Effect of nitriding-sulfurizing composite treatment on the tribological behavior of titanium alloys

A composite layer was prepared on the surface of Ti-6Al-4V alloy by nitriding-sulfurizing composite treatment,and its microstructure and phase structure were examined by scanning electron microscopy（SEM） and X-ray diffraction（XRD）,respectively.The tribological performance was measured to investigate its dependence on the nitriding-sulfurizing composite treatment process.The results indicated that the composite layer was mainly comprised of Ti2N,TiN,and TiS2.It was found that the composite layer exhibited superior tribological properties under dry friction and absolute sliding conditions due to the formation of sulfides with self-lubricating function.

Ion and Gas Nitriding Applied to Steel Tool for Hot Work X38CrMoV5 Nitriding Type: Impact on the Wear Resistance

The present work is to characterize both processes of thermochemical treatments: plasma nitriding and gas. The tests were carried out in collaboration with the Franco-Tunisian heat treatment (F3T) applied to a widely used steel in industrial production as a tool for hot work on X38CrMoV5 (AISI H13). The material underwent a first cycle of hardening heat treatment at 1030℃ followed by two successive incomes at 550℃ and 590℃. After nitriding (ion and gas), the quantification of wear was performed in the laboratory of tribology at SUPMECA (St. Ouen). After defining the test conditions on the alternative tribometer ensuring on one hand a quantitatively sufficient wear and avoiding on the other hand, the phenomenon of jamming. The conditions chosen are: 58.8 N load, frequency 0.5 Hz, friction coefficient μ = 0.5. The wear tracks were scanned using the profilometer Talysurf 5 M type, which allowed us to assess the volume used and the wear rate. Moreover, these tracks were characterized by metallography. What emerges from this work is that the control parameters of ion nitriding ensures a better depth of treatment for the same holding time with a total absence of the white layer known for chipping and fragility.

Low-Temperature Nitriding by Means of SMAT

The microstructure in the surface layer of iron and steel samples can be refined at the nanometer scale by means of a surface mechanical attrition treatment (SMAT) that generates repetitive severe plastic deformation to the surface layer. The subsequent nitriding kinetics of the as-treated samples with the nanostructured surface layer is greatly enhanced so that the nitriding temperatures can be reduce to 300 - 400 °C regions. This enhanced processing method demonstrates both the technological significance of nanomaterials in advancing the traditional processing techniques, and provides a new approach for selective surface reactions in solids. This article reviews the present state of the art in this field. The microstructure and properties of SMAT samples nitrided will be summarized. Further considerations of the development and applications of this new technique will also be presented.

Effect of Treatment Temperature on Iron Nitride Foils Irradiated with Nitrogen Plasma

We investigated the effect of treatment temperature on the magnetic property of iron nitride foils irradiated with nitrogen plasma. The iron nitride foils irradiated with nitrogen plasma were composed of ε-Fe2/3N, γ'-Fe4N and γ nitrogen austenite in α-Fe of the matrix. The saturation magnetization of the iron nitride foils decreased with increasing the surface temperature. The coercive force of the iron nitride foils increased with increasing the surface temperature.

Tribology of nitriding layer, TiN coatings and their complex on AISI D2 steel

The sliding wear and impact wear resistances of D2 steel with nitriding layer, PVD titanium nitride coating and their duplex treatment were investigated. The experimental results suggest that the duplex treatment has the best sliding and impact wear resistances under experimental conditions. And the wear resistance of PVD titanium nitride is better than that of nitriding. The impact wear resistance and wear mechanism of all three surface layers remain unchanged under impact load of 0.2 J or 1 J. All samples end with the same symptom of flaking.

Electrochemical and Tribological Behaviour of Ti6Al4V Subjected to the Duplex SMAT/Plasma Nitriding

In this work,SMAT(surface mechanical attrition treatment)was performed on Ti6Al4V.Plasma nitriding of the SMATed samples was investigated in comparison with coarse-grained samples.The samples were characterized using optic microscope,SEM,TEM and Vickers microhardness tester.The results showed that a significantly thicker compound layer with higher hardness was obtained for the SMATed samples when compared with un-SMATed samples after nitriding.Corrosion resistance of Ti6Al4V in a Ringer’s solution was studied by electrochemical techniques including open circuit potential measurement,potentiodynamic polarization and EIS(electrochemical impedance spectroscopy).Overall,our results identified the beneficial impacts of the duplex SMAT/nitriding treatment on corrosion behaviour of Ti6Al4V.Wear tests were also performed on a ball-on-disc tribometer where the treated samples were rubbed against a 6 mm diameter alumina ball under a normal load of 5 N using Ringer’s solution as lubricant media.The friction coefficient of the SMATed and nitrided samples was reduced compared to the untreated samples.Wear rates demonstrated that SMAT combined with nitriding improved wear resistance of Ti6Al4V alloy.

