Effect of Y 2O 3 addition on the densification and mechanical properties of alumina–niobium carbide composites (original) (raw)
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Sintering behaviour of alumina–niobium carbide composites
Journal of The European Ceramic Society, 2000
Ceramic cutting tools have been developed as a technological alternative to cemented carbides in order to improve cutting speeds and productivity. Al2O3 reinforced with refractory carbides improve fracture toughness and hardness to values appropriate for cutting applications. Al2O3–NbC composites were either pressureless sintered or hot-pressed without sintering additives. NbC contents ranged from 5 to 30 wt%. Particle dispersion limited the grain growth of Al2O3 as a result of the pinning effect. Pressureless sintering resulted in hardness values of approximately 13 GPa and fracture toughness around 3.6 MPa m1/2. Hot-pressing improved both hardness and fracture toughness of the material to 19.7 GPa and 4.5 MPa m1/2, respectively.
Sintering of alumina-niobium carbide composite
International Journal of Refractory Metals & Hard Materials, 1998
Several studies have been focused on particulate-dispersed Al2O3 composites in order to improve both room and high temperature mechanical properties and wear resistance. In the present work Al2O3-NbC composites have been pressureless sintered and their microstructures analysed as a function of NbC and Y2O3 concentration, the latter added as sintering aid. The compositions used in this study were Al2O3-xNbC and (Al2O3 3%Y2O3)-xNbC, (x = 10, 20 and 40 wt%) and the sintering was performed at 1650 °C/30 min and 1750 °C/15 min. A density greater than 96% of the theoretical density was reached even for those materials sintered at 1650 °C. The observed microstructure was more homogeneous for the samples with Y2O3 addition and the Y3Al5O12 phase was detected. The Al2O3 grain growth restraining due to the NbC concentration was more pronouncedly in samples sintered at 1750 °C.
Properties of sintered alumina reinforced with niobium carbide
International Journal of Refractory Metals and Hard Materials, 2009
The presence of carbide or nitride particles in Al 2 O 3 -based composites may produce a pinning effect and inhibit the grain growth of the matrix, which might significantly contribute to the final performance of the composite. Fracture toughness, mechanical strength and wear resistance have been particularly improved by the dispersion of hard particles. This work has the purpose to investigate the potential use of NbC as alumina reinforcing material, as an alternative to other carbides such as TiC, WC and (W, Ti)C. Alumina was mixed with a constant 30 wt.% of carbide in a ball mill, uniaxially hot-pressed at 1600°C and 20 MPa in an inert atmosphere, and characterized. X-ray diffraction revealed that alumina and the added carbide were the only crystalline phases present and no oxidation products were detected. The increase in fracture toughness likely is the result of crack deflection, triggered by carbide particles at the alumina grain boundaries. The results obtained in this work show that alumina reinforced with NbC is a composite material with properties comparable to those of alumina reinforced with WC, TiC or (W, Ti)C, making NbC a good reinforcing material.
Ceramics International, 2018
In the present study, the effect of heating schedules on densification, microstructure and mechanical properties of the Al 2 O 3-3YSZ-Ni composite was investigated. The composites were fabricated by one-step sintering (OSS) at temperatures T for 3 h (T/3 h), and two-step sintering (TSS) starting by preheating to a temperatures T 1 for 0.5 h, followed by a drop in temperature to T 2 equal to 1600°C for 3 h (T 1 /0.5 h, 1600°C/3 h). The contribution of smaller grain size and the improvement of relative density produced by TSS lead to enhanced hardness and fracture strength of the composite without destroying its fracture toughness. The hardness of composites increased with increasing sintering temperature, where its highest value 14.51 GPa was attained at T 1 = 1720°C for TSS. As well, strength was enhanced and reached 417 MPa. However, the toughness for TSS was decreased slightly with increasing T 1 and attained its highest value of 6.21 MPa m ½ at T 1 = 1650°C.
Influence of NbC Content on the Wear Resistance of Alumina/Niobium Carbide Tools
2021
Wear resistance is a fundamental property which defines the lifetime of cutting tools, but the investigation of wear performance of alternative hard materials for traditional WC-Co composites are recent. The present work evaluated the pin-on-disk wear behavior and mechanical properties, i.e., hardness and fracture toughness of spark plasma sintered Al2O3 matrix composites with additions of 5, 15, 25 or 30%wt of niobium carbide NbC. The wear resistance was observed to increase as a function of the NbC content, even though the hardness reached a plateau at 25%wt NbC. The composite behavior was compared to that of other alumina composite tool materials proving to be a promising material for applications such as ceramic cutting tools. The composition A95N5 presented the best combination of values of wear rate: 8.9 mm3/N.m, hardness equal to (17.36±1.72) GPa and fracture toughness of (3.2±0.6) MPa. m1/2.
