Microstructure and mechanical properties of hard carbon films prepared by heat treatment of a polymer on steel substrate

Hard carbon films were prepared on steel substrates by heat treatment of a polymer-poly(phenylcarbyne) at various temperatures in an Ar atmosphere. The influence of heat treatment temperature on the microstructure, surface roughness and mechanical properties of the resulting films was investigated by Raman spectroscopy, atomic force microscopy (AFM), nanoindenter, scratch and ball-on-disk sliding tests. The sp² C fractions of the hard carbon films and the root mean square (RMS) roughness increased as the heat treatment temperature increased. The preparation at 800 °C gave rise to carbon films with the maximum hardness and the hardness dropped with the higher temperature due to graphitization. In addition, with increasing heat treatment temperature, critical load of the carbon films, the ability of friction reduction and wear resistance increased gradually. The influence of the heat treatment temperature on the mechanical properties of the hard carbon films is discussed in combination with the structural analysis.     

Microstructure and hydrogen storage properties of Mg-Sn nanocomposite by mechanical milling

To improve the hydrogen storage properties, the composition and microstructure of Mg-Sn alloys were modified through fabricating Mg/Mg₂Sn nanocomposite by mechanical alloying. The microstructures were characterized by X-ray diffraction and scanning electron microscopy. It is found that Mg₂Sn instead of Mg(Sn) solid solution is preferably formed during milling process. Although Mg₂Sn is not a hydriding phase, the in situ formed nanosized Mg₂Sn facilitates hydrogen absorption/desorption of Mg by forming Mg/Mg₂Sn nanocomposite. The mechanically milled Mg-5 at.% Sn nanocomposite exhibits slightly elevated plateau pressure and destabilized thermodynamics due to the introduction of large amount of interface energy in Mg/Mg₂Sn nanocomposite.     

Structure and mechanical properties of TiAlN-WNx thin films

A combinatorial method was employed to grow TiAlN-WNx films by DC sputtering as well as by High Power Pulsed Magnetron Sputtering (HPPMS) where the W concentration was varied between 10-52 at.% and 7-54 at.%, respectively. Experiments were paired with ab initio calculations to investigate the correlation between composition, structure, and mechanical properties. During all depositions the time averaged power was kept constant. As the W concentration was increased, the lattice parameter of cubic TiAlN-WNx films first increased and then decreased for W concentrations above ≈ 29 at.% (DCMS) and ≈ 27 at.% (HPPMS) as the N concentration decreased. Calculations helped to attribute the increase to the substitution of Ti and Al by W and the decrease to the presence of N vacancies. Young's modulus and hardness were around 385-400 GPa and 29-31 GPa for DCMS and 430-480 GPa and 34-38 GPa for HPPMS, respectively, showing no significant trend as the W concentration was increased, whereas calculations showed a continuous decrease in Young's modulus from 440 to 325 GPa as the W concentration was increased from 0 to 37.5 at.%. The presence of N vacancies was shown to increase the calculated Young's modulus. Hence, the relatively constant values measured may be understood based on N vacancy formation as the W concentration was increased. HPPMS-deposited films exceed DCMS films in Young's modulus and hardness, which may be a consequence of the larger degree of ionization in the HPPMS plasma. It is reasonable to assume that especially the ionized film forming species may contribute towards film densification and N vacancy formation.     

Structure and mechanical properties of Cr–B–N films deposited by reactive magnetron sputtering

Cr–B–N films with various B contents were deposited by reactive magnetron sputtering from the co-deposition of Cr and B targets in the presence of the reactive gas mixture. Comparative studies on microstructure and mechanical properties between CrN and Cr–B–N films with various B contents were conducted. The addition of B to CrN films caused a decrease of the crystallization of the films, while the B existed mainly as amorphous phase of BN compound in the CrBN films. The mechanical properties were also improved. And the Cr–B–N films with 6.1 at.% B content showed highest hardness and lowest wear rate.     

Effects of nickel coating thickness on electric properties of nickel/carbon hybrid fibers

In this work, nickel/carbon hybrid fibers were prepared by the electrolytic plating on carbon fibers in order to improve electric conductivity of the carbon fibers; the effects of nickel content and coating thickness on the electric conductivity of the fibers were studied. The structural properties and surface morphologies of the hybrid fibers were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The electric conductivity of the fibers was measured using a 4-point probe method. As for experimental results, it was observed that the electric conductivity of the nickel/carbon hybrid fibers was dramatically increased in the presence of metallic nickel particles, with the best result in the condition of over 0.75 μm of the thickness due to the minimization of the inner pores.     

