The Effect of γ″ and δ Phase Precipitation on the Mechanical Properties of Inconel 718 Manufactured by Selective Laser Melting: An In Situ Neutron Diffraction and Acoustic Emission Study

The deformation behavior of additively manufactured Alloy 718 in as-built condition and after annealing was studied in situ under tensile loading along the build direction. Pre-characterization by synchrotron X-ray diffraction and electron microscopy revealed a significant amount of γ″ precipitates in the as-built samples, whereas the γ″ phase was entirely consumed and needle-like δ precipitates appeared in the annealed sample. In situ neutron diffraction (ND) and acoustic emission (AE) enabled indirect observation of the role of the precipitates on the mechanical behavior. ND provided information on the load accommodation in the matrix, while AE detected a strong signal from the interaction of dislocations with the δ-phase precipitates during deformation of the annealed samples. The results imply that in the annealed samples the matrix sheds the load to the precipitates, while in the as-built material the matrix bares a significant load.

Acoustic Emission Study of Fatigue Crack Propagation of Weld Joint for X52 Pipeline Steel

The crack propagation of different weld joint samples were detected by acoustic emission (AE) technique. The samples were from the basic metal, weld seam and heat affected zone (HAZ), The results showed that the crack growth rate of basic metal was higher than weld seam and HAZ because of the transverse compressive residual stress in joint. But the coarse of grains was the reason for higher rate of weld seam than that of HAZ. And AE waveforms of crack propagation from three microstructures were different. The most compositions of AE signals were higher frequency of 300KHz for weld seam and lower one of 100KHz for basic metal and HAZ.