Effect of hafnium on the structure and properties of wrought nickel-base alloys

1. In nickel-base alloys hafnium enters into the composition of nitrides of the type Ti(C, N) and Nb(C, N), partially replacing atoms of titanium, niobium, and aluminum in nitrides TiN, NbN, and AlN, and it also enters into the composition of the solid solution and strengthening γ-phase. 2. Hafnium promotes an increase in the amount of MC type carbides with a high carbon content, a reduction in M6C carbides, and removal of carbide liquation in nickel-base alloys. 3. An excess amount of hafnium in alloys leads to formation of primary phases of the type Ni, (Hf, Ti)2, and secondary phases: lamellar phase Ni3 (Ti, Hf) and Ni3 (Nb, Hf). 4. In worked alloys hafnium refines grains and it retards grain growth in the temperature range 1100–1200°C. 5. Hafnium promotes an increase in the strength properties of alloys at 20°C, and it does not alter ductility. Optimum additions of hafnium lead to a marked increase in time to failure for alloys in the temperature range 700–800°C. 6. On adding small amounts of hafnium to alloys there is an increase in the resistance of the metal to cracking near the seam during welding and during heating of welded joints.