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Graphene oxide coated silicon nitride coated powder was prepared by electrostatic self-assembly technique. Microstructure analysis shows that GO is uniformly coated on the surface of silicon nitride and evenly dispersed in the matrix material. The microstructure analysis and performance tests were carried out on ceramic tools with different volume contents of Si3N4@GO coated powder. The results show that when the content of Si3N4@GO is 7. 94 vol%, the comprehensive mechanical properties of Al2O3/WB2/(Si3N4@GO) ceramic tool materials are the best, with the Vickers hardness, flexural strength and fracture toughness 18.7GPa, 740 MPa and 8 .2MPa·m1/2, respectively. Compared with the Al2O3/WB2 ceramic tool material, the ceramic tool with Si3N4@GO coated powder increased the flexural strength and fracture toughness by 30.3% and 36.7%.

Aiming at the contradiction between tribological and mechanical properties of traditional self-lubricating ceramic composites, an advanced self-lubricating ceramic composite with the addition of pure-metal coated solid lubricant powders was developed in terms of microstructural modification of the traditional composites. Core-shell structured h-BN@Ni powders were synthesized by electroless plating technique with hydrazine hydrate as reducing agent. Al2O3/(W,Ti)C/h-BN@Ni composite made by adding h-BN@Ni powders exhibited notable improvements in microstructure and mechanical properties as compared with Al2O3/(W,Ti)C/h-BN composite made by adding uncoated h-BN powders. EDS and TEM analyses showed that the Ni shell particles in the Al2O3/(W,Ti)C/h-BN@Ni composite concentrated around the h-BN core grains and were located at grain boundaries or within the matrix grains. Due to their flaky structure, the h-BN grains had orientation distribution in the as-prepared ceramic composites, which resulted in anisotropies in mechanical properties and tribological behaviors. Dry sliding friction test revealed that the Al2O3/(W,Ti)C/h-BN@Ni composite had lower friction coefficient and higher wear resistance than the Al2O3/(W,Ti)C/h-BN composite. The different h-BN release modes caused tribological behaviors of the friction surface perpendicular to the hot pressing axis (HPA) to be better than those of the friction surface parallel to HPA.

The surfaces of solid lubricant hexagonal boron nitride (h-BN) powders were coated with compacted and integrated Al(OH)3 by heterogeneous nucleation and then the h-BN@Al2O3 composite powders were prepared by calcination under vacuum at 1200 °C for 2 h, as determined by SEM, EDS and XRD. The Si3N4 self-lubricating ceramic cutting tool material with coated h-BN was prepared by vacuum hot pressing. Microstructure analysis showed that the h-BN@Al2O3 particles were dispersed homogeneously in the matrix and that the particles were tightly bound. Vickers hardness was 14.1 GPa, fracture toughness was 7.2 MPa·m1/2, and flexural strength was 732 MPa, as determined by mechanical property testing. The hardness, fracture toughness, and flexural strength of the material were increased by 27.0%, 5.9% and 22.2%, respectively, relative to the material to which uncoated h-BN was added. Cutting tests showed that the Si3N4/TiC/(h-BN@Al2O3) self-lubricating ceramic cutting tool had better antifriction property and wear resistance than the corresponding cutting tool.

ZrB2/SiC/WC ceramic tool materials with a WC content of up to 10 vol% were prepared using spark plasma sintering technology. The mechanical properties at room temperature showed that the ZrB2/SiC/WC ceramic tool material with a WC content of 5 vol% had the best comprehensive mechanical properties, with a hardness, flexural strength, and fracture toughness of 19.1 GPa, 590 MPa, and 4.9 MPa·m1/2, respectively. With the increase in temperature, the hardness and fracture toughness of the ZrB2/SiC/WC ceramic tool materials gradually decreased; however, the flexural strength first increased and then decreased. When the temperature was 600 °C, the flexural strength reached a maximum value of 630 GPa, which was an increase of 6.8% when compared to that at room temperature. The increase in flexural strength was mainly due to the increase in the transgranular fracturing during the fracture process of the ZrB2/SiC/WC ceramic tool material. Dry machining tests of 40Cr hardened steel were performed using ZrB2/SiC/WC ceramic tools. As the cutting speed increased, the tool life gradually decreased, but the surface quality of the workpiece gradually increased. When the cutting speed was 300 m/min, the tool life of the ZrB2/SiC/WC ceramic tool was 15.8 min, and the surface roughness Ra of the workpiece after cutting was between 1.0 and 2.0 μm. According to the wear morphology, adhesive wear was the main form of the ZrB2/SiC/WC ceramic tools.

