In situ formation of TiC particulate composite layer on cast iron by laser alloying of thermal sprayed titanium coating

Commercial flake graphite cast iron substrate was coated with titanium powder by low pressure plasma spraying and was irradiated with a CO₂ laser to produce the wear resistant composite layer. The macro and microstructural changes of an alloyed layer with the traveling speeds of laser beam, the precipitate morphology of TiC particulate and the hardness profile of the alloyed layer was examined. From the results, it was possible to composite TiC particulate on the surface layer by direct reaction between carbon existed in the cast iron matrix and titanium with thermal sprayed coating by remelting and alloying them using laser irradiation. The cooling rate of the laser remelted cast iron substrate without a titanium coating was about 1 × 10⁴ K/s to 1 × 10⁵ K/s in the order under the condition of this study. The microstructure of the alloyed layer consisted of three zones; the TiC particulate precipitate zone (MHV 400–500), the mixed zone of TiC particulate + ledeburite (MHV 650–900) and the ledeburite zone (MHV 500–700). TiC particulates were precipitated as a typical dendritic morphology. The secondary TiC dendrite arms were grown to a polygonized shape and were necking. Then the separated arms became cubic crystal of TiC at the slowly solidified zone. In the rapidly solidified zone near the fusion boundary, however the fine granular TiC particulates were grouped like grapes.     

Laser Surface Alloying of (Pre-placed) SiC and Ni-SiC Coating on Commercially Pure Titanium

Results of laser alloying of 100% SiC and 50% Ni + 50% SiC on commercially pure titanium were presented in this investigation. The high hardness Hv800-1200 obtained at 100% SiC and 50% Ni + 50% SiC alloying conditions were due to the presence of various intermetallic phases such as TiC, TiSi, Ti₅Si₃ and NiTi₂. These intermetallic phases present in the laser alloyed surface were validated by EDXRD analysis and the diffusion of Ni, Si, C in titanium responsible for these phase formations was identified by SIMS study. The alloyed layer microstructure consists of dendrites and its density level depends on laser processing conditions. At low level power density the alloyed layer depth was about 0.5 mm with a constant hardness level, whereas at higher level powerdensity the depth of alloyed layer touched a maximum of 1.6 mm with large fluctuation in hardness.     

Metal matrix composite layers formed by laser processing of commercial purity Ti–SiCp in nitrogen environment

Abstract

Metal matrix composite layer formation by means of laser alloying using 6 μm particle size SiC powder (SiC_p) preplaced on titanium surfaces in a nitrogen environment produced golden coloured tracks and a complete solution of SiC_p in the melt zones under a range of processing conditions. The melt layers consisted of dendrites at the top (titanium nitride based) followed by threadlike particle structures (titanium silicides), and the sizes of dendrites and the threadlike particles werefound to increase with increasing laser power density. The surface layer of the dendrites developed a hardness 4·5–9 times that of the base metal (150 HV), and the deep underlying threadlike structures had a plateau of hardness of aboout 2·8–4 times the base hardness. The metal matrix composite layers were found to be 2–4 times thicker than those produced previously in a helium environment under similar processing conditions. The exothermic reactions due to the formation of titanium nitride, titanium carbide, or titanium carbonitride along with titanium silicide during laser melting of SiC_p coated titanium surfaces under a nitrogen environment are considered to be responsible for the greater melt depth and complete dissolution of ceramic particles, by increasing the temperature of the melt.

MST/3208     

Ti-SiC Composite and TiC Ceramic Layer Formation on Ti6Al4V Surface by Laser Alloying of Pre-Placed SiC Coating

The Ti-6Al-4V alloy pre-placed with SiC coating was laser alloyed using high power CO2 laser. The laser alloyed cross section shows dendrite and Ti-SiC composite layer microstructure and the respective hardness was 650–800 HV and 1500–2000 HV. The observed hardness was 2 to 7 times greater than that measured on the bulk Ti-6Al-4V substrate. The laser alloyed surface produced high temperature ceramic phases such as TiC, TiSi and Ti5Si3. The elemental analysis was qualitatively estimated using SIMS analysis.     

