电沉积纳米晶镍涂层的微结构与性能

采用电沉积法制备了纳米晶镍涂层，讨论了镀液中硼酸浓度对涂层晶粒尺寸的影响，并分别分析了显微硬度与平均晶粒尺寸、磨损体积及摩擦因数的关系。测试了微晶和纳米晶镍涂层的抗高温氧化性。结果表明：当硼酸在镀液中未达到饱和之前，镍的晶粒尺寸随硼酸浓度的增加而减小；当晶粒尺寸在8～20nm范围时，随着晶粒尺寸的减小，涂层的显微硬度增大，滑动摩擦因数和静摩擦因数均有所减小．耐磨性能提高，抗高温氧化性能增强。     

等离子物理气相沉积高熵合金涂层及组织性能

采用等离子物理气相沉积的方法在316L不锈钢表面制备了AlCoCrFeNi高熵合金涂层,研究了喷涂距离和电流对高熵合金涂层物相组成、表面形貌、截面形貌、硬度、结合强度和耐磨性的影响。结果表明,不同喷涂距离和电流下,高熵合金涂层都主要由BCC、B2和FCC相组成;随着电流或者喷涂距离增加,涂层中BCC平均晶粒尺寸先增后减。当喷涂距离为460 mm时,随着电流从1600 A增加至2000 A,涂层平均摩擦系数逐渐增大,表面和截面硬度先减后增,涂层结合力和结合强度先增大后减小,涂层的磨损率先增加后减小;当电流为1800 A时,随着喷涂距离从420 mm增加至500 mm,涂层平均摩擦系数逐渐减小,表面硬度先减后增,截面硬度先增后减,涂层结合力和结合强度逐渐增大,涂层的磨损率逐渐减小。高熵合金涂层的磨损率与涂层表面硬度和内聚强度都有一定相关性。     

电流密度对汽车用碳素钢上镍-铁合金箔性能的影响

研究了电流密度对汽车用碳素钢上镍-铁合金箔性能的影响。采用X射线衍射仪分析了合金箔的相结构,并计算出平均晶粒尺寸;采用显微硬度计测量了合金箔的硬度,并用称重法对合金箔在室温和高温条件下的耐磨性进行了评定。结果表明:随着电流密度的增大,合金箔中铁元素的质量分数表现为下降的趋势,平均晶粒尺寸表现为增大的趋势,硬度则表现为减小的趋势。在室温和高温条件下,合金箔的磨损量随电流密度的增大表现出相同的变化趋势。当电流密度为1.5～2.5A/dm~2时,合金箔的硬度达到4 300MPa左右,耐磨性较好。     

电流密度对银纳米晶镀层微观结构及显微硬度的影响

在硫代硫酸盐体系(无氰)下电沉积制备了银纳米膜,研究了电流密度对电沉积银纳米膜的电流效率、结合强度、微观形貌、晶粒尺寸、织构及显微硬度的影响。镀液组成为:硝酸银44g/L,硫代硫酸钠220g/L,焦亚硫酸钾44g/L,醋酸铵30g/L,硫代氨基脲0.8g/L。结果表明:在电流密度为0.20～0.35A/dm2时,镀层与基体结合良好,电流效率随电流密度的增大而先增加再减小,(111)晶面的择优取向程度逐渐减弱,(222)晶面织构增强,晶粒尺寸略有增加,显微硬度稍有减小。     

基于模具钢基体的Ni-Co合金镀层的性能研究

采用改进的瓦特型镀液,在模具钢(Cr12MoV钢)基体上电沉积Ni-Co合金镀层,并研究了电流密度对合金镀层的成分、表面形貌、硬度和耐磨性的影响。结果表明:随着电流密度的增大,Co的质量分数降低,合金镀层的表面形貌发生明显变化,其硬度先增大后减小,平均摩擦因数先降低后升高。当电流密度达到3A/dm~2时,合金镀层晶粒细化、组织致密,具有较高的硬度(4.57GPa)和良好的耐磨性(平均摩擦因数为0.3)。     

