SUNConferences, Southern African Institute of Industrial Engineering 2013

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Reviewing Alpha Case Risk Potential During Titanium Alloy Machining
Nico Treurnicht

Last modified: 2013-06-20


At temperatures above 500 deg C, titanium alloys react with oxygen to form an alpha case layer on the surface. As the physical properties of the alpha case differs substantially from the alloy itself, fatigue crack inititation sites are created, compromising the fatigue life of the component. Contemporary tool materials such as polycrystalline diamond, binderless cubic boron nitride and even carbides are now able to survive cutting temperatures well above 500 degrees. Furthermore, researchers are reporting improved results with reduced cooling or work material heating that relies on thermal softening of the titanium alloy. Although the machining benefits are undisputed, the question about component fatigue life and aircraft safety remain unanswered.

This review investigates the heating effects of machining on the titanium alloy work piece. Chemical change when a typical alpha + beta alloy is heated and exposed to the atmoshere, is discussed. The heating potential of the machining process of titanium alloys is presented. Published work on the effects of local premachining heating such as laser assisted machining, and high speed machining are analysed. In conclusion expected future trends in machining process design for safe aircraft components are presented.