A combinatorial approach for automotive friction materials: Effects of ingredients on friction performance

Raw materials used in automotive friction formulations were classified using a combinatorial approach into two groups in accordance with their ability to improve the wear properties of the mixture by two-phase friction composites. Components of group one, which improved the wear resistance, include softer additives (graphite, MoS₂, and Twaron), harder additives (Al₂O₃ and steel wool), and organic binder (benzoxazine). Softer additives have low friction coefficient (μ), low wear, and easily transferred debris to the surface of disc. Harder additives have intermediate wear, intermediate μ, and formed iron-containing surface layer transferred from cast iron disc to friction material pad. Benzoxazine has high wear and high μ and there is no transferred layer formed either on disc or pad in the case of benzoxazine used as pad. The wear of two-phase friction materials can be improved by adding Al₂O₃, graphite, MoS₂, steel wool, and Twaron to benzoxazine and four wear improvement mechanisms were proposed: (1) lubrication mechanism (graphite and MoS₂); (2) abrasive mechanism (Al₂O₃); (3) friction layer mechanism (steel wool); (4) reinforced mechanism (Twaron). Components of group two, which produced poor wear resistance, include BaSO₄, BN, B₂O₃, brass chips, CaCO₃, Ca(OH)₂, cashew, copper chips, CuS, Cu₂S, H₃BO₃, iron powder, MgO, oxidized PAN fiber, PMF (SiO₂ + CaO), Sb₂S₃, Ultrafibe (CaSiO₃), and ZrSiO₄.     

Effect of Nanosized Powders on the Structure and Properties of Electrospark Alloyed Coatings

The influence of nanosized additives ZrO₂, Al₂O₃, W, WC, WC-Co, NbC, Si₃N₄ on mass transfer of the SHS electrode material of the Ti-Cr-Ni-C system (SHIM-3B alloy trade mark) is considered. The thickness, continuity, and microhardness of the electrospark coatings alloyed onto the nickel alloy, as well as the coating structure, wear resistance, and the nanosized powder distribution in the coating have been studied. The coatings obtained have been subjected to X-ray analysis. An optimum performance regime of the ALIER-METAL setup for high-frequency electrospark alloying has been determined. It has been found that addition of nanosized powders to the electrode material facilitates thickening of the electrospark alloying (ESA) coatings and improvement of their continuity, hardness, and wear resistance.     

Structure and properties of dispersion-strengthened-with-nanosized particles refractory hard material TiC—Ni-alloy

Some particularities of the effect of nanocomponents such as ZrO₂,Al₂O₃, W, WC, WC—Co, NbC, Si₃N₄ on the combustion process, the structure, and mechanical properties of a novel electrode dispersion-strengthened alloy TiC—40% Ni have been studied. The refractory hard alloy based on titanium and a nickel alloy has been produced by the method of self-propagating high-temperature synthesis. It has been shown that introduction of a nanosized powder causes reduction of the combustion velocity depending on the specific surface area of the additive. It has been found that upon introduction of nanodispersed powders into the green mixture the product structure undergoes significant modification. The ZrO₂ and NbC additives produce a positive effect on the main mechanical characteristics of the alloy (its strength, hardness, and crack resistance). In contrast, these properties are negatively affected by the Al₂O₃ and Si₃N₄ nanopowders. Enhancement of the material bending strength and crack resistance can be achieved by respective addition of WC—Co and W, WC. © 2003 Elsevier Ltd. All rights reserved.     

Metallization development for AIN/W cofired substrate at low temperature

In this paper, metallization properties of AlN/W cofired substrate sintered at 1650°C were studied. The adhesion strength between W and AlN ceramic was improved by some methods, which including addition of several kinds of oxides mixture or metallic particles into W thick film ink. When MgO-Al₂O₃-SiO₂ was used, glass bonding increased the adhesion strength and when metallic particles were added, W conductor resistance decreased obviously.     

Effect of oxide additives on the properties of high temperature superconductor,YBa2Cu3O7

The effect of oxide additives-CuO, SiO₂, Y₂O₃, Bi₂O₃ and ZnO in 1–10 mol% on the sintering and superconducting properties of YBa₂Cu₃O₇ was studied. SEM studies indicated improvement of grain size and interconnectivity due to the additives, the best results being obtained with Bi₂O₃, SiO₂ and Y₂O₃. The superconducting transition temperature is unaffected (92±2 K) even with 10 mol % of the additives. ZnO, however, decreases theT _c as expected.     

