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Nano-crystalline diamond has been extensively researched and applied in the fields of tribology, optics, quantum information and biomedicine. In virtue of its hardness, the highest in natural materials, diamond outperforms the other materials in terms of wear resistance. Compared to traditional single-crystalline and poly-crystalline diamonds, nano-crystalline diamond consists of disordered grains and thus possesses good toughness and self-sharpening. These merits render nano-crystalline diamonds to have great potential in tribology. Moreover, the re-nucleation of nano-crystalline diamond during preparation is beneficial to decreasing surface roughness due to its ultrafine grain size. Nano-crystalline diamond coatings can have a friction coefficient as low as single-crystal diamonds. This article briefly introduces the approaches to preparing nano-crystalline diamond materials and summarizes their applications in the field of tribology. Firstly, nano-crystalline diamond powders can be used as additives in both oil- and water-based lubricants to significantly enhance their anti-wear property. Nano-crystalline diamond coatings can also act as self-lubricating films when they are deposited on different substrates, exhibiting excellent performance in friction reduction and wear resistance. In addition, the research works related to the tribological applications of nano-crystalline diamond composites have also been reviewed in this paper. [ABSTRACT FROM AUTHOR]

Constructing more efficient air/solid/solution tri-interface for carbon-based oxygen reduced reaction (ORR) electrodes and evaluating the effects of layer numbers of graphene supporter loaded with defects on ORR performance are never explored before. We have successfully assembled vertical graphene sheets (VGs) with edge defects as catalyst centers on separated papillary granules formed (SPF) nanocrystalline diamond films (NCD) and firstly prepared high hydrophobic and high sticky carbon-based electrodes with highly efficient ORR performance. The results show that we regulate the VGs from lying to erect, providing hydrophobic surface to super-hydrophobic surface with high sticky. As the surfaces with medium static contact angle (SCAs)(130°∼140°) and high stickiness produce appropriate negative pressure to drag enough electrolyte to soak the VGs and still leave air pockets among SPF to form quantities of air/solid/liquid tri-interface, the VG-on-SPF-NCD electrodes possess better ORR performance. We firstly combine the I D' , I 2D /I G and FWHM 2D values from Raman spectra to express the defects loaded on fewer layers of graphene. It is a more precise way to assess the ORR catalytic active defects on carbon materials. Our results supply a simple way to construct catalytically active VGs on SPF nanocrystalline diamond films. Image 1 [ABSTRACT FROM AUTHOR]

High pressure high temperature (HPHT) was conventionally required for the phase transition from graphite to diamond. Here, we deposited monodispersed Ta atoms on pressed pure graphite substrate in hot filament chemical vapor deposition system and then performed annealing on the sample under ordinary pressure, letting graphite transit to diamond. Specifically, along the longitudinal direction the unannealed sample is divided into three regions of TaC particles, amorphous carbon and graphite, and 2–3 nm sized diamond grains are only observed among the TaC particles. After annealing the sample under 1000 °C for 15 min, diamond grains not only form among TaC particles, but also appear in amorphous carbon region. It is observed that more diamond grains with larger size of 3–10 nm and diamond variant structures i-Carbon (i-C) with the size larger than 30 nm are formed in amorphous carbon region. And more monodispersed Ta atoms are distributed in the amorphous carbon region of the annealed sample. This suggests that monodispersed Ta atoms firstly change graphite into amorphous carbon and then induce its transformation into i-C and diamond. Our results give a different way from HPHT method to prepare diamond based on graphite under ordinary pressure. [Display omitted] [ABSTRACT FROM AUTHOR]

• Thickness of diamond film can be tuned by interlayer's phase component. • An adhering diamond film is obtained using Cr/Cr-Si-N interlayer at N 2 /Ar ratio from 0 to 100%. • Diamond film's adhesion decreases at large N 2 /Ar ratio due to target poisoning effect. It is important to deposit diamond films with controllable thickness on stainless steels to realize their applications in medical apparatus with high precision. Here, the diamond film with various thicknesses was achieved by adjusting the N 2 /Ar flow ratio in deposition of Cr/Cr-Si-N interlayer. The results show that with the ratio increases, Cr(Si) phase that is easily carbonized in the interlayer gradually decreases, continuously shortening the time for carbon supersaturation and leading to the increase of diamond film thickness. With the ratio reaching 50%, the interlayer consists of (Cr,Si)N phase which has lower carbonization rate than Cr(Si), the film is the thickest. At the ratio larger than 50%, (Cr,Si) 2 N phase appears which has low unit cell density. Carbon atoms easily diffuse inward through the phase and those for growth of diamond film decrease, so the film becomes thin again. In addition, the adhesion of the diamond film becomes poor when the ratio is 125%, which can be attributed to the outward diffusion Fe atoms due to the small thickness of interlayer caused by the target poisoning effect. This study provides a new pathway for fabricating thickness-controllable diamond film on stainless steels for high precision apparatus applications. [ABSTRACT FROM AUTHOR]

