Evaluation of CVD‐Deposited SiO₂ as a Sintering Aid for Cubic Boron Nitride Consolidated with Alumina by Spark Plasma Sintering

Abstract

A SiO2 nanolayer, 1.0–2.8 mass% in content, was coated on cubic boron nitride (cBN) powder by rotary chemical vapor deposition (RCVD). The morphology of the SiO2 nanolayer changed from isolated islands to a continuous layer with increasing supply rate of the precursor, tetraethyl orthosilicate. The effect of the SiO2 coating on the sinterability and mechanical properties of cBN for machine‐tool applications was evaluated. The SiO2‐coated cBN (cBN/SiO2) powder was mixed with Al2O3 and consolidated by spark plasma sintering (SPS) at 1473–1873 K. The phase transformation temperature of cBN to hexagonal BN (hBN) in Al2O3–cBN/SiO2 was 1773 K, 100 K higher than that in Al2O3–cBN composites. The highest density of the Al2O3–cBN/SiO2 composites was 99.5% at 30 vol% cBN/SiO2 content, at which the microhardness and fracture toughness were 28 GPa and 4.1 MPa·m1/2, respectively. This indicates that RCVD‐deposited SiO2 is a promising sintering aid for cBN and Al2O3–cBN/SiO2 sintered bodies produced by SPS may be applicable as cutting tools.

Radioluminescence and thermally-stimulated luminescence of SiO₂ glasses prepared by spark plasma sintering

“…Bulk SiO 2 glass samples were prepared by a spark plasma sintering technique based on the work reported by Zhang et al 2) 0.5 g of SiO 2 glass nano-powder (purity 99.9%; SO-E1, Admatechs Co. Ltd.) was loaded in a graphite die with an inner diameter of 10 mm, and the raw powder was kept inside and sealed with two graphite punches. This graphite assembly was then covered by a carbon fabric and loaded into the sintering furnace (La-BOX, NJS).…”

Cubic boron nitride-containing ceramic matrix composites for cutting tools

“…19 50 The hardness increased to 28 GPa. For C cBN > 40 vol%, cBN-containing composites need an ultra-high pressure of over 5 GPa and a high sintering temperature of over 1673 K. The reported H v of TiN-TiB 2 -75 vol% cBN prepared at 5.5 GPa and 1720 K is 57 GPa, and that of pure cBN prepared at 7.7 GPa and 2473-2673 K is 55 GPa.…”

“…Researchers have started coating TiN, TiN-TiB 2 , nickel and SiO 2 onto a cBN powder surface. 43,46,50,58,59 Intensive further work is needed to reveal the benefi cial effects of the coatings on the sintering behavior and mechanical properties of CBCCs.…”

Thermal Stability of TiN Coated Cubic Boron Nitride Powder

“…The influence of Ni [25,26] and SiO 2 [27] coatings on the transformation behavior of cBN particles was investigated to avoid the hBN transformation during the SPS-process. At a sintering temperature of 1400 • C no hBN formation could be detected.…”