Obtaining and properties of rolled products from clad powders NPG-80 and Nibon-20

Abstract

Antifriction tape sealing materials (TSM) are used in the manufacture of turbines. This work studied the mechanism of the increase in thickness of rolled products. The study showed that internal oxides of powder particles, which are reduced during sintering and annealing in hydrogen, cause a change in the size of tapes and compacts from NPG-80 and Nibon-20 clad powders. The distinctive feature of powders used in the work is the presence of a nickel shell around the particle of the solid lubricant (graphite or boron nitride). It was shown that an increase in sintering temperature and heating time to isothermal holding intensifies the growth of the tapes and samples The studies carried out point to a relationship between reduction processes occurring in hydrogen during heating, sintering, and annealing of NPG-80 and Nibon-20 powders with an increase in the thickness of the tape containing the solid lubricant in its composition. An increase in the duration of heating to isothermal holding at 1150 °C is accompanied by an increase in the thickness of rolled stock. Sintering of TSM Nibon-20 in the first mode (4 h to 1150 °C) gives an increase in thickness by 5-7 %, whereas sintering in the second mode (9 h to 1150 °C) gives an increase of 12-13 %. For NPG-80, the increase in thickness is 3-7 % and 8-11 %, respectively. This leads to some decrease in the physical and mechanical properties of TSM. Lower temperatures and higher heating rates are recommended for the sintering of sheet materials from NPG-80 and Nibon-20 in the hydrogen atmosphere. The increase in thickness of TSM from clad powders NPG-80 and Nibon-20 can be avoided if the sintering (heating) is carried out under pressure. By the method of electric rolling and subsequent hot rolling TSM is obtained from Nibon-20.