Effects of Phosphorus Content on the Abnormal Expansion in Mixed Compacts of the Fe-Cu-P Ternary System

Abstract

By using mixed compacts of Fe-8 wt%Cu-P ternary alloys with different P contents, a study of the effect of P contents on the elimination of abnormal expansion was carried out by the dilatometric method and by means of line analysis of the X-ray microanalyser, as described in the previous papers, and in this experiment the X-ray diffraction technique was employed.
The results obtained were as follows:
(1) An abnormal expansion which appeared from 400°C on heating in the mixed compacts over 0.5 wt%P content originates from the heat of formation for Fe-phosphides. However, this type of abnormal expansion cannot be found in a mixed compact of Fe-10 wt%Cu₃P pseudobinary system.
(2) The upper limiting temperature of α Fe-P solid solution is elevated by the preferential diffusion of phosphorus, subsequently the solid copper particles are facilitated to diffuse in the α solid solution, consequently the liquid copper retained in the mixed compacts on heating over 1083°C are reduced. In this manner the abnormal expansion which appeared from the melting temperature of copper on heating can be eliminated by the addition of phosphorus.
(3) At the maximum temperature of 1150°C in this experiment the amount of the γ phase in the sintered compacts decreases with increasing P contents, but the amount of the α phase increases. Enrichment of the α phase region in the compacts results in the uniform distribution of copper in the iron matrix, and facilitate the sintering behaviours.
(4) Dimensions of the compacts at room temperature after isothermal sintering at 1150°C for 1 hr decrease with increasing P content up to 0.7 wt%P and then remain constant.