Luchun Zhou

8.5Nb-TiAl alloy with fine grains

Abstract One 8.5Nb–TiAl-based alloy, whose nominal chemical composition is Ti–45Al–8.5Nb–0.3W–0.3B–0.05Y at% (TAWBY) was presented, including various annealing treatments after cladding insulting forged with homogeneous microstructures. This alloy was developed as cast grains with the size of 25 μm whereas the β (B2) phase exists in TAWBY alloy. The mechanical properties were conducted in the field of tensile tests at ambient and elevated temperature, fracture toughness, and plasticity behavior tests. Finally, the microstructures and phase analysis were also observed by OM, TEM and SEM methods. The mechanical properties for TAWBY alloy were compared with Ti–46Al–5Nb–1W, Ti–48Al–8Nb–1B, Ti–44Al–4Nb–4Zr–1B, Ti–47Al–2Nb–2Cr–4Ta and K5 alloys. TAWBY alloy was shown to have the best properties. Under the same conditions, TAWBY alloy exhibits the same perfect properties as the K5 alloy and so on.

2.7 μm InAs quantum well lasers on InP-based InAlAs metamorphic buffer layers

This work reports 2.7 μm InAs/In0.6Ga0.4As quantum well lasers on InP-based metamorphic InxAl1−xAs graded buffers. X-ray diffraction measurement shows favorable strain compensation effect in the quantum wells. Type-I photoluminescence emission is observed around 2.7 μm at 77 K and red-shifts to 3 μm at 300 K. The continuous-wave lasing wavelength of the laser reaches 2.7 μm at 77 K, which is the longest wavelength from the interband lasing of InP-based antimony-free structures. The threshold current density is as low as 145 A/cm2 and the continuous-wave output power at injection current of 400 mA is over 5 mW.

First light on the 127-element adaptive optical system for 1.8-m telescope

A 127-element adaptive optical system has been developed and integrated into a 1.8-m astronomical telescope in September 2009. In addition, the first light on a high-resolution imaging for stars has been achieved (September 23, 2009). In this letter, a 127-element adaptive optical system for 1.8-m telescope is described briefly. Moreover, star observation results in the first run are reported. Results show that the angular resolution of the system after adaptive optics correction can attain 0.1 arcsec, which approaches the diffraction limit of 1.8-m telescope at 700-900 nm band.

InP-based type-I quantum well lasers up to 2.9 μm at 230 K in pulsed mode on a metamorphic buffer

This work reports on up to 2.9 μm lasing at 230 K of InP-based type-I quantum well lasers. This record long wavelength lasing is achieved by applying InP-based Sb-free structures with eight periods of strain-compensated InAs quantum wells grown on metamorphic In0.8Al0.2As template layers. The continuous-wave threshold current density is 797 A/cm2 and the idealized extrapolated threshold current density for infinite cavity length is as low as 58 A/cm2 per quantum well at 120 K. This scheme is a promising pathway for extending the wavelength range of type-I quantum well lasers on InP substrates.

Atomic imaging of the interface between M23C6-type carbide and matrix in a long-term ageing polycrystalline Ni-based superalloy

Besides the well-known cube-on-cube orientation relationship (OR) between M23C6 carbide and matrix, we have determined a new OR named as the twin-related OR in a long-term ageing Ni-based superalloy on the basis of the extensive and detailed electron diffraction analyses. Furthermore, by means of atomic-resolution high angle annular dark-field imaging technique which is implemented in the aberration-corrected scanning transmission electron microscope, we elucidated the interfacial characteristics between M23C6 and matrix for above two types of ORs. Taking into account of the interfacial characteristics, we propose that the twin-related OR possesses a higher total interfacial energy. Thus, its frequency of occurrence is lower than that of the cube-on-cube OR though both ORs are usually seen in the long-term ageing samples.

