The effect of a small addition of boron on the sintering densification, microstructure and mechanical properties of powder metallurgy Ti–7Ni alloy

• Published in: Journal of alloys and compounds 2013-04, Vol.555, p.339-346
• Main Authors: Luo, S.D., Yang, Y.F., Schaffer, G.B., Qian, M.
• Format: Article
• Language: English
• Subjects: Alloy powders; Alloy systems; Alloying additive; Applied sciences; Boron; Compacting; Condensed matter: structure, mechanical and thermal properties; Deformation and plasticity (including yield, ductility, and superplasticity); Densification; Density; Exact sciences and technology; Intermetallic compounds; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Metals. Metallurgy; Microstructure; Modification; Physics; Powder metallurgy; Powder metallurgy. Composite materials; Production techniques; Refinement; Sintering (powder metallurgy); Technology; Titanium alloys; Titanium base alloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2012.12.068

► A small addition of B produces near fully-dense Ti–7Ni alloy at ⩾1200°C for just 15min. ► The long pre-eutectoid α-laths change to near-equiaxed α-Ti by B. ► Persistent liquid with improved liquid–solid wettability forms due to B. ► Elemental B is more effective than TiB2 as a sintering aid to Ti–7Ni alloy. ► The properties of Ti-7Ni are determined by the eutectoid structure but affected by B. The effect of a small addition of boron (B) on the sintering, sintered microstructure and mechanical properties of a Ti-7Ni alloy (wt.%) compacted from −100 mesh hydride-dehydride (HDH) Ti powder has been investigated systematically. An addition of ⩾0.62%B to the Ti–7Ni alloy resulted in fast, near full-densification (⩾99% relative density) within 15min at 1200°C, compared to 95.6% relative density obtained after 120min at 1200°C without B, compacted at 400MPa in both cases. In addition, the pre-eutectoid α phase changed from long parallel α-laths (up to∼500μm) to near-equiaxed α-Ti throughout the microstructure with an addition of ⩾0.31%B. Elemental B was found to be more effective than TiB2 as a sintering aid for Ti-7Ni. A small addition of B increased both the tensile strength and yield strength of Ti–7Ni but at the expense of tensile ductility. The mechanisms behind each of these observations were discussed.