Solidification Behavior and the Evolution of Phase in Laser Rapid Forming of Graded Ti6Al4V-Rene88DT Alloy

Abstract

The graded material of Ti6Al4V-Rene88DT superalloy, which has shown the potential to be applied in aeroengines, was fabricated from prealloyed metal powders using the technique of laser rapid forming (LRF). A compositional gradient, from 100 pct Ti6Al4V to Ti6Al4V-38 pct Rene88DT, was achieved within a thickness of laser deposit of 54 mm. The solidification behavior and the phase evolution of the compositionally graded material were studied. The results of the X-ray diffraction (XRD) analysis together with the metallographic study showed that a series of phase evolutions, a + b fi a + b + Ti 2 Ni fi b + Ti 2 Ni, along the compositional gradient have occurred. The hardness value of the graded material was measured along the compositional gradient, and the results were explained in terms of the various phases present. The condition for columnar-to-equiaxed transition observed in the graded material was explained, based on Hunt's criterion. Finally, the morphology of b + Ti 2 Ni anomalous eutectic is discussed.

Microstructure evolution in laser solid forming of Ti–50wt% Ni alloy

“…4b) with increasing laser power under high scanning velocity. There are still different opinions about the formation mechanism(s) of anomalous eutectic [20][21][22]. To better underline the structure evolution process, a schematic diagram showing the solidification processes and the forming mechanisms was shown in Fig.…”

The effect of Cu rejection in laser forming of AlCoCrCuFeNi/Mg composite coating

“…7a). Such a transition in growth morphology is common in laser cladding, and is mainly due to the variation in constitutional undercooling resulting from the solute piling up in front of the solid/liquid interface during the processing [36]. In the middle of region II, the HEA particles were mainly surrounded by the Mg phase.…”

Microstructure and tensile properties of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe near β titanium alloy

“…Generally, in directional solidification, solutes will pile up ahead of the solidification interface, and constitutional supercooling will occur. This could lead to the nucleation of equiaxed grains [23,24]. Meanwhile, with the solidification going on, both cooling rate and temperature gradient will decrease at the top of melting pool, and promote the formation of equiaxed grains.…”