The Effect of Heat Treatment and Surface Engineering in Creep Behavior of Ti-6Al-4V Alloy

Ti-6Al-4V is currently used in aeronautic and aerospace industry mainly for applications that require resistance at high temperature such as, blades for aircraft turbines and steam turbine blades. Notable advances have been observed in the development of titanium alloys with the objective of improving the creep properties. Increased oxygen levels are associated with increased microhardness and decreased ductility in titanium. In spite of this, Ti-6Al-4V containing an (α+β) structure continues to be the workhorse of the titanium industry due to their high specific strength, corrosion resistance, excellent high temperature properties and metallurgical stability. The objective of this work was study the the effect of heat treatment and surface engineering in creep behavior of Ti-6Al-4V alloy. The samples were submitted to heat treatment and surface coatings (PIII, laser, thermal spray) to avaliate its creep resistance. Short-term creep tests were performed under load creep tests were conducted with Ti-6Al-4V alloy at 600°C. The creep tests were conducted on a standard creep machine at stress of 125 to 319 MPa. Samples with a gage length of 18.5 mm and a diameter of 3.0 mm were used for all tests. When the Ti-6Al-4V was tested the effect of the oxidation was smaller and the behavior of the creep curves showed that the life time was better in samples submitted to laser Nd:YAG treatment and got highest creep resistance. There was an increasing of ductility of material (final strain) and life time. Occurred a decreasing of steady state creep in function of the reduction of oxidation process, showing that for the Ti-6Al-4V alloy their life time was strongly affected by the superficial treatment by laser. Analysis of the steady-state creep suggests that the creep mechanisms are related to dislocation climb in samples treated by laser.