Ti-Si-N纳米复合薄膜KMC仿真中有效作用势的拟合

为了准确地实现Ti-Si-N纳米复合薄膜生长过程动力学蒙特卡罗(KMC)仿真,采用简单原子之间的有效势拟合了第一性原理计算单粒子在TiN(001)表面的吸附作用和迁移行为.通过计算分别获得Ti、Si、N单粒子沉积在TiN(001)表面有效势的计算参数a、r0和u0.Ti、Si、N单粒子在TiN(001)表面吸附能和迁移激活能拟合相对误差均小于5％,Ti、Si、N单粒子在TiN(001)表面绕2N2Ti岛迁移激活能相对误差小于10％.对势Morse势可以描述简单键性的作用力,对于较复杂的键性其计算原子之间相互作用的准确度降低.     

反应溅射Ti-Si-N纳米晶复合薄膜的微结构与力学性能

采用Ar、N2 和SiH4混合气体反应溅射制备了一系列不同Si含量的Ti Si N复合膜 ,用EDS、XRD、TEM和微力学探针研究了复合膜的微结构和力学性能。结果表明 ,通过控制混合气体中SiH4分压可以方便地获得不同Si含量的Ti Si N复合膜。当Si含量为 (4～ 9)at%时 ,复合膜得到强化 ,最高硬度和弹性模量分别为 34 2GPa和 398GPa。进一步增加Si含量 ,复合膜的力学性能逐步降低。微结构研究发现 ,高硬度的Ti Si N复合膜呈现Si3 N4界面相分隔TiN纳米晶的微结构特征 ,其中TiN纳米晶的直径约为 2 0nm ,Si3 N4界面相的厚度小于 1nm。     

Si3N4复相陶瓷半固态连接的接头组织和界面反应

根据复合材料的强化原理,用Ag-Cu-Ti钎料和TiN颗粒作为复合连接材料在半固态下连接Si3N4复相陶瓷以提高接头强度,研究了接头的组织和界面反应.结果表明,接头由母材/反应层/含微量Ti的Ag-Cu TiN/反应层/母材组成,反应层由含Ti、Si、N三种元素的一些化合物组成;TiN颗粒在Ag-Cu基体中的分布总体均匀,两者之间的界面清晰、结合致密:当TiN的加入量较小时,对连接材料与母材的界面反应没有明显影响.初步的剪切试验结果表明,采用Ag-Cu-Ti加TiN颗粒作为复合连接材料连接Si3N4陶瓷可以提高接头强度.     

采用第一性原理方法研究Nb-Si-N表面单原子绕岛吸附与迁移

针对Nb-Si-N纳米复合薄膜在沉积过程中Nb、Si、N单原子与NbN晶粒相遇之后聚集与分离情况进行了研究。采用基于密度泛函理论(DFT)第一性原理超软赝势平面波计算方法分别计算了Nb、Si、N各单原子在NbN(001)表面绕2N2Nb岛的吸附作用和迁移过程。计算结果表明,Nb、Si、N单原子在2N2Nb岛旁边的吸附能最大位置分别为P3、P1、P2,吸附能分别为7.3067,5.3521和6.7113eV;Nb、Si、N单原子绕2N2Nb岛的迁移所需的激活能分别为2.62,1.35和5.094eV。吸附能与迁移激活能较小的Si原子为激活元素促进了其它原子的扩散进而提高薄膜的致密性。沉积过程中具有较小激活能的Si原子极易围绕2N2Nb岛迁移将NbN晶粒分隔,阻止晶粒长大进而细化晶粒。     

TiN/Si3N4纳米晶复合膜的微结构和强化机制

采用高分辨透射电子显微镜对高硬度的TiN/Si3N4纳米晶复合膜的观察发现,这类薄膜的微结构与Veprek提出的nc-TiN/a-Si3N4模型有很大不同：复合膜中的TiN晶粒为平均直径约10nm的柱状晶,存在于柱晶之间的Si3N4界面相厚度为0.5～0.7nm,呈现晶体态,并与TiN形成共格界面.进一步采用二维结构的TiN/Si3N4纳米多层膜的模拟研究表明,Si3N4层在厚度约＜0.7nm时因TiN层晶体结构的模板作用而晶化,并与TiN层形成共格外延生长结构,多层膜相应产生硬度升高的超硬效应.由于TiN晶体层模板效应的短程性,Si3N4层随厚度微小增加到1.0nm后即转变为非晶态,其与TiN的共格界面因而遭到破坏,多层膜的硬度也随之迅速降低.基于以上结果,本文对TiN/Si3N4纳米晶复合膜的强化机制提出了一种不同于nc-TiN/a-Si3N4模型的新解释.     

