Mechanical Properties Of TiAl Alloys Research Articles

Preparation and Mechanical Properties of TiAl Alloys with Submicron Grain Size

Preparation and Mechanical Properties of TiAl Alloys with Submicron Grain Size

Effect of Nb addition on the plastic behavior of TiAl crystals containing oriented lamellae

TiAl has been focussed on as a potential high temperature material because of its high strength-to-weight and good oxidation resistance. One of the major problems to be solved before practical application is the improvement of ductility of low temperatures. Ti-rich TiAl containing a well-developed lamellar structure composed of [alpha][sub 2] and [gamma] phases shows higher strength and better ductility than the single phase Al-rich TiAl. The mechanical properties of TiAl alloys are well known to be strongly affected by the details of the lamellar structure. In this paper, the authors succeed in obtaining binary TiAl crystal s (48.1 [approximately] 51.6at%Al) containing a single set of lamellae with different lamellar spacings by altering the crystal growth rate and the alloy composition. The mechanical properties are closely related to their lamellar structures and the yield stress is represented as a function of the reciprocal square root of the lamellar spacing similar to a Hall-Petch type relation. Furthermore, the authors find that the deformation mode of the [alpha][sub 2] phase in the lamellae strongly affects the plastic behavior of lamellar TiAl crystals. When the compressive axis is parallel to the lamellar planes ([phi]=0[degrees]), shear deformation occurs across them and 10[bar 1]0 [lt]1[bar 2]10more » [lt] slip can be activated in the [alpha][sub 2] phase. Addition of niobium to Ti[sub 3]Al is known to activate the motion of [lt]11Ba26[gt] type dislocations of 22[bar 2]1 and to improve the ductility. Therefore, in this paper we report the mechanical properties and microstructure of ternary TiAl crystal containing 1.2at%Nb with a single set of lamellae, focussing on the effect of the deformation model t-of the [alpha][sub 2] phase.« less

Ti-Al Alloys Prepared by Ball Milling and Hot Isostatic Pressing

For the powder metallurgical production of Ti-Al alloys, elemental powder blends and prealloyed powders were mechanically alloyed in a planetary ball mill. Thereby metastable solid solutions or amorphous phases are formed depending on the overall composition and the milling conditions. The crystalline phases exhibit an extremely small crystallite size of about 10 - 30 nm. This favors the consolidation of the powders which was performed by hot isostatic pressing in the temperature range between 500 °C and 800 °C. The results show that fully dense Ti-48 at.% Al alloys can be obtained only for a temperature of 800 °C. The crystallite sizes increase during compaction, but remain below about 0.15 µm. This allows the preparation of test specimens to investigate the mechanical properties of Ti-Al alloys with submicron crystallite sizes.

Effect of Carbon and Nitrogen on Mechanical Properties of TiAl Alloys.

The effect of carbon and nitrogen on mechanical properties of single and dual phase γ TiAl alloys was studied in tensile tests at room temperature as functions of content of interstitial elements such as carbon and nitrogen, titanium/aluminum compositional ratio and grain size. The fracture strain in stoichiometric and aluminum-rich TiAl alloys annealed at 1 423 K was improved from nearly zero plastic strain to 0.6-0.8% plastic strain by the addition of 0.3-0.6 at% carbon. In titanium-rich TiAl alloys annealed at 1 423 K and all of titanium-rich, stoichiometric and aluminum-rich TiAl alloys annealed at 1 573 K, tensile fracture strain was decreased by the addition of carbon and nitrogen. Volume of a unit cell in TiAl phase decreased by the addition of a small amount of carbon and nitrogen. The analysis of TiAl-1.0at%C alloys by an X-ray diffractometer showed the presence of Ti2AlC phase.