Hangyue Li

Characterization of Dissimilar Linear Friction Welds of α-β Titanium Alloys

Characterization of dissimilar linear friction weld (LFW) of Ti-alloys has been carried out. The microstructure of a Ti-64 with Ti-6246 weld was analyzed using scanning and transmission electron microscopy. The microtexture of the weld was examined using electron back-scattered diffraction (EBSD) and the microhardness was measured. The dissimilar LFW weld shows an interface at the central weld zone (CWZ) with strong contrast. The element distribution measured using energy-dispersive X-ray spectrometer suggests that only limited atomic diffusion occurred during welding. In the weld region, the hardness of Ti-64 shows an increase while that of Ti-6246 shows a decrease, compared with the respective parent materials in as-welded condition. After post-weld heat treatment, a hardness increase was observed in Ti-6246, while Ti-64 shows no significant hardness increase. Although the EBSD pattern quality is poor in the CWZ at the as-welded condition, the pattern quality of the post-weld heat-treated sample shows that both the Ti-64 and Ti-6246 have similar texture.

Characterization of the Weld Line Zones of an Inertia Friction Welded Superalloy

The Inertia Friction Welding (IFW) process is a high-temperature and high pressure process, with heavy plastic deformation, high power density, fast heating and fast cooling of the weld material. The microstructure produced in the weld line （WL）zones is therefore very different from parent material. A detailed microstructural investigation of the WL zones has been conducted using transmission electron microscopy and scanning electron microscopy. It has been shown that the morphology, energy status and microchemistry of grain boundaries in the WL zones are quite different from those in the parent material. It is also observed that, compared to a bi-modal distribution of intragranular ¢ particles in the parent material, a unimodal distribution of very fine spherical ¢ particles is produced in high density in the WL zones. This work provides a detailed understanding of the physical and chemical changes occurring across the weld line.

Effect of prior oxidation on high cycle fatigue performance of RR1000 and role of oxidation in fatigue crack initiation

Abstract The effect of prior oxidation on the room temperature fatigue life of coarse grained Ni based superalloy, RR1000 has been performed at an R ratio of 0·1 with two pre-oxidation times: 100 and 2000 h at 700°C. These pre-exposures produce extensive oxidation damage. The room temperature high cycle fatigue life of the pre-oxidised specimens has been compared to as received specimens. At a maximum applied stress of 800 MPa a significant fatigue life deficit is observed in the pre-oxidised testpieces. This is accompanied with the observations of significant cracking of the external chromia scale and the intergranular internal oxides within the area of maximum stress. Preferential cracking of oxides may lead to early crack initiation and consequently a reduction in total fatigue life.

Accompanying data for "On the effect of Nb on the microstructure and properties of next generation polycrystalline powder metallurgy Ni-based superalloys"

The data has been labelled with the same designations as used in the corresponding paper. Raw data is provided from differential scanning calorimetry and scanning electron microscopy following the various heat treatments and oxidation analyses. In addition, data is provided from the tensile, creep and dwell tests performed and the outcomes of the mechanical property modelling are also given.

On the Effect of Nb on the Microstructure and Properties of Next Generation Polycrystalline Powder Metallurgy Ni-Based Superalloys

The effect of Nb on the properties and microstructure of two novel powder metallurgy (P/M) Ni-based superalloys was evaluated, and the results critically compared with the Rolls-Royce alloy RR1000. The Nb-containing alloy was found to exhibit improved tensile and creep properties as well as superior oxidation resistance compared with both RR1000 and the Nb-free variant tested. The beneficial effect of Nb on the tensile and creep properties was due to the microstructures obtained following the post-solution heat treatments, which led to a higher γ′ volume fraction and a finer tertiary γ′ distribution. In addition, an increase in the anti-phase-boundary energy of the γ′ phase is also expected with the addition of Nb, further contributing to the strength of the material. However, these modifications in the γ′ distribution detrimentally affect the dwell fatigue crack-growth behavior of the material, although this behavior can be improved through modified heat treatments. The oxidation resistance of the Nb-containing alloy was also enhanced as Nb is believed to accelerate the formation of a defect-free Cr2O3 scale. Overall, both developmental alloys, with and without the addition of Nb, were found to exhibit superior properties than RR1000.