氮氩混合比对TA2真空氮化层结构与性能的影响

采用间歇式真空氮化技术对TA2钛合金进行渗氮处理。探究氮氩混合比对合金氮化层结构和性能的影响规律。结果表明:表面渗氮层主要由TiN和TiN0.3相组成,氮氩比越低其有效硬化层越厚,但会降低有效活性N原子的相对含量,不利于渗层的致密性。适当的氮氩混合比能在TA2表面形成氮化物,N原子有效地向纵深扩散,氮化物层与扩散层结合紧密,过渡良好,硬度梯度平缓;腐蚀电位随着氮氩比的增加呈现逐渐上升趋势,从氮氩比为1∶5时的-0.622V提升到氮氩比为5∶1时的-0.549V,腐蚀电流和腐蚀速率则呈现出逐渐降低的趋势。     

脉冲偏压对低温氮化不锈钢表面结构及摩擦学性能的影响

采用低温等离子体辅助氮化奥氏体不锈钢316L,能够在不破坏其抗腐蚀性能的同时有效提高不锈钢表面的摩擦学性能,研究了不同脉冲偏压下氮化层的结构和摩擦学性能(硬度、摩擦系数和耐磨性)。采用X射线衍射仪研究了脉冲偏压对氮化层相结构的影响;采用光学显微镜和扫描电镜分别观察了氮化层表面和横截面的形貌,并利用能量色散谱测量了氮化层中氮含量及其分布;基于纳米压痕和摩擦磨损结果,研究了脉冲偏压对氮化层摩擦学性能的影响。结果表明:低温氮化后,不锈钢表面形成一层无氮化物析出的单一过饱和固溶体相——扩展奥氏体γN,晶格常数随偏压的增加由0.359增至0.395nm。当脉冲偏压为-300 V时,氮化层厚度达9.45μm,表面硬度达21.0 GPa,摩擦系数降低至0.09,耐磨性能获得显著提高。     

激光和等离子体混合法氮化钛表面

采用激光和氮等离子体混合方法在大气气氛下对钛样品表面进行处理,获得了钛氮化合物表层.利用X射线衍射仪(XRD)对氮化处理后的样品测试,得到了样品的相结构.分别使用该方法与普通激光氮化方法,在相同条件下对样品表面进行氮化处理,结果表明通过混合方法提高了氮化物含量,并有效地抑制了氧化发生.讨论了氮等离子体流量对混合法氮化效果的影响.随着氮等离子体流量的增加,氮化物含量增加;但是当氮等离子体流量＞0.8m3/h后,氮化所需活化氮达到饱和,氮化物含量不再增加.     

Ni-Cr-Co-Mo-W-Ta-Al合金在900℃和1000℃的高温氧化行为

采用X射线衍射(XRD),扫描电镜(SEM)及能谱(EDAX)等方法,研究了Ni-4.66Cr-5.87Co-7.54Mo-2.90W-4.97Ta-6.32Al合金在900℃和1000℃的高温氧化行为。结果表明,合金氧化动力学曲线遵循氧化初期氧化增重速率较快,氧化期间氧化动力学曲线呈波浪式变化,且呈现氧化温度越高波浪式越明显的特征;氧化300h后合金表面氧化物膜分为2层,外层氧化物为NiO、Ni_2Cr_2O_4、Ni_2CoO_4和CoTa_2O_6,分布在外层的CoTa_2O_6抑制基体中元素Al向外扩散,形成内层氧化物Al_2O_3。在氧化期间,合金内部生成了内氮化物AlN,且在合金内部AlN与Al_2O_3成规律性分布,与外氧化膜相邻的为元素Al的内氧化物Al_2O_3区域,远离外氧化膜的基体内部为元素Al的内氮化物AlN区域,随氧化温度升高,内氧化区和内氮化区的深度增加,内氧化物和内氮化物的尺寸增大。     

氮势对奥氏体不锈钢离子渗氮性能的影响

对AIS1304奥氏体不锈钢进行了不同氮势的离子渗氮,利用金相显微镜、轮廓仪、摩擦磨损试验机、X射线衍射仪和显微硬度计测试了经渗氮处理后试样改性层的截面形貌、微观结构、相组成和力学性能,并与未渗氮的试样进行了比较。结果表明：随着氮势的增加,试样表面的渗层深度、磨损程度、显微硬度呈规律性变化;X射线衍射分析表明：低氮势容易形成S相,高氮势有利于氮化物的形成。     

