Fabrication of high hardness and corrosion resistance coatings from Fe-based alloy powders

Gas atomized Fe₅₀Cr₂₄Mo₂₁Si₂B₃ powders were used to form Fe-based alloy coatings by the air plasma spray method. The coatings exhibited high amorphous nature and extremely low porosity of 0.41% in about 200 µm thickness. The Fe-based coating exhibits an average hardness about 1255 Hv. The Fe-based coatings could be potentially applied as functional surface protective coatings.     

电沉积Co-Ni合金镀层结构及硬度的研究

采用氨基磺酸体系电解液电沉积Co-Ni合金，研究了电解液中钴、镍金属离子浓度与合金镍层中钴含量的关系。利用扫描电子显微镜和X射线衍射分析测定了不同钴含量沉积层的微观形貌和晶体结构，同时研究了合金沉积层显微硬度和合金成份的关系及热处理的影响。实验结果表明：电解液中Co^2 /(Co^2 Ni^2 ）在0.1-0.5的范围内时，钴离子的优先共沉积的趋势最强。SEM观察结果和XRD分析测试表明，随着钴镍合金沉积层中钴含量的不断增加，低钴含量合金层粗大的颗粒状结晶逐渐转变为细致、均匀的三角形状结晶，最终又形成中等大小的颗粒状结晶。同时合金层中钴含量的逐渐增加，结构由fcc镍固溶体过渡为fcc的钴固溶体，最后转变为hcp的钴固溶体。并且在形成两个钴固溶体的钴含量范围内（20％－50％和60％－80％），所对应的钴镍合金层的硬度值远大于低钴含量区所具有fcc镍固溶体结构的合金层硬度。     

Adhesion and hardness of ion-plated TiC and TiN coatings

The microhardness and adhesion of TiC coatings on steel and cemented carbide are studied. A comparison with TiN coatings is also made. It is found that the minimum coating thickness in which a reliable microhardness measurement can be made is described satisfactorily by existing standards; departures can be expected if the coating is strongly textured. The critical load for the removal of the coating by the scratch test depends on both the coating and the substrate and is thought to reflect their mechanical properties. It appears that marked variations in the strength and nature of adhesion on cemented carbides can occur.     

Covalent-bonded graphyne polymers with high hardness

Eight covalent-bonded graphyne polymers have been proposed using the newly developed USPEX and CALYPSO methods based on the first-principle calculations. These polymers are energetically more favorable than the corresponding graphyne under ambient pressure, and seven of them are more stable than fullerene C₆₀, indicating their existence possibilities. The mechanical and dynamic stabilities of these crystal structures have been confirmed by calculating their elastic constants and phonon dispersion curves, respectively. The newly developed variable-cell nudged elastic band (VC-NEB) simulations show that the graphyne → polymer transformation exhibits lower energy barrier than the graphite → diamond transformation. Two of the graphyne polymers have been found to be superhard, and the others are hard materials. These graphyne polymers possess tunable electronic properties from metallic to semiconductive.     

Superior hardness and Young's modulus of low temperature nanocrystalline diamond coatings

Nanocrystalline diamond (NCD) coatings with thickness of about 3 μm were grown on silicon substrates at four deposition temperatures ranging from 653 to 884 °C in CH₄/H₂/Ar microwave plasmas. The morphology, structure, chemical composition and mechanical and surface properties were studied by means of Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD), Raman spectroscopy, nanoindentation and Water Contact Angle (WCA) techniques. The different deposition temperatures used enabled to modulate the chemical, structural and mechanical NCD properties, in particular the grain size and the shape. The characterization measurements revealed a relatively smooth surface morphology with a variable grain size, which affected the incorporated hydrogen amount and the sp² carbon content, and, as a consequence, the mechanical properties. Specifically, the hydrogen content decreased by increasing the grain size, whereas the sp² carbon content increased. The highest values of hardness (121 ± 25 GPa) and elastic modulus (1036 ± 163 GPa) were achieved in NCD film grown at the lowest value of deposition temperature, which favored the formation of elongated nanocrystallites characterized by improved hydrophobic surface properties.     

Microstructural characterization and hardness of electrodeposited nickel coatings from a sulphamate bath

Pure nickel plates were produced from a sulphamate bath by electrodeposition. A systematic variation of the current density, in the range 0.005 to 0.25 Acm^–2, resulted in a variation of the coating microstructure and properties. Deposits plated below a current density of 0.01 Acm^–2 had a surface morphology consisting of large, deep crevices surrounding smaller substructures. A banded or laminar type microstructure was observed in cross-section. Above this current density, truncated pyramidal structures, with ridged terraces oriented perpendicular to the growth direction, were found on the surface. The planar dimensions of the pyramidal surface features were found to increase with current density, as well as the columnar grain widths observed in the cross-sectional view. To evaluate the mechanical properties of the coatings, microindentation hardness tests were performed using a Knoop indenter. A Hall–Petch type relationship for the samples deposited at and above 0.01 Acm^–2 was seen.     

