A Comparative Study on Microstructure and Mechanical Properties of Ti‐43/46Al–5Nb–0.1B Alloys Modified by Mo

Abstract

To improve mechanical properties of TiAl-Nb alloys and obtain effects of Al content on microstructure, Ti-43/46Al-5Nb-0.1B-xMo alloys are prepared. Phase constitution, macro-/microstructure volution, and mechanical properties of them are investigated systematically and compared in detail. Results show that the lamellar colony size refines, B2 phase increases and Al-segregation in interdendritic regions aggravates with the increase in Mo content. The increased B2 phase is attributed to the increased Mo segregated at the grain boundaries during β/α transformation, and the aggravated Al-segregation is attributed to the increased Al rejected into the interdendritic areas during L/β solidification. Compressive results show that the strength and strain increase about 150 MPa and 6% when the Mo content increases to 0.8 at% for Ti-43Al-5Nb-0.1B-xMo alloys; they increase about 343 MPa and 4% when Mo content increases to 1.2 at% for Ti-46Al-5Nb-0.1B-xMo alloys. Both the strength and strain decrease when Mo content further increases. The grain refinement strengthening and solid solution strengthening caused by Mo are contributed to the improved strength and strain. However, excessive B2 phase and severe Al-segregation deteriorate the mechanical properties of the alloys, which act as the cracking sources.

Research on Hot Deformation Behavior of Mo‐Containing Ti2AlNb‐Based Alloy

“…Researchers [ 31,32 ] found that the Mo atom in titanium alloys occupies the position of Al or Nb atom in the B2 phase, which causes segregation of Al elements. Figure shows the distribution diagram of the Al element adjacent to the crack of Ti 2 AlNb−2Mo alloy.…”

“…At the same time, under larger loading stress, cracks are easily generated along with the interface of the α 2 /B2 phase and propagate to the substrate of the B2 phase, as shown in Figure 10d,e. Researchers [31,32] found that the Mo atom in titanium alloys occupies the position of Al or Nb atom in the B2 phase, which causes segregation of Al elements. Figure 12 shows the distribution diagram of the Al element adjacent to the crack of Ti 2 AlNbÀ2Mo alloy.…”

“…It indicates that the instability of Ti 2 AlNbÀ0.5Mo alloy at the deformation temperature of 1000 C will be affected by the microstructure and morphology, and cracks easily occur and propagate at the grain boundaries of B2 grains. The instability behavior of Ti 2 AlNbÀ2Mo alloy is determined by the basic characteristics of the phase.Researchers[31,32] found that the Mo atom in titanium alloys occupies the position of Al or Nb atom in the B2 phase, which causes segregation of Al elements. Figure12shows the distribution diagram of the Al element adjacent to the crack of Ti 2 AlNbÀ2Mo alloy.…”

Effects of Al and Mo on Microstructure and Hardness of As-Cast TNM TiAl Alloys

“…Therefore, the size of the lamellar colony, which is formed by the α grain, was small. From the point of view of the β-stable phase, 1 at.% Mo is equal to 4-6 at.% Nb [2,6,24], so an increase of 0.5 at.% Mo can form more β phase, leading to more pronounced grain refinement. However, the α phase appears in the solid phase transformation path of the TNM alloy, when the Al content exceeds 43.5 at.%, and the α-phase region expands with the increase in Al content.…”

Low-Cycle Fatigue Behaviour of Titanium-Aluminium-Based Intermetallic Alloys: A Short Review

“…Although the single-phase alloys offer excellent resistance to environmental attack (oxidation and hydrogen absorption) and initially drew the interest of several researchers, their uttermost lack of ductility and fracture toughness at room temperature, particularly in the binary state rendered them irrelevant for any engineering application [10]. Nevertheless, extensive research has shown that the two-phase (α 2 -Ti 3 Al + γ-TiAl) or multi-phase γ-TiAl based alloys that solidify through the β-phase (i.e., L + β → β) and the α-phase (i.e., peritectic reaction: L + β → α ) with Al composition between 40 and 48 at.% [Ti (40)(41)(42)(43)(44)(45)(46)(47)(48)] have engineering significance [11,12]. These alloys are known as γ-TiAl-based alloys with the γ-(TiAl) and α 2 -Ti 3 Al being the primary and secondary phases, respectively.…”