A new tool for In-Process identification of micro- and macro-defects during Vacuum Arc Remelt processing of reactive and super alloys

It has been well documented that the fluid flow within the melt pool during vacuum arc remelting (VAR) can alter the solidification of the metal, causing changes in both the local chemistry and morphology. These changes manifest as defects such as white spots, freckles, or tree-rings. It is equally well documented that changes in fluid flow are a resultant of the arc dynamics associated with VAR processing. To this end, special attention has been paid to the statistical characterization of the operating conditions to constrain the arc dynamics within an acceptable range. This leads to the creation of “melt recipes” which provide a confidence level that defects aren’t created during the VAR process step. Yet, these types of defects persist even today as evidenced by the Flight 383 (October 28^th, 2016) and similar uncontained engine failure events. As the demand for more efficient engines, for example, drives more extreme operating conditions, the resultant demand for fewer and smaller defects becomes paramount. VARmetric is a new measurement system designed to solve exactly this problem. Utilizing the magnetic fields associated with the arc motion, VARmetric “images” the arc dynamics, providing a real time map of heat flux into the melt pool while also providing the necessary 3-D boundary conditions for a digital twinning approach to ingot quality prediction. Here, we identify certain operating conditions during VAR melting that lead to ingot quality concerns. Many of the conditions reported cannot be identified utilizing the existing suite of measurement tools and where the resultant of those conditions cannot be known until further processing, if at all. Most importantly conditions that lead to the types of defects that could create catastrophic stresses in a component can be identified at their onset.