The structure of the MLC and fabrication sequence of layered structure are disclosed. The base layer is preferably nanoD and is the first deposited layer serving as an accommodation layer on a pretreated substrate. It can be designed with a larger thickness whereas subsequent alternate nano-cBN and nanoD layers are typically prepared with a thickness of 2 to 100 nm. The thickness of these layers can be engineered for a specific use. The deposition of the nanoD layer, by either cold or thermal plasma CVD, is preceded by diamond nucleation on a pretreated and/or precoated substrate, which has the capacity to accommodate the MLC and provides excellent adhesion. Nano-cBN layers are directly grown on nanodiamond crystallites using ion-assisted physical vapor deposition (PVD)
|structure||sphalerite structure||hexagonal structure||Rrhombohedral structure||wurtzite structure|
|Lattice constant(Å)||a=3.615 d=1.565||a=2.5043 c=6.6661||a=2.2507 c=9.999||a=2.5505 c=4.213|
|bonding mode||sp3 hybridized||sp2 hybridized||sp2 hybridized||sp3 hybridized|
|FTIR(cm-1)||783, 82,1367,1616||1065, 1380||1340||1090, 1120, 1230|
|Raman(cm-1)||52,1366||790,1367||1056,1304||950, 1015, 1050,1290|
|Total||4 structure of boron nitride|
This paper studies the performance of these tools in superfinish hard machining. Specimens were machined by a solid PCBN tool and CBN particle coated tools with two different CBN particle size distributions: less than 0.5 and 2 μm. The specimen machined by a tool with small CBN particle coating showed more compressive residual stresses and less thermal damage below the machined surface than other specimens. Furthermore, the specimen machined by a tool with small CBN particle showed less residual stress scatter than other specimens.
The rolling contact fatigue life was predicted by using a rolling contact fatigue life model. The rolling contact fatigue life predictions indicate that the predicted life of the specimen machined by a tool with small CBN particle coating is longer than that of other specimens. The results thus indicate that a tool with small CBN particle coating provides better performance than other tools in superfinish hard machining.