Effect of sintering process on properties of CuSnZn alloy powder

Objectives: Diamond tools are crucial in stone processing, and their performance is directly related to processing quality and cost. With the rise of stone and labor costs, the performance requirements on diamond tools are also increasing, including sharpness, self sharpening, tool life, and cutting efficiency. To improve efficiency and reduce costs, users often increase the cutting machine power and speed, which further requires diamond tools to have higher sharpness and strength at the risk of breakage. A practical method method is to increase the content of tin (Sn) in the segment to enhance its brittleness without changing the diamond concentration and particle size. However, an increase in Sn content will reduce the strength of the segment and may lead to a decrease in the holding force between CuSn alloy and diamond. For example, the commonly used CuSn10 and CuSn15 pre alloy powders in industry have low strength and weak holding force on diamond. Therefore, it is necessary to improve the powder properties and processing technology. Methods: Adding Zn element to CuSn10 alloy powder can improve powder strength and holding force. CuSnZn-x alloy powder (mass fraction of Zn, x=10.00%, 15.00%, 20.00%, 25.00%, 30.00%) was prepared by atomization process. The hot pressing sintering temperatures were 610 ℃, 615 ℃, 630 ℃, 645 ℃, 655 ℃, and the sintering pressure was 21 MPa. The melting temperature of CuSnZn alloy powder was tested using a differential thermal analyzer. The density of the sintered segment was tested using Archimedes drainage method. The bending strength of the sintered segment was tested using mechanical performance testing equipment. The Rockwell hardness of the sintered segment was measured using a Rockwell hardness tester. The microstructure morphology of the sintered segment and its fracture were analyzed using scanning electron microscopy. Other performances of samples with different Zn contents were analyzed and compared as well, namely theoretical density, Rockwell hardness, and flexural strength, to study the influence of Zn content on sample microstructure. Results: With the increase of Zn content, the rate of decrease in melting temperature of CuSnZn alloy powder first increases and then decreases. When the Zn mass fraction is 30%, the melting temperature decreases to 848 ℃, which is 164 ℃ lower than that of CuSn10. As the Zn content increases, the brass in the sintered segment gradually transforms from the α phase to the α+β phase and then the α+β+β´ phase, resulting in a significant increase in the Rockwell hardness of the segment. The bending strength of the sintered segment first increases and then decreases, reaching a maximum value of 542 MPa when the Zn mass fraction is 20.00%. When the mass fraction of Zn is 10.00% and 15.00%, obvious toughness dimples are observed on the fracture surface of the sintered segment, and particle peeling is observed on the fracture surface. The peeling surface is smooth and flat, indicating grain boundary peeling fracture of the phase structure. When the mass fraction of Zn is 20.00% and 25.00%, a large number of cleavage fracture surfaces are observed on the fracture surface of the sintered segment, and a small amount of smooth concave transgranular fracture is observed, which is partially intergranular fracture and partially transgranular fracture. When the mass fraction of Zn is 30.00%, the fracture surface of the sintered segment is flat and smooth, and the crack passes through the phase interface and grain along the hard and brittle structure, which is transgranular fracture. Conclusions: Adding Zn element can effectively reduce the melting point of alloy powder, and with the increase of Zn content, the hardness of sintered samples increases while the toughness decreases. When the Zn content is 30.00%, the melting temperature of CuSnZn alloy powder reaches its minimum value. When the Zn content exceeds 25.00%, the strength of the sintered samples will gradually decrease. Therefore, in actual production, the appropriate amount of Zn addition and sintering process should be selected based on comprehensive consideration of demand.