Heterogeneous Combustion of Ti/Si/C Powders with Estimated Ti3SiC2 Routes Morphologies

In this study, about 62.2 wt% Ti3SiC2 was synthesized via tungsten inert gas (TIG) welding method, as potential in advanced material applications. This arced sample was characterized using XRD and FESEM analysis to observe the phase presence, and its morphology. Ti3SiC2 phase favours to form at 5 s and produces elongated platelets (Ti3SiC2) grain, micro-porous equiaxed (TiC) grain and melt regions (Ti-Si), when observed at the dense surfaces. Meanwhile, fine dendrite, quasi-spherical, and pyramidal grains were observed at the pore sites. The laminate dendrite of Ti3SiC2 was estimated to form at the origin of TiC faced pyramidal crystal, which nucleated toward TiC pyramidal crystal surface at the specific angle.

REFINED DENDRITE AND PRECISE ORIENTATION OF NICKEL-BASED MONOCRYSTAL SUPERALLOY WITH MELT SUPERHEATING TREATMENT

Ni -based monocrystal superalloy with fine dendrite, precise orientation and finally elevated service performance is required as turbine blades in advanced aeroengine. In this paper, the melt superheating treatment is carried out for DD3 single crystal superalloy during directional solidification processing. The thermal gradient of solidification interface remains constant for different melt superheating temperatures with the appropriate superheating treatment regulation. It is shown that with the melt superheating temperature increased from 1500°C to 1640°C and then to 1780°C respectively, both the primary and the secondary dendrite arms are obviously refined and the dendrite segregation ratios of Mo , W and Ti are reduced while the deviation angle of (001) crystal orientation can all be controlled within 5°. The dendrite structure refinement and the crystal orientation consistence should be attributed to the melt structure change and heredity which is caused by the superheating treatment.

Influence of Nucleating Additions on the Crystallization in the CaO-MgO-Al2O3-SiO2 Glass-Ceramics

The crystallization behaviors and microstructural developments in the CaO-MgO- Al2O3-SiO2 glass with Fe2O3, ZrO2 and F as additives were investigated by using scanning electron microscopy, X-ray diffraction and differential scanning calorimetry techniques. In the glass sample with 1.0wt% Fe2O3, only surface crystallization were observed, in which a three-layer compound surface containing the fine dendrite, finer fibrous morphology and particle-shaped crystals was formed respectively from the near free surface to the inner region. The crystalline phases precipitated were anorthite and wollastonite at 1000°C, and diopside at 1040°C. The addition of ZrO2 suppressed the nucleation and growth of the crystalline phases. The addition of another 4.0wt% fluorine into the glass with a pair of 1.0wt% Fe2O3 and 2.0wt% ZrO2 induced the bulk crystallization, the surface and bulk crystallizations were both observed at 1040°C. At the surface, a three-layer morphology, which had similar morphology to the glass with 1.0wt% Fe2O3 was formed. In the bulk region, the block-shaped crystalline phases were precipitated homogeneously in the residual glass.

Laser Welding of SSM Cast A356 Aluminium Alloy Processed with CSIR-Rheo Technology

Samples of aluminium alloy A356 were manufactured by Semi Solid Metals HPDC technology, developed recently in CSIR-Pretoria. They were butt welded in as cast conditions using an Nd:YAG laser. The base metal and weld microstructure were presented. The effect of different heat treatments on microstructure and mechanical properties of the welds were investigated. It was found that the fine dendrite structure of the weld metal contributed for equalizing the mechanical properties of the joint.