Effect of C2H2 gas flow rate on synthesis and characteristics of Ti–Si–C–N coating by cathodic arc plasma evaporation

The influences of C₂H₂ gas flow rate on the synthesis, microstructure, and mechanical properties of the Ti–Si–C–N films were investigated. Quaternary Ti–Si–C–N coatings were deposited on WC-Co substrates using Ti and TiSi (80:20 at.%) alloy target on a dual cathodic arc plasma evaporation system. The Ti–Si–C–N coatings were designed with Ti/TiN/TiSiN as an interlayer to enhance the adhesion strength between the top coating and substrate. The Ti–Si–C–N coatings were deposited under the mixture flow of N₂ and C₂H₂. Composition analysis showed that as the C₂H₂ gas flow increased, the Ti, Si and N contents decreased and the carbon content increased in the coatings. The results showed the maximum nanohardness of approximately 40 GPa with a friction coefficient of 0.7 was obtained at the carbon content of 28 at.% (C₂H₂ = 15 sccm). However, as the C₂H₂ gas flow rate increased from 15 to 40 sccm (carbon content from 25.2 to 56.3 at.%), both the hardness and friction coefficient reduced to 20 GPa and 0.3, respectively. Raman analysis indicated the microstructure of the deposited coating transformed from Ti–Si–C–N film to TiSi-containing diamond-like carbon films structure, which was strongly influenced by the C₂H₂ flow rate and is demarcated at a C₂H₂ flow of 20 sccm. The TiSi-containing diamond-like carbon films reveal low-friction and wear-resistant nature with an average friction coefficient between 0.3 and 0.4, lower than both TiSiN and Ti–Si–C–N films.     

Microstructural control of Cr–Si–N films by a hybrid arc ion plating and magnetron sputtering process

The microstructural evolution of Cr–Si–N films deposited by a hybrid arc ion plating and magnetron sputtering process was investigated by varying the sputtering power of Si target and substrate bias voltage. Detailed nanocomposite microstructures of the films were studied by high-resolution transmission electron microscopy. The results indicated that the incorporation of Si into the growing CrN films at 0 V led to the formation of a nanocomposite containing CrN nanocolumns embedded in amorphous SiN_x matrix or near-amorphous microstructure. For the films having a Si content of ～10 at.% and ～15 at.%, a negative bias voltage of ?50 V resulted in the aggregation of nanocolumns in the amorphous matrix. Further increase of negative bias voltage to ?250 V led to the formation of a three-dimensional CrN/a-SiN_x nanocomposite microstructure. The mechanism of microstructure evolution is discussed by considering the thermodynamic and kinetic factors.     

A comparative study of two kinds of Y and Al modified silicide coatings on an Nb–Ti–Si based alloy prepared by pack cementation technique

Two kinds of Y and Al modified silicide coatings on an Nb–Ti–Si based alloy were prepared by pack cementation technique. The microstructure and oxidation behavior of both coatings were studied. Both coatings had a multiple layer structure, but the outer layers were composed of either Y- and Al-doped (Nb,X)Si₂ or Y-doped (Nb,X)₃Si₅Al₂ + (Nb,X)Si₂ phases, respectively. The former coating could protect the substrate alloy from oxidation at 1250 °C for 100 h, but the latter coating could only endure for less than 20 h. The scale formation mechanisms and microstructural changes of both coatings upon oxidation have been illustrated.     

Microstructure evolution of Ti–Si–C–Ag nanocomposite coatings deposited by DC magnetron sputtering

Nanocomposite coatings consisting of Ag and TiC_x (x < 1) crystallites in a matrix of amorphous SiC were deposited by high-rate magnetron sputtering from Ti–Si–C–Ag compound targets. Different target compositions were used to achieve coatings with a Si content of ～13 at.%, while varying the C/Ti ratio and Ag content. Electron microscopy, helium ion microscopy, X-ray photoelectron spectroscopy and X-ray diffraction were employed to trace Ag segregation during deposition and possible decomposition of amorphous SiC. Eutectic interaction between Ag and Si is observed, and the Ag forms threading grains which coarsen with increased coating thickness. The coatings can be tailored for conductivity horizontally or vertically by controlling the shape and distribution of the Ag precipitates. Coatings were fabricated with hardness in the range 10–18 GPa and resistivity in the range 77–142 μΩ cm.     

