Effects of Dispersed Sulfides in Bronze During Sintering

*Tomohiro Sato*

## **Abstract**

Bronze material sintered as sliding bearing is used. In particular, lead bronze is often used because lead acting as a solid lubricant has excellent friction characteristics. However, lead was replaced by another material according to environmental regulations. One candidate for a lead-free material is a sulfide that is well known as a solid lubricant. In this chapter we describe sintering properties and their mechanical properties. First, we investigate chemical components of copper sulfide system and realize stable phase in bronze matrix. After that, we consider the sintering condition of bronze with sulfide dispersed. The sulfides in the bronze may be subject to chemical reduction during sintering, especially when this is carried out under a reducing atmosphere containing hydrogen gas. The effect of the sulfides on the bronze, with a focus on the hardness of the bronze matrix and the reaction between sulfides and hydrogen gas, was investigated. Not only sinterability but also mechanical properties as hardness are discussed.

**Keywords:** sintering, Cu alloy, bronze, sulfide, hardness, friction

### **1. Introduction**

Copper alloys based on copper and tin are useful materials as the so-called bronze (Cu-Sn alloy). For example, sliding bearings are common in industrial applications. These bearings are often manufactured using a sintering process in the field of powder metallurgy. Specifically, 90 Cu-10 Sn mass% bronze is common and has been developed and manufactured as a base materials of a bearing component.

Lead is a common element for use as industrial additives. This is also an indispensable material for additives for metal casting of Cu alloys and solders. The addition of lead ensures that the pressure resistance of the bronze and brass water devices and the mechanical properties of the solder are maintained. Lead is also useful in the manufacturing process. For example, lead made castability improve in the metal casting method [1, 2], and solderability is also improved due to low melting point of lead [3]. Lead has important applications as a solid lubricant, and lead bronze is a useful material for sliding bearings even though there are many regulations as RoHS and REACH and so on.

However, lead is harmful for human health, especially children and pregnant women. For that reason, various regulations are implemented to protect people.

These regulations or trends will affect industrial manufacturers. As a result, many industries have developed new materials as substitutes for lead.

**140**

*Design and Manufacturing*

ISBN0-394-54698-9

ISBN0-571-11470-9

University, Delft; 2000

[1] Bayley S, editor. The Conran Directory of Design. New York, USA: Villard Books; 1985.

[2] Loewy R. Industrial Design. Faber and Faber; London, UK: 1979.

[3] Broek JJ, Sleijffers W, Horvath I, Lennings AF. Using Physical Models in Design. CAID. The Netherlands: Delft

[4] Isa SS, Liem A. Classifying physical models and prototypes in the design process: A study on the economical and usability impact of adopting models and prototypes in the design process. In: Proceedings of the International Design Conference (DESIGN 2014), Dubrovnik. 2014. pp. 2071-2081

**References**

Bismuth and sulfides are well known as lead substitutes and are candidates for the development of solid lubricants. Bi-bronze castings were used as bimetallic bearings and showed good loading capacity [4]. Potential applications of these castings are pointed out in Ref. [4], and it has been shown that castability was improved using Bi. The machinability of bronze-containing sulfides (Cu2S and ZnS) was investigated. It was concluded that the mechanical properties and machinability of sand casting are the same as the mechanical properties and machinability of Pb-bronze castings [5]. For industrial, it is important that the manufacturing cost is low and that there is a stable supply of raw materials. Bi is far more expensive than S and Cu. Since Bi is a rare metal, the supply of sulfide seems to be superior to that of Bi. As a result, sulfide based on S and Cu is a promising alternative for lead substitution material.

In this study, we will discuss how to influence bronze sulfide which is already atomized. Specifically, the strength of bronze matrix and the reaction between sulfide and hydrogen gas are drawing attention. We clarify composition and atmosphere effective for sintering bronze with sulfide dispersed. In the investigation, solid-state sintering and liquid-phase sintering are compared under reducing atmosphere and inert atmosphere. Hardness as one of the important mechanical properties was also investigated. Moreover, some other sintering conditions and friction properties are also discussed.