Carbon atoms react with Cr and CrN x crystals in the CrSiN interlayer at different reaction rates, which leads to the formation of mosaic structure in the interface, providing high adhesion. With Si and SiN x phases increasing in nanocomposite interlayer, this limits the diffusion of carbon atoms, and causes shorter spikes and even the disappearance of spikes, decreasing the adhesion. • Cr and CrN x react with C atoms at different velocities, causing the formation of spikes. • The Cr-C with mosaic structure improves diamond film's adhesion by mechanical lock. • Amorphous Si and SiN x limit C diffusion, causing shorter spikes and low adhesion. It suffers from poor adhesion to deposit diamond films on steel by using normal metal compound films as an interlayer. Here, high adhesion diamond films were successfully prepared on stainless steel by using Cr/CrSiN nanocomposite film as interlayer. The results show that with Si contents increasing to 10.6 at.%, spikes appear at the interface between diamond films and interlayer, exhibiting high adhesion with hardness increasing to 80 GPa. With Si contents further increasing to 15.5 at.%, the spikes disappear and diamond film peels off even though its hardness still keeps 62 GPa. This indicates that spikes, composed of Cr-C compounds, supply mosaic structure and mechanical lock effects to improve the adhesion. The spikes' composition means that carbon atoms react with Cr/CrN x crystals in interlayer during HFCVD. Under lower Si contents, amorphous SiN x /Si phases are few, Cr/CrN x crystals can easily react with carbon atoms via different velocities, causing the co-existence of longer and shorter Cr-C phase to form the spikes. As Si content increases, more amorphous phases envelop the crystals, limiting the reaction of carbon atoms with Cr/CrN x crystals, so the spikes disappear. This supplies a way to control the adhesion of diamond films by adjusting Si contents to produce different interface structures. [ABSTRACT FROM AUTHOR]

Diamond films deposited on the stainless steel using a Cr/Cr-Si-N interlayer exhibited good adhesion in the Rockwell C indentation, while these films showed a very low critical load under the scratch test, which limits its application in medical devices with a relative motion. In order to solve this problem, we introduce a precarbonization process for the Cr/Cr-Si-N interlayer before the deposition of diamond films, which obviously improves the adhesion under the scratch test of diamond films. Especially, when the precarbonization time is 5 min, the critical load for diamond film under the scratch test reaches 26.6 ± 1.0 N, which is ascribed to the addition of precarbonization process changing the growth of the carbide, resulting in the elimination of pores under the diamond/carbide interface and the formation of jagged interface structure induced mechanical interlocking effect. [Display omitted] • Adhesion under scratch condition is improved after adding a carbonization process. • High adhesion is ascribed to removal of pores under the interface. • Adhesion is the largest when the interface is jagged and no pores are under it. [ABSTRACT FROM AUTHOR]

It is still a challenge to deposit a highly adhering diamond film on the WC-based cemented carbide. Here, we doped Ti into the WC/diamond interfaces to improve the adhesion and investigated the influences of Ti doping on adhesion work, electronic properties and tensile strength of WC (001)/diamond (111) interfaces by using first-principles calculations. The results show that the adhesion work of the C-terminated WC/diamond interface is higher than that of the W-terminated WC/diamond interface. By comparing with the adhesion work at the clean interface, it is shown that Ti-doped interface can lead to a significant improvement in the bonding strength. Besides, the electronic structure indicates that the Ti atom transfers electrons not only to the diamond side but also to the WC side, thus enhancing the charge transfer at the interface. Furthermore, the tensile simulation tests show that the maximum tensile stress increases by 13.46% with no change in the fracture elongation for the W-terminated interface after Ti doping. The maximum tensile stress increases slightly, but the fracture elongation increases by 2% for the C-terminated interface after Ti doping. As a result, this can provide theoretical guidance for the interface modification of WC-based carbide and diamond by doping Ti. • Ti atom segregates easily to the WC/diamond interfaces and forms stable structures. • The adhesion strength can be effectively improved via Ti doping at interfaces. • The charge at the interface is redistributed caused by Ti atom. • Ti doping enhances the tensile properties at the interfaces. [ABSTRACT FROM AUTHOR]