Structure and mechanical properties of arc evaporated Ti-Al-O-N thin films

The structure, mechanical properties, and machining performance of arc evaporated Ti-Al-O-N coatings have been investigated for an Al_0.66Ti_0.34 target composition and O₂/(O₂+N₂) gas flow-ratio varied between 0 to 24%. The coating structure was analysed using SEM, EDX, XRD, XPS, TEM, and STEM. Mechanical properties were analysed using nanoindentation and the deformation behaviour was analysed by probing the nanoindentation craters. The coatings performances in cutting tests were evaluated in a turning application in low carbon steel (DIN Ck45). It is shown that the addition of oxygen into the arc deposition process leads to the formation of a dual layer structure. It consists of an initial cubic NaCl-structure solid solution phase formed closest to the substrate, containing up to 35 at.% oxygen (O/O+N), followed by steady-state growth of a nanocomposite compound layer comprised of Al₂O₃, AlN, TiN, and Ti(O,N). The addition of oxygen increases the ductility of the coatings, which improves the performances in cutting tests. At high levels of oxygen, (> 13 at.%), however, the performance is dramatically reduced as a result of increased crater wear.     

Microstructural and mechanical properties of Al-Mg/Al2O3 nanocomposite prepared by mechanical alloying

The effect of milling time on the microstructure and mechanical properties of Al and Al-10 wt.% Mg matrix nanocomposites reinforced with 5 wt.% Al₂O₃ during mechanical alloying was investigated. Steady-state situation was occurred in Al-10Mg/5Al₂O₃ nanocomposite after 20 h, due to solution of Mg into Al matrix, while the situation was not observed in Al/5Al₂O₃ nanocomposite at the same time. For the binary Al-Mg matrix, after 10 h, the predominant phase was an Al-Mg solid solution with an average crystallite size 34 nm. Up to 10 h, the lattice strain increased to about 0.4 and 0.66% for Al and Al-Mg matrix, respectively. The increasing of lattice parameter due to dissolution of Mg atom into Al lattice during milling was significant. By milling for 10 h the dramatic increase in microhardness (155 HV) for Al-Mg matrix nanocomposite was caused by grain refinement and solid solution formation. From 10 to 20 h, slower rate of increasing in microhardness may be attributed to the completion of alloying process, and dynamic and static recovery of powders.     

Influence of bias on properties of carbon films deposited by MCECR plasma sputtering method

The mirror-confinement-type electron cyclotron resonance(MCECR) plasma source has high plasma density and high electron temperature. It is quite useful in many plasma processing, and has been used for etching and thin-film deposition. The carbon films with 40 nm thickness were deposited by MCECR plasma sputtering method on Si, and the influence of substrate bias on the properties of carbon films was studied. The bonding structure of the film was analyzed by the X-ray photoelectron spectroscopy(XPS), the tribological properties were measured by the pin-on-disk(POD) tribometer, the nanohardness of the films was measured by the nanoindenter, and the deposition speed and the refractive index were measured by the ellipse meter. The better substrate bias was obtained, and the better properties of carbon films were obtained.     

Carbon-based nanostructured composite films: Elastic, mechanical and optoelectronic properties derived from computer simulations

In this review, we present our recent computational work on carbon-based nanostructured composites. These materials consist of carbon crystallites embedded in an amorphous carbon matrix and are modeled here through classical and semi-empirical quantum-mechanical simulations. We investigate the energetics, mechano-elastic, and optoelectronic properties of these materials. Once the stability of the composites is discussed, we move on to the calculation of their elastic moduli and constants, their anisotropy and elastic recovery. At a next step, we focus on diamond composites, which were found to be the most stable among the composites studied, and went beyond the elastic regime to investigate their ideal fracture. Finally, for these materials, the electronic density of states, dielectric function, and optical response were calculated and linked to the disorder in the structures. Our findings unveil the high potential of these materials in nanotechnological applications, especially as ultra-hard coatings.     