添加剂对纳米晶铜膜微观结构及纳米压痕性能的影响

采用电刷镀技术制备不同晶粒尺寸的纳米晶铜膜。利用透射电子显微镜分析电刷镀纳米晶铜膜的微观结构,计算晶粒尺寸范围;利用UNMT-1型纳米力学综合测试系统对电刷镀纳米晶铜膜进行室温纳米压痕实验。由实验可知,添加剂对纳米晶铜膜的晶粒尺寸和压痕硬度均有较大的影响。在添加剂45g/L条件下,平均晶粒尺寸最小为32nm左右,压痕硬度为3.26GPa;在添加剂1g/L条件下,平均晶粒尺寸增大到150nm左右,压痕硬度减小为1.72GPa。     

电铸铜制备小直径薄壁回转体零件

采用3D打印的圆柱体作为芯模电铸铜,得到小直径薄壁回转体零件。配方和工艺条件为:CuSO4·5H2O 200 g/L,浓硫酸60 g/L,Cl-0.05 g/L,pH 1,温度26℃,极间距3 cm,电流密度2~8 A/dm2,阴极表面线速率3.14~12.56 mm/s。研究了电流密度和阴极表面线速率对电铸铜表面形貌和显微硬度的影响。随电流密度或阴极表面线速率增大,电铸铜的晶粒得到有效细化,组织更均匀、致密,显微硬度先增大后减小。电流密度为4A/dm2,阴极表面线速率为9.42 mm/s时,电铸铜的表面形貌最好,显微硬度最高,所得回转体零件表面光滑、平整,厚度均匀。     

脉冲喷射电沉积镍工艺的研究

由于直流电沉积镍使用极限电流密度下,沉积速度低。本文介绍脉冲喷射电沉积的方法制备镍镀层。研究了脉冲频率、占空比、电流密度及糖精对镀层晶粒尺寸的影响。结果表明：镀层晶粒尺寸随脉冲频率、平均电流密度的增大而减小;随空比的增大而增大。少量糖精的加入能有效降低镀层晶粒尺寸。     

峰值电流密度对脉冲镀镍钴合金纳米镀层机械性能的影响

研究了峰值电流密度对脉冲镍钴合金纳米镀层的成分、晶粒尺寸、显微硬度、抗拉强度的影响.结果发现:在一定范围内,峰值电流密度的增大,可以降低镀层钴含量、表面粗糙度和晶粒尺寸,使菜花胞状结构更明显,提高镀层显微硬度(最高可达600 kg/mm2)和抗拉强度(最高可达1 200 MPa).然而,峰值电流密度太大又会使显微硬度和强度下降.与采用类似方法制得的纯镍纳米镀层相比,镍钴镀层的显微硬度并未明显升高.这说明在该纳米材料中,固溶强化效果并不很明显,而以细晶强化为主.     

电流密度对碳化硅电镀镍的影响

以SiC片为基体,分别在直流(DC)电源和脉冲(PC)电源下电镀Ni。研究了电流密度对Ni镀层表面形貌、粗糙度、显微硬度以及SiC和Ni镀层刻蚀选择性的影响。结果表明,随直流电流密度增大,Ni镀层的表面形貌先变好后变差,表面粗糙度先减小后增大,显微硬度和SiC/Ni刻蚀选择比逐渐减小。随脉冲电流密度增大,Ni镀层的表面形貌和粗糙度的变化趋势与直流电镀时相近,但显微硬度和SiC/Ni刻蚀选择比均逐渐增大。当电流密度较大时,在相同电流密度下脉冲电镀Ni层的各项性能均优于直流电镀Ni层。在1.4 A/dm²的平均电流密度下脉冲电镀可获得综合性能较优的Ni镀层。     

Dynamic Compaction of Cubic Boron Nitride Powders

Compacts of cubic boron nitride with 94% of theoretical density and a Vickers microhardness of 30.3 GPa were produced from coarse c-BN powder by a shock compaction technique. The density and microhardness of these compacts depend strongly on the grain size of the starting powders.     

