In-situ formation of nitride particle reinforced titanium aluminide by reactive plasma arc melting process

A reactive plasma are melting process using a mixture of Ar and N-2 as the carrier gas for titanium and aluminum powders has been applied to synthesiz e nitride particle reinforced Ti-34mass%Al intermetallic matrix composites (IMCs). This technique successfully allowed to produce in-situ nitride part icle dispersed IMCs and the volume fractions of nitride increased from 6 vo l% to 54 vol% with increasing mixing ratios of N-2 gas from 10 vol% to 100 vol%. In the IMCs both rod-like Ti(2)AIN and coarse two-phase nitride parti cles consisting of the core of TiN and the outer shell of Ti2AlN were forme d in the matrix of a full lamellar structure or a lamellar containing small amount of equiaxed gamma phase structure. The IMCs had significantly fine grains of which size was about 1/4 that of the unreinforced Ti-34 mass%Al. The Rockwell hardness of the IMCs increased abruptly from 36.5 to 48.4H(RC) with increasing volume fraction of nitride. Unlike the hardness, the tensi le strength of the IMCs had a maximum value of 507 MPa, which was approxima tely 170 MPa higher than that of the unreinforced Ti-34 mass%Al, at 13 vol% nitride, beyond which the strength decreased. The strengthening is derived from complex reinforcing effects of both direct strengthening effects of n itride particles due to the interaction of dislocations with the particles and grain refinement. The degradation in tensile strength at higher volume fractions of nitride is considered to be attributed to higher population of clustered coarse two-phase nitride particles, which can act as crack initi ation and propagation sites. As for the strength at elevated temperatures, the IMC with 13 vol% nitride had higher tensile strengths than the unreinfo rced Ti-34 mass%Al by 100 MPa at 1173 K and 61 MPa at 1273 K.