The Preparation And Properties Of In-situ Synthesized Core-shell Structure Reinforced Aluminum Matrix Composites

Aluminum-based composite materials have been paid attention to by the materials science community because of their unique properties,and are widely used in aerospace and other manufacturing fields.Aiming at problems such as poor wettability and weak wear resistance of the aluminum matrix composite reinforcement and the interface,this paper uses powder metallurgy to prepare aluminum-based composites through the enhanced design of the core-shell structure of intermetallic compounds,and studies the preparation process of core-shell structure.The influence of core-shell structure on the mechanical properties of composite materials.The tribological behavior of aluminum-based composites in dry friction and seawater environments was studied,and the wear mechanism of aluminum-based composites was revealed.The main results and conclusions obtained in this paper are as follows:1.Through the enhanced design of core-shell structure,the aluminum-based wear-resistant composite material was prepared by powder metallurgy.The core-shell structure is mainly composed of Ni₃Al,Ni Al,Al₃Ni intermetallic compounds.The core structure is Ni₃Al intermetallic compound,and the shell layer is a double-layer structure（the secondary outer shell layer of the core is Ni Al intermetallic compound,and the outermost layer is Al₃Ni Intermetallic compounds）.2.The aluminum matrix composites with enhanced core-shell structures show higher mechanical properties.The core-shell structure has a high hardness value（706HV）.The core-shell structure composite material with 15 vol.%Ni₃Al has the highest compressive strength,about 248 MPa.By analyzing the extension of surface cracks during compression,it is found that there are three propagation modes of cracks in core-shell composites.The first is to produce cracks between the aluminum matrix and the core-shell structure.The second is that the crack propagates on the shell structure of the core-shell structure,which can be subdivided into two situations;one is that the crack propagates on the shell structure,and the other is that the crack propagates between the core structure and the shell structure.The third is that the crack passes directly from the core through the entire core-shell structure.The research results show that because the crack propagation in the core-shell structure requires more energy to drive than in the matrix phase,the core-shell structure can inhibit the propagation of the crack,so the aluminum matrix composites with enhanced core-shell structure show higher mechanical properties.3.Under dry sliding conditions,the tribological properties of core-shell structure-reinforced aluminum matrix composites are significantly improved compared with pure aluminum.Under the condition of core-shell structure formed by 15 vol.%Ni₃Al core-shell structure composite material,the composite material reached the optimal friction coefficient and wear rate at 30 N,respectively 0.74 and 6.45×10^-5 mm³?N^-1?m^-1.The formation of the core-shell structure reduces the wear rate and friction coefficient of the material.This is because the formation of the core-shell structure improves the performance of the material,so that the main wear mechanism of the composite material when paired with 316 L steel balls is abrasive wear.When paired with pure aluminum,the main wear mechanism is adhesive wear.Adhesive friction needs to overcome greater friction.Compared with core-shell structure-reinforced aluminum matrix composites,the adhesive friction is effectively reduced,and the friction coefficient is significantly improved.In addition,the intermetallic compound in the core-shell structure has high hardness and good thermal stability,which improves the high temperature softening resistance of the composite material.4.In a seawater environment,the tribological properties of core-shell structure-reinforced aluminum matrix composites are significantly improved compared with aluminum alloys.The aluminum matrix composite with 10 vol.%Ni₃Al has the lowest friction coefficient（about 0.2）,while the aluminum matrix composite with 25 vol.%Ni₃Al has the lowest wear rate(about 1×10^-6 mm³?N^-1?m^-1).The low-friction and low-wear behavior of aluminum-based composites in seawater environment are mainly due to:（1）the lubrication effect of seawater:seawater forms a water film on the friction interface,which plays a certain lubricating effect;（2）the cooling effect of seawater:The friction heat generated during the friction process is absorbed by the seawater,which reduces the friction surface temperature,weakens the softening phenomenon of the material surface,and effectively reduces the adhesive wear;（3）The strengthening effect of the core-shell structure.The core-shell structure composed of intermetallic compounds increases the mechanical properties of the material and reduces the adhesive wear;as the volume fraction of the core-shell structure increases,the abrasive wear of the aluminum matrix composite material increases,resulting in an increase in the coefficient of friction;Compared with the shell structure,as the volume fraction of the core-shell structure increases,the wear of the softer 316 L pair increases.