Effect of Ti particle size on mechanical and tribological properties of TiCN coatings prepared by reactive plasma spraying

Titanium carbonitride (TiCN) coatings were successfully fabricated by reactive plasma spraying (RPS) from agglomerated Ti-graphite feedstock. The effect of Ti particle size on the microstructure and phase composition of plasma sprayed TiCN coatings was investigated. The Vickers microhardness of coatings was measured by a Microhardness Test and the corresponding Weibull distribution were also analyzed. In addition, a pin-on-disk tribometer was employed to determine the trobological properties of coatings. Results show that all the coatings consist of TiC_xN_1−x (0 ≤ x ≤1) and minor Ti₂O phases, and the amount of Ti₂O increases with the increase of Ti particle size. The Weibull distribution of Vickers microhardness of all the coatings shows apparent scattering, while the coating sprayed with Ti particle size of 28 µm exhibits a relatively even distribution. Compared with the coating sprayed with Ti particle size of 14 µm or 48 µm, the coating sprayed with Ti particle size of 28 µm exhibits improved mechanical and tribological properties, which are attributed to the high microhardness and strong bonding strength.     

等离子喷涂纳米结构AT13基涂层硬度的双态分布

利用等离子喷涂技术制备纳米结构AT13基陶瓷涂层,通过SEM观察涂层组织结构并利用HXD-1000显微硬度计测量涂层的Vickers硬度,所得结果与对应成分的常规AT13涂层进行对比,结果表明常规涂层只含有单相层片结构,而纳米结构涂层含有双态分布(完全熔化层片结构和部分熔化颗粒结构),常规涂层的硬度平均值要低于纳米结构涂层,纳米结构涂层中存在依赖于微观结构双态分布的硬度Weibull双态分布,而且完全熔化区的硬度由于组织致密明显高于部分熔化区。采用三因素三水平对等离子喷涂纳米结构涂层工艺进行设计,得到影响涂层硬度的最主要的因素是电压,其次是电流。     

脉冲喷射电沉积纳米晶镍工艺优化研究

采用脉冲喷射电沉积方法在钢基体表面制备了纳米晶镍镀层,研究了占空比、频率、平均电流密度对镀层硬度的影响,并通过正交试验对工艺参数进行优化,用扫描电镜和X-射线衍射仪对镀层表面形貌和晶粒尺寸进行分析。结果表明,制备纳米晶镍镀层的优化工艺参数为:平均电流密度39.8 A/dm2、频率1 000 Hz和占空比20%,此时镀层最致密,硬度最高(530.6 HV),纳米晶镍平均晶粒尺寸最小(13.7 nm)。     

In Situ Synthesis of TiCp/Ni3Al Composites under High Pressure

In this paper, TiC_p/Ni₃Al composites are synthesized in situ at near theoretical density under high-pressure (1.56.5 GPa), high-temperature (1073–1473 K) conditions. The grain size of TiC-reinforced particles is nanometer scale, which influences the Vickers microhardness of the composites. The effect of pressure on the grain size of TiC is discussed.     

Effect of alternating current electric field on microstructure and properties of laser cladding Ni–Cr–B–Si coating

The effects of alternating current (AC) on the morphology, microstructure and property of the laser cladding Ni–Cr–B–Si coatings were studied. The experimental results showed that the surface morphology of the coating was wavy due to the skin effect and the alternating electromagnetic force produced on the surface of the molten pool under the action of the AC. Electric field could increase the nucleation rate and refine grain size, thus the structure in the bottom of the coating transformed from dendrite to equiaxed crystal. However, alternating current did not change the phase type in the coating. Furthermore, due to the refinement of the grain structure at the bottom of the coating, the number of cracks in the coating was reduced by 60%. The average microhardness of the coating increased, and the corrosion resistance was also improved under the AC electric field.     