Nonequilibrium microstructures and their evolution in a Fe–Cr–W–Ni–C laser clad coating

The laser-solidified microstructural and compositional characterization and phase evolution during tempering at 963 K were investigated using an analytical transmission electron microscope with energy dispersive X-ray analysis. The cladded alloy, a powder mixture of Fe, Cr, W, Ni, and C with a weight ratio of 10:5:1:1:1, was processed with a 3 kW continuous wave CO₂ laser. The processing parameters were 16 mm/s beam scanning speed, 3 mm beam diameter, 2 kW laser power, and 0.3 g/s feed rate. The coating was metallurgically bonded to the substrate, with a maximum thickness of 730 μm, a microhardness of about 860 Hv and a volumetric dilution ratio of about 6%. Microanalyses revealed that the cladded coating possessed the hypoeutectic microstructure comprising the primary dendritic γ-austenite and interdendritic eutectic consisted of γ-austenite and M₇C₃ carbide. The γ-austenite was a non-equilibrium phase with extended solid solution of alloying elements and a great deal of defect structures, i.e. a high density of dislocations, twins, and stacking faults existed in γ phase. During high temperature aging, in situ carbide transformation occurred of M₇C₃ to M₂₃C₆ and M₆C. The precipitation of M₂₃C₆, MC and M₂C carbides from austenite was also observed.     

Ni–P amorphous phases obtained by Nd–YAG pulsed laser alloying of deposited Ni–P coating with aluminum

Ni–P electroless deposited coating with crystalline morphology was prepared on aluminum substrate. A Nd–YAG pulsed laser was used to alloy the materials at the condition of power density 5.36 × 10⁹ W/m² and scanning speed 3.0 mm/s. In the laser alloyed layer, Ni–P amorphous phases were found by means of TEM. Electron diffraction patterns and X-ray diffraction results showed that these Ni–P amorphous phases were decomposed as Ni and Ni₃P equilibrium phases when tempered at temperature over 300 °C.     

Simultaneous recrystallization, phosphorous diffusion and antireflection coating of silicon films using laser treatment

Laser technique application to polycrystalline silicon thin-film solar cell fabrication on glass substrates has received appreciable attention. In this paper, a laser-doping technique is developed for plasma-deposited amorphous silicon film. A process involving recrystallization, phosphorous diffusion and antireflection coating can be achieved simultaneously using the laser annealing process. The doping precursor, a phosphorous-doped titanium dioxide (TiO₂) solution, is synthesized using a sol-gel method and spin-coated onto the sample. After laser irradiation, the polycrystalline silicon grain size was about 0.5∼1.0 μm with a carrier concentration of 2 × 10¹⁹ cm^− 3 and electron mobility of 92.6 cm²/V s. The average polycrystalline silicon reflectance can be reduced to a value of 4.65% at wavelengths between 400 and 700 nm, indicating the upper TiO₂ film of antireflection coating.     

The surface characteristics of polyacrylamide-coated silicon carbide powder used in the preparation of highly concentrated ceramics suspensions

Polyacrylamide (PAAM) coating layer was formed by chemical methods on the SiC powder surface. The surface characteristics of polyacrylamide (PAAM)-coated silicon carbide (SiC) powder were analyzed. The carbonyl band of amide and NH₂ deformation absorbing band existed at 1638 cm^–1, 1619 cm^–1 in the Fourier Transform Infrared Spectra (IR). Transmission electron microscopy (TEM) showed clearly the powder was coated by an organic compound layer which was PAAM judged by the reaction. The result of Differential Scanning Thermal Analyses (DSC) and Thermogravimetic (TG) showed the oxidizing decomposion temperature of PAAM was 411.9°C. The coating layer changed the surface characteristics of the SiC powder. At pH = 5, the suspensions of homogeneity and stability with 55 vol% solid content was prepared.     

