Microstructures, Mechanical Properties, and Shape Memory Characteristics of Powder Metallurgy Ti₅₁Ni₄₉ Modified with Boron

摘要

Ti₅₁Ni₄₉ compacts consolidated with persistent liquid-phase sintering usually contain Ti₂Ni networks at the grain boundaries, which cause adverse effects on mechanical properties. With 0.5 and 1.0 at pct B additions, fine TiB forms during heating and sintering and acts as a nucleation site for Ti₂Ni to precipitate within the grain during cooling. The resultant uniform distribution of TiB and Ti₂Ni impedes grain growth and prevents the formation of continuous Ti₂Ni precipitates at grain boundaries. As a result, a significant increase in tensile elongation, and not a decrease, as in most as-cast titanium alloys, is obtained because of these changes. The tensile strength also increases, without deterioration of the shape memory characteristics. The tensile strength and elongation are close to those of wrought TiNi alloys.