Effects of milling and subsequent consolidation treatment on the microstructural properties and hardness of the nanocrystalline chromium carbide powders

The influence of milling and subsequent consolidation treatments on the microstructural properties and hardness of the fabricated Cr₃C₂, Cr₇C₃ and Cr₂₃C₆ ceramic powders are investigated. For this reason, the elemental powders of Cr and C were mixed with proper ratio and then milled to the nanometer crystallite sizes (between 6 and 20 nm) and then were consolidated by using uniaxial cold press and subsequent heat treatment (at 1100 °C for 1 h) in Argon atmosphere. Microstructures of consolidated samples were characterized using X-ray diffraction (XRD) and microhardness measurements. A drastic increase in crystallite size of the samples was observed due to the effect of heat treatment. However, the as-consolidated samples still maintained their nanocrystalline characteristic with an average grain size of less than 100 nm. Besides, a very high hardness of 25 GPa was achieved for the Cr₃C₂ composition. This high hardness is attributed to the formation of carbide phases in the consolidated samples.     

Influence of Temperature on the Inverse Hall-Petch Effect in Nanocrystalline Materials:Phase Field Crystal Simulation

The influence of temperature on the inverse Hall-Petch effect in nanocrystalline(NC) materials is investigated using phase field crystal simulation method.Simulated results indicate that the inverse Hall-Petch effect in NC materials becomes weakened at low temperature.The results also show that the change in microscopic deformation mechanism with temperature variation is the main reason for the weakening of the inverse Hall-Petch effect.At elevated temperature,grain rotation and grain boundary(GB) migration seriously reduce the yield stress so that the NC materials exhibit the inverse Hall-Petch effect.However,at low temperature,both grain rotation and GB migration occur with great difficulty,instead,the dislocations nucleated from the cusp of serrated GBs become active.The lack of grain rotation and GB migration during deformation is mainly responsible for the weakening of the inverse Hall-Petch effect.Furthermore,it is found that since small grain size is favorable for GB migration,the degree of weakening decreases with decreasing average grain size at low temperature.     

Influence of Temperature on in Nanocrystalline Materials： the Inverse Hall-Petch Effect Phase Field Crystal Simulation

The influence of temperature on the inverse Hall-Petch effect in nanocrystalline(NC) materials is investigated using phase field crystal simulation method.Simulated results indicate that the inverse Hall-Petch effect in NC materials becomes weakened at low temperature.The results also show that the change in microscopic deformation mechanism with temperature variation is the main reason for the weakening of the inverse Hall-Petch effect.At elevated temperature,grain rotation and grain boundary(GB) migration seriously reduce the yield stress so that the NC materials exhibit the inverse Hall-Petch effect.However,at low temperature,both grain rotation and GB migration occur with great difficulty,instead,the dislocations nucleated from the cusp of serrated GBs become active.The lack of grain rotation and GB migration during deformation is mainly responsible for the weakening of the inverse Hall-Petch effect.Furthermore,it is found that since small grain size is favorable for GB migration,the degree of weakening decreases with decreasing average grain size at low temperature.     

A quantitative study of the hardness of a superhard nanocrystalline titanium nitride/silicon nitride coating

The hardness of nanocrystalline two-phase TiN/a-SiN_x coatings has been measured by nanoindentation. An optimum hardness is found for the coatings containing 2–5 at.% silicon. In this regime the microstructure combines mechanical confinement effects with optimum load transfer between the phases as illustrated by finite element simulations.     

硬质合金CVD涂层的缺陷分析

对硬质合金CVD涂层刀片的组织缺陷进行了系统分析，发现涂层的主要缺陷为；Al2O3柱晶生长组织，Al2O3局部外延生长，刀片表面有涂层颗粒沉降物，涂层剖面上还出现孔洞、裂纹等生长缺陷。     

Effect of sintering temperature on microstructure and properties of SiC coatings for carbon materials

SiC coating for the graphite materials was prepared by slurry-sintering technique in a vacuum. The phase, microstructure, thickness and resistance against irradiation of the SiC coatings prepared from 1500 to 1800 °C were investigated. Research results showed that, the porous β-SiC coating occurred at 1500 and 1600 °C, while compact β-SiC/Si coatings obtained at 1700 and 1800 °C. The thickness of the coatings was in most cases around 150 μm when the sintering was performed at 1500 and 1600 °C. However, the thickness was decreased, and the crystal size of SiC particles was increased when the sintering temperature was higher than 1600 °C. Thermal fatigue tests showed that, based on the surface morphology changes, the sintering temperature of 1700 and 1800 °C gave much improved irradiation resistance over that of coatings formed at 1500 and 1600 °C.     

