Vasiraju, Venkata 1987- (2012-05). Equal Channel Angular Extrusion of Tungsten Heavy Alloy. Master's Thesis.
Tungsten heavy alloys (WHA's) are composite two phase materials with tungsten particles embedded in an alloy matrix. The alloy matrix can be a binary mixture of Ni with either Fe, Cu, Co or Mn. Owing to their high density and good mechanical properties, these materials are used in a wide range of applications ranging from weights to kinetic energy penetrators. The goal of this thesis was to impart maximum strain to the tungsten heavy alloy via equal channel angular extrusion (ECAE), and evaluate the variation in tungsten particle morphology with level of plastic strain. Severe plastic deformation of tungsten heavy alloys is difficult and challenging. The WHA used in this project was 90W-8Ni-2Fe. Both high temperature and low temperature ECAE processing were done on this material. Successful multi-pass extrusions were possible only with intermediate annealing at 1300C and at low extrusion rates. The microstructures of the processed materials were examined using optical and scanning electron microscopy. The recrystallization behavior and hardness variation with processing were also examined. X-ray diffraction was done to identify the various crystal structures. Three pass extrusions through a 90 degree die angle ECAE tool (total strain of 3.4) of tungsten heavy alloy were successfully achieved. The previous highest level of total strain imparted to WHA by ECAE was 1.91. The hardness, XRD, and recrystallization results were as expected and in accordance with the results found in the literature. The hardness increases dramatically after the first pass and was nearly the same for the second and the third passes. The tungsten particle morphology obtained after the first and the third pass were as expected. However, the morphology of the tungsten particles after the second extrusion via route C was unusual and "popcorn" like, and of a type not reported previously in the literature. The "popcorn" like morphology of the W phase may give rise to unusual and interesting mechanical properties that should be studied further.