Macroscopic micrographs of large microsections

The IOB has deve­lo­ped a new method for crea­ting micro­graphs. For the vali­da­ti­on of the nume­ri­cal simu­la­ti­ons of remel­ting pro­ces­ses it is neces­sa­ry to exami­ne metall­o­gra­phic samples from the real pro­cess. Here, the growth direc­tion of the den­dri­tes as a func­tion of the radi­us is of par­ti­cu­lar inte­rest for the com­ple­te block dia­me­ter. Lar­ge sam­ple pla­tes of up to half a meter in length are often pro­vi­ded for this purpose.

The usu­al pro­ce­du­re requi­res the sam­ple pla­tes to be bro­ken down into small spe­ci­mens with an edge length of just a few cen­ti­me­ters. The spe­ci­mens can then be embedded, ground, polished, etched and then view­ed under a microscope.

This pro­ce­du­re has seve­ral dis­ad­van­ta­ges. First­ly, the spe­ci­mens must first be num­be­red on the rever­se side and then usual­ly cut out by exter­nal com­pa­nies. The resul­ting cuts sub­se­quent­ly result in a gap bet­ween the indi­vi­du­al micros­truc­tu­ral images. On the other hand, with the lat­ter, the ori­en­ta­ti­on of the spe­ci­mens and the num­be­ring must always be taken into account in order to make a sub­se­quent allo­ca­ti­on possible.

The novel method is based on a high-reso­lu­ti­on digi­tal SLR came­ra (50 mega­pi­xels) with macro lens (magni­fi­ca­ti­on 1:1) and a tra­ver­sing unit. The came­ra is moun­ted on the tra­ver­sing unit and posi­tio­ned in front of the lar­ge sam­ple pla­te. A mat­lab con­trol enables the auto­ma­ted pro­ce­du­re and pho­to­gra­phing of the sam­ple. The over­lap­ping indi­vi­du­al images are then com­bi­ned to form a com­ple­te image.

The auto­ma­ted scan­ning of the sam­ple sur­face pre­vents any con­fu­si­on in the posi­ti­on assign­ment. In addi­ti­on, the sam­ple as a who­le is retai­ned and can be reu­sed after the images, if necessary.

Probe mit Lupe

Due to the high reso­lu­ti­on in com­bi­na­ti­on with the ima­ging sca­le of 1:1, the edge length of a pixel cor­re­sponds to about 4 µm on the sam­ple. This method can also be used to mea­su­re secon­da­ry den­dri­te arm distances. As can be seen in the pic­tu­re, the over­all image can be zoo­med into the micros­truc­tu­re at any position.

The maxi­mum sam­ple dimen­si­ons for this method are curr­ent­ly limi­t­ed to approx. 2000 mm x 2000 mm only by the tra­ver­se paths of the tra­ver­sing unit.