Friction and wear properties of iron-copper based powder metallurgy materials under braking conditions

The friction properties and heat resistances of the iron-copper based powder metallurgy friction materials were tested by MM3000 friction and wear testing machine under 7 continuous braking conditions. The wear mechanism of the friction materials at two different rotate speeds (line speed in equivalent radius) was studied by scanning electron microscopy and energy disperse spectroscope analysis. The results show that when the line speed is 19.40 m·s⁻¹, the dynamic friction coefficient of the friction materials decreases slightly with the increase of surface pressure, which is 0.267~0.312 at 0.44 MPa and 0.258~0.308 at 0.80 MPa. Under the continuous braking condition as the line speed of 19.40 m·s⁻¹, the surface pressure of 0.44 MPa, and the braking energy in unit area of 268 J·cm⁻², the dynamic friction coefficient fluctuates greatly, while under the other conditions, the dynamic friction coefficient fluctuates little. With the increase of braking energy, the average dynamic friction coefficient under 7 kinds of continuous braking conditions changes between 0.300~0.334, and the dynamic friction coefficient is above 0.250, without the obvious decline phenomenon, indicating that the iron-copper based powder metallurgy friction materials have the good heat resistance. Under the line speed of 19.40 m·s⁻¹, the friction and wear mechanism of the iron-copper based friction materials is mainly abrasive wear and oxidation wear. Under the line speed of 30.00 m·s⁻¹, the friction and wear mechanism of the iron-copper based friction materials is mainly fatigue wear and oxidation wear.