*3.3.1 First sintering*

**Figure 5** shows the results of optical microscopy observations. Specimens SB8a **Figure 5a**, SBP8a **Figure 5d**, SBP10a **Figure 5e**, and SBP12a **Figure 5f** were well sintered and contained few pores. Specimens SB10a **Figure 5b** and SB12a **Figure 5c** were difficult to observe because the sintered copper layer and steel were not adhered. Previous research has shown that the grain boundaries in copper alloys almost match the boundaries of individual particles (atomized powders); thus, diffusion may occur only at the surface of the particles because many sulfide dots remain in the Cu matrix. However, specimen SB8a had no grain boundaries. This is because of the

**Figure 5.**

*Sectional view of sintered bimetal specimens after their first sintering under a reducing atmosphere [10].*

**147**

**Figure 6.**

*Effects of Dispersed Sulfides in Bronze During Sintering DOI: http://dx.doi.org/10.5772/intechopen.86385*

*3.3.2 Second sintering under reduction atmosphere*

*3.3.3 Second sintering under complex atmosphere*

that used in this study (S = 0.3 mass%).

differences between the sulfur content used in the previous study (S = 2 mass%) and

SBP8inr, SBP10inr, and SBP12inr were well sintered and showed little pores.

alloy were apparently reduced and converted into H2S gas in the furnace.

and the sulfide almost disappeared from the test piece of the copper alloy.

the sulfur in the sulfide is prevented because there is no reducing atmosphere.

was present to a greater extent than in the specimens treated under a reducing atmosphere. At the reduction atmosphere, sulfur-containing sulfides in the copper

In the cases of SBP8, SBP10, and SBP12, our results are similar to those reported in a previous study conducted under batch furnace conditions. Since the Cu-20 Sn powder begins to melt at 1071 K, effective diffusion is caused by liquid-phase sintering in Cu-Sn, since it is lower than the sintering temperature of 1113 K used in this study. **Figure 6a–e** shows the results of optical microscope observation of bimetal SB series and SBP series sintered in inert atmosphere. Samples SB8inr, SB10inr, SB10inr,

In the sintered bronze, a dark brown network that appeared to comprise sulfide

**Figure 7a–e** shows the results of the bimetal after the second sintering under reducing atmosphere. Pores in the sintered copper alloy almost disappeared. However, as shown in **Figure 7b**, the alloy and the steel test piece did not adhere,

In the second sintering process, the copper alloy samples were too sintered, which means that their pores almost disappeared. **Figure 8a–f** is a cross-sectional view of the test piece after the second sintering in an inert atmosphere. All copper alloy specimens were well sintered and almost void-free due to the rolling procedure performed between the first and second sinterings. The sulfide remained in the sample since the reaction in

**Figure 9a–f** is a cross-sectional view of a sintered bimetallic test piece after a second sintering in a reducing atmosphere and a sintered bimetallic test piece after

*Sectional view of sintered bimetal specimens after their first sintering under an inert atmosphere [10].*

#### *Effects of Dispersed Sulfides in Bronze During Sintering DOI: http://dx.doi.org/10.5772/intechopen.86385*

*Design and Manufacturing*

**3.3 Results and discussion**

*3.3.1 First sintering*

The sintering temperature was kept at 1123 K, as described in Section 3.2.1. This temperature made Cu-Sn system in liquid state so that liquid sintering was conducted for SBP8, SBP10, and SBP12. The mesh belt speed was set at 0.43 mm/s (first sintering) and 0.33 mm/s (second sintering). So, test specimens were maintained at 1123 K for 1050 s during the first sintering and for 1368 s during the second sintering. These sinterings were conducted under only reducing atmosphere (indicated as a after the materials in **Table 1**), only inert atmosphere (indicated as b after the materials in **Table 1**), and mixed atmosphere. Some tests were conducted using a complex procedure. They were sintered under inert gas during the first sintering and under reducing gas during the second sintering (indicated as c after the materials in **Table 1**). Under the reducing atmosphere, not only oxygen but also sulfur was able to reduce. Here, the reducing atmosphere was a mixture of H2 gas and N2 gas, and the inert atmosphere consisted only of N2 gas. Sulfur in bronze may react as H2S in the reducing gas. Thus, sintering under an inert atmosphere was also performed to compare the states of sulfur and sulfide bronze. Between the first and the second sinterings, a rolling process was performed, and the thickness of the bimetal was controlled to level the all surface of the Cu side of the bimetal contacted with the roll surface.

**Figure 5** shows the results of optical microscopy observations. Specimens SB8a **Figure 5a**, SBP8a **Figure 5d**, SBP10a **Figure 5e**, and SBP12a **Figure 5f** were well sintered and contained few pores. Specimens SB10a **Figure 5b** and SB12a **Figure 5c** were difficult to observe because the sintered copper layer and steel were not adhered. Previous research has shown that the grain boundaries in copper alloys almost match the boundaries of individual particles (atomized powders); thus, diffusion may occur only at the surface of the particles because many sulfide dots remain in the Cu matrix. However, specimen SB8a had no grain boundaries. This is because of the

*Sectional view of sintered bimetal specimens after their first sintering under a reducing atmosphere [10].*

*3.2.3 Test conditions*

**146**

**Figure 5.**

differences between the sulfur content used in the previous study (S = 2 mass%) and that used in this study (S = 0.3 mass%).

In the cases of SBP8, SBP10, and SBP12, our results are similar to those reported in a previous study conducted under batch furnace conditions. Since the Cu-20 Sn powder begins to melt at 1071 K, effective diffusion is caused by liquid-phase sintering in Cu-Sn, since it is lower than the sintering temperature of 1113 K used in this study. **Figure 6a–e** shows the results of optical microscope observation of bimetal SB series and SBP series sintered in inert atmosphere. Samples SB8inr, SB10inr, SB10inr, SBP8inr, SBP10inr, and SBP12inr were well sintered and showed little pores.

In the sintered bronze, a dark brown network that appeared to comprise sulfide was present to a greater extent than in the specimens treated under a reducing atmosphere. At the reduction atmosphere, sulfur-containing sulfides in the copper alloy were apparently reduced and converted into H2S gas in the furnace.

## *3.3.2 Second sintering under reduction atmosphere*

**Figure 7a–e** shows the results of the bimetal after the second sintering under reducing atmosphere. Pores in the sintered copper alloy almost disappeared. However, as shown in **Figure 7b**, the alloy and the steel test piece did not adhere, and the sulfide almost disappeared from the test piece of the copper alloy.

In the second sintering process, the copper alloy samples were too sintered, which means that their pores almost disappeared. **Figure 8a–f** is a cross-sectional view of the test piece after the second sintering in an inert atmosphere. All copper alloy specimens were well sintered and almost void-free due to the rolling procedure performed between the first and second sinterings. The sulfide remained in the sample since the reaction in the sulfur in the sulfide is prevented because there is no reducing atmosphere.