Structural and mechanical properties of AlTiN/CrN coatings synthesized by a cathodic-arc deposition process

Monolayered AlTiN and Multilayered AlTiN/CrN coatings were synthesized by a cathodic-arc deposition process, using TiAl (with 50/50 and 33/67 at.%) and Cr elemental cathodes. The atomic ratio of Al/(Ti + Al) in the AlTiN coatings was reduced to 0.44 and 0.61, respectively, compared with the corresponding Ti₅₀Al₅₀ and Ti₃₃Al₆₇ cathode materials. The multilayered AlTiN/CrN films showed smaller crystallite size, larger lattice strain, higher hardness, higher residual stress, and better adhesion strength as well than the monolayered AlTi films. The multilayered Al_0.35Ti_0.22N_0.43/CrN coating exhibited the highest hardness of about 38 GPa and the highest H³/E*² ratio value of 0.188 GPa, indicating the best resistance to plastic deformation, among all the coatings studied.     

Preparation and mechanical properties of carbon/carbon composites with high textured pyrolytic carbon matrix

Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon (C/C) composites was 1.89 g/cm³ after depositing for 150 h. The microstructure and mechanical properties of the C/C composites were studied by polarized light microscopy, X-ray diffraction, scanning electron microscopy and three-point bending test. The results reveal that high textured pyrolytic carbon is deposited as the matrix of the composites, whose crystalline thickness and graphitization degree highly increase after heat treatment. A distinct decrease of the flexural strength and modulus accompanied by the increase of the toughness of the C/C composites is found to be correlated with the structural changes in the composites during the heat treatment process.     

Effect of applied dc bias voltage on composition, chemical bonding and mechanical properties of carbon nitride films prepared by PECVD

Carbon nitride films were deposited on Si (100) substrates using plasma-enhanced chemical vapor deposition (PECVD) technique from CH4 and N2 at different applied dc bias voltage. The microstructure, composition and chemical bonding of the resulting films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The mechanical properties such as hardness and elastic modulus of the films were evaluated using nano-indentation. As the results, the Raman spectra, showing the G and D bands, indicate the amorphous structure of the films. XPS and FTIR measurements demonstrate the existence of various carbon-nitride bonds in the films and the hydrogenation of carbon nitride phase. The composition ratio of N to C, the nano-hardness and the elastic modulus of the carbon nitride films increase with increasing dc bias voltage and reach the maximums at a dc bias voltage of 300 V, then they decrease with further increase of the dc bias voltage. Moreover, the XRD analyses indicate that the carbon nitride film contains some polycrystalline C3N4 phase embedded in the amorphous matrix at optimized deposition condition of dc bias voltage of 300 V.     

Effect of pressure on nanocrystalline diamond films deposition by hot filament CVD technique from CH4/H2 gas mixture

The effect of pressure on the deposition of nanocrystalline diamond (NCD) films in a hot filament chemical vapor deposition (HFCVD) system was investigated employing a 1% CH₄ in H₂ gas mixture. With decreasing the growth pressure from 5.0 to 0.125 kPa, a gradual reduction of the diamond grain sizes from sub-micrometer to nanometer scale was observed, accompanied by the decline of surface roughness and the evolution of film cross-sectional morphologies changing from columnar to grainy structures. The pressure also exerted prominent influence on the film growth rate. At 2.8 kPa the growth rate featured a maximum, while decreasing to higher and lower pressures. Such pressure dependence of the diamond growth rate was suggested to result from two competing effects of pressure on the concentration of reactive species near the diamond growth surface. Further, the mechanism for the NCD film formation under low deposition pressures was discussed in light of the high secondary nucleation rate.     

Structure and mechanical properties of nc-TiC/a-C:H nanocomposite films deposited by filtered cathodic arc technique

nc-TiC/a-C:H nanocomposite films were prepared by filtered cathodic arc technique. The influence of C₂H₂/Ar flow ratio on the composition, structure, and mechanical properties of films was investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, nanoindentation, and ball-on-disc tribometry. The films show a nanocomposite structure in which TiC crystallites are embedded in the amorphous matrix of a-C:H phase. C content in films increases with the flow ratio of C₂H₂/Ar, simultaneously, the crystallite size of TiC decreases. Contrary to the nc-TiC/a-C:H films deposited by magnetron sputtering in which the sp3 C content increases with C₂H₂ flow rate, the increase of C₂H₂ flow rate leads to the increase of sp2 C content in films deposited by filtered cathodic arc technique. The nc-TiC/a-C:H films deposited by cathodic arc technique have a pronounced hardness maximum of 30 GPa under the C₂H₂/Ar flow ratio of 12. Tribological performance of films is controlled by the sp2 content in films. Higher sp2 content promotes the formation of graphite-like transfer layer during sliding, and results in lower wear rate and friction coefficient.     

