Page 80 - MSAM-2-4

Materials Science in Additive Manufacturing Laser DED-produced Ti-6Mn-4Mo alloy

on microstructure evolution , the biocompatibility, A B
[1]
[33]
as well as the evolution of electrochemical properties .
[34]
More importantly, DED techniques have been also adopted
to study other Ti-based alloy systems, but the efforts have
[35]
been limited. In this regard, Gong et al. evaluated Ti-Mn
alloy for laser DED technique using a high throughput
method. Yang et al. studied the Ti-20 wt% Mo by coating
[36]
prepared by in situ alloying of pure Ti and Mo powders Figure 1. Micrographs of Ti-6Mn-4Mo powder mixture for directed
during laser cladding. Kang et al. investigated the effect energy deposition experiment. (A) Low-magnification scanning electron
[37]
microscopy image at 50×; (B) close-up view for the minor irregular Mn
of the thermal cycle during the in situ DED production of a particles at ×800.
Ti-Mo alloy with functionally varied composition.
Based on the literature survey, we learned that while Pilot trials were conducted to determine the optimal
additive manufacturing-produced Ti-6Al-6V has been parameters for the DED process, involving variations
extensively studied, the investigation of AM-produced new in laser power and scanning speed. A summary of the
Ti alloys with Mn or Mo additions is still in the infancy different combinations of laser power and scanning speeds
stage. To date, very limited research has been conducted on is presented in Table 1. Basically, the laser power was
using additive manufacturing methods to produce Ti-Mn systematically increased from 200 W to 300 W (the highest
or Ti-Mo binary systems, while the Ti-Mn-Mo ternary possible level for the DED machine) in 50 W increments
system has not been fabricated by either PBF or DED while maintaining a constant scanning speed of 500 mm/
methods to the best of our knowledge. As such, this study min. The final test run (Condition 4) was performed at
intends to bridge the gap, by investigating the feasibility the highest available laser power of 300 W but with an
of using laser DED technique to synthesize a Ti-Mn-Mo increased scanning speed of 1000 mm/min. Evaluation of
ternary alloy through in situ alloying of elemental powders, the deposited material from each condition included an
and exploring the mechanical properties and corrosion assessment of porosity, supported by optical micrograph
resistance of the obtained alloy. images of cross-sections as illustrated in Figure 2. Both
Conditions 2 and 3 exhibited notable pores and voids, while
2. Materials and methods Conditions 1 and 4 displayed significantly lower porosity.
Ultimately, Condition 1, with the least void content, was
2.1. DED experiment chosen for all subsequent experiments.
Elemental titanium (Ti), manganese (Mn), and The selected process parameters used for producing
molybdenum (Mo) powders with particle size ranges Ti-6Mn-4Mo are listed in Table 2. Samples were deposited
from 50 to 150 μm were used in this study. Ti and Mo in two shapes: (i) rectangular blocks of 12 × 60 × 4 mm
powders were spherical while Mn powder was of an and (Figure 3A–3D) (ii) disks with a diameter of 25 mm
irregular shape. Elemental powders of Ti, Mn, and Mo and a height of 2.5 mm (Figure 3E–3F). For the scanning
were mixed in 90:6:4 proportion, respectively, in a low- strategy, a unidirectional scan with 180°-layer rotation was
energy ball milling machine for 2 h. This composition utilized during deposition for the blocks (Figure 3A), while
was chosen due to the promising mechanical properties a spiral strategy was used for disk specimens. The deposited
(such as high strength) reported in literature [5,11] , in which materials were separated from the build plate using a wire
conventional manufacturing processes were employed. electrical discharge machine. Tensile test samples were cut
The powder mixture was dried in an oven for 90 min at out of the rectangular blocks such that their tensile axis
110°C immediately before use. Figure 1 shows the scanning was aligned with the scanning direction (Figure 3B). Half
electron microscopy (SEM) images of the resultant powder of the samples were heat-treated in an induction furnace
mixture. The diameter of powder particles is in the range with Ar atmosphere by heating with a rate of 10°C/min up
of 30 to 150 μm. While most particles are spherical, some to 1000°C, which was maintained for 1 h before furnace
irregular shape particles are present in the mixture, and cooling with the rate of 10°C/min. The heat treatment
they are identified as Mn particles. Ti-6Mn-4Mo deposits strategy was directly adopted from the literature [8,11] for
were obtained using the InssTek MX-Lab AM system similar Ti alloys and is summarized in Figure 4.
equipped with a CNC 3-axis stage, a fiber laser with
maximum power of 300 W and spot size of 0.4 mm. The 2.2. Material characterization
powder mixture was loaded into the hopper and deposited The specimens for optical and SEM observations were first
on a Ti-6Al-4V substrate through a coaxial powder feeding ground using silicon carbide sandpaper with granulation
nozzle together with argon as a shielding gas. down to 1200. Ground samples were then polished with

Volume 2 Issue 4 (2023) 3 https://doi.org/10.36922/msam.2180