Structure,hardness and tribological properties of nanolayered TiN/TaN multilayer coatings

TiN/TaN coatings, consisting of alternating nanoscaled TiN and TaN layers, were deposited using magnetron sputtering technology. The structure, hardness, tribological properties and wear mechanism were assessed using X-ray diffraction, microhardness, ball-on-disc testing and a 3-D surface profiler, respectively. The results showed that the TiN/TaN coatings exhibited a good modulation period and a sharp interface between TiN and TaN layers. In mutilayered TiN/TaN coatings, the TiN layers had a cubic structure, but a hexagonal structure emerged among the TaN layers besides the cubic structure as the modulation period went beyond 8.5 nm. The microhardness was affected by the modulation period and a maximum hardness value of 31.5 GPa appeared at a modulation period of 8.5 nm. The coefficient of friction was high and the wear resistance was improved for TiN/TaN coatings compared with a homogenous TiN coating, the wear mechanism exhibited predominantly ploughing, material transfer and local spallation.     

Adaptive neuro-fuzzy approach for predicting hardness of deposited TiN/ZrN multilayer coatings

This paper presents an adaptive neuro-fuzzy approach based on first order function of fuzzy model for establishing the relationship between control factors and thin films properties of TiN/ZrN coatings on Si(100) wafer substrates. A statistical model was designed to explore the space of the processes by an orthogonal array scheme. Eight control factors of closed unbalance magnetron sputtering system were selected for modeling the process, such as interlayer material, argon and nitrogen flow rate, titanium and zirconium target current, rotation speed, work distance, and bias voltage. Analysis of variance (ANOVA) was carried out for determining the influence of control factors. In this study, with the application of ANOVA, the smallest effect of control factors was eliminated. The adaptive neuro-fuzzy inference system (ANFIS) was applied as a tool to model the deposited process with five significant control factors. The experimental results show that ANFIS demonstrates better accuracy than additive model for the film hardness. The root mean square error between prediction values and experimental values were archived to 0.04.     

Structure, hardness and thermal stability of nanolayered TiN/CrN multilayer coatings

Nanolayered TiN/CrN multilayer coatings were deposited on silicon substrates using a reactive DC magnetron sputtering process at various modulation wavelengths (Λ), substrate biases (V_B) and substrate temperatures (T_S). X-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) were used to characterize the coatings. The XRD confirmed the formation of superlattice structure at low modulation wavelengths. The maximum hardness of the TiN/CrN multilayers was 3800 kg/mm² at Λ=80  Å, V_B=−150 V and T_S=400°C. Thermal stability of TiN, CrN and TiN/CrN multilayer coatings was studied by heating the coatings in air in the temperature range (T_A) of 400-800°C. The XRD data revealed that TiN/CrN multilayers retained superlattice structure even up to 700°C and oxides were detected only after T_A?750°C, whereas for single layer TiN and CrN coatings oxides were detected even at 550°C and 600°C, respectively. Nanoindentation measurements showed that TiN/CrN multilayers retained a hardness of 2800 kg/mm² upon annealing at 700°C, and this decrease in the hardness was attributed to interdiffusion at the interfaces.     

The effects of nitrogen bonding on hardness of AIN/CrN multilayer hard coatings

AIN/CrN multilayer hard coatings with various bilayer thicknesses were fabricated by a reactive sputtering process. The microstructural and mechanical characterizations of multilayer coatings were investigated through transmission electron microscope (TEM) observations and the hardness measurements by nano indentation. In particular, the variation of chemical bonding states of the bilayer nitrides was elucidated by near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Many broken nitrogen bonds were formed by decreasing the bilayer thickness of AIN/CrN multilayer coatings. Existence of optimum AIN/CrN multilayer coatings thickness for maximum hardness could be explained by the competition of softening by the formation of broken nitrogen bonds and strengthening induced by decreasing bilayer thickness.     