Microstructure evolution and hardening mechanisms of Ni-P electrodeposits

Ni-P alloy coatings with different phosphorus contents were prepared by electroplating in a nickel sulfate bath containing phosphorous acid (H₃PO₃). Hardening mechanism, such as dispersion hardening of Ni nano crystals in amorphous matrix of the as-deposited Ni-P coating and coarsening weakening of Ni₃P for the high P coating after 1 h of heat treatment at 400 °C were concluded from the experimental data. Hardening mechanism of Ni-P alloys were further discussed based on the microstructure evolution with increasing deposit P content and during the heat treatment by using high resolution TEM (HR-TEM). A maximum hardness was observed for the as-deposited and heat-treated Ni-P alloys with 4 wt.% and 6 wt.% P, respectively. These composition ranges corresponding to the microstructure with high hardness proposed are believed to be useful for the industrial applications and further study.     

混杂增强AZ91镁合金基复合材料

采用挤压铸造成形法 ,成功地制备了具有不同含量与粒度的石墨颗粒与氧化铝短纤维混杂增强的镁合金基复合材料。对制备工艺、复合材料的显微组织及性能进行了研究 ,结果表明 ,增强相在复合材料中分布均匀 ,基体和增强相界面结合紧密 ,无明显铸造缺陷。复合材料的硬度随石墨含量的增加而降低 ,随石墨颗粒尺寸的细化而增大。     

不同搅拌时间对半固态铝合金坯料制备的影响

ADC12铝合金用机械搅拌方法进行加工能细化晶粒,获得半固态铝合金坯料;本文通过改变搅拌时间制备半固态铝合金,并观察其微观组织、检测其硬度,以寻求最佳的搅拌时间工艺参数取值范围。对试验结果分析后得出：在搅拌温度为580℃、搅拌速度330r／min,固定不变时,搅拌时间25min左右半固态铝合金的金相组织和硬度为最佳。     

Two-phase nanostructured carbon nitride films prepared by direct current magnetron sputtering and thermal annealing

Two-phase nanocrystalline/amorphous carbon nitride films have been successfully prepared by direct current magnetron sputtering and the following thermal annealing at 1000 K. The analysis of Raman spectra supports the existence of sp³-hybridized C-N bonds in the films. The results obtained from X-ray photoelectron spectroscopy (XPS) indicate that the fractional concentration of the tetrahedral bonded crystalline phase in the carbon nitride films is 40%, and the ratio of N:C in the tetrahedral bonded crystalline phase is 1.12:1. Transmission electron microscopy (TEM) investigations indicate that the films contain a very dense and homogenous distribution of nanocrystalline grains, and the lattice parameters of these crystalline phases are in good agreement with the theoretically predicted β-C₃N₄ lattice constant. The films deposited on Si substrates have a high hardness of 40 GPa, and the correlations between the microstructure of the films and their mechanical properties are discussed.     

Hardness and elastic modulus of amorphous and nanocrystalline SiC and Si films

Hydrogen-free amorphous and nanocrystalline films were prepared by magnetron sputtering of the SiC or Si targets. Mechanical properties (hardness, elastic modulus, intrinsic stress) and film structures were investigated in dependence on the substrate bias and temperature. It was found that both hardness and elastic modulus of all amorphous a-SiC films prepared at different substrate temperatures and biases are always lower than those for bulk α-SiC single crystal while the hardness of partially crystalline SiC films is higher and the elastic modulus lower than those for α-SiC one. In contrast, both hardness and elastic modulus of all amorphous Si films are always lower than those for nanocrystalline Si films which show approximately the same value as the Si single crystal.     

晶粒尺寸对纳米晶钴摩擦磨损性能的影响

采用脉冲电沉积法制备了不同晶粒尺寸的纳米晶钴镀层,考察了晶粒尺寸对纳米晶钴硬度和摩擦磨损性能的影响.结果表明:随着晶粒尺寸的减小,钴镀层的硬度显著升高,符合经典的Hall-Petch效应;而纳米晶钴的抗磨性并没有随着晶粒的减小而显著增加,同时其摩擦系数随着晶粒的减小而略有增加.     

气体爆燃喷涂铁铝涂层结构的变化

采用不同的喷涂工艺参数,分别在45钢基体上制备了电弧喷涂铁铝涂层,采用电子探针(EPMA)、X射线衍射(XRD)、光学显微镜和显微硬度计等仪器研究了气体爆燃铁铝涂层的表面形貌、显微硬度、涂层的成分和相结构,结果表明,喷涂工艺的改变明显影响喷涂层的相组成,随着单位时间内提供给粉末能量的减少,得到黑白相间的片层状结构,黑色相是Fe4Al13,白色相是FeAl;增加单位时间内提供给粉末的能量,可以得到均匀的微观组织,成分为FeAl。     

Evolution of morphology and magnetism of Ho(Fe0.5Co0.5)3 intermetallic nanopowders synthesized by HEBM

