Deformation behaviors of as-built and hot isostatically pressed Ti-6Al-4V alloys fabricated via electron beam rapid manufacturing

doi:10.1016/j.jmst.2019.04.032

Abstract

Abstract:

The deformation behavior of as-built and hot isostatically pressed (HIP) Ti-6Al-4 V alloys fabricated using electron beam rapid manufacturing (EBRM) were investigated in this work. The deformation characteristics were characterized using a laser scanning confocal microscope and electron back-scattered diffraction (EBSD). In the as-built sample, prismatic slip was the main mode of deformation, as well as a small amount of basal slip and cross-slip. Some planar slip lines with large length scales were observed across several α lamellae. After hot isostatical pressing, prismatic and basal slip were the main mode of deformation, accompanied by abundant cross-slip and multiple slip, and most of the slip lines were blocked within an α lamellae. These differences in deformation behavior were associated with the coarsening of α laths and the more retained β phase after HIP compared to the as-built alloy. More cross-slip and multiple slip can lead to superior elongation-to-failure and a greater strain hardening effect in the HIP alloy compared to the as-built sample.

Key words: Electron beam rapid manufacturing, Ti-6Al-4V, Hot isostatic pressure, Mechanical properties, Slip behavior

Liu Z., Zhao Z.B., Liu J.R., Wang L., Zhu S.X., Yang G., Gong S.L., Wang Q.J., ang R.Y. Deformation behaviors of as-built and hot isostatically pressed Ti-6Al-4V alloys fabricated via electron beam rapid manufacturing[J]. J. Mater. Sci. Technol., 2019, 35(11): 2552-2558.

Figures/Tables 12

Fig. 1. Typical microstructure of the as-built sample (a, b) and HIP sample (c, d).

Fig. 2. Engineering stress?strain curves of representative tensile samples.

Table 1 Tensile properties of EBRM-produced Ti-6Al-4 V alloy.

Sample	Yield strength, σ_0.2 (MPa)	Ultimate strength, σ_t (MPa)	Elongation (%)
As-built	810 ± 5.0	897 ± 4.6	11 ± 1.2
HIP	780 ± 1.5	876 ± 3.2	14 ± 1.9

Fig. 3. True stress?true strain curves of the plastic portion of the as-built and HIP samples, plotted on logarithmic axes.

Fig. 4. Several typical slip morphologies for the as-built sample (a); at low magnification (b); at high magnification (c).

Fig. 5. Examples of activated slip systems in the tensile sample after 2.0% plastic deformation. The black and red lines represent calculated traces of prismatic and basal slips, respectively.

Fig. 6. Examples of blocked slip lines (a) and slip transferring (b) in as-built tensile samples after 2.0% plastic deformation.

Fig. 7. Several typical slip morphologies for the HIP sample after 2.0% plastic deformation (a); higher magnification (b).

Fig. 8. Examples of activated slip systems in the tensile sample after 2.0% plastic deformation (a) and the relative EBSD maps (b). The blue, red, and green lines represent calculated traces of prismatic, basal, and pyramidal slip systems, respectively.

Table 2 Maximum M factor between the (1-100)[11-20] slip system and various slip systems in the other α-laths.

	Lath 1		Lath 2		Lath 3		Lath 4
	M	μ	M	μ	M	μ	M	μ
Prismatic (1-100)[11-20]→prismatic	0.47	0.36	-	<0.25	0.20	0.31	0.21	0.33
Prismatic (1-100)[11-20]→ basal	0.16	0.30	-	<0.25	0.35	0.47	0.35	0.38
Prismatic (1-100)[11-20]→ <a> pyramidal	0.33	0.46	-	<0.25	0.21	0.37	0.13	0.46
Prismatic (1-100)[11-20]→ <a+c> pyramidal	0.87	0.48	0.92	0.40	0.86	0.35	0.92	0.43

Table 3 Maximum M factor between the (10-10)[-12-10] slip system and various slip systems in the other α-laths.

	Lath 5		Lath 6
	M	μ	M	μ
Prismatic (10-10)[-12-10]→prismatic	0.11	0.35	0.50	0.29
Prismatic (10-10)[-12-10]→ basal	0.87	0.43	0.87	0.40
Prismatic (10-10)[-12-10]→ <a> pyramidal	0.84	0.39	0.85	0.44
Prismatic (10-10)[-12-10]→ <a+c> pyramidal	0.21	0.27	0.20	0.26

Fig. 9. Typical TEM maps of the as-built sample (a) and HIP sample (b) after 2.0% plastic deformation.

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