Influence of Process Variables on the Structure of Mechanically Alloyed Ti_3Al-base Intermetallics

During mechanical alloying variables such as the type of mill,milling intensity,milling time,milling at-mosphere and ball-to-powder weight ratio(BPR)affect the morphology and constitution of the product.The effect of milling time,milling atmosphere and BPR on the nature of the product formed in mechanical-ly alloyed pure Ti and blended elemental binary Ti-Al,and ternary Ti-AI-Nb alloy powders was described.Mechanical alloying of pure titanium results,after long milling times,in the formation of an fcc phase.Inthe binary alloy,a solid solution of aluminum in titanium,an amorphous phase,and a fcc phase form withincreasing milling time.The fcc phase,which is probably a result of TiN formation,occurs more rapidly inair or nitrogen than in an inert atmosphere.Formation of the B2 phase in the ternary alloys depends bothon alloy composition and the milling atmosphere,with 100％ formation in all atmospheres in Ti-25Al-25Nbbut not in Ti-24Al-11Nb,and an inert atmosphere favoring formation.The times required for the formationof the different phases decrease as the BPR increases;but their sequence is unaffected.Based on this infor-mation,“milling maps”which describe phase formation as a function of the BPR and milling time are con-structed.Contamination from the milling balls increased as the BPR was increased.

Influence of Process Variables on the Structure of Mechanically Alloyed Ti_3Al-base Intermetallics