Dependence of mechanical properties on the microstructure characteristics of a near β titanium alloy Ti-7333

doi:10.1016/j.jmst.2018.06.018

Abstract

Abstract:

In this work, the microstructure and the corresponding tensile properties of the rolled Ti-7Mo-3Nb-3Cr-3Al (Ti-7333) alloy before and after the thermal treatments were investigated. The results show that a strong α-fiber texture is developed in the rolled Ti-7333 alloy. The deformed matrix and the texture significantly induce the variant selection of α phase. The high strength of the rolled Ti-7333 alloy is attributed to the <110> texture parallel to the tensile direction and the dispersed α phase within the matrix. After the solution treatment followed by the aging treatment, the texture decreases and the microstructure consists of the equiaxed β grains, the spheroidal α_p phase and various needle-like α variants. Eventually, the alloy could achieve an optimal combination with the strength of about 1450?MPa, the ductility of about 10.5% and a considerable shear strength of about 775?MPa. This balance can be ascribed to the performance of the spheroidal α_p phase and various needle-like α_s variants. The results indicate that the Ti-7333 alloy could be a promising candidate material for the high-strength fastener.

Key words: Near β titanium alloy, Hot-rolled Ti-7333, Texture, Thermal treatment, α phase, Mechanical properties

Ruifeng Dong, Jinshan Li, Hongchao Kou, Jiangkun Fan, Bin Tang. Dependence of mechanical properties on the microstructure characteristics of a near β titanium alloy Ti-7333[J]. J. Mater. Sci. Technol., 2019, 35(1): 48-54.

Figures/Tables 10

Fig. 1. Microstructure analyses of the rolled Ti-7333 alloy: (a) back-scattered electron (BSE) image showing the overall microstructure; (b) the corresponding magnification image showing the αp phase; (c) the corresponding IPF orientation map with low-angle grain boundaries (2°-15°, white color) and high-angle grain boundaries (> 15°, black color) showing the significant texture.

Fig. 2. {100} pole figure for the β phase of the hot-rolled Ti-7333 alloy showing the significant texture components.

Fig. 3. Detailed TEM images of the rolled Ti-7333 alloy showing (a) the dislocations with high density and (b) the needle-like αs phase with a same growth direction (the inset showing the BOR between αs and β phases).

Fig. 4. Tensile properties of the Ti-7333 alloy: (a) the rolled state; (b) after the solution treatments; (c) after the aging treatments followed by the solution treatment.

Fig. 5. Microstructure of Ti-7333 alloy after the solution treatment at 820?°C for 30?min: (a) BSE image (the inset showing the αs preserved on grain boundary); (b) IPF orientation map; the microstructure of Ti-7333 alloy after the solution treatment at 900?°C for 30?min; (c) optical image (the inset showing the electron diffraction of β matrix); (d) IPF orientation map.

Fig. 6. BSE images and TEM images showing the microstructures under different thermal treatment conditions: (a) and (c) 820?°C /30?min, AC?+?500?°C /6?h, AC; (b) and (d) 820?°C /30?min, AC?+?520?°C /6?h.

Table 1 Morphology parameters of αs precipitates under different thermal treatment conditions.

Thermal treatment	Average width (nm)	Average length (μm)	Volume fraction of α phase (%)
820?°C/30?min, AC?+?500?°C/6?h, AC	49.50?±?4.96	1.88?±?0.54	62.09?±?6.43
820?°C/30?min, AC?+?520?°C/6?h, AC	59.67?±?3.86	3.38?±?0.91	60.13?±?5.69

Fig. 7. EBSD analyses of the samples aging-treated at 520?°C for 6?h: (a) band contrast image; (b) the corresponding IPF orientation map; (c) the corresponding pole figures of grain β3 and the α variants within it.

Fig. 8. Comparison of the tensile properties of Ti-7333 alloy and other typical high-strength titanium alloys.

Fig. 9. Shear strength of Ti-7333 alloy after different thermal treatments.

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