Glass–ceramic coatings on titanium alloys for high temperature oxidation protection: Oxidation kinetics and microstructure

A glass–ceramic coating is applied on Ti–6Al–4V alloy for oxidation protection at 800 °C. Its dynamic oxidation and microstructure evolution are investigated. The titanium alloy substrate is effectively protected by the glass–ceramic coating, of which the oxidation develops at constant rate. The linear relationship of oxidation is deduced dm/dt = Dρ(C₁ − C₂)/(bC′), and the diffusion coefficient of oxygen at 800 °C in glass is obtained. Oxygen diffusion through glass coating is the controlling step. After the initial firing, silicide interlayer forms between the glass coating and titanium alloy substrate, where the ratio of Ti/Si decreases after oxidation due to Si diffusion and Ti consumption.     

Thermal expansion of the V5Si3 and T2 phases of the V–Si–B system investigated by high-temperature X-ray diffraction

The thermal expansion anisotropy of the V₅Si₃ and T₂-phase of the V–Si–B system were determined by high-temperature X-ray diffraction from 298 to 1273 K. Alloys with nominal compositions V_62.5Si_37.5 (V₅Si₃ phase) and V₆₃Si₁₂B₂₅ (T₂-phase) were prepared from high-purity materials through arc-melting followed by heat-treatment at 1873 K by 24 h, under argon atmosphere. The V₅Si₃ phase exhibits thermal expansion anisotropy equals to 1.3, with thermal expansion coefficients along the a and c-axis equal to 9.3 × 10^?6 K^?1 and 11.7 × 10^?6 K^?1, respectively. Similarly, the thermal expansion anisotropy value of the T₂-phase is 0.9 with thermal expansion coefficients equal to 8.8 × 10^?6 K^?1 and 8.3 × 10^?6 K^?1, along the a and c-axis respectively. Compared to other isostructural silicides of the 5:3 type and the Ti₅Si₃ phase, the V₅Si₃ phase presents lower thermal expansion anisotropy. The T₂-phase present in the V–Si–B system exhibits low thermal expansion anisotropy, as the T₂-phase of the Mo–Si–B, Nb–Si–B and W–Si–B systems.     

Intermetallic protective coatings on titanium

In the presented work, the powder siliconizing and liquid phase alloying were used for a surface hardening of titanium and to protect titanium against high-temperature oxidation. The powder siliconizing was carried out in a pure Si powder at 900–1100 °C/3–48 h and the liquid phase alloying was realized in an Al–20 wt.% Si melt at 800 °C/5–40 min. It was shown that the coating methods produced hard multi-phase surface layers composed of various kinds of silicides (Ti₅Si₃, Ti₃Si and TiSi) and ternary Ti(Al_XSi_1−X)₂ (τ₂) phase. The binary silicide layers grew in accordance with the parabolic law while the ternary layer grew very rapidly. It was shown that the powder siliconizing at 900–1100 °C/3 h produced sufficiently thick and compact protective layers. The liquid phase alloying at 800 °C/10 min was efficient for preparation of protective layers. The oxidation experiments were conducted at 850 °C in air. Both the powder siliconized and liquid phase alloyed coatings were shown to provide a good protection against high-temperature oxidation.     

Shape memory behavior of Ti–Ta and its potential as a high-temperature shape memory alloy

In this study, the effect of Ta content on shape memory behavior of Ti–Ta alloys was investigated. The shape memory effect was confirmed in Ti–(30–40)Ta alloys. The martensitic transformation start temperature (M_s) decreased by 30 K per 1 at.% Ta. The amount of ω phase formed during aging decreased with increasing Ta. A stable high-temperature shape memory effect was confirmed for Ti–32Ta (M_s = 440 K) during thermal cycling between 173 and 513 K. On the other hand, the high-temperature shape memory effect of Ti–22Nb, which has a similar M_s to Ti–32Ta, exhibited poor stability due to the large amount of ω phase formed during thermal cycling. It is suggested that Ti–Ta is an attractive candidate for the development of novel high-temperature shape memory alloys.     