Influence of Si content and growth condition on the microstructure and mechanical properties of Ti-Si-N nanocomposite films

Thin films of Ti-Si-N have been prepared by ion beam assisted deposition (IBAD) from two Ti and Si targets. The silicon concentration in the deposited coatings is varied between 0 and 23.7 at.%. The influence of Si content and growth conditions on the microstructure and mechanical properties were investigated using XPS, AFM, XRD and nanoindenter. These nanocomposite coatings exhibit improved mechanical properties in comparison with TiN deposited under the same condition. The hardness measured by nanoindentation reached 42 GPa in Ti-Si-N films containing 11.32 at.% of Si, whereas TiN films only had a value of about 18 GPa. AFM showed that the finest grain size of Ti-Si-N appeared to be 5 nm when Si content was 11.32 at.%. From XPS and XRD results, the microstructures of the high hardness samples were found to consist of nanocrystal TiN grains and amorphous Si₃N₄.     

Preparation and mechanical properties of two nickel base alloy coatings achieved by electrospark deposition

Ni398 and Ni818 base alloy coatings were deposited on 1045 steel by electrospark deposition technique (ESD). Forming properties, thickness, microhardness and wear resistance of the coatings were investigated. The chemical composition and crosssection morphology were analyzed through energy dispersive spectrum (EDS) and metalloscope. The results show that the technological parameter window of Ni398 is larger than that of Ni818 electrode. However, other properties of the Ni818 coating, such as thickness and m...     

Structural and magnetic properties of Ni3N synthesized by multidipolar microwave plasma-assisted reactive sputtering

Nickel nitride layers have been synthesized by using microwave plasma-assisted reactive sputtering. In the Ar–N₂ mixture used for the deposition, the Ar partial pressure was kept constant (0.015 Pa) and the N₂ pressure p(N₂) was chosen between 0.014 and 0.045 Pa. The reactive sputtering assisted by microwave multidipolar plasma appears to be a powerful technique for tailoring the stoichiometry of transition metal nitrides. Physical measurements performed on a stoichiometric nickel nitride Ni₃N film deposited prove the non-ferromagnetic behavior of this compound.     

碳纳米管/聚酰亚胺纳米复合材料的制备及动态力学性能和介电性能

依次用混强酸和SOCl2对多壁碳纳米管(MWNTs)进行改性,解决其在有机溶剂的溶解性和在基体聚酰亚胺中分散性问题,并采用光电子能谱(XPS)和透射电镜(TEM)对改性前后的MWNTs进行表征.以4,4'-二氨基二苯醚(ODA)和3,3',4,4'-二苯甲酮四羧酸二酐(BTDA)为原料,以原位聚合法将改性碳纳米管掺杂聚酰亚胺(PI),制备MWNTs/PI纳米复合材料.通过热重分析(TGA)、动态力学分析(DMA)和电容测试对材料的热性能、动态力学和介电性能进行表征.结果表明:加入MWNTs后,材料仍有很好的热稳定性,材料的动态力学性能随MWNTs增加而增强,在50℃和10%(质量分数)MWNTs时储能模量为2.307 GPa,比纯聚酰亚胺(PI)提高23.1%;材料的介电常数随着MWNTs含量的增加明显提高,在IMHz和10%时介电常数为66.7,是纯PI的18.6倍.制备的碳纳米管/聚酰亚胺材料是一种具有优良的热学、动态力学力学和介电性能性能的纳米复合材料.     

Structure and properties of amorphous diamond-like carbon films produced by ion beam assisted plasma deposition

The microstructure and tribological properties of carbon film produced by ion beam assisted plasma deposition in a plasma source ion implantation (PSII) chamber with energies varied from 0 to 30 keV are examined. The process is illustrated schematically, and Raman spectra as well as TEM images and corre-sponding diffraction patterns of carbon films are shown.