SYNTHESIS OF IRON ALUMINIDE MATRIX INSITU COMPOSITES FROM ELEMENTAL POWDERS BY REACTIVE LOW-PRESSURE PLASMA SPRAYING

A premixture of elemental powders of iron and aluminium was supplied as a spray material to synthesize iron aluminide matrix in situ composites by means of reactive low pressure plasma spraying (RLPPS). The aluminium content was varied from 13.9 to 59.2 mass% in the premixtures. Intermetallic matrix composites (IMCs) with a predominant FeAl matrix and exclusive in situ nitride of AlN are synthesized by RLPPS, which is performed using an Fe-32.6mass%Al premixture. AlN formation is better in RLPPS with a premixture as a spray material compared with RLPPS using an expensive FeAl intermetallic powder. Although AlN is an exclusive in situ nitride, the matrix constituents vary with the different aluminium contents in the premixtures. Increasing the aluminium content leads to a change in the iron aluminides from FeAl to FeAl, and Fe2Al5 as the matrix. The iron aluminide with predominantly Fe2Al5 matrix composite showed the highest hardness of over 700 Hv at room temperature. However, the partial decomposition of the in situ nitride AlN occurred through annealing at 1173 K for 86.4 ks in vacuum. The microhardness of sprayed IMCs after the annealing decreases, because of the partial decomposition of AlN. RLPPS could be one of the characteristic fabrication methods of iron aluminide matrix in situ composites which are expected to be an advanced material in wear-resistance applications at medium temperatures.