Precipitation of grain boundary in a laser deposited compositionally graded Ti–8Al–xV alloy – an orientation microscopy study

摘要

A graded ternary Ti–8Al–xV alloy (all compositions in wt) has been deposited using the laser engineered net-shaping (LENS~(TM)) process. A compositional gradient in the alloy, from binary Ti–8Al to Ti–8Al–20V, has been achieved within a length of ～25 mm. The feedstock used for depositing the graded alloy consisted of elemental Ti, Al, and V powders. Due to the columnar growth morphology of the β grains in these LENSTM deposited Ti alloys, the same prior β grain boundary often extends across lengths ～10 mm. Using orientation microscopy techniques in a scanning electron microscope, the crystallography of precipitation of grain boundary β across the same boundary with changing composition has been investigated in detail. It was observed that while most grain boundary β precipitates maintain a Burgers or near-Burgers orientation relationship with only one of the β grains, a few of these precipitates develop a Burgers orientation relationship with the other β grain. In some rare instances, the grain boundary β did not develop a Burgers or near-Burgers orientation relationship with either β grains. Interestingly, in many cases while the grain boundary β maintained Burgers relationship with one of the β grains, precipitates of two different variants decorated the boundary, in a near-alternate fashion.