Research On The Microstructure And Mechanical Properties Of Double-layer Iron-based Powder Metallurgy Material

During the actual use, and some parts are only partially require high mechanical properties. Therefore, we can use the double-layer material, the end of the high properties requirements add a high content of alloying elements to meet the performance, the other end do not add alloying elements, as the base layer.In this paper the base layer of two-layer iron-based powder metallurgy material is Fe-1.2C-5Cu, add the elements of Cr, Mo, Ni, Co respectively or compound to the alloy layer. Research of the microstructure, the radial crushing strength and friction coefficient of the sintered state, the infiltration state and the heat treatment state of the samples.The wet mixing method can improve the uniformity of the mixed powder. The alloy layer and the base layer of twice loading and twice pressing method bonded well, without cracks. With the pressing pressure increasing, the density of the green compacts, the hardness and the radial crushing will increase. but when the pressing pressure increase to650MPa, the growth rate will be reduced.At the sintered state, adding Cr, Mo, Ni elements in alloy layer, there are pearlite and ferrite, as well as some bainite. Respectively adding Cr Element, there are uncombined graphite. Most of bainite obtained by the addition of Mo element. Respectively adding Ni element can get the most fine lamellar pearlite. Respectively adding Co element, get pearlite only. Adding Mo Ni elements at the same time, get the most bainite. Cr. Mo in the sintered samples will gathered, generate carbide and alloy cementite.After the infiltration process, the diffusion of alloy elements is more fully, adding Cr, Mo, Ni element, the alloy layer have a large number of bainite. The carbon content increases at the Cr, Mo enrichment zone. there are a large number of mesh free copper in the infiltrated samples. After the heat treatment process, there are tempered martensite and residual austenite. prone to mesh structure. Adding Ni Co elements in samples appears tertiary cementite at the grain boundary.At the Sintered state, the radial crushing strength of the sample is added Mo is the highest,850MPa. The radial crushing strength of the samples are added Cr. Mo is the lowest. After the infiltration process, the radial crushing strength is increased. The radial crushing strength of the infiltrated sample is added Mo is increased to1227MPa. After the heat treatment process. the radial crushing strength of the samples are added alloy elements will not have much change. Mo can make the friction coefficient of the sintered sample decreased. The average friction coefficient of the sintered sample respectively adding Mo element is0.116. The average friction coefficient of the sintered sample add Mo Co elements at the same time is0.137. After the infiltration process, the density is increased, the average friction coefficient is increased. After the heat treatment process, the average friction coefficient of the samples will not have much change.