Microtexture developed during Laser Metal Deposition (LMD) of Ti-6Al-4V
Résumé
Additive manufacturing of metallic objets has attracted significant attention in a broad range of sectors including aerospace, defense and biomedical. Whereas one of the main advantages of this technique is, from a manufacturing point of view, its versatility, a critical issue is the control of the microstructure that plays a key role on the consistency of the properties. However only a limited number of studies have yet focused on the thorough description of the microstructure by additive manufacturing techniques. The aim of this work was thus to analyze the microstructure of bulk samples prepared by additive manufacturing of Ti-6Al-4V (Ti64) powder by mean of the CLAD® technique (laser blown powder processing) developed at IREPA LASER. The very high cooling rate resulting from this process induced the formation of the martensitic α' phase in the form of thin needles. Using Merengue 2 software developed at LEM3, the analysis of the martensitic phase orientation by EBSD enables the reconstruction of the primary β-phase that formed at high temperature. Microstructural observations performed at various locations within the samples revealed marked heterogeneities in the microstructure. After the first deposited layer characterized by fine and equiaxed β grains, the β grains located in the central region of the samples tend to grow in a direction perpendicular to the deposited layer plan with a coarse columnar structure. By opposition, the grains on the sample side were found to grow at angle of about 60° from the deposited layer plan. The main difference with others additive manufacturing techniques is that, only a weak crystallographic texture was detected in these samples prepared by CLAD®.