PREPARATION OF TITANIUM OVERLAY WELD ALLOY WITH DISPERSED TIC PARTICLES BY PLASMA POWDER WELDING PROCESS

In order to develop a wear-resistant titanium alloy, TiC-dispersed overlay was formed on the surface of titanium substrate by the plasma powder welding process using a new composite powder made from fine TiC particles (1.4 mum) and titanium particles (< 15 mum). For comparison, another TiC-dispersed overlay was also formed using coarse TiC powder (60 approximately 150 mum), which mixed with titanium powder (< 150 mum). Effects of plasma arc current on the dispersion of TiC particles and the hardness of these overlays were examined by mean of metallographic and X-ray diffraction measurements. The following results were obtained. (1) In the case of the Ti-TiC mixed powder, TiC particles sank to the lower part of the overlay and dendritic TiC was in-situ formed at the upper part of the overlay. Although the hardness of the upper part was nearly constant (H(v)240), that of the lower part increased from H(v)260 to H(v)460 as plasma arc current increased from 100 to 200 A. (2) In the case of the Ti/TiC composite powder, TiC particles were completely dissolved into molten titanium. During the solidification process, TiC(x) (X=0.42-0.46) particles having a diameter of 10 approximately 50 mum were in-situ formed and were uniformly dispersed in high density. As plasma arc current increased from 100 A to 200 A, the hardness of this overlay decreased from H(v)1000 to H(v)600. However the hardness was much higher than that of the overlay made from the Ti-TiC mixed powder.