一种镍基合金在900和1000℃的高温氧化行为

采用X射线衍射(XRD),扫描电镜(SEM)及能谱(EDAX)等方法,研究了Cr5.0 Co8.0 Mo0.9W5.5 Ta7.4 Al6.0 Re4.2合金在900和1 000℃的氧化行为。结果表明,氧化动力学曲线遵循氧化初期氧化增重速率较快,氧化期间氧化动力学曲线呈波浪式变化,且呈现氧化温度越高波浪式越明显的特征。在900℃氧化300 h后合金表面氧化物膜分为3层,外层为Ni O、Ni2Cr2O4、Ni2Co O4和Cr Ta O4;中间层为平直的Al2O3层,内氧化层为Al2O3,氧化期间,分布在外层的Cr Ta O4抑制基体中Al向外扩散,并抑制氧化膜的生长,使氧化速度降低。1 000℃时合金表面的氧化物膜分为2层,外层为Ni O、Ni2Cr2O4、Ni2Co O4和Cr Ta O4;内氧化层为Al2O3。在900和1 000℃氧化期间,合金均发生元素Al的内氧化和内氮化,与外氧化膜相邻的区域为元素Al的内氧化区,远离外氧化膜的基体内部形成元素Al的内氮化区,随氧化温度升高,内氧化区和内氮化区的深度增加,内氧化物和内氮化物的尺寸增大。     

气体氮碳共渗中NH3和CO流量对低碳钢渗层组织及其性能的影响

通过调控气体氮碳共渗过程中的NH_3和CO流量来调控气氛中的氮化势和碳势,从而调控共渗层的微观组织和性能。采用扫描电镜、X射线衍射仪、显微硬度计和电化学分析仪研究了气体氮碳共渗过程中的NH_3和CO流量对低碳钢氮碳共渗层的微观组织结构及其性能的影响。研究结果表明:气体氮碳共渗气氛中,随着NH_3流量的增加,化合物层厚度增大但致密性降低;随着CO流量的增加,化合物层致密性逐渐增大,但渗层厚度先增大后减小。氮碳共渗过程中C的加入可抑制γ'相的形成而促进ε相的产生,过量的C会形成θ相,但是C的渗入对渗层腐蚀性能影响较小。NH_3和CO对氮碳共渗过程中的协同作用表现为,当NH_3流量增加时,可相应增加CO流量来获得较厚、致密、耐腐蚀的化合物层。     

Ti5Mo5V3Al-xCr系合金等温时效相变动力学

利用同步X射线衍射技术研究了Ti5Mo5V3Al-xCr(x=1.0,3.0,5.0,7.0和9.0)系列合金在550℃的α+β→β等温相变动力学。结果显示,Ti5Mo5V3Al-xCr系列合金等温相变为长程扩散控制型相变,相变过程可以用JMA方程进行宏观描述。等温时效过程中,1Cr合金的相变速率最快,且随Cr含量的增加,相变速率变慢。Cr含量随平衡态α相含量增加呈线性递减规律。Cr元素含量对合金相变点及平衡态相含量的影响是造成合金系等温相变动力学行为差异的主要原因。     

离子能流密度对AISI304不锈钢氮化层摩擦性能的影响

采用低温等离子体氮化技术,对AISI304不锈钢进行表面氮化处理。考察了离子能流密度对不锈钢氮化层性能的影响。运用X射线衍射、扫描电镜和显微硬度计等分析手段对氮化层的物相组成及表面硬度进行分析及测量;利用球-盘摩擦实验在干摩擦条件下对氮化层的摩擦磨损性能进行测试。结果表明:AISI304不锈钢经低温等离子体氮化处理后,形成单一高氮面心立方相γN。在氮化处理过程中,离子能流密度受工作压力及基片负偏压影响较大。离子能流密度变化能显著影响不锈钢氮化层的摩擦性能,随着离子能流密度的增加,氮化层显微硬度增大,摩擦系数减小,耐磨损性能上升。     

