TiN Composites Research Articles

Corrosion of hot pressed Si 3N 4–TiN composite in sulphuric acid aqueous solution

The corrosion behaviour of an electroconductive Si 3N 4–35 vol% TiN composite, hot pressed with the addition of Al 2O 3 and Y 2O 3 as sintering aids, was studied in 1.8 M sulphuric acid aqueous solution at RT, 40 and 70 °C up to 400 h. The corrosion follows linear kinetics at RT and at 40 °C, involving only the progressive chemical dissolution of grain boundary phases, in the system Al–Y–Si–Ti–O–N. Chemical attack of TiN occurs at 70 °C, while Si 3N 4 is not affected by the selected corrosive environment. The effect of the corrosion on flexural strength, fracture toughness and electrical resistivity were investigated. Very high strength levels are maintained after corrosion for 400 h at room temperature, while the strength decreases of about 10% and 16% after the treatment at 40 and 70 °C, respectively. The electrical resistivity rises after corrosion at 40 and 70 °C, in line with the progressive chemical dissolution of the conductive TiN particles.

Wear and mechanical properties of sintered copper–tin composites containing graphite or molybdenum disulfide

Copper-based sintered composites produced by powder metallurgy processes are now widely used in tribological engineering parts, e.g. bearings and bushes. Also composites based on copper–tin alloys containing a solid lubricant have been developed as self-lubricating materials under extreme conditions of load, atmosphere and temperature. It is well known that the addition of graphite serves to reduce friction and wear in copper–tin alloys. However it should be noted that the addition of graphite or molybdenum disulfide (MoS 2) has an adverse effect on the composites’ mechanical properties. In this paper, the lubricant graphite and MoS 2 powders were coated with Cu to reinforce their bonding to the Cu particles in the composites during sintering. The hardness, microstructure and bending strength of the sintered specimens were examined. The friction and wear properties of the materials were estimated by a cylinder-on-plate wear machine under dry conditions at room temperature in air. Although mechanical properties of the composites decreased with increasing amount of added graphite or MoS 2, the use of Cu-coated lubricant powders improved the bending strength. Graphite was very effective in reducing the wear and friction of the composites. Particularly, the 40 vol.% graphite composites showed a very low coefficient of friction of 0.15. Furthermore, the wear rate of the Cu-coated graphite specimens was much lower than that of the uncoated graphite specimens. By contrast, the wear rates of the MoS 2 composites increased considerably with the amount of MoS 2 addition. This behavior is thought to be due to the absence of MoS 2 and the presence of brittle CuMo 2S 3 compounds in the sintered composites.

Emerging technologies in extraction and processing of metals

The growing need to conserve energy and materials and prevent environmental pollution led to an increased demand for better understanding of potential as well as existing processes. In this context, thermodynamic and transport modeling of materials and processes provides a rapid and cost-effective means of conducting and minimizing the complexity of experimental investigations and developing innovative and environmentally friendly metallurgical processes. This presentation concentrates on some fundamentals on new technologies as extractive metallurgy of copper, lead, aluminum, and other nonferrous metals and processing of nanocomposites. The newer routes of copper smelting and modeling of impurities in copper and lead slags and mattes are reviewed. The copper smelting capacity increased by a factor of 10 during the last three decades, the smelting rate increased by a factor of 6, and the process fuel equivalent decreased by a factor of 2. The a priori prediction, with no adjustable parameters, of impurity capacities of S and As in copper slags and S in lead slags, based on the Reddy-Blander model, is reviewed. Excellent agreement between the model-predicted capacities data and laboratory experimental and industrial data was observed. The model is an invaluable tool for optimization of process parameters in the efficient removal of impurities from the nonferrous-metals smelting and refining processes. A new in-situ processing technology for the production of a lightweight alloy matrix with ceramic particle reinforcements such as SiC in aluminum alloy matrix composites by bubbling reactive gas is reviewed. Thermal plasma processing of a nanoscale aluminum alloy matrix with TiC and TiN composites is discussed. The in-situ formed reinforcements are thermodynamically stable, and the composite particles are of uniform size. The optimum process parameters for the production of composite powders by thermal plasma are discussed. A low-temperature aluminum production and refining process using ionic liquids as electrolytes is reviewed. This newly developed aluminum production process has many advantages over the current industrial process, and the energy consumption is closer to the thermodynamic limit of aluminum production.

