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Comparison of Powder Metallurgy and Liquid Phase Sintering Processes of Molybdenum-Copper Alloy

Powder metallurgy (PM) and liquid phase sintering (LPS) are two common process methods in the preparation of molybdenum-copper alloys. Although both can be used to produce molybdenum copper, there are obvious differences in terms of process, material properties, cost and application fields.

1. Material density and structural uniformity

The powder metallurgy process mainly relies on solid-phase sintering, due to the limited shrinkage of the material in the sintering process, the density of the final product is usually low, and it is difficult to completely eliminate the pores, so the density is generally between 85%~95%. This microporous structure may affect the thermal conductivity and mechanical strength of molybdenum-copper, especially at high temperatures, which may lead to performance degradation.

In contrast, in the liquid phase sintering process, copper melts at the sintering temperature and penetrates into the pores between the molybdenum particles, resulting in a significant increase in the density of the material, typically above 98%. The high-density structure not only improves the thermal conductivity of molybdenum-copper alloys, but also enhances their mechanical strength, making them more suitable for demanding application scenarios.

2. Thermal conductivity matches thermal expansion

Thermal conductivity is one of the key indicators to measure the properties of molybdenum-copper alloys. In the PM process, due to the weak bond between the particles, there may be residual porosity and interfacial thermal resistance inside the material, resulting in a lower thermal conductivity than the material prepared by the LPS process. In the LPS process, the liquid phase osmosis of copper fills the voids between the molybdenum particles, resulting in smoother heat flow channels inside the alloy and therefore higher thermal conductivity. In addition, the high density reduces the thermal fatigue effect of the material and improves thermal stability.

In terms of thermal expansion matching, the molybdenum-copper prepared by the PM process can buffer the stress caused by the difference in the thermal expansion coefficient of molybdenum and copper to a certain extent due to its large number of pores. However, this structure may be fatigue damaged by thermal cycling during long-term use. The material prepared by LPS has a higher compactness, although it is relatively weak in terms of thermal expansion matching, but by optimizing the alloy ratio and sintering conditions, it can effectively reduce the stress concentration problem and improve the service life. 

3. Mechanical properties

Due to the weak particle bonding, molybdenum copper prepared by the PM process usually exhibits low tensile strength and impact resistance, especially in the environment of high temperature or high mechanical stress. The LPS process improves the bonding strength between molybdenum particles through the liquid phase penetration of copper, thereby enhancing the mechanical properties of the overall material, making it have higher wear resistance and crack resistance. 

4. Production cost and process complexity

The PM process is relatively simple, the production process is short, the equipment requirements are low, and it is suitable for large-scale industrial production, so the cost is low. However, due to its relatively low density, additional post-processing (e.g., HIP) may be required to increase the density of the material, which increases the cost to some extent.

The LPS process requires higher temperature control and a protective atmosphere to ensure that the liquid phase of the copper is fully permeable and does not oxidize. At the same time, the process requires precise control of the sintering time to avoid excessive copper loss or the formation of abnormal structures. Therefore, its equipment investment and energy consumption are higher, resulting in higher overall costs than powder metallurgy. In addition, materials prepared by liquid phase sintering often require additional precision machining to meet specific application needs, further increasing production costs.

5. Applicable Scenarios

The PM process is suitable for cost-sensitive, relatively low-performance applications, such as common electronic packaging and thermal modules. The LPS process is suitable for applications that require high performance, such as high-power electronics, aerospace components, etc., especially where high thermal conductivity and high mechanical strength are required.

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