Microstructure and property of Ni60A/WC composite coating fabricated by fiber laser cladding

Laser clad Ni60A/WC composite coating was fabricated on the surface of Q235 steel by using 6 kW fiber laser. The morphology, composition, and microhardness of composite coating were studied by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X‐ray diffraction (XRD), and micro‐hardness tester. The results show that in the process of fiber laser cladding Ni60A/WC composite coating, residual WC particles partially dissolve and react with other elements to form eutectics, which exists in the shape of lumpy, strip and spherical. The main structures of laser cladding are γ‐Ni, WC, W₂C, M₇C₃, M₂₃C₆ etc. From the hardness analysis, the average hardness of the composite coating is four times of the substrate.     

Silicon carbide whisker copper-matrix composites fabricated by hot pressing copper coated whiskers

Copper-matrix SiC whisker composites containing 33–54 vol % SiC whiskers and with < 5 vol % porosity were fabricated by hot pressing SiC whiskers that had been coated with copper by electroless plating followed by electroplating. The highest Brinell hardness of 260 was attained at 50 vol % SiC whiskers. The lowest coefficient of thermal expansion (CTE) of 9.6 × 10^–6°C^–1 (at 25–150°C) was attained at 54 vol % SiC whiskers. The composites exhibited lower porosity, higher hardness, higher compressive yield strength, lower CTE, lower electrical resistivity and higher thermal conductivity than the corresponding composites made by hot pressing mixtures of copper powder and bare SiC whiskers.     

Structural, morphological, and mechanical properties of amorphous carbon and carbon nitride thin films deposited by reactive and ion beam assisted laser ablation

Amorphous carbon nitride thin films have been prepared on Si (100) wafers by nitrogen ion beam assisted Nd:YAG laser ablation techniques. Amorphous carbon and carbon nitride films have also been prepared by the conventional laser ablation techniques for comparison. Raman spectroscopy and spectroscopic ellipsometry have been performed for the films to analyze structural properties, atomic force microscopy to observe surface morphologies, and scratch, acoustic emission, and Vicker hardness test to examine mechanical properties. The amorphous carbon nitride films deposited by the ion beam assisted laser ablation techniques had generally better mechanical properties compared to the amorphous carbon films and amorphous carbon nitride films deposited in N₂ atmosphere. The amorphous carbon nitride films deposited at optimum ion beam current of 10 mA and laser power density of 1.7 × 10⁹ W/cm² showed excellent mechanical properties: root mean square surface roughness of 0.33 nm, friction coefficient of 0.02–0.08, the first crack and critical load of 11.5 and 19.3 N respectively, and Vicker hardness of 2300 [Hv]. It is considered that the films have high potential for protective coatings for microelectronic devices such as magnetic data storage media and heads.     

Nanopatterning of diamond films with composite oxide mask of metal octylates in electron beam lithography

The fabrication of diamond nanopatterns by electron cyclotron resonance (ECR) oxygen plasma with a composite metal octylate mask was investigated using electron beam lithography technology. A high etching selectivity of 14 was obtained with Bi₄Ti₃O₁₂ octylate film as a mask under the plasma-etching conditions of microwave power of 300 W and oxygen gas flow rate of 3 sccm. The metal naphthenates and metal octylates exhibited negative exposure characteristics. The sensitivity of metal naphthenates (1.2×10^–3 C cm^–2) was ten times lower than that of polymethyl methacrylate (PMMA) resist, while that of octylates (8.0×10^–5 C cm^–2) was in good agreement with that of PMMA resist (6.0×10^–5 C cm^–2). The resulting minimum chemical vapor deposited (CVD) diamond line-width of 100 nm with a height of approximately 1 m was fabricated with a Bi₄Ti₃O₁₂ octylate mask.     

