Nintendo Front Car Plates

2 Analysis metallographic metallographic analysis

Oggi sono tornato al Poli a fare ulteriori analisi. Ho rifatto delle misure di micro durezza da affiancare a quelle dell'altra volta, poi ho lucidato il provino e l'ho esaminato per bene alla ricerca di inclusioni, impurità del materiale e corrosione intergranulare.
Il nuovo diagramma del profilo di durezza parla da solo. Ogni punto è una misura (e ci vuole almeno un minuto a farla, tanto per dare un'idea del tempo), ho messo insieme i nuovi e i vecchi valori. È evidente che il primo valore stranamente basso dell'altra volta era un errore di misura. Le cementazioni appaiono molto simili, al limite si può dire che quella del TTR è un po più tosta (più dura e più profonda).
Dopo la lucidatura ho ispezionato il provino with an optical microscope. I did a tour of the big cracks that are damaged in the side of the tooth, recognizing the typical morphology of this type of corruption, which by now I know all too well (I'm writing a thesis in these days). I tried
signs of intergranular oxidation. It is a phenomenon that occurs during cementation, in the period in which the part out of the oven and is cooled in water. The oxidation is usually removed by grinding the whole, but can sometimes be a little 'and in that case acts as a trigger point for fatigue cracks. Nothing, no oxidation.

What I can say now, with reasonable certainty is that the gears are just as good of TTR than the XT, at least in the specimens examined by me (my). The fact that they are damaged first, unfortunately, is not to be found in the quality of the gears themselves but external factors such as design errors, understaffed, misalignment, lack of lubrication, overloads (eg due to absence of the sprocket wheel) etc.. The unfortunately refers to the fact that there is a good chance that among other 25,000 miles I can start writing a new blog ...

With this last post I think I've finished my little adventure of bloggers. I would like to thank all the friends that I have read assiduously, and especially those who have left comments. Hello and next! Olivier

Fatty Liver Gall Bladder

Today I finally managed to go to Milan to do the analysis. Sprockets analyzed are those of the 3rd gear mounted on the clutch and were removed from my bike (TTR600 '99) and the XT's Wish (Forum XT600.it). The wheels show no signs of damage to both contact fatigue (pitting), only that my shot has 26,000 km and the wish of many more (50-80'000).
To isolate a tooth on which to do the analysis I did three cuts: one for the long approximately in the middle of the wheel, and two side (like cake) to remove the tooth. The tooth was then encased in a block of phenolic resin to be able to easily handle. All this can be seen in the first photo. After incorporation, the freshly cut surface of the tooth has been polished by machine with various abrasive papers. Then I attached the sample with a solution of Nital (nitric acid and alcohol) to highlight the hardened layer (you can also see in the picture that is more polished).
At this point I used the micro hardness tester to measure the hardness profiles. The hardness test by pressing a conical tip with a certain force at the surface and studying the imprint left. More material is hard, the smaller footprint, and measuring the latter dates back to hardness. All this happens in a very small scale and is under the microscope: the prints are great for a 20in microns are invisible to the eye. I made a sequence of measures (sewing, in the jargon) from the edge of the tooth (the surface) to about 1 mm in depth, measured every tenth of a millimeter. Plotting the results that jumps out is called the hardness profile.
In the picture there are two aspects to the comparison, let's see what can be said. It is evident that the value of the surface hardness is much greater than that to heart: the material is hardened. This is a classic gears and I expected it to 100%. The value of core hardness is equal in the two-wheel (about 400HV). This tells us that in all probability the material used is the same and is equal also treated in this area (quenching and tempering). Now begins the most critical part in the first value of the cementation of TTR is harder and deeper. This is NOT 'the result I expected: I thought the treatment of TTR was worse than the XT, but it did not appear. But there is a but. The first hardness value is lower than that in TT nell'XT. I do not know explain. It could be a measurement error or it could be the key to the dilemma. The mechanism of damage infatti avviene proprio in quella zona, nei primi 5 centesimi di materiale. Tutto questo ovviamente l'ho scoperto a casa una volta tracciati i diagrammi e quindi non ho potuto fare nessuna prova ulteriore. La prossima volta che vado a Milano rifaccio i profili, misurando con particolare cura nei pressi della superficie. Proverò anche fare delle prove di durezza classiche su quello che resta delle ruote. Se poi è confermata la misura di oggi chiederò aiuto a qualche professorone per cercare di capire com'è possibile che ci sia un profilo di durezza così strano, e magari ci scappa anche qualche analisi al SEM (microscopio elettronico). A presto!