Achieving fully-equiaxed fine β-grains in titanium alloy produced by additive manufacturing

Figures & data

Table 1. Processing parameters for DED.

Laser power (kW)	Scanning velocity (mm/min)	Powder feed rate (kg/h)	Nominal increment (mm)	Spot diameter (mm)
2	900	0.5	0.15	5

Figure 1. The β-grains at the top of Ti6Al4VxNiyB and the initial solidification mechanism of the last layer. (a), (d) Ti6Al4V; (b), (e) Ti6Al4V3Ni; (c), (f) Ti6Al4V3Ni0.05B; (g) grain size d₀ plotted against the inverse Q. (The dashed white lines in a-c separate the equiaxed grains obtained only by solidification from the ones subjected to subsequent thermal-cycling. T_E is the equilibrium liquidus temperature and ΔT_n is the critical undercooling for nucleation).

Table 2. The Q, ΔT₀, m_l, k and Q_i.

Alloy	Q	ΔT0 (K)	Element	ml (K/wt%)	k	Qi
Ti6Al4V	5.1	5.4	Al	5.64	1.15	5.08
			V	0.42	1.01	0.02
Ti6Al4V3Ni	34.02	111.8	Al	6.26	1.09	3.38
			V	0.66	1.0	0
			Ni	−13.80	0.26	30.64
Ti6Al4V3Ni0.05B	39.05	188.7	Al	6.28	1.10	3.77
			V	0.68	0.99	−0.03
			Ni	−13.94	0.26	30.95
			B	−88.70	0.016	4.36

Figure 2. The β-grains at the middle of the Ti6Al4V3NiyB deposits. (a) Ti6Al4V3Ni, (b) Ti6Al4V3Ni0.05B; (c) β-grain size and coarsening degree m; (d) the function of the simulated m with regard to d₀, and the symbols represent the experimental value; the simulated δd_i, d = d₀+Σδd_i, δM_i and M = ΣδM_i with regard to the thermal-cycling number (T_β˂T_p˂T_s) in (e) Ti6Al4V3Ni and (f) Ti6Al4V3Ni0.05B. (T_s and T_β are calculated using Thermo-Calc.).

Figure 3. The microstructures at the middle of the Ti6Al4VxNiyB deposits. As-built: (a) Ti6Al4V, (b) Ti6Al4V3Ni, and (c) Ti6Al4V3Ni0.05B, (d) heat-treated Ti6Al4V3Ni0.05B.

Figure 4. Mechanical properties of Ti6Al4VxNiyB alloys. (a) Representative engineering stress–strain curves; the error bars (UTS and EL) represent one standard deviation. (b) Tensile properties for heat-treated Ti6Al4V3Ni0.05B are comparable with Ti-Cu [6] and Ti6Al4V [10] by DED and the ASTM standard for Ti6Al4V [32]. (c) Anisotropy (the calculation method is shown in [21]).

Figure 5. Fracture surfaces of longitudinal specimens: (a) (c) as-built Ti6Al4V, (b) (d) as-built Ti6Al4V3Ni, Ti6Al4V3Ni0.05B (e) (f) as-built and (g) (h) heat-treated.

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