Binderless Layered BN Toughened cBN for Ultra-precision Cutting

doi:10.15541/jim20210300

Abstract

Abstract:

Poor toughness and high synthesis pressure of binderless cBN limits its application in the field of cutting tool. To enhance its toughness, an advanced layered BN toughened cBN (Lt-cBN) bulk was developed under industrial pressure. Then, the cutting performance and wear resistance of Lt-cBN was analyzed based on the unique microstructure during tungsten carbide cutting. It is found that the Lt-cBN reaches a high fracture toughness of 8.5 MPa·m^1/2, and is capable of realizing ultra-precision cutting of tungsten carbide with smooth surface of roughness lower than R_a 10 nm. The layered BN at the intersection of cBN grains within Lt-cBN contributes to the enhanced toughness, which further slows down the transformation of amorphization as well as the wear rate of the surface layer. Thus Lt-cBN exhibits better cutting performance and wear resistance in contrast to commercial binderless pure cBN material. The wear of Lt-cBN can be explained by the soft partially amorphous layer formed on the flank surface being rubbed and continuously removed in the form of abrasive wear.

Key words: binderless cBN, layered BN, ultra-precision cutting, wear resistance, tungsten carbide

CLC Number:

TH145

CHEN Junyun, SUN Lei, JIN Tianye, LUO Kun, ZHAO Zhisheng, TIAN Yongjun. Binderless Layered BN Toughened cBN for Ultra-precision Cutting[J]. Journal of Inorganic Materials, 2022, 37(6): 623-628.

Figures/Tables 9

Fig. 1 Images of Lt-cBN microstructure with insert showing its bulk (a) and layered BN at the intersection of grains (b)

Fig. 2 Cutting experimental device

Table 1 Surface roughness of tungsten carbide and cutting force

Rake angle/(°)	Tool	Surface roughness, R_a/nm	Rake angle/(°)	Cutting force/N
0	Lt-cBN	13.3	0	0.296
0	NCB100	33.4	0	1.528
-15	Lt-cBN	25.2	-15	2.990
-15	NCB100	41.1	-15	6.018
-30	Lt-cBN	49.6	-30	—
-30	NCB100	52.0	-30	—

Fig. 3 Machined surface morphology (a), chips produced during cutting (b) and mirror-like surface of workpiece (c)

Fig. 4 The maximum width VBmax of the flank wear area

Fig. 5 Morphologies of wear zone on the tool flank

Fig. 6 HRTEM image and the corresponding fast Fourier transform behind the wear zone of Lt-cBN tool

Fig. 7 HRTEM image and the corresponding fast Fourier transform behind the wear zone of NCB100 tool

Fig. 8 Initial microstructure of NCB100 material

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