Preparation and electrical properties of highly (1 1 1) oriented antiferroelectric PLZST films by radio frequency magnetron sputtering

Highly (1 1 1) oriented lead lanthanum zirconate stannate titanate (PLZST) films were synthesized on Pt/Ti/SiO₂/Si substrates by radio frequency (RF) magnetron sputtering. The microstructure and electrical properties of the films were investigated as a function of post-annealing temperature. Smooth and crack-free films obtained by post-annealing at 700 °C for 30 min, and exhibit a dense columnar microstructure with a grain size of ∼0.85 μm. The sputtered PLZST films of nominal composition Pb_0.97La_0.02 (Zr_0.60Sn_0.30Ti_0.10)O₃ display a high saturation polarization of ∼70 μC cm⁻², a low antiferroelectric-to-ferroelectric switching field (<100 kV cm⁻¹), a reasonable dielectric constant and a low loss tangent. This combination of properties makes them attractive for microdevice applications.     

Structural and mechanical properties of corundum and cubic (AlxCr1−x)2+yO3−y coatings grown by reactive cathodic arc evaporation in as-deposited and annealed states

Coatings of (Al_xCr_1?x)_2+yO_3?y with 0.51 ? x ? 0.84 and 0.1 ? y ? 0.5 were deposited on hard cemented carbide substrates in an industrial cathodic arc evaporation system from powder-metallurgy-prepared Cr/Al targets in pure O₂ and O₂ + N₂ atmospheres. The substrate temperature and bias in all the deposition runs were 575 °C and ?120 V, respectively. The composition of the coatings measured by energy dispersive X-ray spectroscopy and elastic recoil detection analysis differed from that of the facing targets by up to 11%. Microstructure analyses performed by symmetrical X-ray diffraction and transmission electron microscopy showed that corundum, cubic or mixed-phase coatings formed, depending on the Cr/Al ratio of the coatings and O₂ flow per active target during deposition. The corundum phase was promoted by high Cr content and high O₂ flow per target, while the cubic phase was observed mostly for high Al content and low O₂ flow per active target. In-situ annealing of the cubic coatings resulted in phase transformation from cubic to corundum, completed in the temperature range of 900–1100 °C, while corundum coatings retained their structure in the same range of annealing temperatures. Nanoindentation hardness of the coatings with Cr/Al ratio <0.4 was 26–28 GPa, regardless of the structure. Increasing the Cr content of the coatings resulted in increased hardness of 28–30 GPa for corundum coatings. Wear resistance testing in a turning operation showed that coatings of Al–Cr–O have improved resistance to crater wear at the cost of flank wear compared with TiAlN coatings.     

Advantages of nanocomposite coatings deposited by high power pulse magnetron sputtering technology

Recent advantages in PVD coatings for cutting tools enable high speed and dry machining with superior cutting parameters in commercial manufacturing sectors. For this reason hard coatings with high oxidation resistance and thermal stability are used for economically justifiable machining. In this regard nc-(Ti,Al)N/a-Si₃N₄ films were sputtered on tungsten carbide cutting tools and WC/Co samples by using the high power pulse magnetron sputtering (HPPMS) technology. Coating composition, microstructure and applied properties were investigated by using X-ray diffraction, scanning electron microscope and nanoindentation. The hardness value was about 29 GPa for a Si content of 3.3 at.%. The grain size was about 6 nm. As this study focuses on the thickness uniformity of the coatings, SEM pictures of the cross-section have been taken around the cutting edge to determine the deposition rate and the film growth. The coatings morphology has been compared to middle frequency and direct current sputtered nanocomposite (Ti,Al,Si)N films. The results demonstrate the enhanced HPPMS coatings properties, including a denser structure, a smoother surface and a favourable thickness uniformity.     

Y and Al modified silicide coatings on an Nb–Ti–Si based ultrahigh temperature alloy prepared by pack cementation process

Y and Al modified silicide coatings were prepared on an Nb–Ti–Si based ultrahigh temperature alloy by co-depositing Si, Al and Y at 1150 °C for up to 10 h, respectively. The deposition of Al and Si occurred in a sequential manner during the pack cementation process. At the initial stage, the element deposited was primarily Al with very little Si and an Al₃(Nb,X) (X represents Ti, Cr and Hf elements) layer formed preferentially. After a short period of holding time, Si started depositing and Si–Al co-deposition took place. However, this Si–Al co-deposition period was not long. When the holding time was longer than 1 h at 1150 °C, Si deposition dominated the coating growth process. The coating growth kinetics at 1150 °C followed a parabolic law. The coating prepared at 1150 °C for 10 h had a multi-layer structure, with a thick (Nb,X)Si₂ outer layer, a thin (Ti,Nb)₅Si₄ middle layer and an Al, Cr-rich inner layer. The coating could protect the Nb–Ti–Si based alloy from oxidation at 1250 °C in air for at least 100 h. The excellent oxidation resistance of the coating was attributed to the formation of a dense scale mainly consisted of TiO₂, SiO₂ and Al₂O₃.     

