Papers by Keyword: Titanium Nitride TiN

Abstract: TiO2 coating on Si3N4-based materials powders (Si3N4, α-Y-sialon, β-sialon) was accomplished by heating the powder suspension containing the precursor (1.0 vol% H2O + Ti(O-i-C3H7)4) from 15 to 40 °C. The success of homogenous coating was confirmed by TEM observation. TiO2 coated on the powder is nitrided with NH3 gas at 800 oC to TiN with uniform particle size 10–20 nm. Spark plasma sintering of composite TiN/ Si3N4-based particles at 1400 - 1600 °C yielded the composite ceramics with a relative density > 96% without sintering additives. Sintered TiN/ Si3N4-based composite ceramics containing 17.5 - 25 vol.% TiN showed a higher electrical conductivity > 103 −1 cm-1, enabling these ceramics to be suitable for electric discharge machining.

Abstract: The mechanical properties of brittle coating structures were characterized by various indentation techniques. The adhesion properties of the coatings were evaluated by in situ scratch and sphere indentation method. Physical vapor deposited TiN coatings on transparent substrates, sapphire, were scratched by diamond cone indenter and in situ observed through the transparent substrate. In situ scratch results reveal that the failure of coating is originated from the damage of the substrate and the plastic deformation of substrate is a primary factor for determining the adhesion breakage. The unique characterization technique for the strength measurement of brittle thin coating has been developed. The strength of the thin coating was evaluated by the sphere indentation on the trilayer structure. The CVD SiC coatings on graphite were characterized by the technique. It is concluded that the microstructure of SiC coatings influences the strength. In this paper, the various indentation technique were applied to evaluate the mechanical properties of TiN and SiC coatings and the effect of microstructure on the reliability of the brittle coating system was discussed.

Abstract: The microstructure and texture in dynamically recrystallized copper and two copper – tin alloys (2wt% and 4.5wt% tin) has been investigated. Specimens were deformed in channel-die plane strain compression to true strains from 0.1 to 1.22 within the temperature range 200°C to 700°C, and the resulting microstructures were investigated with the use of high resolution electron backscatter diffraction (EBSD). Dynamic recrystallization was initiated by the bulging of preexisting high angle grain boundaries (HAGB), and occurred primarily by strain induced boundary migration (SIBM) and twinning. The addition of tin led to an increase in the temperature at which dynamic recrystallization initiated, and furthermore to a smaller dynamically recrystallized grain size. This was attributed to the effects of solute drag causing lower HAGB mobility. Dynamic recrystallization was observed to weaken the deformation texture components of brass and Goss, as well as introduce a cube texture component which generally tended to strengthen with temperature but weaken with increasing tin additions.

Abstract: Machinable BN/Si3N4 and electroconductive TiN/Si3N4 nanocomposites were prepared, using powders synthesized through an in-situ nitridation method in flowing ammonia gas. Due to the homogeneous mixing of various components in the powders, nanocomposites with homogeneous second phase distribution in the matrix were obtained. These nanocomposites showed enhanced strengths and distinctive functionalities. BN/Si3N4 nanocomposite with 20-25vol% BN showed a relatively high strength of over 700 MPa and was able to be machined into complicated shapes with diamond bits. Electroconductive TiN/Si3N4 nanocomposite with 25vol% TiN showed a high strength of 1100MPa and low electrical resistivity of 1.1×10-2 ⋅cm, and was promising for electrical discharge machining.

Abstract: Interaction of lead-free solders with copper substrate represents an important phenomenon in the issue of reliability of solder joints. New experimental data describing phase equilibria in the Cu-In-Sn system after long-time diffusion annealing at the 400 °C/50 hours, 600 °C/310 hours and 600 °C/48 hours will be presented. The composition of solders was: 100 % Sn, 75 % Sn + 25 % In, 50 % Sn + 50 % In, 25 % Sn + 75 % In, 100 % In. The fast quenching method was employed to freeze thermodynamic equilibrium after annealing, followed by metallography, microhardness measurements, SEM (Scanning Electron Microscope) and WDX (Wave Dispersive X-ray) analysis. New phase equilibrium data, together with the data from literature, represent the best existing experimental description of phase equilibria in the system in question. The obtained experimental results of the phase equilibria were compared with the thermodynamic modelling by the CALPHAD (Calculation of Phase Diagrams) method and with other authors.

