Additive manufacturing of Stellite 6 alloy by laser-directed energy deposition: Engineering the crystallographic texture

Abstract

Additive manufacturing (AM) of Stellite 6 alloy using laser-directed energy deposition (L-DED) technology was explored. The impact of argon and nitrogen as the shielding gas atmosphere and of the laser processing parameters on the microstructural characteristics of the L-DED manufactured single- and double-layers of the Stellite 6 alloy were studied. The microstructural characteristics and mechanical properties of the additively manufactured Stellite 6 alloy were investigated using electron backscatter diffraction (EBSD) analysis and indentation micro-hardness measurements. Also, the tribological behavior of the processed Stellite 6 were studied under different loading conditions. Based on the observed structural evolution including the phase transformations, optimized process parameters were established for the building of the main structural wall of the Stellite 6 alloy. Subsequently, the optimized set of processing parameters was analyzed in connection to the crystallographic textural majority of the manufactured alloy. The overall homogenous solidification microstructure of the constructed wall was characterized along different sections, i.e., bottom, middle, and top regions. At the bottom, the microstructure was dominated by gradients due to the solidification mechanism and the formation of a combined equiaxed/columnar dendritic structural morphology upon rapid cooling, resulting in a heterogeneous distribution of mechanical strength. The microstructure mainly consisted of columnar dendrites, generating a dominant textural component of 100<013> with a J-index of 1.62 in the matrix. After L-DED, the hardness of the alloy was found increased up to 565 HV, with a mean value of about 430 HV, depending on the geometrical location across the manufactured alloy wall. Also, a superior wear resistance of 4.91 × 10−5 mm3/Nm under a maximum load of 50 N was observed as a result of the enhanced mechanical properties. In fact, these findings substantiate an exciting approach to develop material properties with respect to processing design in which an advanced alloy is manufactured in a single step without particular post-processing.