Development of Subgrade Technical System for High-speed Railway

There are two phases in the development of China's high-speed railway after the1990s:the research and experiment phase during the Eighth and the Tenth Five-Year Plan periods;the construction and operation phase during the Eleventh and the Thirteenth Five-Year Plan periods.This paper regards the Beijing-Shanghai High-Speed Railway as the corner stone in the development of high-speed railway subgrade system,and proposes suggestions and solutions to the problems which may reduce the service life of subgrade.These solutions and methods can be referred to in future railway projects.

4Cr5MoSiV1热作模具钢循环渗氮及热疲劳行为研究

针对4Cr5MoSiV1热作模具钢在使用过程中经受熔融铝液及冷却液的循环冲击,在热应力作用下容易产生热疲劳失效的问题。采用可控循环气体渗氮的方法分别在回火态和热疲劳态模具钢表面制备无铁氮化合物和有化合物的渗层,进行热疲劳性能测试。结果表明:循环渗氮制备的无化合物的渗层可以有效延缓热疲劳裂纹的萌生,抗热疲劳性能优于有化合物的渗层。同时,在裂纹产生前进行二次渗氮可以补充氮原子,重置压应力并增加硬度,进一步提升热疲劳抗性。

激光硬化与渗氮复合处理H13钢组织与性能

通过激光淬火/离子渗氮复合方法对H13钢进行表面改性处理,从而提高其表面的性能.利用X射线衍射技术、光学显微观察、扫描电子显微观察、能谱分析技术、显微硬度和纳米测试系统以及高频往复磨损试验,分别研究了离子渗氮、激光淬火、以及激光淬火与离子渗氮复合处理对H13钢改性层组织结构、力学性能、摩擦磨损性能的影响过程和影响机理.结果表明:复合处理工艺可以显著改善改性层的综合性能.和单一渗氮处理相比,复合处理改性层硬度和有效硬化层深度分别从1180 HV和80μm提高至1360 HV和550μm,摩擦系数和磨损率分别从0.68和5.78×10^(-8)mm^(3)·N^(-1)·m^(-1)降低至0.59和1.35×10^(-8)mm^(3)·N^(-1)·m^(-1).试样的硬度和耐磨性显著增加,平均摩擦系数明显降低.

表面织构-活性屏离子氮化复合处理对38CrMoAl钢摩擦学行为的影响

【目的】38CrMoAl钢是液压泵柱塞常用材质之一,其表面性能对液压泵长寿命安全服役尤为重要。磨损是液压泵柱塞的主要失效方式,采用表面强化处理能够突破其性能极限,是实现液压泵高性能、高可靠运行的有效途径。【方法】采用表面织构化和活性屏离子氮化的复合处理工艺对38CrMoAl钢进行表面形性调控,以期实现其表面强化方法。先利用激光加工技术在38CrMoAl钢表面制备凹坑织构,再对38CrMoAl钢和表面织构化38CrMoAl钢进行活性屏离子氮化处理。借助球-盘式摩擦磨损试验机研究表面织构-活性屏离子氮化复合处理对38CrMoAl钢摩擦学行为的影响。【结果】结果表明,38CrMoAl钢表面生成了ε-Fe2-3N、γ'-Fe4N和CrN;氮化层表面致密且无明显裂纹和孔洞;氮化层均匀、连续,由白亮层和扩散层组成。氮化层的截面硬度呈梯度分布,试样表面硬度最高,随着距表面距离的增大,硬度逐渐降低。38CrMoAl钢相关试样与Al_(2)O_(3)球的干滑动摩擦结果可知,38CrMoAl钢的摩擦系数为0.40,而表面织构-活性屏离子氮化38CrMoAl钢的摩擦系数为0.36;经复合处理后,38CrMoAl钢的磨损失重降低了92.5%.复合处理显著提高了38CrMoAl钢的摩擦学性能。

