Structure and mechanical properties of the new VT25u heat-resistant titanium alloy

Abstract

1. The VT25u alloy structure is typical of α+β alloys. A feature of this alloy when compared with the structure of other heat resistant titanium alloys is the wide variability of the constituents due to the high total alloying level in the alloy and the presence of tungsten which markedly reduces the diffusion rate. 2. The influence of the structure on the VT25u alloy mechanical properties is essentially similar to its effect on the properties of other heat-resistant α+β titanium alloys. At the same time, the VT25u alloy is characterized by a higher structural sensitivity of the plastic properties and the impact strength. Additionally, deviations are possible from the conventional effect of the structure type on the impact strength, if specimens with cracks (this is less for an alloy with a lamellar structure than for an alloy with a globular structure). The most probable cause of this anomaly is the silicide particles, which are mainly distributed at the grain boundaries in the lamellar structure, and which are larger and present in a greater quantity than is the case in the globular structure. 3. The optimum combination of properties for the VT25u alloy is achieved when 1120 N/mm2 ≤ σ2 0B ≤ 1200 N/mm2. Increasing σ2 0B may result in an inadmissable reduction in the ductility, impact strength, the ductile failure indices, and the multi and low cycle fatigue strength for notched specimens. 4. On a basis of the data obtained, as well as similar results obtained from other VT25u alloy semifinished products with varying structures and strength levels, a table has been produced for predicting the values of all the required properties.