氮化钽薄膜的制备与结构研究

利用磁控反应溅射技术制备了氮化钽薄膜，利用ＴＥＭ、ＸＲＤ技术研究了薄膜的微观结构。研究结果表明：薄膜中多相共存；薄膜晶粒细小（１６ｎｍ左右）；同时还发现，在一定工作压力下，随着氮分压的提高，氮化物晶粒形成的取向改变，即平行于基体表面生长的晶面会有改变。一定工作压力下，制备的氮化钽薄膜硬变高达４０００ｋｇ／ｎｍ＾２以上。本文探讨了氮化钽薄膜高硬度的原因，并且讨论了随氮分压的提高薄膜织构变化的原因。     

A simulation study of the effect of varying nitrogen potential on behavior of precipitation in nitridation of alloys

An atomic model for precipitation of compound in alloys, which couples a cellular automaton model for growth/dissociation of precipitates and a randomwalk model for diffusion, has been developed and programmed for two-dimensional computer simulation. A boundary condition that accounts for both atmospheric nitrogen potential and interface transfer rate of nitrogen at the surface has been set up. A series of simulations were carried out for a qualitative study of the effect of varying nitrogen potential during nitridation of alloy steels on kinetics and morphology of nitride precipitation behavior.     

Modification of Aluminum Properties; by Nitrogen Ion Implantation

The formation of aluminum nitride precipitates using nitrogen ion implantation and the resulting changes of mechanical properties were studied. The modifications depended on the implantation parameters such as fluence, energy and temperature during implantation. Nitrogen implantation was carried out in pure aluminum for single and multi energy modes at various temperatures. The use of several energies during multi-step implantation allowed as to obtain a constant nitrogen concentration of about 130 nm as revealed by Rutherford backscattering spectroscopy (RBS). Grazing incidence X-ray diffraction (GXRD) indicated that hexagonal aluminum nitride was formed. The mechanical properties of nitrogen implanted in aluminum were studied by nanoindentation. Hardness and Young modulus depth profiles were analyzed in order to find the best implantation conditions for the improvement of the surface properties of aluminum.     

Nitriding behaviour of maraging steel: experiments and modelling

The microstructure and the kinetics of growth of the nitrided zone of a Mo-containing maraging steel were investigated by performing gaseous nitriding at temperatures between 713 K (440 °C) and 793 K (520 °C) and at nitriding potentials up to 0.5 atm^?1/2 for both solution-annealed and precipitation-hardened specimens. The microstructure of the nitrided zone was investigated by means of X-ray diffraction (phase constitution; crystal imperfection). Fine, initially largely coherent Mo₂N-type precipitates developed in the nitrided zone. The elemental concentration-depth profiles were determined employing glow discharge optical emission spectroscopy (GDOES). The nitrogen content within the nitrided zone exceeds the nitrogen content expected on the basis of the molybdenum content and the equilibrium solubility of nitrogen in a (stress-free) ferritic matrix: excess nitrogen occurs. A numerical model was applied to predict the nitrogen concentration-depth profile within the nitrided layer. The model describes the dependence on time and temperature of the nitrogen concentration-depth profiles with, as fit parameters, the surface nitrogen concentration, the diffusion coefficient of nitrogen in the matrix, a composition parameter of the formed nitride and the solubility product of the nitride-forming element and dissolved nitrogen in the matrix. Initial values for the surface nitrogen concentration and the composition parameter were determined experimentally with an absorption isotherm and fitted to the measured nitrogen concentration-depth profiles. The results obtained revealed the striking effects of the amount of excess nitrogen and the extent of precipitation hardening on the developing nitrogen concentration-depth profile.     

Influence of hydrogen on mechanical properties of nitrogen supersaturated austenitic stainless steels

Abstract

Alloying austenitic stainless steels with nitrogen up to a concentration of 1 wt-% improves yield strength, tensile strength, and ductility. Further increase in the nitrogen concentration results in chromium nitride precipitation at the grain boundaries and a decrease in the ductility with a change in the fracture mode from ductile to intergranular. Hydrogen charging causes high reversible dilatation in the lattice and remarkable reduction in the ductility. The ductility losses caused by hydrogen are more pronounced at higher nitrogen concentrations and a change of the fracture mode from intergranular to transgranular is observed in steels with more than 1 wt-% nitrogen. Chromium nitride precipitates are shown to have an insignificant role in the hydrogen embrittlement. Hydrogen charging steels with nitrogen concentrations of below 1 wt-% enhances the strengthening effect of nitrogen but, at higher nitrogen concentrations, hydrogen is shown to be detrimental to the strength.     

