Research On Preparation And Microstructure And Properties Of Fe-Cr-W-Ti-Y Superalloy

In this thesis, the development of iron–based superalloys, and mechanical alloying (MA) and MA iron-based superalloys were reviewed. Based on the above work, kinds of Fe–12Cr–2.5W–0.4Ti–0.25Y superalloy powder were prepared by mechanical alloying (MA). Then this superalloy was prepared by annealing, compressing moulding and sintering. The effects of milling time and the content of process controlling agent (PCA) stearic acid (SA) on this superalloy powders and the effects of compressing moulding and sintering process on microstructure and properties of this superalloy were studied, by means of relative density test, hardness test, tensile test, X–ray diffraction analysis (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and energy depressive analysis (EDS).Milling paraments and the content of SA significantly affected flour yield and such powder characteristics as alloying processing, grain size, lattice distortion, et al. When milling time was short, flour yield was high but alloying processing was not intensive. With increasing milling time, flour yield slightly decreased, but alloying processing was intensive, and grain size reached nano size and lattice distortion increased. However, when milling time was too long, grain size remained and lattice distortion decreased. When the content of SA was too high, alloying processing was not ideal. Under the condition of the ball to powder weight ratio 20: 1 and rotation speed 400 rpm, 1.5~2.0 wt% SA and milling time 48 h were helpful to obtain powders with good MA effect and high flour yield.The working hardening effect of MA powders weakened after they were annealed at 900℃for 3 h under hydrogen atmosphere, and they were suit for compressing moulding with pressing strength 600 MPa and holding time 60 s.Milling time and the content of SA obviously affected microstructure and properties of this superalloy. Relative density and hardness of specimen prepared with powders by MA 48 h were higher than those of specimen prepared with powders by MA 24 h. Relative density and tensile strength of specimen prepared with powders containing 2.0 wt% SA by MA 48 h were higher than those of specimen prepared with powders containing 0~1.5wt% SA by MA 48 h. Sintering temperature affected microstructure and properties of this superalloy. When sintering temperature was 1250℃, porosity was low and tensile strength was high.