The effects of additives on the properties and structure of hot-pressed aluminium titanate ceramics

The effects of additives (MgO-Al₂O₃-SiO₂, Al₂O₃-SiO₂, Si₃N₄, SiC) on the properties and structure of hot-pressed aluminium titanate ceramics were studied. The results showed that the bending strength of aluminium titanate ceramics with additives was improved greatly, while the thermal expansion coefficient was also increased due to the change of structure for aluminium titanate ceramics. The results of X-ray diffraction patterns showed that a solid state reaction occurred between the additives and aluminium titanate, and a solid solution was formed.     

Microstructure and thermal conductivity of spark plasma sintering AlN ceramics

Abstract

Dense aluminium nitride ceramics were prepared by spark plasma sintering at a lower sintering temperature of 1700°C with Y₂O₃, Sm₂O₃ and Dy₂O₃ as sintering additives respectively. The effects of three kinds of sintering additives on the phase composition, microstructure and thermal conductivity of AlN ceramics were investigated. The results showed that those sintering additives not only facilitated the densification via the liquid phase sintering mechanism, but also improved thermal conductivity by decreasing oxygen impurity. Sm₂O₃ could effectively improve thermal conductivity of AlN ceramics compared with Y₂O₃ and Dy₂O₃. Observation by scanning electron microscopy showed that AlN ceramics prepared by spark plasma sintering method manifested quite homogeneous microstructures, but AlN grain sizes and shapes and location of secondary phases varied with the sintering additives. The thermal conductivity of AlN ceramics was mainly affected by the additives through their effects on the growth of AlN grain and the location of secondary phases.     

Preparation of In2O3 and tin-doped In2O3 films by a novel activated reactive evaporation technique

High quality films of In₂O₃ and tin-doped In₂O₃ were prepared by a novel activated reactive evaporation technique developed for use with resistively heated evaporation sources. Transparent conducting coatings of In₂O₃ have a sheet resistance of 80 Ω/□ with an optical transparency of more than 95% in the 0.4–1.6 μm wavelength range. Thin (0.4 μm) In₂O₃(Sn) films have a sheet resistance of 25 Ω/□ and an optical transparency as high as 99% at some wavelengths with an average transmission between 0.4 and 1.6 μm of 96%. Thicker films have a sheet resistance as low as 2.2 Ω/□. A comparison of the properties of In₂O₃(Sn) films with those of transparent conducting films produced by other techniques is made.     

Effect of rare-earth oxide additives on the morphology of combustion synthesized rod-like β-Si3N4 crystals

This paper presents the results of synthesizing rod-like β-Si₃N₄ crystals by combustion synthesis (CS) with six rare-earth oxides (Y₂O₃, La₂O₃, CeO₂, Sm₂O₃, Gd₂O₃ and Yb₂O₃) as additives under high nitrogen pressure. The effect of rare-earth oxide additives on the final morphology of rod-like β-Si₃N₄ was investigated and the crystal growth mechanism was discussed in detail. The results reveal that the final morphology of combustion synthesized Si₃N₄ is strongly dependent on the viscosity of liquid formed by the rare-earth oxide and the SiO₂ on the Si powder surface. With the increasing of atomic number of the rare-earth elements, the final morphology is from elongated rod-like crystals to short columnar crystals.     

Mechanisms of destruction of plasma-sprayed heat protecting coatings in heat cycling

The article presents the results of heat cycling tests of plasma-spayed heat protecting coatings consisting of two layers: a lower metal layer based on the alloy CoCrAIY, and an upper ceramic layer based on zirconium dioxide. To stabilize the ZrO₂ partially, the following additives were used: 30% CeO₂, 8% Y₂O₃, 6.2% Y₂O₃. The article examines the conditions of crack propagation on the metal-ceramic interface in dependence on the thickness of the ceramic layer. It is noted that it is expedient to provide an interface between metal and ceramic with nonuniform adhesive bond so that there are sections with higher resistance to the development of destruction.Translated from Problemy Prochnosti, No. 2, pp. 44–47, February, 1994.     

