In any heat treating cycle, there are two important considerations concerning temperature: the temperature of the furnace hot zone which is generating the heat input, and the temperature of the actual workload.

Heating by direct radiation, the main heating mechanism in vacuum, tends to be a slower process than other heating mechanisms such as convection or conduction. As a result, there are times in the heat treating cycle, particularly during heat up, when the load will be at a lower temperature than the furnace hot zone. This is known as temperature lag. READ MORE

Good fixturing and loading practices are essential elements in achieving proper heat treating results and long equipment life.

Fixture materials and design must be appropriate for the processing application.  Maintenance of fixtures is equally important.  The possibility of reactions between the workpieces and baskets or fixtures must also be considered.  High temperature sintering of the workpieces to themselves or the fixtures can occur.  Eutectic melting can also occur when certain chemical compositions come into contact at high temperature.  Selection of a fixture material is influenced by cost, service environment and compatibility with the workpiece and furnace hearth. READ MORE

The Ultimate Cleaning Treatment For Superalloy Repair.

All gas turbine engines require regular overhaul to ensure continued safe operation. During engine overhaul, decisions must be made on whether to replace deteriorated individual parts and assemblies with new components or to repair them. The ultimate decision depends on both technical and commercial criteria. That is, is there a technically sound repair available and, if so, is it economically favorable compared to the cost of a replacement component? Sometimes lack of availability of replacement components may override purely economic criteria. READ MORE 

Once a good fixture design has been developed, careful consideration should next be given to the loading of the workpieces.

Heating in a vacuum depends mostly on the transfer of energy through radiation from the elements to the load.  For uniform heating and cooling, it is important that the workpieces are not shielded by one another.  Pieces within the load should be evenly spaced to ensure even exposure to radiation.  The size, shape and high temperature strength of the workpiece should also be considered during loading.  Alloys with complex shapes and relatively low strength at heat treating temperatures may distort during processing.  In some cases, it may be necessary to support these components with specially designed fixtures. READ MORE

For heat treating purposes, "quenching" can be defined as the rapid cooling of a metal to impart some desired property such as hardness.

Different metals and alloys require different quenching rates to achieve their optimum properties. Regardless of equipment design, gas quenching in vacuum furnaces involve the same basic principles. The gas quenching process normally consists of the following sequence of events. First, the power to the heating elements is shut off. Next, the furnace chamber and quench loop are backfilled with a non-reactive gas, commonly nitrogen or argon. READ MORE

There are several factors to be considered in preparing workpieces for vacuum heat treating or brazing. Cleanliness of the workpieces and baskets or fixtures is very important.

They must be free of oil, dirt, machining lubricants or other contaminants prior to being loaded into the furnace. Some lubricants contain sulphur compounds which can adversely affect the alloys being heat treated. Inadequate cleaning can also cause staining and discoloring of the end product or result in poor braze alloy flow. Contaminants with high vapour pressures will evaporate during heating causing loss of vacuum. The vapours may eventually condense on colder surfaces in the furnace only to re-vaporize to cause contamination problems in subsequent runs. READ MORE

When heat treating or brazing in vacuum, the vapour pressure of the constituents in the materials being processed can be a very important consideration. 

The vapour pressure of a material is that pressure exerted at a given temperature when a material is in equilibrium with its own vapour.  Vapour pressure is a function of both the material and the temperature.  Figure 1 shows approximate vapour pressure curves for a variety of metals and compounds.  The area to the left of each curve represents the conditions of temperature and pressure under which the material exists as a solid.  The area to the right of each curve represents those conditions under which the material exists as a gas (or vapour).