Low pressure carburizing (LPC) in a vacuum furnace is increasingly the preferred method of case hardening for aerospace gears, and acetylene is often one of the gases used in the process. Selective case hardening is common with gears, where certain sections of a part are “stopped off” or “masked” to prevent carburization at those locations. For aerospace parts, the masking used is typically copper electroplating. The low pressures and high temperatures used in LPC lead to copper evaporation, which contaminates the vacuum furnace hot zone and components. In a worst-case scenario, deposited copper can lead to short-circuiting of power feedthroughs. This study looks at the effect of vacuum and partial pressure gases on copper evaporation and its application in production processes.

Titanium use in aerospace and medical applications continues to grow. Alpha case formation is a diffusion reaction that occurs at the surface of titanium when processing at elevated temperature in atmospheres containing oxygen, nitrogen, and/or carbon, with oxygen being the prominent element associated with alpha case. Oxygen is solution strengthening at low concentrations, but greatly decreases ductility and forms alpha case at higher concentrations. Thus, alpha case is brittle and has a detrimental effect on part performance and longevity. Higher temperatures increase alpha case depth. Temperatures less than 550°C (1022°F) limit oxygen mobility and keep case depth from increasing. Above 480°C (896°F), air or water vapor will start to produce alpha case.