Studies on the effect of composition and pre-heating on microstructure and mechanical properties of direct laser clad titanium aluminide

The present study aims at understanding the microstructure, and mechanical properties (micro hardness, nano-hardness, young's modulus and compressive strength) of different commercially available TiAl alloys with the composition of Ti-45Al-2Nb-2Mn-0.8B(4522XD), Ti-44Al-4.5Nb-1Mo-0.15B (TNMB-1) and Ti-47.5Al-2Nb-2Cr (GE4822) developed by direct laser cladding (DLC) using a high power Nd:YAG laser with adapted parameters for laser power, velocity and powder feed rate. DLC has been carried out by feeding the powder into the interaction zone of laser beam and substrate (GE4822), forming a melt pool which subsequently solidifies rapidly, to build bulk volumes with the dimension of 10 × 10 × 10 mm³. The effect of preheating at 1053 K (780 °C) and shrouding environment on the characteristics and mechanical properties has also been studied in details. Direct laser cladding leads to continuous and defect free microstructures. However, the microstructures (both the morphology and grain size) were found to depend on the composition of ternary elements and to some extent on the preheating. There was a marginal coarsening of microstructure when cladding was performed by simultaneous heating. There was predominantly, g and a2 phases present in the microstructure, which was confirmed by detailed transmission electron microscopic observation. There was a marginal decrease in hardness due to heating. The maximum improvement in hardness was found for the alloy 4522XD. A detailed study of compressive property showed that a maximum improvement in compressive strength was observed in alloy 4822 in both with and without pre-heating.