Effects of WC addition on the erosion behavior of high-velocity oxygen fuel sprayed AlCoCrFeNi high-entropy alloy coatings

In this study, AlCoCrFeNi (H1), AlCoCrFeNi+25 wt%WC-10Co (H2), and AlCoCrFeNi+50 wt%WC-10Co (H3) high-entropy alloy (HEA)/tungsten carbide (WC) composite coatings were deposited onto 316 stainless steel substrates by applying the high-velocity oxygen fuel spraying technology. The phase, layered microstructure, microhardness, and erosion behavior of the coatings were analyzed by performing X-ray diffractometry, scanning electron microscope/energy dispersive spectrometry, Vickers microhardness testing, and slurry erosion testing. The effects of WC addition on the erosion behavior and mechanism of the coatings at different flow velocities were investigated. The deposited coatings were compacted and adhered well to the substrate. The AlCoCrFeNi coating was composed of BCC and FCC phases. The porosity of the H1, H2 and H3 coatings were 0.24%, 0.33% and 0.45%, respectively, and were less than 1%. The microhardness of the HEA/WC composite coatings was positively correlated with WC content. The volume loss and rate of volume loss of the coatings decreased with the addition of WC. The erosion mechanism of the AlCoCrFeNi coating was typical ductile wear, with a small amount of interlayer peeling. Furrows, cuttings, and plastic deformation caused by low grazing angles contributed to the failure of the AlCoCrFeNi coating. In the HEA/WC composite coatings, WC protected the HEA from more severe plastic deformation by second-phase strengthening, and the main erosion mechanism of WC was gradual brittle detachment caused by high-grazing-angle erosion in which craters, cracks, and massive spalling were responsible for the erosion process.     

Electrodeposition of Zn–SiC nanocomposite coatings

Zn–SiC composite coatings were obtained on mild steel substrate by electrodeposition technique with high-current efficiency. A slightly acidic chloride bath, containing SiC nanoparticles and gelatine as additive, was used. The electrodeposition was carried out under galvanostatic control with pulsed direct current; the effect of experimental parameters (temperature, average current density and particles concentration) on composition, morphology and structure of the deposit was studied. Coatings were characterized by means of scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffractometry and Vickers microhardness measurements. Zn–SiC electrodeposits with the best characteristics were obtained by performing electrodepositions at 45 °C, with 20 g L^?1 SiC in the bath and with average current density in the range 100–150 mA cm^?2. Under these experimental conditions, homogeneous and compact coatings, with low-grain size and SiC content ranging from 1.7 to 2.1 wt%, were found to be electrodeposited. Microhardness measurements showed for these deposits an increase of about 50 % with respect to those without nanoparticles obtained in the same experimental conditions.     

Optimization of microstructure and properties of composite coatings by laser cladding on titanium alloy

Recently, the current technological progress in developing laser cladding technology has brought new approaches in surface modification of titanium alloys. Herein, composite coatings were fabricated by the laser cladding process on Ti811 alloys using a coaxial powder feeding method. A comprehensive study was performed on the laser energy density (L_ed) and CeO₂ content on the structure distribution, microhardness and tribological properties of the coatings. In addition, the growth mechanism of the TiC–TiB₂ structure was studied based on the Bramfitt two-dimensional lattice mismatch theory. The results indicated that the phase composition of the coating mainly contained TiC, TiB₂, Ti₂Ni, and α-Ti. The optimized coating contributed to uniform microstructure distribution and fine grain size when L_ed was 45 J/mm² and the CeO₂ content was 2 wt%, playing an important role in the best forming quality and properties. Besides, the high matching degree of an interface between TiC (111) and TiB₂ (0001) contributed to the TiC–TiB₂ composite structure, which positively influenced the grain size and distribution of TiC. The microhardness and wear resistance of the 2Ce coating was dramatically enhanced due to the fine grain strengthening and dispersion strengthening effects of CeO₂, contributing directly to generate a high average hardness of 811.67 HV_0.5 with a lower friction coefficient.