The morphology and magnetic properties of bulk and ball – milled Ho(Fe_0.5Co_0.5)₃ intermetallic compounds were studied. The influence of the high energy ball – milling (HEBM) duration for the final size of particles and crystallites was confirmed by a variety of complementary measurement methods. The presence of the main PuNi₃ type of crystal phase was confirmed for crystalline and as – milled samples. The emergence of a partly amorphous phase was confirmed at the end of pulverization (t = 80 h). The synthesis of nanostructured flakes with a thickness of less than 100 nm after applying HEBM for various time periods was confirmed. Additionally, the formation of agglomerates for the prolonged pulverization was evidenced. The non – linear variation of magnetic parameters across milling was observed. Furthermore, a slight exchange bias and deformation of hysteresis loops for as – milled powders was noticed. A quantitative analysis of XPS spectra at the end of grinding process indicates the probable coating of flakes by Fe/Co oxides the amount of which varies over ion etching.     

Microstructure and properties of Al0.3CrFe1.5MnNi0.5Ti x and Al0.3CrFe1.5MnNi0.5Si x high-entropy alloys

In this article, the microstructure, hardness, and corrosion resistance of the Al0.3CrFe1.5MnNi0.5Tixand Al0.3CrFe1.5MnNi0.5Six(x = 0, 0.2, 0.5, 1.0) high-entropy alloys were investigated via X-ray diffraction(XRD)scanning electron microscopy(SEM), digital display Vickers hardness tester, and electrochemical technique These alloys are mainly composed of BCC solid-solution structure. When adding high content of Ti or Si elemen(x C 0.5), some intermetallic compounds are found in the microstructure, which makes the alloys have a high hardness, high brittleness, and easy cracking. While the alloys with low content of Ti or Si(x = 0.2) have a hardness of HV 420–HV 430, and its hardness increases about 14 %compared with that of Al0.3CrFe1.5MnNi0.5. Electrochemical results in 3.5 % NaCl solution show that the alloying elements Ti and Si have a negative influence on the corrosion resistance of the Al0.3CrFe1.5MnNi0.5alloys.     

Mechanical properties of nanocrystalline nickel films deposited by pulse plating

This paper reports the mechanical properties of Ni films fabricated by pulse electrodeposition. Transmission electron microscope revealed that the prepared films had an average grain size of 25 nm with a narrow size distribution and the absence of dislocations. Small grain size leads to an increasing hardness as high as 7.8 GPa while Young's moduli keep a constant bulk value of 215 GPa, resulting in an increasing ratio of hardness (H) to elastic modulus (E). Interestingly, the wear resistance was also improved significantly. Under a constant normal load of 500 μN, the penetration depths of indenter slightly increased from 25 nm to 30 nm and the coefficient of friction varied from 0.12 to 0.20, depending on sliding scans. Depth sensing instrumented indentation experiments performed at different loading rates on specimens revealed an increasing rate-sensitivity of hardness, which concerns with a significantly small activation volume for plastic flow.     

Pulse plated CoP alloy as substitute for hard chromium electrodeposits

Abstract

A watts type cobalt bath containing additives has been used to obtain CoP (1–3 wt-%P) coatings using galvanostatic pulse plating (PP). These CoP alloys, with a nanocrystalline hexagonal close packed (hcp) structure, are a valuable candidate for hard chromium (HC) replacement. The morphology, structure and performance of CoP and HC films were characterised using scanning electron microscopy (SEM), atomic force microscopy (AFM), XRD, microindentation, abrasion, friction and corrosion tests.     

镀TiC金刚石/铝复合材料的热膨胀性能

采用气压浸渗法制备了金刚石体积分数为65%的铝基复合材料,分析了复合材料的显微组织并对热膨胀系数（CTE）进行了测试,研究了镀TiC金刚石/铝复合材料的热膨胀性能。结果表明,金刚石颗粒在铝合金基体中分布均匀,组织致密;TiC镀层有效地改善了金刚石颗粒与铝合金基体间选择性粘结现象,增强了金刚石与基体间的界面结合;镀TiC使复合材料热膨胀系数明显降低,Turner模型和Kerner模型的均值可以预测其热膨胀系数,而对于未镀层的复合材料则可以用Kerner模型进行预测。     

铝青铜片与Q345钢激光熔覆工艺与组织

采用单道熔覆试验,在Q345钢表面激光熔覆铝青铜片,研究激光功率和扫描速度对熔覆层组织及显微硬度分布的影响。结果表明,激光熔覆铝青铜覆层内组织致密,与基体呈冶金结合,随着激光能量密度的增加,熔覆层组织逐渐由细小等轴晶向大量树枝晶过渡,覆层无气孔、裂纹等缺陷。覆层中主要有α相、β相、γ2相、κ相以及Fe相。热影响区硬度最高,覆层次之,基体硬度最低。随着扫描速度的增加,覆层硬度逐渐增加,随着激光功率的增加,覆层硬度逐渐降低。