The Research Of Ni₃Si Based Composites Strengthened And Toughened By Surface-modified Carbon Fiber

Intermetallic compounds Ni₃Si has high strength, excellent oxidation resistance,corrosion resistance（especially the resistance corrosion of sulphuric acid and sulfur dioxide）,contrary to the temperature/strength effect, and the highest temperature can reach 1290 K,therefore, the Ni₃Si can be used as a new type of high-temperature structural materials used in high-temperature and corrosive environment, for example, the aviation, automobile industry,chemical industry. Ni₃Si exist the problem of brittleness at room temperature, restricts its practical application of it as a structural material. This paper modified the short carbon fiber surface by sol gel and electroplating, and put the Cf mixed with Ni₃Si to improve the tenacity of material. The phase, the microstructure, interface of materials, mechanical properties were analyzed, analyze the carbon fiber strengthen mechanism of Ni₃Si, get the following conclusion:1、The short Cf were acid pickling by nitric for 30 minutes, the surface of Cf appered shallow trench, the roughness of surface, activity and hydrophilic was increased, the Cf dispersed in solution easily and keep the structure and property.2、Obtaining the homogeneous and dense layer of Cu on the surface of Cf, the voltage was2 V, and the time is 30 minutes.3、The acid-pickled short Cf disposed by silane coupling agent（KH-792）, according to the proportion（1:3）, add the polyving akohol into AlOOH collosol, compare the influence of the times of coating effect, after once coated, the thickness of coating layer is 0.2 microns; after once coated, the thickness of coating layer is 0.44 microns;4、Through comparing microstructure and properties of Ni₃Si composite material that prepared by hot press sintering and add the Cf which was disposed by copper electroplating,Al2O3 coated once, Al2O3 coated twice and the volume fraction was 10%. The surface of the original Cf badly damaged, the modified surface of Cf is existence intact, the interface of Cf and Ni₃Si is smooth, the coating layer can protect Cf well, restrain the interface reaction effectively. Modified surface of Cf play a strengthening and toughening role in Ni₃Si composite material. The bending strength of original Cf/Ni₃Si material is 342.99 Mpa, the bending strength of Al2O3 coated once Cf/Ni₃Si material is 408.64 Mpa, the bending strength of Al2O3 coated twice Cf/Ni₃Si material is 431.24 Mpa, the bending strength of copper electroplated Cf/Ni₃Si material is 484.44 Mpa. It follows that, Cf of Al2O3 coated twice strengthen the Ni₃Si effectively; At room temperature, the Cf of layer of copper strengthen the Ni₃Si best.5、 Through analyzing the effect of content of Al2O3 coated Cf on microstructure and property of Ni₃Si composite material, the hardness and intensity increased with the incerased of content of Cf when the volume fraction of Cf less than 10%. When the content of Cfincreased from 3% to 8%, the bending strength of materials incerased from 235.98 Mpa to524.02 Mpa. The increase of content of Cf is benefit to composite material property.6、The density Cf/Ni₃Si materials that prepared by hot pressing was low, the effect of density on the whole property of marterials is significant, the project need to research and improve the technology of hot pressed sintering in future.