In order to promote the friction and wear properties of cermet materials, an advanced Ti(C,N) self-lubricating cermet materials with the addition of ceramic coated nano-sized solid lubricant powders (CaF2@Al2O3) was developed. The friction and wear properties of Ti(C,N) self-lubricating cermet materials were studied by spherical disk matching. Results showed that the optimal content of CaF2@Al2O3 powders was 10 vol%, and the addition of CaF2@Al2O3 powders significantly reduced the friction coefficient of cermet. Meanwhile, the multilayer core-shell microstructure can significantly improve the wear resistance of Ti(C,N) based cermet. The higher temperature on the friction contact area made CaF2 change from brittle state to plastic state, which was evenly coated on the friction surface to form the self-lubricating film. On the one hand, as the load increased, the friction coefficient of cermet with multilayer core-shell microstructure decreased, but the wear rate increased. On the other hand, as the friction speed increased, the friction coefficient first increased slightly, then decreased gradually, and then continues to increase after decreasing to the minimum value. Besides, the wear rate first decreased and then increased with the increase of speed. The formation of multilayer core-shell microstructure has good wear-resistance effects on Ti(C,N) cermet, and the decrease of friction coefficient is mainly due to the addition of CaF2.

In order to improve the mechanical property of self-lubricating ceramic cutting tool, (W,Ti)C based ceramic composites with the additions of nano-sized CaF2 solid lubricants were produced by vacuum hot pressing. Results showed that nano-sized CaF2 was mainly located in matrix grains and formed the intragranular self-lubricating nanostructure. The optimal mechanical properties were achieved at 1650 °C and 15 min. The flexural strength, hardness and fracture toughness reaches the maximum of 497 MPa, 16.3GPa and 6.48 MPa·m1/2, respectively. Compared with the ceramic composite without CaF2, the fracture toughness was increased by 13.0%. Dry machining tests of hardened 40Cr steel were performed with these ceramic cutting tools. It indicated that with the additions of nano-sized CaF2 as solid lubricant, the main cutting force and cutting temperature were reduced by 13.2% and 26.9%, the average friction coefficient of rake face was reduced from 0.59 to 0.32. SEM micrograph showed that a self-tribofilm was consistently formed on the rake wear area which has a good self-lubricating effect.

Nano-coated particles and whiskers were used as reinforcing additives for ceramic tool materials to take advantage of synergistic toughening and enhancement mechanisms. An Al2O3/TiC/CaF2@SiO2/SiCw ceramic tool material was fabricated by hot-pressing. Self-lubricating ceramic tool materials toughened by nano CaF2@SiO2 coated particles and SiC whiskers were studied. When the addition content of nano CaF2@SiO2 coated particles was 10 vol% and the content of SiC whiskers was 20 vol%, ceramic tool materials with the best comprehensive properties were obtained. The results showed that the hardness of the ceramic tool material was 16.52 GPa, the flexural strength was 698 MPa, and the fracture toughness was 6.89 MPa m1/2. Compared with the ceramic tool material with 10 vol% nano CaF2 particles and 20 vol% SiC whiskers, the above properties were improved by 7.06%, 31.74% and 19.06%, respectively. The SiC whiskers played a toughening role, while nano CaF2@SiO2 coated particles reduced the porosity, the compactness and also filled between the grain boundaries of the ceramic tool materials during sintering. This improved the interfacial bonding between ceramic grains, which increased the incidence of transgranular fracture in the ceramic tool materials.

A new type of self-lubricating ceramic cutting tool material with the addition of metal coated solid lubricant powders was developed. Nickel coated CaF 2 composite powders with core–shell structure were produced by electroless plating technique. The growth process of nickel coating on the solid lubricant CaF 2 powders was analyzed. The as-prepared self-lubricating ceramic cutting tool material made by adding nickel coated CaF 2 powders exhibited notable improvements in microstructure and mechanical properties, in comparison with the corresponding cutting tool material made by directly adding uncoated CaF 2 powders. Cutting tests show that the new type of self-lubricating ceramic cutting tool has better antifriction property and wear resistance than the corresponding cutting tool.

Since the existed compositional distribution functions are not applicable to the design of functionally graded materials consisting of more than two main components, a multi-component gradient distribution model was proposed during the design process. An advanced Al2O3/(W,Ti)C/CaF2 multi-component graded self-lubricating ceramic cutting tool material was subsequently developed. The flexural strength, hardness, and fracture toughness of the as-developed material were increased by about 25%, 19%, and 6%, respectively, as compared with the corresponding homogeneous material. The cutting tests show that the Al2O3/(W,Ti)C/CaF2 multi-component graded self-lubricating ceramic cutting tool has better wear resistance than the homogeneous cutting tool.