Antibacterial copper-bearing titanium alloy prepared by laser powder bed fusion for superior mechanical performance

doi:10.1016/j.jmst.2022.04.056

Abstract

Abstract:

Copper element was added in pure titanium to produce a new biomedical titanium-copper alloy by laser powder bed fusion (LPBF). Addition of copper can eliminate the mismatch of high strength but poor ductility problem caused by lath α' martensite, which is the usual microstructure of near α titanium alloy fabricated by LPBF. Instead of by the usual trade-off relationship between strength and ductility, which is a long-standing challenge for martensitic titanium alloys, in this study, we proposed a boundary engineering strategy and aim to synergistically enhance the strength and ductility of martensitic titanium alloy fabricated by LPBF. It is hypothesized that whilst both low-angle and high-angle grain boundaries are beneficial to the strength, high-angle grain boundary can simultaneously improve the ductility of materials. To test this strategy, a Ti-5Cu (wt.%) alloy is selected to compare against pure titanium and Ti-6Al-4V at the same laser processing conditions. EBSD, TEM and XRD analysis show that the as-fabricated LPBF Ti-5Cu alloy is comprised of partially tempered martensite with extraordinarily high number density of both high-angle and low-angle grain boundaries as well as low dislocation density. Such microstructure enables a high tensile strength of 940-1020 MPa, which is at a similar level as LPBF Ti-6Al-4V, and an excellent elongation of 13%-16%, twice as much as that of LPBF Ti-6Al-4V. The mechanism of microstructure refinement in LPBF Ti-5Cu at different levels from prior-β grains, martensitic packets, blocks to laths is also discussed.

Key words: Titanium alloy, Laser powder bed fusion, Boundary engineering, Martensite, Mechanical properties

Huan Liu, Hai Wang, Ling Ren, Dong Qiu, Ke Yang. Antibacterial copper-bearing titanium alloy prepared by laser powder bed fusion for superior mechanical performance[J]. J. Mater. Sci. Technol., 2023, 132: 100-109.

Figures/Tables 12

Table 1. LPBF printing parameters in this paper.

Samples	Scanning velocity, v (mm s⁻¹)	Laser power, P (W)	Layer thickness, t (μm)	Hatch spacing, h (μm)	Energy density, $E=\frac{P}{t\nu h}$(J mm⁻³)	Inter-layer time (s)
Ti-1	1000	360	40	100	90	10
Ti-2	1500	360	40	100	60	10
Ti-5Cu-1	1000	360	40	100	90	10
Ti-5Cu-2	1500	360	40	100	60	10
Ti-6Al-4V-1	1000	360	40	100	90	10
Ti-6Al-4V-2	1500	360	40	100	60	10

Fig. 1. EBSD analysis of martensite in as-fabricated LPBF-Ti, Ti-5Cu and Ti-6Al-4V alloys. (A) Inverse pole figures (IPF) images showing blocks interior in martensitic microstructure. (B) Pole figures of LPBF-Ti, Ti-5Cu and Ti-6Al-4V samples. The red circles indicate pairs of parallel planes or directions in α′ and β phases. Note the difference in scale bars between A1/A2 and A3-A6.

Fig. 2. Five types of misorientation among all α' variants (A-L) as a result of ideal Burger OR.

Fig. 3. Identification of different levels of boundaries. (A) In LPBF Ti-1 sample; (B) In LPBF Ti-5Cu-1 sample. Blue lines are the grain boundaries following the Burgers OR, while black lines are the grain boundaries, and red lines are the LAGBs. Note that the magnification is different in (A) and (B).

Table 2. Statistics of substructure size, dislocation density and selected mechanical properties of martensite in LPBF titanium alloy.

Samples	β grain size (μm)	Packet size (μm)	Block width (μm)	Lath width (nm)	ρ (× 10¹³ m⁻²)	σ_0.2 (MPa)	UTS (MPa)	Elongation, δ (%)
Ti -1	258.06 ± 58.0	70.49 ±.490	5.675 ± 5490	1172 ± 249	5.9206ion	588.5 ± 54.5	642.6 ± 6527	19.5 ± 9.2
Ti -2	213.37 ± 13.3	59.38 ±.383	4.887 ± 7383	1151 ± 138	8.0137ion	615.7 ±.6.4	687.6 ± 6413	19.137io
Ti-5Cu -1	52.52 ± 2.52	13.71 ± 7152	1.181 ± 1152	186 ± 8152	8.49 ±.152	837.6 ±.7.4	945.5 ±.552	15.9 ± 5.9
Ti-5Cu -2	43.16 ± 3.16	10.46 ± 4616	0.971 ± 7616	1979616u	9.91 ± 1697	850.4 ±.8.6	1010.8 ± 010.	13.3 ± 3.3
Ti-6Al-4V -1	165.24 ± 65.2	43.12 ± 3.12	1.801 ± 0112	455 ± 5112	24.2 ±.212	969.7 ± 98.5	1019.0-4V -	7.29.0-4
Ti-6Al-4V -2	148.35 ± 48.3	39.675-4V	1.875 ± 5.67	639 ± 9.67	33.0 ±.067	955.3 ± 50.7	1038.2-4V -	6.94.2-4

Fig. 4. Distribution of misorientation angles in LPBF-Ti, Ti-5Cu and Ti-6Al-4V per unit area.

Fig. 5. TEM images of as-fabricated LPBF-Ti, Ti-5Cu and Ti-6Al-4V. (A) Bright-field TEM images of Ti-1, Ti-5Cu-1 and Ti-6Al-4V-1 samples. (B) High angle annular dark field (HAADF) image and X-ray energy dispersive spectrum (XEDS) images inside a martensite block of the Ti-5Cu-1 sample. (C) HAADF and XEDS images inside a martensite block of the Ti-6Al-4V-1 sample.

Fig. 6. XRD analysis to measure dislocation density in LPBF-Ti, Ti-5Cu and Ti-6Al-4V samples. (A) XRD profiles of materials. (B) Dependence of FWHM on the peak positions in LPBF-Ti, Ti-5Cu and Ti-6Al-4V samples. (C) Linear fitting of ln[A(L)]/L2 vs. ln(L) in an L range of 0.1-0.4. (D) Linear fitting of $\text{ }\!\!\Delta\!\!\text{ }K$ vs. $K{{\bar{C}}^{1/2}}$ curves.

Fig. 7. Mechanical properties of materials. (A) Stress-strain curves of LPBF-Ti, Ti-5Cu and Ti-6Al-4V samples. (B) Comparison of tensile strength and elongation of Ti, Ti-Cu, Ti-6Al-4V and some titanium alloys manufactured by different methods. The data of LPBF titanium alloy obtained in this paper are marked by red dotted lines.

Fig. 8. Fractographs of LPBF-Ti, Ti-5Cu and Ti-6Al-4V samples, in which the fibrous region and radiation region were artificially colored in nattier blue and yellow, respectively.

Table 3. Calculation results of K1, K2, μ and M1.

Samples	K₁	K₂	μ	M₁
Ti	311.76	232.93	40,100	1.0160
Ti-5Cu	181.32	168.15	40,400	0.8878
Ti-6Al-4V	213.74	192.18	41,000	1.0566

Fig. 9. Contribution of individual strengthening mechanisms in LPBF-Ti, Ti-6Al-4V and Ti-5Cu alloys.

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