Manufacturers of materials, components, and machines for spacecraft and satellites deployed in space must vigorously test them prior to putting them into service. For example, linear actuator mechanisms on satellites have failed to function properly (extend or retract) because of a loss of tolerance due to the conversion of retained austenite to martensite and subsequent growth of the part due to volume expansion. Had this test not been performed in a simulation chamber at -62ºC (-80ºF) here on Earth, a solar array or communications antenna would not have deployed when the satellite was in orbit and its mission would have been compromised.

In order to ensure thermal and vacuum readiness of these systems prior to lift off, they must be subjected to the extreme vacuum and temperature of space to ensure they can withstand and perform under these harsh conditions without failure. Space simulation (aka space test) chambers are used to perform this testing. The challenging conditions encountered in space and the development of the space simulation chamber are the focus of our discussion.

Experience has shown us that sensitive materials in the presence of minute quantities of unwanted gaseous contaminates can destroy the integrity and shorten the life expectancy of components. It is natural to ask ourselves what can be done to further protect the work in a vacuum environment after the pumps have done their part in reducing the chamber pressure to as low as is economically feasible in a production environment? This task falls on getter materials.

A getter is simply a reactive material that is deliberately placed inside a vacuum system for the purpose of improving the efficiency of that vacuum by scavenging unwanted contaminates. Essentially, when gas molecules strike the getter material, they combine with it chemically or by adsorption so as to be removed from the environment. In other words, a getter eliminates even minute amounts of unwanted gases from the evacuated space. 

IGO is a surface phenomenon that is most often associated with atmosphere gas carburizing. The consequence of IGO (and the concentration gradients that develop during oxide formation) is that the material adjacent to the oxides has modified transformational behavior. Instead of forming martensite on quenching, steels with this condition develop non-martensitic transformation products (e.g. bainite, pearlite), which adversely affect mechanical properties (e.g. hardness, residual stress, bending fatigue).

The rate of diffusion of oxygen into a steel surface is dependent on the oxygen potential of the furnace atmosphere and the process variables (i.e. the depth of oxide penetration is influenced by case depth, time at carburizing temperature, carbon potential and the chemical composition of the steel). During the carburization process, the oxygen atoms (which are about 35% smaller than the iron atoms) are released as a direct result of the presence of water vapor and carbon dioxide in the gas. Oxygen diffuses slowly into the steel surface (as does carbon and hydrogen, albeit more quickly) and migrates to the grain boundaries. Once in the steel, oxygen combines chemically with the elements already present (e.g. chromium, titanium, manganese) that have an affinity for oxygen.

It is not uncommon in the heat treatment industry to hear one talk about high-pressure gas quenching and in doing so refer to terms such as 2 bar, 6 bar or even higher pressures. In scientific terms, a bar is defined as a unit of pressure equivalent to 100 kilopascals. A bar can also be thought of as roughly equal to atmospheric pressure (the amount of force air exerts on the Earth at sea level). To be technically correct, one atmosphere of pressure is 1.01325 bar or to put it another way, one bar is equal to 14.5 psia. Conversion calculators and tables are available to change bar into other units. Another common unit you might come across when talking about (negative pressure) vacuum levels in a vacuum furnace is millibar (mbar), which is 1 x 10-3 bar.

When talking about high-pressure gas quenching you might also hear one say that that they are quenching at 6 bar, to which they might quickly add, “5 bar absolute”. Just what are they trying to say here? Absolute pressure is referenced against a so-called “perfect vacuum” and as such is equal to gauge pressure plus atmospheric pressure. By contrast, gauge pressure is referenced against ambient pressure (14.7 psia), so it is equal to absolute pressure minus atmospheric pressure. So, when one talks about 5 bar absolute, one must add 1 bar of pressure (think of this as going from negative pressure to atmospheric) to arrive at total pressure, in this case 6 bar. As an example, measurements in the English system that relate the pressure of a system to a reference pressure are given by specifying the pressure in terms of pounds per square inch absolute (psia) or pounds per square inch gauge (psig).

We study vacuum science and vacuum engineering in order to better understand the role vacuum technology plays in creating useful engineered products (Fig. 1, Table 1). Manufacturing as we know it, and research and development as we have come to depend upon it, would not exist without the creation and control of the vacuum “atmosphere”.. 

Vacuum techniques are important in both the industrial setting and for the scientific community, whether it be in heat treatment or high-energy physics. At the heart of vacuum processing for manufacturing is the modern vacuum furnace. Ever since the introduction of the electric light at the beginning of the 20th century, society and manufacturing have been linked to advances in vacuum science and engineering. Examples include the development of modern computers to advanced transportation systems; the very fabric of modern society depends on vacuum technology.