Influence of additives content on the high temperature oxidation of silicon nitride based composites

Abstract A life prediction tool for mechanical and electrical applications of electroconductive structural ceramics is essential in order to know the limit for engineering uses. The aim of this work was to study the influence of additives content on the oxidation behaviour, in pure oxygen between 900 and 1400 °C, of two fully dense Si 3 N 4 –35 vol.% TiN composites. For this purpose, a hot pressed material (HP), containing 3.7 wt.% of Y 2 O 3 and Al 2 O 3 as sintering aids, was compared to an hipped material (HIP), containing 0.4 wt.% of the same additives. Up to a temperature T T >∼1200 °C, when the oxidation of the Si 3 N 4 matrix takes place. The formation of a compact silica sub-scale acts as an efficient diffusion barrier leading to asymptotic kinetics, with final weight gains exhibiting a negative temperature dependence. In the case of the HP material, i.e. in presence of a higher content of additives, a deterioration of the protective nature of the scale is provoked by the increased mobility of the impurity cations (Y 3+ , Al 3+ ) linked to a decrease of the viscosity of the secondary glassy phase. The kinetics have a paralinear shape up to 1400 °C, with final weight gains increasing as a function of temperature. Therefore, this study confirms the deleterious influence on oxidation resistance of additives used for a better sintering of powders and the beneficial effect of hot isostatic pressing for which lower amounts of aids are necessary in comparison with hot pressing.

Creep of Duplex Alumina–Titanium Nitride Polycrystalline Microstructures

Compression creep results in an inert atmosphere are presented for fine‐grained Al2O3–TiN composites deformed under a stress range of 10–50 MPa stress and a temperature range of 1250°–1400°C. The effects of TiN content (10–70 vol%) and the preparation route (i.e., reactive versus nonreactive hot pressing) are considered. Al2O3 and TiN both are efficient grain‐growth inhibitors, relative to each other; thus, deformation develops in stable equiaxed microstructures. Except for low TiN contents (10 and 20 vol%), the processing route does not markedly influence the observed strain rates, at least up to a strain of −0.16. In all cases, deformation occurs mainly via interfacial/grain‐boundary sliding, and its rate is enhanced in approximate proportion to the amount of Al2O3/TiN interfacial area. The deformation rate seems to be limited by either some interface reaction or a complex boundary diffusional mechanism that occurs at the Al2O3 grain boundaries.

Factors inducing degradation of properties after long term oxidation of Si 3N 4–TiN electroconductive composites

The effects on strength and electrical conductivity of heat treatments in air at 800, 1000 and 1200 °C for 100 h were evaluated on hot pressed Si 3N 4–35 vol.% TiN composite. The long term oxidation involves microstructural changes at the surface and sub-surface, such as the formation of oxide scales and of a multilayer microstructure under the oxide towards the bulk, due to the involved chemical reactions, the outward diffusion of cations (Ti, Y, Al) and impurities, and inward diffusion of oxygen during heat treatments. At the same time, crystallisation of the grain boundary phase occurs. The decrease of the room temperature (RT) flexural strength reached about 40% in the samples exposed at 1200 °C for 100 h, compared to the as-produced materials. The variation of the electrical resistivity was related to the microstructure modification due to oxidation: the surface oxide scale is an insulator and increases the electrical resistivity from 10 −3–10 −4 to 10 10–10 11 Ω cm. The effects induced by an annealing treatment in argon at 1200 °C for 100 h have also been investigated and compared to those caused by the oxidation.

