Interaction of liquid copper with sintered iron compacts

Interaction of liquid copper with sintered iron is important in brazing, liquid phase sintering and infiltration. In brazing, the penetration of liquid copper into the pores is to be `avoided', whereas in infiltration processes it is `encouraged', and in liquid phase sintering it should be `controlled' so that optimum mechanical properties are achieved. The main objective of the research is to model the interaction by studying the effect of the process variables on the mechanisms of copper interaction in Fe-Cu and Fe-Cu-C systems. This involves both theoretical and experimental considerations. Dilatometric investigations at 950, 1125 and 1200oC, together with metallographic analyses were carried out to clarify the copper growth phenomenon. It is shown that penetration of liquid copper into the iron grain boundaries is the major cause of dimensional changes. Infiltration profiles revealed that copper penetration between the iron interparticle contact points and along iron grain boundaries is a rapid process. The extent of copper penetration depends on the dihedral angle. Large dihedral angles hinder, and small angles promote copper penetration into the grain boundaries. Dihedral angle analysis shows that the addition of 0.6wt.% graphite reduces the number of zero dihedral angle from 27 to 3o and increases the mean dihedral angle from 9.8 to 41.5o. The dihedral angle was lowest at 1125oC and then increased to higher values as the system approached its equilibrium condition. Elementally mixed (E.M.) Fe-Cu compacts showed a rapid expansion at the copper melting point. However, graphite additions reduced compact growth by increasing the mean dihedral angle. In order to reduce the copper growth phenomenon, iron powder was coated with a thin layer of copper by an immersion coating (I.C.) technique. The dilatometric curves revealed an overall shrinkage in the I.C. compacts compared to their corresponding E.M. compacts. Multiple regression models showed that temperature had the most effect on dimensional changes and density had the most contributing effect upon the copper penetration area in the infiltrated powder metallurgy compacts.

The palynology of carboniferous strata in Northumberland off-shore boreholes

The work described represents a palynological study of Carboniferous coal seams of Upper Westphallan. A and Westphalian B age from eight off-shore boreholes sunk by the National Coal Board in Northumberland. When treated chemically the majority of the coal samples yielded well-preserved miospores which were studied by means of the optical and scanning electron microscopes. Systematic descriptions of 151 miospore species belonging to 57 genera, and including 18 new types, are given. One miospore assemblage is recognised from the coals of Upper Westphalian A age and two fUrther assemblages from those of Westphalian B age, These compare with assemblages described by earlier workers from strata of similar age elsewhere, but there are differences in the distributions of some of the more abundant taxa, and some of the stratigraphically significant species are not present. Correlations based on miospore distributions between the coal seams encountered in the eight off-shore boreholes agree fairly closely with those established by the National Coal Board on lithological criteria. Relations are discussed between palynology and palaeoecology and detailed comparisons made with the work of Smith and Butterworth 1967 from the adjacent on-shore area. It is concluded that the miospore assemblages described are restricted in that they contain very low representation of Smith's (1962) Densospore phase. This restriction, due to the relatively rapid subsidence of the depositional area, is reflected in the distributions of some of the less common spores as · well as in the abundances of species such as Densosporites sphaerotriangularis, Lycospora pusilla and Apiculatisporis irregularis.