Die and mould production: die extrusion behaviour of Ti-10V-2Fe-3Al alloy
thesisposted on 23.02.2017, 02:24 by Al-Salihi, Huda Akram
Present study aims is to correlate the microstructural evolution with mechanical flow behaviour for Ti-10V-2Fe-3Al alloy during plastic deformation processes, in order to maintain the desirable microstructure without damage occurrence. Deformation behavior for Ti-10V-2Fe-3Al alloy during elevated temperature compression, tension and extrusion process was examined. Hot compression data at temperatures above and below, as well as at transus temperature (800°C) was examined at three strain rates. The key outcomes are summarized as follow: 1- A reliable phenomenological equation for Ti-10V-2Fe-3Al alloy was developed based on the hyperbolic-sine law to describe the flow stress dependence on the temperature and strain rate during plastic deformation. This phenomenological equation was effectively implemented in the FEM DEFORM2D software to predict damage evolution for Ti-10V-2Fe-3Al alloy during hot compression test. 2- The critical conditions for the initiation of dynamic recrystallization were mathematically determined at deformation temperatures 800°C, 810°C, 850°C and 870°C. 3- Optimize processing parameters by designing processing map for Ti-10V-2Fe-3Al alloy based on the variation of the power dissipation efficiency and instability criteria. The optimum region with higher power efficiency was observed at temperature range (760°C~795°C) and strain rate range (0.01 s-1 ~0.16 s-1). However, the instability region was clearly observed at 760°C and higher strain rate 1s-1, due to the formation of adiabatic shear bands. Extrusion process was carried out at 1000°C and 1100°C and extrusion ratio 8:1 on the samples that had been solution treated at 760°C and 900°C. Dynamic recovery, dynamic recrystallization, abnormal grain growth and surface cracks that might occur during extrusion, were critically identified. It was found that the billet sample that extruded at 1100°C (larger grain size) exhibited abnormal grain growth (in some regions). Further, recrystallized grains were clearly observed in both extrusion temperatures especially in the deformation zone. Simulation results showed that the extrusion temperature and speed are independent variables, and that the material at the centre of the billet does not suffer damage, but beyond a critical radius, damage increases significantly. Critical fracture criteria for Ti-10V-2Fe-3Al alloy based on Cockcroft - Latham were obtained from the hot tensile tests at 760°C 800°C and 870°C and strain rates 0.01s-1, 0.1s-1 and 1 s-1. It was found that the damage value increases as the temperature decreased and strain rate increased.