Tribological Properties And Oxidation Resistance Of Fe₃Si Based Ordered Alloys

Fe₃Si based ordered intermetallic is a candidate for high temperature structural material because its melt point is relatively high and its wear resistance and oxidation resistance are also believed to be good. Fe₃Si contains two of the most cost-effective elements. So, the application prospects of the Fe₃Si based intermetallic are good. However, the applications of Fe₃Si as structural material are hindered because Fe₃Si is brittle and hard as other intermetallics. It is prerequisites for Fe₃Si as structural material to improve its toughness and to investigate its tribological properties and high-temperature oxidation behavior.In the present work, monolithic Fe₃Si,Fe₃Si based alloy and Fe₃Si based composites are prepared by three methods, i.e. mechanical alloying followed by annealing process (MAAP or M2AP), hot-press sintering in medium frequency induction oven and vacuum arc melting. The long range order parameter (LRO) of Fe₃Si powders prepared by M2AP is evaluated. The microstructure, tribological properties and high temperature oxidation resistance of bulk Fe₃Si based alloys prepared by vacuum arc melting are investigated. The following findings and conclusions are reached.First of all, based on alloying modification, mechnical alloying processes of Fe₃Si based ordered intermetallic with different contents of alloying element Al and the LRO of Fe₃Si based ordered alloy are investigated. Fingdings indicated that Fe₃Si based ordered alloy with high LRO value can be prepared by M2AP. The LRO of the milled powders for 10 and 15h annealed at 860℃for 1h is 94.63% and 96.66%, respectively. The introduction of alloying element Al can greatly reduce the LRO values of Fe₃Si based intermetallics.Secondly, Fe₃Si-Cu composite and Fe₃Si based ordered intermetallics alloyed by Cr and Al were fabricated by vacuum arc melting and subsequent hot-pressing motivated by the thought of improving the mechanical and tribological properties of Fe₃Si based ordered intermetallic. The microstructures and mechanical properties of Fe₃Si-Cu and Fe-Si-Cr-Al alloys are examined. Findings indicated that introduction of the plastic phase, i.e. Cu or alloying elements Cr and Al to Fe₃Si can greatly improve its strength at room temperature. TEM analysis indicated that the relationships of crystal orientation between Fe₃Si and Cu at the interface are identified as Cu{220}//Fe₃Si{004} and Cu<100>// Fe₃Si<011>.Thirdly, tribological properties of Fe₃Si, Fe₃Si-Cu composite and Fe₃Si based ordered intermetallics alloyed by Cr and Al are investigated in water lubrication using commercially available AISI 304 stainless steel as baseline. It is found that the tribological properties of Fe₃Si is comparable to that of AISI 304 stainless steel, while the tribological properties of Fe₃Si-10 wt% Cu composite and Fe₇₀Si₂₀Cr₅Al₅ are better than that of monolithic Fe₃Si in water lubricated condition. The wear mechanism of Fe₃Si, Fe₃Si-Cu composite and Fe₃Si based ordered intermetallics alloyed by Cr and Al sliding against Si₃N₄ in water lubrication is all dominated by abrasive wear. The enrichment of Cu on the worn surfaces of Fe₃Si-10 wt% Cu and the transference of Cu to the worn surface of Si₃N₄ are found for Fe₃Si-10 wt% Cu sliding against Si₃N₄. The tribochemical reactions of Si₃N₄ with water are restrained owing to the enrichment and transference of Cu at the tribo-interface of Fe₃Si-10 wt% Cu against Si₃N₄.Besides, the tribological properties and wear mechanisms of Fe₃Si sliding against Si₃N₄ at elevated temperature in air and nitrogen are investigated. High-speed steel W18Cr4V is used as a reference. Findings indicated that the wear rates of Fe₃Si increased as temperature increased at temperatures below 600℃. "Anti-temperature effect" of wear rate of Fe₃Si, which means the wear rate decreased as temperature increased, is found at temperatures between 600℃and 800℃. The marked reduction in wear rates of Fe₃Si from 600℃to 800℃in air is correlated to the in-situ formation of glazed oxide layer on the worn surface of Fe₃Si.Finally, the oxidation properties of Fe₃Si and Fe₃Si based ordered intermetallics alloyed by Cr and Al at 800℃and 900℃are investigated. The kinetic curve for the oxidation of Fe₃Si at 800℃can be divided into two stages, i.e. the kinetic curve followed parabolic rule for the first 10 hr and a linear law for the next 10 hr. The kinetic curve for the oxidation of Fe₃Si obeys a parabolic rule at 900℃. The addition of alloying elements Cr and Al to Fe₃Si can greatly improve the resistance to oxidation at 800℃and 900℃. The oxidation kinetic curve of Fe₃Si based ordered intermetallics alloyed by Cr and Al follow a parabolic rule at 800℃and 900℃.