the powder
mixtures were dried and sifted through a 120 mesh sieve.The
mixed powders were uniaxial pressed in a steel mold of 40 mm in
diameter at a pressure of 30 MPa,followed by cold isostatic
pressing with 300 MPa.Pressureless sintering was carried out in
a graphite-resistance furnaceunder a nitrogen atmosphere.A two-
step sintering procedure was applied,i.e.the samples were first
heated to 1055 1C and held there for 2 h and they were then
further heated to 1500–1650 1C and held there for 2 h(Table1).