Thermal Expansion Coefficient and Mechanical Properties of Friction Stir Welded Invar (Fe-36%Ni)

Two high-temperature pin tools, one a polycrystalline cubic BN and the other of W-25%Re, were used to friction stir weld 12.7 mm thick Invar (Fe-36%Ni) plate. Successful welds were produced at a rotational speed of 600 rev min⁻¹ and travel speeds of 76, 102, and 127 mm min⁻¹. The coefficient of thermal expansion, tensile strength, and microhardness of the welds were measured and found to be essentially unchanged from the parent material. The measured elongation was 52% for the parent material and 30 and 37% for welds made with the W-Re and the polycrystalline cubic BN pin tools. Both pin tools produced comparable welds but the W-Re tool exhibited more wear and left small wear remnants in the weld especially at the weld plunge.