Ph.D. Dissertation Defense by Gregorio R. Murtagian
Friday, August 9, 2004
(Dr. Steven Danyluk, Chair)
"Surface Integrity on Grinding of Gamma-TiAl Intermetallic Compounds"
Gamma-TiAl is an ordered intermetallic compound characterized by high strength to density ratio, good oxidation resistance, and good creep properties at elevated temperatures. However, it is intrinsically brittle at room temperature. This thesis investigates the potential for the use of grinding to process TiAl into useful shapes. Grinding is far from being completely understood, and in particular many aspects of the individual mechanical interaction of the abrasive grit with the material are unknown. The development of new synthetic diamond superabrasives in which shape and size can be controlled raises the question of the influence of those variables on the surface integrity.
The goal of this work is to better understand the fundamentals of the abrasive grit-material interaction in grinding operations, and resultant deformation and surface integrity on lamellar gamma-TiAl. Experimental, analytical, and numerical work was done to elucidate the abrasive grit/material interaction and its effect on surface integrity.
Grinding tests were carried out, by analyzing the effects of grit size and shape, workpiece speed, and wheel depth of cut on the subsurface plastic deformation depth (PDD). A practical method to assess the PDD is introduced based on the measurement of the lateral material flow by 3D non-contact surface profilometry. This method combines the quantitative capabilities of the microhardness measurement with the sensitivity of Nomarski microscopy. The scope and limitations of this technique are analyzed. Mechanical properties were obtained by quasi-static and Hopkinson split-bar compression tests. Residual stress plots were obtained by x-ray.
The abrasive grit/material interaction was accounted by modeling the force per abrasive grit for different grinding conditions, and studying its correlation to the PDD. Numerical models of this interaction were used to analyze boundary conditions, and abrasive size effects on the PDD. An explicit 2D triple planar slip crystal plasticity model of single point scratching was used to analyze the effects of lamellae orientation and grain boundaries on the deformation.