Jin Jiang Yu

Mechanical Behaviour of a Single Crystal Superalloy DD32 - A Comparison with the Alloy SRR99

Stress rupture and tensile properties of a single crystal superalloy DD32 are investigated comparing with the alloy SRR99. It is shown that the alloy DD32 offers an improved creep temperature capability of more than 60°C at higher stresses. The g¢ precipitates in the stress ruptured samples were rafted to P-N type directional coarsening. The fracture mechanism of the stress ruptured samples was initiated from the micropores.

High Energy, High Efficiency Nd: Glass Regenerative Amplifier

To obtain high energy, high efficiency Nd: glass preamplifier used in certain host device, a Nd:glass regenerative amplifier system has been designed. By adjusting the single pass gain and carefully optimizing the cavity mode, the small-scale self-focusing effect in the gain medium was effectively controlled. Maximum pulse energy of 21mJ, pulse width of 2.6ns was obtained at the repetition frequency of 1Hz, corresponding to a high optical to optical conversion efficiency of 11% and amplification ratio of 108. The pulse to pulse energy stability was < 2% rms during 2 h continous operation. The laser has a good beam quality of M2=1.5. The spectrum was measured to be at center wavelength of 1052.915nm.

Influence of Aging Temperature on the Microstructure and Stress Rupture Property of DZ951 Alloy

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.

Design and Analysis of Flat-Top Beam Produced by Diffractive Optical Element

The modified Gerchberg-Saxton (G-S) methods of diffractive optical elements are presented for converting a Gaussian beam into a flat-top beam. The sample points of the input and output planes are discussed based on the sampling principle. The relationship between weighting factor, empirical constant, diffractive efficiency, and intensity uniformity is investigated. The simulation results of different modified methods are calculated when the incident beams are the same. The results show that the intensity uniformity of the output flat-top beam is the best when using the ST modified method.

Microstructure Characteristic of Directionally Solidified NTS-09C Alloy

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.

Recycled Applications of a Single Crystal Superalloy

The effects of application of recycled scraps on the composition, microstructure and mechanical properties of SRR99 alloy were studied. The compositions of recycle master alloy are similar to that of the fresh alloy. However, nitrogen content, the size and amount of microporosity increase significantly with the recycle material proportion. Granular, lamellar and strip-like MC particles mainly represent in the interdendritic regions of the revert alloy. With the addition of the recycled material proportion, the amount of the granular ones rapidly drop and the lamellar ones gently enhance. The stress rupture life decline with the addition of the recycled material proportion. The oxide and sulphide inclusions in revert superalloy can be effectively captured and removed by a foam ceramic filter so that the tensile and stress rupture property has been significantly improved.

Temperature Dependence of High-Cycle Fatigue Behavior of a Ni-Base Single Crystal Superalloy

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.