An Experimental Assessment of the Effects of Heat Treatment on the Microstructure of Ti-47Al-2Cr-2Nb Powder Compacts

Abstract

A detailed and systematic microstructural characterization has been carried out on a Ti-47Al-2Cr-2Nb (at. pct) intermetallic alloy processed by powder metallurgy (PM). Heat-treatment parameters such as isothermal temperature, holding time, and cooling rate were varied in order to produce a series of near-c, duplex, and fully lamellar microstructures. These were then quantitatively analyzed in terms of grain size, surface fraction, lamellar spacing, second-phase spatial distribution, and serrated grain boundary morphology. Owing to these extensive quantitative image analyses, several unusual microstructural features occurring in this wellknown TiAl-based alloy were identified and assessed. First, a dissolution of the smallest c grains was emphasized in subtransus conditions as the isothermal temperature or holding time was increased. Second, the competition that occurs between the a Þ a + c transformation and the direct-ordering a Þ a 2 reaction upon cooling from above the a-transus temperature is mainly governed by the reduction in chemical free energy. Third, new grains were found to nucleate upon cooling, which is presumably induced by a minimization of interfacial energy at prior a grain boundaries. Finally, new c grains were formed as a result of the coarsening of primary c lamellae under furnace-cooled (FC) conditions.

Effect of Post Production Heat Treatment on γ‐Tial Alloys Produced by Gtaw‐ Based Additive Manufacturing Process

“…Both the and phase tend to coarsen when a longer heat treatment time is used, but hinder each other, hereby limiting grain growth. However, as pointed out by [18] these lamellar colonies that are formed in the vicinity of the -transus temperature are not actually stabilised and tend to gradually disappear upon furnace cooling, which offers sufficient time for the phase to grow as individual grains. Meanwhile, the ordering transformation 2 structure as well.…”

Robustness versus Performance Assessment for Different Gamma-TiAl Processing Routes

“…by quantitative image analysis. Moreover, by using specific holding time and cooling rate conditions, unusual phase transformations have been identified in this wellknown 47-2-2 alloy [10].…”

Phase-Tunable Fabrication of Consolidated (α+β)-TiZr Alloys for Biomedical Applications through Molten Salt Electrolysis of Solid Oxides

“…However, there is still a great mismatch of elastic modulus between the titanium-based implants and natural bone , which together with the weak wear resistance of the implants, are currently identified as the major reasons for the bone resorption and loosening of the implant in host bodies. [1][2][3][4][5][6] It has been proven that introducing the β-phase into the R-phase titanium alloys is a potential way to reduce the elastic modulus and enhance the strength, as well as improve the wear resistance and corrosion resistance of the surgical implantation. Such changes may be realized by controlling the elemental composition of the alloys, and/or through thermomechanical processing.…”

“…However, for orthopedic applications, most of these β-stabilizers should be avoided, because they will cause rejection or release metal ions in the physiological environment. [1][2][3][4][5][6] Both titanium and zirconium are fully biocompatible, and their alloys, as reported in the literature, showed enhanced strength relative to pure titanium. [9][10][11] Furthermore, the ZrO 2 in the surface oxide layer could strengthen the wear resistance of the implant.…”