Investigation of the interlayers between cemented carbides and titanium carbide coatings obtained by chemical vapor deposition

Data are presented on the microstructure, microhardness and chemical composition of the interlayers between cemented carbides and chemically vapor-deposited TiC coatings. The carbon: metal ratios of the cubic carbides across the interlayers were obtained by Auger depth profile analysis. The mechanisms of nucleation and diffusional growth of the η-carbide skeleton at the upper layer of the substrate are discussed. It is proposed that a cubic carbide phase acts as a carbon donor and thus inhibits the localized formation of the η-carbide skeleton and retains the integrity of the surrounding network.     

强电流直流伸展电弧法制备硬质合金微型工具的SiC过渡层和金刚石涂层

采用强电流直流伸展电弧化学气相沉积(HCDCA CVD)技术在硬质合金微型工具表面沉积了SiC涂层作为过渡层,并在此基础之上制备了金刚石涂层。实验结果表明,采用HCDCA CVD技术在硬质合金表面制备的SiC纳米涂层连续、致密;此过渡层可有效地抑制硬质合金基体中Co的外向扩散,确保在不进行酸蚀去Co预处理的情况下,金刚石涂层对硬质合金基体具有良好的附着力。切削检测的结果表明,实验所制备的SiC过渡层/金刚石涂层的微型铣刀与未涂层微型铣刀相比,切削刃没有切削屑的粘结,且加工后的工件表面上毛刺较少。这些结果表明,SiC过渡层/金刚石涂层硬质合金微型工具将具有优异的加工性能。     

Reactive deposition of tungsten and titanium carbides by induction plasma

A study is reported on the use of induction plasma technology for the preparation of dense free-standing deposits of tungsten carbide and titanium carbide from metallic powders and methane. Phase analysis by X-ray diffraction indicates that primary carburization of the particles takes place in-flight giving rise to the formation of W₂C and TiC_1–x . Secondary carburization occurs in the deposits resulting in the formation of tungsten and titanium carbides. Microstructures revealed by optical and scanning electron microscopy show uniform small grains of the carbides. The reactive plasma spray-formed tungsten carbide shows transgranular fracture, while pure tungsten deposits show intergranular fracture.     

Formation of technological protective coatings by chemical vapor deposition

We perform the theoretical substantiation of the choice of modifiers of the processes of thermal treatment used to form nanometer and thin-film technological protective coatings (nanolayers), which give new properties to the metal surfaces of the products. This technological procedure is quite new, very promising, and does not require significant changes in the existing technological schemes. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 51–55, September–October, 2006.     

Laser surface modification of titanium substrate for pulsed laser deposition of highly adherent hydroxyapatite

Biomedical implant devices made out of titanium and its alloys are benefited by a modified surface or a bioactive coating to enhance bone bonding ability and to function effectively in vivo for the intended period of time. In this respect hydroxyapatite coating developed through pulsed laser deposition is a promising approach. Since the success of the bioactive ceramic coated implant depends mainly on the substrate-coating strength; an attempt has been made to produce micro patterned surface structure on titanium substrate for adherent hydroxyapatite coating. A pulsed Nd-YAG laser beam (355 nm) with 10 Hz repetition rate was used for surface treatment of titanium as well as hydroxyapatite deposition. The unfocussed laser beam was used to modify the substrate surface with 500–18,000 laser pulses while keeping the polished substrate in water. Hydroxyapatite deposition was done in a vacuum deposition chamber at 400°C with the focused laser beam under 1 × 10⁻³ mbar oxygen pressure. Deposits were analyzed to understand the physico-chemical, morphological and mechanical characteristics. The obtained substrate and coating surface morphology indicates that laser treatment method can provide controlled micro-topography. Scratch test analysis and microindentation hardness values of coating on laser treated substrate indicate higher mechanical adhesion with respect to coatings on untreated substrates.     

Chemical vapor deposition of tungsten oxides: A comparative study by X-ray photoelectron spectroscopy,X-ray diffraction and reflection high energy electron diffraction

Thin films of tungsten compounds have been deposited by pyrolysis of W(CO)₆ on aluminium plates held at 400°C in oxygen or a neutral environment. Such films have been analysed by X-ray photoelectron spectroscopy X-ray diffraction and reflection high energy electron diffraction. Different compounds have been revealed ranging from metalliic tungsten to fully oxidized tungsten. The X-ray photoelectron spectroscopy study of the W_4f doublet has enabled the determination of various oxidation states of tungsten. A rather good agreement is found with the X-ray diffraction and reflection high energy electron diffraction measurements.     

