A joint team from Chinese and US research institutions has published a study in Nature describing the use of pulsed-arc additive manufacturing to print a titanium alloy single crystal reaching 1 m in height. The samples were made of Ti-6Al-4V and included meter-scale rods about 1 cm in diameter as well as test pieces 6 mm and 20 mm in diameter. Because the 20 mm sample was too wide to scan as a whole, the researchers mapped crystal orientation across nine regions along its cross-section and confirmed that it constitutes one continuous single crystal. The team also printed unsupported zigzag lattice structures in which every strut is a single crystal, which the authors say has no precedent. The process is called deep squat pulsed wire arc additive manufacturing (DSP-WAAM), in which the wire is melted in an arc whose current switches between a peak of 200 A and a base value of 20 A. Heat-flow modeling shows that pulsing produces a wide, shallow melt pool and a convex solidification front, which helps eliminate stray grains; a constant peak current would overheat and cause the deposit to collapse, while a constant base current would fail to melt the wire. Layer-by-layer remelting at a layer thickness of about 0.15 mm provides a second safeguard, remelting regions that deviate from epitaxial growth conditions and leaving only the single-crystal portion. Beyond titanium alloy, the team also grew single crystals of tungsten, molybdenum, niobium and a molybdenum-niobium alloy, with orientation deviation below 2 degrees for niobium, below 5 degrees for tungsten and the molybdenum-niobium alloy, and below 8 degrees for molybdenum. In 700 degrees C creep tests, the printed titanium single crystal showed creep resistance about an order of magnitude higher than predicted by grain-size models; tensile tests showed that forged material has higher yield strength below about 500 degrees C, while the single crystal is superior at higher temperatures. The paper states that there is no intrinsic theoretical upper limit on crystal width; what changes with size is the range of usable heat input and scan speed, which must ensure top melting, a protruding solidification front and directional crystal growth. Tungsten, because of its high hardness, brittleness, sensitivity to impurities and severe thermal stress, is prone to microcracking in additive manufacturing, and grain boundaries are the main path for crack propagation; on this basis the authors suggest that single-crystal printing could yield large-area crack-free tungsten parts. Potential applications include reactor components, laser mirrors and lightweight thermal-shielding lattices for extreme-temperature environments, but the commercial viability of the method remains to be demonstrated.