The mechanical behaviour of an ultrafine grained Ti–47Al–2Cr (at%) alloy in tension and compression and at different temperatures

Abstract

A c c e p t e d M a n u s c r i p t Research Highlights Powder metallurgy process has been used to produce UFG Ti-47Al-2Cr (at%) alloy. At room temperature, the UFG alloy was found to be ductile in compression (~ 4%). At elevated temperatures the alloy showed high tensile and compressive ductility. The yield strength at 900 o C is 55MPa in tension and ~ 33MPa in compression. *Research HighlightsPage 2 of 17 A c c e p t e d M a n u s c r i p t AbstractA bulk ultrafine grained (UFG) Ti-47Al-2Cr (at%) alloy has been produced using a powder metallurgy process that combines high energy mechanical milling (HEMM) of a mixture of Ti, Al and Cr powders to produce a Ti/Al/Cr composite powder and hot isostatic pressing (HIP) of the composite powder compact. The purpose of the present study is to determine the mechanical behaviour of the alloy in tension and compression at room temperature (RT) and elevated temperatures, and also to compare the compression behaviour of the material with its tensile behaviour. It has been found that due to the residual pores, lack of full level interparticle bonding and high oxygen content (0.87wt%) in the consolidated samples, the UFG TiAl based alloy has a very low room temperature tensile fracture strength of ~100MPa and shows no tensile ductility. However these microstructural defects and high oxygen content have much less significant effect on the room temperature compressive mechanical properties, and the alloy shows a high compressive yield strength of ~ 1410 MPa, and some ductility (plastic strain to fracture ~ 4%). At elevated temperatures of 800 o C and above, the alloy shows high tensile and compressive ductility as demonstrated by 75% tensile elongation to fracture and no cracking in upset forging with a height reduction of 50% at 900 o C. The yield strength of the alloy at 900 o C is 55MPa in tension and ~ 33MPa in compression, both of which are lower than those of coarse grained TiAl based alloys with similar compositions at 900 o C. This is due to a higher creep rate of the UFG alloy caused by the small grains. The good formability of the UFG TiAl based alloy as reflected by the lower critical temperature above which the alloy becomes highly formable indicates that the material can be used as a suitable precursor for secondary thermomechanical processing and super-plastic forming.

Spark Plasma Diffusion Bonding of TiAl/Ti2AlNb with Ti as Interlayer

“…As described above, the IMC Ti 3 Al looked brittle at room temperature with a transgranular propagation of cracks. Numerous Ti 3 Al IMCs migrated to grain boundary and aggregated at high temperatures [ 31 ], leading to intercrystalline fracture mode.…”

“…Both joints demonstrated brittle characteristics related to differences in the failure location of each joint, with transcrystalline fracture at room temperature and intercrystalline fracture at 650 • C. As described above, the IMC Ti 3 Al looked brittle at room temperature with a transgranular propagation of cracks. Numerous Ti 3 Al IMCs migrated to grain boundary and aggregated at high temperatures [31], leading to intercrystalline fracture mode.…”

Effect of heat treatment on microstructures and mechanical properties in a full lamellar PM TiAl alloy

“…A potential method of overcoming these problems is to use the powder metallurgy (PM) route. In compared of common ingot metallurgy, PM have advantage in eliminating compositional segregation, realizing the macro net-shape forming, and can effectively solve the TiAl intermetallic shaping of difficulty [11][12][13] . It is one of the main preparations for TiAl alloys.…”

Synthesis of Ti-Nb-Ta-Zr Alloys Foams by Powder Metallurgy

“…It is know that biomaterials are solution for bone replacement. Titanium and titanium-based alloys are used due to its superior biocompatibility and corrosion resistance in conjunction with low density and an elastic modulus much more similar to that of human bones [2]. The elastic modulus of titanium and titanium-based alloys are much higher than of human bone (10-30 GPa) [3].…”