| With the development of high-speed and high-energy vehicles for modern transportation tools and power machinery,such as high-speed trains,automobiles,and wind turbines,the higher requirements for high temperature performance of brake friction materials have been put forward to avoid the fatal defects of brake friction materials,which are poor stability of friction coefficient at high temperatures and high wear at high temperatures and short service life.On the other hand,since the severe energy crisis and environmental protection issues are serious,energy conservation and consumption reduction have become the inevitable trend of the development of friction materials.For the purpose of developing green environmental protection and high temperature resistant and high performance friction materials,this thesis reaearches the application of inorganic metakaolin as "non-fired ceramic" geopolymer(GP)raw materials,water glass(Na2Si O3)and Na OH as alkali activators,cement,Graphite powder is a performance regulator and adopts three-dimensional needled carbon fiber felt(3D-CFF)to toughen geopolymers to make green,high-performance 3D-CFF/GP composite friction materials and investigates their friction properties.The main research contents are as follows:Firstly,metakaolin is adopted as a geopolymer raw material,water glass(Na2Si O3)and Na OH are alkali activators,cement and graphite powder are performance modifiers to prepare geopolymers,and universal testing machines,friction testing machines,SEM and XRD are applied.The testing methods are used to test and analyze the properties,and the effects of modulus,liquid-solid ratio,different curing temperature,and different fillers on the compactness,durability,mechanical properties,and friction properties of geopolymers are investigated to obtain high performance 3D-CFF/GP Composite Friction Material Base Material Geopolymer Optimized Formula and Preparation Process.Secondly,the 3D-CFF/GP composite friction material is prepared by dipping the geopolymer slurry into 3D-CFF and curing.Finally,the mechanics,high temperature resistance and friction and wear properties of3D-CFF/GP composite friction materials are investigated by using universal testing machines,friction testing machines,SEM,TG,and XRD testing instruments.The experimental results indicate:(1)The compressive strength of geopolymers rises first and then decreases with the change of water glass modulus.When the water glass modulus is 1.3,the compressive strength is the highest,the porosity is minimum 29.29%,and the density is 1.43 g/cm3;When the water glass modulus is greater than 1.3,the strength is also significantly reduced.When the curing temperature is 60°C,the porosity of the GP is the smallest,and the density and compressive strength are the highest,which are 28.69% and 1.57 g/cm3 respectively.(2)Cement can promote the hardening of geopolymers and shorten the setting time.When the cement content is from 0 to 10%,the initial setting time of the geopolymer is shortened to about 0.7 h.The compressive properties of geopolymer samples increase first and then decrease with the increase of cement content.When the cement content is 5%,the compressive performance is best.(3)The strength of the composite friction material is prepared by 3D-CFF and GP is significantly higher than that of pure GP,and the bending strength increased from 18.89 MPa for GP to 57.18 MPa for composite friction material,which is increased by 3 times.The surface morphology of 3D-CFF/GP composite friction material after 800 cycles of thermal cycling at 800°C for more than 350 times do not change substantially.There is no crack,and its bending strength and compressive strength do not drop much,which has well temperature resistance.(4)The addition of graphite powder reduces the compressive strength,flexural strength and friction coefficient of composite friction materials.Without graphite powder,the average coefficient of friction is 0.55.When the content of graphite is 9%,the friction coefficient is stable at about 0.42,and the friction coefficient of the front piece of ceramic just satisfying the FF standard is 0.42±0.05.When the graphite content was 0%~12%,the wear rate decreases from 12.9×10-7cm3/(N·m)to 1.85×10-7cm3/(N·m). |
PDF Full Text Request