Tribology of Si_3N_4 with different glassy phase content sliding against grey cast iron lubricated with water

摘要

It is known that Si_3N_4 shows excellent tribological properties in water. This is attributed to the hydrolysis of Si_3N_4 itself. The glassy phase content in Si_3N_4 is considered to be an important factor affecting the hydrolysis of Si_3N_4 during friction. In the present paper the effect of glassy phase content in silicon nitride against grey iron in water on its tribological characteristics was investigated. Distilled water and a dilute aqueous solution of sodium silicate were used as lubricants. The experiments were carried out on a type MM-200 wear tester. The total wear displacements of two samples were also monitored on-line to obtain total wear data. When distilled water is used as lubricant, the Si_3N_4/grey iron sliding pairs with 5 wt.precent oxide additives into Si_3N_4, their friction coefficients decrease to 0.02 and the wear losses of the pairs also are the smallest of all test pairs after 10 km of sliding. With increasing 10 wt.precent additives into Si_3N_4 the friction coefficient of the sliding pairs falls down during the test, but their values do not reach 0.02. The wear of the sliding pairs after 10 km of sliding is also quite small, compared to other test pairs with 15, 20 and 30 wt.precent. When dilute aqueous sodium silicate solution is used as lubricant, the friction coefficient values for all test pairs decrease to 0.02 before 4 km of sliding. Their wears after 10 km are also much lower than with lubrication by distilled water. The wear differences among all test pairs are not significant, which indicates that the possibility of tribochemical reaction is identical for all samples with different oxide additive content in this case. On the other hand, sodium silicate, as an excellent corrosion-inhibitive agent for iron can efficiently delay the iron rust during lubrication and extends the commercial application of water as a lubricant.