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.     

Self-propagating high-temperature synthesis of TiCxNy–TiB2 ceramics from a Ti–B4C–BN system

An experimental study on direct formation of TiC_xN_y–TiB₂ ceramics by self-propagating high-temperature synthesis (SHS) was conducted using a Ti–B₄C–BN system. The effects of the C/(C + N) ratio on the combustion behavior and reaction products were investigated. Experimental characterizations of quenched samples show that the combustion reaction started with the formation of highly substoichiometric TiN_y and TiB due to the solid-state reaction between Ti and BN; and then the TiN_y precursor and TiB dissolved back into the titanium melt, forming the Ti–B–N liquid, which in turn transformed to the Ti–B–N–C liquid due to the dissolution of the carbon atoms diffused away from B₄C. Finally, the TiC_xN_y and TiB₂ particles are formed from the melt through the dissolution-precipitation mechanism.     

Effect of assistant RF plasma on structure and properties of SiCN thin films prepared by RF magnetron sputtering of SiC target

Silicon carbon nitride thin films were deposited on Si(1 0 0) substrate at room temperature with different working pressure. The bonding structure and hardness were studied by means of X-ray photoelectron spectroscopy (XPS) and nano-indentation technique. The results showed that the assistant ratio-frequency (RF) plasma had a great effect on the structure and property of the films. The hardness values of the films prepared with assistant RF plasma were higher than those of the films prepared without it. Assisted with RF plasma, sp³C–N bond can be found in the film prepared at low working pressure, and the diamond C–C bond can be easily formed in the film prepared at higher working pressure.     

Wear-resistant Ti–B–N nanocomposite coatings synthesized by reactive cathodic arc evaporation

Wear-resistant Ti–B–N coatings have been synthesized by reactive arc evaporation of Ti–TiB₂ compound cathodes in a commercial Oerlikon Balzers Rapid Coating System. Owing to the strong non-equilibrium conditions of the deposition method, a TiN–TiB_x phase mixture is observed at low N₂ partial pressures, as determined by elastic recoil detection analysis, X-ray diffraction, X-ray spectroscopy, transmission electron microscopy and selected area electron diffraction. The indicated formation of a metastable solid solution of B in face-centered cubic TiN gives rise to a maximum in hardness (>40 GPa) and wear resistance on the expense of increased compressive stresses. A further saturation of the nitrogen content results in the formation of a TiN–BN nanocomposite, where the BN phase fraction was tailored by the target composition (Ti/B ratio of 5/3 and 5/1). However, the amorphous nature of the BN phase does not support self-lubricious properties, showing friction coefficients of 0.7 ± 0.1 against alumina. The effect of an increased bias voltage on structure and morphology was investigated from −20 to −140 V and the thermal stability assessed in Ar and air by simultaneous thermal analysis up to 1400 °C.     

Surface finishing of Ni–Cr–B–Si composite coatings by precision grinding

A Ni–Cr–B–Si/10vol%WC coating material has been precision ground to an optical quality surface finish (<10 nm R_a) using a combination of a very stiff precision machine tool, Tetraform “C”, 76 μm CBN grinding wheels and electrolytic in-process dressing (ELID) assisted grinding. When grinding without ELID, surface finish has been shown to be limited by damage to primary and secondary carbides. This damage may be in the form of carbide pull-out or localised fracture and removal of the larger primary WC particulate. ELID assisted grinding helps maintain CBN grit protrusion and sharpness and thus promotes efficient cutting during grinding, minimising pull-out and localised damage to the harder phases within the coating microstructure. ELID therefore improves both the overall surface finish and surface integrity of the workpiece.     

Oxidation of Ti−B−C−N film deposited on steel

Ti−B−C−N films were deposited on tool steel substrates by a DC magnetron sputtering system, and their oxidation characteristics were investigated at the temperature range of 200°C to 800°C for up to 5 h in air. Ti−B−C−N films were oxidized to TiO₂, which further reacted with FeO to become FeTiO₃. The films did not display good oxidation resistance, owing to the evaporation of B, C and N into the air, film breakage, and poor film adherence owing to the mismatch of the thermal expansion coefficients between film and substrate.     

