Improved thermal and mechanical performances of additively remanufactured Invar alloy via ultrasonic-frequency pulse arc

The remanufacturing of damaged Invar alloy molds requires not only the restoration of geometric dimension but also the replication of thermal and mechanical properties akin to base material (BM). This work presents an innovative wire-arc additive remanufacturing process utilizing an ultrasonic-frequency pulse (UFP) arc, which effectively approximates the thermal-mechanical properties of Invar deposits to those of BM. Comparative analysis with direct current (DC) arc reveals that the UFP arc, under equivalent thermal input, yields an increased melt depth-to-width ratio, promoting the transition from columnar to equiaxed structures of γ-Fe grains and the formation of refine cellular substructure. At UFP frequency of 40 kHz, the Invar repair part achieves equal-strength matching (348 MPa vs. BM: 352 MPa) and exhibits a significantly reduced coefficient of thermal expansion (CTE of 3.7 ×10⁻⁶/K at 230 °C) compared to BM (3.4 ×10⁻⁶/K). Enhanced molten pool flow by UFP arc is crucial for achieving optimal repair quality.