Effect of compacting pressure on shape retention during supersolidus liquid phase sintering of Cu base alloys

Abstract

The compacting pressure is one of the key parameters which affects sintering phenomena, such as fragmentation, rearrangement and densification. However, the type of alloy also has a similar significance which should be considered. To demonstrate the effect of the mentioned parameters, two types of copper base alloys, i.e. Cu-9Sn-8Pb and Cu-28Zn, were investigated in the present study. Prealloyed powders were compacted at 100 and 400 MPa, respectively, and sintered in the range of 890-970°C for 20 min. In situ images of the samples were taken at various sintering conditions, and the shapes were recorded. For both materials, in case of compaction at lower pressure, the gravity-induced distortion known as 'elephant foot' phenomenon was not observed, and the specimens show shape retention during sintering even at higher temperatures, while samples compacted at 400 MPa showed different responses to the sintering conditions: A-shaped distortion (elephant foot) occurred in the bronze alloy, while in the brass alloy O-shaped distortion was observed.

The role of pore evolution during supersolidus liquid phase sintering of prealloyed brass powder

“…In general, two types of pores are more detectable from microstructure of brass samples during SLPS: (a) irregular-shaped pores (primary porosity), and (b) spherical-shaped pores (secondary intragranular porosity). In comparison with other alloys (without volatile components) investigated in previous studies [12,17], the number and size of intragranular pores in brass are significantly higher, which indicates the effect of zinc evaporation on pore formation within the grains. On the other side, the shape of these pores is totally spherical, which corroborates the presence of zinc vapour in the pores (see Figures 4-6).…”

“…The various features of SLPS including densification parameter, shrinkage, microstructure, and mechanical properties of sintered samples have been studied by many researchers [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. A liquid phase flow during sintering causes rapid shrinkage of the part and is frequently used to achieve close to full density with prealloyed powders.…”

“…In another study, Mousapour et al [12] worked on shape retention of Cu base alloys with different compacting pressures during SLPS. They observed that compacting pressure and type of material directly affect the apparent shape of specimens during sintering.…”

On the deflection behaviour of prealloyed alpha brass during sintering: in-situ bending technique and modelling

“…Azadbeh et al [10] reported zinc redistribution among grain boundaries of LP sintered Cu-28Zn samples and ZnO formation during SLPS. In other works [11][12][13][14][15][16], different effects of zinc evaporation on properties of sintered samples and their apparent shape have been reported. In conjunction to the previous works on SLPS of Cu-28Zn it seems that there is a lack of information on the viscous behaviour of brass during SLPS and related microstructural changes.…”

Supersolidus liquid phase sintering of water-atomized low-alloy steel in binder jetting additive manufacturing

“…Notably, some cracks were also found on the oxide layer, which can be attributed to the thinning of oxide film due to the presence of liquid phase that results in dissolution of oxygen in the liquid to re-combine with high oxygen affinity elements (e.g., Mn) [ 39 , 40 ]. Meanwhile, as a result of the high heating rate, reaction vapor products such as CO, H 2 O, and CO 2 that are nearly insoluble in iron-FCC can remain entrapped within pores and lead to pore enlargement through Ostwald ripening as a result of grain growth [ 41 ] or particle rearrangement [ 24 ]. Based on the finding of Ghasemi and Azadbeh et al [ 42 ], large pores migrated to the top of samples due to buoyancy force, while the liquid settled to the bottom area due to gravity.…”