The Research Of C_f/Ni₃Si And C_f/Al₂O₃-Ni₃Si Composites High Temperature Oxidation Resistance

Ni₃Si intermetallic compounds is considered to be one kind of new structural material with great potential development,because of its good high temperature mechanics performance,excellent oxidation resistance,corrosion resistance and abnormal temperature/strength effect?R characteristic?.However its application is limited greatly as a result of its poor brittleness at room temperature.Therefore,in this paper,different surface-modified short carbon fibers were introduced to improve its brittleness at room temperature.And it is necessary for us to understand the high temperature oxidation behavior and mechanisms in the air medium of short carbon fiber-reinforced C_f/Ni₃ Si and C_f/Al₂O₃-Ni₃ Si matrix composites.The analysis is guiding significance to increase the practical application for carbon fiber-reinforced Ni₃ Si matrix compound in the field of high temperature structure.The short carbon fiber-reinforced C_f/Ni₃ Si matrix composite was prepared by hot-pressing sintering,while the C_f/Al₂O₃-Ni₃ Si matrix composite was prepared by sol-gel and SPS sintering method.And on this basis the high temperature oxidation behavior and mechanisms of these two materials were explored in the air medium.The phases and figures of the oxidation products are characterized by SEM,EDS,XRD and so on.The results show that in the high-temperature air at 800 ?,the oxidation products of C_f/Ni₃ Si composite which was prepared without carbon fiber surface modification and gel-coating were Ni O,and the size of NiO particles were small,the morphology was anomalous.While the oxidation products were composed of NiO and a small amount of quartz-type SiO2 and spinel-type Ni2 Si O4 at 1000 ?.The size of the oxidation products was large and the particles have some corners.These two oxide films were both pore and with a lot of defects and micro cracks inside.The scale with duplex layers is found with the oxide films: the outer layer is thick NiO film,the inner is the thin discontinuous SiO2 film.The weight gain curves of C_f/Ni₃ Si matrix composite which was modified by Cu deposited carbon fiber at 800 ? were composed of parabolic and linear.While the weight gain curves of sample treated at 1000 ? is a single parabolic.The scale with three layers is found with the oxide films: the outer layer is CuO film,the middle layer is Ni O film,and the inner is the SiO2 and Ni2SiO4 film.Moreover,the CuO film of the sample treated at 1000 ? is thicker and denser compared with the sample treated at 800 ?.The average thickness of CuO film is about2 mm.Compared with the sample without modification of carbon fiber,the C_f/Ni₃ Si matrix composite which was modified by Cu deposited has a parabolic oxidation kinetics curve,when it was oxidized at 1000 ?.Besides,the stability and compactness were also good enough for the oxide film,the oxidation resistance was raised as well.With the development of the mass fraction of the carbon fiber,the microhardness of C_f/Al₂O₃-Ni₃ Si matrix composite reduced gradually,and the relative increased.The oxidation product of C_f/Al₂O₃-Ni₃ Si matrix composite which was treated at 800 ? is NiO.The size of the oxidation products was small;the surface of the particles was rough and anomalous as well.While the oxidation products of the sample treated at 800 ? are mainly NiO,the spinel-type Ni2SiO4 and a small amount of quartz-type Si O2.But the spinel-type Ni-Si was not been found.Besides that,the oxidation product was large and the particles have some corners,but without any continuous oxidation film was formed throughout the entire process.