Preparation And Friction And Wear Properties Studies Of Carbon Fiber Needled Felt Reinforced Alumina Composites

With the heavy load,high speed tansport technology continuing to develop,the standards of braking materials become higher than before.As a promising frction and wear material,the alumina ceramics must further improve its toughness.In this paper,based on the research ideas of C/C,C/SiC composites and existing research,carbon fiber needled felt reinforced alumina matrix composites was fabricated through“sol infiltration-drying-heat treatment”?SIH?route which used Al₂O₃ sol with high solid content as raw materials.At first,the paper optimized the process preliminarily,and the effects of heat retreatment temperature and SiC coatings acting on the mechanical properties,thermal physical properties,oxidation resistance and thermal shock resistance of C/Al₂O₃ composites were investigated.Then the friction and wear characteristics of C/Al₂O₃ composites were studied.The feasibility of its application as a vehicle brake and an aircraft brake disc was initially explored.The effect of heat treatment temperature between 1100??1600? on mechanical and thermal physical properties was investigated.With the increase of heat treatment temperature,the apparent density and flexural modulus increased,but the bending strength and fracture work changed in wavy manner,and it was highest at 1100??155.9MPa and 6772J/m²? and lowest at 1200??97.4MPa and 1749J/m²?.The fracture work was significantly higher than the monolithic alumina ceramics?fracture work 300J/m²?.With the heat treatment temperature increasing,the thermal conductivity and the coefficient of the thermal expansion improved.Compared with the 1100? heat-treated composites as comparison,the mechanical properties of C/Al₂O₃ composites which were called as C/SiCc/Al₂O₃ composites because the SiC coatings were prepared on the suface of the carbon fiber improved.The tensile strength of C/SiCc/Al₂O₃ composites increased from 63.4MPa to 90.2MPa,the flexural strength increased from 155.9MPa to 168.1MPa,but the fracture work decreased to the 4828J/m².The interlaminar shear strength was improved from10.9MPa to 21.2MPa,and the longitudinal compressive strength?load direction is parallel to the carbon fiber layup direction?augmented from 171.7MPa to 371.3MPa,the horizontal strength?load direction is vertical to the carbon fiber layup direction?increased from 274.2MPa to 468.8MPa.Refering to the service temperature range of the brake materials,the oxidation resistance and thermal shock resistance were investigated in this range.In the static air,the strength of C/Al₂O₃ composites at 600? began to show a significant decline,and the strength retention rate was 57.7% at 1000?.In the thermal shock test at static air,strength retention rate was only 66.6% at 400?.When the temperature reached to1000?,the strength retention rate was 28.3%.SiC coatings gave a high promotion on the high temperature oxidation resistance and thermal shock resistance of the composites.After oxidation at 1000?,the strength retention was still 100%.Through the thermal shock test at 1000?,the strength retention was 83.1%,and was much higher than the composites without coatings.The effects of different friction conditions on the friction and wear properties of C/Al₂O₃ composites were investigated by SRV friction tester.From the lubrication point of view,the coefficient of dry friction was highest.In most friction conditions,the mineral oil and deionized water could reduce the wear volume,but it also led to a decrease in the coefficient of friction?COF?.The deionized water lost the lubrication effect when the friction condition was 150N,10Hz.With the increase of the friction load and sliding frequency?velocity?,the COF and wear volume both increased,and the load had a mutation point.When the value of load reached the mutation point,the corresponding wear volume would be about 4?30 times larger than the wear volume of the load which was less than mutation point.When the temperature of the friction surface was between 100? and 250?,there was a subtantial increase in the friction coefficient and wear volume at 150?.With reference to this standard,the feasibility of using C/Al₂O₃ composites as vehicle brakes has been analysed.Although the composites which were carried out between the 1200? and 1600? had good wear resistance,but the COF was too low to meet the standard.The friction and wear performance of the 1100? heat-treated composites was the best.According to the standard,the 1100? heat-treated composites were suitable for automotive brakes and miniature or light drum brakes of the transport vehicle.The friction and wear properties of C/Al₂O₃ composites were further improved by adding SiC coatings.According to the standard,it met all four types of brake standards.A brake test was carried out using the MM-3000 friction and wear tester.The friction and wear characteristics of C/Al₂O₃ composites against self-grinding and cast iron grinding were tested respectively.The main impact of different friction pairs was on the wear rate and friction surface temperature,and the remaining performances were little influenced.In almost same braking conditions,the COF of C/Al₂O₃ composites was slightly lower than the C/C composites,and the braking time was a little longer,but the wear resistance was much higher.According to the reaserch about the effect of SiC coatings on the friction and wear characteristics in this paper,preparation of the SiC coatings on the surface of carbon fiber could probably improve the material friction coefficient and reduce the braking time,thereby enhance the braking performance.