Magnetic properties of nanocrystalline ferrite TixCo1+xFe2−2xO4 and CoFe2O4 composite thin films

Ti_xCo_1+xFe_2−2xO₄ (0 ≦ x ≦ 0.5) ferrite films and its composite films with CoFe₂O₄ synthesized by a sol–gel method were investigated on crystallographic and magnetic properties. Magnetization decreased with the increase of Ti content while coercive force showed a maximum at x = 0.2 and comparatively high at x = 0.5. Composite films of Ti_0.5Co_1.5FeO₄ and CoFe₂O₄ showed larger H_c and smaller grains.     

Shifting of the morphotropic phase boundary and superior piezoelectric response in Nb-doped Pb(Zr, Ti)O3 epitaxial thin films

A shift of the morphotropic phase boundary (MPB) and a superior piezoelectric response are observed in Nb-doped Pb(Zr_xTi_1?x)O₃ (PNZT) thin films epitaxially grown on Nb-doped SrTiO₃(1 0 0) (Nb:STO) substrates. X-ray diffraction and Raman spectra characterizations confirm that a phase transition from a tetragonal structure to a rhombohedral structure occurs when the Zr/Ti ratio varies from 20/80 to 80/20. The phenomenological theory and experimental analyses suggest that the MPB of epitaxial PNZT thin films is shifted to the higher Zr/Ti ratio (around 70/30) from the conventional ratio (52/48) due to the misfit compressive stress induced by the substrate. A maximum local effective longitudinal piezoelectric coefficient (d₃₃) up to 307 pm V^?1 is observed at a Zr/Ti ratio of 70/30 in the current compositional range, again confirming the shifting of MPB in epitaxial PNZT thin films. These findings offer a new insight for the fabrication of epitaxial PZT thin films at MPB with a superior piezoelectric response.     

The calculation of electronic parameters of an Ag/chitin/n-Si Schottky barrier diode

We have formed polymeric organic compound chitin film on n-Si substrate by adding a solution of polymeric compound chitin in N,N-dimethylacetamide and lithium chloride on top of an n-Si substrate and then evaporating solvent. It has been seen that the chitin/n-Si contact has demonstrated clearly rectifying behavior and the reverse curves exhibit a weak bias voltage dependence by the current–voltage (I–V) curves studied at room temperature. The barrier height and ideality factor values of 0.959 eV and 1.553, respectively, for this structure have been obtained from the forward bias I–V characteristics. Furthermore, the energy distribution of the interface state density located in the semiconductor band gap at the chitin/n-Si substrate in the energy range from (E_c − 0.897) to (E_c − 0.574) eV have been determined from the I–V characteristics. The interface state density, N_ss, ranges from 5.965 × 10¹² cm⁻² eV⁻¹ in (E_c − 0.897) eV to 1.706 × 10¹³ cm⁻² eV⁻¹ in (E_c − 0.574) eV and has an exponential rise with bias this energy range.     

Oxidation resistance and mechanical characterization of silicide coatings on the Nb-18Ti-14Si-9Al alloy

The Nb-Si alloys are attractive candidate for more advanced aircraft engines, however their oxidation resistances are poor. In this work, silicide coatings were prepared on the Nb-18Ti-14Si-9Al substrate, and we present the concern of this Nb-Si alloy with high Al content, and focused the modification effect of Al on NbSi₂ coatings. It is found that composition of the substrate alloy have an essential effect on coatings, which is composed of (Nb,Ti)Si₂ outer layer and (Nb,Ti)Si₂ + (Nb,Ti)₃Si₅Al₂ inner layer. Underneath inner layer, NbAl₃ is formed and surrounded by Nb₅Si₃. Beyond fracture toughness test, the coating still preserved the integrity and tightly adhered to substrate, no cracks nucleated between substrate and the coating. After oxidation at 1250 °C for 50 h, the mass gain of substrate and silicide coating is 398.85 mg/cm² and 2.34 mg/cm² respectively. The excellent oxidation resistance of the coating is proved to benefit from modification effects of high Al in the substrate.     

