Heat Treatment On The Microstructure And Properties Of TC21 Titanium Alloy

This paper details the influence of thermomechanical processing (TMP) on the microstructures and mechanical properties of TC21 titanium alloy, a new alpha+beta alloy with high strength, ductility and toughness developed in China. By using EDS, SEM, TEM and optical microscope, the effect of mi-crostructure on mechanical properties under various conditions of deformation and heat treatment has been investigated and the strengthening and toughening mechanism has been researched. Moreover, the thermal stability of the alloy has been studied.Many valuable results have been obtained in the study. Alpha+beta hot working, ct/p-solution treatment plus aging develops an equiaxed microstruc-ture, which has moderate strength, enough ductile and low fracture toughness and goes with dimpled failure. Whereas beta hot working, a/p-solution treatment plus aging develops a lamellar transformed-beta microstructure, which has high strength, low ductile and high fracture toughness and goes with transgranular brittleness failure. With the ascent of the solution treat temperature or the decrease of cooling rate from the solution treat temperature, the amount of the trajisformed-beta phase increases and so does the tensile strength of the alloy but the ductility decreases. With increase of aging temperature or aging time, the tensile strength increases firstly and then decreases. For optimum strength, ductility and toughness, TMP route is that beta process followed a/p-solution treatment plus aging. The microstructure of the alloy has no much difference after long term aging, while the precipitate of 2-Ti3Al has been identified in electron diffraction patterns. A few interface phase has been observed in this alloy.