Digital photocalorimetric measurements of cooling rates in chill block melt spinning of MmNiCoMnAl5 hydride forming alloy

Abstract

A digital photocalorimetric technique has been developed and applied to obtain in situ temperature measurements from chill block melt spun ribbons of a MmNiCoMnAl5 hydride forming alloy. Compared with conventional colour transmission temperature measurements, this technique offers special advantages in terms of high resolutional and positional accuracy, which under the prevailing experimental conditions are found to be +-29 K and +-0.1 mm respectively. Moreover, it is shown that the cooling rate in the solid state is approximately 2.5 times higher than observed during solidification, indicating that the solid ribbon stays in intimate contact with the wheel surface down to very low metal temperatures before the bond is broken. During this contact period, the cooling regime shifts from near ideal in the melt puddle to near Newtonian towards the end, when heat transfer from the solid ribbon to the wheel becomes the rate controlling step.