Hot working

About: Hot working is a research topic. Over the lifetime, 4512 publications have been published within this topic receiving 70521 citations.

Processing maps for hot working of titanium alloys

Abstract: In recent years, processing maps are being used to design hot working schedules for making near-net shapes in a wide variety of materials. In this paper, the results obtained on the characterization of hot working behavior of titanium and its alloys using the approach of processing maps are described. In commercial purity α titanium, dynamic recrystallization (DRX) domain occurs at 775°C and 0.001 s−1 with an efficiency of power dissipation [2m/(m+1) where m is the strain rate sensitivity of flow stress] of 43%. The DRX domain shifts to higher strain rates when the interstitial impurity content is lowered. In the near-α and α-β alloys like IMI 685, Ti–6Al–4V, the preform microstructure has a significant influence on the processing maps. For example, in the transformed β (Widmanstatten) preform microstructures, these alloys exhibit a domain of spheroidization at lower temperature and a domain of β superplasticity at higher temperatures, both occurring at slow strain rates. These domains merge at the β transus because of the occurrence of damage processes which lower the tensile ductility. On the other hand, processing maps on alloys with equiaxed preform microstructure exhibit a clear superplasticity domain in the α-β range and the β phase undergoes DRX with a power dissipation efficiency of ≈45–55%. Titanium materials in general, exhibit wide flow instability regimes due to adiabatic shear bands formation at higher strain rates and hence careful process design has to be adopted for successful forging and microstructural control.

Flow behavior and globularization kinetics during hot working of Ti–6Al–4V with a colony alpha microstructure

Abstract: The effect of process variables on flow response and microstructure evolution during hot working of Ti–6Al–4V with a colony alpha preform microstructure was established using isothermal hot compression tests. Testing was conducted on material with prior-beta grain sizes of 100 μm or 400 μm at strain rates of 0.001–10 s−1, test temperatures between 815 and 955°C, and height reductions of 40–80%. All of the flow curves exhibited a peak stress followed by moderate flow softening. The absence of a grain/colony size dependence of flow behavior, coupled with relatively low values of the strain rate sensitivity of the flow stress (∼0.05–0.30), led to the conclusion that deformation was controlled by dislocation glide/climb processes. Flow softening was interpreted in terms of deformation heating and substructure/texture evolution. The dependence on strain rate and temperature of the kinetics of dynamic globularization of the colony microstructure was complex and appeared to be of second-order importance compared to the effects of strain per se, thus suggesting the dominance of dislocation-type processes for the control of globularization as well.