基于TiC_(0.5)N_(0.5)/Si_3N_4复相陶瓷基体的PVD及CVD涂层刀具性能

首先,以15vol%或25vol%的TiC0.5N0.5粉体为导电第二相,利用热压烧结法制备了TiC0.5N0.5/Si3N4复相陶瓷;然后,分别通过物理气相沉积(PVD)和化学气相沉积(CVD)技术在TiC0.5N0.5/Si3N4陶瓷刀具表面沉积了CrAlN和TiN/Al2O3/TiN涂层;最后,通过对TiC0.5N0.5/Si3N4刀具进行连续切削灰铸铁实验,研究了TiC0.5N0.5含量和涂层类型对刀具磨损特征的影响,并探讨了刀具的磨损机制。结果表明:TiC0.5N0.5含量的增加有利于提高TiC0.5N0.5/Si3N4复相陶瓷刀具基体的硬度和电导率,但对耐磨性和切削寿命的影响较小;采用PVD技术沉积CrAlN涂层时,随着TiC0.5N0.5含量的增加,涂层的厚度、结合强度和硬度都得到提高,涂层刀具的磨损性能显著提高,切削寿命也明显延长;而采用CVD技术沉积TiN/Al2O3/TiN涂层时,TiC0.5N0.5含量的变化对涂层的厚度、结合强度和硬度基本没有影响,TiN/Al2O3/TiN涂层刀具整体切削性能变化不大。CrAlN涂层和TiN/Al2O3/TiN涂层都可明显改善TiC0.5N0.5/Si3N4复相陶瓷刀具的耐磨性和切削寿命;相对于TiN/Al2O3/TiN涂层,CrAlN涂层具有更高的涂层硬度和粘着强度,但TiN/Al2O3/TiN涂层具有较大的涂层厚度,TiN/Al2O3/TiN涂层刀具表现出更加优异的耐磨性和切削寿命。TiC0.5N0.5/Si3N4复相陶瓷刀具的磨损机制以机械摩擦导致的磨粒磨损为主,伴随有少量的粘结磨损。     

Ti基复合材料界面反应扩散的微观分析

通过SiC连续纤维增强Ti基复合材料的制备及在不同条件下的热处理试验,利用TEM,SEM,EDS及XRD分析技术研究复合材料的界面反应以及产物相的形成.研究结果表明:SiC /Ti复合材料界面发生了反应扩散,反应元素C,Ti,Si在界面反应层中出现浓度波动;界面反应产物被确认为是Ti3SiC2 ,TiC和 Ti5Si3,在靠近SiC侧出现Ti3SiC2和Ti5Si3单相区,靠近Ti基体侧为Ti5Si3单相区,中间为TiC Ti5Si3双相区;SiC/Ti复合材料界面相序列为SiC┃Ti3SiC2┃Ti5Si3┃TiC Ti5Si3┃Ti5Si3┃Ti.     

Recalescence behaviour of rapid solidification in the deeply undercooled Ni-B hypereutectic alloy and formation mechanism of anomalous eutectic

以Ti--Al--Si合金作为合金化填充材料, 用氮氩混合等离子气体对SiCp/Al基复合材料进行等离子弧原位焊接, 研究了Ti-Al-Si对焊缝的组织和性能的影响. 结果表明: 填加Ti-75Al-5Si合金时, 熔池中Si和Ti的联合作用有效抑地制了针状脆生相Al4C3的生成, 形成了稳定的熔池, 得到了以TiN、AlN 、TiC和Ti5Si3等为二次增强相的焊缝. 焊缝的组织致密, 结合良好, 其最大拉伸强度为225 MPa     

Ti-Al-Si对SlOp/Al基复合材料等离子弧焊焊缝的组织与性能的影响

以Ti-Al-Si合金作为合金化填充材料,用氮氩混合等离子气体对SiCp/Al基复合材料进行等离子弧原位焊接,研究了Ti-Al-Si对焊缝的组织和性能的影响.结果表明:填加Ti-75Al-5Si合金时,熔池中Si和Ti的联合作用有效抑地制了针状脆生相Al4C3的生成,形成了稳定的熔池,得到了以TiN、AlN、TiC和Ti5Si3等为二次增强相的焊缝.焊缝的组织致密,结合良好,其最大拉伸强度为225 Mpa.     

