Nano Cr Interlayered CrN Coatings on Steels

CrN coated steels assisted with a nano Cr interlayer were investigated. The Cr nano-interlayers were prepared by sputter deposition with a thickness about 70-100 nm. CrN coatings were also prepared by sputter deposition on the Cr nano-interlayers. The crystal structures, microhardness, and scratch resistance of CrN/Cr coatings were determined. Results show that the Cr nano-interlayers improve scratch resistance and the microhardness of CrN coated steels. A rapid heat treatment with infrared （IR） was performed for coated specimens in the attempt to improve bonding, With IR heat treatments, the beneficial effect of the Cr nano-interlayers was clearly observed. Without the Cr nano-interlayers, severe cracks on the surface of coatings were observed after IR heat treatment. However, with a Cr interlayer, no cracks on the surface of CrN coatings were observed after the heat treatment. The scratch resistance of coatings was also affected by the Cr nano-interlayers. The scratch track was clean and showed significantly smaller amount of scratch debris for CrN coatings with Cr interlayers than those without the Cr nano-interlayers. The microhardness of coatings with the Cr nano-interlayers is higher than those without the Cr nano-interlayers after IR heat treatment. The Cr and CrN phase have been identified with X-ray diffraction analysis, and the results show that the higher the nitrogen content in the sputtering gas, the stronger the CrN peaks observed in the diffraction patterns are.     

Microstructure and mechanical properties of Cr doped WCoB based cermets by spark plasma sintering and first principle calculation

WCoB based cermet is a potential hard alloy to replace WC-Co cermets with high hardness and corrosion resistance. WCoB based cermets with different Cr doping contents were fabricated by spark plasma sintering in liquid phase sintering stage. The densification behavior, phase composition, microstructure and mechanical properties of Cr doped WCoB cermets were investigated by XRD, EDS and SEM. Due to the lower density of Cr,the density of WCoB cermets decreased with the increasing of Cr doping content. The phase composition consisted of Cr doped WCoB, unreacted W, Co–Cr binary binder phase. When the doping content exceeded11.736 wt%, the Cr enrichment zones appeared, which was harmful to the TRS. The increasing of Cr doping content contributed to the increase of unreacted W phases content and the formation of pores. The maximum value of Vickers hardness was 1751 Hv0.5 at 9.356 wt% Cr doping content. The variation trend was explained by first principle calculation, which is consistent with Hv-Zhou hardness model.     

Atomic modeling for the initial stage of chromium passivation

The well-known anti-corrosive property of stainless steels is largely attributed to the addition of Cr,which can assist in forming an inert film on the corroding surface.To maximize the corrosion-resistant ability of Cr,a thorough study dealing with the passivation behaviors of this metal,including the structure and composition of the passive film as well as related reaction mechanisms,is required.Here,continuous electrochemical adsorptions of OH-groups of water molecules onto Cr terraces in acid solutions are investigated using DFT methods.Different models with various surface conditions are applied.Passivation is found to begin in the active region,and a fully coated surface mainly with oxide is likely to be the starting point of the passive region.The calculated limiting potentials are in reasonable agreement with passivation potentials observed via experiment.     

Structure and magnetic properties of ZnO:Cr prepared by Cr ion implantation into ZnO crystals

ZnO:Cr layer was prepared by Cr ion implantation into ZnO bulk crystals. The structural, optical, and magnetic properties of the ZnO:Cr layer were studied with X-ray diffraction, photoluminescence, and superconductor quantum interferometer, respectively. The ZnO:Cr layer implanted Cr with a dose of 5 10 16 cm 2 remained wurtzite structure and exhibited near-band-edge photoluminescence at 3.365 eV with full-width at half-maximum of 8.4 meV at 10 K. The magnetic measurement showed that the ferromagnetism changed at room temperature by different Cr concentration. For samples implanted to high doses, remanent magnetization reached 1.805 10 -4 emu/g and coercive field was 244.5 Oe. Hall effect measurement showed a decrease of the resistivity from 251.7 cmto 28.6 cmafter annealing at 800 ℃. The magnetism is interpreted by bound magnetic polarons, which were taken into account of the process that electrons were locally trapped by oxygen vacancies and occupied the orbitals that overlapped with d shell of neighboring Cr ions.     

