰值氮浓度20%(原子分数)、最大显微硬度1 510 HV0.1 N、单一面心结构的γΝ相改性层。分别采用WTM-2E球盘式磨损仪和PARSTAT2273电化学工作站,研究了干摩擦条件下γN相/Si_3N_4陶瓷球的摩擦磨损行为和在3.5%NaCl溶液中的电化学腐蚀行为,揭示了γN相改性层的耐磨抗蚀机理。结果表明:γΝ相改性层的磨损机制由原不锈钢的黏着磨损转变为氧化磨损,摩擦系数由0.88降低至0.65,磨损体积由0.13 mm~3降低到9.50×10-3mm~3,耐磨性能显著提高;γΝ相改性层阳极极化曲线未发生点蚀击穿过程,容抗弧直径增大,相位角平台变宽;采用等效电路Rs-(Rct//CPE)拟合的电荷转移电阻Rct由原不锈钢的1.006×105Ω·cm~2增至1.377×106Ω·cm~2,计算的双电层电容Cdl由88.4m F/cm~2降低至77.8 m F/cm~2,抗蚀性能明显得到了改善。     

无镍铬低比重铸造不锈钢的组织和性能的研究

设计并制备出一种新型无镍铬铸造不锈钢材料。利用光学显微和扫描电镜对其组织物征进行了观察，并对其力学性能、耐热耐蚀性进行了测试研究。结果表明：本文所设计的无镍铬不锈钢具有优异的力学性能，良好的高温抗氧化性和耐海水腐蚀性，且达到ＺＧ３０４、ＺＧ３０４不锈钢的性能指标。     

电爆法制备纳米铜颗粒的微结构特征及其氧化行为研究

本文利用扫描电镜（SEM）、高分辨透射电镜（HRTEM）、X-射线衍射（XRD）和热分析技术等,对电爆法制备的纳米铜（Cu）颗粒的微观形貌、晶体结构特征,以及高温氧化性能进行了较为详细的表征和测试。实验发现,1）纳米铜（Cu）颗粒具有完整的晶体结构,有轻微的软团聚,粒径分布在60～80nm之间,平均粒径约为78nr／l;颗粒表面有一层钝化的非晶态膜。2）在空气气氛中,从室温加热到1200℃时,其氧化过程中的相转变为Cu→CuO2→CuO→CuO2,即,在198℃开始被氧化,在275℃后完全被氧化;低温时,主要产物为CuO;而高温时,主要为Cu2O。     

激光选区熔化成型316L不锈钢的工艺参数对硬度与微观组织的影响

激光选区熔化(Selective laser melting,SLM)技术能够制备复杂的一体化空间构件,是金属增材制造的主要方法之一.然而,目前SLM技术仍存在一些问题,如工艺参数对性能的影响规律复杂等,这极大地限制了SLM技术的推广和应用.因此,选择激光功率、扫描速度、扫描间距和相邻层之间的旋转角度四种SLM工艺参数进行分析,设计正交实验,制备了316L不锈钢材料的试样,表征了SLM成型试样的尺寸精度、相对密度和硬度,并观察其宏观结构和微观组织.以激光能量密度为因变量,研究其对成型316L不锈钢材料性能的影响,实现了多输入变量到单输入变量的降维,简化了SLM工艺参数对成型材料力学性能和微观结构的复杂影响规律.结果表明,当输入的激光能量密度在65～90 J/m3之间时,316L不锈钢的相对密度在99.6％以上;当激光功率为180 W、扫描速度为870 mm/s时,316L不锈钢的晶粒均匀,其形状近似正六边形,晶粒度为0.4μm.SLM成型的316L不锈钢相对密度与硬度有一定的关联性,当相对密度高于99.0％时,试样的硬度较高,约为250HV.