PROPERTIES OF TITANIUM-ALUMINIDE LAYER FORMED BY LOW-PRESSURE PLASMA SPRAYING

TiAl alloyed powder was sprayed onto a substrate surface by the low pr essure plasma spraying (LPPS) process. The microstructure and properti es of sprayed TiAl layers were examined and compared with those of a T iAl bulk plate. As-sprayed TiAl layer consisted of gamma fine grains w hose average grain size was 90 nm including a small amount of alpha(2) . The sprayed layer had a hardness value of 589 Hv at room temperature and above 400 Hv even at 1073 K. Although the hardness value dropped to 225 Hv at 1173 K, it was still comparable to that of a TiAl bulk pl ate at room temperature. The microstructure and mechanical properties of the sprayed TiAl layers changed only slightly when exposed to a hig h temperature of up to 973 K for 48 h. Although the hardness values of sprayed TiAl layers decreased to 350 Hv when annealed al 1273 K for 2 4 h and more because of the occurrence of grain growth, the hardness v alues were significantly higher than that of a TiAl bulk plate. Tensil e strength above 400 MPa, which was almost equal to that of a TiAl bul k plate, was obtained for sprayed TiAl layers both in as-sprayed and a nnealed (at 1273 K for 24 h) conditions. Therefore, sprayed TiAl layer s were found to be a feasible hardfacing layer at elevated temperature s.