等离子热丝化学气相沉积金刚石膜工艺参数研究

采用等离子热丝化学气相沉积(PHFCVD)装置进行了金刚石薄膜的制备实验。实验条件为：氢气流量为200sccm,甲烷流量为2～12sccm,基体温度为700～900℃,偏压为0～400V,真空室压力为4kPa。通过实验得出了甲烷含量、基体温度和偏压对沉积金刚石膜的影响,并运用扫描电子显微镜(SEM)、原子力显微镜(AFM)和X射线衍射(XRD)等测试方法对金刚石薄膜进行了观察分析。     

Chemical vapor deposition of spectrally selective surfaces for high temperature photothermal conversion

Chemical vapor deposition was adapted to the fabrication of multilayer thin film systems of the spectral selectivity required for photothermal solar energy conversion. The systems operate on the principle of an absorber-reflector tandem, the absorption of the solar photons being accomplished by a layer of polycrystalline or amorphous silicon and the thermal emittance being reduced by a silver or molybdenum reflector. The surfaces were tested for several thousand hours at 500°C without degradation of their optical performance.     

The effects of oxygen on diamond synthesis by hot-filament chemical vapor deposition

The effects of oxygen addition on the synthesis of diamond are extensively studied by using the hot-filament chemical vapor deposition (HFCVD) method, in which it is simple and easy to control the deposition parameters independently. Diamond films are deposited on silicon wafers under the conditions of substrate temperature 530–950 C; total reaction pressure 700–8000 Pa; and methane concentration 0.4–2.4% in both CH₄–H₂ and CH₄–H₂–O₂ systems.At deposition conditions of low substrate temperature, high CH₄ concentration or high total pressure, soot-like carbon and/or graphite are deposited without oxygen addition. When even a small amount of oxygen (about 0.6%) is added, well-faceted diamond films are observed in scanning electron microscopy micrographs and a sharp diamond peak in the Raman spectra appears. The range of deposition parameters for high-quality diamond syntheses are extended by oxygen addition (low substrate temperature, high methane concentration and high reaction pressure).     

Surface modification of high aspect ratio structures with fluoropolymer coatings using chemical vapor deposition

Initiated chemical vapor deposition (iCVD) was used to coat the internal surfaces of high aspect ratio capillary pore membranes and silicon trenches with poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA). The presence of the fluoropolymer coating along the pore walls of the membranes was confirmed using X-ray photoelectron microscopy, electron microprobe analysis, and contact angle measurements. The results of this study demonstrate that the iCVD process can be used to conformally coat high aspect ratio microstructures (up to 80:1) with organic polymers.     

Effect of laser power on electrical conductivity of BaTi5O11 films prepared by laser chemical vapor deposition method

BaTi₅O₁₁ films were prepared on Pt/Ti/SiO₂/Si substrates by a laser chemical vapor deposition method. The effect of laser power (P _L) on the electrical conductivity of the BaTi₅O₁₁ films was investigated. The electrical resistivity of the grains was much higher than that of the grain boundaries, which indicated that the electrical conductivity along the grain boundary was dominant. For the BaTi₅O₁₁ films, the conduction was mainly attributed to oxygen vacancies, and the electrical conductivity was strongly affected by their microstructures and the concentration of the charge carriers. With increasing the P _L, the grain size increased and the grain-boundary density decreased, which resulted in the decrease of the electrical conductivity. At the same time, the increase of T _dep led to higher concentration of charge carriers, which resulted in the increase of electrical conductivity.     

以液态碳硅烷为先驱体制备CVD SiC涂层

合成了液态碳硅烷并对其结构进行了分析,以液态碳硅烷为先驱体在900 ℃、低压的条件下采用化学气相沉积工艺制备了SiC涂层.实验结果表明,液态碳硅烷是以Si-C键为主链的数种低分子聚合物的混合物,分子组成中不含氧和腐蚀性元素,可通过分馏得到具有合适沸点的先驱体.涂层表面光滑且质硬,沉积产物为较纯的部分结晶的β-SiC.     

直流热阴极CVD金刚石薄膜生长特性研究

为了获得高质量的金刚石薄膜,采用直流热阴极化学气相沉积系统分别在不同基片温度和不同碳源气体含量条件下生长金刚石薄膜,利用Raman光谱、SEM和XRD检测方法研究了基片温度和碳源气体含量对金刚石薄膜生长特性的影响.结果表明,金刚石薄膜与基片Mo之间有Mo2C的过渡层存在;1000℃的温度能够促进金刚石晶体的生长,抑制其他碳杂质的形成,CH4体积分数为2%适于快速生长高纯度的金刚石薄膜.     

Adhesion of TiC and TiN coatings prepared by chemical vapour deposition on WC-Co-based cemented carbides

Adhesion energies of CVD-prepared TiC and TiN coatings on WC-Co-based cemented carbides are determined on the basis of an energy formulation of the scratch test. Values found for the adhesion energyW areW _TiC=10 J m^–2 andW _TiN=46 J m^–2.     

