Effect of milling time on powder characteristics and mechanical performance of Ti4wt%Al alloy

Abstract

In the present study, Ti-4wt%Al (Ti4Al) mixture and CPTi were milled in a horizontally orientated planetary ball mill for different duration to investigate the effect of milling time on the crystallographic as well as morphological evolution and mechanical properties of sintered powder compacts. Result shows that solubility of aluminium in the titanium lattice improves with milling time. Crystallites size reduces progressively from 98 nm to 41 nm and 32 nm for Ti4Al and CPTi powders respectively, while lattice strain increases with milling duration. Particles got flattened and fractured causing variation in particle size from 13 μm to 1 μm for Ti4Al with the milling progression. Ti4Al powder mixture homogeneity enhances with advancement of milling. Green density and sintered density also vary with milling time because of the morphological change in milled powder. Sintered relative density (Srd) reduces with milling time and attained the values 0.75 and 0.74 for Ti4Al and CPTi sintered compacts made of unmilled powders. The Srd for the Ti4Al and CPTi sintered compacts made of 16 h milled powders are found to be 0.60 each. In order to get porous structure and to investigate the porosity trend with milling time, milled powders were cold compacted at low pressure. Compressive deformation study of sintered porous structure was carried out. It was observed that the yield strength and elastic modulus of the sintered products were affected with milling time. This was primarily due to variation of porosity which again influenced by the powder characteristics at different milling time. The yield strengths and elastic modulus of Ti4Al sintered compacts were always higher than CPTi. The values of yield strengths vary between 398 MPa to 52 MPa, while elastic modulus has its highest and lowest values 69 GPa and 14 GPa for the Ti4Al sintered compacts made of unmilled powder mixture and 16 h milled powder.