Corrosion behavior of high-strength spring steel for high-speed railway

The corrosion resistance and evolution of corrosion products in medium-carbon high-strength spring steels were investigated in a neutral salt spray (5wt% NaCl solution). A formation model of γ-FeOOH and a transformation model describing the conversion of γ-FeOOH to α-FeOOH were constructed. The results indicated that, at the initial corrosion stage, the corrosion resistance was gradually improved with the addition of Cr; however, with the addition of alloying element V, the corrosion resistance decreased. These results were attributed mainly to the initial corrosion stage being closely related to the matrix microstructure parameters such as grain-boundary character and dislocation density. After the rust layer was formed at a later corrosion stage, the corrosion resistance was reinforced with the addition of Cr and V because Cr strongly influenced the composition, structure, and morphology of the corrosion products. The results presented herein show that Cr was conducive to the transformation of γ-FeOOH into α-FeOOH. Moreover, V and Cr exhibited obvious synergy and were enriched in the inner layer of the corrosion products.     

Thermal stability and magnetic properties of Fe–Co–M–Zr–Nb–Ge–B(M=Mo,Cr) bulk metallic glasses

Fe62Co8 xMxZr6Nb4Ge1B19(M=Mo, Cr) bulk metallic glasses were synthesized in the diameter range up to 2 mm by copper mold casting,which exhibit high thermal stability and large glass-forming ability. The super-cooled liquid region diminishes by the dissolution of Mo. The addition of 2 at% Cr leads to the broading of the liquid region remarkably, resulting in the improvement of thermal stability. The crystallization takes place through a single exothermic reaction, accompanying the precipitation of more than three kinds of crystallized phases such as α-Fe,Fe2Zr and ZrB2. The Fe-based alloys show soft ferromagnetic properties. The saturation magnetization(ss) decreases with increasing Mo or Cr content while the saturated magnetostriction increases with raising Mo or Cr content. There is no evident change in the ssand coercive force(Hc)with annealing temperature below the crystallization temperature, which suggests a more relaxed atomic configuration the glasses have. The crystallization causes a substantial enhancement in both ssand Hc. Each soft magnetic property of the glasses containing Cr with higher thermal stability is superior to that of the alloys containing Mo.     

Comparative study on the corrosion behavior of X52, 3Cr,and 13Cr steel in an O_2–H_2O–CO_2 system: products,reaction kinetics,and pitting sensitivity

The corrosion behaviors of X52, 3Cr low-alloy steel, and 13Cr stainless steel were investigated in an O_2–H2O–CO_2 environment at various temperatures and O_2–CO_2 partial-pressure ratios. The results showed that the corrosion rates of X52, 3Cr, and 13Cr steels increased with increasing temperature. The corrosion rates slowly increased at temperatures less than 100°C and increased sharply when the temperature exceeded 100°C. In the absence of O_2, X52, 3Cr, and 13Cr exhibited uniform corrosion morphology and Fe CO3 was the main corrosion product. When O_2 was introduced into the system, various forms of Fe_2O_3 appeared on the surface of the samples. The Cr content strongly influenced the corrosion resistance. The 3Cr steel with a low Cr content was more sensitive to pitting than the X52 or 13Cr steel. Thus, pitting occurred on the surface of 3Cr when 1.25 MPa of O_2 was added; this phenomenon is related to the non-uniform distribution of Crin 3Cr.     

Comparative study on the corrosion behavior of X52, 3Cr,and 13Cr steel in an O2-H2O-CO2 system:products,reaction kinetics,and pitting sensitivity

The corrosion behaviors of X52, 3Cr low-alloy steel, and 13Cr stainless steel were investigated in an O₂-H₂O-CO₂ environment at various temperatures and O₂-CO₂ partial-pressure ratios. The results showed that the corrosion rates of X52, 3Cr, and 13Cr steels increased with increasing temperature. The corrosion rates slowly increased at temperatures less than 100℃ and increased sharply when the temperature exceeded 100℃. In the absence of O₂, X52, 3Cr, and 13Cr exhibited uniform corrosion morphology and FeCO₃ was the main corrosion product. When O₂ was introduced into the system, various forms of Fe₂O₃ appeared on the surface of the samples. The Cr content strongly influenced the corrosion resistance. The 3Cr steel with a low Cr content was more sensitive to pitting than the X52 or 13Cr steel. Thus, pitting occurred on the surface of 3Cr when 1.25 MPa of O₂ was added; this phenomenon is related to the non-uniform distribution of Cr in 3Cr.     

