DYNAMIC FRACTURE CHARACTERISTICS OF INJECTION MOLDED TITANIUM ALLOY COMPACTS

摘要

Dynamic fracture characteristics are important for the application of titanium and its alloys in various industrial fields. The fatigue properties of metal injection molded (MIM) titanium and Ti-6Al-4V compacts were evaluated. Fatigue strength in rotating bending was found to be about one-third of the static tensile strength; this is attributed to cracking initiated at surface pores. With the addition of chromium or TiB_2 to Ti-6Al-4V, the sintered compacts exhibited a fine grain size, resulting in higher fatigue strength. Hot isostatic pressing (HIP) was used to further consolidate chromium-containing Ti-6Al-4V, resulting in >99% of the pore-free density (PFD) and an attendant fatigue strength >350 MPa. Crack-propagation behavior was studied by surface replication of Ti-6Al-4V specimens containing chromium at 80% fatigue life to understand the role of residual porosity. Surface cracks were present running from pore to pore, thereby limiting fatigue strength.