Thermal stability of in situ formed Si3N4–Si2N2O–TiN composites

Abstract To investigate the potential of in situ formed Si 3 N 4 –Si 2 N 2 O–TiN composites, mixtures of Si 3 N 4 with TiO 2 and TiN powders were hot-pressed. Seven different compositions were successfully densified at 1650 °C resulting in various Si 3 N 4 -, Si 2 N 2 O- and TiN-volume fractions. The effect of elevated temperatures (up to 1400 °C) on the microstructure of these composites was explored, using internal friction measurements with the impulse excitation technique (IET) and high temperature X-ray diffraction (HTXRD). The bulk microstructure of the tested composites is stable up to 1400 °C, both with respect to the crystalline phase composition, as well as the intergranular glass phases. Sample surfaces are affected due to the reducing atmosphere in which IET and HTXRD tests are performed (N 2 or vacuum). This involves the silicon oxynitride phase, which is not stable at temperatures above 1300 °C in the presence of a substantial amount of amorphous intergranular phase. Based on the results of indentation toughness and hardness tests, a high-Si 2 N 2 O/high-TiN/β-Si 3 N 4 is selected as most promising for further development.

Graphite–Tin composites as anode materials for lithium-ion batteries

Graphite–tin composites were produced by high-energy bail-milling. X-ray diffraction and HREM observation showed that graphite became amorphous and tin became nanocrystalline after the intensive ball milling. The element Sn was encapsulated in the ductile graphite matrix on a nanometer scale. Electrochemical tests show that the lithium storage capacity increases with the addition of Sn, which could be attributed to the reaction of Sn with Li to form Li x Sn alloys. The volume expansion due to the alloying process may be buffered by the amorphous graphite matrix. The C 0.9Sn 0.1 electrode can deliver a discharge capacity of 1250 mAh/g in the initial cycle. Generally, the capacity of the ball-milled C, C 0.9Sn 0.1 and C 0.8Sn 0.2 electrodes decrease with cycling quite quickly, but the C 0.9Sn 0.1 and C 0.8Sn 0.2 electrodes have better cyclability than that of the ball-milled graphite electrode. The combination of C and Sn could be an anode material with high capacity for lithium-ion batteries.

Microstructure and current-voltage characteristics of bronze processed niobium tin composites

Bronze route conductors are widely used for high field purposes. To shift their limits to even higher fields it is decisive to understand the role that microstructure plays in controlling the current-voltage characteristic. Microstructural properties of Nb/sub 3/Sn are crucially determined by the reaction heat treatment. Therefore, several heat treatments on samples of a commercial composite were performed. The reaction temperatures extend from 600/spl deg/C up to 750/spl deg/C. SEM micrographs were taken from filaments at different positions within the samples. These micrographs were used to carry out a quantitative analysis of grain size. To investigate the connection of microstructural and electrical properties, resistive measurements of the current-voltage characteristic at magnetic fields up to 15 T and 4.2 K were performed.

Microstructural characterization of electroconductive Si 3N 4–TiN composites

Electroconductive Si 3N 4–TiN composites from Si and TiN powders have been fabricated by in situ reaction-bonding and post-sintering under N 2 atomosphere. The values of fracture strength and electrical resistivity in the Si 3N 4–50 wt.% TiN composite were 531 MPa and 2.5×10 −2 Ω cm, respectively. The dispersion of TiN particles inhibited the abnormal growth of rod-like Si 3N 4 grains with large size in diameter. An amorphous phase observed in most grain boundaries and triple points is attributed to liquid phase sintering. Many dislocations formed by the difference of thermal expansion coefficients were observed in Si 3N 4 and TiN grains.

