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Materials Science in Additive Manufacturing Multi-material Ti6Al4V-B4C through L-DED

must be examined. Additive manufacturing (AM) has and compression testing. These tests were performed to
many benefits over traditional manufacturing, including evaluate whether a radial structure of two Ti alloys would
the ease of constructing multi-material structures. These exhibit synergistic behavior, potentially surpassing the
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multi-material structures facilitate the study of different performance of the control Ti alloy.
arrangements of multiple alloys within a single structure.
Structures manufactured with different alloys have been 2. Materials and methods
used for various applications, such as coating hard materials 2.1. Processing of Ti64 and Ti64-B4C radial
onto soft but ductile ones to improve wear resistance composite (RC) structures
and thin layers of high thermally conductive materials
onto poor conductors to increase the high-temperature Samples were printed using a FormAlloy (Spring Valley,
applications of an alloy. Thus, different structure designs CA, USA) five-axis DED AM system. The Ti6Al4V (Ti64)
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were investigated to further improve an alloy’s mechanical powder was purchased from AP&C (GE Additive, USA),
properties. Radial bimetallic structures have demonstrated and non-spherical-B C (B4C) powder (particle size: 15
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the potential to enhance the mechanical properties of a – 45 µm) was attained from Reade Advanced Materials
cylinder. 11,12 This has led to the development of an annular (USA). The build chamber was maintained at an O level of
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toolpath for manufacturing the cylinders used in this study. <20 ppm during the print in an argon-filled environment.
The control and first treated samples were monolithic in The powders were sieved to ensure that the powders had
design, using the control alloy and composite; the second a particle size between 15 µm and 63 µm. Although DED
treated sample was constructed using both the control systems prefer a coarser powder particle size of 45 – 150 µm,
and composite, with the core consisting of the control and the printing parameters were optimized to accommodate
composite shell. This could potentially increase the service finer powder particle size. The radial shape was designed,
life of components made from Ti6Al4V, which requires and the corresponding G-code was written to print.
high temperature and wear resistance. Coating the exterior Figure 1A displays an example of the toolpath for six sample
with the composite could enhance these properties without layers. Nominal dimensions are oversized to avoid rough
compromising the excellent properties of Ti6Al4V. exterior and uneven surfaces after machining. The radial
toolpath requires different scan speeds of the laser head for
Alloys of Ti and boron carbide (B4C) have been studied the annular sections of the cylinders. The scan speed for
for high-temperature and wear applications due to the the Ti64 varied from 1000 to 1200 mm/min, while the scan
increased formation of TiC and TiB within the matrix, speed for Ti6Al4V + 5wt.% B4C (Ti64-B4C) varied from
leading to improvements in the properties mentioned 400 to 600 mm/min. The Ti64-B4C powders were mixed
above. 13-16 Both TiC and TiB form around the particle due and ball-milled for 30 min to achieve a homogeneous
to local concentrations of boron and carbon exceeding mixture. Three sets of samples were printed: monolithic
the required levels for formation within the matrix. Thus, Ti64, monolithic Ti64-B4C, and a RC cylinder comprising
the particles become bonded to the matrix, forming a a Ti64 core and Ti64-B4C cylindrical shell, with one
metal matrix composite (MMC). Manufacturing these example displayed in Figure 1B. With the different types
MMCs requires extensive parameter optimization for of samples and treatments, to simplify the terminology,
successful production. 14,17 With AM, these optimizations the monolithic Ti64 samples will be referred to as Ti64,
can be achieved more rapidly compared to conventional the monolithic Ti64-B4C samples as Ti64-B4C, and the
manufacturing methods. This benefit facilitates the easier RC samples as RC. The layer height for both monolithic
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production of MMCs when utilizing directed energy types (Ti64 and Ti64-B4C) was 0.295 mm, while that of RC
deposition (DED)-based AM. was 0.21 mm. The laser power used for Ti64 and Ti64-B4C
Previous studies have used various AM types, including cylinders were 320 and 350 W, respectively, while that of RC
powder-based DED to wire arc DED, 12,19 to develop multi- samples used both laser powers depending on the section
material structures through alloying composites, and of the sample. With FormAlloy, the powder feeders, seen
,
bimetallics. 12,19,20 However, these studies did not focus in Figure 1E, use a feed rate of rotations per minute (RPM)
on radial bimetallic structures involving MMCs. Herein, to determine the rate at which the powder is delivered to
cylinders were produced using powder-based DED to the deposition head of the printer. For all sample types, a
additively manufacture a control and two treated samples. feed rate of 0.26 RPM was used. With monolithic samples,
After the fabrication of the cylinders, they were subjected the carrier gas flow rate used was 8 L/min, and the shield
to various tests, including X-ray diffraction (XRD) for gas flow rate was 12 L/min. For RC samples, the powder
phase analysis of the control and treated samples, energy feeders’ carrier gas flow rate was 6 L/min, and the shield
dispersive spectroscopy (EDS), Vickers microhardness, gas flow rate was 15 L/min.

Volume 3 Issue 3 (2024) 2 doi: 10.36922/msam.3571