Consolidation of iron powders through the influence of phosphate thin films

In this work, the compaction and sintering behaviour of iron-phosphated powders have first been studied. Then, the iron powders consolidation mechanism has been investigated under the influence of the phosphating treatment, by means of mechanical tests. Iron powders with spongy grains have been used in order to be first phosphated. Then, green compacts with both untreated and phosphated grains have been prepared. The compaction behaviour of the powders has been analysed using the Heckel law. It indicates that the phosphating process does not influence the compaction behaviour. Besides, a desaggregation stage of the powders occurs at the end of the compaction process. The subsequent sintering of these green compacts does not induce any significant evolution of the densities values. Moreover, the sintering conditions have been optimised in order to be a compromise between the persistence of the phosphate film and the strengthening. Then, strength properties of compacts made of densified iron powders are studied and the influence of the initial phosphating treatment is explored. The mechanical strength increases under the influence of either the phosphating treatment or the sintering process. Moreover, when both are combined, it leads to the better characteristics. The phosphate film acts as a binding agent and the corresponding green body gets its strength only by the retentive force of the metallic phosphate. By sintering, the sampleʹs strength is increased by metallic bonds that mainly occur by necks formation. In sintered compacts obtained from phosphated iron powders, the strength is the most important as revealed by the fracture morphology where transgranular brittle fracture is indicative of reinforced links between powder grains.