Thermal conductivity of high-temperature Si–B–C–N thin films

In this study, thermal transport was investigated for ceramic films with different silicon, boron, carbon, and nitrogen (Si–B–C–N) compositions. In order to investigate the effect of morphology on thermal barrier properties, the microstructure of these materials was varied from amorphous to nanocrystalline. Thermal conductivity trends of several ceramic thin films were characterized with a time-domain thermoreflectance (TDTR) technique. Samples containing two different Si–B–C–N chemical compositions were created by reactive magnetron sputtering and then subjected to annealing at temperatures up to 1400 °C. The room temperature thermal conductivity of the samples prepared via a 50% Ar/50% N₂ gas mixture remained constant near 1.3 W m⁻¹ K⁻¹, while samples prepared via a 75% Ar/25% N₂ gas mixture exhibited an increase in the thermal conductivity of 2.2 W m⁻¹ K⁻¹ (or higher). X-ray diffraction data demonstrated that the former samples were amorphous, while the latter samples formed silicon nitride (Si₃N₄) crystals. The experiments reveal which Si–B–C–N film composition remains stable in the amorphous state at high temperatures, thereby retaining lower thermal transport properties. These material aspects are ideal for thermal barrier applications such as non-oxide based ceramic coatings for high-temperature protective systems of aircrafts, as well as surfaces of cutting tools and optical devices.     

Annealing Ni nanocrystalline on WC–Co

The effects of annealing temperature on nanocrystalline sputter-deposited Ni thin films (500 nm) deposited on WC–Co (4 wt.%) were investigated. Special attention was focused on quantitative evaluation of residual stress and Ni diffusion into the WC–Co, after heat treatment, from 873 to 1273 K. The estimated level of residual stress, as measured by X-ray diffraction, is around −1.3 ± 0.1 GPa for the as-deposited film, whereas after annealing at 1273 K it decreases significantly.Atomic force microscopy shows that high annealing temperature results into an exponential increase of the roughness. An intermixing between the nanocrystalline Ni and the Co from WC substrate occurs, as it is revealed by quantitative depth-resolved Rutherford backscattering spectrometry analysis and also supported by X-ray photoelectron spectroscopy. We ascribe a significant stress relief with the increasing annealing temperature to the diffusion process. The understanding of this process is particularly important in WC–Co parts with the surface treated with Ni in order to improve the maximum surface service temperature.     

Wear resistance of laser-clad Ni–Cr–B–Si alloy on aluminium alloy

Using a 5 kW CO₂ laser, two kinds of plasma-sprayed coatings, Ni–Cr–B–Si and Ni–Cr–B–Si+WC alloys, were remelted on aluminium alloy. The wear resistance of both laser-treated samples and plasma-sprayed samples were investigated using a pin-on-disc sliding friction wear tester. A scanning electron microscope (SEM) was used to analyse the abrasion phenomena of the samples and a transmission electron microscope (TEM) was used to study the microstructure of the laser-clad zone. Experimental results showed that the laser-clad samples had double the wear resistance of the plasma-sprayed samples, and that the laser-clad Ni–Cr–B–Si sample exhibited the highest wear resistance. The results of wear surface analysis showed that the microstructure of the alloyed layer of the laser-clad samples was quite compact and the surfaces were also very smooth, and there was less peeling phenomenon of the granules. The microstrucutre of the plasma-sprayed sample was rather loose and there were a lot of granular peelings left on the worn surface. A study of the microstructure showed extensive amorphous and ultra-crystalline structures in the laser-clad zone, to which the increase in hardness and wear resistance may be attributed.     

