Study Of Copper-matrix Friction Materials By Powder Metallurgy And Its High Temperature Fatique Wear Properties And Dynamic Behaviors

This thesis focuses on the study of copper-based friction materials by powder metallurgy and their high temperature fatique wear properties and dynamic behaviors.(1) Three formulas for copper-based friction materials are proposed based on the previous work by others. The wt % of copper in the three formulas are 68~75,69-76,and 65-68, respectively. The test samples were made via compressive sintering. The mechanical and heat conductive parameters were measured, which showed that the heat conduction of the third material was slightly higher. The frictional wear tests for the three materials were conducted on MM-1000 test machine with 30CrSiMoVA steel as the couple material, referring to the JB3063-82 standard. The test samples were circular rings with inner and outer diameters of 53mm and 75mm, respectively. The working condition for measuring the variation of the coefficient of friction with the rotation speed was as follows: rotation speeds ~ 1000, 2000, 3000, 4000 and 5000r/min, respectively, pressure ~ 0.98MPa, and rotational inertia momentum ~ 0.196N.m.s. The pressure was adjusted to the desired value, and braking was performed three times at each rotation speed. Upon completion of a test, the sample and its couple were both cooled down to room temperature, and the changes in the height were measured on spots. The working condition for measuring the variation of the coefficient of friction with the pressure was as follows: rotation speed ~ 3000r/min, rotational inertia momentum ~ 0.196N.m.s., and the braking pressure ~ 0.5, 0.8, 1.1, 1.4, and 1.7 MPa, respectively. Through these tests, the third material was found to be superior in both stability and frictional wear property.(2) The high temperature fatigue wear behavior of this material was investigated. The relation between the wear and temperature was fitted approximately, and the failure of the material was analyzed. The experiments were conducted on the TE77 high temperature fatigue wear test machine with wheel steel as the couple material. It was shown from the experiments that, the coefficient of friction was relatively low at room temperature and gradually decreased with increasing temperature in the range from 100 C to 350 C, with cohesion taking place at 500 C. From this, the critical temperature for the fatigue wear of the material was determined to be 350 C. The fatigue wear at room temperature and 300C was most insignificant, and the microscopic analysis showed that at 300C a solid lubricant layer formed at the material surface and there was phase transition relating to the surface structure. At 500 C, the coefficient of friction increased, the microcracks extended beneath the sliding surfaces and gradually coalescence, leading to the spallation of the tribological surfaces and the increase in the wear fraction. The X-ray analysis for the 300 C sample showed that the components of the surface oxide changed after fatigue friction, from FeO to FeN dominant, and solid lubricant layer of BN and PbO etc. formedwhich reduced the wear. One source for the origin of the furrow and microcracks was due to the hard particles of SiO2 that spall and took part in the friction during the process of the fatigue wear.(3) The dynamic behavior of this material under shock loading was investigated, and a dynamic constitutive model was proposed. Quasi-static tests at strain rates of 10-4 /s~10-3 /s were performed before the dynamic tests in order to make a comparison and also acquire parameters for numerical simulations. The elastic moduli and elastic and plastic Poisson's ratios were measured. The static curves showed the strain-hardening effect. The static compression failure was due to shear failure, and dislocation erosion hold were seen on the surface of the test cylinder. Shock tests were conducted on Hopkinson pressure bar at strain rates of 250,560,780,1000 and 1600/s, respectively. Strain rate hardening effect was observed at rates under 1000/s, whereas weakening effect was seen at higher rates, which means that 1000/s is the critical shock strain...