渗氮时间对G13Cr4Mo4Ni4V钢组织及硬度的影响

对渗碳G13Cr4Mo4Ni4V钢进行渗氮热处理,研究渗氮时间对G13Cr4Mo4Ni4V钢复合层、渗碳层和心部的微观组织变化,以及硬度的影响。结果表明:渗氮处理后的G13Cr4Mo4Ni4V钢复合层和渗碳层由碳化物、回火马氏体和少量残余奥氏体组成,心部由板条马氏体及少量碳化物组成。渗氮90 h后G13Cr4Mo4Ni4V钢表面洛氏硬度提高,但波动性增大。渗氮50 h后的G13Cr4Mo4Ni4V钢渗层显微硬度最大,可达960 HV,渗氮层厚度为0.17 mm,有效渗碳层厚度为1.67 mm;而渗氮90 h后的G13钢显微硬度最大可达到906 HV,渗氮层厚度为0.19 mm,有效渗碳层厚度为1.26 mm。有效渗碳层厚度的降低与渗氮过程中碳元素向内扩散导致基体碳浓度降低有关,而显微硬度的降低与网状碳化物的析出降低了基体碳元素含量有关。

离子渗氮对38CrMoAl钢组织及摩擦磨损性能影响

560℃下,以氮气和氩气的混合气体为氮源,对38CrMoAl钢表面进行离子渗氮,研究了离子渗氮后38CrMoAl钢的磨擦磨损性能。结果表明,随着混合气体中N2体积分数增大,渗氮层厚度增加,渗氮层表面硬度呈现先增大后减小的趋势。通过调节混合气体中N_(2)的体积分数,可以改变活性氮原子数量从而改变渗氮层的物相组成,当N_(2)和Ar体积比2∶3时,渗氮层中以γ′-Fe4N相为主相、ε-Fe_(2-3)N相为次相;当N2和Ar体积比3∶2时,渗氮层中ε-Fe_(2-3)N相成为主相、γ′-Fe_(4)N相为次相。与基体材料相比,离子渗氮试样具有更小的摩擦系数,耐磨性得到提高,在N2和Ar体积比3∶2时,渗氮试样的化合物层厚度为21.4μm,平均摩擦系数达到0.26,表现出良好的耐磨性。摩擦磨损机制为疲劳磨损、磨粒磨损和氧化磨损。

Band Engineering and Morphology Control of Oxygen‑Incorporated Graphitic Carbon Nitride Porous Nanosheets for Highly Efficient Photocatalytic Hydrogen Evolution

Graphitic carbon nitride(g-C3N4)-based photocatalysts have shown great potential in the splitting of water.However,the intrinsic drawbacks of g-C3N4,such as low surface area,poor diffusion,and charge separation efficiency,remain as the bottleneck to achieve highly efficient hydrogen evolution.Here,a hollow oxygen-incorporated g-C3N4 nanosheet(OCN)with an improved surface area of 148.5 m2 g^−1 is fabricated by the multiple thermal treatments under the N2/O2 atmosphere,wherein the C–O bonds are formed through two ways of physical adsorption and doping.The physical characterization and theoretical calculation indicate that the O-adsorption can promote the generation of defects,leading to the formation of hollow morphology,while the O-doping results in reduced band gap of g-C3N4.The optimized OCN shows an excellent photocatalytic hydrogen evolution activity of 3519.6μmol g^−1 h^−1 for~20 h,which is over four times higher than that of g-C3N4(850.1μmol g^−1 h^−1)and outperforms most of the reported g-C3N4 catalysts.

Low-Cost Preparation of Boron Nitride Ceramic Powders

The amorphous boron nitride ceramic powders were prepared at 750-950 ℃ by the low-cost urea route, and the effects of preparation temperatures, molar ratios of the raw materials and oxidation treatment on the composition, structure and surface morphology of the products were investigated through FT-IR, XRD and SEM. The results show that the products ceramize and crystallize gradually with the increase of the temperature. When the molar ratio and reaction temperature are 3：2 and 850 ℃, respectively, the products have high purity, compact structure and nice shape. The oxidation treatment at 450 ℃ will not impair the composition and structure of boron nitride but effectively remove the impurities.

