An Al 2 O 3 /TiC ceramic cutting tool with the additions of CaF 2 solid lubricant was produced by hot pressing. The fundamental properties of this ceramic cutting tool were examined. Dry machining tests were carried out on hardened steel and cast iron. The tool wear, the cutting forces, and the friction coefficient between the tool–chip interface were measured. It was shown that the friction coefficient at the tool–chip interface in dry cutting of hardened steel and cast iron with Al 2 O 3 /TiC/CaF 2 ceramic tool was reduced compared with that of Al 2 O 3 /TiC tool without CaF 2 solid lubricant. The mechanisms responsible were determined to be the formation of a self-lubricating film on the tool–chip interface, and the composition of this self-lubricating film was found to be mainly CaF 2 solid lubricant, which was released and smeared on the wear track of the tool rake face, and acted as lubricating additive between the tool–chip sliding couple during machining processes. The appearance of this self-lubricating film contributed to the decrease of the friction coefficient. Cutting speed was found to have a profound effect on this self-lubricating behavior.

Self-lubrication of sintered ceramic tools with CaF2 additions in dry cutting

Al2O3/TiC ceramic composites with the additions of CaF2 solid lubricants were produced by hot pressing. The effect of the solid lubricant on the microstructure and mechanical properties of the ceramic composite has been studied. The friction coefficient and wear rates were measured using the ring-block method, and the tribological behaviors were discussed in relation to its mechanical properties and microstructure. Results showed that additions of CaF2 solid lubricants to Al2O3/TiC matrix led to a decrease in the flexural strength, fracture toughness, and hardness compared to a conventional Al2O3/TiC composite. The friction coefficient of Al2O3/TiC/CaF2 ceramic composites when sliding against both cemented carbide and hardened steel decreased with an increase in CaF2 content up to 15 vol.%. The reason is that the CaF2 released and smeared on the wear surface, and acted as solid lubricant film between the sliding couple. When the content of CaF2 solid lubricant is less than 10 vol.%, the wear rate of Al2O3/TiC/CaF2 composites decreases with an increase in CaF2 content, with further increases in CaF2 content, the wear rate of Al2O3/TiC/CaF2 composites increases rapidly. This is due to the large degradation of mechanical properties in samples with high CaF2 contents.

Tribological behaviors of hot-pressed Al2O3/TiC ceramic composites with the additions of CaF2 solid lubricants

Microstructure and mechanical properties of hot-pressed Al2O3/TiC ceramic composites with the additions of solid lubricants

Sliding wear tests against 45# hardened steel were performed on Al2O3/TiC ceramic composites with the additions of CaF2 solid lubricants. The friction coefficient and wear rates were measured. The wear surface features were examined by scanning electron microscopy. Results showed that the friction coefficient and the wear rate decreased with the increase of CaF2 content up to 10 vol%, with further increases in CaF2 content, the wear rate increased rapidly. The mechanisms responsible were determined to be an in-situ formed self tribofilm between the ring-block sliding couple. SEM observations showed that two types of tribofilms are formed on the wear surface depending on the CaF2 content. A dense self tribofilm with a smooth surface associated with small friction coefficient and low wear rate was formed by the releasing and smearing of CaF2 solid lubricants on the wear surface when with 10 vol% CaF2 content. This dense self tribofilm acted as solid lubricant film between the sliding couple, and thus significantly reduced the friction coefficient and the wear rate. Breakdown of the tribofilm on the surface associated with a large wear rate was observed on samples with 15 vol% CaF2 content. This is due to the large degradation of mechanical properties of the composite with higher CaF2 contents.

Self-lubricating mechanisms via the in situ formed tribofilm of sintered ceramics with CaF2 additions when sliding against hardened steel

Tribological behavior and lubrication mechanism of self-lubricating ceramic/metal composites: The effect of matrix type on the friction and wear properties

T Jenkins

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