Thermal effects on subsurface damage during the surface grinding of titanium aluminide

Increased demands on aerospace and automotive designs have pushed engineers to consider new materials that can withstand extreme conditions, while maintaining their material properties. One material that has been introduced as a possible alloy for jet engine components is an intermetallic compound called titanium aluminide (TiAl). The specific alloy that has shown the greatest promise is dual-phase (α₂ and γ) TiAl.; Titanium aluminide has enhanced high temperature strength, good oxidation and burn resistance, high elastic stiffness, and low density. The high strength to weight ratio makes it especially appealing; its density is approximately half that of nickel alloys currently used as turbine airfoils. TiAl is very brittle near ambient temperature, which makes it very difficult to machine. Grinding is a machining process used to achieve good surface finishes, maintain tight tolerances, generate contoured surfaces, and process difficult-to-machine materials. As a high-energy process, grinding can generate large temperature rises in the workpiece being machined. Previous research has developed a theoretical model to predict the depth of plastic deformation during the surface grinding of TiAl. This model did not account for the variation in material properties due to temperature changes.; This research has focused on improving the model for plastic deformation during surface grinding of TiAl through a three-stage approach: (1) material properties were established as a function of temperature; (2) temperatures during grinding were evaluated; and (3) subsurface plastic deformation was investigated.; Using the facilities at Oak Ridge National Laboratory's High Temperature Materials Lab, several material properties were established as a function of temperature, ranging from room temperature to 800°C: thermal diffusivity (α), specific heat (c_p), thermal expansion (TE), thermal conductivity (k), Vickers hardness (H_v), Young's modulus (E), and Poisson's ratio (v). Temperatures during grinding were established theoretically using J. C. Jaeger's moving heat source theory; numerically using heat transfer principles; and experimentally with an embedded thermocouple technique. The variable properties allowed for the modification of the theoretical subsurface damage model, which was validated using a technique called the bonded interface method. The completion of this research provides valuable information, useful in the introduction of titanium aluminide into new engineering applications.