Papers by Author: Shou Ren Guo

Abstract: Microstructure and mechanical properties of Ni-Cr alloys with various contents of Phosphorus (P) have been investigated. It is found that the increase of phosphorus refined dendritic structures in as-cast alloys and decreased micro-segregation of Chromium (Cr) element. α-Cr which precipitated during hot-rolling process was obviously inhibited by phosphorus because of its prior occupancy on grain boundaries and decreasing precipitation driving force of α-Cr. Tensile and impact properties were examined on samples under different heat treatments. Though the yield strength of as-rolled alloys was increased by precipitation of α-Cr, the elongation and impact energies were reduced. It is worthy to note that impact energies of samples solutioned at 950°C increased with the increasing phosphorus. The results indicated that dislocations are markedly effected by phosphorus which is probably the reason for improving impact energies.

Abstract: The hot deformation behavior and microstructure of rolled Inconel 625 alloy have been studied from 930°C to 1180°C, and at strain rate from 10 s-1 to 80 s-1, respectively. The results indicate that, as deformation temperature rises, both peak flow stress (PFS) and recrystallization critical strain (RCS) decrease; as the strain rate increases, the PFS is enhanced, but the RCS drops. When the deformation temperature is within 1100°C and 1180°C, the grain size coarsens markedly with the temperature increasing. When the deformation temperature is lower than 1100°C，a higher strain rate is helpful for grain refinement. However, when the temperature is beyond 1100°C,the effect of strain rate on the grain size is reduced.

Abstract: The effects of P on element segregation, Laves phase dissolution and elemental diffusion in GH706 alloy have been investigated. The results show that P promotes the segregation of Nb and Ti. Phosphorus was enriched in Laves phase, which enhanced the precipitation of blocky Laves phase, while constrained the formation of eutectic Laves phase. Moreover, more needle-like phase was formed around blocky Laves phase in high P-doped alloy. It also demonstrated that P slightly lowered the melting-point of Laves phase. During the homogenization process, P hindered the diffusion of Nb which blocks the diffusion of Nb and dissolution of Laves phase, and complicated the homogenization treatment.

Abstract: The effect of phosphorus in some typical wrought superalloys including IN718, GH761 and GH4133 has been studied. Phosphorus was not dissolved in the γ matrix of superalloys and was segregated in the residual liquids seriously during solidification, and the solidification of the alloys added with phosphorus was always finished by the precipitation of a phosphorus bearing phase. Two factors controlling the segregation tendency of a minor element were determined, one is the solubility of the element in the matrix, another is the precipitation temperature of a phase in which the element is absorbed. The detrimental effect of phosphorus on the solidification could be eliminated by a proper homogenization treatment. Phosphorus improved the stress rupture properties of the alloys with a fine grain structure. By combining the grain refinement with phosphorus addition, the properties of GH761 alloy was improved efficiently.