Quasi-static chip formation of intermetallic titanium aluminides

Abstract

As a result of the development of new materials for high temperature applications the potential for mass reduction and increased process temperatures is constantly being expanded. Intermetallic c-TiAl alloys can meet these demands to a large extent. The properties necessary for these applications have an adverse effect on the machinability however and render intermetallic titanium aluminides as difficult to machine materials. Cutting operations tend to produce damaged surfaces which are unsuitable for the intended applications. As the basis for a reliable and economic cutting technology, the chip formation of the intermetallic TiAl alloy TNBV5 has been examined in quasi-static cutting experiments. Observations showed that increased workpiece temperatures lead to a transition of the chip formation from segmented to continuous chips. By decreasing the undeformed chip thickness crack-free surfaces could be produced at low workpiece temperatures. In this case other mechanisms than the thermal activation of slip systems must be the reason for the observed large plastic deformations. The theory that hydrostatic pressure leads to this behavior is substantiated by the results of finite element simulations. This offers the possibility for damage free machining at lower cutting speeds, thus enabling the use of conventional tool materials at an acceptable tool life.

In situ strain measurement in the chip formation zone during orthogonal cutting

“…The setup, which could also be used for the creation of chip roots, was integrated in a tension/compression test machine (Fig. 1a) [8].…”

Machinability of titanium aluminides: A review

“…such as dry machining, minimum quantity lubrication, conventional flood cooling, high-pressure lubricant supply, and cryogenic cooling systems. 3,44,53,75,76,88,89 Sub-surface microstructural alterations and hardened layer have been reported in all lubrication conditions experienced.…”

“…principle to titanium aluminides, it must be taken into account that the temperature for chip formation must exceed the brittle-ductile transition temperature (BDTT) of 600-700 C, 75 as a consequence of this characteristic, the application of this approach is more difficult in titanium aluminides. However, studies by Uhlmann et al 76 show that this procedure is possible. After machining a preheated workpiece to a temperature of 300 C, the number and size of cracks in the machined surface were significantly smaller than at room temperature.…”

High-throughput dry drilling of titanium aluminide

“…The possibility of Ti and Ni based alloys in improving the engine performance has been extensively studied and further scope of improvement is exhausted [4]. These requirements initiated the investigation and expansion activities in the development of new high performance materials such as titanium aluminide (TiAl) intermetallic alloys.…”