| In the new era,the military war mode has higher requirements for the mobility of army armored vehicles.As one of the key parts affecting the performance of armored diesel engines,the weight,and performance of the cylinder head are the key factors restricting the performance of the engine.At present,the cylinder heads of armored vehicles are mainly made of Al alloy and cast iron.Among them,the bearing capacity of aluminum alloy is relatively weak and the service temperature is low,which is mainly suitable for diesel engines with low power density.Cast iron possesses a strong bearing capacity,but its density is high,which is difficult to reduce weight and cannot meet the requirements of armored vehicles in future.Therefore,it is of great significance to study new iron-based alloys with low density and high performance.In the present work,the austenitic matrix powder(Fe-20wt.%Mn-9wt.%Al-1.3wt.%C),ferrite matrix powder(Fe-4wt.%Mn-6wt.%Al-0.04wt.%C),NiAl powder with B2 structure and TiAl powder with B2 structure were prepared by the mechanical alloying process.B2 NiAl(30wt.%-60 wt.%),TiAl(7 wt.%-10 wt.%)reinforced austenitic and ferrite matrix composites were prepared by hot pressing sintering technique,and their microstructure,density,thermal conductivity and compression properties were tested and analyzed.The conclusions are as follows:1)Austenite based powder,ferrite based powder,NiAl and TiAl intermetallic compound powder with B2 structure were prepared by mechanical alloying method.With the ball milling time increasing,the particle size of the initial powder mixture decreases significantly at first.When the powder particle refinement limit is reached,further ball milling has little effect on the average size of powder particles;In the powder particles after ball milling,the layered composite structure formed by different components is further refined into nano-scale multilayers with the increment of ball milling time.Because of the defects induced by ball milling,solid-state alloying reaction occurs between different components and finally the corresponding alloy is formed.The results further show that the optimum ball milling time for the formation of austenite based low-density iron-based alloy and ferrite based low-density iron-based alloy is 20 h and 10 h,respectively.The optimum ball milling time for NiAl and TiAl intermetallic compound formation is 50 h and 30 h.2)Austenitic and NiAl matrix composites were prepared by vacuum sintering technology.The microstructure of NiAl reinforced austenitic matrix composites is mainly composed of austenite,NiAl and k-carbide phases.The microstructure of TiAl reinforced austenitic matrix composites mainly contains austenite,TiAl and k-carbide phases.With the addition of TiAl increasing from 7 wt.%to 10 wt.%,the microstructure of the alloy gradually homogenizes,the annular TiAl phase diffuses and fuses with the austenite matrix phase at the ring center.The microstructure of NiAl reinforced ferritic matrix composites is mainly composed of ferrite and B2 structure NiAl,while the microstructure of TiAl reinforced ferritic matrix composites is mainly composed of ferrite and TiAl.With the increase of NiAl and TiAl content,the microstructure of the materials gradually increases and the uniformity decreases.3)The results of B2 structure NiAl and TiAl reinforced austenitic matrix composites show that with the increase of NiAl content,the overall density of the materials decreases gradually,while the hardness,compressive strength and thermal conductivity increase gradually.With the increase of TiAl content,the overall density of the material decreases gradually,while its hardness and thermal conductivity increase first and then decrease.When the NiAl content increases to 60 wt.%,the material density is only 5.74 g/cm~3,which is 12.37%lower than that of the austenitic iron-based alloy matrix.The hardness is 61.85 HRC,the compressive strength is 2742.78 MPa,and the thermal conductivity is 22.25 W/m·K at 600?,which is 21.85%,24.36%and 59.16%higher than that of austenitic iron-based alloy matrix respectively.When the content of TiAl is 9 wt.%,the hardness is 52.91 HRC,the compressive strength is 2433.29MPa,and the thermal conductivity at 600?is 16.09 W/m·K,which is 4.24%,10.33%and7.41%higher than that of austenitic matrix alloy,respectively.Compared with NiAl phase,the reinforcing effect is weak.The overall fracture type of the two austenitic matrix composites is brittle fracture and the fracture mode is cleavage fracture.4)The performance test results of NiAl and TiAl reinforced ferrite matrix composites with B2 structure show that with the increase of NiAl and TiAl content,the material density gradually decreases,the hardness gradually increases,and the compressive strength first increases and then decreases.When the NiAl content increases to 50 wt.%,the overall density of the material is only 6.37 g/cm~3,which is 4.78%lower than that of ferrite iron-based alloy matrix.The hardness is 54.21 HRC and the compressive strength is 2767.41 MPa,which is14.10%and 68.23%higher than that of austenitic iron-based alloy matrix,respectively.When the TiAl content increases to 9 wt.%,the overall density of the material is 6.64 g/cm~3,which is slightly lower than that of the matrix material.The hardness is 50.36 HRC and the compressive strength is 1906.83 MPa,which is 6.00%and 16.04%higher than that of austenitic iron-based alloy matrix respectively,which is weaker than that of NiAl phase.The fracture type of the two ferritic matrix composites is brittle fracture,and the fracture mode is cleavage fracture. |
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