| Copper-based powder metallurgy materials are widely used in high-speed train brake linings because of their excellent braking performance.As the speed of high-speed trains continues to increase,higher demands are placed on the anti-consumption properties of materials,the effectiveness and reliability of braking,and improvement of performance has become one of the most important issues in the field of friction material research.For copper-based friction materials composed of multiple components,the advantages of each component are the key to improving the material properties.Therefore,it is necessary to clarify the role of each component.However,the interaction between the components and the formation of the third body is not conducive to the identification of the impact of specific components on friction performance.In this paper,the basic evolution and failure modes of graphite,silicon dioxide and chromium in the formation of the third body are studied for the two-component and multi-component copper-based friction materials.It explores the relationship between interactions between multiple components and the third body.The relationship between the shape of the third body and the friction coefficient under different friction conditions is clarified;the relationship between the state of the third body and the friction coefficient is explored by using the external chrome powder as the third body to disturb the friction interface.1.For the copper-graphite specimen,the graphite particles on the surface of the specimen were broken up after the low-speed friction was thrown into the external third-body chromium,and the third film of the graphite was difficult to form,which reduced the stability of the friction coefficient of the material.At high speed,the external third body chromium is strongly combined with the matrix and is not easily peeled off.At the same time,the elongated third external body chromium acts as a pinning graphite and improves the stability of the friction coefficient.2.For the copper-silica material,the external third body chromium powder scattered at the low speed is used as a friction increasing point to be pinned on the surface of the material to increase the friction coefficient.Under high-speed friction conditions,the surface of the silica is easily broken,and the highly mobile third-body chromium plays a role in reducing and stabilizing the friction coefficient.3.For multi-component copper-based friction materials,the chromium in the friction material has pinning and hindrance to abrasive debris,while chromium is elongated in the friction along the rubbing direction.the ability of the matrix to hold the chromium particles is reduced,resulting in detachment of the chromium particles.When exogenous third body chromium is thrown in,at a low speed of 300 rpm,exogenous chromium powder is pinned on the surface of the sample as an increase in friction component,resulting in an increase in the surface roughness and an increase in the friction coefficient;At 500 rpm,the friction coefficient was reduced after the chromium powder was sprayed.The reason was that the chromium particles that were extruded and sheared into sheets enhanced the adhesion of the graphite,making the lubrication effect of the graphite enhanced.At 500 rpm,the friction coefficient was reduced after the chromium powder was sprayed.The reason was that the chromium particles that were extruded and sheared into sheets enhanced the adhesion of the graphite,making the lubrication effect of the graphite enhanced.At high-speed 1500 rpm,chromium content in the friction layer was increased after the chromium powder was thrown in,and the adhesion was enhanced,resulting in an increase in the friction coefficient.4.In multi-component copper-based friction materials,the friction condition is 0.51 MPa,the friction speed is 200 rpm,and the friction coefficient is about 0.369.The diameter of the chromium particles showed a linear increase,which was specifically increased from 71 ?m at the initial 0 s to 120 Lm at the time of 100 s,resulting in a 0.2 ?m/s elongation of the first 100 s chromium particle diameter.Under the same friction conditions,when the friction coefficient is around 0.3725,The percentage of the area covered by graphite and its debris on the sample surface increased linearly from the 64%to 96%in the first 90s,thus,the percentage increase rate of graphite and its debris on the surface of the sample under this condition was increased by 0.356%. |
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