Preparation And Properties Of Lightweight High Performance Feal Matrix Composites By Powder Metallurgy

The change of future war mode puts forward higher requirements for the lightweight and power density of diesel engine.At present,lightweight and high power have become the development direction of diesel engine.As one of the key components of diesel engine,the service conditions of diesel engine cylinder head will become harsher,which will put forward higher requirements for the performance of materials.The traditional cast iron material has limited weight reduction space,and the high temperature mechanical properties of aluminum alloy are poor,which is unable to meet the use requirements.Therefore,it is of greatsignificance to develop a new material with low density and excellent mechanical properties for the development of high power density diesel engine in the future.In this paper,Fe and Al were selected as matrix materials,and B2-FeAl powder was prepared by mechanical alloying and heat treatment.The bulk was prepared by hot pressing sintering.The effect of holding time(1.0 h,1.5 h,2.0 h,2.5 h,3.0 h)on the microstructure and properties of the material was investigated under the condition of sintering temperature 1050?,pressure 25 MPa;NiAl/FeAl composites(NiAl content is 10wt.%,20wt.%,30wt.%,40wt.%,50wt.%,60wt.%),CNTs/FeAl composites(CNTs content is 0.2wt.%,0.5wt.%,0.8wt.%,1.1wt.%)and(0.8wt.%CNTs,30wt.%NiAl)/FeAl composites were prepared by referring to the optimal process.The effects of the content of NiAl and CNTs in B2 structure on the microstructure,mechanical properties and oxidation properties of FeAl intermetallic compounds were investigated.The conclusions are as follows.The results show that there are a small amount of AlFe₃C_0.5 phase and Al₂O₃ phase in the B2-FeAl bulk prepared under different hot pressing holding time,and the distribution of each phase is gradually uniform with the increase of holding time;When the holding time was 2 h,the density and density reached a stable level,which were 4.926 g·cm-3 and 99.5%respectively;The hardness,tensile strength and compressive strength increased first and then decreased with the increase of time,and reached the maximum when the holding time was 2.5 h.Therefore,the optimal holding time of hot pressing sintering is 2.5 h.NiAl/FeAl composites with different NiAl contents were prepared by hot pressing sintering at 1050?,25 MPa and 2.5 h.The composites were composed of B2-NiAl,B2-FeAl and a small amount of AlFe₃C_0.5 and Al₂O₃.With the increase of NiAl content,no new phase was formed.The density increases with the increase of NiAl content,and reaches the maximum when NiAl content is 60%.The hardness and compressive strength increase first and then decrease with the increase of NiAl content.When the NiAl content is 30%,it reaches the maximum value,which is 34.5%and 40.8%higher than that of FeAl,respectively;When the content of NiAl increases to 60%,the oxidation weight gain of the composite is 0.19 mg·cm-2,which is 81%lower than that of FeAl;At this time,the oxide on the surface of the oxidized sample is mainly composed of Al₂O₃,Fe₂O₃ and a small amount of NiO.According to the comprehensive structure and properties,30wt.%is the best proportion of NiAl.The CNTs/FeAl block composites were prepared under the sintering temperature of 1050?,pressure of 25 MPa and holding time of 2.5 h(CNTs/FeAl composite powder is treated by suitable ultrasonic,then wet grinding and finally dispersant).The main phases of the composites include FeAl,Al₂O₃ and AlFe₃C_0.5 with uniform microstructure distribution.The hardness,tensile strength and compressive strength of CNTs/FeAl composites first increase and then decrease with the increase of CNTs content.The maximum value of CNTs content is 0.8wt.%,which is 53%,25.5%and 9.5%higher than that of FeAl respectively.After adding CNTs,the oxidation resistance of CNTs/FeAl composites is obviously improved,and the oxidation weight gain of CNTs/FeAl composites is one order of magnitude lower than that of FeAl;With the further increase of CNTs content,the oxidation weight of the material was almost unchanged,about 0.19 mg.cm-2;The surface oxides are mainly Al₂O₃ and Fe₂O₃.The results show that 0.8wt%is the best proportion of CNTs.The(0.8wt.%CNTs,30wt.%NiAl)/FeAl composites were prepared by hot pressing sintering at 1050?,25 MPa and 2.5 h.The composites were mainly composed of B2-FeAl,B2-NiAl,AlFe₃C_0.5 and a small amount of Al₂O₃,and B2-NiAl was evenly distributed in the matrix.The hardness of the product was 57.3HRC,and the compressive strength was 2303.3 MPa,which was 59.1%and 57.9%higher than FeAl;The oxidation weight of the product decreased 86.34%compared with that of pure FeAl.