Simultaneous Synthesis and Sintering of Al2O3/TiN Composites using Capsule-free N2-HIPing from Al2O3 and Fine Ti mixed Powder Compacts

Synthesis of dense materials with the compositions of Al2O3/Mo2N=100/0 ~ 40/60 vol% has been attempted directly from Al2O3/Mo mixed raw powder compacts using capsule-free N2 hot isostatic pressing (HIP). During HIPing [1500°C/(16~20)MPa]/1h], solid/gas reaction between Mo and N2 was introduced to form Mo2N. Most sintered composites consisting of only Al2O3 and Mo2N phases reached a higher relative density than 98.0% with closed pores nevertheless capsule-free HIPing. Distribution of Mo2N particles just formed suppressed the grain growth of Al2O3 during sintering. Mechanical properties, such as bending strength (Σb), Vickers hardness (HV), fracture toughness (K1C), and other properties have been evaluated as a function of their compositions. The best mechanical values of Σb (c.a. 573 MPa), HV (c.a. 20.3 GPa) and K1C (c.a. 5.00 MPa･m1/2) were attained at the composition of Al2O3/Mo2N=90/10 vol%, due to a high density (98.6%) and small grain size of Al2O3 matrix (Gs c.a. 4.70 μm). Further addition of Mo2N reduced the sinterability of matrix grains, resulting in low densities of around 90% at the 40/60 vol% composition.

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Fabrication of TiN Particle-Dispersed Al2O3 Composites Utilizing High N2-Pressure SHS

Eurasian Chemico-Technological Journal ◽

10.18321/ectj75 ◽

2011 ◽

Vol 13 (3-4) ◽

pp. 115

Author(s):

Ken Hirota ◽

Hajime Yagura ◽

Katsuya Takaoka ◽

Masaki Kato

Keyword(s):

Mechanical Properties ◽

Fracture Toughness ◽

Thermal Decomposition ◽

High Pressure ◽

Bending Strength ◽

Hot Isostatic Pressing ◽

Mixed Powder ◽

Second Stage ◽

Powder Compacts ◽

Tin Content

Fabrication of fine TiN particle-dispersed dense Al2O3 composites with the compositions of Al2O3/TiN=100/0~90/10 vol% has been conducted from Al2O3/(Ti,TiN0.3) mixed powder compacts by capsule-free hot isostatic pressing (HIP) utilizing high-pressure N2 SHS. Fine Ti powders (φ ~ 0.3 μm) with TiN0.3 phase were prepared by thermal decomposition of planetary ball-milled fine TiH2 powders at 400°C (673 K) for 1 h in a vacuum, followed by heating in N2 at 200 °C (473 K) for 2 h. The Al2O3 powder compacts (relative densities of 57.2-57.8%) with homogeneously dispersed (Ti,TiN0.3) particles were prepared. The mixed powder compacts were hot isostatically pressed (HIPed) under the conditions of 1350°C (1623 K) at 7 MPa N2 for 1 h, followed by the heating at the same temperature for 2 h under 196 MPa-N2. At the first stage of heating [1350°C (1623K)/7MPa/1h], solid/gas reaction of SHS between (Ti,TiN0.3) and N2 was introduced to form TiN and densification of the Al2O3 powder compacts up to the relative density of 92-93% with closed pores was performed. And at the sequent second stage [1350 °C (1623K)/196MPa/2h], densification of the most of pre-sintered composites consisting of Al2O3 and TiN reached higher relative densities than 98.5%. Dispersion of TiN particles (~φ 0.30 μm) in the composites suppressed the grain growth of Al2O3 during HIP-sintering. Mechanical properties, such as bending strength (σb), Vickers hardness (HV), fracture toughness (K1C), and electrical resistivity (ρ) of the composites were evaluated as a function of TiN content; the maximum values of σb=640 MPa, HV=19.5 GPa, and KIC=4.5 MPa・m1/2 were obtained in the Al2O3/TiN=97/3~95/5 vol% composites. Among the composites, the lowest ρ value of 2.6×103 Ω・m was attained at Al2O3/TiN=90/10 vol% composite.

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