Nucleation control of diamond synthesized by microwave plasma CVD on cemented carbide substrate

Diamond was coated on to cemented carbide substrate by microwave plasma CVD, in which nucleation control of diamond crystals was investigated under constant deposition conditions; total pressure 30 torr, CH₄ flow rate 1 ml min^–1, H₂ flow rate 199 ml min^–1 and microwave power 550 W. Nucleation tends to occur selectively on the edge part of WC grains of the cemented carbide substrate with coarse WC grain size of about 1 m, where the nucleation density was 9×10⁶ cm^–2. The density increased to about 5×10⁷ cm^–2 when using a finegrained substrate (WC grain size 0.5 m). A considerably enhanced nucleation was observed by introducing a number of fine microflaws on to the substrate surface. Microflawing treatment with diamond fine powder (grain size 0–1/4 m) suspended in an ultrasonic cleaner bath was effective for increasing the diamond nucleation density up to 5×10⁸ cm^–2. The grain size of grown diamond crystals decreased with increasing microflawing time.     

Synthesis and characterization of titanium-45S5 Bioglass nanocomposites

Titanium-45S5 Bioglass nanocomposites were synthesized by the combination of mechanical alloying and powder metallurgy process. The structure, mechanical and corrosion properties of these materials were investigated. Microhardness test showed that the obtained material exhibits Vicker’s microhardness as high as 770 HV_0.2 for Ti-20 wt.% 45S5 Bioglass, which is more than three times higher than that of a conventional microcrystalline titanium (225 HV_0.2). Additionally, titanium-10 wt.% of 45S5 Bioglass nanocomposites (i_c = 1.20 × 10⁻⁷ A/cm², E_c = −0.42 V vs. SCE) were more corrosion resistant than microcrystalline titanium (i_c = 2.27 × 10⁻⁶ A/cm², E_c = −0.36 V vs. SCE). In vitro biocompatibility of these materials was evaluated and compared with a conventional microcrystalline titanium, where normal human osteoblast (NHOst) cells from Cambrex (CC-2538) were cultured on the disks of the materials and cell growth was examined. The morphology of the cell cultures obtained on Ti-10 wt.% 45S5 Bioglass nanocomposite was similar to those obtained on the microcrystalline titanium. Mechanical alloying and powder metallurgy process for the fabrication of titanium-45S5 Bioglass nanocomposites with a unique microstructure, higher hardness, lower Young’s modulus and better corrosion resistance, in comparison to microcrystalline titanium, were developed. On the other hand, Ti-10 wt.% 45S5 Bioglass composites posses higher fracture toughness compared to 45S5 Bioglass. The proper modification of chemical composition and microstructure of Ti-bioceramic nanocomposites can expand the use of titanium in the biomedical fields.     

Laser Damage Threshold and UV Absorption of Doped Potassium Dihydrogen Phosphate Crystals

The effects of Pb, Ca, and Si impurities on the laser damage threshold and UV absorption of KH₂PO₄ crystals were studied. The laser damage threshold was found to be 6 × 10¹¹ W/cm² in crystals containing 5 × 10^–5 wt % and to decrease nonlinearly at higher impurity contents.     

TiOx interlayer characterization for sol–gel derived Pb(Zr, Ti)O3 thin films on titanium foil

Pb(Zr, Ti)O₃ films were prepared on titanium foil using sol–gel processing. The films were of large area, crack-free, uniform, with perovskite structure and exhibiting strong adhesion to the titanium foil substrate. Films and the interface region between the film and the substrate were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and dielectric property measurements. The measurements revealed the formation of a TiO_x layer at the interface between the film and the foil. The thickness of the TiO_x interlayer increases with increasing annealing temperature, and was amorphous when annealed below 600 °C. The dielectric properties of films depend on the thickness of the TiO_x interlayer. Films on Ti foil with dielectric constant of 200–400, dielectric loss <5%, leakage current of <1×10^–7 A cm^–2 at 100 kV cm^–1 and breakdown field strength of 0.6–1.13 MV cm^–1 were demonstrated. The TiO_x interlayer resulted in asymmetric C–V hysterisis behavior attributed to trapped charge in the vicinity of the TiO_x interlayer and to elastic mismatch strain.     