Single-step fabrication of nanolamellar structured oxide ceramic coatings by metal-organic chemical vapor deposition

Oxide ceramic coatings in the system Y2O3-Al2O3-ZrO2 were fabricated in laboratory scale by using a MOCVD unit. A hot wall reactor was used along with different precursor feeding systems. Most experiments were carried out by using powder flash evaporation including a screw feeder for precursor powder delivery. For comparison, further samples were fabricated by using band flash evaporation and continuous evaporation from a crucible. Oxygen was used in all cases as reactant gas. Aluminium-tris-2,4-pentanedione (Al(acac)3), yttrium-tris-2,2,6,6-tetramethyl-3,5-heptanedione (Y(thd)3) and zirconium-tetrakis-2,2,6,6-tetramethyl-3,5-heptanedione (Zr(thd)4) were applied as metal-organic precursors because of their similar vaporization behaviour under the given conditions. The coating stoichiometry was varied from pure alumina to complex ternary compositions in the system Y2O3-Al2O3-ZrO2. Both kinds of ternary coatings fabricated by using flash evaporation methods show a nanolamellar microstructure in the as deposited state. Heat treating experiments at 1200 degrees C for up to 5 days enhance the lamellar character of the coating deposited by using powder flash evaporation. The lamellar microstructure is due to alternating YSZ enriched layers and YAG enriched layers in this state. However, the coating fabricated by using band flash evaporation shows a dense interpenetrating network of YSZ and YAG after heat treating instead of a lamellar microstructure observed in the as deposited state.     

Effect of laser power on microstructure and dielectric properties of BaTi5O11 films prepared by laser chemical vapor deposition method

BaTi₅O₁₁ films were prepared on Pt/Ti/SiO₂/Si substrates by a laser chemical vapor deposition method. The effect of laser power (P _L) on microstructure and dielectric properties of the BaTi₅O₁₁ films was investigated. With increasing P _L from 62 to 108?W, the deposition temperature (T _dep) monotonously increased from 872 to 951?K. At T _dep?=?920?K (P _L?=?90?W), the BaTi₅O₁₁ film had $ (\overline{3} 01) $ preferred orientation. At T _dep?≥?938?K (P _L?≥?98?W), the preferred orientation changed to $ (\overline{3} 22)/(\overline{2} 23) $ . The deposition rate (R _dep) was 154.8–177.6?μm?h^?1. With increasing T _dep, the surface morphologies changed from rectangular to pyramidal, and the dielectric constant (ε _r) increased from 18.3 to 21.4 at 1?MHz and 300?K.     

Microstructure and properties of tungsten heavy alloys fabricated by laser direct deposition

In this paper, tungsten heavy alloys (THAs) were fabricated by laser direct deposition technology. The phase composition, microstructure and the influences of Fe and Co content on the properties of THAs were investigated. The results showed that the laser deposition layers were composed by W, Ni₄W and Ni, fine and dense columnar crystals were distributed between non-melting W particles. The direction of crystals growth nearly paralleled the deposition direction at the bottom of deposition layers and nearly paralleled the scanning direction at the top. Both Fe and Co could increase the tensile strength of THAs and the elongation of W–Ni–Co alloys was higher than W–Ni–Fe alloys.     

Features of nanostructured coatings obtained by laser deposition of carbon nanotubes

The effect of carbon nanotubes (CNTs) on the surface mechanical strength and transparency of various soft optical materials for the UV and IR spectral range, semiconductors, metals, and plastics has been studied. The prospects of using laser surface processing and applying field-oriented CNTs are demonstrated. It is established that the laser deposition of CNTs leads to a two- to tenfold increase in the surface strength and a 2–10% modification of the optical transmission spectrum of materials.     

Nano structured physical vapor deposited coatings by means of picosecond laser radiation

Molding of nano structures by injection molding leads to special requirements for the tools e.g., wear resistance and as low as possible release forces of the molded components. On the other hand it is not allowed to affect the replication precision. Physical vapor deposition is one of the promising technologies for applying coatings with adapted properties like high hardness, low roughness, low Young's modulus and less adhesion to the plastics melt. Although physical vapor deposition technology allows the deposition of films on micro structures without changing the structure significantly, film deposition on nano structures and small micro structures leads to a relevant change in surface topography. For this reason direct structuring of physical vapor deposition coatings might be beneficial. In this paper structuring was done using a picoseconds ultraviolet laser, Lumera Laser "Rapid," with a master oscillator power amplifier system at 355 nm. Two different coatings were deposited by magnetron sputter ion plating physical vapor deposition technology for laser structuring tests ((Cr, Al)N, (Cr, Al,Si)N). After deposition, the coatings were analyzed by common techniques regarding hardness, Young's modulus and morphology. The structures were analyzed by scanning electron microscopy. The results show a high potential for laser structuring of coatings deposited via physical vapor deposition. Linear structures with sizes between 400 nm and 10microm were realized.