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    STUDIA PHYSICA - Ediţia nr.2 din 2011  
         
  Articol:   BEHAVIOURS IN THERMAL EXPANSION OF NICKEL-BASED, COBALT-BASED AND IRON-BASED ALLOYS CONTAINING VERY HIGH CARBON CONTENTS.

Autori:  . 		 
       
         
  Rezumat:  Nine model ternary alloys, (Bal. Ni, Co or Fe) - 30Cr - (4, 4.5 or 5C) were elaborated by foundry and subjected to microstructure examinations and dilatometry experiments up to 1200°C, in order to examine the thermal expansion behaviours of alloys used for applications requiring high hardness and wear-resistance. All of these alloys are of a hyper-eutectic type with presence of coarse acicular proeutectic carbides in addition to a (matrix carbides) - eutectic compound. Graphite is also present in the nickel alloys and in the carbon-richest cobalt alloy. Hardness is high (nickel alloys, about 300Hv) and even very high (cobalt alloys, about 600Kv), and maximal (about 700Hv) with the graphite-free iron alloys in which the volume carbide fraction can be higher than 50%. The great difference of thermal expansion coefficient between matrix and carbides leads to curious dimensional variations during temperature changes as well as during the isothermal stage following the heating up to 1200°C, consequently to intense interactions at the microstructure scale. This reveals the progressive stress accumulation during heating, due to both the great difference of thermal expansion between matrix and carbides and the especially high quantities of the latter in such alloys.

Keywords: nickel alloys, cobalt alloys, iron alloys, high chromium, very high carbon, thermal expansion, chromium carbides, graphite 

  
         
     
         
         
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