Microstructure, Tensile, and Creep Behavior of Boron-Modified Ti-15Al-33Nb (at.%)

Abstract

The effect of boron on the microstructure, tensile, and creep behavior of a Ti-15Al-33Nb (at. pct) alloy was investigated. In addition to the normal constituent phases present in the unmodified alloy, the boron-modified alloys contained borides enriched in titanium and niobium. These borides made up to 9 pct of the volume and were present in the form of needles/ laths. Boron additions of 5 at. pct resulted in significant strengthening and stiffening and reduced elongation-to-failure. Smaller boron additions of 0.5 at. pct did not as significantly impact the RT tensile properties, but reduced the 650°C yield strength by 45 pct. Constant load, tensile-creep experiments were performed in the stress range of 150 to 400 MPa and the temperature range of 650°C to 710°C, in both air and vacuum environments. The addition of 5 at. pct boron significantly improved the creep resistance, whereas the addition of 0.5 at. pct boron degraded the creep resistance. In-situ tensile-creep experiments indicated that localized grain boundary cracking was prevalent at the prior-b grain boundaries.

A comparison of field assisted hot pressing and hot isostatic pressing for gas atomized Ti–22Al–26Nb(at.%) and Ti–22Al–26Nb–5B(at.%) powders

“…Though the compacts were both processed under the same pressure and temperature profile, the Ti-22Al-26Nb-5B compact exhibited 0. compact was less than half that of the Ti-22Al-26Nb compact, see Table III and Figures 15a-d, which is likely a result of both the increased Vf of borides and 2 phase, both of which can impede grain growth [9,26,32,[41][42][43]45].…”

“…Using the lattice parameters determined through density functional theory simulations by Trinkle [56] (i.e. a=0.6184nm, b=0.31262nm, c=0.46833nm), selected area diffraction (SAD) patterns and EBSD Kikuchi patterns obtained from the B-rich phase present in a Ti-15Al-33Nb-5B alloy [9] have been successfully indexed according to the space group and lattice site occupancies of the B27 orthorhombic crystal structure [20].…”

“…Research efforts during the past few decades have resulted in the development of titanium (Ti) based intermetallic alloys with a balanced combination of room temperature (RT) elongation-tofailure (f), fracture toughness, RT and elevated-temperature strength, creep resistance, and oxidation behavior [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In particular, Ti2AlNb intermetallic alloys has been investigated due to their potential use in structural aerospace applications [6][7][8][9]18,[20][21][22][23][24][25][26][27][28][29][30][31][32].…”

“…Research efforts during the past few decades have resulted in the development of titanium (Ti) based intermetallic alloys with a balanced combination of room temperature (RT) elongation-tofailure (f), fracture toughness, RT and elevated-temperature strength, creep resistance, and oxidation behavior [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In particular, Ti2AlNb intermetallic alloys has been investigated due to their potential use in structural aerospace applications [6][7][8][9]18,[20][21][22][23][24][25][26][27][28][29][30][31][32]. Such intermetallic alloys differ from -based TiAl intermetallic alloys in that their constituent phases may include the ordered intermetallic orthorhombic (O) phase, based on Ti2AlNb, the ordered hexagonally-closepacked (HCP) intermetallic 2 phase, based on Ti3Al, and the body-centered-cubic (BCC) phase, whose ordering is dependent upon composition [21,22,[33][34][35].…”

“…The addition of small amounts of B to Ti2AlNb and TiAl intermetallics and conventional Ti alloys, such as Ti-6Al-4V(wt.%) and Ti-6Al-2Sn-4Zr-2Mo-0.1Si(wt.%), has been shown to significantly decrease the grain size and/or lamellar spacing leading to significant benefits including increasing tensile strength and fatigue and creep resistance [9,20,[41][42][43][44][45][46][47][48][49][50]. In addition, it reduces the time spent on expensive and energy-intensive thermomechanical processing used to 1 henceforth all compositions will be given in atomic percent unless otherwise specified.…”