Influence of AST additives on the stability of PTCR characteristics and microstructure in ferroelectric ceramics

(Ba_0.69Pb_0.31)TiO₃ ceramics were prepared using Al₂O₃, SiO₂, additives and excess of TiO₂ (AST). The characteristics of positive temperature coefficient of resistivity (PTCR) was studied and the corresponding microstructures were investigated using atomic force microscopy and scanning electron microscopy. The results showed that the PTCR effect was related to the AST additives. The maximum value of resistivity in the ceramics with lower content of or without Al₂O₃ and SiO₂ additives was much lower than in those with AST additives. Ceramics with low AST content, which were heated by electric field to a temperature much higher than their Curie temperature, lost the PTCR effect after the electric field stimulation. The microstructure observations revealed that re-crystallization took place in the ceramics with lower content of or without AST additives resulting in the loss of the PTCR effect.     

Effect of sintering additives on the behaviour of SiC whisker-reinforced Si3N4 composites

The effects of sintering additives on the microstructural development, whisker stability, oxidation resistance and room-temperature mechanical properties of the SiC whisker-reinforced Si₃N₄ matrix composites were investigated. Seven different combinations of Y₂O₃ and Al₂O₃ were used as sintering additives. The composites containing 20 vol % SiC whiskers were densified by hot pressing. The microstructure of the resulting composites was characterized using X-ray diffraction, scanning and transmission electron microscopy. Oxidation testing of the composite at 1400 °C was conducted to investigate the relationship between matrix compositions and oxidation resistance. The flexural strength, fracture toughness and crack propagation patterns were also characterized and correlated with the microstructural features.     

Study on microstructure and properties of Ni-based alloy/Y2O3-deposited metals by laser cladding

Laser cladding of Ni-based alloy/Y₂O₃ (Yttrium Oxide) powder on 6061 aluminum alloy was carried out using 3 kW CW Nd:YAG laser to strengthen and improve hardness and corrosion resistance of substrate. Metal matrix composite composed of aluminum substrate, Ni-based alloy, refining and dispersion strengthening Y₂O₃, and particle hardening W, Cr was obtained. The microstructure and morphology, phase identification, element diffusion, and composition analysis of the Ni-based alloy/Y₂O₃-deposited metal and deposited metals/6061 aluminum substrate interface were examined using scanning electron microscopy (SEM), Electron Probe Micro-analyzer (EPMA) with energy-dispersive spectrometer (EDS) analysis. The micro-hardness distribution and corrosion-resistance property were investigated also. The results showed: (1) with the addition of Y₂O₃, more fine microstructures consisted of isometric crystal, white acicular crystal, and fringe crystal, primary phases were mainly Ni₃Al, NiAl, NiAl₃, W, α-Al, and Cr _x C. (2) Micro-hardness of deposited metals was 780–1100 HV_0.2 and distributed smoothly near interface. The corrosion rate of aluminum substrate was nearly twice that of deposited metals with addition of Y₂O₃.     

Effect of additives on some properties of silicon oxynitride ceramics

Silicon oxynitride ceramics are formed by reaction sintering of silicon nitride and silica with certain metal oxide additives. The reaction rate during sintering and the subsequent properties of silicon oxynitride are affected by the quantity and kinds of additives. The reaction rate increased for addition of equal molar amounts of ZrO₂, ZrO₂ (+2.8 mol % Y₂O₃), AlO_1.5, LnO_1.5, CeO₂, MgO, in that order (where Ln=Nd, Sm, Gd, Dy, Er, Yb and Y). The lanthanide oxide (1.5 mol %)-doped silicon oxynitride ceramics had a high fracture toughness, because crack deflection occurred due to the precipitation of an intergranular crystalline phase with a high thermal expansion coefficient compared with silicon oxynitride. The oxidation rate was higher with an increasing quantity of additive. In samples containing an intergranular crystalline phase, stability of the crystalline phase is an important factor and could impair the oxidation resistance of silicon oxynitride ceramics.     

Sintering of Sb2O3-doped ZnO

The effect of Sb₂O₃ on the densification of ZnO was studied and compared with that for additives such as ZnSb₂O₆,-Zn₇Sb₂O₁₂, and Sb₂O₄. Addition of up to 2.0 mol% Sb₂O₃ raised the densification temperature of ZnO from 600° C to 1000° C regardless of doping level and the particle size of Sb₂O₃. Addition of other antimony-additives, however, slowed down the densification of ZnO, and the densification temperature increased with increasing amount of additives. Results of TG, XRD and SEM showed that the observed densification characteristics in Sb₂O₃-doped ZnO are explained by the volatile nature of Sb₂O₃. Thus, Sb₂O₃ evaporates during oxidation at about 500° C and condenses on the ZnO particle surfaces as a noncrystalline phase of an unknown composition, which checks the material transport across ZnO particles resulting in the retarded densification.     