The plastic deformation of copper-2 at. % cobalt alloy single crystals

Copper-2 at. % cobalt alloy single crystals containing coherent and/or incoherent spherical cobalt precipitates (60 Å相似文献   

Ion-nitriding of an Fe-19 wt % Cr alloy

The ion-nitriding behaviour of an Fe-18.75wt% Cr alloy was investigated at 803 K under constant plasma conditions. Both a thin surface layer of-Fe₄N and an internal-nitriding layer were observed. The nitride formed in the internal-nitriding layer was found to be CrN, rather than Cr₂N. The hardness of the nitriding layer rises to Hv=1200 due to small CrN precipitates. The growth rate of the internal nitriding layer, in the present alloy is controlled by a nitrogen diffusion process in the matrix metal,-iron. Because such ion-nitriding behaviour is analogous to that of internal-oxidation, the growth rate of nitriding was discussed according to the rate equation to that of internal-oxidation. The nitrogen diffusion in the present alloy is scarcely affected by the CrN precipitates.     

大功率CO2激光原位直接反应合成TiN/Ti 复合材料的研究

使用大功率CO₂激光原位直接反应合成TiN /Ti 复合材料, 分析了材料的微观结构、物相组成、成分及显微硬度分布。结果发现: 氮化层是富钛结构的, 由TiN 相和α-Ti 构成, TiN 以枝晶形式在氮化层均匀分布。材料横截面显微硬度连续变化。氮化层的氮化程度随激光作用时间的增加而增加, 辐照的激光能量密度越高, 氮化层的厚度越大。激光功率密度, 激光扫描速度, 氮气喷射压强分别为3. 35×105W·cm-2, 300mm·min-1, 0.35M Pa 时, 材料表面硬度值达到Hv1600, 氮化层的厚度有350Lm。      

Corrosion behavior of PIRAC nitrided Ti-6Al-4V surgical alloy

Hard titanium nitride (TiN) coatings were obtained on the surface of Ti-6Al-4V alloy using an original PIRAC nitriding method, based on annealing the samples under a low pressure of monatomic nitrogen created by selective diffusion of N from the atmosphere. PIRAC nitrided samples exhibited excellent corrosion resistance in Ringer's solution in both potentiodynamic and potentiostatic tests. The anodic current and metal ion release rate of PIRAC nitrided Ti-6Al-4V at the typical corrosion potential values were significantly lower than those of the untreated alloy. This, together with the excellent adhesion and high wear resistance of the TiN coatings, makes PIRAC nitriding an attractive surface treatment for Ti-6Al-4V alloy surgical implants.     

Beneficial effects of nitrogen on austenite antibacterial stainless steels

Nitrogen is a significant alloying element in austenite stainless steels. The aim of this paper is to evaluate the effects of nitrogen on the microstructure and properties of austenite antibacterial stainless steels. Two austenite antibacterial stainless steels containing copper and different nitrogen concentration (0.02 and 0.08 wt%, respectively) were fabricated. The microstructures and composition analysis were carried out using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and Auger electron spectroscopy (AES). The epsilon copper-rich precipitates are spherical and less than 20 nm in size, with a cube-on-cube orientation relationship with the matrix. They are dispersed on the steel surface with a mean space of about 200 nm. Nitrogen cannot only improve the antibacterial property but enhance significantly the corrosion resistance in chloride media. Nitrogen compensates the harmful effect of epsilon copper precipitates on the corrosion resistance. The nitrogen concentration in the surface of N-2 steel is four times as much as in the surface of N-1 steel. Nitrogen enrichment in the steel surface improves the corrosion resistance. The presence of higher nitrogen increases the strength and decreases the ductility of austenite antibacterial stainless steel, which could be related to the variation of stacking-fault energy associated with nitrogen concentration.