Effects of Complexes and pH Buffer Solution in Electrokinetic Oxidation Treatment on Sediments Chromium Removal

Three electrokinetic(EK) experiments were designed to study the remediation efficiency of Cr(Ⅲ) by EK-oxidation method and to investigate the influence of complexes and p H buffer solution in EK-oxidation process. Sediments Cr(Ⅲ) can be oxidized into Cr(Ⅵ) effectively by KMn O4, but the oxidation efficiency is not proportional to the dose of oxidant, and chemical oxidation process leads to a bit lower buffering capacity of the sediment. Compared with the simple EK remediation, the removal efficiency of total Cr in the sediments increased 32.6% by EK-oxidation method, and the concentrations of total chromium in the sediment showed increasing trend from the cathode to the anode after EK-oxidation treatment. The p H control and KMn O4 improved the removal of Cr(Ⅵ) and total Cr from the sediments. Due to stronger complexation action of citric acid with Cr(Ⅲ) in sediments, citric acid in the catholyte obviously increased the removal rate of total Cr in sediments. Finally, the removal rate of total Cr from sediments reached 60.9% by adding complex and controlling the p H of cathode and anode pond solution on EK-oxidation processes.     

Effects of Cr and Mo elements on the microstructures and compressive properties of the in situ (TiC_xN_y–TiB_2)/Ni cermets

In-situ(TiC_xN_y–TiB_2)/Ni cermets with 70 wt%TiC_xN_y–TiB_2 were successfully fabricated by combustion synthesis and hot pressing sintering in Ni-Ti-B_4C-BN powder systems.The microstructures,density,compressive properties,and hardness of the TiC_xN_y–TiB_2/Ni cermets with the addition of 0–8 wt%Cr/Mo to the Ni-Ti-B_4C-BN powder systems were compared and analysed.The results showed that the ceramic particles distributed uniformly in the cermets,and the size of the ceramic particles reduced with the Cr/Mo addition.Both Cr and Mo addition can improve the hardness,compressive properties,and fracture strains of the cermets.The hardness,compressive strength,and fracture strain of the(TiC_xN_y–TiB_2)/(Ni+Cr)cermets increased from 1561 HV,2.94 GPa,and 2.9%to 1864 HV,3.65 GPa,and 3.4%,respectively when the Cr content increased to 5 wt%.The hardness and compressive strength of the(TiC_xN_y–TiB_2)/(Ni+Mo)cermets increased from 1561 HV and 2.94 GPa to 1902 HV and 3.43 GPa,respectively when the Mo content increased to 8 wt%.The cermets with Cr had better compressive properties than the cermets with Mo.     

Comparative study on the corrosion behavior of X52, 3Cr,and 13Cr steel in an O2–H2O–CO2 system: products,reaction kinetics,and pitting sensitivity

The corrosionbehaviors of X52, 3Cr low-alloy steel, and 13Cr stainless steel were investigated inanO2–H2O–CO2 environment at varioustemperaturesand O2–CO2partial-pressure ratios. The results showed thatthe corrosion rates of X52, 3Cr, and 13Cr steels in-creased with increasing temperature. The corrosion ratesslowly increased at temperaturesless than100℃ and increased sharply when the temperature exceeded100℃. In the absence of O2, X52, 3Cr, and 13Cr exhibited uniform corrosion morphology and FeCO3 was the main corrosion product. When O2 was introduced into the system, various forms of Fe2O3 appeared on the surface of the samples. The Cr content strongly influenced the corrosion resistance. The 3Cr steel with a low Cr content was more sensitive to pitting than the X52 or 13Cr steel. Thus, pitting occurred on the surface of 3Cr when 1.25 MPa of O2 was added; this phenomenon is related to the non-uniform distribution of Cr in 3Cr.     

Local electronic structure and magnetic properties of （Ga,Cr）N

Modern electronic devices utilize the charge degree of freedom of electrons to process information in semiconductors and the spin degree of freedom to store information in magnetic materials. For example, inte- grated circuits and high–frequency devices …     

Cr(VI)-苯酚共存污染体系中的光催化反应研究

采用焙烧的P-25 TiO2作为光催化剂,研究了Cr(VI)-苯酚共存污染体系中Cr(VI)的光催化还原及苯酚的光催化氧化,并考察了pH值、气氛和初始浓度等对其光催化性能的影响。结果表明,Cr(VI)-苯酚共存体系中Cr(VI)及苯酚的去除率均较Cr(VI)和苯酚的单一体系高;酸性条件下有利于Cr(VI)的光催化还原,中性条件下苯酚的光催化降解率最高;气氛对Cr(VI)-苯酚共存体系中Cr(VI)的光催化还原及苯酚的光催化氧化均无明显影响;增大苯酚浓度可以有效的提高该体系中Cr(VI)的光催化还原,增大Cr(VI)浓度可以有效的提高该体系中苯酚的光催化氧化;Cr(VI)离子的光催化还原遵循L-H动力学规律,而苯酚的光催化氧化符合一级反应动力学规律。     

