First-principle Calculations And Their Validation For The Effect Of Y Element On The Interface Of Cf/Al Composites

In order to improve the interfacial bonding state of Cf/Al composites,matrix alloying has been researched at home and abroad.While at this stage of the study lack of theoretical research.The interface model of Cf/Al composites was calculated by the first-principle method,and the influence of Y elements on the interface was investigated.The microstructures of the composites were observed by SEM and TEM,and their transverse tensile properties,interlaminar shear properties and bending properties were tested and the interfacial state and its effect on the strength and toughness of the composites were analyzed.The calculations based on CASTEP show that the calculated value of adhesion work of Cf/Al interface model is 0.111 J?m-2,Cf/Al interface is a stable interface for its value is positive.Large interfacial spacing between Al and C and the defective graphite ring structure result in no significant charge transfer between the two.For the Cf/Al interface with the rare earth element Y replacing Al,the adhesion work has a more substantial increase.From the calculation of lattice defect energy,it can be seen that the model is the most stable system when replacing the first layer of Al atoms,which shows that Y is easier to converge to interface.By comparing the influence of other alloying elements on the Cf/Al interface,it was found that the increase of the interfacial adhesion work was the greatest,and the addition of the Y element to the matrix had the most obvious effect on the Cf/Al interface.In this paper,Cf/1199,Cf/Al-1Y(with Y content of 1%)and Cf/Al-3Y(with Y content of 3%)composites were prepared.It was found that when the content of Y was 1wt.%,Y was not only uniformly dispersed in the Al matrix but also diffused into the carbon fiber,but the content in the matrix was still higher than that in the carbon fiber.When Y content increased to 3wt.%,the distribution is more concentrated in the interface,and it was consistent with the calculations of lattice defect energy.It is found that there are a large number of fine rod-shaped Al4C3 at the interface of Cf/Al composites with pure Al matrix,less Al4C3 and some bulk Al3 Y precipitates appeared at the interface of Cf/Al-1Y composites.Spherical Al3 Y phase is found in the matrix of Cf/Al-3Y composites and also in the interface with a large size,and there are a small amount of Al4C3 phase with a small size in the interface.The thermodynamic analysis of the effect of Y content on the interfacial reaction of Cf/Al composites shows that the addition of Y increases the Gibbs free energy of Al4C3 reaction and makes it difficult to proceed.It shows that Y can hinder the formation of Al4C3 and the increase in Y content of the inhibition will be more obvious,consistent with the calculated results.Mechanical properties of Cf/1199,Cf/Al-1Y and Cf/Al-3Y composites were tested.The bending strength of the composites increased by about 82.4MPa,16.1% when the content of Y was 1wt.% while the bending strength of the composites decreased when the content of Y was 3wt.%.The interlaminar shear strength decreased by 14.5% and the fracture energy increased by 41.9% after adding 1wt.% Y in the matrix,which indicated that the interface brittleness was alleviated.The transverse tensile strength of the matrix increased by 53.9% after adding 1wt.% Y,and its toughness increased.