Ideally, the relative density of the alloy should be 100%, but in the actual production process, this value is difficult to achieve due to the influence of various factors. Therefore, a copper-tungsten alloy with a relative density of no less than 97% is considered an ideal W-Cu alloy. So, what factors will affect the relative density of alloys?
First of all, we have to mention the raw ingredients. The oxygen content in tungsten powder is a key factor. When tungsten powder contains too many oxides, these oxides will hinder the tight bonding between metal elements because the wettability between metal elements and oxides is poor. This means that controlling the oxygen content in the powder is a key step to improve the density of the alloy.
Secondly, surface oxide is also a factor that cannot be ignored. During the press forming process, the surface oxide makes it difficult for the powder to undergo plastic deformation due to its high elastic modulus, which in turn leads to a reduction in the relative density of the formed blank. Similarly, during the sintering process, insufficiently reduced powder will produce water vapor, which is also detrimental to the densification of the product.
In addition, the purity and oxygen content have a direct impact on the wettability of tungsten powder. High purity, low oxygen content tungsten powder can provide good wettability, thereby ensuring good copper infiltration effect. When the oxygen content of tungsten powder increases, the wetting angle between tungsten and copper liquid will increase, and the wettability will become worse.
Finally, the particle size of tungsten powder is also an important influencing factor. Tungsten powder with different particle sizes will have different bridging effects and contact surfaces during the pressing process, which directly affects the pressure required to press to the same density. Generally speaking, coarser tungsten powder particles are easier to reach the required density during pressing. This is because the coarse particles have a stronger bridging effect and can better transmit the pressing pressure, thereby making the particles more closely combined. In contrast, the porosity of fine porous tungsten powder is relatively small, which means that the fine powder has greater free energy during sintering, which is more conducive to sintering. Therefore, fine powder is more conducive to densification of tungsten-copper alloy.