Sustainable preparation of graphene-analogue boron nitride by ball-milling for adsorption of organic pollutants

The method of fabricating low-cost adsorbents with high activity and durability via a convenient and ecofriendly procedure is of great importance to wastewater treatment. Herein, a high-efficient mechanical exfoliation strategy was proposed to facilely prepare few-layered graphene-analogue boron nitride(BN) via a one-step non-organic solvent assisted wet ball mill procedure. Ball-milling treatment increased the specific surface area of BN 3.5-fold by reducing the thickness to ~3 layers with 45 min. The exfoliated BN exhibited strikingly improved sorption performance to organic contaminants with around 124% and 116% increased removal efficiency respectively for oxytetracycline(OTC) and Rhodamine B(RhB) as compared to the bulk BN. Batches sorption experiments showed that the sorption processes were thermodynamic endothermic, and well fitted to pseudo-second-order kinetic model and Freundlich isotherm equation. The π-π stacking interaction, hydrophobic effect and electrostatic interaction were proposed as the dominated sorption mechanism. In addition, no significant decline in adsorptive removal ability for the sorbent after 5 times recycling. The results indicate that the ball-milling exfoliation is a fast, green,sustainable and promising strategy for synthesis of highly potent BN based two-dimensional layered adsorbents.

High-Temperature Thermodynamic Investigation of Nano-Dispersed Nitrides Obtained in Thermal Plasma

The nitrides of transient metals have a high hardness, thermal stability, remarkable wear resistance in aggressive chemical mediums, melted metals and alloys, high corrosion resistance, and low coefficient of electric resistance. Under the conditions of low-temperature argon plasma （LTP）, thermodynamic investigations were conducted in the process of obtaining of A1N, TiN and Si3N4 in a temperature range of 1000 K to 6000 K. To investigate the thermodynamic possibility of obtaining nitrides, a computer model was used which provided the equilibrium composition of gaseous and solid phases at different temperatures. The conditions for chemical equilibrium of the system were based on the minimization of Gibbs＇ energy.

Effects of oxidation treatment on properties of SiO_(2f)/SiO_2-BN composites

The silica fiber reinforced silica and boron nitride-based composites(SiO2f/SiO2-BN) were prepared firstly via the sol-gel method and then the urea route,and the effects of oxidation treatment on the component,structure,mechanical and dielectric properties of the composites were investigated.The results show that the oxidation treatment at 450 °C will not impair the structure of boron nitride,and carbon is the main impurity with the excessive urea.The density of SiO2f/SiO2-BN composites is 1.81 g/cm3,and the flexural strength and elastic modulus are 113.9 MPa and 36.5 GPa,respectively.After oxidation treatment,the density varies to 1.80 g/cm3,and the flexural strength and elastic modulus are decreased to 58.9 MPa and 9.4 GPa,respectively.The mechanical properties of the composites are severely damaged,but they still exhibit a good toughness.The composites show excellent dielectric properties with the dielectric constant and loss tangent being 3.22 and 0.003 9,respectively,which indicates that the oxidation treatment is ineffective to improve the dielectric properties of SiO2f/SiO2-BN composites.

The Effect of Heat Treatment Atmosphere on Hardening of Surface Region of H13 Tool Steel

The main objective of the die heat treatment is to enhance the surface hardness and wear properties to extend the die service life. In this paper, a series of heat treatment experiments were conducted under different atmospheric conditions and length of treatment. Four austenitization atmospheric conditions were studied and although each heat treatment condition resulted in a different hardness profile, it did not affect the results for gas nitriding. All samples subjected to the nitriding process produced similar thicknesses of hardened case layer with average hardness of 70 - 72 HRC if the initial carbon content is not too low. It was shown that heat treatment without atmospheric control results in a lower hardness on the surface since the material was subjected to decarburization effect. The stainless steel foil wrapping around the sample and heat treatment in a vacuum furnace could restrict the decarburization process, while pack carburization heat treatment resulted in a carburization effect on the material.

Effect of Cryogenic and QPQ Compound Treatment on the Microstructures and Performance of High Speed Steel

China’s High-speed steel cutting tools hold a considerable share in the global market. However, the overproduction of low-end HSS tools causes serious resource waste and low efficiency, which has become one of the major problems in the tool industry in China. So a new Surface Modification technology is developed, which can make the low-end HSS tools into the high-end ones. On the analysis of the mechanism of cryogenic and quenching-polish-quenching(QPQ), the cryogenic and QPQ compound treatment are studied by using ?8 HSS(M2) drills. The nitriding layer and the base of the drill bit are Studied and analyzed, and the mechanism of compound treatment is discussed by the technological parameters adjustment and the combination test of cryogenic, nitrogen, tempering procedures, and several analysis methods such as the optics metallographic microscope, the scanning electronic microscope (SEM), X-ray diffraction and micro hardness. The cutting test is done on the drills by cryogenic treatment, QPQ treatment and cryogenic and QPQ compound treatment separately. The results indicates that the cutting life of HSS (M2) drill can be increased dramatically by cryogenic and QPQ compound treatment.