The High Temperature Confocal Scanning Laser Microscope (HT-CSLM) is used to image metallurgical reactions and transformations at temperatures up to 1700oC. Using a scanning laser combined with confocal optics, the CSLM is able to image the sample's surface, in spite of the glow, and detect clear changes in contrast. The confocal nature detects only signals from the focal plane while decreasing the intensity of signals from other planes. The laser further increases the signal / noise ratio. This makes the CSLM ideal for imaging surfaces at high temperature.
The instrument has recently been upgraded to include an in-situ compression/tension stage allowing for the observation of phenomena such as recrystallization, deformation due to inclusion and measurement of material expansion due to temperature changes. With the previous high temperature stage being used for a range of investigations such as exploring peritectic solidification, slag-metal emulsification, oxide fluxing and isothermal solidification due to chemistry changes.
The equipment works on the premise of a gold-plated elliptical furnace which serves to reflect the IR-radiation from a halogen bulb (in 1 focal point) to the sample (in the second focal point). The sample is held in a crucible of suitable material on a platinum ring, to which a control thermocouple is attached to. This temperature reading is sent to an external temperature controller, which uses the reading to control the amperage (and therefore the intensity) of the halogen lamp.
The video output from the HT-CSLM in sent to a computer by way of analog-digital converter and is recorded by a software package. The temperature controller is connected to a computer by serial port, and so can have two-way communication with the program. Examples of HT-CSLM images and movies are shown here. Due to the surface imaging and high temperatures, the equipment is highly sensitive to atmospheric purity, as such pre-getters and filters are used to achieve up to parts per-trillion levels of oxygen when required.
The instrument has also been developed to offer unique capabilities such as: in-situ powder addition, thermal imaging of temperature gradients, high resolution cross imaging for sessile drop testing and gas humidification for moisture experimentation.
Solidification of peritectic steel:
Austenite - ferrite transformation of HSLA steel at 700oc
Austenite – bainite & martensite