Ti—Al—Si对SiCp/Al基复合材料等离子弧焊焊缝的组织与性能的影响

以Ti-Al-Si合金作为合金化填充材料,用氮氩混合等离子气体对SiCp/Al基复合材料进行等离子弧原位焊接,研究了Ti-Al-Si对焊缝的组织和性能的影响.结果表明：填加Ti-75Al-5Si合金时,熔池中Si和Ti的联合作用有效抑地制了针状脆生相Al4C3的生成,形成了稳定的熔池,得到了以TiN、AlN、TiC和Ti5Si3等为二次增强相的焊缝.焊缝的组织致密,结合良好,其最大拉伸强度为225 MPa.     

The effects of oxygen partial pressure on BST thin films deposited on multilayered bottom electrodes

Ba_0.5Sr_0.5TiO₃ (BST) thin films have been deposited by r.f. magnetron sputtering on silicon and platinum-coated silicon substrates with different buffer and barrier layers. BST films deposited on Si/SiO₂/SiN/Pt and Si/SiO₂/Ti/TiN/Pt multilayer bottom electrode have been used for the fabrication of capacitors. XRD and SEM studies were carried out for the films. It was found that the crystallinity of the BST thin film was dependent upon oxygen partial pressure in the sputtering gas. The role of multilayered bottom electrode on the electrical properties of Ba_0.5Sr_0.5TiO₃ films has been also investigated. The dielectric properties of BST films were measured. The results show that the films exhibit pure perovskite phase and their grain sizes are about 80–90 nm. The dielectric properties of the BST thin film on Si/SiO₂/Ti/TiN/Pt electrode was superior to that of the film grown on Si/SiO₂/SiN/Pt electrode.     

Interaction of Si3N4 with titanium at elevated temperatures

In relation to the joining of silicon nitride ceramics to metal, the reaction products and the reaction mechanism between Si3N4 and titanium have been investigated under a nitrogen or an argon atmosphere at temperatures of 823–1573 K. Using Si3N4/titanium powder mixtures, reaction rates were determined by thermogravimetric (TG) analysis, and reaction products were examined by X-ray diffraction. At higher temperatures and on prolonged heating, reaction products were changed in the following orders: TiN2, TiN2+TiN, TiN+TiSi2+Si, TiN+Si and TiN (nitrogen atmosphere) and TiN2+Ti5Si5, TiN2+TiN+Ti5Si3 and TiN+TiSi2+Si (argon). By relating these results to TG measurements, a full understanding of the reaction mechanism between Si3N4 and titanium was acquired. This revised version was published online in November 2006 with corrections to the Cover Date.     

The CVD of Ceramic Protective Coatings on SiC Monofilaments for Use in Titanium Based Composites

TiB₂, TiC and TiN protective coatings have been deposited onto SiC monofilament fibers by the CVD technique using a cold-wall reactor at reduced pressure. The effect of deposition conditions on the morphology, microstructure, phase composition and adherence of the coatings were studied. The physical and chemical compatibility of these ceramic coatings with SiC filaments together with titanium-alloy matrices were assessed and compared. Dense and uniform TiB₂ coatings have been deposited successfully onto SiC monofilaments. The coating is stable on the SiC fiber and acts as an effective: barrier against the vigorous SiC/Ti-6Al-4V interfacial reaction. The adhesion of TiC on SiC fibers is comparatively weaker than the TiB₂ coating. There was no significant reaction found at the interface of TiC/Ti except at the interface of TiC/SiC. Examination of the TiN coatings showed severe cracking and spalling, hence TiN could not provide protection in a Ti-alloy matrix.     

