Damping Property And Microstructure Of The Interface Of 16Mn Steel/Zn Composite

Metal matrix composites (MMCs) have been one of the key research subjectsin materials science during the past three decades. Developed countries have givenserious attention to MMCs because of their high specific strength, high specificmodulus, high-temperature properties and low expansion coefficient. Most of thework has been dealing with light metal matrices for application in combinationwith high strength and/or stiffness (boron fibre, SiC fibre) in aerospace, defenseand automobile industries.In engineering designs, particular attention has to be paid to mechanicalvibrations, because it will lead to rupture by fatigue of metal materials. Mechanicalvibrations can be reduced in many ways, for instance by using external dampers orby increasing some inertial masses. However, these solutions are not alwaysapplicable. Thus, metal engineering materials simultaneously need a high dampingcapacity and good mechanical properties. But these properties are oftenincompatible in simplex metals because the microscopic mechanisms involved instrengthening and damping are not independent. A high damping capacity isobserved in materials exhibiting poor mechanical properties, for instance low yieldstress or hardness. It is well known that the high damping capacity in elastic rangeof pure Zinc is associated with a very weak tensile strength. On the contrary, steelspresent good mechanical properties and a low level of damping. It would thereforebe of interest to search for new composite simultaneously exhibiting goodmechanical properties and high damping in this paper.In this paper, two metal materials (16Mn steel and pure Zn) were selected and16Mn steel/Zn composite was fabricated by casting technique. The area ofhysteresis loops (means of energy) and logarithmic decrement of vibrationalamplitude (means of free attenuation) illuminated damping capacity of 16Mnsteel/Zn. Mechanical properties and interfacial microstructures of the compositewere examined by means of tensile and cyclic tests, SEM, EDS, XRD analysis andVickers-hardness measurement. Micro-crack initiation, propagation of the cracksand tensile fracture character of 16Mn steel/Zn composite under axial tensionwere investigated. The major research efforts of the present study were as follows:(1) Tensile and cyclic properties of 16Mn steel/Zn compositesStress-strain curve of 16Mn steel/Zn composite under tension could beobserved between stress-strain curves of 16Mn steel and zinc with the sameconditions in room temperature. Crosshead speed had nearly no influence on thetress-strain curve of steel/Zn composite. The strength of steel/zinc composite undertension decreased with increasing volume percentage of zinc. Cyclic hardeningprocess of 16Mn steel under ±0.5%,±1%,±1.5% strains and with 20 cycles wasnot prominent. However, the maximum tension and compression stresses under±1%,±1.5% strains increased after each cycle, suggesting a cyclic hardeningprocess has taken place. The stresses at maximum strains of the same strain, whichincreased with increasing number of cycles, tended to stabilize with further cycling.The phenomenon of cyclic hardening was more prominent with increasing cyclicstrain.(2) Damping property of 16Mn steel/Zn compositeThere were two methods of evaluating damping property of 16Mn steel/Zncomposite. ①means of energy, the area that was calculated through integratinghysteresis loops reflects damping capacity of materials. The larger the area was, thebetter the damping capacity became. ②means of free attenuation, owing to theattenuation of systemic vibration through energy dissipation, logarithmicdecrement of vibrational amplitude illuminated damping capacity of composite.Because vibrational energy was in direct proportion to the square of amplitude,measuring the ratio of amplitude next to amplitude would work out energydissipation.A contrast between hysteresis loops of 16Mn steel and of steel/Zn compositeconcluded that, under ±0.5%,±1% strains the areas of composite were larger thanthe areas of 16Mn steel, which showed great damping property of composite, andunder ±1.5% strain the areas were the very reverse, because of the plasticdeformation response of zinc in composite. The areas of the compression partialloops ?WC were slightly larger than the areas of the tension partial loops ?WTin composite at the same strain and cycle. The areas of the full loops ?WSgradually tended to stabilize at the same strain with further cycling andsubsequently energy dissipation of steel/Zn composite increased with increasingstrain. The experiments of free attenuation for several different materials have beenperformed. Results showed that logarithmic decrement of zinc and 16Mn steel wasabout the same and that logarithmic decrement of steel/Zn composite varying withtesting direction was better than two simplex materials. Higher decrement of Bdirection than A direction meaned that energy dissipation was fast along B direction.Logarithmic decrement of steel/Zn composite increased with increasing zinc layer. (3) Interfacial microstructure of 16Mn steel/Zn composites The interfacial behavior between zinc and 16Mn steel were preliminarilyrevealed by the studies of the interfacial microstructures of 16Mn steel/Zncomposites. ①It was indicated by SEM analysis that the presence of the bandedinterface between 16Mn steel and zinc was a layer with a width of 40~50um andflat near steel and serration near zinc were found at the interface. ②It wasilluminated by EDS analysis that the content of Fe element distributing in theinterface was higher than zinc and that the content of Zn element was much morein the interface than steel but as much as zinc because the diffusion of Zn elementtowards steel was difficult during the transition from liquid state to solid state. Theinterface was a diffused layer of Zn element and Fe element. ③According to XRDanalysis and Vickers-hardness measurement, interdiffusion reactions between ironand zinc at 550℃should lead to the formation of the following Fe-Zn intermetalliccompound: Γ-Fe11Zn40, δ-FeZn7, FeZn10 and ξ-FeZn13. The interdiffusion zoneconsisted of a thin layer of Γand δphases about 10um in contact with steel,followed by a layer of ξphase in contact with zinc. When Vickers-hardness value...