BN0.5O0.4C0.1: Carbon- and oxygen-substituted hexagonal BN

Hexagonal boron nitride (hex BN) containing significant amounts of C and O substituting for N (hex BCNO) was synthesized at 75 kbar and 1700°C from mixtures of C, B₂O₃, and amorphous B contained in a hex BN crucible. Hex BCNO is a minor constituent of the product and occurs as small, <30 nm diameter, rounded pseudohexagonal particles adhering to materials with the α-rhombohedral B structure. Electron energy-loss spectroscopy with a transmission electron microscope was used to quantify their elemental ratios. Up to 50% of the N in hex BN is replaced by C and O, e.g., BN_0.49O_0.38C_0.11. The electron energy-loss near-edge fine structure of the core-loss edges was used to elucidate the possible structures of hex BCNO. The core-loss edges of B, C, N, and O exhibit orientation-dependent intensity changes, which indicates that they occupy similar anisotropic bonding sites in graphite-like BCNO layers. For a composition of BN_0.5O_0.4C_0.1, regions with B–N₃, B–N₂O, and B–NO₂ units predominate. In addition, some grains have significant quantities of B–O₃ and B–C₃ units. Boron–boron bonding is either absent or infrequent.     

A novel Al–Ti–B alloy for grain refining Al–Si foundry alloys

Al–Ti–B refiners with excess-Ti (Ti:B > 2.2) perform adequately for wrought aluminium alloys but they are not as efficient in the case of foundry alloys. Silicon, which is abundant in the latter, forms silicides with Ti and severely impairs the potency of TiB₂ and Al₃Ti particles. Hence, Al–Ti–B alloys with excess-B (Ti:B < 2.2) and binary Al–B alloys are favored to grain refine hypoeutectic Al–Si alloys. These grain refiners rely on the insoluble (Al,Ti)B₂ or AlB₂ particles for grain refinement, and thus do not enjoy the growth restriction provided by solute Ti. It would be very attractive to produce excess-B Al–Ti–B alloys which additionally contain Al₃Ti particles to maximize their grain refining efficiency for aluminium foundry alloys. A powder metallurgy process was employed to produce an experimental Al–3Ti–3B grain refiner which contains both the insoluble AlB₂ and the soluble Al₃Ti particles. Inoculation of a hypoeutectic Al–Si foundry alloy with this grain refiner has produced a fine equiaxed grain structure across the entire section of the test sample which was more or less retained for holding times up to 15 min.     

Electrochemical properties and surface analysis of Cu–Zr–Ag–Al–Nb bulk metallic glasses

The electrochemical properties and surface characteristics of Cu–Zr–Ag–Al–Nb bulk metallic glasses (BMGs) were investigated. The alloys exhibit excellent corrosion resistance after immersion in 1N H₂SO₄ and 1N NaOH. The corrosion rates of the alloys in chloride-ion-containing solutions significantly decrease by alloying with Nb element. The formation of Zr- and Nb-enriched surface films could be responsible for the high corrosion resistance.     

Combustion synthesis of Ti(C, N)–TiB2 from a Ti–C–BN system

In this paper, a simple way of fabricating TiC_xN_y–TiB₂ ceramics through the combustion reaction of Ti, C and BN powder mixtures in an argon atmosphere is reported with an emphasis on the effects of the C/(C + N) ratio on the SHS reaction behaviors and mechanism. With the increase in the C/(C + N) ratio, the combustion temperature shows a zigzag variation behavior; the combustion wave velocity displays a similar variation tendency as did in the combustion temperature while the ignition delay time increases progressively. XRD results confirmed that TiC_xN_y–TiB₂ could form in all the samples. Microstructural observations revealed that both TiC_xN_y and TiB₂ grains had fine sizes of less than 1 μm in the products when the C/(C + N) ratio was lower than 0.5. Based on the characterization of quenched samples, the formation mechanism of the titanium carbonitride is proposed. Namely, the formations of TiN_0.3 and TiN are followed by the incorporation of C in TiN_x to form the titanium carbonitride solid solution.     

Rutile-type titanium oxide films synthesized by filtered arc deposition

A filtered arc-deposition system was used to synthesize titanium oxide films by evaporating titanium ions in an oxygen environment. Fourier transform infrared spectroscopy and X-ray diffraction analysis show that the films exhibit the rutile-type structure. X-ray photoelectron spectroscopy reveals that a small amount of Ti²⁺ and Ti³⁺ still exists although Ti⁴⁺ is the main component in the films. The preferred orientation of the films is dependent on the substrate bias and oxygen pressure. Titanium oxide films with (101) and (002) preferred orientation were prepared by changing substrate bias and oxygen pressure. Ultraviolet–visible absorption spectroscopy was used to determine the optical band gap of the prepared films. The results show that the band gap of the films prepared under zero substrate bias is 2.39 eV. When the substrate bias is larger than −100 V, the optical band gap of the films is about 3.33 eV.     

