Characterization of Prealloyed Ti-6Al-4V Powders from EIGA and PREP Process and Mechanical Properties of HIPed Powder Compacts

doi:10.1007/s40195-017-0540-4

Abstract

Abstract:

Prealloyed Ti-6Al-4V powders were prepared by electrode induction melting gas atomization (EIGA) and plasma rotating electrode process (PREP) in this work. A comparative study of EIGA and PREP powders for hot isostatic pressing (HIPing) compaction was conducted. Characterization of important technological parameters such as particle size distribution, powder surface morphology and flowability was carried out. Microstructure and mechanical properties of Ti-6Al-4V powder compacts HIPed from EIGA and PREP powders were also investigated. The results showed that the EIGA powder has a finer average particle size and higher tap density, while the PREP powder has better flowability and less pores. Micropores can be observed in heat-treated EIGA powder compacts by X-ray tomography and the porosity was found to be about 0.02%. There are no micropores (≥4 μm) to be detected in heat-treated PREP powder compacts. Transgranular fracture mode as well as micropores contributes to the scatter in fatigue property of heat-treated PREP powder compacts. The respective advantages and disadvantages of both EIGA and PREP powders for producing Ti-based complex parts through HIPing were also discussed.

Key words: Ti-6Al-4V, Prealloyed powder, Hot isostatic pressing, Near-net shape forming

Rui-Peng Guo, Lei Xu, Bernie Ya-Ping Zong, Rui Yang. Characterization of Prealloyed Ti-6Al-4V Powders from EIGA and PREP Process and Mechanical Properties of HIPed Powder Compacts[J]. Acta Metallurgica Sinica (English Letters), 2017, 30(8): 735-744.

Figures/Tables 15

Table 1 Chemical compositions of Ti-6Al-4V powders (wt%)

Powder	O	N	H	Al	V	Fe	Si	C	Ti
EIGA	0.110	0.001	0.001	6.05	4.04	0.05	0.05	0.03	Bal.
PREP	0.092	0.015	0.004	5.95	4.07	0.13	0.04	0.01	Bal.

Fig. 1 Geometries and dimensions of specimens for a tensile, b impact, c high-cycle fatigue tests

Fig. 2 Particle size distributions of EIGA and PREP Ti-6Al-4V powders

Fig. 3 Ti-6Al-4V powder surfaces: a EIGA, b PREP, c, d are higher magnifications of a, b

Fig. 4 Cross-sectional microstructure of Ti-6Al-4V powders: a EIGA, b PREP

Fig. 5 Cumulative particle size distribution and relationship between the frequency of gas bubble and powder size range for EIGA Ti-6Al-4V powder

Table 2 Summary of tap density and flowability of EIGA Ti-6Al-4V powders with different powder fractions

Powder fraction (μm)	Tap density	Flowability (g/s)
Powder fraction (μm)	Tap density	Φ 6 (mm)	Φ 8 (mm)	Φ 10 (mm)
180-250	0.495	10.3	18.9	58.9
120-180	0.583	13.8	23.6	71.4
80-120	0.635	17.4	26.8	96.0
60-80	0.661	6.8	9.1	45.2
0-60	0.664	5.8	7.6	36.8
0-250	0.680	12.4	19.8	67.6

Fig. 6 Contour map of flowability of EIGA Ti-6Al-4V powder

Fig. 7 Microstructure for Ti-6Al-4V powder compacts: a as-HIPed EIGA, b as-HIPed PREP, c heat-treated EIGA, d heat-treated PREP samples. 1 Lamellar α grain gathered in colonies; 2 nodular α grain

Table 3 Phase evolution of Ti-6Al-4V powder compacts after duplex annealing

Condition	Phase	V_p (%)	[M] (wt%)
Condition	Phase	V_p (%)	Ti	Al	V
EIGA HIPed	α	94.1	90.7/90.7/91.6	7.1/7.2/6.6	2.2/2.1/1.8
EIGA HIPed	β	5.9	77.8/80.1/82.4	3.7/4.7/4.2	18.5/15.3/13.4
EIGA heat-treated	α	84.5	91.2/90.9/90.9	6.9/6.8/6.9	1.9/2.3/2.2
EIGA heat-treated	β	15.5	85.5/85.6/85.1	5.0/4.4/4.9	9.5/9.9/10.0
PREP HIPed	α	95.3	90.9/91.6/91.7	6.2/5.6/6.2	1.9/2.8/2.1
PREP HIPed	β	4.7	88.1/86.2/86.5	4.9/4.2/4.4	6.2/9.6/9.1
PREP heat-treated	α	87.3	91.4/90.8/91.4	7.2/7.4/7.1	1.4/1.8/1.5
PREP heat-treated	β	12.7	87.8/87.8/86.7	5.7/5.6/5.5	6.5/6.6/7.8

Fig. 8 Micro-CT images for mapping the pore size distribution of a heat-treated EIGA [11], b heat-treated PREP Ti-6Al-4V specimens

Table 4 Room temperature tensile, impact toughness and HCF properties of Ti-6Al-4V powder compacts

Sample	E (GPa)	0.2% Y.S. (MPa)	UTS (MPa)	El. (%)	R.A. (%)	A (kJ/m²)	HCF (MPa)
As-HIPed EIGA	117	849	935	17.5	48	580	520 [11]
Heat-treated EIGA	117	888	995	18.5	47	515	540 [11]
As-HIPed PREP	115	834	905	17.0	42	680	NA
Heat-treated PREP	115	857	944	19.5	46	630	510

Fig. 9 Tensile fracture surfaces of Ti-6Al-4V alloy: a as-HIPed EIGA, b heat-treated EIGA, c as-HIPed PREP, d heat-treated PREP specimens

Fig. 10 S-N curves for heat-treated Ti-6Al-4V samples. Runout specimens are marked with arrows

Fig. 11 Fatigue fracture surface of heat-treated PREP Ti-6Al-4V samples: aσmax = 520 MPa, Nf = 3,374,525, bσmax = 560 MPa, Nf = 2,695,330, cσmax = 520 MPa, Nf = 427,160, dσmax = 600 MPa, Nf = 1,977,904

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