Ti–TiN hardmetals prepared by in situ formation of TiN during reactive ball milling of Ti in ammonia

Vapour deposition of titanium nitride on WC/Co or hard ferrous-based cutting tips generally results in significant increases in cutting tool life. However, a major limitation of such nitrided tips is that they cannot be resharpened for re-use. Although monolithic TiN may be too brittle for cutting tool applications, with appropriate microstructural design, Ti–TiN composites should have the required combinations of toughness, ductility, hardness, wear resistance and thermal conductivity to replace coated tips for a range of machining applications. We report the synthesis of monolithic Ti–TiN composites from nanostructural precursor powders. Reactive ball milling of Ti in nitrogen or ammonia under controlled conditions eventually results in the formation of nanostructural TiN. Furthermore, by ending the reaction after an appropriate period a homogeneous and uniform mixture of Ti and TiN phases can easily be produced. Due to the highly reactive, nanostructural nature of the powder product this synthesis route has the potential to eliminate wetting problems generally associated with the current technology of conventional liquid-phase sintering. Moreover, by controlling nitriding gas pressure changes during milling good control of both the Ti to TiN ratio and final crystallite size distributions can be achieved. It was found that precursor Ti–TiN nanostructural powders synthesised in this way can be successfully compacted and liquid phase sintered without sintering aids. Such compacts show high densities and nanoindentation hardnesses in the range of 18–23 GPa. Structural characterization was performed using X-ray analysis, transmission and scanning electron microscopy as well as optical microscopy. The mechanical properties were characterised using micro- and macroindentation techniques.

Multifunctional Si 3N 4/(β-SiAlON+TiN) layered composites

Layered multifunctional ceramic composites on the base of Si 3N 4 and TiN have been prepared by tape casting. The reaction conditions for in situ preparation of β-SiAlON + TiN composite were optimised and dense Si 3N 4/(β-SiAlON + TiN) layered materials were prepared by hot pressing. The bending strength and fracture toughness of layered materials measured in the direction perpendicular to the layer alignment were remarkably higher (1184 MPa and 9.75 MPa m 1/2) in comparison to the “monolithic” β-SiAlON + TiN composite (647 MPa and 4.71 MPa m 1/2). High anisotropy was achieved for the electrical resistance of the layered materials in parallel (6.10 −2 Ω cm) and perpendicular (5×10 11 Ω cm) direction to the layer alignment.

Electrochemical lithiation of tin and tin-based intermetallics and composites

This article gives an overview on lithium alloys and lithium alloying metals for use as anodes in ambient temperature rechargeable lithium batteries. After a brief introduction about advantages and drawbacks of lithium alloy anodes and a chronological review of their development, principle concepts to overcome the problems with the dimensional stability of the metallic host materials will be presented. Recent work on promising multiphase (composite and/or intermetallic) tin-based lithium alloying materials will be highlighted.

Tribotechnical characteristics of electric spark coatings made of TiN composites

Tribotechnical characteristics of electric spark coatings made of TiN composites

In Situ synthesis of TiN-reinforced Si3N4 matrix composites using Si and sponge Ti powders

Dense Si3N4-TiN composites from Si and sponge Ti (0–40 wt %) powders were produced by in situ reaction-bonding and post-sintering under N2 atomosphere. The fracture strength and toughness of Si3N4-17% TiN composite were found to be 537.9 MPa and 10.4 MPa m1/2, respectively. In the reaction-bonded bodies, Si3N4 grains were constructed with α- and β-Si3N4 structure as well as TiN and some amounts of residual Si phase. After post-sintering, the residual Si and α-Si3N4 grains were transformed to β-Si3N4 grains with rod-like shape. No intermetallic compounds (e.g., TiSi2, Ti5Si3 and Ti5Si4) were formed at the interfaces between Si3N4 and TiN grains. The main toughening mechanisms were crack deflection and crack bridging caused by rod-like Si3N4 grains which were randomly dispersed in sintered body. Microcracking due to the dispersion of in situ formed TiN particles also contributed to the toughening of the sintered body.

