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Engineering Science in
Additive Manufacturing EST manipulates structure of Ti-6Al-4V/Cu

maintained a corresponding relationship to prevent coating side and exhibited an embedded morphology
random variations in the test results. (Figure 2E, F, H, I, K, and L). After EST, the MBZ exhibits
a protrusion toward the Ti-6Al-4V side, manifesting as
2.3. Microstructural characterization a distinct boundary line, as shown in Figure 2F, I and L.

Before microstructural characterization, cylindrical This indicates that the thermal effects of EST soften the
samples were sectioned using EDM. The sample surfaces Ti-6Al-4V coating. Under pressure, the coating undergoes
were ground using 600#, 1200#, 2000#, and 4000# plastic deformation, forming an embedded, serrated-like
sandpaper. Subsequently, the observation surfaces were region.
polished using a mixture of 0.04 μm SiO suspension The XRD characterization of the phase of Ti-6Al-4V
2
and H O in a 3:2 volume ratio. Scanning electron coating before and after EST are shown in Figure 3.
2
2
microscopy (SEM; JSM-IT800, JEOL, Japan) was Before EST, there is no CuTi diffraction peak in the EST-0
employed to analyze the coating and the microstructure in Figure 3A. CuTi diffraction peaks appeared in the
of defects at the Ti-6Al-4V/Cu-Cr-Zr interface. Grain Ti-6Al-4V coating after EST, as shown in Figure 3B-D.
orientation characteristics were observed via electron Meanwhile, the intensity of α phase diffraction underwent
backscatter diffraction (EBSD) and subsequently analyzed changes after EST, and the (002) crystal plane diffraction
using AztecCrystal software (Oxford Instruments, UK). peaks disappeared for α-Ti in EST-1, as shown in
Simultaneously, the phase composition of the samples was Figure 3B. The intensity of (101) crystal plane diffraction
characterized using X-ray diffraction (XRD) with Cu Kα peaks decreased after EST-2, as shown in Figure 3C. The
radiation at 40 kV and 30 mA. The scan was performed intensity of the (002) and (101) crystal plane diffraction
with a step size of 0.025°, a scan speed to 1°/min, and a 2θ peaks of α-Ti increased in EST-3, as shown in Figure 3D.
range of 30°–90°. The microstructure of the samples was The variation in grain orientation is due to the phase
characterized using SEM and EBSD. All microstructural transition induced by the thermal effect of EST. 31
characterization regions are shown in Figure 1C.
Figure 4A-D show the line scan results corresponding
2.4. Mechanical properties to Figure 2A, D, G, and J, respectively, indicating significant
diffusion phenomena at the Ti-6Al-4V/Cu-Cr-Zr
Microhardness testing was performed on samples before interface. The MBZ width without EST treatment was 27.4
and after EST using a HUAYIN HV-1000A microhardness μm (Figure 4A). After EST, the MBZ exhibited a widening
tester. To ensure measurement accuracy, a 6×6 square trend, with MBZ widths of 50.2 μm, 43.6 μm, and 235.5
array of sampling points was employed, which were spaced μm for the EST-1, EST-2, and EST-3 samples, respectively
0.2 mm apart. The sampling point layout is shown in (Figure 4B-D). The elemental distribution curves in the
Figure 1C. A load of 200 g was applied with a dwell time MBZ exhibit a step-like pattern, indicating the formation
of 10 s. Shear tests were conducted on an MTS C43 testing of Cu-Ti intermetallic compounds in this region. Based
machine with a shear rate of 0.05 mm/min. Shear samples on the atomic ratios of different elements within the MBZ,
were prepared by splitting a cylindrical sample vertically the presence of Cu Ti and CuTi phases was confirmed.
into two equal halves, as illustrated in Figure 1C. The shear Following EST, the elemental concentrations in the MBZ
2
3
test fixture was designed according to the specimen to region showed a gradual decrease, indicating diffusion of
13
determine the shear strength of the coating. Subsequently, elements under the influence of EST. This phenomenon
the relevant shear strength was calculated based on the is attributed to the thermal effects of EST preferentially
shear pressure and the specimen’s cross-sectional area. acting on high-energy interface regions.
3. Results and discussion The EST process generally occurs at temperatures
above 800°C, while reaction βTi + Ti Cu ↔ αTi occurs at
3.1. Microstructure evolution of Ti-6Al-4V/Cu-Cr-Zr 2
around 700°C, leading to precipitation of large amounts of
To investigate the effect of EST on the Ti-6Al-4V/Cu-Cr-Zr αTi in the MBZ . When the temperature reaches 950°C,
32
interface, the microstructure of the metallurgical bonding the Ti-Cu alloy will melt to produce the liquid phase
zone (MBZ) was analyzed before and after EST treatment (as (Liquid, L), at which the reaction L + Ti Cu ↔ αTi will
2
shown in Figure 2). The morphology of the MBZ revealed occur, and when the temperature reaches about 965°C,
that the untreated interface exhibited a relatively flat state the eutectic reaction of L + Ti Cu ↔ CuTi will occur at
2
with minimal undulations, as depicted in Figure 2A-C. the bonding zone. When the temperature continues to
Following EST at different current densities, the MBZ increase to 990°C, the precipitation of the Ti Cu phase
2
formed a serrated profile at the Ti-6Al-4V interface. occurs, L + βTi ↔ Ti Cu. Based on the above reaction
2
This bonding zone protruded toward the Ti-6Al-4V equations, when the thermal effect of EST on Ti-6Al-4V/

Volume 1 Issue 4 (2025) 4 doi: 10.36922/ESAM025430030