Influence of Electroshocking Treatment on Microstructure and Mechanical Properties of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Thin-Wall Specimen Manufactured by Laser Melting Deposition

doi:10.1007/s40195-023-01576-x

Abstract

Abstract:

In order to improve the properties of titanium alloys manufactured by laser melting deposition (LMD), the electroshocking treatment (EST) was proposed in this work. The effects of EST on microstructure and mechanical properties of LMD Ti-6.5Al-3.5Mo-1.5Zr-0.3Si were investigated. The results showed that the width of the heat affected band decreased and disappeared under the thermal and athermal effects of EST, resulting in the uniform microstructure. In the microstructure, the α laths became coarser gradually, and the quantity of α/β interface was reduced. The reduction of the quantity of α/β interface leads to make less resistant to dislocation, resulting in the reduction in hardness and strength. The discontinuous grain boundary α phase and nucleation α colony near grain boundary inhibited the crack propagation and improved the ductility. Summary, EST can manipulate the microstructure and improve the mechanical properties of LMD titanium alloys.

Key words: Electroshocking treatment (EST), Laser melting deposition (LMD), Titanium alloy, Microstructure, Mechanical properties

Yan Wen, Xuan Sun, Jian Zhou, Bingliang Liu, Haojie Guo, Yuxin Li, Fei Yin, Liqiang Wang, Lechun Xie, Lin Hua. Influence of Electroshocking Treatment on Microstructure and Mechanical Properties of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Thin-Wall Specimen Manufactured by Laser Melting Deposition[J]. Acta Metallurgica Sinica (English Letters), 2024, 37(1): 145-158.

Figures/Tables 12

Table 1 Chemical composition of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si powder (wt%)

Ti	Al	Mo	Zr	Si
Bal.	6.68	3.70	1.64	0.25

Fig. 1 a Morphology of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si powder; b particle size distribution; c LMD scanning pattern; d the selected position in LMD specimen for tensile experiment; e the dimension of specimen for EST and tensile experiment; f the photographs of an as-built specimen and a tensile specimen

Table 2 LMD process parameters and EST parameters of specimens

Specimen number	Laser power (w)	Spot diameter (mm)	Powder feeding speed (g/h)	Layer thickness (mm)	Scanning speed (mm/min)	Thin-wall specimen size (mm³)	Current density during EST (A/mm²)	EST time (s)
EST0	800	3	400	0.75	450	70 × 3 × 15	72	0
EST1								0.4
EST2								0.6
EST3								0.8

Fig. 2 a Schematic diagram of EST; b the waveform and frequency of pulse current during EST; c the temperature curve and fitting curve of specimens during EST under three parameters; d the diagram of tensile specimen; e OM and SEM observation area in middle (M) areas; f XRD test area; g hardness measurement area in the upper (U), middle (M), and bottle (B) areas of specimen. Where the test areas in figures e, f and g are located in the gray area marked in d

Fig. 3 OM micrographs of specimens before and after EST: a EST0; b EST1; c EST2; d EST3. HAB is marked by two yellow dotted lines, and ILB is marked by two blue dotted lines

Fig. 4 SEM images of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si before and after EST: a EST0; b EST1; c EST2; d EST3. EG means primary β equiaxed grain, CG means primary β columnar grain

Fig. 5 Magnified morphologies of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si before and after EST: a EST0; b EST1; c EST2; d EST3. αCGB means the continuous grain boundaries with α phase, αGB means the grain boundaries of α phase, αcolony means the α colony, βresidual means the residual β phase, αs means the secondary acicular α phase

Fig. 6 Microstructure morphologies of HAB before and after EST: a EST0; b EST1; c EST2; d EST3. a1-d1 showing the selected areas outside HAB; a2-d2 showing the selected internal areas of HAB. The yellow dotted box in c2, d1 and d2 is the residual β phase area, from which the αs phase is precipitated

Fig. 7 XRD patterns of LMD specimens before and after EST: a XRD image from 30° to 90°; b the magnified diffraction angle from 34° to 42°; c the magnified diffraction angle range of 34.5°-36.5°, 38°-39° and 40°-41°, which are corresponding to the (100) (002) and (101) peaks

Fig. 8 Mechanical properties of LMD specimens before and after EST: a microhardness; b tensile properties

Fig. 9 Fracture morphology of specimens before and after EST: a EST0; b EST1; c EST2; d EST3, a1-d1 showing the magnified images of selected area in a-d, respectively

Fig. 10 Schematic diagram of effects of EST on grain boundary, colony and αlath: a microstructure of specimen before EST; b microstructure variation of αlath under thermal effect; c microstructure variation of αlath under athermal effect, causing by the non-uniform current; d microstructure variation under EST with 0.4 s; e microstructure variation under EST with 0.6 s; f microstructure variation under EST with 0.8 s. αCGB means the continuous grain boundary of α phase, αGB means the grain boundary of α phase, αcolony means the α colony, αlath means the α lath, αs means the secondary acicular α phase

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