Mixed Grain Structure and Mechanical Property of Ti-6Al-4V-0.5BN (wt%) Alloy Fabricated by Selective Laser Melting

doi:10.1007/s40195-022-01507-2

Abstract

Abstract:

A novel Ti-6Al-4V-0.5BN (wt%) alloy fabricated by selective laser melting exhibited mixed grain structure containing band distributed columnar and equiaxed prior-β-Ti grains. The mixed grain structure, microstructure within prior-β-Ti grains and compressive properties have been characterized and discussed. The band thickness ratio of columnar to equiaxed prior-β-Ti grains was 3:1. The columnar grains were 10 ± 4 μm in width and 53 ± 24 μm in length, the equiaxed grains were 7 ± 4 μm in size. There were nano- to micron-scaled α-Ti/β-Ti laths within prior-β-Ti grains and nano-scaled TiB along prior-β-Ti grain boundaries. The heterogeneous distribution of prior-β-Ti grain boundaries and TiB particles contributed to the hardness difference between the bands of columnar and equiaxed prior-β-Ti grains. BN addition resulted in the mixed grain structure in the SLMed Ti64 alloy, forming a multi-scaled microstructure, which contributed to high compressive yield strength of 1648 MPa. This work provided a new strategy to regulate the microstructure for the additive manufactured Ti alloys.

Key words: Selective laser melting, Ti-6Al-4V alloys, Prior-β-Ti grains, Strength

Liqing Wang, Zhen Zhang, Zhanyong Zhao, Shenghua Zhang, Peikang Bai. Mixed Grain Structure and Mechanical Property of Ti-6Al-4V-0.5BN (wt%) Alloy Fabricated by Selective Laser Melting[J]. Acta Metallurgica Sinica (English Letters), 2023, 36(6): 917-925.

Figures/Tables 7

Fig. 1 Morphologies of Ti64, BN and Ti64-0.5BN powders: a Ti64; b BN; c Ti64-0.5BN; d distribution of Ti and B in c

Fig. 2 Schematic diagram of the SLM process and the samples

Fig. 3 Grain morphologies of the SLMed Ti64-0.5BN alloy: a, b optical microstructure; c, d IPF-BD mapping of α-Ti laths inside columnar and equiaxed prior-β-Ti grains; e, f IPF-BD mapping of reconstructed columnar and equiaxed prior-β-Ti grains (The white parts in c, d and e, f represented areas could not be indexed or reconstructed.)

Fig. 4 TEM images of the SLMed Ti64-0.5BN alloy: a bright-field image with α-Ti, β-Ti and TiB; b, c distribution of Al and V, respectively; d HRTEM of α-Ti and TiB; e FFT diffraction spot of TiB and corresponding IFFT image; f FFT diffraction spot of α-Ti and corresponding IFFT image

Fig. 5 Schematic diagram of the prior-β-Ti grain morphology in SLMed Ti64-0.5BN alloy

Fig. 6 Mechanical property of the SLMed Ti64-0.5BN alloy: a compressive stress-strain curves; b microhardness of the columnar and equiaxed prior-β-Ti grains; c and d CYS and UCS of Ti64 with different alloying elements or ceramic particle additions

Table 1 Comparisons of microstructure and mechanical properties of AMed Ti64, Ti64-BN and Ti64-N alloys

Materials	Grains	Second phase	Hardness (HV)	CYS (MPa)	UCS (MPa)	Maximum strain (%)	Ref.
Ti64-0.5BN	β: C 10 ± 4 μm in width and 53 ± 24 μm in length E 7 ± 4 μm in size α: 0.7 ± 0.2 μm in width, aspect ratio of 1.7-1.8	TiB: nanoscale Solid solution of N	C: 557 ± 9.6 E: 645 ± 30	1648 ± 1.7	1966 ± 24	6.545 ± 0.3	Present work
Ti64	β: C 337 μm in width and a few millimeters in length α: 0.55 μm in width, aspect ratio of > 10	—	342.4 ± 1.2	921 ± 18	1198 ± 5	24.2 ± 1.1	[8]
Ti64-0.4BN (nanotubes)	β: E 9 μm in size α: 0.5 μm in width, aspect ratio of ~ 2.1	TiB: nanoscale Solid solution of N	433.8 ± 1.7	1407 ± 2	1678 ± 12	14.3 ± 1.0	[8]
Ti64-0.64 N	β: — α': 1-10 μm in length	AlN, TiN: 1-5 μm	511	1721 ± 30	2010 ± 38	2.60 ± 0.4	[32]

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