Abstract:
The use of Wire + Arc Additive Manufacturing (WAAM) to manufacture high-
speed projectiles, such as missiles, is currently an industry challenge due to the
nature of high-speed flight and the extreme environment that components are
exposed to. Alloys that are suitable for high-speed flight are creep resistant
superalloys, this is due to the aggressive heating environment experienced by
objects in high-speed flight, and the need for performance at extremely high
temperatures. These materials are currently expensive and difficult to
manufacture, which is less than ideal for non-recoverable systems such as
airborne weapons. The development of missile systems requires flight tests to be
affordable and operate in quick succession, to which rapid prototyping offers a
significant advantage. The use of traditional manufacturing methods and supply-
chain for this purpose are logistically challenging and expensive, mainly due to
loss of material though machining. The use of WAAM in a rapid prototyping
capability is the driver for this research. To be able to use the process to
manufacture and prototype components for high-speed applications, would, if
possible, be an excellent solution to reducing the amount of time and money that
it currently costs to flight-test and develop these systems. WAAM could also be
used for final design production.
The effect WAAM route has on the high temperature properties of superalloys is
largely unknown. This research is therefore focused on the development of the
WAAM process, and selection of alloys suitable for high-speed flight and for
WAAM deposition. Four creep-resistant superalloys underwent deposition using
a plasma WAAM process and the resulting material was characterised to
understand how WAAM affects high temperature performance. The research also
investigates post-deposition heat-treatment of these alloys and develops
parameters for inter-pass machine hammer peening to improve material
performance.
The findings from this project increases the understanding between the WAAM
process and superalloy strengthening mechanisms and develops a method to
increase the performance of additive manufactured material. The most
appropriate alloys for both WAAM and the high-speed flight application were
ranked and down selected based on their anticipated performance and
weldability. The selected alloys then underwent extensive testing from room
temperature to 1000 °C, to understand the performance of WAAM built structures
at high temperature. The microstructure is examined throughout and found key
differences between solid-solution strengthened and age hardened alloys which
effects performance. Finally, in-process machine hammer peening was
investigated for age hardened Rene 41 and found to greatly increase the
performance to match that of the wrought material.