Preparation of Ti+Ti6Si2B powders by high-energy ball milling and subsequent heat treatment

The present work reports on the preparation of two-phase Ti_SS+Ti₆Si₂B alloys by high-energy milling and subsequent heat treatment. The milled and heat-treated products were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and microanalysis via WDS. Results indicated the dissolution of silicon and boron atoms into the Ti lattice to form supersaturated solid solutions during the ball milling of Ti–10Si–5B and Ti–20Si–10B powders. TiB₂ precipitates were formed during ball milling, and the metastable structures were decomposed due to the released heat from its exothermic formation. After heat treatment at 1100 °C for 4 h, the equilibrium microstructures of the Ti–10Si–5B and Ti–20Si–10B alloys indicated the majority presence of the Ti and Ti₆Si₂B phases. TiB precipitates were found in Ti–10Si–5B and Ti–20Si–10B powders after heat treatment at 1200 °C for 16 h, indicating that the composition was moved from two-phase Ti+Ti₆Si₂B region to the three-phase Ti+Ti₆Si₂B+TiB field.     

Cladding of pre-blended Ti–6Al–4V and WC powder for wear resistant applications

In this paper, a cladding investigation to achieve uniform distribution of WC particles which is crack-free, non-porous and without delamination using a 2 kW IPG Ytterbium doped, continuous wave, fibre laser with 1070 nm wavelength was reported. The single track deposition of a pre-blended powder, 27 wt.% Ti–6Al–4V/73 wt.% WC with a particle size range of 40–120 μm was made on Ti–15V–3Cr–3Sn–3Al substrate using a co-axial nozzle and a standard powder feeding system. The laser cladding samples were subjected to various microstructure examinations, microhardness and micro-abrasion tests. The results revealed that the best clad layers were achieved at an energy density of 111.10 J.mm^?2, 15–18.3 mm.s^?1 traverse speed; (583–667) mg.s^?1 powder feed rate with substrate surface irradiated by laser beam raising its temperature to about 200 °C. This resulted in a uniform distribution of WC within the clad and the results obtained from SEM, EDS and XRD revealed that the WC particles experienced surface melting with some diffusion into the matrix, thus promoting excellent bonding with the matrix and the formation of titanium and tungsten carbides, which include TiC and W₂C. The emergence of β-Ti, TiC and W in the clad resulted in enhanced hardness values. The mean value of microhardness in clad matrix is 678 HV when measured from the top of a transverse cross section of the clad sample into the interface region with the Ti substrate which has a hardness of 396 HV. Wear tests indicated the wear resistance of the clad was seven times that of the Ti alloy substrate.     

Shape memory behavior and internal structure of Ti–Ni–Cu shape memory alloy thin films and their application for microactuators

Internal structure and shape memory behavior of Ti–38.3Ni–9.3Cu (at.%) thin films heat-treated at 873 K, 923 K, 973 K and 1023 K were investigated by TEM observation and thermal cycling tests under various constant stresses. The thin film heat-treated at 873 K contained two types of precipitates, i.e., fine platelets and Ti₂Ni particles. The density of the platelets decreased with increasing heat-treatment temperature and annihilated completely when the heat-treatment temperature reached 973 K. The Ti₂Ni precipitates increased in volume fraction with increasing heat-treatment temperature from 873 K to 923 K, then their volume fraction was almost kept constant above 923 K. The recoverable strain decreased and the M_s increased with increasing heat-treatment temperature from 873 K to 923 K. Both the recoverable strain and the M_s became almost constant when the heat-treatment temperature was above 923 K. A diaphragm-type microactuator utilizing a Ti–38.0Ni–10.0Cu (at.%) thin film was fabricated. The diaphragm was square with the width of 500 μm. The actuation properties were investigated under conditions of both quasi-static and dynamic actuation. The M_s and the transformation temperature hysteresis of the microactuator were determined to be 352 K and 6 K, respectively. The microactuator operated at a working frequency of 100 Hz.