Microstructure and grain refining performance of a new Al–Ti–C–B master alloy

A kind of Al–Ti–C–B master alloy with a uniform microstructure is prepared using a melt reaction method. It is found that the average grain size of α-Al can be reduced from 3500 to 170 μm by the addition of 0.2 wt.% of the prepared Al–5Ti–0.3C–0.2B and the refining efficiency does not fade obviously within 60 min. It is considered that the TiC_xB_y and TiB_2−mC_n particles found at the grain center are the effective and stable nucleating substrates for α-Al during solidification, which accounts for the good grain refining performance.     

The effect of substrate bias voltage on PbTe films deposited by magnetron sputtering

The PbTe films were deposited onto ITO glass substrate by radio frequency magnetron sputtering. Effect of external direct current electrical field applied between substrate and target on the quality of films was investigated. Stylus surface profile, X-ray diffraction (XRD), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the films. The film thickness was measured by a conventional stylus surface profile. The crystal structure and lattice parameters of films were determined by using XRD. The surface morphology of the films was measured by AFM. The absorption coefficients and optical band gaps of films were found from FTIR. The sheet resistance of the samples was measured with a four-point probe and the resistivity of the film was calculated. All the obtained films were highly textured with a strong (2 0 0) orientation. With increasing bias voltage to −30 V, the property of crystal structure, surface morphology and absorption coefficients and resistivity were improved. However, further increase of substrate bias leads to transformation of the property.     

Electrodeposition of sol–gel films on Al for corrosion protection

Sol–gel films were electrodeposited on aluminum electrodes following the methodology we have developed and is based on applying negative potentials. This increases the pH at the surface, causing acceleration of the polymerization. Our process follows the “two step method”, in which the monomer is first hydrolyzed in acidic solution (pH 4) and only then the negative potential is applied, which consumes protons and releases hydroxyl ions, thus enhancing the condensation.Films made of different monomers, i.e., tetraethoxysilane (TEOS), methyl trimethoxysilane and phenyl trimethoxysilane (PTMOS), were prepared, characterized and examined for their corrosion inhibition properties. Potentiodynamic polarization, electrochemical impedance spectroscopy, optical and scanning electron microscopy as well as atomic force microscopy have been used as a means of film characterization. Hydrophobic and steric silanes, such as PTMOS showed a considerable corrosion inhibition capacity as compared to the capacity exhibited by less hydrophobic and steric derivatives such as TEOS. The difference between the conventional dip-coating method and the electrodeposition approach for depositing sol–gel films was also examined, indicating a clear advantage of the latter.     

The Zn-rich corner of the 450 °C isothermal section of the Zn–Bi–Fe–Ni quaternary system

Following up on recent studies of the isothermal section of the Zn–Fe–Ni, Zn–Fe–Bi and Zn–Bi–Ni ternary systems at 450 °C, the Zn-rich corner of the 450 °C isothermal section of the Zn–Bi–Fe–Ni quaternary system with the Zn being fixed at 93 at.% was determined experimentally using the equilibrated alloys approach. The specimens were investigated by means of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). It was found there exist 4 two-phase regions, 5 three-phase regions and 2 four-phase regions. Two liquid L (Zn) and L (Bi) can coexist with T, ζ and δ-Ni in this isothermal section, no new phase was found in this study.     

In situ composite formation in the Ni–(Cu)–Ti–Zr–Si system

In situ composites were synthesized by arc melting Ni–(Cu)–Ti–Zr–Si alloys. The X-ray diffraction patterns of rapidly cooled cast strips show a primary Ni(Ti, Zr) B2 structure superimposed on the diffuse scattering maxima from the amorphous phase. Compression test results show that the composite starts to yield at 1200 MPa and fractures at 1900 MPa.