LaB6 and TiB2 electrodes for the alkali metal thermoelectric converter

LaB₆ and TiB₂ electrodes for the alkali metal thermoelectric converter (AMTEC) were prepared from the respective powders by a screen-printing method and their electrode properties were investigated. Optimum values were obtained for particle size, thickness and porosity of electrode. When the vacuum level of the low-temperature side of the AMTEC increased above 10 Pa, the power density decreased remarkably. These results can be interpreted as different electrode processes in the AMTEC: (1) a charge transfer process, (2) surface diffusion on the electrode, (3) desorption from electrode particles, and (4) vapour-phase diffusion in the electrode pore. The maximum power density was 0.54 W cm^–2 (LaB₆) and 0.24 W cm^–2 (TiB₂ at 800 °C.     

Mechanical and thermal properties of silicon-carbide composites fabricated with short Tyranno® Si-Zr-C-O fibre

Silicon carbide (SiC) composites reinforced with 10–50 mass% (10.5–51.2 vol%) of short Tyranno® Si-Zr-C-O fibre (average length 0.5 mm) and 0–10 mol% of Al₄C₃as a sintering aid were fabricated using the hot-pressing technique. Firstly, the effect of Si-Zr-C-O fibre addition on the relative density (bulk density/true density) of the SiC composite hot-pressed at 1800 °C for 30 min was examined by fixing the amount of Al₄C₃to be 5 mol%. Although the relative density was reduced to 87.4% for 10 mass% of Si-Zr-C-O addition, further increases in the amount of Si-Zr-C-O fibre increased density to a maximum of 92.8% at 40 mass% of fibre addition. Secondly, the effect of varying the amount of Al₄C₃addition on the relative density was examined by fixing the amount of Si-Zr-C-O fibre to be 40 mass%. The optimum amount of Al₄C₃addition for the fabrication of dense SiC composite was found to be 5 mol%. The fracture toughness of the hot-pressed SiC composites with 20–40 mass% of Si-Zr-C-O fibre addition (amount of Al₄C₃: 5 mol%) was 3.2–3.4 MPa · m^1/2and approximately 1.5 times higher than that (2.39 MPa · m^1/2) of the hot-pressed SiC composite with no Si-Zr-C-O fibre addition. SEM observation showed evidence of Si-Zr-C-O fibre debonding and pull-out at the fracture surfaces. The hot-pressed SiC composite with 5 mol% of Al₄C₃and 40 mass% of Si-Zr-C-O fibre additions showed excellent heat-resistance at 1300 °C in air due to the formation of a SiO₂layer at and near exposed surfaces.     

Improvement of SiCf/SiC density by slurry infiltration and tape stacking

SiC fiber-reinforced SiC–matrix ceramic composites (SiC_f/SiC) were fabricated by vacuum infiltration of a SiC slurry into Tyranno™-SA grade-3 fabrics coated with a 200 nm-thick pyrolytic carbon (PyC) layer followed by hot pressing using a transient eutectic-phase. The density of the composite was improved using a special infiltration apparatus with a pressure gradient and alternating tape insertion between fabrics. Their overall properties were compared with those of monolithic SiC and composite containing chopped fibers. Although the density of the composites decreased with increasing fiber fraction, SiC_f/SiC containing 50 vol.% fibers had a density of 3.13 g/cm³, which is the highest reported thus far. The composites containing continuous fibers had a maximum flexural strength of 607 MPa and a step increase in the stress–displacement behavior during the three-point bending test due to fiber reinforcement, which was not observed in the monolith.     

Structural, optical and photoelectrochemical properties of brush plated CdSe x Te1 − x thin films

CdSe _x Te_{1 – x} films have been deposited by the brush plating technique for the first time, on titanium and conducting glass substrates at room temperature. These films were annealed in argon atmosphere at 475°C for 15 min. Their structural, optical and photoelectrochemical (PEC) properties are presented and discussed. The power conversion efficiency has been found to be 9.0% at 60 mW cm^–2white light illumination. A peak quantum efficiency of 0.7 has been obtained for the films of composition CdSe_0.7Te_0.3. Donor concentration of 10¹⁷cm^–3and electron mobility of 60 cm²V^–1sec^–1were obtained.