Alumina-carbon composites with high hardness
The addition of particulate carbon into oxide ceramics can significantly improve their durability and wear characteristics due to the lubricating properties of carbon. In the present work an alumina-carbon composite was prepared by pyrolytic cracking in inert atmosphere of the organic compounds added as lubricants, wetting agents and dispersants in the course of freeze granulation of an alumina powder. Carbon in the form of submicron-sized isometric graphitic inclusions was homogeneously distributed within the dense alumina matrix prepared by hot pressing. SiC was also formed by carbothermal reduction of the SiO 2-based sintering additive. The matrix consisted of submicron alumina grains. The Vickers hardness of the carbon-containing composites was higher than the hardness of their carbon-free counterparts (18 and 22 GPa respectively for carbon-free and carbon containing liquid phase sintered aluminas). The fracture toughness was not affected markedly by graphite incorporation.
Advanced Alumina Composites Reinforced with Nb-Based Alloys
Advanced Engineering Materials, 2002
Functional and structural ceramics are characterized by their excellent wear resistance and hardness as well as good thermal and chemical stability. However, in most cases ceramic materials exhibit very low fracture toughness, which limits their technical application. In recent decades, metal±ceramic composites have been developed to overcome the brittle behavior of monolithic ceramics.
Journal of The American Ceramic Society, 2005
A series of silicon carbide-based ceramics with different sintering additives were liquid-phase sintered to high densities. Yb 2 O 3 in combination with AlN was used as the additive, instead of the commonly used Y 2 O 3 -AlN, to improve the refractoriness of the secondary phase. Thermo-chemical decomposition of AlN was sufficiently suppressed with the use of nitrogen overpressure and reasonable weight loss was achieved in the different additive containing SiC ceramics without a reactive powder bed. Use of the heavier rare-earth element modified the liquid phase formed during sintering and reduced the phase transformation controlled grain growth rate, compared with Y 2 O 3 doped materials. It also permitted microstructure tailoring through post-sintering heat treatments in nitrogen. Materials with self-reinforced microstructures, formed as a result of anisotropic grain growth, were obtained. Improved fracture toughness (4.5-5 MPa/m 1/2 ) and good flexural strength retention up to 14001C were also observed.
Effects of Y2O3 on the mechanical properties of Ti/Al2O3 composites of hot pressing sintering
Materials Science and Engineering: A, 2015
Ti/Al 2 O 3 composites with Y 2 O 3 additions varied from 0 vol.% to 1.5 vol.% were fabricated by vacuum hot pressing sintering and the effect of Y 2 O 3 additions on the mechanical properties of the composites was investigated. The composite with 1.0 vol.% Y 2 O 3 addition showed superior density (relative density of 97.46%), hardness (micro-hardness of 13.34 GPa), strength (flexural strength of 488.08 MPa) and toughness (fracture toughness of 8.15 MPa m 1/2 ) when sintered at 1450 1C for 30 min under the pressure of 30 MPa. It can be seen from the SEM images that the fracture mode of the Ti/Al 2 O 3 composites has changed from the intergranular fracture into a mixture of intergranular and transgranular fracture with the addition of Y 2 O 3 . The mechanism of that was confirmed as the inhibition of the interfacial reactions between Ti and Al 2 O 3 . However, excessive Y 2 O 3 additions ( 41.0 vol.%) would greatly reduce the yield of Ti-Al intermetallic compounds, which weakened the "pinning effect" caused by the compounds, and finally degraded the mechanical properties of the composites.
Ceramics International, 2014
Alumina-based composite ceramic tool materials reinforced with carbide particles were fabricated by the hot-pressing technology. Choice of metallic phase added into the present composite ceramic was based on the distribution of residual stress in the composite. The effects of metallic phase on microstructure and mechanical properties of composites were investigated. The metallic phase could dramatically improve room temperature mechanical properties by refining microstructure, filling pores and enhancing interfacial bonding strength. However, it also led to sharp strength degradation at high temperature because the metallic phase was easier to be oxidized and get soft at high temperature in air. The effects of metallic phase on strengthening and toughening were discussed. The improved fracture toughness of composite with metallic phase was attributed to the lower residual tensile stress in the matrix and the interaction of more effective energy consuming mechanisms, such as crack bridged by particle, crack deflection and intragranular grain failure.