Abstract
Dual-phase Ni3Al-based alloys feature extensive applicability even under high-temperature conditions. We selectively modified the microstructure of a representative dual-phase Ni3Al-based alloy from equi-axed grains to unidirectional grains, using a kW-class high-power laser irradiation technique. On employing the laser probe to linearly scan the Ni-9 at.% Al-16 at.% V alloy specimen, the laser-irradiated region was partially molten and then immediately solidified from the two edges of the molten pool toward the center. Laser irradiation under low-speed scanning increased the molten pool width. The grains in the laser-irradiated region extended preferentially from the two edges toward the center; their crystal orientation was similar to adjacent substrate grains, suggesting epitaxial growth. Therefore, the unidirectional orientation of grains could be extended via wide-range scanning using laser irradiation. This suggests that the microstructure of the alloy can be selectively modified to unidirectional orientated grains by optimizing laser irradiation conditions, such as the power density, scanning speed, and scanning paths. The hardness of the laser-irradiated region decreased due to the phase transformation from the ordered Ni3Al and Ni3V phases to the disordered fcc phase. However, the hardness improved to a value comparable to that of the alloy subjected to heat treatment at 980 °C for 1 h.
Highlights
Dual-phase Ni3 Al-based alloys composed of two different intermetallic phases, namely γ0 -Ni3 Al (Strukturbericht symbol: L12 ) and γ”-Ni3 V (D022 ), are promising for use in high-performance components at high temperatures, such as turbine blades, engines, and friction stir welding tools [1,2,3].these applications require materials with excellent combinations of mechanical properties, toughness, corrosion resistance, and microstructural stability at high temperatures
An alloy ingot with a nominal composition of Ni-9 at.% Al-16 at.% V doped with 50 ppm B was prepared, such that the composition was representative of dual-phase Ni3 Al-based alloys
The laser probewere traveled alongvia two paths—a abrasion line scan of 20 mm and a wide-range electrochemically polished with a methanol solution of sulfuric acid at using a voltageofof scan; this was achieved by repeating the laser irradiation process ten times
Summary
Dual-phase Ni3 Al-based alloys composed of two different intermetallic phases, namely γ0 -Ni3 Al (Strukturbericht symbol: L12 ) and γ”-Ni3 V (D022 ), are promising for use in high-performance components at high temperatures, such as turbine blades, engines, and friction stir welding tools [1,2,3] These applications require materials with excellent combinations of mechanical properties, toughness, corrosion resistance, and microstructural stability at high temperatures. Large thermal gradients and rapid solidification processes can achieve a finer dendrite arm spacing, leading to a reduction of elemental segregation and casting defects They are expected to improve the mechanical properties. We report the selective microstructure modification, from equiaxed to unidirectional orientated grains, of a representative dual-phase Ni-based alloy using a focused single-mode fiber laser with a kW-class high power density This approach is expected to achieve a rapid cooling rate, resulting in a large temperature gradient in a narrow, but deep region
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