| Iron-based powder metallurgy sintered material and parts are widely used in powdermetallurgy industry. One of the research targets for powder metallurgy technique isdeveloping the iron-based sintered material with high performance and low cost. In order tocater the dominant trend of manufacturing low alloy, low cost iron-based sintered materials, inthis paper, iron-based powder metallurgy sintered material with high performance and lowcost was studied. The purpose of this study is to replace Ni, Mo and other expensive elementsby using low cost Mn element and then high density Fe-2Cu-0.5Mn-0.9C sintered materialwas optimized. The mechanical properties, densification mechanism，sintering behaviour andultrasonic fatigue behaviours of high density iron-based powder metallurgy materials werestudied, as well as the influence of Mn addition on the preparation, properties and sinteringprocess. Our research provides technical guidance for the application of Mn-containingiron-based sintered material and it has important academic significance and practical value.The main results show that:The mechanical properties and sintering behaviour of Fe-Cu-Mn-C series materials areaffected by different manganese content. Partially pre-alloyed Fe-2Cu-0.5Mn-0.9C sinteredmaterial was fabricated by die-wall lubricated warm compaction with good mechanicalproperty and uniformly distributed microstructure. The sintered material has a density ofhigher than7.3g/cm3, tensile strength of715MPa, Rockwell hardness of97HRB and impactenergy of23J. The tensile fracture mode is tough-brittle mixed fracture. The green densityof material under cold, warm compaction increases with increasing pressure. The greenrelative density of Fe-2Cu-0.5Mn-0.9C is able to reach at94.9%and96.0%under warmcompaction (700MPa,120℃) and high velocity compaction respectively. The content ofmanganese also influences the sintering process. Excess of manganese within sinteredmaterial will probably lead to internal oxidation and material strength reduction. But it hasgood strengthening effects if adding appropriate amount of manganese. During initialsintering period of Fe-Cu-Mn-C series materials, manganese alloying elements transfers intoiron matrix through the connecting pore-networks. Additionally, evaporation condensation ofMn is the diffusion mechanism during sintering process. The manganese vapor causesmaterial expansion and lowers sintered density slightly during the pre-sintering and initialsintering period, while density increases due to pores closing and porosity networksdisappearing gradually as sintering time extended. What is more, elevated sintering temperature contributes to slight sintering shrinkage of the material, which partially offsetmaterial expansion.Surface properties of warm compacted Fe-2Cu-0.5Mn-0.9C material such as the surfacedensity, micro hardness and residual stress are improved by shot peening. However, thetensile strength and fracture characteristics are not changed after shot peening. Fretting weartests between sintered materials and GCr15steel show that the main wear and frictionmechanism is fatigue spalling (at low load) and abrasive wear (at high load) under oillubrication. However, observation of dry friction surfaces indicates that mixed wearmechanism, including abrasive wear, adhesive wear, oxidation wear and plastic transfer. Thesurface wear area of specimen can be reduced by shot peening. The fretting wear property ofshot peen can be improved under lower loading, while only early stage friction of which canbe elevated under higher loading. The wear mechanism of shot peened material is similar withsintered material, but adhesive wear degree of shot peened material is significantly less thansintered material.Ultrasonic fatigue testing method is a high efficiency technology, which can be successfullyapplied in very high cycles fatigue testing of iron-based powder metallurgy sintered materials.The ultrasonic fatigue S-N curve decreases continuously. The ultrasonic fatigue limit existsand the axial fatigue strength of Fe-2Cu-0.5Mn-0.9C are393,289and213MPa for thecorresponding conditions of106,107and108cycles, respectively. The ultrasonic fatigue cracksources of fracture are located at voids or inclusions. Dimples and cleavage planes areobserved in the fatigue fracture, which is similar with that of tensile fracture. Some ultrasonicfatigue striations are distributed in fracture under ultra-high cycle. Fatigue fracture modelshows that the number of fatigue cycles of crack growth stage is inversely proportional to thesquare of fatigue stress in high-cycle fatigue ultrasonic test. The crack growth stage is only asmall part of the whole ultrasonic fatigue life. Crack initiation stage accounts for the most ofthe fatigue life. The axial ultrasonic fatigue strengths of Fe-2Cu-2Ni-1Mo-1C are312,249and199MPa for the corresponding conditions of106,107and108cycles, respectively. Thefatigue strength is less than that of Fe-2Cu-0.5Mn-0.9C sintered material. There is no obviousrelationship between the defect size and the fatigue cycles. In addition, the stress intensityrange factor of defects reduces with the gradual increase of the number of fatigue cycles. Thefatigue fracture characteristics of iron-based sintered material are similar with each other.Crack sources of fracture are located at voids or inclusions near the surface under high cyclebut it moves to the internal sites under ultra-high cycle. What is more, the symmetricalbending ultrasonic fatigue strengths of Fe-2Cu-0.5Mn-0.9C are402,331and273MPa for the corresponding conditions of106,107and108cycles, respectively. |
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