Abstract: In this study the effect of thermomechanical treatment on the microstructure of austenite and martensite and the mechanical properties of a medium carbon silicon chromium spring steel with different levels of impurities is investigated. Results are presented for conventional heat treatment and for thermomechanical treatment (TMT). Compared to conventionally heat treated samples austenite deformation improves strength and ductility. Thermomechanically treated samples are not prone to embrittlement by phosphorous. TMT influences the shape and distribution of carbides within the matrix and at prior austenite grain boundaries. It is shown that utilization of TMT is beneficial for increasing the ultimate tensile strength to levels above 2200 MPa and at the same time maintaining the ductility obtained at strength levels of 1500 MPa by conventional heat treatment. The endurance limit is increased and embrittlement does not occur.

Abstract: The nitriding process is one of the common methods for surface hardening, and consists of heat treatment in a furnace for many hours. The nitriding behavior and strengthening mechanism of Ti added steels in the nitriding process, which is applicable to a high temperature and rapid process such as the continuous annealing of steel strip, were investigated. The sheets were hardened only near the surface. The hardening of the surface layer is due to the formation of clusters or fine precipitates with disc-like shape consisting of titanium and nitrogen. The maximum hardness depends on the content of Ti in the steel while the annealing time and the concentration of NH3 influence the depth of the hardened zone affected by nitriding. It is thought that the hardening only near surface improve bending stiffness without significant increase of yield stress. So there is a possibility that the surface hardening improves the dent resistance of automobile outer panels without significant worsening of the surface deflection. To study these behaviors theoretically, a model for predicting the precipitation behavior due to nitriding has been developed. The experimental results can be reasonably explained by the model calculations. And also, the estimation of the amount of strengthening was carried out. It indicated that the strengthening mechanism is mainly the precipitation hardening of TiN that could be Ti nitrides or Ti-N clusters.

Abstract: The recycling of scrap steels can be difficult due to the tramp elements that they can contain. During the steelmaking process, tramp elements such as Cu and Sn are difficult to be removed; and it is these elements that cause surface cracking of steels during hot rolling process (i.e. Cu and Sn liquid embrittlement).The paper consists of three different experiments into the suppression of surface cracking during the hot rolling process. For the oxidation in air, the surface cracking most severely occurred in the specimens which were oxidized around 1100°C in the tested range of 950-1200°C after a 1250°C heating. For the change in oxidation atmosphere from air to water vapor, the surface cracking occurred more severely although the mass gains were smaller in water vapor than in air oxidation. For the addition of Si and Ni in the water vapor conditions of 0%-30%H2O, the surface cracking was found to be suppressed effectively when the mass gain increased. The Cu and Sn enriched alloys at the scale/steel interface were closely observed by optical microscopy and scanning electron microscopy. The mechanism for suppression of the surface cracking was explained in terms of back diffusion of Cu and Sn into the steel and/or occlusion of Cu and Sn into the scale through the development of a rugged scale/steel interface.

Abstract: The bond interface of a TLP (Transient Liquid Phase) bonded tin has been observed with a TEM to investigate the effect of the liquid phase on the behavior of the superficial oxide film at the interface during the bonding process. In the solid-state-diffusion bonded joint without filler, abundant oxide inclusions were observed to be distributed within a region of a few 100 nm widths along the bond interface. In comparison with this, the liquid phase introduced by the eutectic reaction of the bismuth filler with the tin substrate decreased the width of the interfacial region involving abundant oxide inclusions to form a rather layer structure a few 100 nm thick consisting mainly of SnO2. It also enhanced the annihilation of the uncontacted areas at the interface. The layer of the oxide became discontinuous and coalesced with an increase in bonding temperature and pressure, and areas where no oxide inclusion could be observed at the interface were increased, when the liquid phase was formed. Owing to these effects, the bond strength rose at lower bonding temperatures and pressures when the bismuth filler was applied.

Abstract: One of the authors proposed a non-equilibrium powder metallurgy process, which enables the fabrication of a near net-shape product using TiC and TiN/Silicide ceramic composites. The PM process in combination with mechanical alloying (MA) and Spark Plasma Sintering (SPS) are applied to produce nano-grain composite, TiC/Ti5Si3. Powders of elements Ti and SiC whose composition is Ti-20 mass%SiC are blended for MA. After the alloying, the MA powder whose average particle size is 20~30 μm, has amorphous-like structures, and then the MA powder is compacted by SPS. Results of compression-tests indicate the occurrence of unusual hightemperature deformation behaviors such as low flow stress at the lower deformation temperature or at the high initial strain rates were observed in the SPS compacts. TEM observations of the deformed compacts after the compression-tests indicate the microstructure has no-strain equiaxial - grains and clear boundaries. This serves as proof of a superplasticity deformation. In addtion, the results of the XRD analysis of the compressed-compacts show that new phases are formed during the compression-test. Therefore, the above deformation is attributed to a "pseudo" superplasticity in which the phase transition of metastable microstructure occurs during the deformation.