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Materials Science in Additive Manufacturing Additive manufacturing of NASA HR-1 angled walls

from A-286 and JBK-75 alloys. NASA HR-1 was designed The LP-DED process has some limitations, such
to improve strength and corrosion resistance while as geometric build angles, variations in thickness and
offering superior weldability compared to A-286 and JBK- surface texture, and the potential for process defects. It
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75. The alloy’s chemical modifications include an increased has been shown that walls with angles >30° begin to fail
nickel and molybdenum content to mitigate solidification during deposition, whereas failure occurs at angles above
fractures. In addition, the tungsten content was increased 45° in laser powder bed fusion. In addition, varying the
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to enhance the solution hardening treatment and reduce orientation of the build can lead to different degrees of
the formation of the acicular η-Ni Ti phase. Furthermore, anisotropic characteristics in the AM microstructure. To
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titanium and aluminum levels were also elevated to optimize the LP-DED process, the build parameters must
promote the formation of spherical γ’ precipitates, thereby be adjusted during printing to strike a balance between
improving the alloy’s strength. The chromium and build deposition rates and geometric resolutions. Key
vanadium volume fractions were maintained to ensure parameters include laser power and spot size, powder
that NASA HR-1 retains the high corrosion resistance flow rate, gas flow rate, travel speed, layer height, and
characteristic of A-286 and JBK-75 alloys. 1,2 hatching. High laser power is particularly important
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The alloy NASA HR-1 is used in aerospace components, for alloys like NASA HR-1, as it has a high melting point
particularly in liquid rocket engines. These components, such and high thermal conductivity that enables rapid heat
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as regeneratively cooled nozzles, are designed to withstand dissipation. Consequently, laser power levels between
extreme conditions, including high temperatures, high 1,200 W and 3,000 W are essential for effectively additively
cyclic pressures, and hydrogen-rich environments, which manufacturing this alloy using LP-DED. Increased laser
render materials susceptible to hydrogen embrittlement. 1,3-5 power may produce deeper melt pools, allowing higher
Conventionally, regeneratively cooled nozzles were deposition rates and thus, enhancing raw material
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produced using vacuum induction melting and vacuum utilization efficiency. It is also crucial to maintain a
arc remelting, followed by hot or cold rolling to fabricate balance between these parameters, as they can alter the
individual parts that are subsequently assembled into thermodynamics during solidification, which, in turn,
the final engine components. This conventional process affects the microstructure and mechanical properties
is expensive and time-consuming. In contrast, additive of the alloy. 1,10,11 The primary objective of this study is to
manufacturing (AM) processes, such as laser powder direct assess the impact of different laser power settings and build
energy deposition (LP-DED), are being explored as viable angles on the microstructure and mechanical properties
alternatives due to their potential to reduce production costs of walls following heat treatment. The variables used in
and facilitate the fabrication of large-scale components with this study were selected based on previous research that
complex features. In addition, AM is considered more demonstrated variations in performance when using
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sustainable than traditional manufacturing processes, such 1,070 W and 2,620 W before any heat treatment. This study
as casting and powder metallurgy, which have low efficiency evaluated the effectiveness of heat treatment in achieving
in terms of material utilization and energy consumption. a homogeneous microstructure across all angled walls. In
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At present, AM is employed across different industries, addition, mechanical properties such as microhardness,
including aerospace, oil and gas, industrial, power, and tensile strength, and low cycle fatigue (LCF) were compared
energy, to create new components and repair damaged to evaluate different manufacturing parameters for angled
parts. DED is capable of producing parts from a range walls in component fabrication.
of high-performance materials, such as stainless steel, 2. Materials and methods
titanium, nickel, cobalt, and aluminum-based alloys. For
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instance, Inconel 718 has been manufactured using the Angled walls with a thickness of 13 mm were built
same technology and has shown an ultimate tensile strength using rotary-atomized NASA HR-1 powder supplied by
(UTS) of 711 MPa and a yield strength (YS) of 464 MPa Homogenized Metals Inc. (HMI; USA) in a boxed-shaped
after heat treatment. These mechanical properties can be structure, employing two different sets of parameters,
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achieved by designing a suitable heat treatment process 1,070 W and 2,620 W. This geometry was chosen to
that facilitates the creation of the desired microstructure. facilitate the formation of desired build angles. The layer
The LP-DED process involves creating a melt pool using a height, travel speed, and powder feed rate are shown in
laser while simultaneously feeding metal powder into the Table 1. These parameters were modified to create the
melt pool; this powder melts and solidifies during cooling. desired build angle and laser power settings. The walls were
In addition, the use of an inert gas is essential to prevent deposited at angles of 0°, 20°, and 30° relative to the build
any contamination between layers during the deposition direction, as shown in Figure 1. The walls were heat treated
process. 11 in the following order: Stress relief, homogenization,

Volume 4 Issue 1 (2025) 2 doi: 10.36922/msam.8069