Resulting morphologies on quenching of titanium aluminide alloys

Abstract

The effect of alloying elements (aluminium, silicon, niobium, and zirconium) on the mechanism and morphology of the allotropic transformation Ti-β(bcc) → Ti-α(hcp), occurring during the quenching of binary, ternary, and quaternary titanium aluminide alloys, has been studied. The alloys investigated were (at.-%) Ti–16Al, Ti–16Al–1Si, Ti–16Al–3·5Si, Ti–14Al–1Si–1Nb, Ti–14Al–1Si–1Zr, Ti–22Al, Ti–22Al–1Si, Ti–22Al–3·5Si, Ti–20Al–1Si–1Nb, and Ti–20Al–1Si–1Zr. The allotropic transformation in these alloys presented a very narrow temperature range for the formation of all possible α morphologies resulting from quenching. The different morphologies of α phase observed have been correlated with the competing mechanisms of β decomposition. The morphological observations indicated that small variations in thermodynamic and kinetic conditions in the β phase might account for changes in the mechanisms of formation and growth of the α phase. Additionally, the effect of the alloying elements on the ordering reaction α → α₂ occurring during quenching has been investigated. Silicon addition promoted the formation of columnar α₂ domains during quenching.     

Adhesive B-doped DLC films on biomedical alloys used for bone fixation

The long-term failure of the total hip and knee prostheses is attributed to the production of wear particles at the articulating interface between the metals, ceramics and polymers used for surgical implants and bone-fixtures. Therefore, finding an adhesive and inert coating material that has low frictional coefficient should dramatically reduce the production of wear particles and hence, prolong the life time of the surgical implants. The novel properties of the non-toxic diamond-like carbon (DLC) coatings have proven to be excellent candidates for biomedical applications. However, they have poor adhesion strength to the alloys and biomaterials. The addition of a thin interfacial layer such as Si, Ti, TiN, Mo and Cu/Cr and/or adding additives such as Si, F, N, O, W, V, Co, Mo, Ti or their combinations to the DLC films has been found to increase the adhesion strength substantially. In our study, grade 316L stainless steel and grade 5 titanium alloy (Ti-6Al-4V) were used as biomaterial substrates. They were coated with DLC films containing boron additives at various levels using various Si interfacial layer thicknesses. The best film adhesion was achieved at 8% and 20% on DLC coated Ti-6Al-4V and grade 316L substrates, respectively. It has been demonstrated that doping the DLC with boron increases their adhesion strength to both substrates even without silicon interfacial layer and increases it substantially with optimum silicon layer thickness. The adhesion strength is also correlated with the hydrogen contents in the B-DLC films. It is found to reach its maximum value of 700 kg/cm² and 390 kg/cm² at 2/7 and 3/6 for CH₄/Ar partial pressures (in mTorr ratio) for Ti-6Al-4V and 316L substrates, respectively.     

Effect of Si3N4 Addition on the Mechanical Properties, Microstructures, and Wear Resistance of Ti-6Al-4V Alloy

In order to improve the wear resistance of Ti-6Al-4V, different amounts of Si3N4 powder were added into the alloy powder and sintered at 1250℃. Porous titanium alloy with higher wear resistance was successfully fabricated. At sintering temperature, reaction took place and a new hard phase of Ti5Si3 formed. The mechanical properties of the fabricated alloys with different amounts of Si3N4 addition were investigated. The hardness of Ti-6Al-4V, which is the index of wear resistance, was increased by the addition of Si3N4. Amounts of Si3N4 addition have very significant influences on hardness and compressive strength. In present study,titanium alloy with 5 wt pct Si3N4 addition has 62% microhardness and 45% overall bulk hardness increase,respectively. In contrast, it has a 16.4% strength reduction. Wear resistance was evaluated by the weight loss during wear test. A new phase of Ti5Si3 was detected by electron probe microanalyzer （EPMA） and X-ray diffraction （XRD） method. The original Si3N4 decomposed during sintering and transformed into titanium silicide. Porous structure was achieved due to the sintering reaction.     

