IN-SITU SYNTHESIS OF TIB WHISKER-REINFORCED TITANIUM BY MECHANICAL ALLOYING

Elemental titanium-amorphous boron and elemental titanium-titanium diboride (TiB2) mixed powders were mechanically alloyed to strengthen the conventional titanium-boron binary alloy by the dispersion of TiB. The mechanically alloyed (MA) powders obtained were heated in vacuum for degassing, and then consolidated by hot isostatic pressing (HIP) to investigate the microstructures and mechanical properties. The MA powders prepared from elemental titanium and amorphous boron could be converted into Ti-TiB composite powders by heating above 773 K for 3.6 ks, while the MA powders from elemental titanium-TiB2 needed the heating above 1073 K for 3.6 ks. The morphological feature of TiB as an in-situ reaction product was whisker or needle-like shape. Namely, TiB fiber-reinforced titanium can be prepared by the in-situ precipitation of TiB whisker or needle-like crystals. The maximum diameter of this reaction product was about 500 nm, while the maximum size of titanium matrix grains ranges from 3 to 5 mu m. The crystal grains of the titanium matrix and the TiB crystals in this alloy system became smaller as the HIP'ping temperature decreased. The mechanical properties of Ti-TiB composites were significantly improved by the whisker or needle-like precipitation of TiB and the refining of titanium grains.