Hejja, Andras A2015-04-302015-04-302015-04-30http://hdl.handle.net/10539/17597A dissertation presented to the Faculty of Engineering University of the Witwatersrand, infulfilment of th e requiromento for the degree of Doctor of Philosophy This work was carried out in the Department of Metallurgy of the University of the Witwatersrand under the supervision of Professor D.D, Howat, B *Sc.(G laB )f P h .D .f F«I»Mf F,M»I#C* Johannesburg September, 1975enThesis