铬的单一或复合污染及镧对水稻幼苗生长的影响

研究铬单一污染和铬+铅、铬+镉复合污染对水培水稻幼苗生长的影响及镧对重金属污染的作用。结果表明:低浓度的铬浸种可促进水稻的生长,当铬浓度达到8mg/L时严重抑制水稻生长。镉明显增强铬对水稻生长的毒害作用,而铬与铅复合污染对水稻的伤害则由于二者的相互反应轻于单一污染。250mg/L三氯化镧能够缓解较高浓度重金属污染造成的伤害,促进水稻幼苗的正常生长。     

零价纳米铁对水中Cr(VI)的吸附动力学研究

 为开发新型环境材料,改进治理技术以控制或修复污染水体中Cr(Ⅵ),采用NaBH₄还原Fe³⁺制备纳米级零价铁(NZVI).X射线衍射(XRD)及扫描电镜(SEM)测试表明,制备的纳米铁颗粒纯度高、粒径小、粒度均匀.以Cr(VI)为研究对象,批试验考查了溶液初始浓度、NZVI投加量、温度等条件对去除效果的影响,研究了NZVI对Cr(VI)的吸附动力学.结果表明,室温、pH值为6-7时,NZVI加入量为0.15g/L,水体中Cr(VI)浓度为30.0mg/L时,Cr(VI)最大吸附量为198.02mg/g,Cr(VI)在NZVI上的吸附符合准二级动力学方程.实验结果显示,纳米零价铁能快速去除水体中Cr(VI);溶液初始浓度、NZVI投加量等是影响Cr(VI)脱除的主要因素,Cr(VI)去除率随反应温度和NZVI投加量升高而升高,随初始浓度升高而降低.实验表明,该纳米铁在废水除铬领域具有较好的应用前景.     

硬度对钢蜗轮副用材料磨损行为的影响

为了探讨硬度对钢蜗轮副材料磨损行为的影响,为研究钢蜗轮副合理的硬度配对提供试验依据。通过不同的热处理工艺,使12Cr2Ni4低碳合金钢获得了5种不同硬度的试样,然后在无润滑,室温条件下,在SRVⅣ微动磨损试验机上考察了硬度对12Cr2Ni4钢-18Cr2Ni4WA钢摩擦副磨损行为的影响。结果表明：试验条件下,随着12Cr2Ni4钢硬度的增加,12Cr2Ni4钢的磨损体积减小,其偶件18Cr2Ni4WA钢的磨损体积增大,当12Cr2Ni4钢硬度位于HRC39-HRCAl之间时,摩擦副双方的磨损量相等;12Cr2Ni4钢的相对耐磨性和摩擦系数都随12Cr2Ni4钢硬度的增加而增大,最大的相对耐磨性和摩擦系数的最大值均约为0．9。     

聚酰胺树脂对Cr(Ⅲ)和Cr(Ⅵ)富集分离的研究

以戊二醛、三乙烯四胺、乙二胺为原料,制备了聚酰胺树脂.用聚酰胺树脂填充分离柱,在1 mol/L的酸度条件下,以5 mL/min的流速洗脱Cr(Ⅵ),Cr(Ⅵ)被全部吸附而Cr(Ⅲ)不被吸附.被吸附的Cr(Ⅵ)用10g/L氢氧化钠从聚酰胺分离柱上洗脱.分离的Cr(Ⅲ)和Cr(Ⅵ)用棓花青褪色光度法在530 nm下分别测定其含量.此法对10 mg/L的Cr(Ⅵ)和Cr(Ⅲ)测定的相对标准偏差分别为1.24%和1.41%,加标回收率为92.0%和96.8%,实验结果令人满意.     

1673K下BaO-BaF_2-Cr_2O_3渣系的热力学性质

１６７３Ｋ下,采用－ＭｏＣｒ＋Ｃｒ２Ｏ３ＺｒＯ２（ＭｇＯ）｛Ｃｕ＋Ｃｒ｝ａｌｏｙ＋（Ｃｒ２Ｏ３）ｓｌａｇＭｏ＋固体电解质电池测定了ＢａＯＢａＦ２Ｃｒ２Ｏ３渣系中Ｃｒ２Ｏ３的活度．研究结果表明,Ｃｒ２Ｏ３的活度随其浓度升高而升高,随ＸＢａＯ／ＸＢａＦ２升高而降低．根据实验及Ｘ射线衍射结果推测了该渣系的等温相图,并作出了该渣系中Ｃｒ２Ｏ３的等活度图．