*3.3.3 Second sintering under complex atmosphere*

**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

**Figure 6.** *Sectional view of sintered bimetal specimens after their first sintering under an inert atmosphere [10].*

**Figure 7.**

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

**Figure 8.**

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

a first sintering in an inert atmosphere. The copper alloys in all the specimens were completely sintered and contained fewer pores than the specimens sintered only under inert atmosphere for both their primary and secondary sinterings. However, the sulfide content of the sintered bronze became inclined from the surface side to the interface side. So, a simple quantitative method of EDS was used for SPB10c.

As shown in **Figure 10a** and **b**, the sulfur on the front side disappeared, and in the simple quantitative method, only 0.2 mass% sulfur was detected. On the other hand, as shown in **Figure 10c** and **d**, the sulfur on the interface side remained, and 2.2% by mass of sulfur was detected. Therefore, the second sintering under reducing atmosphere resulted in the removal of sulfur from the surface of the copper alloy. Because the sulfide peak is small as shown in **Figure 4**, it

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bronze.

**Figure 10.**

**Figure 9.**

was difficult to detect sulfide by XRD in the cross section of bimetal. Therefore, apply EDS observation. For reference, XRD results (not cross-sectional views) of sintered bronze are shown in the figure. Bornite was also detected as shown in **Figure 11**. The figure shows the results of XRD for the sintered sulfide-dispersed

*SEI images and sulfur peak of SPB10c after their second sintering [10].*

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

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

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

**Figure 9.**

*Design and Manufacturing*

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**Figure 8.**

**Figure 7.**

a first sintering in an inert atmosphere. The copper alloys in all the specimens were completely sintered and contained fewer pores than the specimens sintered only under inert atmosphere for both their primary and secondary sinterings. However, the sulfide content of the sintered bronze became inclined from the surface side to the interface side. So, a simple quantitative method of EDS was used for SPB10c. As shown in **Figure 10a** and **b**, the sulfur on the front side disappeared, and in the simple quantitative method, only 0.2 mass% sulfur was detected. On the other hand, as shown in **Figure 10c** and **d**, the sulfur on the interface side remained, and 2.2% by mass of sulfur was detected. Therefore, the second sintering under reducing atmosphere resulted in the removal of sulfur from the surface of the copper alloy. Because the sulfide peak is small as shown in **Figure 4**, it

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

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

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

**Figure 10.**

*SEI images and sulfur peak of SPB10c after their second sintering [10].*

was difficult to detect sulfide by XRD in the cross section of bimetal. Therefore, apply EDS observation. For reference, XRD results (not cross-sectional views) of sintered bronze are shown in the figure. Bornite was also detected as shown in **Figure 11**. The figure shows the results of XRD for the sintered sulfide-dispersed bronze.

**Figure 11.** *XRD of sintered sulfide-dispersed bronze.*

#### *3.3.4 Hardness*

**Figures 12** and **13** show the Vickers hardness values of steel specimens and sintered copper alloys. As shown in **Figure 12**, the hardness of steel was almost the same during sintering and rolling. For steel, these thermal and operating conditions did not affect to change their microstructure and strength. It was important that the bimetallic bushing does not change the properties of the steel. As a result, manufacturing conditions were suitable for bimetal. As shown in **Figure 13a**–**c**, the results were divided into three categories depending on the sintering atmosphere. For all of the test groups that received their initial sintering, the high Sn content alloys are harder in each group. It is known that the Cu-Sn alloy becomes hard when the Sn content increases within the range of the Sn content of the test piece examined in this study. As a result, the basic characteristics of the Cu-Sn alloy in the sintered Cu alloy and the sulfide content in the Cu alloy had almost no influence on the hardness of the base material. After the rolling step, some samples became harder, but the other samples were not hard.

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**Figure 13.**

*Vickers hardness of Cu matrix [10].*

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

The increase in hardness of some specimens may be the result of work hardening during rolling, and the lack of increase in hardness of other specimens may be a result of the destruction of the interface formed by solid diffusion between the powders. When the hardness of SB group and SBP group after the second sintering is compared, Sn group is harder than Sn content (viz., 8, 10, 12 mass% Sn). After the second sintering, Cu3Sn which was one of the intermetallic compounds was precipitated or crystallized. In this series, liquid sintering may occur during sintering. As a

result, matrices with low tin content become softer after sintering.

**Figure 12.** *Vickers hardness of steels under inert atmosphere [10].*

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

*Design and Manufacturing*

*3.3.4 Hardness*

*XRD of sintered sulfide-dispersed bronze.*

**Figure 11.**

**Figures 12** and **13** show the Vickers hardness values of steel specimens and sintered copper alloys. As shown in **Figure 12**, the hardness of steel was almost the same during sintering and rolling. For steel, these thermal and operating conditions did not affect to change their microstructure and strength. It was important that the bimetallic bushing does not change the properties of the steel. As a result, manufacturing conditions were suitable for bimetal. As shown in **Figure 13a**–**c**, the results were divided into three categories depending on the sintering atmosphere. For all of the test groups that received their initial sintering, the high Sn content alloys are harder in each group. It is known that the Cu-Sn alloy becomes hard when the Sn content increases within the range of the Sn content of the test piece examined in this study. As a result, the basic characteristics of the Cu-Sn alloy in the sintered Cu alloy and the sulfide content in the Cu alloy had almost no influence on the hardness of the base material. After the rolling step, some samples became harder, but the other samples were not hard.

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**Figure 12.**

*Vickers hardness of steels under inert atmosphere [10].*

The increase in hardness of some specimens may be the result of work hardening during rolling, and the lack of increase in hardness of other specimens may be a result of the destruction of the interface formed by solid diffusion between the powders.

When the hardness of SB group and SBP group after the second sintering is compared, Sn group is harder than Sn content (viz., 8, 10, 12 mass% Sn). After the second sintering, Cu3Sn which was one of the intermetallic compounds was precipitated or crystallized. In this series, liquid sintering may occur during sintering. As a result, matrices with low tin content become softer after sintering.

**Figure 13.** *Vickers hardness of Cu matrix [10].*

Moreover, some specimens only sintering under inert atmosphere shown in **Figure 13b** were not harder than specimens only sintering under reduced atmosphere shown in **Figure 13a**, relatively. Reducing atmosphere might progress sintering under the same sintering temperature.

From these results, by using pre-alloyed atomizing bronze-containing sulfides, decreasing mechanical properties as hardness were not observed.

### **3.4 Summary**

The effect of sulfur or sulfide on the mechanical properties of bronze specimens sintered under reducing inert gas atmosphere was investigated by subjecting water-atomized sulfide-dispersed bronze specimens to sintering. Furthermore, solid-phase sintering and liquid sintering were compared for the same Sn content. By using pre-alloyed atomizing bronze-containing sulfides, no mechanical properties were observed that decreased significantly as hardness. The sulfide content of the specimens decreased during sintering in a reducing atmosphere. With regard to mechanical properties such as hardness, the Sn content affected the properties regardless of whether the specimen had undergone solid-phase sintering or liquid sintering. In contrast, the sulfur and sulfide content and mechanical properties had no correlation.
