Advanced Materials Research Vols. 194-196

Abstract: Effects of high pressure heat treatment on the microstructure refinement and corrosion resistance of brass were studied by means of metallographic observation, SEM/EDX, profilometer and CH1660A electrochemical instrument. Brass were heated from 23°C to 700°C and kept at 700°C for 10 minutes under high pressure of 1GPa, 3GPa, 4GPa and 6GPa, respectively. The results show that high pressure heat treatment has great influence not only on the microstructure refinement of the alloy but also on its corrosion resistance in HCl solution. Under 3GPa, the refined microstructure can be found and the corrosion resistance of the alloy changes into much worse. However, under a higher pressure of 6GPa, the corrosion resistance increases and the microstructure refining effect is not obvious. All the findings of this work were elucidated in terms of the change in the formation and growing of the crystal under a high pressure heat treatment condition.

Abstract: The influence of deformation on dechromization of CuCr alloy in H₃PO₄ solutions was investigated by static immersion corrosion tests. The properties of undeformed and deformed alloys were characterised by XRD, Metallograph, SEM and X-ray fluorescence spectrometer respectively. It is observed that the deformation plays an important role in dechromization of CuCr alloys in H3PO4 solutions. Compared with undeformed one, the deformed CuCr alloy’s incubation time of corrosion is shortened, the concentration and temperature of H₃PO₄ solutions needed for dechromization decrease. Consequently the tendency of dechromization increases. Surface analysis showed that the microstructure of the dechromization layer is scarcely influenced. Finally, the dechromisation mechanism was discussed.

Abstract: By means of measuring creep curves and microstructure observation, the influence of the element Re on creep behaviour of the single crystal superalloy has been investigated. Results shown that the creep resistance of nickel-based superalloy with element Re may be obviously improved and the 2% Re superalloy had lower strain rate and longer creep lifetimes compared with Re-free single crystal alloy. The activation energy and stress exponent of the 2% Re superalloy during steady state creep were measured to be Q =478.6 kJ/mol and n = 5.1 respectively. The deformed features of the 2% Re alloy during primary creep are dislocation slipping in the matrix channels, dislocation networks are formed by dislocation reaction, and creep resistance may be improved when networks on the γ/γ’ phases interfaces. In the tertiary creep stage, deformation mechanism is the <110> super-dislocation shearing into the rafted γ’ phase.

Abstract: Aging treatment of Cu-17Fe alloy was investigated by a vacuum heat treating furnace in high magnetic furnace. The microstructures were documented using scanning electron microscopy (SEM). The solid solubility of Fe in Cu matrix was analysed by energy spectrometer (EDS). The mechanical properties were measured with a Vickers hardness tester. The electrical conductivity was measured with a micro-ohmmeter. The results showed that high magnetic field can promote spheroidization of the Fe dendrites, the spheroidization intensifies and the solid solubility decreases with the increasing magnetic induction intensity of the high magnetic field exerted to the alloy, the solid solubility of Fe is minimum when the magnetic induction intensity is 10T at 500°C during precipitation. And Cu-17Fe alloy has a good strength/conductivity combination of 110Hv/63%IACS after aging treatment of 10T at 500°C for 1h.

Abstract: The precipitates of bending-age-formed ternary Al-4.31Cu-1.51Mg alloy were studied with load of 6.05 kg aged at 190°C. Transmission electron microscopy and electron diffraction has been used to observe the microstructures of the bend-age-formed alloy. The results show that there is no preferential alignment of S phase or GPB zones in the alloys with load compared with that without load. It is interesting to find that the length of S phase is shorter in age-formed sample than that without load. Dislocations generated after loaded can provide enough nucleation sites for the nucleation and growth of S phase.

Abstract: The use of P92 is becoming more and more widespread in high temperature steam pipe of super-ultracritical power station boilers, it’s key material for the manufacture of boiler’s four main pipes. The properties of P92 are closely related with its microstructure, and the microstructure of P92 has strong relationship with its’ composition and hot processing technology. Three types of P92 with different composition have been prepared. The relationship of delta ferrite between composition, smelting and heat forging process has been investigated for these three samples. The results show that the delta ferrite can be avoided by the adjustment of composition and making process, the delta ferrite will occurred in the matrix of P92 which without delta ferrite before heat treatment if the heat temperature exceed 1200°C , the delta ferrite existed in P92 ingot matrix resulted from the composition cannot be eliminated by hot working and heat treatment.

Abstract: The effects of trace boron on microstructure and mechanical properties of β type Ti-9V-3Al-3Cr-3Zr-3.5Mo (wt. %) alloy have been investigated in this study. Upon the addition of 0.02 wt. % boron, the grain size of the B-modified alloy was almost four times smaller than that of the B-free alloy. Accordingly, the tensile strength and elongation of B-modified alloy increased from 712 MPa and 14.6 % to 813 MPa and 17.9 %, respectively, mainly due to the effect of grain refinement.

Abstract: Based on the empirical electron theory of solids and molecules (EET), the valence electron structures (VESs) of the strengthening phases Al₈Fe₄Ce and Al₄Ce in Al-Fe-Ce alloy were calculated, then the relationships between the VESs and strengthening, stability of the alloy and grain refining were analyzed. The results show that the distribution of the bond network of Al₈Fe₄Ce is uniform, the third and the fourth bonds in the bond network of Al₄Ce is the weakest segment of the whole bond network structure, and the strongest bond in the bond network of Al₈Fe₄Ce and Al₄Ce is stronger than that of the matrix of the alloy. The VES of Al₈Fe₄Ce is favourable to stability of the alloy. During solidifying of the alloy, because the bonds formed by Ce atom and its adjacent atoms are all strong, that hinders Al atoms adjacent to Ce atom to involve in the growth of other grains and at the same time hinders the growth of the Ce atom group, so the structure of the alloy can be refined.

Abstract: The effect of the Sr + RE complex modifications on microstructure and mechanical properties of Al-40 wt% Si alloy were investigated. The results show that Sr + RE complex modification not only on primary silicon and eutectic silicon with modification, but also on dendrite α significantly refine. When the addition of RE remain unchanged, with increasing of the addition of Sr, the primary silicon firstly changes from polygonal block or large plate to small block, then to large polygonal block, edge and corner passivations. The eutectic silicon firstly changes into a fine start with a long needle-like fibrous or branched further to a short stubby dendrite or worm-like, The eutectic silicon changes from needle to a fibrous sheet plus short rod, then to short rod end for the dense, or even granular. The dendrite α changes from highly developed dendritic to equiaxed and uniform distribution. In addition, with increasing of the addition of Sr, the mechanical properties has been significantly improved, tensile strength increased by 37%, elongation is more than double, the hardness increased by 21%. When the Sr addition is between 0.05 wt% and 0.077 wt%, the microstructure and mechanical properties are the best.

Abstract: The influence of cold-worked and aging processes on the microstructures, mechanical properties and conductivity of Cu-Cr-Y alloy has been experimentally investigated. Samples were cut from ingot of Cu-0.8 wt.%Cr-0.05 wt.%Y alloy. They were solution-treated, cold rolled and aging treated. The results show that the Cu-Cr-Y alloy, with 70% deformation and aging at 480°C for 24min, can reach an excellent combination of microhardness and conductivity. The microhardness and conductivity is about 143HV and 84%IACS, respectively. The microstructures by transmission electron microscopy (TEM) show that the fine and dispersed distributed Cr precipitate, which form due to decomposition of the supersaturated solid solution during aging, is responsible for the peak maximum microhardness as it is predominantly present in the peak aged hardening condition.