High-strength zirconium diboride-based ceramic composites consolidated by low-temperature hot pressing

Abstract

Two compositions of ZrB₂-based ceramic composites containing Si₃N₄, Al₂O₃ and Y₂O₃ have been hot-pressed at different temperatures between 1673 and 1773 K for 60 min in vacuum. The densification behavior of the composites was examined during the sintering process. The microstructures of the composites were characterized by scanning electron microscopy, and the crystalline phases were identified by x-ray diffraction. The effects of Al₂O₃ and Y₂O₃ additives on the densification behavior and flexural strength were assessed. A relative density of ～95% was obtained after sintering at 1723 K or higher temperatures. The microstructures of the composites consisted of (Zr,Y)B₂, α-Si₃N₄ and Y₃(Al,Si)₅O₁₂ phases. The room-temperature flexural strength increased with the amount of additives and approached 1 GPa.     

High-strength zirconium diboride-based ceramic composites consolidated by low-temperature hot pressing

Two compositions of ZrB₂-based ceramic composites containing Si₃N₄, Al₂O₃ and Y₂O₃ have been hot-pressed at different temperatures between 1673 and 1773 K for 60 min in vacuum. The densification behavior of the composites was examined during the sintering process. The microstructures of the composites were characterized by scanning electron microscopy, and the crystalline phases were identified by x-ray diffraction. The effects of Al₂O₃ and Y₂O₃ additives on the densification behavior and flexural strength were assessed. A relative density of ∼95% was obtained after sintering at 1723 K or higher temperatures. The microstructures of the composites consisted of (Zr,Y)B₂, α-Si₃N₄ and Y₃(Al,Si)₅O₁₂ phases. The room-temperature flexural strength increased with the amount of additives and approached 1 GPa.     

Kapitza resistance and thermal conductivity of Kapton in superfluid helium

We have determined simultaneously the Kapitza resistance, R_K, and the thermal conductivity, κ, of Kapton HN sheets at superfluid helium temperature in the range of 1.4–2.0 K. Five sheets of Kapton with varying thickness from 14 to 130 μm, have been tested. Steady-state measurement of the temperature difference across each sheet as a function of heat flux is achieved. For small temperature difference (10–30 mK) and heat flux density smaller than 30 W m⁻², the total thermal resistance of the sheet is determined as a function of sheet thickness and bath temperature. Our method determines with good accuracy the Kapitza resistance, R_K=(10540±444)T⁻³×10⁻⁶ K m² W⁻¹, and the thermal conductivity, κ=[(2.28±0.54)+(2.40±0.32)×T]×10⁻³ W m⁻¹ K⁻¹. Result obtained for the thermal conductivity is in good agreement with data found in literature and the Kapitza resistance’s evolution with temperature follows the theoretical cubic law.     

Effects of additives on sintering and some properties of calcium phosphates with various Ca/P ratios

The effects were studied of additives on the sintering and properties such as the compressive strength and chemical durability of ceramics of calcium pyrophosphate, tricalcium phosphate and hydroxyapatite. In improving the compressive strength of these calcium phosphates, the effect of additives was found to be in the order Na₂OCaF₂>MgOgAl₂O₃, SiO₂ for the case of single-doping, and was most marked in the combination of Na₂O-MgO-Al₂O₃ for the complex addition. It was also found that the chemical durability of the calcium phosphates was improved greatly by using a single or complex additives.     

Microstructure and thermal conductivity of AIN ceramics containing additives

The effect on AIN ceramic of the addition of Y₂O₃, Yb₂O₃, Er₂O₃ and CaO were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermal conductivity measurements. The effect of grain boundary segregation and second phase distribution on the thermal conductivity are discussed. The Er₂O₃-CaO-and the Yb₂O₃-CaO-AIN ceramics have a higher thermal conductivity than the CaO-and the Y₂O₃-CaO-AIN ceramics. This is explained on the basis of the free energy of formation (G°), the vaporization of the sintering additives and the microstructural development. Oxidation of freshly cleaned surfaces of those AIN ceramics was studied.