Unique High-Temperature Mechanical Behavior of CuCrZr Alloy Additive-Manufactured by Laser Powder Bed Fusion

It is generally known that the Cu-Cr-Zr (CuCrZr) alloy series strengthened by various intermetallic phases exhibits superior thermal/electrical conductivity and high strength in terms of industrial applications such as electric devices, thermal management in automobiles, and aerospace. It is necessary to understand the precipitation behavior in the CuCrZr alloys. The precipitation morphologies and the strengthening phenomenon by Cr-rich or Cu-Zr intermetallic phases have been studied in conventional wrought-type CuCrZr alloys. Recently, laser powder bed fusion (L-PBF), which is one of the most representative metal additive manufacturing processes, enables the manufacture of metallic components. The L-PBF process is being applied to manufacture induction-heating coils of Cu alloys with complex shapes. In terms of applications to induction-heating coils, a sufficient strength level is required at elevated temperatures in service, whereas there are few reports of the high-temperature mechanical performance of L-PBF processed CuCrZr alloys. In particular, The L-PBF process using a scanning laser beam to selectively melt consecutive bedded powder layers is characterized by a high solidification rate. The effect of microstructural features formed in the rapid solidification on mechanical behavior remains unclear. In this study, we systemically investigated the effect of microstructural features on the high-temperature strength of L-PBF processed CuCrZr alloys using tensile tests at elevated temperatures.<br/>Rectangular alloy samples with a size of 15~60 × 60 × 70 mm³ were fabricated using the gas-atomized CuCrZr ternary alloy powder and SLM280PS machine (SLM Solutions GmbH, Germany) under a laser scan speed of 0.6 m/s and laser power of 400 W. The applied laser-scanning hatch distance, powder-bed thickness, and beam focus size were 0.07 mm, 0.03 mm, and 0.08 mm, respectively. The L-PBF processed CuCrZr alloys exhibited microstructure consisting of a number of melt pools (a depth of approximately 100 μm) that were formed by local melting and rapid solidification using scanning laser irradiation. A much higher content of Cr (1.0 mass %) is soluted in the Cu matrix than the solubility of Cr in Cu (approximately 0.3 mass%) due to the non-equilibrium solidification state. As a result of the tensile test of L-PBF processed CuCrZr alloy at room temperature (RT) and elevated temperatures, the 0.2% proof stress was increased to 350 MPa at a testing temperature of 500 °C. This is a unique temperature-dependent strength when compared to that of cast pure Cu and conventional CuCrZr alloy, as reported in previous studies. Transmission electron microscopy revealed that the dislocations interacted with nano-sized Cr-rich precipitates formed inside the supersaturated solid solution of the Cu matrix during the tensile test at 500 °C. The Cr-rich precipitates would be metastable fcc-(Cu, Cr) phase that was often observed in annealed samples at 400 to 500 °C. That is, the unique microstructural characteristics (i.e., such as supersaturation of Cr in Cu matrix) of L-PBF processed CuCrZr alloy contributed to the unique temperature-dependent mechanical behavior. This study demonstrates the possibility of the L-PBF process to realize superior high-temperature strength of CuCrZr alloy.