Investigation of forged-like microstructure produced by a hybrid manufacturing process

This paper aims to summarize the microstructure characterization of parts that were produced using a hybrid manufacturing process consisting of laser metal deposition (LMD) and friction stir processing (FSP). This research was conducted to investigate the evolution of the microstructure following FSP and LMD and to study the possibility of producing or repairing parts with a forged-like microstructure using this hybrid technique.

The microstructure of the nugget regions obtained in the substrate weld, stir over deposit and deposit over stir experiments was investigated.

Highly refined grain size in the order of 1-2 μm was observed where FSP was performed over laser-deposited Ti–6Al–4V. Large equiaxed grains were observed in the experiment where subsequent deposition was carried over the stir. A decreasing grain size was also observed in the dilution zone (DZ) inside the nugget from the stir surface to the bottom of the DZ.

A highly refined microstructure formed from FSP is able to increase the fatigue life by delaying the fatigue crack initiation. Peters et al. (1980) reported that reducing the grain size from 12-15 μm to 1-2 μm in an equiaxed Ti–6Al–4V alloy corresponded with about 25 per cent increase in fatigue strengths at 10,000,000 cycles.

This proposed technical approach is a novel and effective method to produce forged-like parts using a metal additive manufacturing process.