Phenomena of nanotube nucleation and growth on new ternary titanium alloys

Ti-30Nb-xZr and Ti-30Ta-xNb alloys have been investigated using various methods of surface nanotube formation. Ternary Ti-30Nb-xZr (x = 3 and 15 wt%) and Ti-30Ta-xNb (x = 3 and 15 wt%) alloys were prepared by using high-purity sponge Ti (Grade 4, G&S Titanium, USA), Ta, Zr and Nb spheres. The two groups of ternary Ti alloys were prepared using a vacuum arc melting furnace. Nanotube formation was carried out with a conventional three-electrode configuration with the Ti alloy specimen, a platinum counterelectrode, and a saturated calomel (SCE) reference electrode. Experiments were performed in 1 M H3PO4 with small additions of NaF (0.1-0.8 wt%), using a potentiostat. Nanotubes formed on the surfaces of the two ternary Ti alloys were examined by field emission scanning electron microscopy, EDS and XRD. The Ti-30Ta-xZr alloys had microstructure with entirely needle-like constituents; the thickness of the needle-like alpha-phase increased as the Zr content increased. The Ti-30Nb-xZr alloys had equiaxed microstructures of the beta-phase, and increasing amounts of the needle-like alpha phase appeared at the grain boundaries of the beta-phase as the Zr content increased. The nanotubes were nucleated and grew mainly on the beta phase for the Ti-30Ta-3Zr and Ti-30Nb-3Zr alloys, which had nanotubes with uniform shape, but the nanotubes were nucleated at the alpha phase for the Ti-30Ta-15Zr and Ti-30Nb-15Zr alloys, which had nanotubes with irregular shape and diameters of two sizes. The diameter and depth of the nanotubes could be controlled, depending upon the alloy composition and composition of the surface oxide films (TiO2, Nb2O5, Ta2O5, and ZrO2). It is concluded that this research that selection of the appropriate alloying element can allow significant control of the nanotopography of these Ti alloy surfaces and that it is possible to control the surface nanotube size to promote long-term osseointegration for clinical dental or orthopedic use.     

Suppression of platinum penetration failure in Ti/Pt/Au beam lead metal systems using a TiN diffusion barrier

In this paper we report the ability of a TiN diffusion barrier to suppress metal penetration which induces junction-shorting failure in a Ti/Pt/Au beam lead metal system on polycrystalline silicon. Practical devices, known as stepped electrode transistors, were prepared with and without the TiN layer, and the junction-shorting failure during heat treatment at 280–500 °C was investigated. Median lives at 300 °C of 2 × 10⁵ h and 1.2 × 10³ h and activation energies of 1.8 eV were and 1.8 eV were obtained with and without the TiN layer respectively. Failure analysis, carried out by Si Kβ soft X-ray spectroscopy using an electron microprobe, showed that the junction-shorting failure was dominated by platinum penetration equivalent to the localized growth of platinum silicide.     

Preferred growth of epitaxial TiN thin film on silicon substrate by pulsed laser deposition

Epitaxial TiN thin films on silicon substrates were prepared by pulsed excimer laser (KrF, 34 ns) ablation of a hot-pressed TiN target in nitrogen gas atmosphere. X-ray diffraction (XRD) showed that the preferred orientations of TiN thin films did not change with substrate temperatures, nitrogen gas pressure and film thickness; however, they did change with the orientations of substrates. The epitaxial orientation relationships between high-quality epitaxial TiN thin films and silicon substrates [2 4 2] TiN [2 4 2] Si, (1 1 1) TiN(1 1 1) Si and [3 1 1] TiN [3 1 1] Si, (1 0 0) TiN(1 0 0) Si. The full-width at half-maximum (FWHM) of the rocking curve of XRD and the minimum channelling yield of Rutherford backscattered spectroscopy (RBS) of the epitaxial TiN thin film were estimated to be 0.3 ° and 7.3%, respectively, indicating excellent crystalline quality of the grown film. X-ray photoelectron spectroscopy confirmed that the binding energies of Ti 2p 3/2 and N 1s core levels in epitaxial thin film were 455.2 and 397.1 eV, respectively, corresponding to those of TiN bulk. By calibrating the RBS spectra, the chemical composition of TiN thin films was found to be titanium-rich. The typical surface roughness of TiN thin film observed by scanning probe microscopy was about 1.5 nm. © 1998 Chapman & Hall