Liquid-Phase Sintering and Properties of Si3N4–TiN Composites

Densification during liquid-phase sintering of Si3N4–TiN was studied in the presence of Y2O3. The content of TiN was varied from 0–50 mass%. During the densification Y-silicate was formed. The amount of silicate increased with both decreasing fraction of TiN and increasing isothermal heating time. Density, fracture toughness, and electrical resistivity were measured as a function of TiN content. It was found that the density and fracture toughness increased with increasing TiN content. The electrical resistivity drops drastically, from 1010 mΩ for sintered Si3N4 to 10−3 mΩ for sintered Si3N4–TiN composite containing 30 vol% TiN.

Mechanical and tribological properties of nanocrystalline and nanolaminated surface coatings

The mechanical and tribological (friction/wear)properties were determined for nanocrystalline aluminum, as-sputtered Ti, Zr and Cu films, and nanolaminated Al-Al 2O 3, TiTiN, TiCu and TiZr composite films. The aluminum grain size varied between 15 and 10 6 nm. The Al and Ti layer thicknesses in Al-Al 2O 3 and TiTiN composites ranged from 70 to 500 nm and from 150 to 450 nm, respectively. Within the grain size range of 15–100 nm, the hardness of the aluminum follows a Hall-Petch type relationship. The hardness of the TiTiN and Al-Al 2O 3 fllms also follows a Hall-Petch relationship with the Ti orAl layer thickness. The TiCu composites show a softening effect with decreasing Ti layer thickness. The coefficient of friction and wear rate for nanolaminated TiTiN and Al-Al 2O 3 composites are consistently reduced as the metal layer thickness is reduced. The micromechanisms responsible for the differences in mechanical and tribological properties are examined and the results compared with published literature.

Manufacture and properties of Al 2O 3–TiN particulate composites

Dense Al 2O 3–TiN composites with 5–25 vol% TiN were manufactured by hot pressing technique. The effect of the content of a dispersion-toughening aid, TiN, on the mechanical properties, electrical resistivity, oxidation resistance and wear resistance were studied and related to the microstructure. The ceramics with a content of 25 vol% TiN were characterized by the highest strength, 567 MPa, and the lowest electrical resistivity, 2·5×10 −3 Ω.cm. The material was suitable for electrical discharge machining.

R‐Curve Behavior of Silicon Nitride–Titanium Nitride Composites

The R–curve for Si3N4−40 wt% TiN composites was estimated by the indentation‐strength method and compared to that of monolithic Si3N4 with duplex microstructure. Both materials exhibited rising R‐curve behavior. The Si3N4‐TiN composites, however, displayed better damage tolerance and higher resistance to crack growth. From TEM observation, it was inferred that this superior performance of Si3N4‐TiN composites can be attributed mainly to stress‐induced microcracking at hete rophase (Si3N4/TiN) boundaries.

Microstructural, inductive and electrical characterizations of granular Bi 2Sr 2CaCu 2O 8/Pb or PbO composites

Granular composites made from the high T c superconductor Bi-2212 and lead are prepared by two ways, whether pressing and heating just above the melting temperature of Pb (as called pressed composites) or pressing and heating at medium temperature near 650°C (as called sintered composites). In this latter case, a large reaction occurs during the sintering between Pb, PbO and the ceramics, as the microstructural study shows. Inductive measurements give evidence of the existence of an imaginary part in the a.c. susceptibility, which is the indication of a coupling between grains and the percolation of electronic currents through the sample. The percolation threshold occurs for a composition Bi-2212 vol.%≈25, as assessed by magnetization measurements. From the electrical response, it is established that pressed composites exhibit a semiconducting electrical behaviour in contrast to similar Bi-2212/tin composites previously studied. No 3D-percolation threshold of the normal conduction by lead is observed. However, for the sintered composites, the superconducting transition exists but it is not complete and is interrupted by a semiconducting behaviour on the surface of grains, which becomes predominant below 45 K upon cooling.