Normal and abnormal grain growth in tungsten polycrystals

The grain growth has been studied in high-purity flat W polycrystals at 2000 degrees C in vacuum. The onset of abnormal grain growth proceeds without inhibition of the normal grain growth. After appearing of the large abnormal grains the areas with small "normal" grains exist very long. The polycrystal has a bimodal grain structure, both normal and abnormal grains continue to grow. The orientations of individual grains were determined with aid of the electron backscattering diffraction method in the contact area between the abnormally growing large grains and normal matrix. In samples of a larger thickness the abnormal grain growth do not appear in the time period studied. The influence of the formation of new grain boundaries with a high mobility on the onset of abnormal grain growth and similarities with the abnormal grain growth in Al alloys are discussed.