Study of microstructural transformations and dimensional variations during liquid phase sintering of 10% tin bronzes produced with different copper powders

Abstract

predicted by the phase diagram, by simply considering the composition of the material. Among them, liquid phase may The microstructural evolution during sintering of form which in uences the sintering mechanisms and the 10% bronzes obtained by mixing elemental powders dimensional behaviour. 4 ± 6 Therefore, the study of the copperwas studied, in order to investigate the mechanisms tin interaction does not have a simple microstructural responsible for microstructural homogenisation, coninterest only, but has a noticeable impact on the process solidation of the green compacts, and dimensional design and control and on the technological properties of variation. The eVect of the copper powder was also the components. studied using an electrolytic and an atomised com-The present study investigates the transformations which mercial powder. As a consequence of the diVerent occur during sintering of 10% Sn bronzes obtained by mixes surface area and surface chemistry, and of the presence of elemental copper and tin powders and the in uence of of internal pores and microcavities in the atomised the copper powder. In fact, two diVerent copper powders copper powder, the two mixes display signi cantly were used, one electrolytic and the other water atomised, diVerent dimensional behaviour but, under speci c time the latter having been speci cally developed as an alternative and temperature conditions, they give rise to the same to the former for the production of bearings. Dilatometry dimensional variation and the same microstructural was used as the experimental technique to sinter green parts characteristics.P M /0962 because of its sensitivity to phase transformations involving speci c volume changes, such as the formation of the liquid Dr M enapace, D r Zadra, and Professor M olinari phases. 7, 8 A detailed microstructural characterisation was

Contamination during the high-energy milling of atomized copper powder and its effects on spark plasma sintering

“…An important result is that the amount of oxygen and carbon residual is halved after sintering, confirming the release of some gases, especially CO and CO 2 . The final oxygen content (0.21 and 0.37%) can be attributed to the presence of magnesium in the starting powder, which easily oxidizes at high temperature and promotes the formation of stable magnesium oxide [30]. Figure 9 displays the lower punch displacement curves for the as atomized powder (dashed line) and the milled powder after 20 minutes (solid line) and after 200 minutes (bold line), respectively.…”

Effect of plasma nitrocarburising on fatigue resistance of low alloy Cr–Mo sintered steel

“…As an example, in a previous work on bronze bearings, it was observed that in particular f circle influences the mechanical strength, while f shape has to change in a wide range to give an appreciable effect. 19 Together with the mean values of the whole population, the shape factors of the 10% of the biggest pores, which are the most detrimental for the fatigue resistance, 20 are listed. The large pores have a similar roundness and a more irregular profile than the others.…”

Influence of Mg on sintering of 90/10 elemental bronze

“…The phases present in these samples were identified by metallographic examination under optical microscope and with the support of the EDXS microanalysis at SEM, as done in a previous work. 2 At 450uC all the compacts have the same microstructure, constituted by a matrix of Cu, with e phase areas surrounded by d phase, at the original Sn particles sites. At 550uC the sample containing the maximum Mg amount is different from the others.…”

“…In a previous paper 2 it has been demonstrated that Mg influences sintering, as well, because of its high affinity for oxygen and the great stability of its oxide. 3 First, magnesium slows down the copper-tin interaction, which is responsible for the formation of liquid phases during sintering and of the homogeneous a solid solution in the final microstructure, which ensures the best mechanical and tribological properties.…”

“…Magnesium also reduces the wettability of the copper powder by liquid tin. 2 Moreover, very fine MgO particles are present on the surface of the powder particle and their quantity was observed to increase with the sintering temperature and time 5 because of the interaction with oxygen present in the powder and in the atmosphere, despite the low dewpoint adopted (sintering of bronze bearings is carried out in a nitrogen/hydrogen atmosphere and the presence of some water vapour cannot be avoided). These particles do not stop the transport phenomena responsible for sintering, however they tend to slow down sintering in the solid phase, so that green parts have to be sintered over 800uC, to take advantage of the presence of the peritectic liquid.…”