cBN→hBN Phase Transformation During Sintering of cBN and Al Powders at High Pressures and Temperatures

Consolidation of cubic and hexagonal boron nitride composites

“…Phase transformation of the metastable cBN phase to the stable hBN phase reduced sample densities in our preliminary runs (method 1), similar to previous workers [16]. Impurities and cBN surface area are two factors that are demonstrated to increase cBN to hBN phase transformation [30].…”

“…All grinding processes will result in some degree of contamination in the finished product, so the choice and overall purity of grinding media are an important consideration for applications that are sensitive to even ppm or ppb levels [12][13][14][15]. Also phase transformation of cBN to hBN is a potential challenge when consolidating cBN outside of its stability field [16]. The current methods for consolidating cBN have limitations in size, shape, and potential for contamination.…”

Cubic boron nitride-containing ceramic matrix composites for cutting tools

“…However, later experiments suggested that the P-T phase boundary could be shifted to lower pressures, where cBN is a thermodynamically stable phase under ambient conditions depending on the purity of the binders, the initial structure of the material and sintering parameters (time, temperature, pressure, etc.). 20,22,23 Shulzhenko et al observed that cBN dispersion affects the cBN-hBN phase transformation in cBN-Al composites. 20 With better dispersion of the cBN powder, the peaks in the cBN-hBN transformation curve shift to lower temperatures, while the addition of aluminum cause it to shift to higher temperatures.…”

“…20,22,23 Shulzhenko et al observed that cBN dispersion affects the cBN-hBN phase transformation in cBN-Al composites. 20 With better dispersion of the cBN powder, the peaks in the cBN-hBN transformation curve shift to lower temperatures, while the addition of aluminum cause it to shift to higher temperatures. Petrusha et al found that the cBN-hBN transformation mechanism depends on the initial structure of the cBN.…”

“…[13][14][15][16][17][18] Due to this viewpoint in earlier studies, dense products of cBN and cBN-containing composites (CBCCs) were usually fabricated through a highpressure and high-temperature (HPHT) sintering process using either hBN or cBN powder with binders such as aluminum, titanium, niobium, TiN or Al 2 O 3 . [19][20][21] The pressures adopted were usually 5 GPa or even higher, which elevated the production costs for CBCCs. However, later experiments suggested that the P-T phase boundary could be shifted to lower pressures, where cBN is a thermodynamically stable phase under ambient conditions depending on the purity of the binders, the initial structure of the material and sintering parameters (time, temperature, pressure, etc.).…”