The Sintering of Polycrystalline Cubic Boron Nitride:The Function of Al-Si Alloy
Date Issued
2008
Date
2008
Author(s)
Chu, Hung-Yu
Abstract
Cubic boron nitride (cBN) is a high pressure synthetic material, having extreme hardness just next to diamond. Among superhard materials, cBN is the most stable when it applies at high temperature (>1000℃). Prior studies show that Silicon (Si) reacts hardly with cBN at temperatures as high as 1500℃, which imposes difficulty for the formation of superhard material, C-Si3N4. In this research, we use Aluminum (Al) as a major reagent to react with cBN and Silicon (Si) as an inhibitor for AlN formation to modulate free Nitrogen (N). The newly generated free N, which can not react timely with Al to form AlN, may react with Si to form Si3N4. There are two major parts in this research. Part I includes the sintering experiments at high temperature (1350℃) in vacuum, and part II is sintering under ultra-high pressure and high temperature (HTHP) (1350℃, 5.5 GPa). The results from low pressure experiments show that Si reacts successfully with BN to form Si3N4, although the density and mechanical property of the sintering body have not reach the requirement. This result infers that we can also successfully sinter Si3N4 –bearing body with better mechanical property at HTHP. In part II with HTHP experiment, we successfully synthesized superhard PcBN (Hv 5400) from Si-Al and cBN. We also repeated this experiment with nano cBN particle. The result indicates that mechanical property of PcBN sintering body using nano particles is no better than micro particles. Experiments by adding two materials B4C and AlN in Si-Al and cBN show the increase of amorphous materials in the sintering body which resulted in the observed deterioration of entire mechanical property of PcBN .
Subjects
PcBN
HTHP
Type
thesis
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