InAs/In0.83Al0.17As quantum wells on GaAs substrate with type-I emission at 2.9 μm

This work reports on InAs quantum wells (QWs) grown on GaAs-based metamorphic In0.83Al0.17As buffers for type-I mid-infrared (MIR) emission. X-ray diffraction and Raman measurements show that the GaAs-based quantum wells have similar lattice and strain conditions with the InP-based structure. Atomic force microscope shows the smoother surface of the structure on GaAs substrate. For the GaAs-based quantum wells, favorable photoluminescence emission at 2.9 μm at 300 K has been achieved, and the optical quality is comparable to the structure on InP substrate. It is promising to employ this metamorphic quantum well structure for the demonstration of GaAs-based antimony-free mid-infrared lasers.

Progress on the 127-element adaptive optical system for 1.8m telescope

The 127-element adaptive optical system for the 1.8m astronomical telescope is being developed. In this system, the wavefront correction loop consists of a 127-element deformable mirror, a Hartmann-Shack (H-S) wavefront sensor, and a high-speed digital wavefront processor. The tracking system consists of a tip-tilt mirror, a tracking sensor and a tracking processor. The wavelength for the H-S wavefront sensor ranges from 400-700nm. The imaging observation wavelengths range from 700-1000nm and 1000-1700nm respectively. In this paper, the optical configuration of 1.8m telescope will be briefly introduced. The 127-element adaptive optical system is described in detailed. Furthermore, the preliminary performances and test results on the 127-element adaptive optical system is reported.

Interfacial precipitation of the M5B3-type boride in Ni-based superalloys

Abstract Microstructural characteristics of an experimental Ni-based superalloy with boron addition subjected to a long-term ageing treatment were systematically investigated by various kinds of transmission electron microscopy technique. Based on detailed electron diffraction analyses, we found that there are many nanosized M5B3 precipitates in our long-term ageing alloys, which keeps a good orientation relationship with the γ/γ′ matrix. Furthermore, the precipitation characteristics of M5B3 phase were clarified. It is found that the M5B3-type boride prefers to precipitate at the γ/γ′ interfaces and low-angle grain boundaries. These interfacial nanosized precipitates can play the role of pinning effect and are expected to be advantageous for postponing the γ′ rafting and low-angle grain boundary migration to some extent at high temperature.

Performance on the 61-element upgraded adaptive optical system for 1.2-m telescope of the Yunnan Observatory

The 61-element upgraded adaptive optical system for the 1.2m telescope of Yannan Observatory for astronomical observation had been in operation since May 2004. In this paper, the 61-element upgraded adaptive optical system for 1.2m telescope of Yunnan Observatory will be briefly described. The performance on the 61-element upgraded adaptive optical system is analyzed. Furthermore, the observational results for the stars will be presented.

Microstructural characterization of the M23C6 carbide in a long-term aged Ni-based superalloy

Abstract The microstructural features of M23C6 carbide in a long-term aged heat- and corrosion-resistant Ni-based superalloy have been investigated in detail using various kinds of transmission electron microscope (TEM) techniques. It is found that TEM contrast, which is related to structural and chemical inhomogeneities inside the grains, always exists in the interior of grains in the alloy. The structure of these inhomogeneous regions has been determined to be the same as that of the γ′ and t-M23C6 phases, where t-M23C6 indicates a transitional and metastable phase. Although possessing the same structure as the M23C6 phase, the chemical composition of the t-M23C6 is different from that of the M23C6 phase. Compared with M23C6, t-M23C6 is richer in Ni, Co, Al and Ti but poorer in W, Mo and Cr. This phenomenon of structural and chemical inhomogeneity demonstrates that pristine M23C6 carbide (p-M23C6) precipitated in standard heat-treated samples is unstable. Therefore, upon long-term ageing treatment, Ni, Co, Al and Ti may locally enrich inside the p-M23C6 phase, finally forming the γ′ phase, which can be described by the decomposition reaction p-M23C6 → M23C6 + γ′.