Analysis of hardness of nanocrystalline coatings of aluminum-rich Ti1???x Al x N

Titanium aluminum nitride coatings were fabricated by a d.c. magnetron sputtering system from a Ti?CAl (60/40?wt%) target. Coatings were deposited on steel substrates, at a substrate temperature of 250?°C and a bias voltage of ?80?V. The nitrogen flow was varied from 1·5?C6?sccm and the Ar flow was kept constant at 20?sccm. The morphology and microstructure of the coatings were analysed by X-ray diffraction and scanning electron microscopy. The results of X-ray diffraction showed the presence of two cubic crystalline phases, TiN and AlN, which were confirmed by X-ray photoelectron spectroscopy. The Vicker hardness was obtained by the effective model of indentation. It was observed that the hardness of the coatings decreases from 22·8?C9·5?GPa with an increased nitrogen content from 1·5?C4·5?sccm. Subsequently, the hardness increased to 22·1?GPa by increasing nitrogen to 6?sccm. The behavior of hardness with grain size variation is consistent with the Hall-Peth relationship. The high value in the hardness of the coatings is mainly attributed to small grain sizes and the compressive stress present.     

The mechanical properties of wear-resistant coatings: II: Experimental studies and interpretation of hardness

In the preceding paper we described a law of mixtures model of hardness for hard coatings on soft substrates. In this paper we validate this model with extensive experimental measurements of hardness for titanium nitride and tungsten-titanium carbide deposited onto a range of metallic and non-metallic substrates. The goodness of fit obtained using this model is found to be superior to that obtained using other models described in the literature. In addition, it is found that the hardness behaviour of coated systems is sensitive to both the relative sizes of the plastic zones of the substrate and coating (as calculated from the spherical cavity model for indentation) and the degree of adhesion of coating to substrate. Hence it is concluded that the hardness test may provide information complementary to that provided by the scratch adhesion test.     

A device for simultaneous determination of the impact resistance and hardness of insulating coatings of pipelines

We propose a hand-operated device for simultaneous determination of the impact resistance and hardness of anticorrosive insulating coatings, which completely models the work of a U-1 standard vertical impact testing machine. The proposed device is a prototype of the Poldi impact hardness gauge, however, unlike the latter, our device is used with a hammer of mass 1 kg, which equates it to the U-1 impact testing machine and enables one to determine simultaneously the hardness and impact resistance of protective coatings. When the hammer strikes, the indenter contacts simultaneously with the coating and indicator metal (a square bar), which has been calibrated on the U-1 impact testing machine and a stationary hardness gauge. This calibration results in a relation between the diameter of indentation and the energy of impact with a one-kilogram weight. Striking upon our device with a one-kilogram weight, measuring the diameter of indentation on the bar, and using the relation mentioned above, we can find the impact resistance, and the ratio between the diameters of indentations on the bar and coating enables us to determine its hardness according to GOST 18661-73.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 2, pp. 116–119, March–April, 2004.     

Homogenization of hardness distribution and distortion in high pressure gas quenching

Quenching with gases rather than oil or other liquid media has the advantages of reducing the risks concerning health and environment, while simultaneously homogenizing the quenching results and minimizing distortion due to a wide range of possible process parameter variations and the pure convective heat transfer. In this contribution, a coupled solution for increasing homogenization of quenching results within high pressure gas quenching will be presented. In the first stage, an experimental test facility was set up for flow investigations and in the second stage a numerical simulation model was generated. The numerical and experimental results of the flow through the chamber were compared for several boundary conditions. Finally, after complete verification of the simulation, the model may be used to assist in parameter variation for optimization of homogeneous high pressure gas quenching.     

高硬质NR/BR并用胶的增硬补强体系研究

研究了苯甲酸、酚醛树脂和高苯甲烯/C8树脂三类增硬补强剂对高硬质NR/BR并用胶的增硬补强效果.实验结果表明:苯甲酸增硬效果明显,尤其用量在3.0份时,胶料硬度大幅度提高,但是对其它力学性能有一定的损害;酚醛树脂的增硬效果最好,特别适合于制作邵A硬度95以上的超高硬度制品;高苯乙烯/C8树脂的增硬程度相对较小,但是所获得胶料的综合物理性能最好.     

非晶陶瓷涂层对耐高温液锌涂层耐腐蚀性能的影响

热镀锌技术是钢铁材料表层最为有效的防腐蚀手段。为进一步提高耐锌蚀涂层的使用寿命,采用等离子喷涂技术在熔锌装备表面制备了多级耐锌蚀复合涂层及非晶陶瓷涂层,并利用XRD和SEM对其物相组成、结构及形貌进行了研究。结果表明,非晶陶瓷涂层与熔融锌液存在着不浸润,但耐锌蚀涂层仍然会被腐蚀,镀锌装备内部由于存在温度差使得熔融锌液会进行上下、左右的流动,对非晶层会产生冲刷作用,长时间的冲刷会使非晶层变薄,直至消失。非晶陶瓷涂层的制备在一定程度上降低了加热管的导热性,但可以通过加大功率来进行弥补,封孔后的耐锌蚀涂层的热震性能提高了6倍,使用寿命是原来的2.2倍,延长寿命效果显著。