High Temperature Deformation Behavior of Beta-Gamma TiAl Alloy

Abstract

In this study, high-temperature deformation behavior of newly developed beta-gamma TiAl alloys was investigated in the context of the dynamic-materials model (DMM). Processing maps representing the efficiency of power consumption for microstructure evolution were constructed utilizing the results of compression test at temperatures ranging from 1000oC to 1200oC and strain rates ranging from 10-4/s to 102/s and Artificial Neural Network simulation method. With the help of processing map and microstructural analysis, the optimum processing condition for the betagamma TiAl alloy was investigated. The role of β phase was also discussed in this study.

Hot isostatic pressing and heat treatment development of powder metallurgy beta gamma titanium aluminide alloys

“…Very little is known about the deformation of either the ordered or disordered P phase when it coexists with y and 012, however, it can be assumed that deformation occurs on the <111>{110} slip system as is usually observed for bcc materials [43]. At elevated temperature the P phase is much softer than both the y or 012 phases and as a result is much more easily deformed [40]. Additionally, the P phase can act as a 55 lubricating layer for the other phases during deformation therefore significantly improving the hot workability of the alloy even with only small volume fractions of the P phase present in the microstructure [40], As a result, beta gamma TiAl has been shown to have superior hot workability and machinability than conventional gamma TiAl alloys…”

“…Efforts are now being made to remove the p phase from the microstructure following hot working in order to improve the high temperature properties [55,56,57]. The P phase has also been shown to significantly improve the ductility, but does not give any obvious improvement in damage tolerance [18,40,58]. The fracture toughness of the wrought processed Ti-42Al-10V was satisfactory with an absorption energy of 5 J/cm in a Charpy impact test [56],…”

“…When producing beta gamma ingots for wrought processing it is important to consider both the volume fraction, as well as the morphology of the P phase. It has been shown that forging becomes easier when the volume fraction of P phase is largest [40], Furthermore, an ingot with fine homogeneously dispersed p particles in the matrix has been shown to be significantly better than an ingot with coarse P particles that are not finely dispersed [40]. In an ingot with coarse P particles, deformation during forging or extrusion is concentrated in the p phase and therefore causes flow localization [40].…”

“…However, with the addition of the p phase the hot workability of beta gamma TiAl alloys is significantly improved, making forging and extrusion in generally available facilities possible, therefore significantly reducing the cost [44]. As mentioned in previous sections, the P phase has a low yield strength at high temperatures, therefore it carries most of the deformation during hot 66 working [43], The p phase also acts as a lubrication layer for other phases during deformation [40].…”

“…Not unlike gamma TiAl alloys, the success of a given forging or extrusion process is dependent on the strain rate and temperature at which the process is conducted. The best formability is achieved at the temperature and strain rate at which the material dissipates the power most efficiently [40]. The processing map in Figure 38 shows the power dissipation efficiency for different temperatures and strain rates of an alloy with the composition Ti-42Al-6Nb-3Mn-0.2B.…”