Papers by Author: Zhuang Qi Hu

Abstract: The wetting behavior and the interaction at the liquid-solid interface are significant in preparation of metallic glass composite. In this paper, the wetting behavior and the interfacial interaction between Ti_32.8Zr_30.2Ni_5.3Cu₉Be_22.7 (denoted as ZT3) bulk metallic glass (BMG) alloy melt and Ti6Al4V (denoted as TC4) substrate at different temperatures were investigated using sessile drop method. The results show that ZT3 alloy melt wetted the substrate well. With the increase of temperature, the droplet spread out rapidly and then came to equilibrium gradually. The equilibrium contact angle under 1273 K stabilized at about 15°. Dendrite phase generated at the interface during the wetting progress. The composition of the interface product transformed from Ti_69.8Zr_24.2Al_2.2V₁Cu_2.8 to Ti_73.6Zr_15.3Al₅V_2.7Cu_2.6Ni_0.8 with the temperature rising from 973 K to 1273 K. Meanwhile, the dissolution of the TC4 substrate increased with increasing the temperature.

Abstract: The directionally solidified Nb-Ti-Si-Cr-Al-Ta-Hf-C-B (NTS-09C) superalloys were prepared by HRS method. This alloy with strong orientations of (Nb, Ti)ss and Nb-silicide along the growth direction consists of (Nb,Ti)ss, (Nb,Ti)3Si, Nb5Si3, MC carbide and C14 Laves phases. Not only the morphologies and compositions of various phases have been systemically studied, but also the formation mechanisms have been analyzed and discussed in detail.

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: A single crystal Ni-base superalloy was prepared with five withdrawal rates: 2, 4, 6, 7 and 10 mm/min. Microstructures including dendrite arm spacing, element segregation, and porosity of the as-cast superalloy were investigated. The results showed that as the withdrawal rate increasing, the primary and secondary dendrite arm spacing decreased markedly, the γ/γ′ eutectic became smaller and more dispersive. Meanwhile, when withdrawal rate was higher, W, Ti, Ta and Al segregated in comparatively larger extent. Furthermore, as the withdrawal rate increasing, the amount of alloy microporosity increased, though the size of which decreased gradually. It can be concluded that the withdrawal rate of 4 mm/min and 6 mm/min are optimal for the experimental alloy.

Abstract: The effect of rhenium on the microstructure and mechanical properties of single crystal superalloys with a nominal composition of Ni-3Cr-12Co-1Mo-6W-6Al-8Ta-0.1Hf-(0, 2, 4) Re has been studied. With the rise of rhenium content, the size of as-cast  particles becomes smaller. Rhenium addition elevates the incipient melting temperature and slows down the solid solution process. Even after 2000h prolonged aging both at 950°C and 1050°C, no topologically close-packed phase precipitation is found in the three alloys with Re content up to 4%. Re retards the  coarsening and is beneficial to improving the stress rupture life. The deformation mechanisms together with the dislocation configuration have been studied and discussed.

Abstract: Multifarious fracture features, such as coarse rive-like, micro holes, rugged and flat fracture surface, were systematically investigated in the monolithic Cu46-xZr45Al7Gd2Agx (x=0, 0.5) bulk metallic glasses. The fracture planes presented different angles with the loading direction. These fracture features were completely different from the typical fracture characteristics of amorphous alloys, i.e. vein-pattern and fracturing approximately along the maximum shear stress plane. On the other hand, some tiny strips with about 50 nm intervals were also detected on the flat fracture plane. The preliminary discussions on the formation mechanisms of these exceptional features were presented.

Abstract: a kind of as-cast nickel-base single crystal superalloy was TLP bonded using Ni-Cr-B amorphous foil at different temperatures. Special attention is paid to the formation of boride in diffusion zone of TLP joints at different conditions. The chemical composition and microstructure of borides were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At different bonding temperature, M3B2 precipitates appear distinct morphologies. At 1200°C, both blocky and plate-like borides formed owing to the diffusion of boron atoms into base metal and precipitation during the cooling process. At 1230°C or above, due to the diffusion of boron atoms the constitutional liquation of original γ/γ′ eutectics in the base metal occurs and borides formed when the system was cooled to room temperature. The analysis of TEM results reveals that M3B2 has a tetragonal structure and is rich in Mo, W, and Cr elements.

Abstract: Effect of different aging temperatures on microstructure and stress rupture properties of DZ951 alloy were investigated in this paper. The results show that the shape of carbide changed from script-like in as-cast alloy to block during different aging treatments. MC carbide degrades into M23C6 at the aging temperature of 970°C, which made alloy have a better combination of strength and ductility than that at other aging temperatures. The size of γ′ phase increases and the shape of γ′ phase changed from sphere (870°C) to quasi-cuboid (920°C) and cuboid (970°C) with the increasing aging temperature. The stress rupture life of DZ951 alloy at 1100°C/60MPa improves with the increased of aging temperature. The fractographs at different conditions showed a ductile fracture mode.

Abstract: Smooth specimens of single crystal (SC) superalloy SRR99 with [001] orientation were subjected to high-cycle fatigue (HCF) loading at temperatures of 700°C, 760°C, 850°C and 900°C in air atmosphere. The results demonstrated that conditional fatigue strength reached the maximum at 760°C and decreases with increasing temperature. Analysis on fracture surface showed a trend for cleavage rupture at 850°C and 900°C and ductile rupture at 700°C and 760°C. Fatigue cracks initiated at the surface or subsurface were primarily responsible for the ultimate failure. The influence of testing temperature on fatigue lifetime was studied by examining evolution of the microstructure through SEM observation. With the process of cyclic loading at elevated temperatures, the primary cuboidal γ′ precipitates tended to agglomerate and spheroidized, meanwhile a larger number of secondary γ′ particles were formed in the γ matrix in specimens fatigue tested at 700°C, which would have a significant effect on the high temperature properties.