Thermal Mismatch Stress And Interface Control Of (Anti-perovskite+SiCnw)/Al Matrix Composite

In the field of aerospace,precision instruments needed to maintain dimensional stability under complex temperature changes,and required low-density and near-zero expansion materials.In this paper,the anti-perovskite Mn-N compounds with negative thermal expansion properties were selected as inhibitors of thermal expansion coefficient of aluminum alloys.The anti-perovskite Mn-N compounds was successfully fabricated by pressure infiltration to reinforce aluminum matrix composite,and through the introduction of the silicon carbide nanowires?Si Cnw?with low expansion,high modulus and high aspect ratio,this could further reduce the thermal mismatch stress in the composite and improve the strength of the matrix.The microstructure of Mn_3.2Zn_0.5Sn_0.3N/Al composite at different fabrication temperatures was studied.The SEM results showed that the thickness of interface layer of the composite fabricated at 800 ? was 10 ?m,that of the composite fabricated at 750 ? was 6 ?m,and that of composite fabricated at 700 ? was 1 ?m.The results of line scan showed that the interface micro region of composite was a complex combination of phase composition,which could be divided into two regions,the linear diffusion region and the interface reaction region.By adopting the method of ultrasonic direct mixing of anti-perovskite Mn-N compounds and Si Cnw,it was found that the density of the composite was 3.36g/cm³ when ?Si Cnw:?Mn_3.2Zn_0.5Sn_0.3N=1:9,and that of the composite was 3.13g/cm³ when ?Si Cnw:?Mn_3.2Zn_0.5Sn_0.3N=1:4.The study found that sicnw was relatively fluffy,and the volume fraction of the reinforcement would be decreased by direct introduction of sicnw.The method of introducing Si Cnw into the composite system was improved,the composite materials of 30%Si Cnw/Al:Mn₃Zn_0.7Ge_0.3N=1:6 and 30%Si Cnw/Al: Mn₃Zn_0.7Ge_0.3N = 1:3 were respectively fabricated by mixing the aluminum-based composite material?30%Si Cnw/Al?particles with high content of Si Cnw and the antiperovskite manganese-nitrogen compound.The density of the composite was 4.26 g/cm³ and 4.10 g/cm³ respectively.SEM results showed that the thickness of the interface layer in the composite was 1?m.The thermal expansion properties of the composite were studied.Under different fabrication temperatures,it was found that the thermal expansion coefficient of Mn_3.2Zn_0.5Sn_0.3N/Al composite decreased with the decrease of fabrication temperature.The properties of(Si Cnw+Mn_3.2Zn_0.5Sn_0.3N)/Al composite were studied.It was found that the volume fraction of reinforcements in the composite decreased when sicnw was introduced directly.Although the mechanical properties increased from 145MPa?no Si Cnw?to 220MPa(?Si Cnw:?Mn_3.2Zn_0.5Sn_0.3N=1:9),the thermal expansion coefficient of the composite also increased sharply.For the(30%Si Cnw/Al + Mn₃Zn_0.7Ge_0.3N)/Al composite,the composite fabricated by mixing 30%Si Cnw/Al with anti-perovskite manganese-nitrogen compound was introduced into sicnw.The volume fraction of Mn_3.2Zn_0.5Sn_0.3N in the composite was basically unchanged,and it had excellent thermal expansion properties,which the lowest thermal expansion coefficient reached 0.25×10-6K-1(?30%Si Cnw/Al:?Mn₃Zn_0.7Ge_0.3N=1:3).The mechanical properties research showed that the three-point bending strength of the composite was increased from 199MPa?no 30%Si Cnw/Al?to 265MPa(?30%Si Cnw/Al:?Mn₃Zn_0.7Ge_0.3N=1:6)and 325 MPa,and that was increased by up to 63%(?30%Si Cnw/Al:?Mn₃Zn_0.7Ge_0.3N=1:3).A three-dimensional thermal stress calculation model based on the actual shape was established by adopting the finite element method.The research showed that the introduction of sicnw reduced the stress from 2000 MPa to 1000 MPa,and sicnw could significantly reduce the thermal mismatch stress of the composite.At the same time,the next step was to further reduce the thermal mismatch stress by coating,simulation showed that the coating could reduce the thermal stress from 2000 MPa to 1000 MPa.The coating structure could also effectively reduce the thermal mismatch stress in the composite.